首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   377篇
  免费   23篇
耳鼻咽喉   1篇
儿科学   14篇
妇产科学   4篇
基础医学   46篇
口腔科学   3篇
临床医学   29篇
内科学   58篇
皮肤病学   50篇
神经病学   13篇
特种医学   13篇
外科学   70篇
综合类   7篇
预防医学   23篇
眼科学   5篇
药学   24篇
肿瘤学   40篇
  2023年   6篇
  2022年   8篇
  2021年   23篇
  2020年   2篇
  2019年   14篇
  2018年   18篇
  2017年   11篇
  2016年   16篇
  2015年   19篇
  2014年   18篇
  2013年   16篇
  2012年   30篇
  2011年   28篇
  2010年   8篇
  2009年   8篇
  2008年   23篇
  2007年   27篇
  2006年   19篇
  2005年   19篇
  2004年   13篇
  2003年   11篇
  2002年   5篇
  2001年   5篇
  2000年   2篇
  1999年   2篇
  1998年   3篇
  1997年   1篇
  1996年   2篇
  1994年   1篇
  1992年   3篇
  1991年   4篇
  1989年   2篇
  1988年   2篇
  1987年   5篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1978年   1篇
  1976年   2篇
  1975年   2篇
  1973年   1篇
  1972年   2篇
  1969年   2篇
  1968年   2篇
  1966年   2篇
  1964年   1篇
  1961年   1篇
  1959年   1篇
排序方式: 共有400条查询结果,搜索用时 15 毫秒
1.
Thirty rhizobacteria isolated from maize grown in Pakistani and Indonesian soils were evaluated for their morphological characteristics, nitrogen fixation, P-solubilization, indole acetic acid (IAA) and siderophores production. Nitrogenase activity was detected in nineteen isolates ranging from 21.8-3624 n moles C2H4 produced/h/mg protein. Most of the isolates produced IAA, ten were capable of siderophore production while four were P-solubilizers. Ultrastructural studies of Pseudomonas sp. F14 indicated characteristic rhizospheric colonization within 48 h that was observed to change considerably with the passage of time from few bacteria to micro colonies. Random amplified polymorphic DNA (RAPD) analysis of 30 bacterial strains using 30 oligonucleotide primers resulted in considerable level of genetic diversity, with genetic distance ranging from 2-16%. Indonesian isolates were found to be more diverse as compared to Pakistani isolates. The characterization and screening of rhizobacteria of maize rhizosphere has helped in selection of isolates F7, LS-1, 3.1.1.C, F2, F3 and F13 as superior strains for use as bioinoculant. Moreover isolate F14 identified, as Pseudomonas fulgida by partial 16S rRNA sequence analysis is a novel strain regarding its tremendous potentials for inoculum production to enhance the yield of maize.  相似文献   
2.
Pakistan's public sector is organized in a federal system with many management and planning functions devolved to the 4 provincial governments. Provincial health secretariats lead on most policy and planning decisions for health services. The provinces employ health personnel, although the national Public Service Commission controls some key aspects of human resources management. Reporting the findings of a training needs assessment (TNA) for health personnel in the provincial health services of Punjab, the authors show how TNA can be used systematically to improve the quality of health professional training. They also discuss the extent to which better training could contribute to improved health management capacity in Pakistan, and describe the context and problems of Pakistan's health services, focusing upon management capacity, and the methods and results of a training needs assessment conducted to address the problems. A final section covers the usefulness of the TNA method in Pakistan and its applicability to other countries. Moreover, the implications of decentralization and the problems of preparing training plans in the absence of decentralized structures are discussed.  相似文献   
3.
In this study, a lead zirconate titanate (PZT)/in situ polymerized polyurethane (PU) composite with three-dimensional (3D) reduced graphene oxide (rGO) as the conductive phase was prepared and the potential of 3D rGO to enhance the damping properties was investigated. The conductivity and damping properties of the composite were systematically investigated. The results show that the conductive threshold of the composite is reached at a very low rGO content of about 0.7 wt% by using the 3D rGO structure. The best damping performance of the piezoelectric damping composite is achieved at the conductive threshold, where the loss factor is 0.22 (almost 41%) higher and the temperature range where tan δ ≥ 0.3 is 13.2 °C (almost 84%) wider than those of the PU matrix. A composite consisting of only PU and rGO sheets without the 3D structure was prepared for comparison. The conductive threshold of this composite is more than 0.9 wt% and the highest tensile strength is 5.63 MPa when the rGO content is 0.6 wt%, indicating that the 3D structure reduces the use of the conductive phase and does not significantly affect the tensile strength of the matrix.

Piezoelectric damping composite with 3D rGO as the conductive phase that possesses good damping properties with the conductive threshold as low as 0.7 wt%.  相似文献   
4.
Pakistan faces huge challenges in meeting its international obligations and agreed Millennium Development Goal targets for reducing maternal and child mortality. While there have been reductions in maternal and under-5 child mortality, overall rates are barely above secular trends and neonatal mortality has not reduced much. Progress in addressing basic determinants, such as poverty, undernutrition, safe water, and sound sanitary conditions as well as female education, is unsatisfactory and, not surprisingly, population growth hampers economic growth and development across the country. The devolution of health to the provinces has created challenges as well as opportunities for action. This paper presents a range of actions needed for change within the health and social sectors, including primary care, social determinants, strategies to reach the unreached, and accountability.  相似文献   
5.
BackgroundValues of fractional flow reserve (FFRCT) by coronary computed tomography angiography (CTA) decline from the ostium to the terminal vessel, irrespective of stenosis severity. The purpose of this study is to determine if the site of measurement of FFRCT impacts assessment of ischemia and its diagnostic performance relative to invasive FFR (FFRINV).Methods1484 patients underwent FFRCT; 1910 vessels were stratified by stenosis severity (normal; <25%, 25–50%, 50–70%, and >70% stenosis). The rates of positive FFRCT (≤0.8) were determined by measuring FFRCT from the terminal vessel and from distal-to-the-lesion. Reclassification rates from positive to negative FFRCT were calculated. Diagnostic performance of FFRCT relative to FFRINV was evaluated in 182 vessels using linear regression, Bland Altman analysis, and receiver operating characteristic (ROC) curves.ResultsPositive FFRCT was identified in 24.9% of vessels using terminal vessel FFRCT and 10.1% using FFRCT distal-to-the-lesion (p ?< ?0.001). FFRCT obtained distal-to-the-lesion resulted in reclassification of 59.6% of positive terminal FFRCT to negative FFRCT. Relative to FFRINV, there were improvements in specificity (50% to 86%, p ?< ?0.001), diagnostic accuracy (65% to 88%, p ?< ?0.001), positive predictive value (50% to 78%, p ?< ?0.001), and area-under-the-curve (AUC, 0.83 to 0.91, p ?< ?0.001) when FFRCT was measured distal-to-the-lesion.ConclusionFFRCT values from the terminal vessel should not be used to assess lesion-specific ischemia due to high rates of false positive results. FFRCT measured distal-to-the-lesion improves the diagnostic performance of FFRCT relative to FFRINV, ensures that FFRCT values are due to lesion-specific ischemia, and could reduce the rate of unnecessary invasive procedures.  相似文献   
6.
7.
8.
For the purpose of re-describing the Eimeria species that infect the turkey (Meleagris gallopavo) and to establish benchmark biological information linked to genetic markers for each species, a strain of Eimeria meleagrimitis Tyzzer 1929 was obtained from a litter sample from a turkey farm in Minnesota, USA in 2008. Multiple pure lines were derived by infecting turkey poults with a single oocyst; one of these lines was then used to re-describe biological and morphological features of E. meleagrimitis in the turkey and to designate a neotype of E. meleagrimitis in the turkey. Oocyst morphometrics of this line matched those of this species as originally described by Tyzzer (Am J Hyg 10:269–383, 1929). Three asexual generations of merogony (the first generation of meronts large in size and the second and third generations small) were detected in the intestines before the onset of gametogony; no developmental stages were detected in the cecal pouches. No mortality was induced by this line of E. meleagrimitis even when turkey poults were infected with high doses of oocysts (up to 5?×?105 oocysts/bird) and despite the ability of E. meleagrimitis to induce severe mucosal damage in the upper and middle duodenum. Macroscopic lesions were characterized to provide a graded lesion scoring guide that should assist assessment of the severity of infections with this species in infected turkeys. The pathogenicity of the strain was investigated, and a significant reduction in weight gain and feed conversion ratio was observed with doses of 104 oocysts/bird or more. The maximum yield of oocysts in the feces was obtained when birds were inoculated with 5?×?103 oocysts.  相似文献   
9.
Cutaneous leishmaniasis is rarely seen in the United States. Four Cuban immigrants traveled along the same route at different times from Cuba to Ecuador, then northward, including through the Darién Jungle in Panama. These patients had chronic ulcerative non-healing skin lesions and were given a diagnosis of leishmaniasis.Leishmaniasis is a vector-borne disease caused by the protozoan parasite of the genus Leishmania and is spread by the bite of sand flies from the sub-family Phlebotominae.1 There are various clinical manifestations of leishmaniasis, including cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis, and visceral leishmaniasis. Cutaneous leishmaniasis occurs at the site of the bite, with lesions forming weeks to months later starting with a papule, which then develops into a nodule or plaque-like lesion and progresses to a painless ulceration with an indurated border.We report four cases of CL caused by Leishmania (Viannia) panamensis in Cuban immigrants who traveled through the Darién Gap Jungle between Colombia and Panama on their journey north to the United States. This region has been shown to have high transmission rates of leishmaniasis,2 and, in 2012, Panama experienced an outbreak beyond expected endemic rates.3 This case series highlights a previously underappreciated immigration route to the United States for Cubans and the need to include leishmaniasis as a differential diagnosis for non-healing skin ulcers in this patient population.During May 2012–April 2013, four persons who had recently immigrated to the United States from Cuba came to the National School of Tropical Medicine at Baylor College of Medicine''s (BCM) Tropical Medicine Clinic for non-healing skin ulcers. All four persons reported a similar route of travel from Cuba to Texas (Figure 1), although at different times. Each person began their journey by flying to Quito, Ecuador, where they then traveled by bus through Colombia, passing through the cities of Pasto and Cali to Quibdo. In Quibdo, they took a short flight to Bahia Solano, Colombia, where a boat ride then transported them to Punta Ardita near the Panama border. They then traveled by foot through the thick jungle in Darién, Panama, for 5–15 days. During this time, they slept outdoors and reported numerous insect bites. Once through the Darién area, they traveled northward until they entered the United States at the Mexican border.Open in a separate windowFigure 1.Map showing immigration route of a cluster of Cuban patients with cutaneous leishmaniasis caused by Leishmania (V.) panamensis. Note the travel by foot through the thick jungle of the Darién National Park, Panama, where they likely contracted the disease.Once in the United States, the four persons sought medical care at outside clinics for skin lesions that had developed within two months after they passed though the Darién. They were treated for presumed infection with Staphylococcus aureus. The antibiotics had no therapeutic effect, and the lesions continued to grow and develop into non-healing, painless ulcers with accompanying satellite lesions. Once in Houston, Texas, the four persons were directed to the Department of Dermatology at BCM (
PatientAge, years/sexLesion location; size; presence of satellite lesions (+/−)Diagnosis and pathogenDuration of disease before initiation of treatmentTreatment course
138/FProximal right posterior arm; 5 cm; (+)CL L. (V.) panamensis3 monthsAmBisome (days 1–5, 14, 21)
246/MDistal left forearm; 2 lesions: 4 cm and 3 cm; (+)CL L. (V.) panamensis2 monthsAmBisome (days 1–5, 14, 21); then itraconazole (daily, 30 days)
343/MVertex of scalp, 8 more lesions on eyes, legs, and torso; 5 cm, other lesions 1 cm; (+)CL L. (V.) panamensis2 weeksAmBisome (days 1–5); then pentostam (daily, 20 days)
443/FLeft malar area; 1.5 cm; (+)CL L. (V.) panamensis3 monthsAmBisome (days 1–5, 14)
Open in a separate window*CL = cutaneous leishmaniasis.Patient 1 was a 38-year old woman with a three-month history of an expanding, painless, pruritic ulcer who had a 5-cm ulcer on her proximal right arm, along with several satellite lesions covered with crusts, as well as a 1.5-cm erythematous papule with central ulceration covered in crust on her right thigh. Patient 2 was a 46-year old man who had a two-month history of two erythematous, scaly plaques with central ulceration on the left forearm (Figure 2A). Patient 3 was 43-year old man with a two-month history of non-healing, tender lesions that on presentation were a 5-cm crusted nodule at the vertex of the patient''s scalp and two right parietal 1 cm papules, as well as a fluctuant nodule on his right lower leg. Patient 4 was a 43-year old woman who had a two-month history of a slowly expanding, painless lesion on her cheek, which on examination was a 1.5-cm eroded nodule on her left malar area and four papules above the main lesion (Figure 2C). All of the patients reported the lesions appearing from two weeks to two months after traveling through the Darién area. No lesions were noted before traveling through this region. The patients all denied systemic complaints including fevers, chills, night sweats, and weight loss, and were otherwise normal on physical exam. No mucosal involvement was noted in any of the patients upon exam.Open in a separate windowFigure 2.Skin ulcers of two of the four Cuban immigrants to the United States with cutaneous leishmaniasis caused by Leishmania (V.) panamensis. A, Patient 2 , showing two erythematous, scaly plaques with central ulceration and diameters of 3 cm and 4 cm on the left forearm. B, Patient 2 at six months post-treatment showing good resolution of the lesions. C, Patient 4, showing a 1.5-cm eroded nodule on left malar area and four papules above the main lesion. D, Patient 4 at three months post treatment showing with good resolution of the lesions.For each of the patients, a punch biopsy was performed by the Department of Dermatology for diagnosis by histologic analysis by BCM, and species-specific polymerase chain reaction and culture performed by the Centers for Disease Control and Prevention (Atlanta, GA). All biopsy specimens showed dense inflammatory infiltrates in the dermis with numerous histiocytes, lymphocytes, and intracellular structures within macrophages. These structures were identified as small organisms with kinetoplasts suggestive of Leishmania amastigotes. Numerous dermal plasma cells were also seen in biopsy specimens from patients 1, 2, and 4. Biopsy specimens from patient 3 showed dermal multinucleated giant cells, and scattered dermal eosinophils were observed in biopsy specimens from patient 4. Using polymerase chain reaction, PCR, CDC identified L. (V.) panamensis, a parasitic infection found in Belize, Colombia, Costa Rica, Ecuador, Honduras, Nicaragua, Panama, and Venezuela.4All the patients were treated with liposomal amphotericin B (AmBisome), 3 mg/kg/day for 5 days, followed by two infusions at the same dose on days 14 and 21 to complete a total treatment of 21 mg/kg,5 a dosing found to be effective in treating CL.6 In an attempt to minimize infusion-related reactions, the patients were pre-treated with 50 mg of diphenhydramine and 650 mg of acetaminophen, and hydrated with 500 mL of normal saline before each infusion.6 Despite this treatment, patient 1 experienced a mild self-resolving infusion-related reaction with chills and a headache. Three patients experienced an elevation of the creatinine level (two times the reference value) that resolved within days.Patients were followed-up by the Tropical Medicine Clinic over several months because healing of these ulcers is slow. Patients 1 and 4 had good resolution (Figure 2D), and patient 2 had a small, 1-cm, dry, scabbed lesion at five months post-treatment. Concern over incomplete resolution led to a 30 day course of itraconazole, 200 mg twice a day, which led to good resolution of the lesion and a leishmaniasis-negative biopsy result (Figure 2B). Patient 3 had the most extensive disease, with 13 lesions upon presentation, and during his treatment with liposomal amphotericin B, continued to have disease progression. Concern for treatment failure led to additional therapy with intravenous sodium stibogluconate (pentostam), starting at 50% of the dose (10 mg/kg/day), and increasing to 75% (15 mg/kg/day) on day 5, then 100% (20 mg/kg/day) on day 10 to complete a total of 20 days of therapy, as recommended by the Parasitic Diseases Branch of CDC (personal communication). Currently, his lesions are resolving well.Liposomal amphotericin B was chosen because all patients had extensive disease, and in the case of patient 4, the lesion was on her face, where scarring is undesirable. Liposomal amphotericin B therapy for CL has been shown clinically to be effective, with improved lesion resolution and less toxicity than sodium stibogluconate.1,612 Treatment not only promotes healing of the cutaneous lesion, but also reduces the risk of subsequent mucosal involvement.13,14 Up to 12% of CL cases are at risk of later developing mucocutaneous leishmaniasis, depending on the subspecies of Leishmania Viannia; either braziliensis or guyanensis have the highest risk.15 Mucocutaneous leishmaniasis presents as cutaneous lesions in addition to mucosal destruction, most commonly of the nose, mouth, or nasal septum. Mucosal destruction can be disfiguring and may occur years after the development of cutaneous lesions.This report highlights a previously underappreciated immigration route for Cubans through Central America, which places immigrants at risk for a number of emerging tropical diseases, including leishmaniasis. Physicians should be aware of this immigration route when treating Cuban immigrants and include leishmaniasis in the differential diagnosis when treating non-healing skin ulcers in this patient population. Liposomal amphotericin B can be a well-tolerated and efficacious treatment of CL caused by L. (V.) panamensis.  相似文献   
10.
Development and evaluation of a simulator-based laparoscopic training program for surgical novices     
Emmeline Nugent  Nicole Shirilla  Adnan Hafeez  Diarmuid S. O’Riordain  Oscar Traynor  Anthony M. Harrison  Paul Neary 《Surgical endoscopy》2013,27(1):214-221

Background

The use of simulation to train novice surgeons in laparoscopic skills is becoming increasingly popular. To maximize benefit from simulation, training needs to be delivered and assessed in a structured manner. This study aimed to define performance goals, demonstrate construct validity of the training program, and evaluate whether novice surgeons could reach the preset performance goals.

Methods

Nine expert laparoscopic surgeons established performance goals for three basic modules of an augmented-reality laparoscopic simulator. The three laparoscopic modules were used by 40 novice surgeons and 40 surgical trainees (postgraduate years [PGYs] 1–4). The performance outcomes were analyzed across the different groups (novice, PGYs 1 and 2, PGYs 3 and 4, expert) to determine construct validity. Then 26 recruited novices trained on the three modules with the aim of reaching the performance goals.

Results

The results demonstrated a significant difference in performance between all levels of experience for time (p < 0.001), motion analysis (p < 0.001), and error score (p < 0.001), thus demonstrating construct validity. All 26 novice surgeons significantly improved in performance with repetition for the metrics of time (p < 0.001) and motion analysis (p < 0.001). For two of the modules, the proficiency goals were reached in fewer than 10 trials by 80 % of the study participants.

Conclusion

Basic skills in laparoscopic surgery can be learned and improved using proficiency-based simulation training. It is possible for novice surgeons to achieve predefined performance goals in a reasonable time frame.  相似文献   
1 [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] 下一页 » 末  页»
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号