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   3220篇
  免费   171篇
  国内免费   28篇
耳鼻咽喉   10篇
儿科学   74篇
妇产科学   65篇
基础医学   601篇
口腔科学   119篇
临床医学   276篇
内科学   591篇
皮肤病学   34篇
神经病学   318篇
特种医学   121篇
外科学   266篇
综合类   19篇
预防医学   270篇
眼科学   58篇
药学   312篇
中国医学   22篇
肿瘤学   263篇
  2023年   38篇
  2022年   104篇
  2021年   141篇
  2020年   89篇
  2019年   90篇
  2018年   100篇
  2017年   88篇
  2016年   104篇
  2015年   81篇
  2014年   141篇
  2013年   169篇
  2012年   267篇
  2011年   262篇
  2010年   138篇
  2009年   141篇
  2008年   200篇
  2007年   202篇
  2006年   192篇
  2005年   181篇
  2004年   123篇
  2003年   149篇
  2002年   130篇
  2001年   45篇
  2000年   29篇
  1999年   27篇
  1998年   15篇
  1997年   10篇
  1996年   4篇
  1995年   16篇
  1994年   8篇
  1993年   11篇
  1992年   12篇
  1991年   10篇
  1990年   10篇
  1989年   8篇
  1988年   7篇
  1987年   8篇
  1986年   10篇
  1985年   10篇
  1984年   10篇
  1983年   4篇
  1982年   3篇
  1980年   4篇
  1979年   3篇
  1976年   4篇
  1975年   3篇
  1973年   2篇
  1972年   2篇
  1970年   2篇
  1967年   2篇
排序方式: 共有3419条查询结果,搜索用时 15 毫秒
61.
ObjectiveTo estimate the nutritional risk in children 2 to 6 y old.MethodsThe sample consisted of 3058 children enrolled in public and private schools in nine Brazilian cities. The assessment of nutrient intake was based on 1-d data combining direct individual weighing of foods and a food diary. A second evaluation of food consumption was conducted in a subsample to estimate the usual intake.ResultsThere was low prevalence of inadequate intake of vitamin B6 (<0.001%), riboflavin (<0.001%), niacin (<0.001%), thiamin (<0.001%), folate (<0.001%), phosphorus (<0.1%), magnesium (<0.1%), iron (<0.5%), copper (<0.001%), zinc (<0.5%), and selenium (<0.001%). However, 22% of children younger than 4 y and 5% of children older than 4 y consumed fiber quantities larger than the adequate intake. Approximately 30% of the sample consumed more saturated fat than recommended. The prevalence of inadequate vitamin E intake ranged from 15% to 29%. More than 90% of the children had an inadequate vitamin D intake. In children older than 4 y, the prevalence of inadequate calcium intake was approximately 45%. Sodium intake was higher than the upper intake level in 90% of children younger than 4 y and 73% of children older than 4 y.ConclusionsThe prevalence of inadequate dietary intake was low for most nutrients. However, fiber, calcium, and vitamin D and E intakes were lower than recommended. Moreover, children consumed large amounts of sodium and saturated fat.  相似文献   
62.
Heart valve prosthesis unquestionably improve quality of life and survival of patients with severe valvular heart disease, but the need for antithrombotic therapy to prevent thromboembolic complications is a major challenge to clinicians and their patients. Of the articles analyzed, most were retrospective series of cases or historical cohorts obtained from the database. The few published randomized trials showed no statistical power to assess the primary outcome of death or thromboembolic event. In this article, we decided to perform a systematic literature review, in an attempt to answer the following question: what is the best antithrombotic strategy in the first three months after bioprosthetic heart valve implantation (mitral and aortic)?After two reviewers applying the extraction criteria, we found 1968 references, selecting 31 references (excluding papers truncated, which combined bioprosthesis with mechanical prosthesis, or without follow-up).Based on this literature review, there was a low level of evidence for any antithrombotic therapeutic strategy evaluated. It´s therefore interesting to use aspirin 75 to 100 mg / day as antithrombotic strategy after bioprosthesis replacement in the aortic position, regardless of etiology, for patients without other risk factors such as atrial fibrillation or previous thromboembolic event. In the mitral position, the risk of embolism, although low, is more relevant than in the aortic position, according to published series and retrospective cohorts comprised mostly of elderly non-rheumatic patients.The current evidence is limited to have a consistent and safe level of evidence regarding the best therapeutic strategy. Based on these studies, 75 to 100 mg/day of aspirin is interesting as antithrombotic strategy after implantation of aortic bioprosthesis, regardless of etiology, for patients with no other risk factors such as atrial fibrillation or previous thromboembolic event. As for mitral bioprosthesis, the risk of embolism, although low, is more relevant than in the aortic position, according to published series and retrospective cohorts - usually elderly non rheumatic patients.  相似文献   
63.
BACKGROUND: In patients with a first symptomatic pulmonary embolism (PE), the risk of recurrence is unknown. We therefore investigated the risk of recurrence among patients with spontaneous symptomatic PE and among those with deep vein thrombosis (DVT) without symptoms of PE. METHODS: After discontinuation of secondary thromboprophylaxis for a first venous thromboembolism (VTE), we prospectively observed 436 patients for an average of 30 months. Patients with secondary VTE, natural inhibitor deficiencies, lupus anticoagulant, cancer, long-term antithrombotic therapy, vena cava filters, or pregnancy were excluded. The study outcome was objectively documented recurrent symptomatic VTE. RESULTS: Recurrent VTE was seen among 28 (17.3%) of 162 patients with symptomatic PE and among 26 (9.5%) of 274 patients with DVT without symptoms of PE. Compared with patients with DVT, the relative risk of recurrent VTE among patients with symptomatic PE was 2.2 (95% confidence interval, 1.3-3.7; P =.005). The relative risk was not affected by age, sex, presence of factor V Leiden or prothrombin G20210A, hyperhomocysteinemia, or high factor VIII levels. Compared with patients with DVT without symptoms of PE, patients with symptomatic PE had an adjusted relative risk of PE at recurrence of 4.0 (95% confidence interval, 1.3-12.3; P =.03). CONCLUSION: Patients with a first symptomatic PE not only have a higher risk of recurrent VTE than those with DVT without symptoms of PE, but are also at high risk of symptomatic PE at recurrence.  相似文献   
64.
Background:The effects of long-distance walking on the cardiovascular system have been little studied.Objectives:The general objective of this study was to verify these effects on the behavior of diastolic function and the cardiac biomarkers CK-MB (mass), troponin T, and NT-proBNP, in amateur athletes.Method:This longitudinal study, conducted in 2015, evaluated participants during the following 5 stages: E0 (baseline) before starting the trajectory and the others, E1, E2, E3, and E4, at the end of each day, totaling 244.7 km. At all stages, the biomarkers NT-proBNP, CK-MB (mass), and troponin T were measured. Echocardiogram was performed to analyze the E, A and E'' waves. P < 0.05 was adopted as significant.Results:The study evaluated 25 participants, with an average age of 46 ± 10.5 years and body mass index of 20.2 ± 2.3 kg/m2. Increased values were found for NT-proBNP from E0 to E1, E2, E3, and E4 (p < 0.001), CK-MB (mass) from E0 to E2 (p < 0.001), and E'' wave from E0 to E1, E2, E3, and E4 (p < 0.001). Positive correlations were identified between the following: CK-MB (mass) and troponin T (E1: r = 0.524, p = 0.010; E4: r = 0.413, p = 0.044); CK-MB (mass) and NT-proBNP (E4: r = 0.539, p = 0.006); and E/A and E'' (E0: r = 0.603, p < 0.001; E1: r = 0.639, p < 0.001; E4: r = 0.593, p = 0.002). A negative correlation was found between CK-MB (mass) and E/A (E1: r = −0.428, p = 0.041).Conclusion:The effects of intense, prolonged, and interspersed physical activity were verified based on significant variations in the behavior of CK-MB (mass), NT-proBNP, and the E'' wave. Notwithstanding the alterations found, there were no criteria suggestive of myocardial damagePalavras-chave: Walking, Biomarkers, Biological, Blood Pressure, Troponin-T, Natriuretic Peptide Brain, Athletes, Echocardiography, Doppler/methods  相似文献   
65.
Abstract:  We have recently shown that melatonin antagonizes damage-induced apoptosis by interaction with the MT-1/MT-2 plasma membrane receptors. Here, we show that melatonin interferes with the intrinsic pathway of apoptosis at the mitochondrial level. In response to an apoptogenic stimulus, melatonin allows mitochondrial translocation of the pro-apoptotic protein Bax, but it impairs its activation/dimerization The downstream apoptotic events, i.e. cytochrome c release, caspase 9 and 3 activation and nuclear vesiculation are equally impaired, indicating that melatonin interferes with Bax activation within mitochondria. Interestingly, we found that melatonin induces a strong re-localization of Bcl-2, the main Bax antagonist to mitochondria, suggesting that Bax activation may in fact be antagonized by Bcl-2 at the mitochondrial level. Indeed, we inhibit the melatonin anti-apoptotic effect (i) by silencing Bcl-2 with small interfering RNAs, or with small-molecular inhibitors targeted at the BH3 binding pocket in Bcl-2 (i.e. the one interacting with Bax); and (ii) by inhibiting melatonin-induced Bcl-2 mitochondrial re-localization with the MT1/MT2 receptor antagonist luzindole. This evidence provides a mechanism that may explain how melatonin through interaction with the MT1/MT2 receptors, elicits a pathway that interferes with the Bcl-2 family, thus modulating the cell life/death balance.  相似文献   
66.
Pseudomonas aeruginosa san ai is a promising candidate for bioremediation of cadmium pollution, as it resists a high concentration of up to 7.2 mM of cadmium. Leaving biomass of P. aeruginosa san ai exposed to cadmium has a large biosorption potential, implying its capacity to extract heavy metal from contaminated medium. In the present study, we investigated tolerance and accumulation of cadmium on protein level by shotgun proteomics approach based on liquid chromatography and tandem mass spectrometry coupled with bioinformatics to identify proteins. Size exclusion chromatography was used for protein prefractionation to preserve native forms of metalloproteins and protein complexes. Using this approach a total of 60 proteins were observed as up-regulated in cadmium-amended culture. Almost a third of the total numbers of up-regulated were metalloproteins. Particularly interesting are denitrification proteins which are over expressed but not active, suggesting their protective role in conditions of heavy metal exposure. P. aeruginosa san ai developed a complex mechanism to adapt to cadmium, based on: extracellular biosorption, bioaccumulation, the formation of biofilm, controlled siderophore production, enhanced respiration and modified protein profile. An increased abundance of proteins involved in: cell energy metabolism, including denitrification proteins; amino acid metabolism; cell motility and posttranslational modifications, primarily based on thiol-disulfide exchange, were observed. Enhanced oxygen consumption of biomass in cadmium-amended culture versus control was found. Our results signify that P. aeruginosa san ai is naturally well equipped to overcome and survive high doses of cadmium and, as such, has a great potential for application in bioremediation of cadmium polluted sites.

When exposed to cadmium a highly resistant strain P. aeruginosa san ai responds by an increased metalloprotein expression (particularly denitrification proteins), an enhanced respiration, and a pronounced thiol-disulfide protein modifications.  相似文献   
67.
Nonunion treatment has a high rate of success, although recalcitrant nonunion may determine the need for amputation. Therefore, new treatment options are continuously investigated in order to further reduce the risk of nonunion recurrence. This study aimed to (a) develop a new large animal model for bone atrophic nonunion and (b) compare the efficacy of demineralized bone matrix (DBM) and DBM in combination with mesenchymal stem cells (MSC) in the new nonunion model. The new model consists of a noncritical, full‐thickness segmental defect created in the sheep tibia, stabilized by an intramedullary nail, and involves the creation of a locally impaired blood supply achieved through periosteum excision and electrocauterization of the stump ends. Six weeks after defect creation, lack of hard tissue callus and established nonunion was observed in all operated tibiae both by radiographic and clinical evaluation. Nonunion was treated with allogeneic DBM or autologous MSC cultivated on DBM particles (DBM + MSC) for 1 day before implantation. Twelve weeks after treatment, radiographic, microtomographic, histologic, and histomorphometric analysis showed the formation of bone callus in DBM group, whereas the fracture healing appeared at an early stage in DBM + MSC group. Torsional strength and stiffness of the DBM group appeared higher than those of DBM + MSC group, although the differences were not statistically significant. In conclusion, a new sheep bone nonunion model resembling the complexity of the clinical condition was developed. DBM is an effective option for nonunion treatment, whereas MSC do not improve the healing process when cultivated on DBM particles before implantation.  相似文献   
68.

Objectives

The aim of the study is to assess the weight loss programme with regards to the long-term effectiveness of weight reduction and weight maintenance, using completion rate and BMI, blood sugar, cholesterol and blood pressure levels as outcomes. The aim of the study also includes identifying the factors associated with adherence to the programme.

Methods

The programme was developed by a multidisciplinary team. It included 6 months of introduction and another 18 months of maintenance. The data for 397 participants was collected after 24 months.

Results

346 participants have completed the introduction and 123 have completed the programme. In the introduction, the average weight loss was 12% of the initial weight. The participants, who completed the full programme, lost 9.4% of their initial weight. The participants also significantly (p<0.05) reduced their blood sugar and cholesterol levels, as well as their blood pressure. The factors associated with adherence to the programme are: age over 50, lower educational levels, lower initial weight and higher weight loss in the introduction.

Conclusions

The multi-disciplinary approach to obesity treatment was effective for a selected group of people. The proportion of dropouts was relatively high, but still low compared to similar programmes. Group treatment and mutual support are of a great importance in bringing about and maintaining the changes.  相似文献   
69.

BACKGROUND

Evidence suggests that expressed emotion (EE) and family burden (FB) are phenomena that interact, but there is a lack of studies that analyze this association in patients in first-episode psychosis.

AIM

This study evaluated the relationship between EE and FB in relatives of patients in first-episode psychosis.

METHOD

A convenience sample of 71 family members of patients being assisted in an outpatient care unit participated in the study. We used a form with sociodemographic and clinical variables of family members and patients, the Family Questionnaire-Brazilian Portuguese Version and the Brazilian version of the Burden Interview. The data were obtained via semi-structured interviews. Statistical analyses included Fisher's exact tests, Mann Whitney tests, Spearman correlations, and Student's t-tests.

RESULTS

Our results showed high levels of EE and its component emotional over-involvement (EOI) among relatives, and a strong correlation between critical comments (CC) and EOI and FB measurements. In addition, family members with elevated EE levels showed higher means for FB and this difference was significant.

CONCLUSIONS

Mental health nurses are expected to consider these concepts for proposing nursing interventions to first-episode psychosis patients and their relatives.  相似文献   
70.
Bone regeneration is a long-term process requiring proper scaffolding and drug delivery systems. The current study delivers a three-dimensional (3D) scaffold prepared by blend centrifugal spinning loaded with the osteogenic supplements (OS) β-glycerol phosphate, ascorbate-2-phosphate and dexamethasone. The OS were successfully encapsulated into a fibrous scaffold and showed sustained release for 30 days. Furthermore, biological testing showed the osteoinductive properties of the scaffolds on a model of human mesenchymal stem cells and stimulatory effect on a model of osteoblasts. The osteoinductive properties were further proved in vivo in critical size defects of rabbits. The amount of bone trabecules was bigger compared to control fibers without OS. The results indicate that due to its long-term drug releasing properties, single step fabrication process and 3D structure, the system shows ideal properties for use as a cell-free bone implant in tissue-engineering.

Bone regeneration is a long-term process requiring proper scaffolding and drug delivery systems.  相似文献   
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