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   5145篇
  免费   375篇
  国内免费   20篇
耳鼻咽喉   64篇
儿科学   263篇
妇产科学   112篇
基础医学   697篇
口腔科学   148篇
临床医学   431篇
内科学   1128篇
皮肤病学   59篇
神经病学   482篇
特种医学   137篇
外国民族医学   1篇
外科学   536篇
综合类   32篇
一般理论   3篇
预防医学   444篇
眼科学   78篇
药学   474篇
中国医学   11篇
肿瘤学   440篇
  2023年   32篇
  2022年   93篇
  2021年   135篇
  2020年   110篇
  2019年   149篇
  2018年   148篇
  2017年   107篇
  2016年   137篇
  2015年   148篇
  2014年   193篇
  2013年   262篇
  2012年   383篇
  2011年   364篇
  2010年   194篇
  2009年   205篇
  2008年   342篇
  2007年   319篇
  2006年   275篇
  2005年   295篇
  2004年   257篇
  2003年   221篇
  2002年   204篇
  2001年   100篇
  2000年   80篇
  1999年   84篇
  1998年   56篇
  1997年   39篇
  1996年   25篇
  1995年   21篇
  1994年   32篇
  1993年   29篇
  1992年   41篇
  1991年   34篇
  1990年   38篇
  1989年   33篇
  1988年   28篇
  1987年   28篇
  1986年   20篇
  1985年   32篇
  1984年   22篇
  1982年   11篇
  1981年   16篇
  1980年   10篇
  1979年   20篇
  1978年   10篇
  1976年   12篇
  1975年   11篇
  1974年   12篇
  1973年   11篇
  1972年   12篇
排序方式: 共有5540条查询结果,搜索用时 15 毫秒
71.
OBJECTIVE: To examine the association between the parent's language of interview and the access to care for children with special health care needs (CSHCN). METHODS: We used the 2001 National Survey of Children with Special Health Care Needs to compare socio-demographic characteristics and health care access variables among CSHCN with parents who interviewed in English and another language. Additional multivariate analyses explored the effect of language of interview on access to health care for the subgroup of Hispanic respondents. RESULTS: CSHCN with non-English-speaking parents were from less-educated and lower-income families and were more likely to lack insurance and have conditions that greatly affected their activities. These children were also more likely to have inadequate insurance (odds ratio [OR]=11.29), have an unmet need for family support services (OR=1.88), lack a personal doctor or nurse (OR=1.98), lack a usual source of care (OR=1.89), and lack family-centered care (OR=1.74). Non-English-speaking parents were more likely to report having employment consequences (OR=1.94) and spending over $500 out-of-pocket annually on the child's health care needs (OR=1.49). The likelihood of Hispanic children experiencing health care access barriers compared with non-Hispanic children was reduced when language was controlled for and several disparities between Hispanic children and other children became insignificant. CONCLUSIONS: CSHCN with non-English-speaking parents were more likely to be from disadvantaged families and to experience barriers to access than were CSHCN with English-speaking parents. Systems of care for CSHCN should consider the needs and challenges experienced by families whose primary language is not English.  相似文献   
72.
Bothrops asper venom (BaV) causes systemic and local effects characterized by an acute inflammatory reaction with accumulation of leukocytes and release of endogenous mediators. In this study, the effects of BaV on the release of the cytokines IL-1, IL-6 and TNF-alpha and the eicosanoids LTB4 and TXA2 in the peritoneal cavity of mice were analyzed. We also investigated the participation of beta2 integrin chain, l-selectin, LFA-1, ICAM-1 and PECAM-1 adhesion molecules in the BaV-induced leukocyte accumulation. Levels of proinflammatory cytokines IL-6 and TNF-alpha, as well as eicosanoids LTB4 and TXA2 were significantly increased after BaV injection (250 microg/kg), whereas no increment in IL-1 was observed. Anti-mouse l-selectin, LFA-1, ICAM-1, PECAM-1 and beta2 integrin chain monoclonal antibodies resulted in a reduction of neutrophil accumulation induced by BaV injection compared with isotype-matched control injected animals. These data suggest that BaV is able to induce the activation of leukocytes and endothelium to express adhesion molecules involved in the recruitment of neutrophils into the inflammed site. Furthermore, these results showed that BaV induces the release of cytokines and eicosanoids in the local of the venom injection; these inflammatory mediators may be important for the initiation and amplification of the inflammatory reaction characteristic from Bothrops sp envenomation.  相似文献   
73.
BACKGROUND: The MLL 11q23 translocation arises in utero and is present in 75% of infant leukemias. That MLL+ acute myeloid leukemia (AML) can arise following chemotherapy with DNA topoisomerase II (DNAt2) inhibitors suggests that these substances, which also occur naturally in foods, may contribute toward infant leukemia. We hypothesized that maternal consumption of dietary DNAt2 inhibitors during pregnancy would increase the risk of infant leukemia, particularly AML(MLL+). METHODS: This Children's Oncology Group case-control study consisted of 240 incident cases of infant acute leukemia [AML and acute lymphoblastic leukemia (ALL)] diagnosed during 1996 to 2002 and 255 random digit dialed controls. Maternal diet during pregnancy was determined through a food frequency questionnaire. An index of specific foods identified a priori to contain DNAt2 inhibitors as well as vegetables and fruits were created and analyzed using unconditional logistic regression. RESULTS: There was little evidence of an association between the specific DNAt2 index and leukemia overall and by subtype. An exception was AML(MLL+); odds ratios (95% confidence intervals) comparing the second to fourth quartiles to the first were 1.9 (0.5-7.0), 2.1 (0.6-7.7), and 3.2 (0.9-11.9), respectively (P for trend = 0.10). For the vegetable and fruit index, there were significant or near-significant inverse linear trends for all leukemias combined, ALL(MLL+), and AML(MLL-). CONCLUSION: Overall, maternal consumption of fresh vegetables and fruits during pregnancy was associated with a decreased risk of infant leukemia, particularly MLL+. However, for AML(MLL+) cases, maternal consumption of specific DNAt2 inhibitors seemed to increase risk. Although based on small numbers, these data provide some support for distinct etiologic pathways in infant leukemia.  相似文献   
74.
PURPOSE: The long-term survival of children between age 12 and 24 months with stage 4 neuroblastoma and nonamplified MYCN (MYCN-NA) has not been defined previously. PATIENTS AND METHODS: Survival for stage 4 MYCN-NA neuroblastoma patients enrolled onto Children's Cancer Group (CCG) protocols 321P2 (1986 to 1991) and 3891 (1991 to 1996) was analyzed. Treatment consisted of intensive alkylator-based induction chemotherapy with or without autologous bone marrow transplantation (ABMT) with or without 13 cis-retinoic acid. Survival was analyzed by age strata less than 12, 12 to 18, 18 to 24, and more than 24 months at diagnosis. Patients younger than 12 months were treated on the moderate-intensity CCG protocol 3881. RESULTS: Forty-three patients with stage 4 MYCN-NA disease enrolled onto CCG-321P2 (n = 17) or CCG-3891 (n = 26) were between 12 and 24 months of age at diagnosis. After a median follow-up of 94 months (range, 4 to 140 months), the 6-year event-free survival (EFS) for the 12- to 18-month age group was superior to that of the 18- to 24-month age group (74% +/- 8% v 31% +/- 12%; P = .008). The EFS for children older than 24 months with stage 4 MYCN-NA neuroblastoma was 23% +/- 3%, and for children younger than 12 months was 92% +/- 3%. CONCLUSION: Children diagnosed with stage 4 MYCN-NA neuroblastoma in the second year of life form a transitional group between infants and older children in terms of prognosis. Patients between 12 and 18 months of age have significantly better long-term survival than that of older children treated with intensive chemotherapy with or without ABMT. These patients may not benefit from additional intensification of therapy beyond that provided in earlier clinical trials and may even maintain this high survival rate with less intensive therapy.  相似文献   
75.
BACKGROUND: Deep-vein thrombosis (DVT) and pulmonary embolism (PE) are the most important causes of morbility and mortality in patients submitted to surgical intervention: some peculiar factors of laparoscopic surgery can modify their risk. The aim of this study is to evaluate possible variations of the fibrinolytic system after cholecystectomy. METHODS: Eighteen patients affected by symptomatic and non-complicated gallstones have been included in this study. They were divided into two groups of nine patients each: the first group was submitted to laparoscopic cholecystectomy (LC) and the second to open cholecystectomy (OC). Antitrombin III (ATIII), fibrinogen degradation products (FDP), tissue plasminogen activator (tPA), and plasminogen activator inhibitor (PAI) have been evaluated preoperatively and 6, 12, 24 and 48 hours after the operation. RESULTS: The levels of ATIII did not present significantly variations. The FDP in both groups were significantly increased 48 hours after open cholecystectomy. Levels of PAI instead were increased in comparison to the basal values at 6, 12, 24, 48 hours with p < 0.05; p < 0.01 and p < 0.05 respectively in patients submitted to OC, in the LC group no variations were observed; a comparison between the groups showed a significant modification (p < 0.05) only at the 12th hour. CONCLUSIONS: The early mobilization of patients in the postoperative course and the lower invasion of LC can oppose the prothrombotic effect in the lower limbs.  相似文献   
76.
Whereas the presynaptic action of Crotalus durissus terrificus venom is well-established, Bothrops venoms have historically been considered to have only postsynaptic and muscular effects. However, some studies have also suggested a presynaptic action for these venoms. In this work, we used chick biventer cervicis preparations to compare the presynaptic actions of two Bothrops venoms (B. insularis and B. neuwiedi) with that of C. d. terrificus venom. At 10 microg/ml, all venoms produced irreversible blockade of the twitch tension responses, with no reduction in acetylcholine (ACh)-induced contractures and only a slight decrease in potassium induced-contractures. The times (in min) required to produce 50% neuromuscular blockade (C. d. terrificus: 16.3+/-0.7, n = 8; B. insularis: 30.0+/-1.9, n = 5; B. neuwiedi: 42.0+/-2.0, n = 8; mean +/- SEM) were significantly different among the venoms (p < 0.01). Lowering the temperature at which the experiments were done (from 37 to 24 degrees C) prevented neuromuscular blockade by the three venoms, indicating that enzyme activity may be involved in this response. At concentrations capable of causing complete neuromuscular blockade, creatine kinase release remained close to levels seen in control preparations incubated with Krebs solution alone (500-1200 IU/l). Commercial crotalic antivenom, but not bothropic antivenom, protected against the neuromuscular blockade caused by B. insularis and B. neuwiedi venoms. These observations indicate that bothropic venoms may contain components which act presynaptically in a manner similar to C. d. terrificus venom, and that at low venom concentrations a direct action on skeletal muscle does not contribute to this presynaptic neurotoxicity.  相似文献   
77.
The in vitro metabolism of MK-0767 [(+/-)-5-[(2,4-dioxothiazolidin-5-yl) methyl]-2-methoxy-N-[[(4-trifluoromethyl)-phenyl] methyl]benzamide], a novel 2,4-thiazolidinedione (TZD)-containing peroxisome proliferator-activated receptor alpha/gamma agonist, was studied in rat, dog, monkey, and human liver microsomes and hepatocytes, as well as in recombinant human CYP3A4-containing microsomes. Twenty-two metabolites (some at trace levels) were detected by liquid chromatography-tandem mass spectrometry analysis. All appeared to be phase I metabolites except for a glucuronide conjugate of a hydroxylated metabolite that was detected at trace levels. A constant neutral loss scan experiment performed on a triple quadrupole mass spectrometer proved to be very useful for resolving the metabolites from endogenous compounds. It was observed that the initial site of metabolism of MK-0767 was at the TZD ring leading to two major metabolites, namely the 5-hydroxy-TZD metabolite (M24) and the mercapto metabolite (M22). The latter was formed via the cleavage of the TZD ring with the elimination of the carbonyl adjacent to the sulfur atom. The structure of M24 was established by accurate mass measurements and NMR analysis. This hydroxy-TZD metabolite might represent an important precursor for a group of metabolites formed by TZD ring opening and subsequent loss of the sulfur moiety. The mercapto metabolite, on the other hand, is probably the key precursor for the TZD ring-opened metabolites with retention of the sulfur, even though the detailed mechanism of the ring scission remains to be characterized. From these studies, it was concluded that the TZD ring was the major site of metabolism of MK-0767. All the metabolites produced in vitro from human preparations were detected in the corresponding preparations from the nonclinical species.  相似文献   
78.

Purpose

Using planning target volume (PTV) to account for setup uncertainties in stereotactic body radiation therapy (SBRT) of lung cancer has been questioned because a significant portion of the PTV contains low-density lung tissue. The purpose of this study is to (1) investigate the feasibility of using robust optimization to account for setup uncertainties in volumetric modulated arc therapy plan for lung SBRT and (2) evaluate the potential normal tissue–sparing benefit of a robust optimized plan compared with a conventional PTV-based optimized plan.

Methods and materials

The study was conducted with both phantom and patient cases. For each patient or phantom, 2 SBRT lung volumetric modulated arc therapy plans were generated, including an optimized plan based on the PTV (PTV-based plan) with a 5-mm internal target volume (ITV)-to-PTV margin and a second plan based on robust optimization of ITV (ITV-based plan) with ±5-mm setup uncertainties. The target coverage was evaluated on ITV D99 in 15 scenarios that simulated a 5-mm setup error. Dose-volume information on normal lung tissue, intermediate-to-high dose spillage, and integral dose was evaluated.

Results

Compared with PTV-based plans, ITV-based robust optimized plans resulted in lower normal lung tissue dose, lower intermediate-to-high dose spillage to the body, and lower integral dose, while preserving the dose coverage under setup error scenarios for both phantom and patient cases.

Conclusions

Using ITV-based robust optimization, we have shown that accounting for setup uncertainty in SBRT planning is feasible. Further clinical studies are warranted to confirm the clinical effectiveness of this novel approach.  相似文献   
79.
BACKGROUND: The purpose of this study was to evaluate the role of dynamic contrast-enhanced magnetic resonance imaging (dMRI) in detecting bone marrow involvement in cancer patients. PATIENTS AND METHODS: We studied 50 consecutive patients with histologically confirmed malignant dissemination to the bone marrow, using dMRI of the lumbosacral spine. Time-signal intensity curves were generated from regions of interest (ROIs) obtained from areas of obvious bone marrow disease (group B). In 16 patients from group B with focal disease, ROIs were also placed on areas with apparently normal bone marrow on static magnetic resonance images (group C). Twenty-two patients with no history of malignancy were used as a control group (group A). Wash-in (WIN) and wash-out (WOUT) rates, time to peak (TTPK), time to maximum slope (TMSP) values and WIN/TMSP ratios were calculated for each patient. Mean values for the three groups were compared statistically. Six patients from group B had follow-up dMRI after chemotherapy: four patients achieved a clinical partial response and two had resistant disease. RESULTS: A significant difference was found between groups A and B for all values. Between groups A and C, in spite of the similar static MRI appearance, all values were significantly different. Between groups B and C, a significant difference was found for WIN, WOUT rates and WIN/TMSP ratio. Follow-up dMRI data analysis correlated well with clinical staging. CONCLUSIONS: dMRI can distinguish normal from malignant bone marrow. It may identify malignant bone marrow infiltration in patients with negative static MRI and serve as both a diagnostic and prognostic tool for patients with bone marrow malignancies.  相似文献   
80.
The study of intra and interlayer excitons in 2D semiconducting vdW heterostructures is a very hot topic not only from a fundamental but also an applicative point of view. Due to their strong light–matter interaction, Transition Metal Dichalcogenides (TMD) and group-III nitrides are particularly attractive in the field of opto-electronic applications such as photo-catalytic and photo-voltaic ultra-thin and flexible devices. Using first-principles ground and excited-state simulations, we investigate here the electronic and excitonic properties of a representative nitride/TMD heterobilayer, the AlN/WS2. We demonstrate that the band alignment is of type I, and low energy intralayer excitons are similar to those of a pristine WS2 monolayer. Further, we disentangle the role of strain and AlN dielectric screening on the electronic and optical gaps. These results, although they do not favor the possible use of AlN/WS2 in photo-catalysis, as envisaged in the previous literature, can boost the recently started experimental studies of 2D hexagonal aluminum nitride as a good low screening substrate for TMD-based electronic and opto-electronic devices. Importantly, our work shows how the inclusion of both spin-orbit and many-body interactions is compulsory for the correct prediction of the electronic and optical properties of TMD/nitride heterobilayers.  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