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   6733篇
  免费   645篇
  国内免费   12篇
耳鼻咽喉   81篇
儿科学   252篇
妇产科学   214篇
基础医学   808篇
口腔科学   77篇
临床医学   1037篇
内科学   1272篇
皮肤病学   87篇
神经病学   742篇
特种医学   98篇
外科学   573篇
综合类   91篇
一般理论   8篇
预防医学   1094篇
眼科学   131篇
药学   451篇
中国医学   6篇
肿瘤学   368篇
  2023年   96篇
  2022年   135篇
  2021年   259篇
  2020年   194篇
  2019年   280篇
  2018年   281篇
  2017年   239篇
  2016年   208篇
  2015年   221篇
  2014年   312篇
  2013年   351篇
  2012年   541篇
  2011年   549篇
  2010年   259篇
  2009年   187篇
  2008年   375篇
  2007年   350篇
  2006年   319篇
  2005年   265篇
  2004年   248篇
  2003年   207篇
  2002年   178篇
  2001年   101篇
  2000年   73篇
  1999年   68篇
  1998年   32篇
  1997年   30篇
  1996年   25篇
  1995年   26篇
  1994年   19篇
  1993年   27篇
  1992年   63篇
  1991年   71篇
  1990年   67篇
  1989年   55篇
  1988年   30篇
  1987年   44篇
  1986年   55篇
  1985年   47篇
  1984年   23篇
  1983年   30篇
  1981年   34篇
  1979年   52篇
  1977年   25篇
  1976年   20篇
  1975年   25篇
  1974年   33篇
  1973年   34篇
  1972年   40篇
  1971年   24篇
排序方式: 共有7390条查询结果,搜索用时 387 毫秒
11.
PURPOSE: To evaluate qualitative wall motion assessment vs. quantitative wall thickening for the assessment of subtle changes in myocardial systolic function using cine MRI. METHODS: Cine MR images were obtained in 5 canines with a significant coronary artery stenosis and in 2 controls on a 1.5T scanner. Qualitative results were obtained using a numerical scoring system; quantitative analysis was performed using a semi-automatic segmentation program. The techniques were matched and compared using Spearman correlations. RESULTS: All correlations in the experimental group revealed significant but weak to moderate relationships between the qualitative and quantitative results (e.g., at-risk tissue rho = 0.363, p < 0.0001; remote tissue rho = 0.275, p = 0.0002), with each identifying changes in regional function that ensued following creation of the stenosis. Intra-observer variability was reasonable in both methods when repeat analysis on a subset of the data was performed, with both techniques showing a significant correlation between the repeated measurements (quantitative - rho = 0.52, p < 0.0001; qualitative - rho = 0.54, p < 0.0001). CONCLUSION: Both methods were able to detect very limited wall motion abnormalities present in the canines with significant stenosis and either method gives comparable results.  相似文献   
12.
Phase II clinical trials are performed to investigate whether a novel treatment shows sufficient promise of efficacy to justify its evaluation in a subsequent definitive phase III trial, and they are often also used to select the dose to take forward. In this paper we discuss different design proposals for a phase II trial in which three active treatment doses and a placebo control are to be compared in terms of a single‐ordered categorical endpoint. The sample size requirements for one‐stage and two‐stage designs are derived, based on an approach similar to that of Dunnett. Detailed computations are prepared for an illustrative example concerning a study in stroke. Allowance for early stopping for futility is made. Simulations are used to verify that the specified type I error and power requirements are valid, despite certain approximations used in the derivation of sample size. The advantages and disadvantages of the different designs are discussed, and the scope for extending the approach to different forms of endpoint is considered. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
13.
The epithelial cells of the colonic mucosa of the animal have proved impossible to culture using standard tissue culture techniques. Immortalization of adult colonic epithelial cells has been unsuccessful due to the lack of DNA synthesis in these cells once they are isolated from the tissue. Recently an unique transgenic mouse bearing a temperature sensitive mutant of the known immortalizing gene, SV40 large T has become available. The advantage of this mouse is that the SV40 large T gene is expressed in every cell. Active immortalizing protein is produced in each cell at the permissive temperature. We have used colonic mucosa from these mice to initiate cultures of epithelial cells from the colon of adult mice. The cells grow readily at the permissive temperature but die within 7 days at the non-permissive temperature. The methods used to develop these cultures are described.  相似文献   
14.
15.
As part of the Canadian Wildlife Service monitoring of great blue herons in British Columbia, eggs were collected from three colonies with low, intermediate, and high levels of PCDD and PCDF contamination: Nicomekl, Vancouver, and Crofton, respectively. One egg from each nest was used for chemical analysis by GC-MS; the others were hatched. Liver microsomes were prepared from the heron chicks and used for determination of cytochrome P-450-dependent activities. No erythromycin N-demethylase activity was found in any sample. Ethoxyresorufin O-dealkylase activity in the Nicomekl group was similar to that in pigeons, a control altricial species. The ethoxyresorufin activity in the herons from the Crofton colony was 2.6-fold higher than in the Nicomekl group. The Vancouver colony was intermediate. No difference among the three heron colonies was found in pentoxyresorufin O-dealkylase activity, although levels were 20-33 times that in the pigeon. Chemical analysis was carried out on paired heron eggs. Vancouver and Crofton eggs contained 13.5 and 21 times the levels of 2,3,7,8-TCDD compared to the Nicomekl group. The Crofton eggs contained higher levels of several other contaminants also. A highly significant correlation (p less than .001) was found between ethoxyresorufin O-dealkylase and 2,3,7,8-TCDD concentrations. The correlation coefficient did not change when ethoxyresorufin O-dealkylase was compared to total chemical contamination using several toxic equivalency factors. Multiple regression analysis resulted in only one predictor variable for ethoxyresorufin O-dealkylase: 2,3,7,8-TCDD.  相似文献   
16.
Mildly elevated maternal plasma homocysteine (Hcy) levels (hyperhomocysteinemia) have recently been observed in some neural tube defect (NTD) pregnancies. Plasma levels of Hcy are governed by both genetic and nutritional factors and the aetiology of NTDs is also known to have both genetic and nutritional components. We therefore examined the frequency of relatively common mutations in the enzyme cystathionine β-synthase (CBS), which is one of the main enzymes that controls Hcy levels, in the NTD population. Neither the severely dysfunctional G307S CBS allele nor the recently reported 68 bp insertion/I278T CBS allele was observed at increased frequency in the cases relative to controls. We therefore conclude that loss of function CBS alleles do not account for a significant proportion of NTDs in Ireland.  相似文献   
17.
The author’s reviewed their experience with a formalized outplacement project used in New York State during 1984 to preserve continuity of employment for those affected by staff reductions in state MR facilities. Mr. Torino’s perspective is agencywide, reflecting his responsibility for manpower management throughout New York State’s 20 MR/DD facilities. Mr. Whitehead’s experience was based on his work at one of the centers involved, Craig developmental—a hundred-year-old rural facility, serving a five-county region south of Rochester. The paper was presented at the 1984 AMHA annual meeting in Chicago. JAMES J. WHITEHEAD is currently deputy director at Craig Development Center, a state-operated facility in upstate New York. He has an M.A. from Syracuse University and an M.B.A. from the State University of New York at Buffalo. Jim has written articles for the AMHA Journal in the past— one in 1983 dealing with the general area of cutback management in mental health. He’s also a past president of New York State’s AMHA Chapter. THOMAS M. TORINO is director of human resource management, New York State Division of Alcohol and Alcohol Abuse. He’s had 13 years of human relations management experience and has done consulting with other states on ways to reduce the impact of MH/MR facility closings. Tom has a master’s degree in public administration from the State University of New York at Albany’s Rockefeller College.  相似文献   
18.
A closed femur fracture pain model was developed in the C57BL/6J mouse. One day after fracture, a monoclonal antibody raised against nerve growth factor (anti-NGF) was delivered intraperitoneally and resulted in a reduction in fracture pain-related behaviors of approximately 50%. Anti-NGF therapy did not interfere with bone healing as assessed by mechanical testing and histomorphometric analysis. INTRODUCTION: Current therapies to treat skeletal fracture pain are limited. This is because of the side effect profile of available analgesics and the scarcity of animal models that can be used to understand the mechanisms that drive this pain. Whereas previous studies have shown that mineralized bone, marrow, and periosteum are innervated by sensory and sympathetic fibers, it is not understood how skeletal pain is generated and maintained even in common conditions such as osteoarthritis, low back pain, or fracture. MATERIALS AND METHODS: In this study, we characterized the pain-related behaviors after a closed femur fracture in the C57BL/6J mouse. Additionally, we assessed the effect of a monoclonal antibody that binds to and sequesters nerve growth factor (anti-NGF) on pain-related behaviors and bone healing (mechanical properties and histomorphometric analysis) after fracture. RESULTS: Administration of anti-NGF therapy (10 mg/kg, days 1, 6, and 11 after fracture) resulted in a reduction of fracture pain-related behaviors of approximately 50%. Attenuation of fracture pain was evident as early as 24 h after the initial dosing and remained efficacious throughout the course of fracture pain. Anti-NGF therapy did not modify biomechanical properties of the femur or histomorphometric indices of bone healing. CONCLUSIONS: These findings suggest that therapies that target NGF or its cognate receptor(s) may be effective in attenuating nonmalignant fracture pain without interfering with bone healing.  相似文献   
19.
To examine the relationship between demographic, clinical and psychosocial variables and diabetes self-care management in Mexican type 2 diabetic patients. Cross-sectional study of 176 consecutive patients with type 2 diabetes aged 30-75 years, attending a tertiary health-care center in Mexico City. A brief medical history and previously validated questionnaires were completed. The study group consisted of 64 males/112 females, aged 55 +/- 11 years, mean diabetes duration of 12 +/- 8 years and HbA1c of 9.0 +/- 2.0%, 78.4% reported following the correct dose of diabetes pills or insulin, 58% ate the recommended food portions, and 44.3% did exercise three or more times per week. A good adherence to these three recommendations was observed in only 26.1% of the patients. These patients considered as a group were characterized by a greater knowledge about the disease (P < 0.00001), regular home blood glucose monitoring (P < 0.01), an inner perception of better diabetes control (P = 0.007), good health (P = 0.004) and better communication with their physician (P < 0.02). A poor adherence to two or the three main diabetes care recommendations was associated with a depressive state (OR 2.38, 95% CI 1.1-4.9, P < 0.01) and a history of excessive alcohol intake (OR 4.03, 95% CI 1.1-21.0, P = 0.03). Poor adherence to standard diabetes care recommendations is frequently observed in patients with type 2 diabetes attending a specialized health care center in Mexico City. Depression must be identified and treated effectively.  相似文献   
20.
To date, there is no clinicopathological correlation of adrenal medullary transplant cases in patients with survival beyond a few years. Postmortem examination of a brain from a patient with Parkinson's disease (PD), 16 years after autologous adrenal medullary transplant, was performed using tyrosine hydroxylase (TH) and chromogranin A. The patient experienced a four-year initial improvement in motor function followed by resumption of the progressive nature of her disease that continued until her death. She expired 16 years following grafting. At autopsy, TH stain of the brain revealed severe loss of TH-immunoreactivity in the substantia nigra and Lewy bodies, confirming the diagnosis of PD. The transplant site was identified by the presence of scarring and there was complete absence of any TH staining cells at the site of the transplant. There were few surviving cells staining with chromogranin A. The absence of TH-staining cells in the transplant 16 years after surgery provides further evidence that adrenal medullary transplants do not survive in the long term.  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