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   6846篇
  免费   671篇
  国内免费   64篇
耳鼻咽喉   56篇
儿科学   163篇
妇产科学   119篇
基础医学   856篇
口腔科学   539篇
临床医学   731篇
内科学   1303篇
皮肤病学   64篇
神经病学   590篇
特种医学   239篇
外科学   1073篇
综合类   113篇
一般理论   15篇
预防医学   692篇
眼科学   70篇
药学   500篇
中国医学   9篇
肿瘤学   449篇
  2021年   104篇
  2020年   60篇
  2019年   108篇
  2018年   113篇
  2017年   95篇
  2016年   100篇
  2015年   110篇
  2014年   177篇
  2013年   240篇
  2012年   312篇
  2011年   396篇
  2010年   201篇
  2009年   162篇
  2008年   350篇
  2007年   420篇
  2006年   396篇
  2005年   361篇
  2004年   306篇
  2003年   326篇
  2002年   314篇
  2001年   131篇
  2000年   159篇
  1999年   117篇
  1998年   82篇
  1997年   76篇
  1996年   74篇
  1995年   64篇
  1994年   49篇
  1992年   122篇
  1991年   91篇
  1990年   106篇
  1989年   81篇
  1988年   100篇
  1987年   81篇
  1986年   92篇
  1985年   73篇
  1984年   80篇
  1983年   80篇
  1982年   59篇
  1981年   50篇
  1980年   42篇
  1979年   51篇
  1978年   60篇
  1977年   58篇
  1976年   42篇
  1975年   46篇
  1974年   56篇
  1973年   47篇
  1972年   58篇
  1971年   45篇
排序方式: 共有7581条查询结果,搜索用时 15 毫秒
1.
2.
Using data on waterfowl band recoveries, we identified spatially explicit hotspots of concentrated waterfowl movement to predict occurrence and spatial spread of a novel influenza A virus (clade 2.3.4.4) introduced from Asia by waterfowl from an initial outbreak in North America in November 2014. In response to the outbreak, the hotspots of waterfowl movement were used to help guide sampling for clade 2.3.4.4 viruses in waterfowl as an early warning for the US poultry industry during the outbreak . After surveillance sampling of waterfowl, we tested whether there was greater detection of clade 2.3.4.4 viruses inside hotspots. We found that hotspots defined using kernel density estimates of waterfowl band recoveries worked well in predicting areas with higher prevalence of the viruses in waterfowl. This approach exemplifies the value of ecological knowledge in predicting risk to agricultural security.  相似文献   
3.
4.
5.
6.
Exhaled nitric oxide (FENO) is raised in atopy. The mechanism for this is unclear. The aim of this study was to investigate whether the number of AAT repeats in intron 20 of the NOS1 gene, recently associated with variations in FENO in adults with asthma and cystic fibrosis, was associated with the raised FENO in healthy atopic children. Eighty-seven healthy children (44 girls, 42 atopic, age range 6–18 years) underwent measurements of FENO, spirometry, airway responsiveness and skin prick testing. Genotyping was carried out to determine the number of AAT repeats. There was no association between the number of AAT repeats and FENO in either the whole sample of healthy children (n = 87) or in the subsample of healthy atopics (n = 42). However, a greater number of atopic children had two high repeat alleles compared with non-atopic children (33.3% vs. 13.6%, respectively, p = 0.03). This suggests that variations in the NOS1 gene may contribute to atopy without this relationship being reflected by FENO.  相似文献   
7.
Tissue distribution studies, utilizing whole-body autoradiography and organ dissection techniques, were conducted in male Fischer 344 rats following the oral administration of 14C-dapoxetine HCl, a potent serotonin reuptake inhibitor. The preliminary study using whole-body autoradiography proved invaluable in locating radioactivity in an organ not usually harvested in a tissue distribution study, namely the preputial gland. Selected organs, based on whole-body autoradiography findings, were dissected from rats and analyzed for radiocarbon content by liquid scintillation counting and for parent drug and N-dealkylated metabolites by extraction and HPLC analysis. Highest concentrations of radiocarbon were observed in the organs of absorption and elimination (ileum, cecum, stomach, duodenum, liver, colon, and kidney) but notable quantities were observed in the lung and preputial and Harderian glands. Most tissues had returned to background radioactive levels 72 h after dosing but persistent concentrations of radiocarbon were present in the preputial gland and liver one week after the single dose of 14C-dapoxetine. Analysis by HPLC demonstrated the presence of parent drug and N-desmethyl metabolite (nor-dapoxetine) in those organs examined; however, the majority of the radioactivity remained unidentified.  相似文献   
8.
Most publications citing the effectiveness of renal extracorporeal shock wave lithotripsy have used plain abdominal radiography to assess residual calculi after treatment. We compared radiologist sensitivity and specificity in the detection of calculi on plain abdominal radiographs versus conventional film-screen and digital renal tomograms in extracorporeal shock wave lithotripsy patients. Of the patients 50 were imaged before and within 24 hours after lithotripsy. Six radiologists evaluated the resultant 300 studies for the presence and location of calculi. The mean sensitivity for digital tomograms was 83% for pre-lithotripsy and post-lithotripsy studies, which was significantly higher than for plain abdominal radiography and conventional tomography after lithotripsy. However, there were significantly more false positive stone diagnoses associated with digital tomogram interpretation. Signal detection analysis verified the over-all superiority of digital tomography for post-extracorporeal shock wave lithotripsy imaging. Calculus detection by conventional and digital tomography is superior to detection by plain abdominal radiography. However, because we did not perform delayed imaging, it is not possible to say what impact digital tomography might have on the management of extracorporeal shock wave lithotripsy patients.  相似文献   
9.
Thirty-two castrated male crossbred growing pigs (average initial wt 26.9 kg) were used to determine the effect of a high level of dietary protein (37%) compared with a normal level of protein (15%) on enterobacteria and Campylobacter sp. inhabitation in the large intestine and on visceral organ hypertrophy and the interrelationships between these two factors. Pigs were kept in pairs (eight pens of two pigs/diet) and fed their respective diets and libitum. Eight pigs (two pens of two pigs fed each diet) were killed at wk 4, 8, 12 and 16 without fasting. Fecal samples were obtained every 2 wk from animals scheduled for necropsy at 16 wk, and colon contents were obtained from all pigs at necropsy; samples were enumerated individually for enterobacteria and Campylobacter sp. Weights of heart, lungs, liver, kidneys, perirenal fat and empty stomach, small intestine and large intestine were recorded at necropsy. Stomach, cecum and proximal colon were sectioned for histopathologic examination. Daily body weight gain was depressed by high dietary protein, but liver and kidneys were heavier in the high protein group than in controls at each time interval. Mild lymphoid hyperplasia of Peyer's patches in the small intestine in some pigs in both groups was indicative of antigenic stimulation but not of pathologic significance. There was no effect of diet on counts of enterobacteria or Campylobacter sp. in feces or colon contents during the 16-wk experiment. We conclude that the hypertrophic response of the tissues of growing pigs to high dietary protein is not the result of the presence of Campylobacter sp. or enterobacteria in the colon contents.  相似文献   
10.
Three antimycotic N-substituted imidazoles, clotrimazole, tioconazole and miconazole, were able to induce hepatic microsomal cytochrome P-450 and monooxygenase reactions in both male and female hamsters to an extent similar to that seen with phenobarbital treatment. Imidazole treatment did not alter the cytochrome P-450 concentration, and ketoconazole treatment decreased it. Cytosolic sulfo- and glutathione transferases were not significantly altered by any imidazole. Induction of microsomal morphine glucuronosyltransferase activity by each compound generally paralleled the effect on cytochrome P-450 in females but induction was not evident in males. Clotrimazole treatment, in contrast to phenobarbital treatment, also caused a large induction of l-naphthol glucuronosyltransferase in females. The potential for antimycotic imidazoles to alter the hepatotoxicity of compounds will require consideration of the inductive changes in both Phase I and Phase II drug metabolizing enzymes in addition to their known inhibitory effects on Phase I oxidations. The inductive effects differ for each imidazole, and in the hamster model, depend upon the sex of the animal.  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