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   2503143篇
  免费   209598篇
  国内免费   8106篇
耳鼻咽喉   34491篇
儿科学   80420篇
妇产科学   64171篇
基础医学   371816篇
口腔科学   69446篇
临床医学   231169篇
内科学   488370篇
皮肤病学   59155篇
神经病学   200244篇
特种医学   94537篇
外国民族医学   510篇
外科学   374026篇
综合类   59737篇
现状与发展   43篇
一般理论   880篇
预防医学   192069篇
眼科学   58032篇
药学   189627篇
  79篇
中国医学   9694篇
肿瘤学   142331篇
  2021年   24144篇
  2019年   30694篇
  2018年   37284篇
  2017年   31371篇
  2016年   34596篇
  2015年   38969篇
  2014年   50189篇
  2013年   68680篇
  2012年   85915篇
  2011年   90748篇
  2010年   59141篇
  2009年   53244篇
  2008年   82120篇
  2007年   85650篇
  2006年   86054篇
  2005年   82872篇
  2004年   78374篇
  2003年   75593篇
  2002年   72778篇
  2001年   111208篇
  2000年   113550篇
  1999年   95115篇
  1998年   27875篇
  1997年   24446篇
  1996年   24700篇
  1995年   23309篇
  1994年   21464篇
  1993年   20105篇
  1992年   72442篇
  1991年   70492篇
  1990年   68752篇
  1989年   65986篇
  1988年   60529篇
  1987年   59363篇
  1986年   55404篇
  1985年   53135篇
  1984年   39395篇
  1983年   33460篇
  1982年   19911篇
  1979年   35924篇
  1978年   25686篇
  1977年   21252篇
  1976年   20352篇
  1975年   21865篇
  1974年   26173篇
  1973年   24825篇
  1972年   23237篇
  1971年   22070篇
  1970年   20275篇
  1969年   19336篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The regional distribution of the phenylalanine-sensitive ATP-sulphurylase in fetal calf brain coincides with demyelinated lesions observed in the central nervous systems of untreated PKU patients. This would be expected if this species of ATP-sulphurylase played a role in the pathogenesis of brain dysfunction in the untreated or poorly controlled phenylketonuria patient.  相似文献   
992.
993.
994.
The value of maternal C-reactive protein (CRP) levels as predictors of fetal and maternal infective morbidity and fetal mortality was assessed prospectively over a 6-month period in all cases of premature rupture of the fetal membranes or suspected premature labour. Statistical analysis of results showed that CRP at a level of 1.32 mg/dl is a sensitive marker of infective morbidity in mother and neonate. Furthermore, there was a significant association between raised CRP levels and low-birth-weight babies, suggesting that intra-uterine infection is a major cause of prematurity in the study population.  相似文献   
995.
Transport of 45Ca from the lumen to the venous effluent was studied in duodena of normal, vitamin D3-replete (+D) chicks perfused through the celiac artery with 130 pM 1,25(OH)2D3 or vehicle. Administration of actinomycin D 3 h prior to perfusion did not alter the unstimulated transport rate or diminish the response to exogenous 1,25(OH)2D3: After 40 min exposure to the seco-steroid, 45Ca in the vascular effluent was 140% of control levels. The anti-microfilament agent cytochalasin b and the ionophore monensin, an inhibitor of Golgi function, similarly failed to suppress 1,25(OH)2D3-stimulated calcium transport. In pilot studies, Golgi and basal-lateral membrane fractions were prepared from duodenal epithelium of vitamin D-deficient (-D) chicks treated with vehicle or 650 pmol of 1,25(OH)2D3 in vivo 2 h, 10 h, or 15 h before sacrifice, as well as from +D birds. Analyses of Golgi fractions for cathepsin B (CB) activity revealed a biphasic response with time, increasing to 200% of -D levels 2 h after 1,25(OH)2D3 administration and in equivalent preparations from +D birds. Less pronounced increases in acid phosphatase activity were observed in the same membrane fractions. In basal-lateral membranes, enhanced CB activity was detectable 10 h after 1,25(OH)2D3 in vivo, rose to 155% of -D levels at 15 h, and to 245% of controls in fractions from +D birds, whereas acid phosphatase was 75%, 81%, and 125% of controls, respectively, at these times.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
996.
997.
A study of intravenous (i.v.) cannula usage for medical emergencies admitted to hospitals in the Newham Health District was undertaken during two defined periods (24 and 35 days). Almost half the cannulas inserted (47%) were not flushed following an initial bolus injection of heparinized saline. The duration that cannulas remained in a vein ranged from 24 hours to 8 days (median 2 days) and inflammation around the cannula site was related to the length of time since insertion but unrelated to whether the cannula was flushed regularly or to the type of fluid used. Our findings indicate a substantial wastage of i.v. cannulas due to difficulties with insertion and suggest that isotonic saline, without heparin, is effective in maintaining cannula patency for 48 hours. It is concluded that these findings are not unique to the Newham Health District and worthwhile financial savings should be achieved throughout the NHS if clinicians reconsider the indications and use of i.v. cannulas for their patients.  相似文献   
998.
M.A. Sabbahi  E.M. Sedgwick   《Brain research》1987,423(1-2):125-134
The H-reflex of 120 soleus motoneurons was recorded using fibre EMG. The recovery profile of these motoneurons was studied during monitoring surface H-reflex records in 28 adult subjects. The spectrum of motoneurons tested was homogeneous with two extremes of neurons having different characteristics. A motoneuron population (forming about 69% of our sample) had a high threshold level for electrical stimuli, short recovery time, and short recovery fringe time (called type A). A second population of motoneurons (forming about 20-30% of our sample) had a low threshold level for electrical stimuli, long recovery fringe time (called type B). During an isometric muscle contraction every motoneuron showed an early shift in recovery time (i.e. each had a shorter recovery time) with shortened recovery fringe time. These changes were larger for motoneurons type B than motoneurons type A. With paired identical electrical stimuli of varying interstimulus intervals a motoneuron may fire in response to the conditioning and test stimuli giving an H2, but not in response to both stimuli. This occurred for interstimulus intervals of 4-11 ms. A strong inhibition period was recorded with interstimulus intervals of 12-80 ms in which all motoneurons did not show any recovery. Most motoneurons recovered in orderly fashion between 80 and 300 ms of interstimulus interval, and this recovery coincided with the fast recovery recorded in surface H-reflex. All motoneurons were recovered by 3000 ms of interstimulus intervals. These findings emphasize the importance of eliciting the H-reflex every 3-5 s in H-reflex methodology in order to be assured that all excited motoneurons have been recovered.  相似文献   
999.
1000.
Two hundred and thirty pregnancies were studied in 196 diabetic women. Seven women with babies found to have major malformations had a higher median first trimester haemoglobin A1 (12.9%) than the median HbA1 (10.8%) in those with normal babies (p = 0.06). No relationship was found between the occurrence of minor malformations and first trimester maternal haemoglobin A1. Two of the seven congenital malformations were diagnosed antenatally at a time when therapeutic abortion could be offered. Expert antenatal ultrasound scanning should be offered to all pregnant diabetic women as poor glycaemic control at the time of conception and organogenesis, as evidenced by raised first trimester HbA1, predisposes to congenital malformation.  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