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   3853篇
  免费   369篇
  国内免费   13篇
耳鼻咽喉   32篇
儿科学   164篇
妇产科学   135篇
基础医学   623篇
口腔科学   64篇
临床医学   328篇
内科学   824篇
皮肤病学   86篇
神经病学   357篇
特种医学   80篇
外科学   513篇
综合类   87篇
一般理论   3篇
预防医学   396篇
眼科学   73篇
药学   266篇
中国医学   6篇
肿瘤学   198篇
  2022年   28篇
  2021年   61篇
  2020年   26篇
  2019年   71篇
  2018年   74篇
  2017年   72篇
  2016年   51篇
  2015年   66篇
  2014年   101篇
  2013年   122篇
  2012年   227篇
  2011年   214篇
  2010年   116篇
  2009年   110篇
  2008年   167篇
  2007年   216篇
  2006年   196篇
  2005年   154篇
  2004年   174篇
  2003年   154篇
  2002年   149篇
  2001年   123篇
  2000年   78篇
  1999年   124篇
  1998年   39篇
  1997年   36篇
  1996年   40篇
  1995年   27篇
  1994年   38篇
  1993年   27篇
  1992年   71篇
  1991年   51篇
  1990年   52篇
  1989年   53篇
  1988年   53篇
  1987年   61篇
  1986年   72篇
  1985年   61篇
  1984年   50篇
  1983年   40篇
  1982年   33篇
  1981年   39篇
  1980年   30篇
  1979年   41篇
  1978年   32篇
  1977年   31篇
  1976年   26篇
  1974年   27篇
  1973年   34篇
  1971年   25篇
排序方式: 共有4235条查询结果,搜索用时 15 毫秒
31.
A rapid simultaneous enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies was investigated for herpes simplex virus (HSV) detection. All HSV isolated (n = 127) were detected, whereas no response was obtained with HSV negative preparations. Equivalent results were obtained from 275 of 277 clinical specimens in the monoclonal ELISA and in an ELISA using polyclonal antibodies, confirming that appropriately selected monoclonal antibodies may be as efficacious as polyclonal antibodies in antibody-based assays. In clinical specimens, the rate of HSV detection (sensitivity) relative to tissue culture isolation was low for both assays, and the major factor responsible for this was the low concentration of virus present in some specimens. The sensitivity of ELISA obtained in routine use varied with different panels of unselected specimens and was related to the speed of development of the cytopathic effect. These results emphasise the need for caution in assigning a definitive sensitivity level to ELISA tests evaluated on different panels of specimens.  相似文献   
32.
Reduced concentrations of selenium in mild Crohn''s disease.   总被引:2,自引:0,他引:2       下载免费PDF全文
The concentrations of selenium, zinc, and copper were determined in whole blood, plasma, and leucocytes in 20 patients with relatively mild Crohn's disease, nine of whom were being treated with steroids, and compared with those of a control group. There was a significant decrease in the concentration of selenium in the leucocytes as well as in whole blood and plasma in the patients. Steroids seemed to affect only the concentrations of zinc and copper in plasma. The concentrations of copper and zinc in whole blood, plasma, and leucocytes in patients not taking steroids were not significantly different from those of the control group. The observations suggest that those patients with an apparently satisfactory whole body concentration of copper and zinc may still be at risk of a decrease in the body content of selenium.  相似文献   
33.
The reversibility and cation selectivity of the K(+)-Cl(-) cotransporter (KCC), which normally extrudes Cl(-) out of neurons, was investigated in dissociated lateral superior olive neurons of rats using the gramicidin perforated patch technique. Intracellular Cl(-) activity (alpha[Cl(-)](i)) was maintained well below electrochemical equilibrium as determined from the extracellular Cl(-) activity and the holding potential, where the pipette and external solutions contained 150 mM K(+) ([K(+)](pipette)) and 5 mM K(+) ([K(+)](o)), respectively. Extracellular application of 1 mM furosemide or elevated [K(+)](o) increased alpha[Cl(-)](i). When the pipette solution contained 150 mM Cs(+) ([Cs(+)](pipette)), alpha[Cl(-)](i) increased to a value higher than the passive alpha[Cl(-)](i). An increase of alpha[Cl(-)](i) with the [Cs(+)](pipette) was not due to the simple blockade of net KCC by the intracellular Cs(+) since alpha[Cl(-)](i), with the pipette solution containing 75 mM Cs(+) and 75 mM K(+), reached a value between those obtained using the [K(+)](pipette) and the [Cs(+)](pipette). The higher-than-passive alpha[Cl(-)](i) with the [Cs(+)](pipette) was reduced by 1 mM furosemide, but not by 20 microM bumetanide or Na(+)-free external solution, indicating that the accumulation of [Cl(-)](i) in the [Cs(+)](pipette) was mediated by a KCC operating in a reversed mode rather than by Na(+)-dependent, bumetanide-sensitive mechanisms. Replacement of K(+) in the pipette solution with either Li(+) or Na(+) mimicked the effect of Cs(+) on alpha[Cl(-)](i). On the other hand, Rb(+) mimicked K(+) in the pipette solution. These results indicate that K(+) and Rb(+), but not Cs(+), Li(+), or Na(+), can act as substrates of KCC in LSO neurons.  相似文献   
34.
35.
Bulk endocytosis is the process by which nerve terminals retrieve large amounts of synaptic vesicle membrane during periods of strong stimulation intensity. The process is rapidly activated and is most probably calcium dependent in a similar manner to synaptic vesicle exocytosis. This article briefly summarizes the current knowledge of bulk endocytosis with respect to its activation, kinetics and molecular mechanism. It also presents recent data from our laboratory showing that the dephosphorylation of a group of endocytosis proteins called the dephosphins by the Ca2+-dependent protein phosphatase calcineurin is key to the activity-dependent stimulation of the process. Possible downstream effectors of calcineurin are discussed such as the large GTPase dynamin I and its phosphorylation-dependent interaction partner syndapin I.  相似文献   
36.
BACKGROUND: Previous research suggests that childhood sexual abuse is associated with high rates of retrospectively reported medical utilization and medical problems as an adult. The goal of this study was to determine if abused females have higher rates of medical utilization using self-report and objective measures, compared with non-abused females. A further goal was to determine whether findings of prior research would be replicated when childhood physical abuse level was controlled. This study also examined the moderating impact of depressed mood on current health measures in this population. METHODS: Six hundred and eight women recruited from a health maintenance organization completed self-report measures of health symptoms for the previous month and doctor visits for the previous year. Objective doctor records over a 2 year period were examined for a subset of 136 of these women. RESULTS: Results showed significantly more self-reported health symptoms and more self-reported doctor visits in abused participants compared with those who reported no childhood history of sexual abuse. Objective doctor visits demonstrated the same pattern with abused participants exhibiting more visits related to out-patient surgery and out-patient internal medicine. In addition, persons who were both sexually abused and depressed tended to visit the emergency room more frequently and to have more in-patient internal medicine and ophthalmology visits than sexually abused participants who reported low depressed mood and non-abused controls. CONCLUSIONS: These results replicate prior studies and suggest that current depression may moderate the relationship between sexual abuse and medical problems in adulthood.  相似文献   
37.
38.
In Kinetoplastids, protein-coding genes are transcribed polycistronically by RNA polymerase II. Individual mature mRNAs are generated from polycistronic precursors by 5' trans splicing of a 39-nt capped leader RNA and 3' polyadenylation. It was previously known that trans splicing generally occurs at an AG dinucleotide downstream of a polypyrimidine tract, and that polyadenylation is coupled to downstream trans splicing. The few polyadenylation sites that had been examined were 100-400 nt upstream of the polypyrimidine tract which marked the adjacent trans splice site. We wished to define the sequence requirements for trypanosome mRNA processing more tightly and to generate a predictive algorithm. By scanning all available Trypanosoma brucei cDNAs for splicing and polyadenylation sites, we found that trans splicing generally occurs at the first AG following a polypyrimidine tract of 8-25 nt, giving rise to 5'-UTRs of a median length of 68 nt. We also found that in general, polyadenylation occurs at a position with one or more A residues located between 80 and 140 nt from the downstream polypyrimidine tract. These data were used to calibrate free parameters in a grammar model with distance constraints, enabling prediction of polyadenylation and trans splice sites for most protein-coding genes in the trypanosome genome. The data from the genome analysis and the program are available from: .  相似文献   
39.
40.
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