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   8391篇
  免费   351篇
  国内免费   71篇
耳鼻咽喉   55篇
儿科学   180篇
妇产科学   96篇
基础医学   959篇
口腔科学   139篇
临床医学   521篇
内科学   2197篇
皮肤病学   138篇
神经病学   631篇
特种医学   366篇
外科学   1144篇
综合类   38篇
一般理论   1篇
预防医学   328篇
眼科学   197篇
药学   889篇
中国医学   35篇
肿瘤学   899篇
  2023年   51篇
  2022年   92篇
  2021年   163篇
  2020年   93篇
  2019年   105篇
  2018年   128篇
  2017年   121篇
  2016年   126篇
  2015年   115篇
  2014年   150篇
  2013年   236篇
  2012年   395篇
  2011年   423篇
  2010年   258篇
  2009年   214篇
  2008年   379篇
  2007年   473篇
  2006年   437篇
  2005年   446篇
  2004年   458篇
  2003年   400篇
  2002年   439篇
  2001年   227篇
  2000年   264篇
  1999年   252篇
  1998年   148篇
  1997年   124篇
  1996年   88篇
  1995年   77篇
  1994年   70篇
  1993年   72篇
  1992年   178篇
  1991年   156篇
  1990年   156篇
  1989年   153篇
  1988年   137篇
  1987年   136篇
  1986年   131篇
  1985年   129篇
  1984年   87篇
  1983年   58篇
  1982年   37篇
  1981年   33篇
  1980年   30篇
  1979年   54篇
  1978年   29篇
  1977年   24篇
  1976年   22篇
  1975年   30篇
  1969年   34篇
排序方式: 共有8813条查询结果,搜索用时 15 毫秒
71.
Phosphorylcholine (PC) antibodies in serum from patients with pulmonary infection, and from normal individuals, were studied. Anti-PC antibodies were detectable in the serum from normal individuals at mean concentrations of 320 g/ ml for the IgG class and 110 g/ml for the IgM class. Concentrations of anti-PC antibodies which were higher than normal for both the IgG and IgM classes were observed in the serum in pulmonary infection (1,440 g/ml and 210 g/ml, respectively). Despite the significant difference in the concentration of anti-PC antibodies, the PC-specific B cell precursor frequency in the peripheral blood lymphocytes showed no difference between normal individuals and the patients with pulmonary infection, or between the acute phase and the chronic phase in a single patient with chronic pulmonary infection. Serologically, the purified IgG anti-PC antibody did not share the cross-reactive idiotype of TEPC 15, which is the most common idiotype of the murine anti-PC antibodies. However, the purified IgM anti-PC antibody expressed a very weak cross-reactive idiotype of TEPC 15. It appears from these studies that human anti-PC antibodies may play an important biological role in pulmonary infection by microorganisms which possess a PC determinant.  相似文献   
72.
Human saliva chromogranin A (CgA) is clinically promising as a psychological stress marker. However, expression of CgA is poorly understood in humans, although salivary gland localization of CgA in other mammals, such as rodents and horses, has been demonstrated. In the present study, we investigated the expression and localization of CgA in the human submandibular gland (HSG) using various methods. CgA was consistently localized in serous and ductal cells in HSG, as detected by immunohistochemistry and in situhybridization. Reactivity was stronger in serous cells than in ductal cells. In addition, strong immunoreactivity for CgA was observed in the saliva matrix of ductal cavities. Western blotting gave one significant immunoreactive band of 68 kDa in the adrenal gland, HSG and saliva. Finally, CgA was detected in secretory granules of serous and ductal cells by immunoelectron microscopy. In conclusion, CgA in humans is produced by HSG and secreted into saliva.  相似文献   
73.
The effects of FK506, a new immunosuppressive agent, on the rat thymus were investigated using the immunoperoxidase technique and flow cytofluorometry using monoclonal antibodies. Flow cytometric analysis of the thymus revealed that the proportion of cells labelled positively with OX7 (Thy-1 antigen), OX8 (CD8, T cytotoxic/suppressor cells) and W3/25 (CD4, T helper cells and macrophages) increased following treatment, with FK506, 1 mg/kg body weight for 14 days. A marked reduction of the thymic medulla following treatment was clearly demonstrated by staining with OX18 (MHC class I) and OX6 (MHC class II). Changes produced by FK506 were also observed in the cortical area of the thymus, being especially marked in the subcapsular area and around the blood vessels by staining with OX6, PKK-1 (alpha-cytokeratin), AB-1040 (type IV collagen), and AB-1220 (laminin). Eventually FK506 treatment resulted in patchy reduction of OX-6, PKK-1, AB-1040 and AB-1220 positive area in the cortex. This evidence suggests that FK506 may impair the thymic microenvironment and subsequently disturb the thymocyte maturation.  相似文献   
74.
In a Japanese family, a propositus and his mother had crossed polydactyly type I. A maternal grandaunt also had preaxial polydactyly of the feet. The findings that both of the mother and son had the identical type of polydactyly are consistent with an autosomal dominant inheritance with variable expressivity. Other explanations include X-linked recessive inheritance, polygenic inheritance, and a chance occurrence of the 2 different kinds of polydactyly.  相似文献   
75.
The infrared sensory membranes of pit organs of pit vipers have an extremely rich capillary vasculature that forms many vascular loops, each serving a small number of infrared nerve terminals. We clarified the ultrastructure of capillary pericytes in the pit membranes by scanning and transmission electron microscopy, and examined the immunoreactivity in their cytoplasm to two contractile proteins: smooth muscle alpha-actin (SM alpha-actin) and desmin. The capillary pericytes had two major cytoplasmic processes: thickened primary processes that radiate to embrace the endothelial tube and flattened secondary processes that are distributed widely on the endothelium. Coexpression of SM alpha-actin and desmin was observed in the pericytes of entire capillary segments, and SM alpha-actin was characterized by prominent filament bundles directed mainly at right angles to the capillary long axis. This expression pattern was different from that of capillary pericytes of the scales, where SM alpha-actin was expressed diffusely in the cytoplasm. In a series of electron microscopic sections, we often observed the pericyte processes depressing the endothelial wall. We also observed a close relationship of the pericytes with inter-endothelial cell junctions, and pericyte processes connected with the endothelial cells via gap junctions. From these findings, we surmised that capillary pericytes in the pit membrane have a close functional relationship with the endothelium, and through their contractile and relaxing activity regulate capillary bloodflow to stabilize production of infrared nerve impulses.  相似文献   
76.
77.
In order to investigate the mechanism of urinary tract stone formation, we analyzed protein components in urine and the stone. Urinary proteins of healthy subjects and urolithic patients as well as protein components urinary tract stone of the urolithic patients were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Electrophoretic patterns of urinary proteins of the patients differed from those of healthy subjects after separating protein patterns into those larger than 66kDa or smaller than 30kDa. Protein constituents of urinary tract stone were mainly separated into 18 bands ranging from 26.8 to 143 kDa. Major bands among these 18 bands differed among stones from different patients. On western blotting, the developed intensities of Tamm-Horsfall protein (THP) were fainter than those of healthy subjects. Whereas intensities of albumin (ALB) were stronger than those of healthy subjects. Moreover, blotting patterns of THP of the patients on non-reducing SDS-PAGE were obviously broad. Thus, we suggest that analysis of fractionated urinary proteins or protein components of urinary tract stone may provide a tool for monitoring the prognosis or relapse in the patients.  相似文献   
78.
The system diethylzinc/optically active alcohol was examined as catalyst for asymmetric-selective polymerization of propylene oxide. Optically active alcohols with rigid structure are effective for the asymmetric selection. D (–)-1-Methoxypropanol-2 as well as poly(D -propylene oxide) of low molecular weight with hydroxyl end groups select L (–)-propylene oxide. ?Catalyst control”? mechanism of the stereoselection in the polymerization is suggested on this and other bases.  相似文献   
79.
To elucidate the pathogenesis of adenovlrus type 12 (Ad12)-induced rat retinal tumor, an experimental animal model of human retinobiastoma (RB), DNA analysis, in situ hybridizatlon and immunohistochemlstry were performed. The adenovirus oncogene EIA was detected in the host genome by Southern blot hybridization. Examined retinal tlssues did not show any histological changes, but the number of retinal cells lmmunoreactive with an antibody to proliferating cell nuclear antigen (PCNA) increased with the course of study. In in situ hybridization, E1A gene expression was recognized at the Inner granular layer of the retina at an early stage arer virus inoculation, and subsequently, N-myc gene expression was recognized at the same region. No alteration was found in the retinoblastoma susceptibility gene ( Rb gene) expression. The product of the virus oncogene integrated into the host genome could induce an Increase in N-myc expression, without any abnormality of the Rb gene itself. Results from the present study could be useful in clarifying the tumorige-nesis of this experimental model.  相似文献   
80.
The cortical masticatory area (CMA) elicits rhythmic jaw movements in response to repetitive stimulation and is involved in the control of mastication. Based on jaw movement patterns, the CMA is divided into two parts. One is the part of the CMA in which a T-pattern similar to jaw movements during food transport in natural mastication is evoked by electrical stimulation. The other is more dorsomedially located, and during chewing a C-pattern similar to jaw movements can be induced. However, it is still not known which region of the putamen receives projections from the CMA and whether projections originate from both parts of the CMA. In this study, electrophysiological and histological experiments were undertaken in rabbits to investigate projections from the CMA to the putamen. Both experiments showed that the ventral region of the putamen received projections from the CMA. The density of the projections from the CMA area inducing the T-pattern seemed to be higher than that from the area inducing the C-pattern. Furthermore, the peak latency of the evoked potentials from stimulation of the CMA area inducing the T-pattern was shorter than that from stimulation of the area inducing the C-pattern. The data obtained from the present study indicate the functional role of the ventral region of the putamen in the regulation of mastication, and further suggest that the corticostriatal pathway is involved in the transition between behavioral jaw movement patterns.  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