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   35675篇
  免费   1450篇
  国内免费   1132篇
电工技术   1101篇
综合类   527篇
化学工业   4514篇
金属工艺   2732篇
机械仪表   1501篇
建筑科学   1145篇
矿业工程   194篇
能源动力   1237篇
轻工业   2287篇
水利工程   357篇
石油天然气   633篇
武器工业   80篇
无线电   4457篇
一般工业技术   8237篇
冶金工业   5306篇
原子能技术   459篇
自动化技术   3490篇
  2024年   67篇
  2023年   263篇
  2022年   548篇
  2021年   810篇
  2020年   592篇
  2019年   639篇
  2018年   846篇
  2017年   799篇
  2016年   873篇
  2015年   831篇
  2014年   1168篇
  2013年   2257篇
  2012年   1666篇
  2011年   2247篇
  2010年   1716篇
  2009年   1855篇
  2008年   1870篇
  2007年   1803篇
  2006年   1554篇
  2005年   1369篇
  2004年   1138篇
  2003年   1039篇
  2002年   1032篇
  2001年   951篇
  2000年   879篇
  1999年   930篇
  1998年   1961篇
  1997年   1354篇
  1996年   1155篇
  1995年   696篇
  1994年   595篇
  1993年   497篇
  1992年   315篇
  1991年   324篇
  1990年   220篇
  1989年   245篇
  1988年   159篇
  1987年   126篇
  1986年   99篇
  1985年   104篇
  1984年   74篇
  1983年   69篇
  1982年   64篇
  1981年   58篇
  1980年   45篇
  1979年   31篇
  1977年   50篇
  1976年   81篇
  1975年   27篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
It is essential to know how the immune system acts in different neurological diseases, some of them non very well known or of unknown etiology at all. It was applied Reiber and Felgenhauer's formula in 56 patients with different diseases. IgA, IgM, IgG and albumin were quantified in sera and cerebrospinal fluid by simple immunodiffusion. It was observed more frequent IgG local synthesis and IgA in this sample.  相似文献   
123.
Introduction of the broadband integrated services digital network (B-ISDN) will enable network users to make use of advanced multimedia, multiparty services. With this aim in view, RACE II project R2044, MAGIC, is investigating long-term signalling requirements, architecture and protocols for B-ISDN. New service concepts are being developed in MAGIC which will provide more flexibility when compared to narrowband ISDN (N-ISDN). The service requirements and other signalling requirements, such as the separation between call and associated connections at the network-node interface, are used to determine the distribution of functions over the network. The signalling protocols which are used to exchange the signalling information are subsequently developed. These signalling protocols are simulated to prove the performance and the feasibility of call handling concepts  相似文献   
124.
125.
126.
The changes in the intestinal mucosal permeability were observed by quantitatively assessing plasma to luminal clearance of 99mTc-labeled DTPA, and the influence of platelet activating factor (PAF) on it was investigated. The results showed that intestinal permeability was significantly elevated after severe burn and was positively correlated with increase in PAF in the intestinal tissue (r = 0.94, P < 0.01). PAF antagonist therapy could significantly attenuate postburn intestinal mucosal permeability. It is concluded that PAF is one of the important factors causing increased intestinal permeability after severe burn.  相似文献   
127.
Tetragonal zirconia polycrystalline (TZP) ceramics containing SiC reinforcement in the form of fine particles (nano-scale), particles (micro-scale), whiskers and platelets were synthesized by hot-pressing. The effects of morphology and grain size of SiC reinforcement on the strength and fracture toughness at room temperature were investigated. The addition of SiC (in whatever form) caused decreases in strength and toughness at room temperature with the exception of whisker-reinforced materials. Toughness fell off with increasing temperature, but nevertheless retained about one-half of the room-temperature value for that particular SiC reinforcement. However, the whisker- and particle-reinforced materials had higher K lc values at high temperature than fine particle- or platelet-reinforced materials, with values in excess of 7 MPa m1/2 at 1000 °C. The microstructure was examined for SiC whisker-reinforced/TZP materials by TEM and HREM, to examine the nature of the whisker/zirconia interface.  相似文献   
128.
129.
Crescentic glomerulonephritis in interferon-gamma receptor deficient mice   总被引:1,自引:0,他引:1  
Activation of macrophages by T cells is considered an initiating event in glomerular crescent formation. Since interferon-gamma (INF gamma) is a key mediator in T-cell-mediated activation of macrophages, we decided to test its role in a model of crescentic glomerulonephritis. An anti-glomerular basement membrane (GBM) serum was injected intravenously in presensitized wild-type or IFN gamma receptor deficient (IFN gamma(R)-/-) mice. Glomerulonephritis with glomerular crescents and tubulointerstitial inflammation developed in both strains, even though most evaluated morphological parameters and proteinuria indicated a less severe pathology in the mutant mice compared to the wild type. Thus, IFN gamma is not essential either for glomerular crescent formation or for tubulointerstitial involvement in anti-GBM glomerulonephritis in mice. In conclusion, the role of macrophages in this model might have been overestimated, or other cytokines may compensate for deficient IFN gamma signaling in the activation of macrophages.  相似文献   
130.
To pick up serum high risk lithogenic factors predisposing one to gallstone formation and protective factors against gallstone formation in gallbladder. We compared serum lipid and apolipoprotein level of patients with gallbladder stone (stone group) with that of patients without gallbladder stone (control group). The correlation between serum lipid, apolipoprotein level and bile lipid level, cholesterol saturated index (CSI), characteristics of lipidemia in different kinds of gallbladder stones were studied. The results showed that the increase of serum Apo A1, C2 and E level in the stone group was more significant than in the control group. But there was no statistical significance in TC, TG, LDL-C, HDL-C, Apo A2, B, C3 level between the stone and control groups. These results suggested that serum apolipoproteins perhaps are more sensitive parameters than serum lipids in distinguishing patients with stones from those without stones. There were different profiles of serum lipid and apolipoproteins in different chemical types of gallbladder stones. Increased level in serum LDL-C, Apo B and ratio of LDL-C/HDL-C were characterized by an index for cholesterol stone, otherwise that in serum TG and Apo C2 an index for pigment stones. There was a positive correlation between serum total cholesterol (TC) or Apo B, C2, C3 and cholesterol amount or CSI in gallbladder bile. Therefore, TC, Apo B, C2, C3 could be considered as high risk lithogenic factors. A positive correlation existed between serum HDL-C and lecithin in gallbladder or common bile duct (CBD) bile as well as between HDL-C and bile acids in CBD bile. Thus, HDL-C might be a protective factor against gallstone formation in gallbladder.  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