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   10857篇
  免费   137篇
  国内免费   6篇
电工技术   72篇
综合类   4篇
化学工业   1092篇
金属工艺   113篇
机械仪表   207篇
建筑科学   233篇
矿业工程   33篇
能源动力   188篇
轻工业   529篇
水利工程   47篇
石油天然气   12篇
武器工业   2篇
无线电   640篇
一般工业技术   1174篇
冶金工业   5902篇
原子能技术   118篇
自动化技术   634篇
  2021年   63篇
  2020年   49篇
  2019年   53篇
  2018年   59篇
  2017年   70篇
  2016年   71篇
  2015年   59篇
  2014年   105篇
  2013年   237篇
  2012年   160篇
  2011年   255篇
  2010年   181篇
  2009年   185篇
  2008年   213篇
  2007年   207篇
  2006年   216篇
  2005年   152篇
  2004年   167篇
  2003年   159篇
  2002年   140篇
  2001年   144篇
  2000年   135篇
  1999年   274篇
  1998年   1646篇
  1997年   964篇
  1996年   688篇
  1995年   394篇
  1994年   374篇
  1993年   426篇
  1992年   144篇
  1991年   162篇
  1990年   159篇
  1989年   174篇
  1988年   149篇
  1987年   156篇
  1986年   155篇
  1985年   155篇
  1984年   104篇
  1983年   95篇
  1982年   102篇
  1981年   137篇
  1980年   135篇
  1979年   96篇
  1978年   95篇
  1977年   214篇
  1976年   405篇
  1975年   85篇
  1974年   47篇
  1973年   68篇
  1972年   46篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Free-living nematodes may harbor, protect, and disperse bacteria, including those ingested and passed in viable form in feces. These nematodes are potential vectors for human pathogens and may play a role in foodborne diseases associated with fruits and vegetables eaten raw. In this study, we evaluated the associations between a free-living soil nematode, Caenorhabditis elegans, and Escherichia coli, an avirulent strain of Salmonella Typhimurium, Listeria welshimeri, and Bacillus cereus. On an agar medium, young adult worms quickly moved toward colonies of all four bacteria; over 90% of 3-day-old adult worms entered colonies within 16 min after inoculation. After 48 h, worms moved in and out of colonies of L. welshimeri and B. cereus but remained associated with E. coli and Salmonella Typhimurium colonies for at least 96 h. Young adult worms fed on cells of the four bacteria suspended in K medium. Worms survived and reproduced with the use of nutrients derived from all test bacteria, as determined for eggs laid by second-generation worms after culturing for 96 h. Development was slightly slower for worms fed gram-positive bacteria than for worms fed gram-negative bacteria. Worms that fed for 24 h on bacterial lawns formed on tryptic soy agar dispersed bacteria over a 3-h period when they were transferred to a bacteria-free agar surface. The results of this study suggest that C. elegans and perhaps other free-living nematodes are potential vectors for both gram-positive and gram-negative bacteria, including foodborne pathogens in soil.  相似文献   
73.
A novel strategy was utilised to assess the risk to health from exposure to polycyclic aromatic hydrocarbons (PAHs). Ambient monitoring was carried out by personal sampling. Urinary thioethers (UTh) and urinary 1-hydroxypyrene (1-HP) were utilised for biological monitoring. Urinary d-glucaric acid (UDGA) and sister chromatid exchange (SCE) in peripheral blood lymphocytes were used as biological effect markers. The population was categorised into exposed and control groups according to the external dose of PAHs. The excretion of 1-HP in the controls over the 3-day period showed a relatively stable baseline, while the exposed showed a significant increase over the same period of time. SCE frequency in the exposed population was significantly different from controls.  相似文献   
74.
The sector - also known as the proportional, geometric, or military compass - was an analog calculating instrument used widely from the late 16th century until modern times. The origins and usage of this commonly encountered instrument are not well known. This article provides historical background on the sector's invention and on its precursor instruments, and describes the uses for many of the scales commonly found on these instruments.  相似文献   
75.
76.
77.
78.
Literature suggests that a complex and often hostile relationship exists between the science and practice of clinical psychology. Contributors to this conflict of viewpoints are reconsidered within the proposition that there are different roads to discovery and that there may be good reasons to keep the science and practice of clinical psychology somewhat separate. Results of a national survey of 325 psychologists are reviewed that support the view that psychological practitioners value research and consider their practices to be augmented by scientific findings. However, they are in need of vehicles of communication that will help them translate scientific findings into practice. Results suggest that practitioners do more to understand scientific findings than scientists do to understand the problems that face clinical practitioners. Ways to facilitate communication between and among these groups are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
79.
80.
A competitive enzyme-linked immunoadsorbent assay (ELISA) technique has been developed to facilitate quantitative analysis of the earliest step in the initiation of the extrinsic pathway of coagulation, i.e., complex formation of factor VII/VIIa with tissue factor. The ELISA measures the binding of biotinylated human plasma factor VII to relipidated recombinant human tissue factor. Quantitation of the relative affinity (expressed as IC50) of any factor VII molecular population or structural analogue for tissue factor can be determined by competitive binding. Subnanomolar concentrations of both wild-type recombinant human factor VII (rFVII) and rFVII(R152Q), a mutation at the FVII activation site, competed effectively with biotinylated plasma-derived factor VII in binding to tissue factor. In contrast, the affinity of rFVII(R79Q), a mutation in the first epidermal growth factor-like domain, was 12-fold lower. Following activation of rFVII(R79Q), its affinity for tissue factor and enzymatic activity increased 4-fold and 6-fold, respectively. For wild-type rFVII, enzymatic activity rose significantly following activation. However, its affinity for tissue factor was unchanged. We conclude that both the activation state of factor VII and the mutation of amino-acid residues within the first epidermal growth factor-like domain may alter the affinity of factor VII for tissue factor.  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