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   4444篇
  免费   59篇
  国内免费   11篇
电工技术   30篇
综合类   1篇
化学工业   596篇
金属工艺   206篇
机械仪表   84篇
建筑科学   93篇
矿业工程   10篇
能源动力   51篇
轻工业   294篇
水利工程   31篇
石油天然气   5篇
无线电   433篇
一般工业技术   635篇
冶金工业   1655篇
原子能技术   51篇
自动化技术   339篇
  2021年   34篇
  2019年   40篇
  2018年   37篇
  2017年   26篇
  2016年   51篇
  2015年   29篇
  2014年   45篇
  2013年   152篇
  2012年   92篇
  2011年   129篇
  2010年   88篇
  2009年   118篇
  2008年   135篇
  2007年   119篇
  2006年   116篇
  2005年   107篇
  2004年   105篇
  2003年   101篇
  2002年   90篇
  2001年   80篇
  2000年   94篇
  1999年   100篇
  1998年   355篇
  1997年   265篇
  1996年   215篇
  1995年   146篇
  1994年   104篇
  1993年   159篇
  1992年   85篇
  1991年   69篇
  1990年   69篇
  1989年   64篇
  1988年   72篇
  1987年   92篇
  1986年   54篇
  1985年   67篇
  1984年   39篇
  1983年   45篇
  1982年   44篇
  1981年   45篇
  1980年   48篇
  1979年   30篇
  1978年   48篇
  1977年   59篇
  1976年   83篇
  1975年   40篇
  1974年   33篇
  1973年   32篇
  1972年   31篇
  1970年   33篇
排序方式: 共有4514条查询结果,搜索用时 15 毫秒
21.
The performance of Nd3+-doped fibre amplifiers is limited by strong excited-state absorption (ESA) of the signal, and, even for fluorozirconate glasses, ESA prevents the important region below 1320 nm from being used. To quantify this limitation and explore alternative host materials, ESA and stimulated-emission cross sections have been measured for a representative group of glass compositions. These parameters have been used in an accurate fiber-amplifier model to provide the first quantitative comparisons of performance for Nd3+ -doped glasses in the 1300-nm band as a function of host  相似文献   
22.
A modification of the classical banyan switching network architecture, called the dilated slipped banyan, is described. This architecture is recursive and switching networks of any size perform permutation switching under a simple switching rule. They also exhibit column-control and dilation, properties that are particularly relevant to guided-wave and free-space photonic technologies. A photonic switching network, with this dilated slipped banyan architecture, is proposed as the hub of an all-optical active-star local-area network. The switching assignment at this hub is time-multiplexed on a fixed schedule that is known to all the terminals. This all-optical local-area network provides the equivalent of full-connectivity with high simultaneous data rates between every pair of terminals. A 16-terminal local-area network with 100 Mb/s of contention-free bandwidth between every pair of terminals is described  相似文献   
23.
24.
The coagulation system plays a major role in the formation of the infected endocardial vegetation in bacterial endocarditis. Since monocytes can express tissue factor (TF) on their surfaces, they are thought to be responsible for the extrinsic activation of the coagulation cascade during this disease. The present study used an in vitro model in which fibrin plates, isolated adherent monocytes, and Streptococcus sanguis were used as an analog for endocardial vegetations. Adherence to fibrin by itself was found to stimulate TF expression on the monocytes, but stimulation by S. sanguis significantly increased TF expression, which was found to be maximal at a bacterium-to-monocyte ratio of 9 or more.  相似文献   
25.
26.
Twenty diabetic patients with neuropathy underwent clinical and neurophysiological evaluation together with a detailed morphometric assessment of capillary pathology in endoneurial and epineurial microvascular beds of the sural nerve. Morphological data were compared with ten non-diabetic control subjects. There were no significant differences in control subjects between basement membrane area, endothelial cell area, endothelial cell profile number or luminal area of endoneurial when compared with epineurial capillaries. In contrast, when compared with epineurial capillaries, endoneurial capillaries from diabetic patients demonstrated a significant increase in basement membrane (p < 0.001) and endothelial cell (p < 0.001) area and a significant reduction in luminal area (p < 0.001). There was no significant difference in endothelial cell profile number between endoneurial and epineurial capillaries amongst diabetic patients. Previous studies have demonstrated a good correlation between the degree of microangiopathy and measures of neuropathic severity. In the present study increased endoneurial capillary basement membrane area was significantly related to reduced peroneal nerve conduction velocity (p < 0.001), myelinated fibre density (p < 0.001) and elevated vibration (p < 0.05) and thermal (p < 0.001) perception. Increased endothelial cell area and reduced luminal size were related to a reduced peroneal nerve conduction (p < 0.05, p < 0.01, respectively), reduced myelinated fibre density (p < 0.05, p < 0.01) and elevated thermal perception (p < 0.05, p < 0.001). Epineurial capillary basement membrane, endothelial cell and luminal area failed to relate to measures of neuropathic severity.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
27.
We compared the data from four growth hormone (GH) immunoassays for analyzing 24-h GH profiles in four apparently normal subjects and four obese subjects (508 serum samples). The detection limit was 0.02 microgram/L for one immunochemiluminometric assay (ICMA), 0.1 microgram/L for two IRMAs, and 0.4 microgram/L for one RIA. All GH pulses with a peak ICMA value > 1 microgram/L were detected by each of the other methods. Overall, the correlation coefficient between the values obtained with all four assays exceeded 0.90. However, for GH concentrations < or = 0.25 microgram/L, acceptable concordance (r2 > or = 0.80) was reached only between the ICMA and one IRMA; between the ICMA and the RIA, concordance was acceptable only for GH concentrations > or = 10 micrograms/L. In the normal subjects, the percentage of undetectable values was 0% with the ICMA but 29% with one of the IRMAs; in obese subjects, the corresponding values were 12% and 38%.  相似文献   
28.
This article provides a brief overview of the history of autonomous mental development as a discipline  相似文献   
29.
30.
The definition of an empirically supported treatment (EST) arguably embodies 2 untested assumptions: (a) that different manualized renditions of the same therapy are functionally equivalent and (b) that therapies can be reliably applied independently of therapist, setting, and format. These assumptions were tested as applied to cognitive therapy (CT), using process data from a large multisite study (N=235) that included 3 cognitive and 6 alternative therapies. Although the non-CTs were more variable than the CTs on 2 of 4 dimensions studied (directiveness and emotional arousal), there was considerable variation among the 3 CTs, even when implemented in the current context of rigorous training, manualization, and adherence checks. Results are discussed as related to the assumptions underlying EST criteria. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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