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   59683篇
  免费   1832篇
  国内免费   801篇
电工技术   828篇
综合类   63篇
化学工业   9790篇
金属工艺   3390篇
机械仪表   1714篇
建筑科学   1371篇
矿业工程   191篇
能源动力   1710篇
轻工业   5648篇
水利工程   569篇
石油天然气   1453篇
武器工业   2篇
无线电   4738篇
一般工业技术   13507篇
冶金工业   11435篇
原子能技术   850篇
自动化技术   5057篇
  2022年   381篇
  2021年   738篇
  2020年   666篇
  2019年   799篇
  2018年   1435篇
  2017年   1382篇
  2016年   1480篇
  2015年   1120篇
  2014年   1533篇
  2013年   3793篇
  2012年   2514篇
  2011年   2812篇
  2010年   2283篇
  2009年   2502篇
  2008年   2363篇
  2007年   2471篇
  2006年   1845篇
  2005年   1571篇
  2004年   1546篇
  2003年   1398篇
  2002年   1362篇
  2001年   1328篇
  2000年   1150篇
  1999年   1260篇
  1998年   3515篇
  1997年   2552篇
  1996年   2005篇
  1995年   1271篇
  1994年   993篇
  1993年   1043篇
  1992年   682篇
  1991年   650篇
  1990年   598篇
  1989年   560篇
  1988年   446篇
  1987年   464篇
  1986年   429篇
  1985年   461篇
  1984年   352篇
  1983年   337篇
  1982年   348篇
  1981年   357篇
  1980年   394篇
  1979年   364篇
  1978年   316篇
  1977年   510篇
  1976年   803篇
  1975年   321篇
  1974年   307篇
  1973年   323篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
We derive a linear correspondence between the variables of an encoder and those of a corresponding syndrome former. Using the derived correspondence, we show that the log-likelihood ratio of an information bit conditioned on a received sequence can be equally calculated using the syndrome trellis. It is shown that the proposed method also applies to recursive systematic convolutional codes which are typical constituent codes for turbo codes. Moreover, we show that soft-in syndrome decoding considering a priori probabilities of information bits is possible in the same way as for Viterbi decoding based on the code trellis. Hence, the proposed method can be applied to iterative decoding such as turbo decoding. We also show that the proposed method is effective for high-rate codes by making use of trellis modification.  相似文献   
92.
Based on the concept of complete stress–strain diagrams, we propose a new model describing the law of stress distribution in the prefracture zone in plastic materials in view of the type of the stressed state.  相似文献   
93.
94.
95.
Investigation into polishing process of CVD diamond films   总被引:1,自引:0,他引:1  
A new technique used for polishing chemical vapor deposition (CVD) diamond films has been investigated, by which rough polishing of the CVD diamond films can be achieved efficiently. A CVD diamond film is coated with a thin layer of electrically conductive material in advance, and then electro-discharge machining (EDM) is used to machine the coated surface. As a result, peaks on the surface of the diamond film are removed rapidly. During machining, graphitization of diamond enables the EDM process to continue. The single pulse discharge shows that the material of the coated layer evidently affects removal behavior of the CVD diamond films. Compared with the machining of ordinary metal materials, the process of EDM CVD diamond films possesses a quite different characteristic. The removal mechanism of the CVD diamond films is discussed.  相似文献   
96.
97.
98.
Based on the heat and mass transfer model validated by experiment, the performance of the plate solar ice-maker is analyzed systemically with the opinion of two-type characteristic parameters, which includes parametric effects of adsorbent bed of solar ice-maker and outer parameters referring to circumstance. A large number of simulations were undertaken to test the performance of the refrigerator for various collector design parameters and environmental parameters. These works are beneficial to further study the optimization design of a solar cooling system.  相似文献   
99.
The authors compared in a controlled clinical study two groups of patients after a first renal transplantation treated by triple drug immunosuppressive therapy. In a group of 31 patients the triple combination comprised Sandimmune Neoral. In the control group there were 30 patients who received Sandimmune. No differences were found between the two groups as regards the effectiveness of this treatment and the authors did not confirm a lower incidence of rejections described in patients treated with Sandimmune Neoral. They confirmed, however, a lower interindividual variability of Cy-A levels assessed specifically in patients treated with Sandimmune Neoral.  相似文献   
100.
The osteogenic growth peptide (OGP) is a 14mer mitogen of osteoblastic and fibroblastic cells. Physiologically, OGP is present in high abundance in human and other mammalian sera. Most of the serum OGP is complexed noncovalently to heat sensitive, high molecular weight OGP-binding proteins (OGPBPs). Changes in serum OGP levels that follow bone marrow ablation and the low doses of exogenous OGP required for the stimulation of bone formation suggest a regulatory role for the OGPBPs. In the present work, the OGP binding activity was monitored by competitive binding to [3-125I(Tyr10)]-sOGP and the corresponding complexes were demonstrated on nondenaturing cathodic polyacrylamide gel electrophoresis. We show that OGP binds to both native and activated human plasma alpha 2-macroglobulin (alpha 2M). alpha 2M was also immunoidentified in reduced and nonreduced SDS-polyacrylamide gel electrophoresis of OGP-affinity purified plasma-derived proteins. Immunoreactive OGP was detected in commercial preparations of both forms of alpha 2M; OGP was purified to homogeneity from the commercial preparation of activated alpha 2M. In MC3T3 E1 cells, native alpha 2M, at concentrations < 50 ng/mL, had a substantially increased mitogenic effect in the presence of synthetic, native-like, OGP (sOGP). Similar amounts of activated alpha 2M inhibited the sOGP proliferative effect. These results suggest that the native alpha 2M enhances the immediate availability of OGP to its target cells. Activated alpha 2M may participate in the removal of OGP from the system.  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