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   103016篇
  免费   1354篇
  国内免费   1230篇
电工技术   1924篇
综合类   139篇
化学工业   10530篇
金属工艺   5463篇
机械仪表   3190篇
建筑科学   2038篇
矿业工程   159篇
能源动力   2973篇
轻工业   6067篇
水利工程   706篇
石油天然气   676篇
武器工业   15篇
无线电   15952篇
一般工业技术   21772篇
冶金工业   25250篇
原子能技术   1382篇
自动化技术   7364篇
  2022年   459篇
  2021年   706篇
  2020年   533篇
  2019年   683篇
  2018年   1143篇
  2017年   1104篇
  2016年   1180篇
  2015年   930篇
  2014年   1500篇
  2013年   4682篇
  2012年   2578篇
  2011年   3854篇
  2010年   3104篇
  2009年   3721篇
  2008年   3895篇
  2007年   4080篇
  2006年   3690篇
  2005年   3326篇
  2004年   3177篇
  2003年   3024篇
  2002年   2673篇
  2001年   2970篇
  2000年   2718篇
  1999年   3075篇
  1998年   9439篇
  1997年   6153篇
  1996年   4761篇
  1995年   3162篇
  1994年   2787篇
  1993年   2723篇
  1992年   1628篇
  1991年   1593篇
  1990年   1518篇
  1989年   1322篇
  1988年   1171篇
  1987年   861篇
  1986年   887篇
  1985年   916篇
  1984年   803篇
  1983年   698篇
  1982年   699篇
  1981年   682篇
  1980年   567篇
  1979年   476篇
  1978年   414篇
  1977年   533篇
  1976年   958篇
  1975年   299篇
  1974年   276篇
  1973年   256篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The propagation and dispersion characteristics of picosecond electrical pulses in a suspended coplanar waveguide (SCPW) are investigated, and it is shown that the SCPW is a very promising transmission structure for ultrashort pulses. Numerical results for the modal dispersion of the SCPW are presented and compared to those of the conventional CPW, and a field-coupling theory is used to explain the evolution in the dispersion behavior. An evaluation based on the numerical analysis shows that a SCPW with properly controlled dispersion can exhibit a five times improvement in pulse transmission capability compared to the conventional CPW. Both computer simulations and experimental measurements show a substantial suppression in pulse distortion as well, compared to conventional CPWs  相似文献   
992.
Serum p53 protein levels were measured in 36 patients with small cell lung cancer (SCLC) and 35 patients with benign lung diseases in order to evaluate the relationship of these levels to clinicopathological features of SCLC. Serum levels of p53 protein were measured by an enzyme-linked immunosorbent assay, p53 protein level was 23.92 +/- 6.78 pg/ml in patients with SCLC, and similar to that (17.47 +/- 2.86 pg/ml) in patients with benign lung diseases. By the clinical stage of SCLC, the mean level of p53 protein was 16.68 +/- 4.62 pg/ml in 21 patients with limited disease, and lower than that in 15 patients with extensive disease (34.05 +/- 14.84 pg/ml) (P = 0.23). The levels of p53 protein were not correlated with age, smoking index, or presence of cancer history for patients with SCLC. However, immunohistochemical examination disclosed a mild correlation between the expression of p53 protein by SCLC tumor and p53 protein serum level (r = 0.45, P = 0.02). Two patients with SCLC had an elevated serum level of p53 protein (> 2 S.D. above the mean for benign lung diseases). However, measurement of p53 protein serum level was not found to be clinically useful for detection of SCLC.  相似文献   
993.
A method for the analysis of deformed patterns is presented and analyzed. The image is transformed into a new set of coordinates in which the deformation has a particular simple form. A number of deformations are considered. The practical implementation of the method is discussed. Similar aspects of biological vision are also considered  相似文献   
994.
The 3DP (3-Dimensional Processor), a parallel-computing architecture that targets problems that have a 3-D numerical structure and require numerous calculations on 3-D vectors, is described. The 3DP architecture differs from traditional scalar architectures in that it operates directly on vectors. It differs from general parallel architectures in that it can solve problems that predict the behavior of highly coupled systems, and it differs from vector architectures in that it runs efficiently on length-3 vectors. Object-oriented programming on the 3DP and programming the 3DP in C++ are discussed. 3DP performance is reviewed, and the current implementation of the 3DP architecture, as an attached processor that plugs directly into Sun host VMEbus, is described  相似文献   
995.
996.
Several studies have demonstrated the existence of a murine NK1.1+ alphabeta T cell subset expressing V alpha14+ TCR alpha-chains with highly conserved invariant junctional sequences and able to secrete Th2 cytokines when exposed to CD1+ stimulator cells. In humans, alphabeta T cells carrying invariant V alpha24+ TCR alpha-chains highly homologous to those expressed by murine NK1.1 cells have been recently described. Here we show that these cells (referred to as V alpha24inv T cells) and murine NK1.1+ alphabeta T cells resemble each other in several ways. First, like their murine counterparts, T cells expressing high levels of V alpha24inv TCRs can be either CD4- CD8- double negative (DN) or CD4+, but they never express heterodimeric CD8 molecules. Second, most V alpha24inv T cells are brightly stained by NKRP1-specific mAb but not by mAb directed against other type II transmembrane proteins of the NK complex. Third, DN and particularly CD4+ V alpha24inv T cells are greatly enriched for IL-4 producers. The concomitant expression of highly conserved TCRs of a particular set of NK markers and of Th2 cytokines in human and murine alphabeta T cells suggests a coordinate acquisition of these phenotypic and functional properties. Furthermore, the relatively high frequency of human V alpha24inv T cells, which are presently shown to represent on average 1/500 PBL, and the high interindividual variations of the size of this cell subset under physiologic conditions go for a major role played by alphabeta T cells carrying invariant TCR in a large array of immune responses.  相似文献   
997.
This paper describes a simple and effective way to modify an existing hard-switched flyback power converter into a circuit with zero-voltage switching (ZVS) and zero-current switching (ZCS). The key improvement is to turn the unattractive features of the coupled inductor leakage inductance and snubber capacitor into attractive ones. The coupled inductor leakage inductance and snubber are used to form a quasi-resonant circuit to facilitate ZVS/ZCS of all power devices. The operating principles of the power converter and experimental results are presented  相似文献   
998.
The composition of whey proteins from ruminant Mongolian domestic animals was analyzed and a comparative study between camel (Camelus bactrianus) and dromedary (Camelus dromedarius) was made. Whey proteins were separated by ion-exchange chromatography and identified by polyacrylamide gel electrophoresis, amino acid composition and N-terminal sequence determination. The main components of wheys of yak and khainak were nearly identical with their bovine counterparts. Three different forms of α-lactalbumin were isolated in the whey of Camelus bactrianus and two from Camelus dromedarius. As shown by classical biochemical and immunological studies, β-lactoglobulin was absent from whey of both Camelus. Camel whey basic protein (CWBP), having no analogy with known milk and nonmilk proteins, was identified in the whey of Camelus bactrianus and Camelus dromedarius and its N-terminal sequence was determined.  相似文献   
999.
Pulmonary sequestration is a relatively rare anomaly. The arterial supply usually is derived from the aorta or its major branches. We present a 65-year-old female patient with pulmonary sequestration receiving arterial supply from the right coronary artery, complicated with sick sinus syndrome.  相似文献   
1000.
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