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   1353篇
  免费   49篇
  国内免费   4篇
电工技术   13篇
综合类   4篇
化学工业   141篇
金属工艺   9篇
机械仪表   31篇
建筑科学   26篇
矿业工程   1篇
能源动力   29篇
轻工业   58篇
水利工程   6篇
石油天然气   1篇
无线电   130篇
一般工业技术   136篇
冶金工业   619篇
原子能技术   10篇
自动化技术   192篇
  2023年   17篇
  2022年   37篇
  2021年   63篇
  2020年   40篇
  2019年   52篇
  2018年   43篇
  2017年   34篇
  2016年   43篇
  2015年   26篇
  2014年   37篇
  2013年   47篇
  2012年   47篇
  2011年   53篇
  2010年   32篇
  2009年   33篇
  2008年   25篇
  2007年   18篇
  2006年   15篇
  2005年   12篇
  2004年   13篇
  2003年   7篇
  2002年   8篇
  2001年   9篇
  2000年   8篇
  1999年   36篇
  1998年   172篇
  1997年   112篇
  1996年   86篇
  1995年   60篇
  1994年   35篇
  1993年   38篇
  1992年   14篇
  1991年   9篇
  1990年   7篇
  1989年   8篇
  1988年   14篇
  1987年   8篇
  1986年   4篇
  1985年   11篇
  1983年   3篇
  1982年   2篇
  1981年   3篇
  1980年   7篇
  1979年   2篇
  1977年   15篇
  1976年   32篇
  1973年   4篇
  1971年   1篇
  1963年   1篇
  1955年   1篇
排序方式: 共有1406条查询结果,搜索用时 140 毫秒
141.
We propose a new generic flow formulation for Failure-Independent Path-Protecting (FIPP) p-cycles subject to multiple failures. While our new model resembles the decomposition model formulation proposed by Orlowski and Pioro (Networks, 2011) in the case of classical shared path protection, its originality lies in its adaptation to FIPP p-cycles. When adapted to that last pre-configured pre-cross connected protection scheme, the bandwidth sharing constraints must be handled in a different way in order to take care of the sharing along the FIPP p-cycles. It follows that, instead of a polynomial-time solvable pricing problem as in the model of Orlowski and Pioro (Networks, 2011), we end up with a much more complex pricing problem, which has an exponential number of constraints due to some subtour elimination constraints. Consequently, in order to efficiently solve the pricing problem, we consider: (i) a hierarchical decomposition of the original pricing problem; (ii) heuristics in order to go around the large number of constraints in the pricing problem. Performance evaluation is made in the case of FIPP p-cycles subject to dual failures. For small to medium size networks, the proposed model remains fairly scalable for increasing percentages of dual failures, and requires much less bandwidth than p-cycle protection schemes (ratio varies from 2 to 4). For larger networks, heuristics are required in order to keep computing times reasonable. In the particular case of single link failures, it compares very favorably (5 to 10 % of bandwidth saving) to the previously proposed column generation ILP model of Rocha, Jaumard and Stidsen (Telecommun. Syst., 2012).  相似文献   
142.
143.
In presenting a unifying concept for chronic inflammation and lymphoid organogenesis, we suggest that lymphotoxin's (LT, LT-alpha, TNF-beta) crucial role in these processes is pivotal and similar. Chronic inflammatory lesions that developed in the kidney and pancreas at the sites of transgene expression in rat insulin promoter-LT (RIP-LT) mice resembled lymph nodes with regard to cellular composition (T cells, B cells, plasma cells, and antigen-presenting cells), delineated T and B cell areas, primary and secondary follicles, characteristic morphologic and antigenic (ICAM-1, VCAM-1, MAdCAM-1, and PNAd) features of high endothelial venules, and ability to respond to antigen and undergo Ig class switching when obtained from mice immunized with SRBC. The vascular changes, with the exception of PNAd, appear to be the direct consequence of transgene derived LT expression, as they were also observed in RIP-LT mice lacking mature T and B cells. These data show that LT-induced chronic inflammation has the characteristics of organized lymphoid tissue.  相似文献   
144.
An alkylation method of docetaxel at the C-10 position has been established by a radical coupling reaction using a 10-xanthate derivative of 7-O-TES-10-deacetylbaccatin III and appropriate alkenes. In addition the cytotoxic activity of 10-alkylated docetaxel analogs was evaluated. Among these analogs, a derivative having a methoxycarbonyl group at the end of the alkyl moiety exhibited more potent cytotoxic activity than docetaxel.  相似文献   
145.
146.
Utilizing the Escherichia coli/pGex vector expression system incorporating a thrombin cleavage site, full-length (residues -6-243) and truncated forms of proapolipoprotein AI (proapoAI), terminating at amino acid residues 222, 210, 150, and 135, were purified to levels of at least 5 mg/L, after thrombin cleavage. Assessed by circular dichroism, the helical contents of L-alpha-dimyristoylphosphatidylcholine-associated forms of human plasma-derived apolipoprotein AI (apoAI) and recombinant proapoAI were comparable, being 69% and 65%, respectively. Circular dichroism measurements of the lipid-associated complexes of the truncated forms showed that between the sequence of residues 150-222 no additional helicity was gained until the carboxyl-terminal sequence was present in the molecule, indicating that the carboxyl terminus of the protein is required for the formation of helix within this central region. While tryptophan residues were more than 86% accessible, as assessed by iodide quenching, in the two truncated forms, proapoAI-6-135 and proapoAI-6-150, for both free and complexed protein, this figure fell to about 50% for full-length recombinant proapoAI, further indicating the influence of the carboxyl terminus on the structure of the whole protein. While cross-linking human plasma apoAI in solution with dithiobis-(succinimidyl propionate) revealed high molecular weight oligomers by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, recombinant proapoAI did not strongly form complexes larger than trimers. None of the truncated proapoAI molecules formed oligomers larger than trimers. The shortest form, proapoAI-6-135, only dimerized. Initial results from lecithin:cholesterol acyltransferase activation (apoAI peptide concentration 0.2 microM) indicated that truncation of the 21 carboxy-terminal amino acids resulted in a drop of approximately 53% in activation and 33 residues a drop of 67% relative to the full-length protein. Overall these results indicate the important influence of the carboxyl terminus on the structure of apoAI.  相似文献   
147.
Transient currents in cross-linked polyethylene (XLPE) have been investigated by using different parameters: temperature T, electrical field Ep and hydrostatic pressure P. Anomalous discharging currents flowing in the same direction as charging currents were observed from T=30 to 70°C, P=0.1 to 30 MPa and Ep=13 to 33 kV/mm. The space charge was measured using the pressure wave propagation method (PWP). Theoretical calculation revealed that this anomalous behavior can result from charge migration under a partial blocking condition at the electrodes. We discuss theoretical results which are in reasonable agreement with our discharge current measurements  相似文献   
148.
149.
150.
In many critical applications of digital systems, fault tolerance has been an essential architectural attribute for achieving high reliability. This paper considers the problem of determining the optimal number of redundant channels in a digital communication system. The expected system cost is obtained. We determine the number of redundant channels minimizing the expected system cost. A numerical example illustrates the techniques.  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