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   24737篇
  免费   283篇
  国内免费   559篇
电工技术   368篇
综合类   157篇
化学工业   2329篇
金属工艺   1019篇
机械仪表   1190篇
建筑科学   1481篇
矿业工程   624篇
能源动力   170篇
轻工业   4905篇
水利工程   795篇
石油天然气   472篇
武器工业   63篇
无线电   1916篇
一般工业技术   7986篇
冶金工业   430篇
原子能技术   236篇
自动化技术   1438篇
  2023年   36篇
  2022年   46篇
  2021年   70篇
  2020年   49篇
  2019年   39篇
  2018年   71篇
  2017年   34篇
  2016年   46篇
  2015年   59篇
  2014年   132篇
  2013年   112篇
  2012年   2188篇
  2011年   2811篇
  2010年   559篇
  2009年   288篇
  2008年   2056篇
  2007年   1981篇
  2006年   1723篇
  2005年   1584篇
  2004年   1345篇
  2003年   1152篇
  2002年   1064篇
  2001年   870篇
  2000年   951篇
  1999年   671篇
  1998年   538篇
  1997年   425篇
  1996年   410篇
  1995年   363篇
  1994年   335篇
  1993年   245篇
  1992年   286篇
  1991年   264篇
  1990年   265篇
  1989年   224篇
  1988年   179篇
  1987年   232篇
  1986年   236篇
  1985年   240篇
  1984年   215篇
  1983年   194篇
  1982年   204篇
  1981年   157篇
  1980年   134篇
  1979年   89篇
  1978年   68篇
  1977年   28篇
  1975年   27篇
  1965年   29篇
  1964年   26篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
MEASUREMENTOFTHERMODYNAMICPROPERTIESOFLIQUIDAlMgALLOYS①LuGuiminandQiuZhuxianP.O.Box317,ScholofMaterialsScienceandMetalurgy,N...  相似文献   
992.
FUZZYDECISIONMAKINGFORSELECTIONOFINFORMATIONSYSTEMDEVELOPMENTAPPROACH①ChenXiaohongandLiuMaiColegeofBusinesandManagement,Centr...  相似文献   
993.
MICROSTRUCTUREANDMECHANICALPROPERTIESOF(Nb,Ti)CNICKELBASESUPERALLOY①CaiKefeng,NanCewenandMinXinminStateKeyLaboratoryofAdvanc...  相似文献   
994.
SURVEYOFGEOLOGYLancangvolcanicbeltliesinthesouthwesternpartofYunnanProvince,P.R.Chinaandfromnorthtosouth,throughChanglin,Lan...  相似文献   
995.
The knowledge of the molecular basis of communication in bumblebee communities is limited. None of the enzymes that participate in pheromone production have been characterized. Here, we cloned the gene encoding the Delta(9) desaturase from cDNA prepared from the total RNA of the pheromone gland and fat bodies of Bombus lucorum male. Functional expression of BlucNPVE desaturase in Saccharomyces cerevisiae and GC-MS analyses revealed its preference for C(18) saturated fatty acids. This suggests that Delta(9) desaturase is involved in the desaturation of metabolic fatty acids stored in triacylglyceroles (TAGs), because oleic acid is the most abundant fatty acid bound in TAG in B. lucorum and it is present in low concentration in the pheromone blend. The incubation of pheromone precursors with a dissected labial gland as well as direct injection of labelled pheromone substrates into B. lucorum males revealed that esterification of pheromone products occurs in the labial gland. These results support both the biosynthesis of pheromones from common lipids and the de novo synthesis of unsaturated pheromones in the labial gland.  相似文献   
996.
HIV cell fusion and entry have been validated as targets for therapeutic intervention against infection. Bicyclams were the first low-molecular-weight compounds to show specific interaction with CXCR4. The most potent bicyclam was AMD3100, in which the two cyclam moieties are tethered by a 1,4-phenylenebis(methylene) bridge. It was withdrawn from clinical trials owing to its lack of oral bioavailability and cardiotoxicity. We have designed a combinatorial library of non-cyclam polynitrogenated compounds by preserving the main features of AMD3100. At least two nitrogen atoms on each side of the p-phenylene moiety, one in the benzylic position and the other(s) in the heterocyclic system were maintained, and the distances between them were similar to the nitrogen atom distances in cyclam. A selection of diverse compounds from this library were prepared, and their in vitro activity was tested in cell cultures against HIV strains. This led to the identification of novel potent CXCR4 coreceptor inhibitors without cytotoxicity at the tested concentrations.  相似文献   
997.
998.
Surrogate endpoints in oncology research and practice have garnered increasing attention over the past two decades. This activity has largely been driven by the promise surrogate endpoints appear to hold: the potential to get new therapies to seriously ill patients more rapidly. However, uncertainties abound. Even agreeing upon a definition of a "valid" surrogate endpoint has not been a straightforward exercise; this article begins by highlighting differences in how this term has been previously captured and applied, as well as laying out the basic criteria essential for its application in advanced colorectal cancer. Ideally, these elements include (but are not limited to) ease of measurement, rapid indication of treatment effect, and, most importantly, reliable and consistent prediction of the true impact of a treatment on the ultimate outcome of interest: overall survival. The strengths and weaknesses of current potential surrogate endpoints in advanced colorectal cancer, including performance status, carcinoembryonic antigen plasma level, overall response rate, time to progression, and disease-free survival, are each considered in turn. Finally, limitations of surrogate endpoints in the clinical setting, including challenges in extrapolation to new therapies, and the incomplete provision of information about potential adverse effects, are discussed. Work remains to be done between physicians and statisticians to bridge the gap between that which is statistically demonstrable and that which will be clinically useful.The term ;surrogate endpoint' was virtually unknown by most oncologists 15 years ago. A search in PubMed [http://www.ncbi.nlm.nih.gov] based on the words ;surrogate and cancer' shows that more than 2000 papers were published in medical journals in the last 20 years, with a dramatic increase of interest in the last five years. Interestingly, the same trend is observed when the words ;surrogate and heart' are entered into PubMed, suggesting that the issue of surrogate endpoints goes beyond the field of oncology, although the frequency of discussion varies (Figure 1; note different y-axis scales for oncology and cardiology).The goal of the present paper is to discuss the main issues surrounding surrogate endpoints from a clinician's point of view, using as an example surrogate endpoints of overall survival (OS) in advanced colorectal cancer (ACC).  相似文献   
999.
Although labile protons that are exchanging rapidly with those of the solvent cannot be observed directly, their exchange rate constants can be determined by indirect detection of scalar-coupled neighboring nuclei. We have used heteronuclear NMR spectroscopy to measure the exchange rate constants of labile protons in the side chains of lysine and arginine residues in ubiquitin enriched in carbon-13 and nitrogen-15 at neutral pH. Exchange rate constants as fast as 40x10(3) s(-1) were thus measured. These results demonstrate that NMR spectroscopy is a powerful tool for the characterization of lysine NH3(+) and arginine NH groups in proteins at physiologically relevant pH values.  相似文献   
1000.
Now that the human genome has been decoded, the demand for novel therapeutic concepts, such as gene and stem cell therapy, is higher than ever before. Although new and better pharmaceutical agents are available, their efficient delivery to the intracellular site of action is still a serious challenge. A possible solution to this problem is the use of cell-penetrating peptides as delivery vectors, including derivatives of human calcitonin (hCT). The aim of this study was to synthesise novel branched hCT-derived peptides for the noncovalent delivery of nucleic acids. The uptake of the resulting oligocationic peptides into various cell lines as well as primary cells was monitored by fluorescence microscopy. To determine the appropriate peptide-plasmid charge ratios for efficient cell transfection, electromobility shift assays were carried out. Finally, flow cytometric and fluorescence microscopic studies of gene expression highlighted two novel hCT-derived peptides as highly effective in the delivery of noncovalently complexed plasmid DNA. Thus, the absence of cytotoxicity paired with highly efficient cell internalisation and transfection rates, in primary cells as well, make both peptides powerful candidates as drug delivery vectors, especially for plasmid DNA, for both in vivo and ex vivo therapeutic applications.  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