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   4284篇
  免费   151篇
  国内免费   2篇
电工技术   61篇
综合类   10篇
化学工业   806篇
金属工艺   153篇
机械仪表   96篇
建筑科学   232篇
矿业工程   12篇
能源动力   81篇
轻工业   332篇
水利工程   17篇
石油天然气   9篇
武器工业   1篇
无线电   387篇
一般工业技术   681篇
冶金工业   965篇
原子能技术   79篇
自动化技术   515篇
  2023年   40篇
  2022年   36篇
  2021年   79篇
  2020年   40篇
  2019年   74篇
  2018年   80篇
  2017年   62篇
  2016年   101篇
  2015年   71篇
  2014年   111篇
  2013年   184篇
  2012年   135篇
  2011年   182篇
  2010年   139篇
  2009年   122篇
  2008年   132篇
  2007年   139篇
  2006年   126篇
  2005年   106篇
  2004年   114篇
  2003年   97篇
  2002年   98篇
  2001年   70篇
  2000年   104篇
  1999年   123篇
  1998年   252篇
  1997年   180篇
  1996年   147篇
  1995年   84篇
  1994年   71篇
  1993年   85篇
  1992年   48篇
  1991年   50篇
  1990年   40篇
  1989年   46篇
  1988年   43篇
  1987年   48篇
  1986年   33篇
  1985年   35篇
  1984年   40篇
  1983年   40篇
  1982年   30篇
  1980年   38篇
  1979年   35篇
  1978年   39篇
  1977年   62篇
  1976年   90篇
  1975年   28篇
  1974年   36篇
  1973年   29篇
排序方式: 共有4437条查询结果,搜索用时 0 毫秒
971.
Six matricaria esters (MEs) and two matricaria lactones (MLs), isolated from members of the tribe Astereae (Asteraceae), were tested against Mycobacterium tuberculosis and M. avium, using a radiorespirometric bioassay. (2Z,8Z)-ME and (2E-8Z)-ME gave minimum inhibitory concentrations (MICs) of 50 micrograms ml-1 against M. tuberculosis and respective MICs of 25 and 50 micrograms ml-1 against M. avium. The (4Z,8Z)-ML, (2Z)-8-dehydro-ME and (2Z,8Z)-10-angeloyloxy-(2Z,8Z)-ME showed respective MICs of 12.5, 25, 25 micrograms ml-1 against M. tuberculosis and MICs of 50, 25, 25 micrograms ml-1 against M. avium, respectively. The MICs of (2Z,8Z)-10-tigloyloxy-ME and (2E,8Z)-10-angeloyloxy-ME and (4E,8Z)-ML ranged from 50 to > 100 micrograms ml-1 against both pathogenic mycobacteria.  相似文献   
972.
There is increasing evidence that tumor expressed genes induce immune responses in cancer patients. To identify meningioma expressed antigens, we established a meningioma expression library which was screened with autologous serum. Out of 20 positive cDNA clones eight share high sequence homologies as determined by sequence analysis. These eight clones can be grouped into three classes which differ in length and which are characterized by specific sequence variations. The longest open reading frame was found to be 2412 bp encoding an immunoreactive antigen termed meningioma expressed antigen 6 (MEA6). Using five sequence specific primer pairs, somatic hybrid panel mapping revealed locations of the three classes on several human chromosomes including chromosomes 2, 3, 6, 7, 9, 13 and 14. The mapping results were confirmed by fluorescence in situ hybridization. RT-PCR showed consistent expression of all classes in several meningiomas and additional tissues using the same set of primer pairs as for chromosomal mapping. The expression data were confirmed by northern blot analysis. For the predicted amino acid sequence BLASTX revealed a homology to a human C219-reactive peptide which was previously isolated by an antibody directed against p-glycoprotein. Sequence properties of the MEA protein include an acidic activation domain, a proline-rich region and two coiled-coil domains indicating protein binding and activation functions.  相似文献   
973.
The future perspectives of the European Textile Industry strongly depend on innovations to add new values to textiles and fibres due to the increasing imports of low‐price products from Asian markets. To functionalize fibers and textiles the plasma technology is of special interest as a dry and versatile process. Mainly due to cost aspects, this technique did not become widely accepted within the textile sector up to now. High‐tech materials (e.g. medicinal devices) or niche products beside classical treatments like dyeing or soil resistance, however, are of economical importance. Possible applications using plasma as well as suitable reactors are presented.  相似文献   
974.
The pyrometallurgical processing of spent fuel from the integral fast reactor (IFR), an advanced reactor under development at Argonne National Laboratory, will generate a chloride salt waste containing the alkali-metal, alkaline-earth, and some of the rare-earth fission products. Salt-occluded zeolite A, formed by equilibrating simulated molten waste salt and zeolite A, has been investigated as an immobilization matrix for this salt waste. In this concept, the chloride waste salt is loaded into the zeolite cavities, and cesium and strontium from the salt are preferentially sorbed by the zeolite. Experiments showed that the salt-occluded zeolite powders are leach resistant and radiation stable. The conclusion is that the salt-occluded zeolite is a promising immobilization matrix for the IFR waste salt.  相似文献   
975.
As increasing amounts of genomic sequence from many organisms become available, and as DNA sequences become a primary reagent in biologic investigations, the role of annotation as a prospective guide for laboratory experiments will expand rapidly. Here we describe a process of high-throughput, reliable annotation, called framework annotation, which is designed to provide a foundation for initial biologic characterization of previously unexamined sequence. To examine this concept in practice, we have constructed Genome Annotation and Information Analysis (GAIA), a prototype software architecture that implements several elements important for framework annotation. The center of GAIA consists of an annotation database and the associated data management subsystem that forms the software bus along which other components communicate. The schema for this database defines three principal concepts: (1) Entries, consisting of sequence and associated historical data; (2) Features, comprising information of biologic interest; and (3) Experiments, describing the evidence that supports Features. The database permits tracking of annotation results over time, as well as assessment of the reliability of particular results. New framework annotation is produced by CARTA, a set of autonomous sensors that perform automatic analyses and assert results into the annotation database. These results are available via a Web-based query interface that uses graphical Java applets as well as text-based HTML pages to display data at different levels of resolution and permit interactive exploration of annotation. We present results for initial application of framework annotation to a set of test sequences, demonstrating its effectiveness in providing a starting point for biologic investigation, and discuss ways in which the current prototype can be improved. The prototype is available for public use and comment at http://www.cbil.upenn.edu/gaia.  相似文献   
976.
The oxidation of sulfide in oxygen-saturated aqueous solutions is accelerated by dissolved or silica-bonded cobalt phthalocyanines. On the basis of thermodynamical considerations it is postulated that the catalyst enhances the formation of disulfide as the initial elementary reaction step. The following reaction steps are largely unaffected by the catalyst, as indicated by a product ratio sulfate/thiosulfate=0.86, comparable to that of the uncatalyzed autoxidation. A Langmuir-Hinshelwood formalism is developed for the catalytic reaction step and is demonstrated to fit best with the kinetics. In addition, from the kinetic data free enthalpies for the adsorption of HS? (i) at the dissolved phthalocyanine (ΔG = ?17.6 kJ/mole) and (ii) at the immobilized complex (ΔG = ?20.0 kJ/mole) are calculated.  相似文献   
977.
978.
Assessed the impact of political partisanship and audience support (ADS) on the impressions individuals form of political figures. 115 undergraduates (aged 18–43 yrs) read a speech which had supposedly been given by a member of Parliament from northern Ontario. Results indicate that perceptions of the politician were affected by both partisanship and ADS. Partisanship influenced perceptions of the politician's integrity, with the politician being perceived as having greater integrity when he gave a nonpartisan speech (inconsistent with his party's stand) than when he gave a partisan speech. ADS influenced perceptions of the politician's strength, with the politician who spoke to a hostile audience being perceived as stronger than the politician who spoke to a supportive audience. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
979.
980.
A source of drain current mismatch of transistors in a 1.75-μm analog CMOS process is described. Matching of closely spaced transistors is degraded by capacitor topography created prior to the gate level. The effects extend over distances greater than 30 μm and are not reduced by common-centroid layout techniques. Symmetry and wafer position dependencies of the mismatch lead to an explanation of the effect. The topography is thought to interfere with the radial flow of gate level photoresist as it is spun on the wafer. Thickness variations in the photoresist result in channel length variations in the transistors following patterning. Transistor matching is improved by more than a factor of two with the use of a tri-level photoresist sequence at the gate level. Simple theoretical expressions and more exact numerical simulations support the explanation of channel length differences as the source of the measured mismatch. These calculations suggest how mismatch due to channel length, dopant concentration, or gate-oxide thickness may be differentiated with simple current-voltage measurements  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