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   433534篇
  免费   6678篇
  国内免费   1488篇
电工技术   7943篇
综合类   573篇
化学工业   65754篇
金属工艺   14715篇
机械仪表   12299篇
建筑科学   12399篇
矿业工程   946篇
能源动力   11794篇
轻工业   46735篇
水利工程   3496篇
石油天然气   1953篇
武器工业   19篇
无线电   56781篇
一般工业技术   79321篇
冶金工业   79592篇
原子能技术   5710篇
自动化技术   41670篇
  2021年   3308篇
  2020年   2243篇
  2019年   2942篇
  2018年   4409篇
  2017年   4518篇
  2016年   4734篇
  2015年   3871篇
  2014年   6384篇
  2013年   20357篇
  2012年   11133篇
  2011年   15846篇
  2010年   12136篇
  2009年   13778篇
  2008年   14695篇
  2007年   14950篇
  2006年   13334篇
  2005年   12550篇
  2004年   12223篇
  2003年   11881篇
  2002年   11507篇
  2001年   11645篇
  2000年   10618篇
  1999年   11104篇
  1998年   25438篇
  1997年   18517篇
  1996年   14570篇
  1995年   11403篇
  1994年   10084篇
  1993年   9709篇
  1992年   7259篇
  1991年   6965篇
  1990年   6557篇
  1989年   6239篇
  1988年   5995篇
  1987年   4989篇
  1986年   4946篇
  1985年   6098篇
  1984年   5667篇
  1983年   4880篇
  1982年   4569篇
  1981年   4521篇
  1980年   4279篇
  1979年   4139篇
  1978年   3826篇
  1977年   4643篇
  1976年   6261篇
  1975年   3166篇
  1974年   3036篇
  1973年   2917篇
  1972年   2336篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This study employed two perspectives to investigate media attention given women congressional candidates. The first perspective is that media attention may be explained by typical and normal media processes, such as focusing on incumbents. The second perspective considers a partisan explanation in which media attention is weighted more to Democratic candidates than Republican candidates. This study employs two established sources, Vanderbilt's Television News Index and Abstract and Information Access's National Newspaper Index , to examine the national media attention of Democratic and Republican women congressional candidates in 1990 and 1992. The investigation determined that media attention is related to whether the candidates are running for the Senate or House, incumbency, and state population. The results also reveal that party is a statistically significant factor associated with media attention. The investigation also determined that ethnic candidates tend to receive slightly less attention from the print media than nonethnic candidates.  相似文献   
52.
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features  相似文献   
53.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications  相似文献   
54.
55.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency  相似文献   
56.
Canny  J. 《Computer Journal》1993,36(5):409-418
  相似文献   
57.
58.
The study presents a hypothesis on how randomness could be simulated by human subjects. Three sources of deviation from randomness are predicted: (1) the preferred application of overlearned production schemata for producing sequences of digits, (2) a wrong concept of randomness, and (3) the impossibility to monitor for redundancies of higher- than those of first-order. Deviations of random generation of digits produced by healthy subjects, patients with chronic frontal lobe damage, and patients with Parkinson's disease from random sequences produced by a computer program can be explained by the differential influence of these factors. Whereas incorrect concepts of randomness and limits on monitoring capacity distinguished all sequences produced by humans from actual random sequences, persistence on a single production strategy distinguished brain-damaged patients from controls. Random generation of digits appears to be a theoretically transparent and clinically useful test of executive function.  相似文献   
59.
The deletion of nine residues from the C-terminus of the bacterialchloramphenicol acetyltransferase (CAT) results in depositionof the mutant protein in cytoplasmic inclusion bodies and lossof chloramphenicol resistance in Escherichia coli. This foldingdefect is relieved by C-terminal fusion of the polypeptide withas few as two residues. Based on these observations, efficientpositive selection for the cloning of DNA fragments has beendemonstrated. The cloning vector encodes a C-terminally truncatedCAT protein. Restriction sites in front of the stop codon allowthe insertion of target DNA, resulting in the production ofproperly folded CAT fusion proteins and regained chloramphenicolresistance. The positive selection of recombinants is accomplishedby growth of transformants on chloramphenicol-containing agarplates. The method appears particularly convenient for the cloningof DNA fragments amplified by the PCR because minimal informationto restore CAT folding can be included in the primers. The cloningof random sequences shows that the folding defect can be relievedby fusion to a wide variety of peptides, providing great flexibilityto the positive selection system. This vector may also contributeto the determination of the role of the C-terminus in CAT folding.  相似文献   
60.
Several in vivo and in vitro methods for monitoring immunological properties of two allergoids obtained by formaldehyde treatment of ovalbumin (OA) were developed. The calculated molecular weight of allergoids was 80 kD (OA-F1) and 165 kD (OA-F2), respectively. The allergenic activity in vitro of allergoids in mast-cell histamine release assay was 1000 times lower than of OA. Both allergoids showed reduced ability to induce passive cutaneous anaphylaxis in the Sprague-Dawley rats or systemic anaphylaxis in Dunkin-Harley guinea-pigs. The ability of OA and allergoids to bind to the OA-specific IgE antibodies was measured in vivo by the inhibition of passive cutaneous anaphylaxis (PCA-inhibition). Allergoid binding to IgE was 51-66% lower than the native allergen. Moreover, the avidity of OA-specific IgG antibodies, measured by ELISA-inhibition, for allergoids and allergen was of the same order. Allergoids induced a different pattern of humoral immune response from that, induced by the native allergen. Thus, after immunization of BALB/c mouse, both allergoids induced a higher production of IgG and a lower production of IgE than OA, only OA-F2 induced a lower production of IgG1. The differences in the IgA response to the immunogens was not significant. Delayed hypersensitivity studies in the BALB/c mouse showed that allergoids were 5- to 12-times less effective in inducing a cell-mediated immune response than OA. The present study provides a battery of immunological methods for preclinical testing of modified allergens.  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