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   442571篇
  免费   8445篇
  国内免费   1399篇
电工技术   9178篇
综合类   1218篇
化学工业   72801篇
金属工艺   14937篇
机械仪表   12532篇
建筑科学   12996篇
矿业工程   1119篇
能源动力   11503篇
轻工业   47221篇
水利工程   3526篇
石油天然气   1921篇
武器工业   14篇
无线电   56557篇
一般工业技术   83090篇
冶金工业   75371篇
原子能技术   5702篇
自动化技术   42729篇
  2021年   3598篇
  2020年   2655篇
  2019年   3214篇
  2018年   4805篇
  2017年   4740篇
  2016年   5228篇
  2015年   4582篇
  2014年   6974篇
  2013年   21726篇
  2012年   11372篇
  2011年   15905篇
  2010年   12696篇
  2009年   14309篇
  2008年   14964篇
  2007年   15274篇
  2006年   13525篇
  2005年   12629篇
  2004年   12196篇
  2003年   11855篇
  2002年   11483篇
  2001年   11549篇
  2000年   10577篇
  1999年   11056篇
  1998年   24346篇
  1997年   17874篇
  1996年   14225篇
  1995年   11294篇
  1994年   10032篇
  1993年   9650篇
  1992年   7356篇
  1991年   7002篇
  1990年   6610篇
  1989年   6343篇
  1988年   6043篇
  1987年   5097篇
  1986年   5060篇
  1985年   6245篇
  1984年   5884篇
  1983年   5074篇
  1982年   4732篇
  1981年   4726篇
  1980年   4421篇
  1979年   4306篇
  1978年   3954篇
  1977年   4745篇
  1976年   6289篇
  1975年   3387篇
  1974年   3237篇
  1973年   3262篇
  1972年   2542篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices  相似文献   
52.
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   
53.
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   
54.
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   
55.
56.
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   
57.
Canny  J. 《Computer Journal》1993,36(5):409-418
  相似文献   
58.
59.
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   
60.
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   
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