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   325437篇
  免费   5663篇
  国内免费   718篇
电工技术   7436篇
综合类   956篇
化学工业   54493篇
金属工艺   10544篇
机械仪表   9176篇
建筑科学   8501篇
矿业工程   1020篇
能源动力   8666篇
轻工业   32703篇
水利工程   2647篇
石油天然气   3736篇
武器工业   8篇
无线电   39994篇
一般工业技术   61114篇
冶金工业   56799篇
原子能技术   5477篇
自动化技术   28548篇
  2021年   2886篇
  2020年   2237篇
  2019年   2674篇
  2018年   4125篇
  2017年   3814篇
  2016年   4082篇
  2015年   3266篇
  2014年   5173篇
  2013年   15584篇
  2012年   7852篇
  2011年   10492篇
  2010年   8613篇
  2009年   9936篇
  2008年   9980篇
  2007年   9920篇
  2006年   8767篇
  2005年   8132篇
  2004年   7953篇
  2003年   7683篇
  2002年   7436篇
  2001年   7653篇
  2000年   7267篇
  1999年   7630篇
  1998年   17818篇
  1997年   12951篇
  1996年   10277篇
  1995年   8040篇
  1994年   7347篇
  1993年   7113篇
  1992年   5422篇
  1991年   5177篇
  1990年   5062篇
  1989年   4932篇
  1988年   4800篇
  1987年   4028篇
  1986年   4170篇
  1985年   4863篇
  1984年   4420篇
  1983年   4176篇
  1982年   3740篇
  1981年   3939篇
  1980年   3606篇
  1979年   3572篇
  1978年   3323篇
  1977年   3953篇
  1976年   4982篇
  1975年   2964篇
  1974年   2837篇
  1973年   3008篇
  1972年   2400篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The influence of prior austenite grain size on the transformation behaviour and microstructural development of C-Mn-Ni weld metals was investigated. It was found that increasing the grain size depressed the start temperature of grain-boundary ferrite and slightly increased the acicular ferrite start temperature. The microstructural products also changed from a boundary-dominated effect in the small grain sizes, to an intragranular-dominated effect in the large grain sizes, and at the same time, the morphology of the acicular ferrite was seen to change to a larger aspect ratio.  相似文献   
993.
Übersicht Die folgende Arbeit verfolgt u. a. auch didaktische Absichten. Das Biot-Savartsche Gesetz wird oft falsch oder mindestens sehr mißverständlich dargestellt und auch auf unzulässige Weise benutzt. Ausgangspunkt der Mißverständnisse ist die auch in vielen Lehrbüchern anzutreffende unkorrekte Aussage, man könne einem von StromI durchflossenen Linienelement ds ein magnetostatisches Feld dB [entsprechend der Gleichung (32) des folgenden Beitrags] zuordnen. Im folgenden werden derartige Aussagen untersucht und in modifizierter Form korrekt dargestellt.
Remarks concerning the Law of Biot-Savart
Contents The following paper is at least partly of a didactic nature. The Biot-Savart law of magnetostatics is often interpreted in an illegitimate manner and consequently applied incorrectly. The source of these misunderstandings and errors is the incorrect statement that a magnetic field dB [as given by equation (32) of this paper] is caused by an electric currentI flowing along a line element ds, a statement very popular also in many textbooks. Questions related to this problem are investigated and widespread misleading statements are replaced by correct ones.
  相似文献   
994.
The most influential study of the person–environment (P–E) fit approach to stress was conducted by J. R. French et al (1982). Unfortunately, this study operationalized fit using various transformations of difference scores, thereby introducing numerous substantive and methodological problems. In the present study, the authors reanalyze data from French et al, using a procedure described by J. R. Edwards (in press) that avoids problems with difference scores and captures the underlying 3-dimensional relationship between environment, person, and strain. Results resolve ambiguities in the French et al findings and identify relationships between environment, person, and strain that, although consistent with P–E fit theory, cannot be adequately represented by fit measures such as those used by French et al. Implications for P–E fit research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
995.
Surface forces nonuniformity within the volume of a capillary system for a given structure has been examined in terms of its effect on a wetting fluid distribution. This approach enables the distribution for a porous body with a uniform structure to be quantified using a specific function for the pore volume size distribution. The surface forces nonuniformity effect is illustrated using a fibrous structure impregnated with molten copper.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 8(368), pp. 66–69, August, 1993.  相似文献   
996.
We isolated a mutant defective in C-terminal farnesyl cysteine:carboxyl methyltransferase activity from a screen for mutations causing a -specific sterility. A genomic fragment was cloned from a yeast multi-copy library that restored mating. Both the cloned gene and the sterile mutation were allelic to the STE14 gene. A ste14-complementing 2·17 kb BamHI fragment subclone was sequenced and found to encode a 239 amino acid protein with a molecular weight of 27,887 Daltons. The hydrophobicity profile of the methyltransferase reveals the presence of at least five potential transmembrane domains. In comparisons of the C-terminal methyltransferase amino acid sequence with those in the PIR and Swiss protein databases, no significantly similar sequences were found nor were conserved regions from other methyltransferases present.  相似文献   
997.
998.
999.
1000.
A diode pumped, commercially packaged, thulium doped fluoride fiber amplifier (TDFFA) operating in the region of 0.8 μm has been characterized. The unit is capable of producing large small signal gains, low noise figures and high saturated output powers. A power amplifier slope efficiency of 62% has been achieved at 810 nm. The same TDFFA unit was used in a series of systems experiments, at data rates of 310 Mb/s and 1.2 Gb/s, in the first telecommunications window. The results of this work indicate that data can be transmitted over ≈10 km lengths of both singlemode and standard transmission fiber, while still allowing significant margin to split the signal to a number of customers. The application of the TDFFA could therefore have significant benefit for future LAN/MAN type systems architectures involving large signal splits to customer's premises  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