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   27214篇
  免费   719篇
  国内免费   33篇
电工技术   351篇
综合类   14篇
化学工业   5968篇
金属工艺   521篇
机械仪表   467篇
建筑科学   1237篇
矿业工程   332篇
能源动力   654篇
轻工业   1769篇
水利工程   234篇
石油天然气   245篇
无线电   1754篇
一般工业技术   4125篇
冶金工业   6286篇
原子能技术   270篇
自动化技术   3739篇
  2022年   249篇
  2021年   418篇
  2020年   268篇
  2019年   349篇
  2018年   427篇
  2017年   373篇
  2016年   490篇
  2015年   395篇
  2014年   620篇
  2013年   1660篇
  2012年   946篇
  2011年   1211篇
  2010年   929篇
  2009年   980篇
  2008年   1163篇
  2007年   1076篇
  2006年   988篇
  2005年   893篇
  2004年   753篇
  2003年   724篇
  2002年   720篇
  2001年   492篇
  2000年   402篇
  1999年   456篇
  1998年   475篇
  1997年   465篇
  1996年   493篇
  1995年   465篇
  1994年   466篇
  1993年   447篇
  1992年   436篇
  1991年   273篇
  1990年   414篇
  1989年   392篇
  1988年   345篇
  1987年   411篇
  1986年   354篇
  1985年   450篇
  1984年   473篇
  1983年   405篇
  1982年   382篇
  1981年   300篇
  1980年   303篇
  1979年   358篇
  1978年   304篇
  1977年   245篇
  1976年   223篇
  1975年   248篇
  1974年   218篇
  1973年   226篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
The 2011 AASHTO Roadside Design Guide (RDG) contains perhaps the most widely used procedure for choosing an appropriate length of need (LON) for roadside barriers. However, this procedure has several limitations. The procedure uses a highly simplified model of vehicle departure, and the procedure does not allow designers to specify an explicit level of protection. A new procedure for choosing LON that addresses these limitations is presented in this paper. This new procedure is based on recent, real-world road departure trajectories and uses this departure data in a more realistic way. The new procedure also allows LON to be specified for a precisely known level of protection – a level which can be based on number of crashes, injury outcomes or even estimated crash cost – while still remaining straightforward and quick to use like the 2011 RDG procedure.  相似文献   
3.
4.
To enhance the understanding of the behavior and effects of the precipitation of MnO2 particles in the subsurface generated during in situ chemical oxidation (ISCO) using permanganate, laboratory batch experiments were completed to examine the influence that varied reaction matrix conditions have on the generation and properties of manganese oxides. The conditions examined include organic material type and concentration, permanganate concentration, pH, and the presence of calcium (as a representative divalent cation) in solution. Experimental studies included: (1) spectrophotometric examination of permanganate depletion and manganese oxides generation over time during reactions with trichloroethene; (2) scanning electron microscopy analyses of manganese particle morphology; (3) particle size distribution (filtration) characterization studies; and (4) optical particle sizing and numeration studies. Bench-scale, batch experiments were conducted to focus on fundamental chemical properties affecting particle development under varied potential environmental conditions. The amount of manganese oxides particles that develop, grow, and potentially settle as a result of permanganate ISCO of organic contaminants is a function of the particle size and concentration, the time allowed for particle development, and the impact of matrix conditions on the ability of particles to agglomerate.  相似文献   
5.
The perceived locations of paired auditory images, simulating direct sounds and their echoes, have been recently studied in budgerigars (Melopsittacus undulatus; M. L. Dent & R. J. Dooling, 2003a, 2003b). In this article, the authors extend those experiments to include measurements of the precedence effect using a discrimination paradigm in two additional bird species: canaries (Serinus canaria) and zebra finches (Taeniopygia guttata). Although time courses of summing localization, localization dominance, and echo thresholds were similar across all species, budgerigars had slightly higher overall levels of discrimination. The results from these experiments add further support that the precedence effect in birds is similar to that found in other animals and that the ability to suppress echoes that might degrade localization and auditory object perception may be a general property of the vertebrate auditory system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
6.
An implicit assumption of several causal reasoning models is that readers adopt the goals of a narrative's protagonist during text comprehension. In apparent violation of this assumption, readers participating in Experiment 1 of the present study drew inferences relevant to a protagonist's goal even when that goal was already satisfied from the perspective of the protagonist. In Experiments 2 and 3, participants were explicitly asked to view the text situation from the point of view of the protagonist. In this case, the goals of the reader and the protagonist should be the same. In these experiments, participants focused on the goals of the protagonist only when those goals had not been satisfied from the perspective of the protagonist. These results are discussed in terms of reader- and character-based perspectives and in terms of text characteristics that cue perspective taking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
7.
In order to provide a highly efficient, long-duration form of hemodialysis, we developed nocturnal hemodialysis. Patients were dialyzed nightly at home for 8 – 10 hours, 6 – 7 nights/week. We kept the dialysate flow at 100 mL/min and the blood flow at 250 – 300 mL/min. Patients were monitored remotely from the hospital through a computer connection. An internal jugular line was used as an access. We have trained 12 patients over 30 months and have accumulated 160 patient-months worth of data. The patients tolerated the dialysis very well and slept through the night. There was a significant improvement in their sense of well-being. Nightly Kt/V was 0.99. Weekly removal of phosphate was two times as high and β 2 -microglobulin four times as high as conventional hemodialysis. All patients have discontinued their phosphate binders and have increased their dietary phosphate and protein intake. Hypertension was controlled with fewer medications, and erythropoietin dosages decreased. Complications were infrequent and included catheter occlusion and infections. Reusing the dialyzers decreased the cost of the treatment to levels similar to continuous ambulatory peritoneal dialysis. Nocturnal hemodialysis represents a viable dialysis modality that combines high quality, low cost, and excellent tolerance.  相似文献   
8.
9.
10.
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