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   718892篇
  免费   7986篇
  国内免费   1346篇
电工技术   13125篇
综合类   699篇
化学工业   114314篇
金属工艺   28554篇
机械仪表   22612篇
建筑科学   16445篇
矿业工程   5048篇
能源动力   17768篇
轻工业   62254篇
水利工程   8417篇
石油天然气   17036篇
武器工业   65篇
无线电   75628篇
一般工业技术   142490篇
冶金工业   127586篇
原子能技术   17533篇
自动化技术   58650篇
  2021年   6509篇
  2019年   6256篇
  2018年   10669篇
  2017年   10897篇
  2016年   11390篇
  2015年   7180篇
  2014年   12152篇
  2013年   32411篇
  2012年   19102篇
  2011年   25823篇
  2010年   20655篇
  2009年   23113篇
  2008年   23520篇
  2007年   23345篇
  2006年   20495篇
  2005年   18416篇
  2004年   17618篇
  2003年   17210篇
  2002年   16755篇
  2001年   16294篇
  2000年   15710篇
  1999年   15498篇
  1998年   36399篇
  1997年   26184篇
  1996年   20383篇
  1995年   15725篇
  1994年   14135篇
  1993年   13835篇
  1992年   10819篇
  1991年   10314篇
  1990年   10349篇
  1989年   10109篇
  1988年   9732篇
  1987年   8689篇
  1986年   8524篇
  1985年   9711篇
  1984年   8940篇
  1983年   8439篇
  1982年   7687篇
  1981年   7812篇
  1980年   7540篇
  1979年   7521篇
  1978年   7443篇
  1977年   8276篇
  1976年   10478篇
  1975年   6718篇
  1974年   6410篇
  1973年   6529篇
  1972年   5584篇
  1971年   5198篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
891.
High cycle fatigue of bolted connections Extensive tests regarding the influences on the fatigue of bolt‐nut‐connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence.  相似文献   
892.
893.
On the basis of the behavioral approach system (BAS) dysregulation theory of bipolar disorder, this study examined the relation between occurrence of a BAS activation-relevant life event--goal striving--and onset of hypomanic and depressive episodes and symptoms. In particular, the authors examined the relation between preparing for and completing final exams (a goal-striving event) and onset of bipolar spectrum episodes and symptoms in college students with bipolar II disorder or cyclothymia (i.e., "soft" bipolar spectrum conditions). One hundred fifty-nine individuals with either a bipolar spectrum disorder (n=68) or no major affective psychopathology (controls; n=91) were further classified on the basis of whether they were college students (i.e., completed final exams). Consistent with the BAS dysregulation theory, preparing for and completing final exams was associated with an increase in hypomanic but not depressive episodes and symptoms in individuals with a soft bipolar spectrum diagnosis. Furthermore, self-reported BAS sensitivity moderated the presence of certain hypomanic symptoms during final exams. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
894.
Presents an obituary for Hans Hermann Strupp, internationally acclaimed clinical psychologist and psychotherapy research pioneer, who died October 5, 2006, in Nashville, Tennessee, following a long struggle with Parkinson's disease. Hans Strupp elicited unusual respect across disciplines, including psychiatry and medicine, and across national boundaries in numerous countries. Hans was truly a person of great distinction; he brought honor to his friends, his discipline, his university, his nation, and his family. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
895.
896.
897.
Experimental Study of Ice Jam Thickening under Dynamic Flow Conditions   总被引:1,自引:0,他引:1  
River ice jams are a common occurrence on northern rivers, and their formation can present a severe flood risk to nearby communities. As more and more river regulation projects are developed to provide an alternative to fossil fuels for electrical power-generating capacity, our need to understand the mechanisms associated with ice jam formation under variable flow conditions becomes more vital. This is because, at present, hydropeaking operations are often severely curtailed during the ice-affected seasons due to concerns that sudden flow fluctuations might instigate ice jams and associated flooding. Here, an experimental investigation explores the effects of rapid increases in discharge on ice jam formation and evolution. It is found that the thickness of ice jams formed under highly dynamic flow conditions tend to be slightly thinner than those formed during steady carrier flows for comparable discharges. Also, despite the highly dynamic nature of these consolidation events, the resulting ice thicknesses appear reasonably well approximated by steady flow theory.  相似文献   
898.
Recent research has proposed the use of asphalt and tall-oil-pitch emulsions for stabilizing radioactive contamination deposited on surfaces in urban areas. The objective of this project was to investigate whether surface applied emulsions could capture airborne radioactive particulate. Laboratory experiments included wind-blown particulate capture studies using an acrylic column and particulate retainment experiments using a wind box capable of producing wind speeds of 96?km/h. A probe methodology was developed to relate particulate retainment to a tack force on the emulsion surface. Experiments were also performed to determine the potential for such emulsions to absorb particulate matter into their emulsion matrix. Tall-oil-pitch emulsions outperformed asphalt emulsions in terms of particulate retention, tack force, and the ability to absorb magnesium silicate. Both tall-oil-pitch and asphalt emulsions were capable of extracting 22–24?g?m?2 of powder from particulate-laden airflow. Tall-oil-pitch emulsions were capable of retaining as much as 5–10% of magnesium silicate powder applied (i.e., retainment densities of 10–20?g?m?2) even after seven?days of curing and after applying 96.5?km/h (60?mph) wind. Tall-oil-pitch emulsions were able to absorb surface-applied magnesium silicate (approximately 0.1–0.2?g of magnesium silicate per 1.0?g of emulsion within three?days) into their emulsion matrix, preventing the magnesium silicate from being exposed to the external environment. Initial results with these five different emulsion formulations suggested particulate capture was feasible. Future emulsion formulations (i.e., longer curing times with greater acid concentrations) should be tested to optimize this postdetonation response strategy.  相似文献   
899.
900.
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