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   206723篇
  免费   15836篇
  国内免费   208篇
电工技术   3298篇
综合类   135篇
化学工业   43404篇
金属工艺   9808篇
机械仪表   6473篇
建筑科学   4770篇
矿业工程   1889篇
能源动力   3571篇
轻工业   15749篇
水利工程   3032篇
石油天然气   8734篇
武器工业   13篇
无线电   21693篇
一般工业技术   49702篇
冶金工业   28786篇
原子能技术   6946篇
自动化技术   14764篇
  2020年   2642篇
  2019年   4709篇
  2018年   6048篇
  2017年   6474篇
  2016年   7177篇
  2015年   5565篇
  2014年   6781篇
  2013年   11298篇
  2012年   7002篇
  2011年   7762篇
  2010年   7058篇
  2009年   7463篇
  2008年   7051篇
  2007年   6821篇
  2006年   5857篇
  2005年   5240篇
  2004年   5035篇
  2003年   4860篇
  2002年   4732篇
  2001年   4593篇
  2000年   4451篇
  1999年   3714篇
  1998年   7216篇
  1997年   5298篇
  1996年   3912篇
  1995年   2977篇
  1994年   2664篇
  1993年   2774篇
  1992年   2283篇
  1991年   2333篇
  1990年   2436篇
  1989年   2351篇
  1988年   2341篇
  1987年   2216篇
  1986年   2285篇
  1985年   2322篇
  1984年   2226篇
  1983年   2146篇
  1982年   1991篇
  1981年   2207篇
  1980年   2067篇
  1979年   2273篇
  1978年   2440篇
  1977年   2443篇
  1976年   3107篇
  1975年   2246篇
  1974年   2309篇
  1973年   2347篇
  1972年   2155篇
  1971年   1914篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
Cattle access to streams has been linked globally with degradation of stream water quality, driven largely by bank erosion and resultant instream, fine sediment deposition. The majority of evidence on such effects is however based in arid and semiarid regions of the United States and Australia, with few studies relating to cool temperate climates such as Northwest Europe. In this study, “Quorer” resuspendable sediment samples were taken from riffle geomorphic units upstream (control) and at two points downstream (pressure and recovery) of cattle access points in headwater streams in agricultural catchments in Ireland to assess levels of deposited stream sediment. Samples were taken in April/May (2016) prior to the grazing season and in October (2016) at the end of the grazing season. Sites in good‐high ecological status catchments and less than good ecological status catchments were included in the study. Higher levels of sediment were found downstream of cattle access points in both good‐high status and less than good status catchments; however, the impacts of access points were spatially confined to, in most cases, the area immediately downstream of the point of access. There was a strong correlation between deposited sediment mass and organic matter (OM) mass, with levels of OM increasing linearly with deposited sediment mass. Levels of measured sediment were negatively correlated with riparian habitat health (measured using a qualitative habitat assessment). The results of this study highlight the need for measures to prevent cattle access to headwater streams where access points can be many in order to manage local habitat quality and downstream water quality issues.  相似文献   
93.
International Journal of Computer Vision - Anticipating future situations from streaming sensor data is a key perception challenge for mobile robotics and automated vehicles. We address the problem...  相似文献   
94.
Theoretical Foundations of Chemical Engineering - A choline chloride–sulfosalicylic acid deep eutectic solvent (DES) is proposed for dissolving the oxides Co(II), Cu(II), Zn(II), Fe(III),...  相似文献   
95.
Atomic Energy - The results of calculations and experimental determination of the neutronics characteristics of the IRT-T research reactor are presented. The IRT-T reactor is a pool reactor with...  相似文献   
96.
97.
This paper considers the state‐dependent interference relay channel (SIRC) in which one of the two users may operate as a secondary user and the relay has a noncausal access to the signals from both users. For discrete memoryless SIRC, we first establish the achievable rate region by carefully merging Han‐Kobayashi rate splitting encoding technique, superposition encoding, and Gelfand‐Pinsker encoding technique. Then, based on the achievable rate region that we derive, the capacity of the SIRC is established in many different scenarios including (a) the weak interference regime, (b) the strong interference regime, and (c) the very strong interference regime. This means that our capacity results contain all available known results in the literature. Next, the achievable rate region and the associated capacity results are also evaluated in the case of additive Gaussian noise. Additionally, many numerical examples are investigated to show the value of our theoretical derivations.  相似文献   
98.
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included.  相似文献   
99.
When solving a mathematical problem, students who do not have sufficient conceptual understanding may perform poorly and exhibit misconceptions. This study was aimed to examine students' conceptual understanding and significant misconceptions when solving number sense‐related problems. An online three‐tier diagnostic test was administered to 125 fifth‐grade students with varied socio‐economic backgrounds in Hong Kong. Only 14.40% of the students exhibited high performance with high confidence, indicating that these students had a profound conceptual understanding of number sense. In addition, the majority of the students (66.40%) did not demonstrate number sense; these students exhibited several significant misconceptions and could solve the questions only by using a rule‐based method or guessing. Accordingly, most students performed unsatisfactorily on number sense‐related problems. This study is imperative in identifying early predictors and provides information for further compatible interventions in the teaching and learning of number sense in Hong Kong in particular and worldwide in general.  相似文献   
100.
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