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   30221篇
  免费   1350篇
  国内免费   145篇
电工技术   573篇
综合类   240篇
化学工业   6583篇
金属工艺   576篇
机械仪表   656篇
建筑科学   1652篇
矿业工程   153篇
能源动力   922篇
轻工业   2339篇
水利工程   329篇
石油天然气   247篇
武器工业   4篇
无线电   2450篇
一般工业技术   5304篇
冶金工业   4890篇
原子能技术   216篇
自动化技术   4582篇
  2023年   306篇
  2022年   522篇
  2021年   782篇
  2020年   508篇
  2019年   600篇
  2018年   750篇
  2017年   662篇
  2016年   866篇
  2015年   768篇
  2014年   975篇
  2013年   1840篇
  2012年   1488篇
  2011年   1923篇
  2010年   1414篇
  2009年   1350篇
  2008年   1424篇
  2007年   1320篇
  2006年   1176篇
  2005年   946篇
  2004年   870篇
  2003年   804篇
  2002年   755篇
  2001年   568篇
  2000年   465篇
  1999年   461篇
  1998年   840篇
  1997年   618篇
  1996年   497篇
  1995年   469篇
  1994年   427篇
  1993年   399篇
  1992年   290篇
  1991年   203篇
  1990年   284篇
  1989年   269篇
  1988年   229篇
  1987年   238篇
  1986年   238篇
  1985年   274篇
  1984年   246篇
  1983年   233篇
  1982年   220篇
  1981年   205篇
  1980年   174篇
  1979年   202篇
  1978年   174篇
  1977年   194篇
  1976年   244篇
  1975年   167篇
  1974年   127篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Final-offer salary arbitration in major league baseball offers a unique institutional arrangement that creates a naturally occurring, non-equivalent-groups, repeated measures research design. The structural arrangements allow for examination of anticipatory expectancy effects and assessment of behavioral responses consistent with equity theory predictions. In addition, equity theory can be tested without the methodological problems inherent in defining the referent other. Performance and mobility were examined for major league baseball position players who won and lost their arbitration hearings. Prearbitration performance significantly predicted arbitration outcome. A significant relationship was noted between losing arbitration and postarbitration performance decline. Losers were significantly more likely to change teams and leave major league baseball. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
102.
The authors attempt to provide a better understanding of the differences between the normal memory decline characteristic of age-associated memory impairment (AAMI) and the pathological decline typical of mild Alzheimer's disease (AD). Batteries of traditional memory tests and computer-simulated everyday-memory tests discriminated between the 2 groups, which were matched on age, gender, and education, with reasonable degrees of accuracy (87.5% and 88.4%, respectively). False positives were the most frequent classification errors when using either battery. These results indicate that it is possible to use ecologically valid memory assessment paradigms without sacrificing discriminant validity. The clinical significance of discriminating mild AD from AAMI is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
103.
Responds to the points made by R. Cropanzano and K. James (see record 1991-00462-001) concerning the article by R. D. Arvey et al (1989). The authors acknowledge that the Arvey et al study is based on a single design, makes use of a small and special sample, and, as such, is vulnerable to threats of internal and external validity. Nevertheless, after providing a more comprehensive conceptual and empirical context for the study, and after reviewing a number of the issues raised by Cropanzano and James, the authors conclude that it is not premature to accept the idea that work attitudes are partially genetically influenced. Indeed, the authors use behavioral genetic theory, together with data gathered in the Arvey et al study, to make specific point predictions regarding the outcomes of an array of studies that easily can be undertaken. Finally, the authors acknowledge that the comments and issues raised by Cropanzano and James, along with the interchange, can offer directions for future research in this important area. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
104.
Image and geometry processing applications estimate the local geometry of objects using information localized at points. They usually consider information about the tangents as a side product of the points coordinates. This work proposes parabolic polygons as a model for discrete curves, which intrinsically combines points and tangents. This model is naturally affine invariant, which makes it particularly adapted to computer vision applications. As a direct application of this affine invariance, this paper introduces an affine curvature estimator that has a great potential to improve computer vision tasks such as matching and registering. As a proof-of-concept, this work also proposes an affine invariant curve reconstruction from point and tangent data.  相似文献   
105.
106.
Finite element methods for dynamic analysis employing elements with drilling degrees of freedom are presented. The formulation is based on a variational principle in which displacements and rotations are interpolated independently. The issue of zero masses corresponding to rotational degrees of freedom is addressed and techniques for defining consistent and lumped rotational mass matrices are presented.  相似文献   
107.
108.
109.
Ben M. Benjamin  Emily C. Douglas 《Fuel》1986,65(12):1735-1739
The object of this paper is to demonstrate the usefulness of the transalkylation reaction for determining chemical structural features of products derived from coal. For example, the method is applied to derivatized coals, coals modified by thermolysis, and materials physically or chemically separated from coals. Data are presented for the pyridine soluble and insoluble parts of two coals, an O-methylated coal, a Birch reduced coal, a solvent refined coal, and a coke. Similarities and differences in chemical make-up of these materials are discussed.  相似文献   
110.
Invertebrate communities from different coastal marsh‐plant communities were compared along wave‐exposure gradients using data from 1994, 1998 and 1999. Data were subjected to correspondence analyses to search for patterns in invertebrate communities in relation to plant‐community structure and wave exposure. In 1994, quantitative plant‐ and sediment‐invertebrate samples were taken from nine habitats: four from inland, subsurface‐connected marshes and five from littoral, emergent marshes. In 1998, sweep‐net samples were taken from 13 plant communities: six on the exposed and seven on the protected side of an island. In 1999, 2–3 plant communities/sites were sampled with sweep nets from four sites around the Bay so that intersite differences between inner, less‐exposed and outer, more‐exposed habitats could be examined. In all three studies, correspondence analyses separated inland, protected or inner sites from littoral, exposed or outer sites, suggesting differences in invertebrate‐community structure. For example, Hydracarina and Asellidae occurred in large numbers in inland sites, but were less common or absent from exposed, littoral sites. Littoral marshes also separated along an exposure gradient with Tanytarsini and Orthocladiinae collectors of organic particles occurring in very high numbers in outer, exposed areas where organic particles from the pelagic zone entered the marsh. Certain plant‐community types clustered together (e.g. wet meadow and Scirpus) while others, such as Typha, stands clustered according to exposure to waves suggesting the importance of both plant‐community structure and wave exposure in determining invertebrate‐community structure. We present a conceptual model that suggests that invertebrates in Great Lakes' marshes are distributed along gradients of decreased mixing of pelagic water and increases in sediment organic matter from outer to inner marsh and between littoral and adjacent inland marshes. Some invertebrates do best on one end of these gradients, while the majority are generalists found across habitat types.  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