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   21861篇
  免费   631篇
  国内免费   24篇
电工技术   231篇
综合类   17篇
化学工业   4572篇
金属工艺   507篇
机械仪表   397篇
建筑科学   953篇
矿业工程   90篇
能源动力   546篇
轻工业   1436篇
水利工程   271篇
石油天然气   205篇
武器工业   1篇
无线电   1565篇
一般工业技术   3514篇
冶金工业   4909篇
原子能技术   176篇
自动化技术   3126篇
  2022年   149篇
  2021年   248篇
  2020年   204篇
  2019年   270篇
  2018年   305篇
  2017年   310篇
  2016年   374篇
  2015年   296篇
  2014年   468篇
  2013年   1264篇
  2012年   776篇
  2011年   984篇
  2010年   776篇
  2009年   788篇
  2008年   919篇
  2007年   980篇
  2006年   807篇
  2005年   760篇
  2004年   670篇
  2003年   622篇
  2002年   596篇
  2001年   377篇
  2000年   378篇
  1999年   383篇
  1998年   518篇
  1997年   440篇
  1996年   411篇
  1995年   384篇
  1994年   330篇
  1993年   387篇
  1992年   332篇
  1991年   259篇
  1990年   294篇
  1989年   299篇
  1988年   285篇
  1987年   271篇
  1986年   295篇
  1985年   318篇
  1984年   323篇
  1983年   309篇
  1982年   249篇
  1981年   273篇
  1980年   264篇
  1979年   270篇
  1978年   236篇
  1977年   247篇
  1976年   240篇
  1975年   202篇
  1974年   188篇
  1973年   188篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
传统的高精密电容检测和阻抗检测应用需要将一套收集的分立器件巧妙的组合起来以提供完整的测量解决方案。这种方法不仅在器件选择方面十分耗时,并且由于各个应用之间即使有很小的差异,也需要做大量设计验证、评估、优化和鉴定。  相似文献   
62.
Finite element simulations of the high-temperature behavior of single-phase γ, dual-phase α2+γ, and fully lamellar (FL) α2+γTiAl intermetallic alloy microstructures have been performed. Nonlinear viscous primary creep deformation is modeled in each phase based on published creep data. Models were also developed that incorporate grain boundary and lath boundary sliding in addition to the dislocation creep flow within each phase. Overall strain rates are compared to gain an understanding of the relative influence each of these localized deformation mechanisms has on the creep strength of the microstructures considered. Facet stress enhancement factors were also determined for the transverse grain facets in each model to examine the relative susceptibility to creep damage. The results indicate that a mechanism for unrestricted sliding of γ lath boundaries theorized by Hazzledine and co-workers leads to unrealistically high strain rates. However, the results also suggest that the greater creep strength observed experimentally for the lamellar microstructure is primarily due to inhibited former grain boundary sliding (GBS) in this microstructure compared to relatively unimpeded GBS in the equiaxed microstructures. The serrated nature of the former grain boundaries generally observed for lamellar TiAl alloys is consistent with this finding.  相似文献   
63.
Factor V Leiden mutation was initially detected in thrombophilic patients and relatives by PCR RFLP (Restriction Fragment Length Polymorphism) according to Bertina (1). This technique presents some drawbacks and the current trend is to simplify the diagnosis. We describe a technique of Allele Specific Amplification (ASA) which is optimized in terms of reliability: an additional mismatch in antepenultimate position enables to obtain the same specificity as PCR RFLP. Furthermore, coamplification of internal control warrants an optimal sensitivity. All the PCR have been simplified: the DNA extraction improvement allows to analyse the genotype with only a few microliters of whole blood whatever the anticoagulant and the procedure of preservation (freezing, dried blood spots, storage at +4 degrees C for several days). This technique saves time. Moreover, full automation of the ASA technique may be shortened thanks to the lack of extraction and the positive/negative reading of the PCR signal.  相似文献   
64.
This multiple baseline study investigated the effectiveness of a cognitive-behavioral self-management training package on the consistent use of specific classroom survival skills. Participants were three adolescent males with learning disabilities in Grades 7 and 8. The training package involved a multicomponent strategy focused on the improvement, maintenance, and cross-classroom generalization of targeted classroom preparedness skills. Following intervention, the training procedures were systematically faded. Results demonstrated more consistent use of targeted classroom survival skills by all three students in both learning support and mainstream generalization settings. Long-term maintenance of the intervention effects was observed for two students in both settings. Three social validity measures revealed positive results. Implications for self-management in secondary education settings are discussed.  相似文献   
65.
The road to employee empowerment runs between true commitment on the one side and enforced compliance and chaos on the other. By following this column's guidelines, IS managers can steer their organizations to success and help free employees to be more creative in terms of both quality and productivity.  相似文献   
66.
The interpretation of archaeologically-derived skeletal series is dependent on the elements and portions of elements preserved for examination. Bone and bone portion survival is affected by factors, both intrinsic and extrinsic to the elements themselves, that influence deterioration and preservation. Among the intrinsic variables, the density of the element and element portion are particularly important with respect to the degree of preservation. Recently reported bone mineral density values from a contemporary human sample are compared to the survival of prehistoric limb bones of the Crow Creek specimens, a fourteenth-century massacre skeletal series. The contemporary density values are positively correlated with Crow Creek element and element portion survival. Two calculations of bone mineral density, however, are more closely related to preservation than a third. Such density information has implications for assessing minimum number of elements and individuals and documenting taphonomic processes.  相似文献   
67.
Helical distributions of stokeslets can valuably model microbial locomotion through a fluid, and also the flow field generated, wherever a flagellum actively executes helical undulations (as in many single-celled algae and protozoa) or where (as in many bacteria) the action of rotary motors causes a passive structure of helical shape (which may be a flagellum or else the cell body itself) to rotate. Here, previous biomechanical studies of such modes of locomotion are extended to include analyses of three-dimensional flow fields. In some cases, a rotlet field (curl of a stokeslet) needs to be incorporated in the models. For example, spirochete swimming is modelled by combined helical distributions of stokeslets and rotlets; the computed flow field being confined to within distances of less than twice the radius of the cell body's helical shape from its axis, while including a powerful jet-like interior flow through the coils of the swimming spirochete.  相似文献   
68.
Lorentz [1] pioneered the representation of flows at very low Reynolds number by a surface distribution of stokeslets — whose strengths, nowadays, are computed by surface-velocity collocations. That method is here compared with a representation widely used in flagellar hydrodynamics, by a curvilinear distribution of stokeslets and dipoles along the flagellar centreline; with the velocity of each cross-section expressed as a centreline value of the combined fields of singularities beyond a certain cutoff distance. The latter is also a good representation, and offers moreover some computational advantages. This paper establishes the equivalence of the two representations, and identifies those properties of Stokes flows which make both the dipoles and the cutoff essential to that equivalence.  相似文献   
69.
70.
Treatment of the addictions is changing. Psychosocial treatment programs and research projects have changed the way helping professionals view, treat, and prevent drug abuse. This article reviews the contributions included in this special series; they encompass several general issues facing psychologists who conduct treatment, research, and teaching in the field of addictive behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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