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   420955篇
  免费   4603篇
  国内免费   1273篇
电工技术   7699篇
综合类   311篇
化学工业   63721篇
金属工艺   22300篇
机械仪表   15629篇
建筑科学   9142篇
矿业工程   3377篇
能源动力   9453篇
轻工业   28789篇
水利工程   5221篇
石油天然气   10785篇
武器工业   24篇
无线电   44623篇
一般工业技术   89353篇
冶金工业   68613篇
原子能技术   10692篇
自动化技术   37099篇
  2021年   3189篇
  2019年   3083篇
  2018年   12078篇
  2017年   12521篇
  2016年   9688篇
  2015年   4012篇
  2014年   6210篇
  2013年   15771篇
  2012年   11684篇
  2011年   19462篇
  2010年   16731篇
  2009年   16994篇
  2008年   17131篇
  2007年   18504篇
  2006年   10082篇
  2005年   12011篇
  2004年   10254篇
  2003年   9604篇
  2002年   8607篇
  2001年   8182篇
  2000年   7812篇
  1999年   7861篇
  1998年   19584篇
  1997年   13872篇
  1996年   10636篇
  1995年   8045篇
  1994年   6957篇
  1993年   7114篇
  1992年   5298篇
  1991年   5276篇
  1990年   5038篇
  1989年   4999篇
  1988年   5013篇
  1987年   4363篇
  1986年   4403篇
  1985年   4971篇
  1984年   4632篇
  1983年   4343篇
  1982年   3957篇
  1981年   3971篇
  1980年   3904篇
  1979年   3931篇
  1978年   3915篇
  1977年   4330篇
  1976年   5293篇
  1975年   3515篇
  1974年   3382篇
  1973年   3519篇
  1972年   3061篇
  1971年   2790篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The paper discusses optimal control of ecosystem state for observation of a generalized monotonically varying random parameter. A model is proposed for the controlled vector random process, whose components are assigned acceptable ranges and the observations are performed discretely. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 6, pp. 40–44, June, 2006.  相似文献   
92.
Co-browsing is an activity in which a group of users navigate their way through of a set of Web pages together for a shared purpose. Effective co-browsing among users with different device capabilities requires a shared understanding of those Web pages. This paper demonstrates the concept of shared viewpoints (SVPs), and personal viewpoints (PVPs), for co-browsing, before detailing a framework for implementing these concepts. Finally, the effectiveness of the framework is presented through a perceptual experiment.  相似文献   
93.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction.  相似文献   
94.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient, the duration of the degassing operation, and the vacuum used in the treatment. __________ Translated from Metallurg, No. 7, pp. 68–69, July, 2006.  相似文献   
95.
Holmes  N. 《Computer》2006,39(2):112-111
Using a temporary substitution of format, the author offers a fairy tale to demonstrate that we can’t expect understanding when computers take the place of humans in our interactions with service providers.  相似文献   
96.
The bond behavior of prestressing strands is of great importance for the capacity of precast prestressed concrete structures. In the present study, the bond behavior of three-wire strands, and some influencing parameters, were examined by means of steel encased pull-through and push-in tests. The three mechanisms: adhesion, friction and other mechanical actions were found to be present at the strand-concrete interface at different slip values. The results from the experiments showed that the micro roughness of the strand surface strongly affected the initial bond response of the strand, that is the adhesion in the interface. The maximum bond capacity of indented three-wire strands was found to be directly connected to the geometric properties of the strand indents. The influence of the concrete strength on the bond capacity of the strand was hard to interpret. However, the density of the concrete matrix was found to be a better parameter for determine the influence of the concrete rather than the compressive strength.  相似文献   
97.
Note on B-splines, wavelet scaling functions, and Gabor frames   总被引:3,自引:0,他引:3  
Let g be a continuous, compactly supported function on such that the integer translates of g constitute a partition of unity. We show that the Gabor system (g,a,b), with window g and time-shift and frequency-shift parameters a,b>0 has no lower frame bound larger than 0 if b=2,3,... and a>0. In particular, (g,a,b) is not a Gabor frame if g is a continuous, compactly supported wavelet scaling function and if b=2,3,... and a>0. We give an example for our result for the case that g=B/sub 1/, the triangle function supported by [-1,1], by showing pictures of the canonical dual corresponding to (g,a,b) where ab=1/4 and b crosses the lines N=2,3,.  相似文献   
98.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended.  相似文献   
99.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(tγ), shows a decreasing trend with step strain. The experimental results indicate that G(tγ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(tγ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(tγ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior.  相似文献   
100.
Using Java-based tools in multimedia collaborative environments accessed over the Internet can increase an application's client base. Most operating systems support Java, and its "compile once-run everywhere" architecture is easy to maintain and update. The Java-based tools presented here let users share Internet resources, including resources originally designed for single use.  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