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   154373篇
  免费   2083篇
  国内免费   670篇
电工技术   3148篇
综合类   199篇
化学工业   24519篇
金属工艺   5825篇
机械仪表   5019篇
建筑科学   4524篇
矿业工程   378篇
能源动力   4014篇
轻工业   17449篇
水利工程   1155篇
石油天然气   625篇
武器工业   5篇
无线电   20959篇
一般工业技术   29276篇
冶金工业   24171篇
原子能技术   2350篇
自动化技术   13510篇
  2019年   879篇
  2018年   1141篇
  2017年   1190篇
  2016年   1327篇
  2015年   1119篇
  2014年   1877篇
  2013年   6739篇
  2012年   3300篇
  2011年   4742篇
  2010年   3703篇
  2009年   4269篇
  2008年   4783篇
  2007年   5047篇
  2006年   4473篇
  2005年   4198篇
  2004年   4077篇
  2003年   3973篇
  2002年   4004篇
  2001年   4034篇
  2000年   3797篇
  1999年   3755篇
  1998年   6769篇
  1997年   5333篇
  1996年   4535篇
  1995年   3753篇
  1994年   3408篇
  1993年   3221篇
  1992年   2799篇
  1991年   2703篇
  1990年   2643篇
  1989年   2641篇
  1988年   2482篇
  1987年   2186篇
  1986年   2145篇
  1985年   2576篇
  1984年   2328篇
  1983年   2204篇
  1982年   2074篇
  1981年   2000篇
  1980年   1866篇
  1979年   1877篇
  1978年   1777篇
  1977年   2096篇
  1976年   2573篇
  1975年   1584篇
  1974年   1431篇
  1973年   1457篇
  1972年   1196篇
  1971年   1118篇
  1970年   949篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Poly(vinyl alcohol) is crosslinked in dilute solution (c=0.1 wt%) with glutaraldehyde. The reaction product is characterized by viscometry and gel permeation chromatography (g.p.c.). The intrinsic viscosity decreases with increasing degree of crosslinking and does not depend on temperature. G.p.c. reveals that the reaction product is not homogeneous, but consists of a mixture of particles with different sizes, possibly both intra- and intermolecularly crosslinked molecules. The intramolecularly crosslinked molecules are smaller in size than the initial polymer molecules and their size depends on the degree of crosslinking. They possess a narrow particle size distribution even if the initial polymer sample had a broad molecular weight distribution.  相似文献   
142.
Reduced glutenin is separated by gel permeation high-performance liquid chromatography into three major and five minor fractions, which significantly differ in their amino acid compositions. By reversed-phase high performance liquid chromatography, about 20 glutenin components are obtained. These can be classified into three groups according to their amino acid compositions: a hydrophilic group with relatively high values of Glx and Phe, a more hydrophobic group with a high content of Gly, and a strongly hydrophobic group with higher values of Val and Leu. Groups 1, 2 and 3 contain middle-, high- and low-molecular-weight (MMW-, HMW-, LMW-) subunits respectively.  相似文献   
143.
144.
145.
Efficient data layout is an important aspect of the compilation process. A model for the creation of perfect memory maps for large-scale parallel machines capable of user-controlled partitionable single-instruction-multiple data/single-program-multiple data (SIMD/SPMD) operation is developed. The term perfect implies that no memory fragmentation occurs and ensures that the memory map size is kept to a minimum. A major constraint on solving this problem is based on the single program nature of both the SIMD and SPMD modes of parallelism. It is assumed that all processors within the same submachine used identical addresses to access corresponding data items in each of their local memories. Necessary and sufficient conditions are derived for being able to create perfect memory maps, and results are applied to several partitionable interconnection networks  相似文献   
146.
This paper covers the experimental investigation and theoretical calculation of losses in a planar inductor under load. Finite-element software is used to perform the loss calculations. Thermally controlled experiments are performed for a range of frequencies to validate the corresponding finite-element method loss calculations. The thermal dependence of the loss mechanisms is also considered.  相似文献   
147.
The last dozen years have produced almost 50 English language articles on the synthesis of separation systems [1]. Most work has considered separating a single relatively ideal mixture into sharply split, usually pure-component products using systems of single-feed, two-product distillation columns. Of late, the work has considered heat-integrating these columns to reduce energy consumption. Present research will very likely produce valuable results for nonsharp separations.Earlier approaches developed both algorithmic- and heuristic-based tree search algorithms for discovering the better systems of non-heat-integrated columns. New results permit the design of heat-integrated systems.The paper highlights the above developments.  相似文献   
148.
Modifications of solid water and their transitions are described as they relate to cryo electron microscopy. In particular, the various amorphous states (amorphous polymorphs) as they exist below 100 K are extensively investigated. The “high-density” midification exhibits a lower viscosity than the “low-density” form. Differences are also observed in the mechanism of void formation due to electron irradiation: in the high-density form, voids are formed — not, however, in the low-density form. Together with the reaction to radiation damage, the physical properties of amorphous solid water are discussed with respect to embedding of organic specimens. Finally, the conditions and pitfalls associated with preparation of thin and entirely vitrified ice layers by shock-freezing are described.  相似文献   
149.
K-winner networks.   总被引:2,自引:0,他引:2  
A special class of mutually inhibitory networks is analyzed, and parameters for reliable K-winner performance are presented. The network dynamics are modeled using interactive activation, and results are compared with the sigmoid model. For equal external inputs, network parameters that select the units with the larger initial activations (the network converges to the nearest stable state) are derived. Conversely, for equal initial activations, networks that select the units with larger external inputs (the network converges to the lowest energy stable state) are derived. When initial activations are mixed with external inputs, anomalous behavior results. These discrepancies are analyzed with several examples. Restrictions on initial states are derived which ensure accurate K-winner performance when unequal external inputs are used.  相似文献   
150.
We report on the Langmuir-Blodgett film deposition and plasma etching of cadmium distearate on n-Gao.47Ino.53As to form a high-barrier-height Schottky barrier. Using this technique to form the gate electrode, we fabricated a 1?m-gate-length inverted InP-GalnAs modulation-doped field-effect transistor (MODFET) with an extrinsic transconductance of 170mS/mm and a cutoff frequencyfT of 19 GHz.  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