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   409625篇
  免费   5009篇
  国内免费   1411篇
电工技术   7900篇
综合类   426篇
化学工业   61217篇
金属工艺   16862篇
机械仪表   12631篇
建筑科学   9942篇
矿业工程   1872篇
能源动力   10502篇
轻工业   36266篇
水利工程   4032篇
石油天然气   6595篇
武器工业   70篇
无线电   50709篇
一般工业技术   77824篇
冶金工业   75252篇
原子能技术   8869篇
自动化技术   35076篇
  2021年   3160篇
  2019年   3066篇
  2018年   5183篇
  2017年   5220篇
  2016年   5550篇
  2015年   3656篇
  2014年   6308篇
  2013年   18015篇
  2012年   10354篇
  2011年   14201篇
  2010年   11239篇
  2009年   12814篇
  2008年   13588篇
  2007年   13462篇
  2006年   11931篇
  2005年   11000篇
  2004年   10608篇
  2003年   10171篇
  2002年   9834篇
  2001年   9880篇
  2000年   9393篇
  1999年   9678篇
  1998年   23042篇
  1997年   16530篇
  1996年   12927篇
  1995年   10034篇
  1994年   8747篇
  1993年   8650篇
  1992年   6714篇
  1991年   6317篇
  1990年   6051篇
  1989年   5836篇
  1988年   5631篇
  1987年   4955篇
  1986年   4822篇
  1985年   5608篇
  1984年   5243篇
  1983年   4796篇
  1982年   4417篇
  1981年   4601篇
  1980年   4281篇
  1979年   4229篇
  1978年   4005篇
  1977年   4759篇
  1976年   5929篇
  1975年   3657篇
  1974年   3622篇
  1973年   3685篇
  1972年   3019篇
  1971年   2808篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features  相似文献   
45.
46.
47.
We present the design of E-kernel, an embedding kernel on the Victor V256 message-passing partitionable multiprocessor, developed for the support of program mapping and network reconfiguration. E-kernel supports the embedding of a new network topology onto Victor's 2D mesh and also the embedding of a task graph onto the 2D mesh network or the reconfigured network. In the current implementation, the reconfigured network can be a line or an even-size ring, and the task graphs meshes or tori of a variety of dimensions and shapes or graphs with similar topologies. For application programs having these task graph topologies and that are designed according to the communication model of E-kernel, they can be run without any change on partitions connected by the 2D mesh, line, or ring. Further, E-kernel attempts the communication optimization of these programs on the different networks automatically, thus making both the network topology and the communication optimization attempt completely transparent to the application programs. Many of the embeddings used in E-kernel are optimal or asymptotically optimal (with respect to minimum dilation cost). The implementation of E-kernel translated some of the many theoretical results in graph embeddings into practical tools for program mapping and network reconfiguration in a parallel system. E-kernel is functional on Victor V256. Measurements of E-kernel's performance on V256 are also included  相似文献   
48.
Variations in lipid profile and incidence of vascular events were evaluated. Group 1 had a 29.3% reduction of total and a 38.3% reduction of LDL cholesterol as against reductions of 9% and 9.6% respectively in group 2. No significant difference was observed between the two groups as far as the vascular events considered were concerned. Pravastatin is an effective and safe drug. The lack of influence on the evolution of vascular disease would appear to be correlated to the small number of subjects studied and the short follow-up.  相似文献   
49.
Nutrient uptake by the hindlimb was investigated utilising the arteriovenous difference technique in 5 Thoroughbred horses fed to maintenance a diet of 100% roughage or 52% oat grain and 48% roughage. Arterial blood was obtained from a catheter inserted into the carotid artery while venous blood was simultaneously collected from a catheter placed into the iliac vein via the medial saphenous vein. The arteriovenous difference for glucose was significant and represented a mean extraction of 10 +/- 1% with no effect of diet. If fully oxidised, glucose uptake (corrected for lactate and pyruvate arteriovenous difference) was sufficient to account for 78 +/- 13% or 107 +/- 15% of the oxygen consumed by the hindlimb in horses fed a roughage or 52% oat grain diet respectively. Acetate was also a major metabolite of the hindlimb, showing a 39 +/- 5% extraction with no effect of diet. However, the 52% oat grain diet did induce a significant decline in the concentration of acetate in arterial blood. The potential contribution to oxidation in the hindlimb was significantly reduced from 32 +/- 4% in horses fed roughage to 21 +/- 3% when fed 52% oat grain. D-3-Hydroxybutyrate uptake could account for 9 +/- 1% of the oxidation by the hindlimb with no effect of diet. The technique for measuring nutrient uptake across the hindlimb using the arteriovenous difference is relatively simple and would be valuable in investigating fuel use by muscle during exercise.  相似文献   
50.
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