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   391143篇
  免费   4478篇
  国内免费   1104篇
电工技术   7082篇
综合类   349篇
化学工业   62693篇
金属工艺   16140篇
机械仪表   11658篇
建筑科学   9351篇
矿业工程   2157篇
能源动力   9252篇
轻工业   38036篇
水利工程   3938篇
石油天然气   7596篇
武器工业   34篇
无线电   41909篇
一般工业技术   73137篇
冶金工业   73774篇
原子能技术   9223篇
自动化技术   30396篇
  2021年   3185篇
  2019年   3032篇
  2018年   5163篇
  2017年   5121篇
  2016年   5450篇
  2015年   3584篇
  2014年   6176篇
  2013年   16925篇
  2012年   9942篇
  2011年   13644篇
  2010年   10804篇
  2009年   12270篇
  2008年   12543篇
  2007年   12606篇
  2006年   11147篇
  2005年   9995篇
  2004年   9642篇
  2003年   9129篇
  2002年   9116篇
  2001年   9048篇
  2000年   8683篇
  1999年   8750篇
  1998年   21381篇
  1997年   15238篇
  1996年   11762篇
  1995年   9014篇
  1994年   7849篇
  1993年   7715篇
  1992年   5882篇
  1991年   5546篇
  1990年   5654篇
  1989年   5553篇
  1988年   5298篇
  1987年   4742篇
  1986年   4708篇
  1985年   5402篇
  1984年   5069篇
  1983年   4609篇
  1982年   4376篇
  1981年   4492篇
  1980年   4225篇
  1979年   4175篇
  1978年   4190篇
  1977年   4752篇
  1976年   6159篇
  1975年   3679篇
  1974年   3541篇
  1973年   3724篇
  1972年   3106篇
  1971年   2901篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor  相似文献   
52.
53.
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   
54.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency  相似文献   
55.
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   
56.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information technologies and systems by the Ukrainian State Committee, of Science and Technology.  相似文献   
57.
58.
59.
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   
60.
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   
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