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   428964篇
  免费   4934篇
  国内免费   1731篇
电工技术   7907篇
综合类   394篇
化学工业   64767篇
金属工艺   20299篇
机械仪表   13461篇
建筑科学   9858篇
矿业工程   2626篇
能源动力   10382篇
轻工业   35259篇
水利工程   4586篇
石油天然气   8955篇
武器工业   25篇
无线电   49536篇
一般工业技术   85950篇
冶金工业   79483篇
原子能技术   10090篇
自动化技术   32051篇
  2021年   3483篇
  2019年   3317篇
  2018年   5793篇
  2017年   5745篇
  2016年   6198篇
  2015年   3955篇
  2014年   6635篇
  2013年   18704篇
  2012年   10560篇
  2011年   14283篇
  2010年   11568篇
  2009年   12828篇
  2008年   13464篇
  2007年   13446篇
  2006年   11968篇
  2005年   10984篇
  2004年   10324篇
  2003年   10298篇
  2002年   10095篇
  2001年   10300篇
  2000年   9483篇
  1999年   10000篇
  1998年   24658篇
  1997年   17439篇
  1996年   13585篇
  1995年   10213篇
  1994年   8948篇
  1993年   9048篇
  1992年   6715篇
  1991年   6671篇
  1990年   6212篇
  1989年   6081篇
  1988年   6079篇
  1987年   5227篇
  1986年   5236篇
  1985年   6038篇
  1984年   5550篇
  1983年   5138篇
  1982年   4696篇
  1981年   4692篇
  1980年   4599篇
  1979年   4501篇
  1978年   4500篇
  1977年   5162篇
  1976年   6868篇
  1975年   4000篇
  1974年   3776篇
  1973年   3859篇
  1972年   3335篇
  1971年   3013篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
The article describes the experience of implementing patient-focused care from a physician's perspective. Pitfalls that guarantee failure are presented, many of which are avoidable with early participation by all parties involved: administrators, nursing staff, physicians, and patients. Contamination of the process with downsizing needs, lack of support for staff in dealing with necessary change, loss of administrative commitment, and withholding of appropriated funds are among the key errors to be avoided.  相似文献   
53.
The ITER magnet system consists of structurally linked sets of toroidal (TF) and poloidal (PF) field coils, central solenoid (CS), and various support structures. The coils are superconducting, force flow Helium cooled with a Kapton-Glass-Epoxy multilayer insulation system. The stored magnetic energy is about 100GJ in the TF system and 20GJ in the PF-CS. Coils and structure are maintained at 4 K by enclosing them in a vacuum cryostat. The cryostat, comprising an outer envelope to the magnets, forms most of the second radioactivity confinement barrier. The inner primary barrier is formed by the vacuum vessel, its ports and their extensions. To keep the machine size within acceptable bounds, it is essential that the magnets are in close proximity to both of the nuclear confinement barriers. The objective of the magnet design is that, although local damage to one of the barriers may occur in very exceptional circumstances, large scale magnet structural or thermal failure leading to simultaneous breaching of both barriers is not credible. Magnet accidents fall into three categories: thermal (which includes arcing arising from insulation failure and local overheating due to discharge failure in the event of a superconductor quench), structural (which includes component mechanical failure arising from material inadequacies, design errors and exceptional force patterns arising from coil shorts or control failures), and fluid (Helium release due to cooling line failure). After a preliminary survey to select initial faults conceivable within the present design, these faults are systematically analyzed to provide an assessment of the damage potential. The results of this damage assessment together with an assessment of the reliability of the monitoring and protective systems, shows that the magnets can operate with the required safety condition.  相似文献   
54.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration  相似文献   
55.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method  相似文献   
56.
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies  相似文献   
57.
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models  相似文献   
58.
Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(√(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel  相似文献   
59.
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   
60.
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices  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