全文获取类型
收费全文 | 508306篇 |
免费 | 5808篇 |
国内免费 | 2128篇 |
专业分类
电工技术 | 8623篇 |
综合类 | 2696篇 |
化学工业 | 75312篇 |
金属工艺 | 24807篇 |
机械仪表 | 16385篇 |
建筑科学 | 11932篇 |
矿业工程 | 3166篇 |
能源动力 | 11411篇 |
轻工业 | 38645篇 |
水利工程 | 5773篇 |
石油天然气 | 9273篇 |
武器工业 | 25篇 |
无线电 | 58366篇 |
一般工业技术 | 101036篇 |
冶金工业 | 81912篇 |
原子能技术 | 10316篇 |
自动化技术 | 56564篇 |
出版年
2021年 | 3463篇 |
2019年 | 3297篇 |
2018年 | 19656篇 |
2017年 | 18552篇 |
2016年 | 15789篇 |
2015年 | 4515篇 |
2014年 | 6810篇 |
2013年 | 18831篇 |
2012年 | 13500篇 |
2011年 | 23216篇 |
2010年 | 19384篇 |
2009年 | 18098篇 |
2008年 | 19900篇 |
2007年 | 20800篇 |
2006年 | 12065篇 |
2005年 | 12100篇 |
2004年 | 11357篇 |
2003年 | 11376篇 |
2002年 | 10602篇 |
2001年 | 10382篇 |
2000年 | 9641篇 |
1999年 | 10047篇 |
1998年 | 24701篇 |
1997年 | 17462篇 |
1996年 | 13619篇 |
1995年 | 10221篇 |
1994年 | 8958篇 |
1993年 | 9056篇 |
1992年 | 6726篇 |
1991年 | 6691篇 |
1990年 | 6209篇 |
1989年 | 6079篇 |
1988年 | 6087篇 |
1987年 | 5226篇 |
1986年 | 5236篇 |
1985年 | 6038篇 |
1984年 | 5550篇 |
1983年 | 5137篇 |
1982年 | 4696篇 |
1981年 | 4691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.
N. Mitchell A. Alekseev R. Gallix D. Holland R. Meyder A. Panin M. Shimada F. Wong E. Zapretelina 《Journal of Fusion Energy》1997,16(1-2):25-35
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.
Fahmy H.I. Develekos G. Douligeris C. 《Selected Areas in Communications, IEEE Journal on》1997,15(2):226-237
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.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
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.
Sugawara F. Aoki K. Yamaguchi H. Sasaki K. Sasaki T. Fujisaki H. 《Electron Device Letters, IEEE》1997,18(10):483-485
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.
Watanabe H. Komori J. Higashitani K. Sekine M. Koyama H. 《Semiconductor Manufacturing, IEEE Transactions on》1997,10(2):228-232
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