全文获取类型
收费全文 | 491571篇 |
免费 | 5771篇 |
国内免费 | 2010篇 |
专业分类
电工技术 | 9020篇 |
综合类 | 842篇 |
化学工业 | 71005篇 |
金属工艺 | 19437篇 |
机械仪表 | 15238篇 |
建筑科学 | 11580篇 |
矿业工程 | 2472篇 |
能源动力 | 12202篇 |
轻工业 | 41055篇 |
水利工程 | 5120篇 |
石油天然气 | 8970篇 |
武器工业 | 107篇 |
无线电 | 60984篇 |
一般工业技术 | 96646篇 |
冶金工业 | 90436篇 |
原子能技术 | 11512篇 |
自动化技术 | 42726篇 |
出版年
2021年 | 3806篇 |
2019年 | 3741篇 |
2018年 | 6385篇 |
2017年 | 6523篇 |
2016年 | 6865篇 |
2015年 | 4436篇 |
2014年 | 7559篇 |
2013年 | 21212篇 |
2012年 | 12321篇 |
2011年 | 16914篇 |
2010年 | 13230篇 |
2009年 | 15113篇 |
2008年 | 16068篇 |
2007年 | 16034篇 |
2006年 | 14143篇 |
2005年 | 12974篇 |
2004年 | 12734篇 |
2003年 | 12409篇 |
2002年 | 11945篇 |
2001年 | 11987篇 |
2000年 | 11408篇 |
1999年 | 11843篇 |
1998年 | 28008篇 |
1997年 | 20029篇 |
1996年 | 15593篇 |
1995年 | 12135篇 |
1994年 | 10711篇 |
1993年 | 10658篇 |
1992年 | 8177篇 |
1991年 | 7651篇 |
1990年 | 7379篇 |
1989年 | 7189篇 |
1988年 | 6734篇 |
1987年 | 5984篇 |
1986年 | 5949篇 |
1985年 | 6780篇 |
1984年 | 6274篇 |
1983年 | 5735篇 |
1982年 | 5445篇 |
1981年 | 5502篇 |
1980年 | 5383篇 |
1979年 | 5070篇 |
1978年 | 4974篇 |
1977年 | 5677篇 |
1976年 | 7211篇 |
1975年 | 4373篇 |
1974年 | 4291篇 |
1973年 | 4369篇 |
1972年 | 3580篇 |
1971年 | 3255篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
Younan N.H. Cox B.I. Taylor C.D. Prather W.D. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):394-398
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz 相似文献
72.
Varani L. Reggiani L. Kuhn T. Gonzalez T. Pardo D. 《Electron Devices, IEEE Transactions on》1994,41(11):1916-1925
We present a microscopic interpretation of electronic noise in semiconductor materials and two-terminal devices. The theory is based on Monte Carlo simulations of the carrier motion self-consistently coupled with a Poisson solver. Current and voltage noise operations are applied and their respective representations discussed. As application we consider the cases of homogeneous materials, resistors, n+nn + structures, and Schottky-barrier diodes. Phenomena associated with coupling between fluctuations in carrier velocity and self-consistent electric field are quantitatively investigated for the first time. At increasing applied fields hot-carrier effects are found to be of relevant importance in all the cases considered here. As a general result, noise spectroscopy is found to be a source of valuable information to investigate and characterize transport properties of semiconductor materials and devices 相似文献
73.
A method is given for calculating the monitoring reliability parameters (MRP) for an engineering system with allowance for the drift in the measurement error of the means of measurement (MM). The approach is based on introducing a biased MM error distribution into the traditional formulas for the conditional probabilities of spurious and unobserved failure. The bias at the center of the distribution is determined by the systematic error at the given instant. An example is given to illustrate the performance in MRP calculation.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 12–13, January, 1994. 相似文献
74.
75.
76.
Carroll R.D. Merritt S.W. Branciforte E.J. Tanski W.J. Cullen D.E. Sacks R.N. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(3):416-418
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal 相似文献
77.
MB Heyman JM LaBerge KA Somberg P Rosenthal C Mudge EJ Ring JD Snyder 《Canadian Metallurgical Quarterly》1997,131(6):914-919
The transjugular intrahepatic portosystemic shunt procedure is an accepted treatment for adults with complications of portal hypertension. We performed a retrospective review of all pediatric TIPS placements performed at the University of California, San Francisco between 1990 and 1996. Twelve procedures were attempted in nine children, with a mean age (+/- SD) of 9.4 +/- 3.9 years (range, 5 to 15 years) and a mean weight of 31 +/- 18 kg (range, 16 to 70 kg). The indications for TIPS placement were portal hypertension complicated by chronic variceal hemorrhage not controlled with sclerotherapy (n = 7) and hypersplenism with thrombocytopenia (n = 2). TIPS placement was successfully completed initially in seven of nine (78%) patients. Unfavorable vascular anatomy was the cause of failure in two cases. The seven patients who underwent successful TIPS placement were followed up for an average of 136 days (range, 1 to 800 days); two still have patent shunts, three underwent liver transplantation, one had a splenorenal shunt after stenosis, and one died of underlying liver disease. Variceal bleeding was controlled in four of five patients who successfully underwent TIPS placement. Shunt occlusion occurred in four patients; patency was restored by transjugular shunt revision in three, and a splenorenal shunt was performed in one. 相似文献
78.
We report here a series of observations-most of which the reader can experience directly-showing that distinct components of patterned visual stimuli (orthogonal lines of a different hue) vary in perception as sets. Although less frequent and often less complete, these perceptual fluctuations in normal viewing are otherwise similar to the binocular rivalry experienced when incompatible scenes are presented dichoptically. 相似文献
79.
Presents the Satellite Communications Network Expert (SaNE), a knowledge-based aid designed to provide engineering support for fault diagnosis. The SaNE is composed of two elements: a satcom network model, which simulates the structure and functionality of a system based loosely upon a large military satcom network, and a diagnostic component, which uses knowledge- and model-based reasoning techniques to analyse system anomalies and diagnose possible causes for the alarms such networks generate. The development cycle is described, emphasising lessons learnt during development and testing and the advantages and disadvantages of the techniques applied. The goal of the SaNE project is primarily commercial acceptance rather than innovation. The authors illustrate how novel concepts can be implemented in a practical system without compromising this goal 相似文献
80.