全文获取类型
收费全文 | 518688篇 |
免费 | 7178篇 |
国内免费 | 1799篇 |
专业分类
电工技术 | 9869篇 |
综合类 | 528篇 |
化学工业 | 79140篇 |
金属工艺 | 18013篇 |
机械仪表 | 15098篇 |
建筑科学 | 14876篇 |
矿业工程 | 1182篇 |
能源动力 | 13754篇 |
轻工业 | 54915篇 |
水利工程 | 4070篇 |
石油天然气 | 2289篇 |
武器工业 | 17篇 |
无线电 | 68236篇 |
一般工业技术 | 95378篇 |
冶金工业 | 94593篇 |
原子能技术 | 7053篇 |
自动化技术 | 48654篇 |
出版年
2021年 | 3233篇 |
2019年 | 3045篇 |
2018年 | 4598篇 |
2017年 | 4667篇 |
2016年 | 5020篇 |
2015年 | 4155篇 |
2014年 | 6962篇 |
2013年 | 23974篇 |
2012年 | 12290篇 |
2011年 | 17735篇 |
2010年 | 13704篇 |
2009年 | 15703篇 |
2008年 | 16980篇 |
2007年 | 17422篇 |
2006年 | 15639篇 |
2005年 | 14636篇 |
2004年 | 14198篇 |
2003年 | 13869篇 |
2002年 | 13490篇 |
2001年 | 13677篇 |
2000年 | 12653篇 |
1999年 | 13224篇 |
1998年 | 29113篇 |
1997年 | 21493篇 |
1996年 | 17130篇 |
1995年 | 13547篇 |
1994年 | 12122篇 |
1993年 | 11583篇 |
1992年 | 9009篇 |
1991年 | 8533篇 |
1990年 | 8164篇 |
1989年 | 7898篇 |
1988年 | 7537篇 |
1987年 | 6448篇 |
1986年 | 6352篇 |
1985年 | 7747篇 |
1984年 | 7179篇 |
1983年 | 6420篇 |
1982年 | 6024篇 |
1981年 | 5903篇 |
1980年 | 5546篇 |
1979年 | 5421篇 |
1978年 | 5048篇 |
1977年 | 6165篇 |
1976年 | 8112篇 |
1975年 | 4284篇 |
1974年 | 4050篇 |
1973年 | 3958篇 |
1972年 | 3191篇 |
1971年 | 2805篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
A study was undertaken to determine fertility in a group of females who as children had been operated on for appendicitis. The 134 women operated on for appendicitis were reviewed. Their ages ranged from 2-18 years at the time of appendectomy. Our data show that perforated appendicitis before puberty has little if any role in the etiology of tubal infertility. 相似文献
142.
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
143.
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
144.
145.
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
146.
A simple phenomenological model for giant magnetoresistance (GMR) is employed for current and field parallel (CIP) to the magnetic multilayer planes in ordinary and discontinuous multilayer films. To our knowledge, it is the first model to include hysteresis in the field (H) dependence of the GMR. The computed GMR versus H curves qualitatively reproduce the GMR hysteresis seen experimentally. In particular, two GMR peaks are found to be symmetrically placed about H=0, and the GMR hysteresis curve itself is found to have an inverted butterfly shape. Also seen in the computed results is the general increase in GMR magnitude found for annealed discontinuous multilayer films. Various parameter variations are examined in the computed results. While the model reproduces GMR hysteresis quite well and the general increase in GMR for discontinuous multilayer films, it does not, in its present form, account for the oscillations seen in the GMR when the nonmagnetic layer thicknesses are varied, which is expected as a strictly quantum mechanical result 相似文献
147.
The water sorption behaviour of several cross-linked gelatin-based systems were investigated and compared. The systems were
gelatin, gelatin/ethyleneglycol, gelatin/polyoxypropylenediamine, and gelatin/polyethylene oxide. For all the systems, an
increased water gain was obtained by raising the concentration of the second component, while the swelling was reduced by
an increase of the cross-linking density.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
148.
J Havick 《The Journal of communication》1997,47(2):97-111
This study employed two perspectives to investigate media attention given women congressional candidates. The first perspective is that media attention may be explained by typical and normal media processes, such as focusing on incumbents. The second perspective considers a partisan explanation in which media attention is weighted more to Democratic candidates than Republican candidates. This study employs two established sources, Vanderbilt's Television News Index and Abstract and Information Access's National Newspaper Index , to examine the national media attention of Democratic and Republican women congressional candidates in 1990 and 1992. The investigation determined that media attention is related to whether the candidates are running for the Senate or House, incumbency, and state population. The results also reveal that party is a statistically significant factor associated with media attention. The investigation also determined that ethnic candidates tend to receive slightly less attention from the print media than nonethnic candidates. 相似文献
149.
The sudden onset of hypertension mandates investigation for secondary causes. We report the case of a young man with a very rare systemic fungal disease that included massive unilateral perirenal adenopathy. Treatment was associated with the abrupt onset of severe hypertension. Imaging studies suggested progressive constriction of one kidney with treatment, presumably as a result of healing adenopathy. We suggest that this case is a new example of hypertension secondary to constrictive perinephritis (Page kidney). 相似文献
150.