首页 | 官方网站   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   1620389篇
  免费   25251篇
  国内免费   7095篇
工业技术   1652735篇
  2021年   15790篇
  2020年   12059篇
  2019年   14846篇
  2018年   17835篇
  2017年   17351篇
  2016年   22664篇
  2015年   17774篇
  2014年   29083篇
  2013年   88515篇
  2012年   38831篇
  2011年   53245篇
  2010年   45075篇
  2009年   52812篇
  2008年   48875篇
  2007年   46753篇
  2006年   47285篇
  2005年   42448篇
  2004年   44316篇
  2003年   44016篇
  2002年   42593篇
  2001年   39928篇
  2000年   37922篇
  1999年   37943篇
  1998年   61700篇
  1997年   49276篇
  1996年   41995篇
  1995年   34700篇
  1994年   32123篇
  1993年   31778篇
  1992年   27205篇
  1991年   24499篇
  1990年   24664篇
  1989年   23744篇
  1988年   22304篇
  1987年   20453篇
  1986年   19976篇
  1985年   23306篇
  1984年   23061篇
  1983年   20909篇
  1982年   19665篇
  1981年   19822篇
  1980年   18446篇
  1979年   18929篇
  1978年   18137篇
  1977年   18793篇
  1976年   21287篇
  1975年   16284篇
  1974年   15763篇
  1973年   15882篇
  1972年   13313篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
961.
The effect of long-term feeding (252 days) of three supplemental levels of α-tocopheryl acetate (actual 0, 360 and 1290 IU/head/day) on meat quality was evaluated in Holstein and beef breed steers. Tissue vitamin E concentrations were increased by each increment of supplementation. The color display life of fresh beef under simulated retail conditions was extended 2 to 5 days by vitamin E and lipid oxidation was markedly reduced. Microbial population was not affected by level of supplementation. No deterioration in sensory quality occurred for steaks from supplemented steers that were displayed until the time steaks from unsupplemented steers discolored.  相似文献   
962.
In the frame of a preliminary investigation the oven-dry density and some morphological fibre characteristics have been compared among different Balsam poplar clones. The analysis of variance in an one-way layout has been used as a statistical test. The test power has been estimated from a given initial sample tree size. The recommended sample tree size could be considerably reduced for the main investigation programme to follow. Nevertheless the necessary accuracy of the statistical results could be kept. An uneffective over-expenditure of labour and time could he decisively avoided.  相似文献   
963.
964.
Gilbenclamide, a widely used potent hypoglycaemic agent was solubllized using β -Cyclodextrin and β -Cyclodextrin derivatives. Complexes were prepared by kneading method in a molar ratio of 1:1 of the drug and the cyclodextrlns respectively. The Glibenclamide β -Cyelocextrin complex was characterized and evaluated by I.R. studies, Differential Scanning Calorimotry 6 X-ray diffractometry. The in-vitro dissolution rates of drug from inclusion complexes of β Cyclodextrins and its derivatives were compared. A significant Improvement In dissolution lor, rates of Gllbenclamide was observed with Inclusion complexes of all the Cyclodextrins. However, the solubilizing effect was more in case of β-Cyclodextrin derivatives.  相似文献   
965.
966.
Adam  J.A. 《Spectrum, IEEE》1994,31(10):24-26
The author focusses on advances in equipment that offset physically functional limitations. He discusses how disabled and elderly people are using aids that enhance mobility (walking a certain distance, lifting a weight, or climbing stairs) as well as sensory faculties (seeing print, hearing conversation, and speaking intelligibly)  相似文献   
967.
The time-scattering of an electromagnetic wave by a wedge-shaped region in a lossy medium, both with frequency dependent electric characteristics, is analyzed for plane wave and line source illuminations. New exact analytical expressions, satisfying explicitely the causality and allowing useful physical decompositions of the field, are obtained in these cases, using the particularities of the harmonic response in Sommerfeld-Maliuzhinets integral, especially original properties of the spectral function attached to it.  相似文献   
968.
Fractal error for detecting man-made features in aerial images   总被引:3,自引:0,他引:3  
A technique is proposed for aiding photointerpreters in detecting man-made features in aerial reconnaissance images. The technique, which uses a metric called fractal error, is based on the observed propensity of natural image features to fit a fractional Brownian motion model. Man-made features usually do not fit this model well, and consequently the fractal error metric may be used as a discriminant function for detecting man-made scene features  相似文献   
969.
The authors demonstrate 10 Gbit/s optical soliton transmission in a recirculating loop through the use of a monolithically integrated MQW-DFB-LD/MQW-EA modulator light source. The timing jitter due to the Gordon-Haus effect is successfully reduced by the optical bandpass filters conventionally used in the cascaded EDFAs to avoid the accumulation of amplified spontaneous emission. The transmission distance of 7200 km is achieved at a bit error rate of 10-9  相似文献   
970.
a-Si alloy three-stacked solar cells have been studied to improve the stabilized efficiency of a-Si: H based solar cells. Based on the analysis by the individual characterization method of the component cells in stacked type cells, the a-Si :H middle cell was replaced with an a-SiGe :H cell. Furthermore, the optical confinement technology was improved to obtain a high-output current with thin i-layer thickness in the a-SiGe :H bottom cell. By this device design, the initial conversion efficiency was improved up to 12.4% and more than a 10% stabilized efficiency was obtained in a-SiC :H/a-SiGe :H/a-SiGe :H three-stacked cells. These cell characteristics were confirmed by measurements at the JQA Organization (the former JMI Institute).  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-23

京公网安备 11010802026262号