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   1903543篇
  免费   51344篇
  国内免费   22165篇
电工技术   54963篇
技术理论   45篇
综合类   31263篇
化学工业   330196篇
金属工艺   84188篇
机械仪表   65872篇
建筑科学   74296篇
矿业工程   23154篇
能源动力   59308篇
轻工业   143113篇
水利工程   22383篇
石油天然气   59624篇
武器工业   2939篇
无线电   233225篇
一般工业技术   326963篇
冶金工业   212860篇
原子能技术   37681篇
自动化技术   214979篇
  2022年   19838篇
  2021年   28926篇
  2020年   21929篇
  2019年   22715篇
  2018年   26432篇
  2017年   27065篇
  2016年   31499篇
  2015年   30818篇
  2014年   45487篇
  2013年   107401篇
  2012年   59048篇
  2011年   74715篇
  2010年   65260篇
  2009年   71827篇
  2008年   66662篇
  2007年   63163篇
  2006年   65001篇
  2005年   57735篇
  2004年   53726篇
  2003年   52297篇
  2002年   50485篇
  2001年   46720篇
  2000年   44883篇
  1999年   45198篇
  1998年   61985篇
  1997年   51097篇
  1996年   44690篇
  1995年   37494篇
  1994年   34218篇
  1993年   32861篇
  1992年   28532篇
  1991年   25239篇
  1990年   25215篇
  1989年   24100篇
  1988年   22429篇
  1987年   20427篇
  1986年   19622篇
  1985年   22772篇
  1984年   22686篇
  1983年   20587篇
  1982年   19551篇
  1981年   19679篇
  1980年   18280篇
  1979年   18651篇
  1978年   17913篇
  1977年   18086篇
  1976年   19743篇
  1975年   16070篇
  1974年   15543篇
  1973年   15663篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Many current implementations of protocols such as the Transmission Control Protocol/Internet Protocol (TCP/IP) are inefficient because data are often accessed more frequently than necessary. Three techniques that reduce the need for memory bandwidth are proposed. The techniques are copy-on-write, page remapping, and single-copy. Afterburner, a network-independent card that provides the services that are necessary for a single-copy protocol stack, is described. The card has 1 MByte of local buffers and provides a simple interface to a variety of network link adapters, including HIPPI and asynchronous transfer mode (ATM). Afterburner can support transfers to and from the link adapter card at rates up to 1 Gbit/s. An implementation of TCP/IP that uses the features provided by Afterburner to reduce the movement of data to a single copy is discussed. Measurements of the end-to-end performance of Afterburner and the single-copy implementation of TCP/IP are presented  相似文献   
992.
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   
993.
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   
994.
Chronic hepatitis C has been demonstrated to be associated with hepatic iron overload, and the hypothesis that the disease activity of hepatitis C is associated with iron cytotoxicity was tested in male volunteer blood donors. Sera with either antibody to hepatitis C virus or hepatitis B surface antigen were selected for determination of ferritin concentration and alanine aminotransferase activity. A correlation between serum ferritin concentration (Y; microgram/l) and alanine aminotransferase activity (X; IU/l) was found in donors with antibody to hepatitis C (log Y = 0.65 x log X + 0.98, r = 0.53, and P < 0.01). The correlation was lower in donors with hepatitis B surface antigen (r = 0.37; P < 0.01). Hepatitis C virus infection probably induces time-dependent iron accumulation associated with the progression of disease activity, while hepatitis B virus infection results in a variety of iron loads with different clinical features. The high disease activity related to hyperferritinemia suggests the presence of iron-induced liver damage in donors with hepatitis C.  相似文献   
995.
996.
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   
997.
998.
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   
999.
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   
1000.
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   
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