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   460667篇
  免费   3922篇
  国内免费   890篇
电工技术   7798篇
综合类   311篇
化学工业   69582篇
金属工艺   25887篇
机械仪表   17291篇
建筑科学   9447篇
矿业工程   4968篇
能源动力   8988篇
轻工业   26422篇
水利工程   6524篇
石油天然气   15550篇
武器工业   33篇
无线电   44557篇
一般工业技术   105772篇
冶金工业   68472篇
原子能技术   14511篇
自动化技术   39366篇
  2021年   3999篇
  2019年   3940篇
  2018年   12408篇
  2017年   12828篇
  2016年   11233篇
  2015年   4799篇
  2014年   7800篇
  2013年   17820篇
  2012年   13004篇
  2011年   19730篇
  2010年   16764篇
  2009年   17209篇
  2008年   17638篇
  2007年   18671篇
  2006年   11109篇
  2005年   11933篇
  2004年   10983篇
  2003年   10710篇
  2002年   9512篇
  2001年   8985篇
  2000年   8960篇
  1999年   8468篇
  1998年   17693篇
  1997年   13236篇
  1996年   10269篇
  1995年   7886篇
  1994年   7292篇
  1993年   7271篇
  1992年   5972篇
  1991年   5973篇
  1990年   5844篇
  1989年   5802篇
  1988年   5593篇
  1987年   5229篇
  1986年   4981篇
  1985年   5534篇
  1984年   5285篇
  1983年   5015篇
  1982年   4632篇
  1981年   4796篇
  1980年   4671篇
  1979年   4898篇
  1978年   5075篇
  1977年   5347篇
  1976年   6564篇
  1975年   4582篇
  1974年   4559篇
  1973年   4644篇
  1972年   4015篇
  1971年   3719篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Extraction of Cs, Sr, Eu, U, Np, and Am with mixtures of dipicolinic acid diamides with chlorinated cobalt dicarbollide was studied. A synergistic effect was revealed.  相似文献   
92.
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec.  相似文献   
93.
Analogue switch for very low-voltage applications   总被引:2,自引:0,他引:2  
A new analogue switch suitable for operation at very low-voltage supply in a standard CMOS technology is presented. The proposed switch is based on 'quasi-floating-gate' transistors and has a simple and compact structure. For illustrative purposes, two sample-and-hold circuits operating from a single supply voltage close to the threshold voltage of a transistor, and using the proposed technique, are presented. Experimental results obtained from prototypes in a 1.5 /spl mu/m CMOS technology are provided.  相似文献   
94.
95.
This study investigates the effect of extraction methods on the color of date syrup and the potential use of microwave power for syrup processing. Sugar solutions were extracted from dates by boiling, soaking and blending. Color and sugar content of the extracted solutions were measured, and the percentage of sugar extracted form the total fruit sugar determined. Boiling was found to be the most efficient method of extraction whereby 74% of total samples sugar was extracted. In contrast, only 54.2% of fruit sugar was extracted by blending and 42% by soaking. In addition, solutions extracted by soaking and blending had a foaming problem in the subsequent concentration process. The extraction method had no effect on the product final color. The extracted solution was concentrated using two heating methods: conventional and microwave heating at a 600 W capacity and a frequency of 2450 MHz applied at three power levels: 10, 7, and 6. In the heating process, 180 minutes were needed to achieve a 77% degrees Brix using convective heating, while it took 81, 138, and 166 minutes of microwave heating at power level 10, 7, and 6, respectively to achieve the same concentration. Water activity of the syrup was measured within a sugar content range of 50 to 80% degrees Brix and the sugar concentration at which the product is shelf stable was determined at 76%.  相似文献   
96.
Algebraic theory of optimal filterbanks   总被引:1,自引:0,他引:1  
We introduce an optimality theory for finite impulse response (FIR) filterbanks using a general algebraic point of view. We consider an admissible set /spl Lscr/ of FIR filterbanks and use scalability as the main notion based on which performance of the elements in /spl Lscr/are compared. We show that quantification of scalability leads naturally to a partial ordering on the set /spl Lscr/. An optimal solution is, therefore, represented by the greatest element in /spl Lscr/. It turns out that a greatest element does not necessarily exist in /spl Lscr/. Hence, one has to settle with one of the maximal elements that exist in /spl Lscr/. We provide a systematic way of finding a maximal element by embedding the partial ordering at hand in a total ordering. This is done by using a special class of order-preserving functions known as Schur-convex. There is, however, a price to pay for achieving a total ordering: there are infinitely many possible choices for Schur-convex functions, and the optimal solution specified in /spl Lscr/ depends on this (subjective) choice. An interesting aspect of the presented algebraic theory is that the connection between several concepts, namely, principal component filterbanks (PCFBs), filterbanks with maximum coding gain, and filterbanks with good scalability, is clearly revealed. We show that these are simply associated with different extremal elements of the partial ordering induced on /spl Lscr/ by scalability.  相似文献   
97.
The studies show that in the combined use of biological and chemisorption stages of treatment, a deeper degree of removal of industrial pollutants from wastewaters is attained. The chemisorption stage allows stabilizing the treatment process in different concentration-temperature drops and increasing the degree of removal of synthetic surfactants (SSF), petroleum products, and nitrogen compounds. The possibility of regulating the selectivity of the treatment process by varying the composition of the chemisorption material is demonstrated.  相似文献   
98.
99.
It is demonstrated that the density of binary glasses upon variation of the molar content of the modifier in their compositions obeys a parabolic dependence, whose parameters can be used to estimate the extent and type of reactions between the components. The reaction parameters in glasses that are prone to liquation are lower by an order of magnitude and have the negative sign.  相似文献   
100.
In studying a series of fibre samples spun in steady-state conditions, the following was found: as a function of the conditions of processing Armos fibre, two structural modifications of the polymer can form; intensive crystallization of the modification corresponding to the 28.7° reflection begins in heat treatment above 220°C; above 320°C, intensive crystallization of the modification corresponding to the 14.25° reflection is observed; at 360°C, symbatic enhancement of the intensities of both reflections with a weak change in the other structural parameters of the fibre is observed.  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