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   721390篇
  免费   7897篇
  国内免费   1739篇
电工技术   12524篇
综合类   524篇
化学工业   111470篇
金属工艺   32619篇
机械仪表   23586篇
建筑科学   17050篇
矿业工程   5288篇
能源动力   16045篇
轻工业   56173篇
水利工程   8609篇
石油天然气   18213篇
武器工业   43篇
无线电   79391篇
一般工业技术   151248篇
冶金工业   120103篇
原子能技术   18463篇
自动化技术   59677篇
  2021年   5875篇
  2019年   5624篇
  2018年   10077篇
  2017年   10368篇
  2016年   11102篇
  2015年   6942篇
  2014年   11857篇
  2013年   31561篇
  2012年   18593篇
  2011年   25084篇
  2010年   19905篇
  2009年   22415篇
  2008年   23443篇
  2007年   23395篇
  2006年   20269篇
  2005年   18510篇
  2004年   18062篇
  2003年   17613篇
  2002年   17128篇
  2001年   17076篇
  2000年   16202篇
  1999年   16107篇
  1998年   34469篇
  1997年   25675篇
  1996年   20032篇
  1995年   15813篇
  1994年   14282篇
  1993年   14099篇
  1992年   11136篇
  1991年   10929篇
  1990年   10731篇
  1989年   10303篇
  1988年   9942篇
  1987年   8909篇
  1986年   8832篇
  1985年   10111篇
  1984年   9602篇
  1983年   8797篇
  1982年   8201篇
  1981年   8348篇
  1980年   8036篇
  1979年   8177篇
  1978年   8202篇
  1977年   9009篇
  1976年   11429篇
  1975年   7237篇
  1974年   7178篇
  1973年   7162篇
  1972年   6212篇
  1971年   5570篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
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   
62.
The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production.  相似文献   
63.
64.
Research suggests that schizotypal personality disorder (SPD) is a part of the spectrum of schizophrenia-related illnesses. This article hypothesizes that a deficit in the representation and maintenance of context is a core cognitive disturbance in schizophrenia and that SPD individuals should demonstrate context-processing deficits. To test this hypothesis, the authors administered 3 versions of their AX-CPT task, designed to assess context processing, to 35 healthy controls and 26 individuals with DSM-IV SPD. They also administered working memory and selective attention tasks. SPD individuals displayed context representation deficits similar to those found in schizophrenia but did not show the same additional deficits in context maintenance. Context processing was strongly associated with working memory and selective attention performance in the SPD individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
65.
In this letter, bandpass filters with one or two tunable transmission zeros are proposed. The reconfigurable transmission zeros are implemented through varactors in combination with tapped quarter-wavelength stubs. Based on mixed mode simulations including EM simulation and circuit simulation, the proposed filters were designed and fabricated on low-cost FR4 board. The measurement results verified the design concepts.  相似文献   
66.
Nash equilibria of packet forwarding strategies in wireless ad hoc networks   总被引:8,自引:0,他引:8  
In self-organizing ad hoc networks, all the networking functions rely on the contribution of the participants. As a basic example, nodes have to forward packets for each other in order to enable multihop communication. In recent years, incentive mechanisms have been proposed to give nodes incentive to cooperate, especially in packet forwarding. However, the need for these mechanisms was not formally justified. In this paper, we address the problem of whether cooperation can exist without incentive mechanisms. We propose a model,based on game theory and graph theory to investigate equilibrium conditions of packet forwarding strategies. We prove theorems about the equilibrium conditions for both cooperative and noncooperative strategies. We perform simulations to estimate the probability that the conditions for a cooperative equilibrium hold in randomly generated network scenarios.. As the problem is involved, we deliberately restrict ourselves to a static configuration. We conclude that in static ad hoc networks where the relationships between the nodes are likely to be stab le-cooperation needs to be encouraged.  相似文献   
67.
Fifty-eight commercial yogurt products of seven brands (which claimed to include bifidobacteria) were obtained from local stores in Greensboro, North Carolina, USA. These products were examined at 0, 1, 2, 3 and 4 weeks for the viability of bifidobacteria and yogurt starter culture during refrigerated storage at 4°C. Our results showed that bifidobacteria counts were variable, ranging from 0 to 5.5 log cfu/mL. The average yogurt starter culture counts ranged from 5.20 to 8.87 log cfu/mL and 7.51–8.94 log cfu/mL for Lactobacillus delbrueckii spp. bulgaricus and Streptococcus thermophilus , respectively. Of the 58 products tested, only 44 products (76%) contained viable cultures. Viability of bifidobacteria in yogurt samples remained within the same levels during 3 weeks of storage at 4°C; however, the bacterial count started to decline during the fourth week. These results suggest optimal beneficial consumption of yogurt foods with live bifidobacteria should occur within 3 weeks of production. Results obtained from this research could be used by the industry to develop new technologies to ensure consumers receive high-quality products.  相似文献   
68.
Towards intelligent dressing   总被引:1,自引:0,他引:1  
The aim of this article is to state the principles of an intelligent monitoring and control system for the grinding machine, comprising the dressing process as well as grinding stability.  相似文献   
69.
This paper provides an overview of the main aspects of modern fluorescence microscopy. It covers the principles of fluorescence and highlights the key discoveries in the history of fluorescence microscopy. The paper also discusses the optics of fluorescence microscopes and examines the various types of detectors. It also discusses the signal and image processing challenges in fluorescence microscopy and highlights some of the present developments and future trends in the field.  相似文献   
70.
V. I. Pipa 《Semiconductors》2006,40(6):665-667
Radiative lifetimes of nondegenerate electrons and holes distributed uniformly in a semiconductor layer either deposited on a substrate or bounded by two dielectric media are calculated. The obtained expression takes into account the radiation reabsorbtion and interference effects and determines the dependences of the radiative lifetimes on the refractive indices of the external media and on the layer thickness.  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