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   113353篇
  免费   6113篇
  国内免费   1921篇
电工技术   4476篇
技术理论   13篇
综合类   4611篇
化学工业   20316篇
金属工艺   4499篇
机械仪表   4844篇
建筑科学   6699篇
矿业工程   1941篇
能源动力   3107篇
轻工业   12828篇
水利工程   1746篇
石油天然气   3931篇
武器工业   534篇
无线电   10526篇
一般工业技术   15319篇
冶金工业   10238篇
原子能技术   1007篇
自动化技术   14752篇
  2025年   254篇
  2024年   2190篇
  2023年   1941篇
  2022年   2940篇
  2021年   4245篇
  2020年   3584篇
  2019年   3163篇
  2018年   3759篇
  2017年   3719篇
  2016年   3854篇
  2015年   3932篇
  2014年   4919篇
  2013年   6818篇
  2012年   6629篇
  2011年   7012篇
  2010年   5696篇
  2009年   5360篇
  2008年   5321篇
  2007年   4949篇
  2006年   4373篇
  2005年   3743篇
  2004年   2934篇
  2003年   2634篇
  2002年   2401篇
  2001年   2042篇
  2000年   2129篇
  1999年   2495篇
  1998年   4133篇
  1997年   2930篇
  1996年   2359篇
  1995年   1701篇
  1994年   1433篇
  1993年   1143篇
  1992年   684篇
  1991年   532篇
  1990年   453篇
  1989年   417篇
  1988年   349篇
  1987年   272篇
  1986年   214篇
  1985年   194篇
  1984年   155篇
  1983年   111篇
  1982年   132篇
  1981年   137篇
  1980年   132篇
  1978年   58篇
  1977年   152篇
  1976年   278篇
  1973年   65篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Cyclamate and its metabolite cyclohexylamine affect male fertility in high dose animal studies, but this affect has not been investigated in epidemiological studies. This paper reports the first epidemiological study designed to investigate the possibility of a relationship between cyclamate and cyclohexylamine and male fertility in humans, in which 405 cases of clinically defined infertility in men and 379 controls were surveyed. Semen evaluation, urine analysis for cyclamate and cyclohexylamine and dietary questionnaires were compared between cases and controls. No evidence was found of a significant association between cyclamate intake and male infertility; neither high cyclamate nor high cyclohexylamine excretion were associated with elevated risk. The lack of association remained after adjusting by age, area of residence, education, total energy intake and other variables. No significant correlations were observed between cyclamate intake, metabolism or excretion, and sperm count and motility. The results demonstrate no effect of cyclamate or cyclohexylamine on male fertility at the present levels of cyclamate consumption.  相似文献   
12.
A jet-printed digital-lithographic method, in place of conventional photolithography, was used to fabricate 64 /spl times/ 64 pixel (300 /spl mu/m pitch) matrix addressing thin-film transistor (TFT) arrays. The average hydrogenated amorphous silicon TFT device within an array had a threshold voltage of /spl sim/3.5 V, carrier mobility of 0.7 cm/sup 2//V/spl middot/s, subthreshold slope of 0.76 V/decade, and an on/off ratio of 10/sup 8/.  相似文献   
13.
Reconstruction algorithms and their numerical examples of acoustical tomography based on the second-order Born transform perturbation approximation are presented. The reconstruction algorithms in the second-order Born approximation are similar in form to those in the first-order Born approximation. Replacing the angular spectrum of the scattered wave in the first-order case by the result of applying a first-order operator to the angular spectrum of the scattered wave or applying a second-order operator to the angular spectrum of the incident wave leads to the second-order reconstruction algorithms. Also, comparisons of reconstruction algorithms of the first- and second-order Born approximations are given, and they show that the second-order Born approximation algorithms have a distinct advantage over the first-order approximations in many cases  相似文献   
14.
The effect of the atomic mobility on a film surface has been studied by using a three-dimensional atomistic thin-film deposition model which simulates three-dimensional thin-film images, surface profiles and cross-sectional area pictures. In addition, quantitative results of surface RMS roughness, average film thickness, atomic coordination number and its distribution, and solid fraction of the deposited thin films, were obtained from the simulations. When the film surface mobility increased from 0.3 to 3.0, RMS roughness decreased from 6.5 to 1.1, solid fraction increased from 0.27 to 0.56 and average film thickness decreased from 40 to 28, due to the reduction of the voids within the film. The full-width half magnitude of the atomic coordination distribution became narrower indicating the increased degree of crystallization. With increase in surface mobility crossing the boundary to 1.5, the film evolved from a porous or loose columnar structure with voids, to a densely packed fibrous grain structure which can be categorized by the zone structure models.  相似文献   
15.
本文实验研究了BHP的浓度对产生O2(1△)的影响。实验结果表明:当BHP浓度大于3.5M时,Cl2利用率以及O2(1△)的产率将不依赖于BHP浓度的变化而变化,同时,实验结果表明,使用低浓度的BHP对COIL的操作是可行的。  相似文献   
16.
17.
我的家     
我生于东京的银座,那是个靠近传统花街柳巷、歌舞升平的地方,在童年的记忆里那里随时随地都是一片华美景象。而在这些景象的背后有一排排美丽的临街二层长屋建筑,大都是料亭,还有颇有风致的砖结构剧场。那时父母在这里经营着咖啡馆,街上的行人总是把店里挤得满满的。数年前父亲  相似文献   
18.
To detect faults in a time-dependent process, we apply a discrete wavelet transform (DWT) to several independently replicated data sets generated by that process. The DWT can capture irregular data patterns such as sharp "jumps" better than the Fourier transform and standard statistical procedures without adding much computational complexity. Our wavelet coefficient selection method effectively balances model parsimony against data reconstruction error. The few selected wavelet coefficients serve as the "reduced-size" data set to facilitate an efficient decision-making method in situations with potentially large-volume data sets. We develop a general procedure to detect process faults based on differences between the reduced-size data sets obtained from the nominal (in-control) process and from a new instance of the target process that must be tested for an out-of-control condition. The distribution of the test statistic is constructed first using normal distribution theory and then with a new resampling procedure called "reversed jackknifing" that does not require any restrictive distributional assumptions. A Monte Carlo study demonstrates the effectiveness of these procedures. Our methods successfully detect process faults for quadrupole mass spectrometry samples collected from a rapid thermal chemical vapor deposition process  相似文献   
19.
20.
The development and test of a PLC control program takes time, increases equipment down-time, and might damage hardware due to program errors. All of these problems can be eliminated if there is a computer simulation system for testing control programs off line. This paper presented a new method, called Direct Sequential Method, for simulating PLCs. This method resolves a ladder logic sequentially by applying a series of logic deductions. This simulation system has been implemented in C and tested successfully.  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