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   243272篇
  免费   3150篇
  国内免费   1241篇
电工技术   4829篇
综合类   264篇
化学工业   35411篇
金属工艺   10861篇
机械仪表   7066篇
建筑科学   6238篇
矿业工程   481篇
能源动力   6273篇
轻工业   24147篇
水利工程   1836篇
石油天然气   1335篇
武器工业   3篇
无线电   31035篇
一般工业技术   44878篇
冶金工业   50106篇
原子能技术   3860篇
自动化技术   19040篇
  2021年   1564篇
  2019年   1424篇
  2018年   2321篇
  2017年   2223篇
  2016年   2444篇
  2015年   1907篇
  2014年   3159篇
  2013年   10793篇
  2012年   5449篇
  2011年   7786篇
  2010年   6284篇
  2009年   6962篇
  2008年   7558篇
  2007年   7658篇
  2006年   7031篇
  2005年   6519篇
  2004年   6244篇
  2003年   6261篇
  2002年   6239篇
  2001年   6371篇
  2000年   5801篇
  1999年   6417篇
  1998年   16558篇
  1997年   11597篇
  1996年   8948篇
  1995年   6689篇
  1994年   5907篇
  1993年   5727篇
  1992年   4051篇
  1991年   3994篇
  1990年   3582篇
  1989年   3504篇
  1988年   3440篇
  1987年   2907篇
  1986年   2842篇
  1985年   3413篇
  1984年   3050篇
  1983年   2743篇
  1982年   2547篇
  1981年   2568篇
  1980年   2430篇
  1979年   2271篇
  1978年   2235篇
  1977年   2808篇
  1976年   4171篇
  1975年   1899篇
  1974年   1795篇
  1973年   1783篇
  1972年   1460篇
  1971年   1317篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
An applicability of quinone biomarker to the analysis of hillslope runoff was investigated. At first, quinone profiles of three streams as well as a hillslope runoff in a forested headwater catchment were compared. The quinone composition of hillslope runoff differed from others. Moreover, there were remarkable differences in quinone profile of hillslope runoff under different rainfall conditions. Then, the behavior of quinone biomarker during the increase and decrease of hillslope runoff after a rainfall event was examined. The fractional changes in Q-9 (H2), Q-10 (H2), Q-11, MK-6 and MK-10 suggested the effect of interflow.  相似文献   
972.
973.
Self-knowledge is a concept that is present in several philosophies. In this article, we consider the issue of whether or not a learning algorithm can in some sense possess self-knowledge. The question is answered affirmatively. Self-learning inductive inference algorithms are taken to be those that learn programs for their own algorithms, in addition to other functions.
La connaissance de soi est un concept qui se retrouve dans plusieurs philosophies. Dans cet article, les auteurs s'interrogent à savoir si un algorithme d' apprentissage peut dans une certaine mesure posséder la connaissance de soi. lis apportent une reponse positive a cette question. Les algorithmes d'inference inductive autodidactes sont ceux qui font l'apprentissage de programmes pour leurs propres algorithmes, en plus d' autres fonctions.  相似文献   
974.
A monolithic microwave frequency divider IC with an operating range of 1.4?5.3 GHz was developed and fabricated in a standard bipolar technology. The circuit operates on the principle of `regenerative frequency division?. Compared to the most popular divider concepts based on a master-slave D-flip-flop, an almost twice as high input frequency can be divided, provided that the same technology is used. A further advantage is the low power consumption.  相似文献   
975.
This paper uses X-ray absorption spectroscopy to study the electronic structure of the high-k gate dielectrics including TM and RE oxides. The results are applicable to TM and rare earth (RE) silicate and aluminate alloys, as well as complex oxides comprised of mixed TM/TM and TM/RE oxides. These studies identify the nature of the lowest conduction band d* states, which define the optical band gap, Eg, and the conduction band offset energy with respect to crystalline Si, EB. Eg and EB scale with the atomic properties of the TM and RE atoms providing important insights for identification high-k dielectrics that meet performance targets for advanced CMOS devices.  相似文献   
976.
Electrochemical implantation was performed at Ni electrodes to form DyNi2 films at 0.55 V (vs. Li+/Li), 0.62 V, and 0.70 V for 0.5-5.0 h in a molten LiCl-KCl-DyCl3 (0.50 mol%) system at 700 K. It was found that the DyNi2 films grew linearly with time with coulomb efficiency of about 100%. The obtained growth rates were higher at more negative potentials, i.e., 0.47 μm min−1 at 0.55 V, 0.32 μm min−1 at 0.62 V, and 0.14 μm min−1 at 0.70 V. On the analogy of the metal oxide growth, the observed rapid and linear growth of DyNi2 films may be explained by the existence of the outer and inner DyNi2 layers.  相似文献   
977.
The stationary and time-resolved polariton radiation in ultrahigh quality AIGaAs layers have been studied. It has been found that elastic exciton-exciton collisions lead to the appearance of a low-energy line of polariton radiation. We show that the rate of exciton-to-polariton transitions caused by elastic exciton-exciton collisions is determined not only by the density of the excitonic gas, but also by its temperature; this is in accordance with existing theoretical predictions. The text was submitted by the authors in English.  相似文献   
978.
Parity space approach and H2 approach are two important fault detection approaches. This paper studies the relationship between these two approaches, which reveals frequency domain characteristics of the optimal solution of the parity space approach on the one side and provides a numerical solution of the H2-optimal design of residual generators on the other side.  相似文献   
979.
Ultraviolet (UV) disinfection is becoming increasingly popular as an alternative disinfection technology to chlorination in recent years. In this study, we investigated the photoreactivation of Escherichia coli following medium-pressure (MP) UV disinfection of synthetic water by a bench-scale collimated beam apparatus. The UV doses ranged from 1.6 -19.7 mWs/cm2 and photoreactivation was investigated for 6 hours under fluorescent light. In addition, chloramination was applied after UV disinfection to investigate its ability to control photoreactivation. It was found that photoreactivation occurred for all UV doses tested and the increase in bacteria numbers ranged from 0.04 to 1.35 log10. However, the degree of photoreactivation decreased with increased UV doses. Chloramination experiments revealed that the addition of 0.5 mg/l of monochloramine resulted in suppression of photoreactivation for 1 hour only. An increased monochloramine dose of 1 mg/l was found to prevent photoreactivation for the entire duration of the experiment. The results of this study have shown that photoreactivation occurs even after MP UV disinfection, although it is of a lesser extent at higher UV doses. This study has also established that secondary chloramination can effectively suppress and eliminate photoreactivation with a chloramine dose of 1 mg/l.  相似文献   
980.
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