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   9690篇
  免费   362篇
  国内免费   6篇
电工技术   93篇
综合类   12篇
化学工业   1881篇
金属工艺   152篇
机械仪表   176篇
建筑科学   549篇
矿业工程   22篇
能源动力   225篇
轻工业   730篇
水利工程   76篇
石油天然气   29篇
武器工业   1篇
无线电   601篇
一般工业技术   1746篇
冶金工业   2161篇
原子能技术   149篇
自动化技术   1455篇
  2022年   67篇
  2021年   147篇
  2020年   110篇
  2019年   135篇
  2018年   184篇
  2017年   173篇
  2016年   198篇
  2015年   164篇
  2014年   253篇
  2013年   641篇
  2012年   406篇
  2011年   550篇
  2010年   384篇
  2009年   419篇
  2008年   443篇
  2007年   471篇
  2006年   441篇
  2005年   379篇
  2004年   334篇
  2003年   314篇
  2002年   257篇
  2001年   179篇
  2000年   183篇
  1999年   193篇
  1998年   225篇
  1997年   191篇
  1996年   197篇
  1995年   186篇
  1994年   150篇
  1993年   144篇
  1992年   149篇
  1991年   96篇
  1990年   97篇
  1989年   118篇
  1988年   117篇
  1987年   106篇
  1986年   104篇
  1985年   111篇
  1984年   111篇
  1983年   112篇
  1982年   63篇
  1981年   85篇
  1980年   70篇
  1979年   62篇
  1978年   86篇
  1977年   63篇
  1976年   60篇
  1975年   53篇
  1974年   47篇
  1972年   47篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A method is presented for controlling cryptographic key usage based on control vectors. Each cryptographic key has an associated control vector that defines the permitted uses of the key within the cryptographic system. At key generation, the control vector is cryptographically coupled to the key by way of a special encryption process. Each encrypted key and control vector are stored and distributed within the cryptographic system as a single token. Decryption of a key requires respecification of the control vector. As part of the decryption process, the cryptographic hardware verifies that the requested use of the key is authorized by the control vector. This article focuses mainly on the use of control vectors in cryptosystems based on the Data Encryption Algorithm.  相似文献   
72.
Carbon films have been produced using a graphite hollow cathode and an r.f. plasma of hydrogen or hydrogen and argon. No hydrocarbon gas was used. The films were subjected to heat treatments up to 700 °C in air. The optical properties of the films were studied using Fourier transform IR, UV-visible, Raman, ellipsometry and photoluminescence techniques before and after the annealing. Films prepared without argon have a narrower band gap and a different photoluminescence response from films prepared with argon. The index of refraction was seen to have values between 1.7 and 2.2 depending on the preparation conditions. The optical band gap of the films was generally greater than 2 eV and the annealing process both increased the gap and reduced the density of states responsible for the large photoluminescence signal.  相似文献   
73.
A cellular automata model is used to simulate a variety of granular chute flows. The model is tested against several case studies: flow down a chute, flow past an obstacle, chute flow in which complex, counter-rotating vortices result in streamwise surface stripes and flow near a boundary. The model successfully reproduces experimental observations in all of these cases. These results lead us to propose that simple, rule-based, models such as this can improve our detailed understanding of dynamics and flow within an opaque granular bed.  相似文献   
74.
The authors developed and meta-analytically examined hypotheses designed to test and extend work design theory by integrating motivational, social, and work context characteristics. Results from a summary of 259 studies and 219,625 participants showed that 14 work characteristics explained, on average, 43% of the variance in the 19 worker attitudes and behaviors examined. For example, motivational characteristics explained 25% of the variance in subjective performance, 2% in turnover perceptions, 34% in job satisfaction, 24% in organizational commitment, and 26% in role perception outcomes. Beyond motivational characteristics, social characteristics explained incremental variances of 9% of the variance in subjective performance, 24% in turnover intentions, 17% in job satisfaction, 40% in organizational commitment, and 18% in role perception outcomes. Finally, beyond both motivational and social characteristics, work context characteristics explained incremental variances of 4% in job satisfaction and 16% in stress. The results of this study suggest numerous opportunities for the continued development of work design theory and practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
76.
This paper presents the concept of a process signature for the use of online signature analysis and defect detection in the layered manufacturing (LM) of ceramic sensors and actuators. To achieve the high quality of parts built by the fused deposition of ceramics (FDC), an online process-monitoring system is implemented to detect the processing defects. Using a process signature extracted from the image of a layer captured by the monitoring system, an ideal image is created that is then compared to the original image to detect and identify the defects. Some results of signature analysis and defect detection for single-material and multi-material parts are also presented.Received: 22 July 1999, Accepted: 21 October 2001, Published online: 29 October 2003 Correspondence to: Mohsen A. JafariThis work was supported by the Office of Naval Research under grant # N-0014-96-1-1175. Ref. US Patent # S-5738817, April 14, 1998.  相似文献   
77.
Review of book: Stephen Mitchell. Can Love Last? The Fate of Romance Over Time. New York: Norton, 2002, 223 pp. Reviewed by Timothy J. Zeddies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
Working collaboratively, psychologist educators and trainers at the doctoral, internship, and postdoctoral levels; credentialers; practitioners; and students offer 8 proposals for psychologists to consider in recognizing, assessing, and intervening with problems of professional competence in students and practicing professionals. In the proposals, the authors address the following topics: definitions and categories; preparing the system; self-assessment; remediation; diversity; communication across various levels of the system; confidentiality; and ethical, regulatory, and legal underpinnings. They also propose future directions for the assessment of problems in professional competence in both students and practicing psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
79.
In many data analysis problems, it is useful to consider the data as generated from a set of unknown (latent) generators or sources. The observations we make of a system are then taken to be related to these sources through some unknown function. Furthermore, the (unknown) number of underlying latent sources may be less than the number of observations. Recent developments in independent component analysis (ICA) have shown that, in the case where the unknown function linking sources to observations is linear, such data decomposition may be achieved in a mathematically elegant manner. In this paper, we extend the general ICA paradigm to include a very flexible source model, prior constraints and conditioning on sets of intermediate variables so that ICA forms one part of a hierarchical system. We show that such an approach allows for efficient discovery of hidden representation in data and for unsupervised data partitioning.  相似文献   
80.
Data from 2 daily diary studies of stress, negative affect, and drinking were used to examine the correspondence between global self-reports of drinking to cope (DTC) and within-person stress/negative affect-drinking associations. In Study 1, 83 community-residing drinkers recorded data in nightly booklets on negative events, perceived stress, negative affect, and drinking for 60 consecutive days. In Study 2, 88 community-residing drinkers recorded data on negative events and negative interpersonal exchanges nightly and negative affect and drinking in near-real time on palmtop computers for 30 consecutive days. Both studies showed only modest correspondence between self-reported DTC and between-person differences in within-day, daily, and weekly associations between stress/negative affect and drinking. The findings indicate that individuals who report higher DTC simply may drink across a wider variety of conditions than those who report relatively lower DTC. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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