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   39295篇
  免费   1583篇
  国内免费   75篇
电工技术   399篇
综合类   31篇
化学工业   7856篇
金属工艺   801篇
机械仪表   823篇
建筑科学   2108篇
矿业工程   126篇
能源动力   1180篇
轻工业   3150篇
水利工程   463篇
石油天然气   123篇
武器工业   5篇
无线电   2675篇
一般工业技术   6741篇
冶金工业   7220篇
原子能技术   291篇
自动化技术   6961篇
  2023年   265篇
  2022年   521篇
  2021年   781篇
  2020年   568篇
  2019年   714篇
  2018年   878篇
  2017年   783篇
  2016年   922篇
  2015年   821篇
  2014年   1133篇
  2013年   2555篇
  2012年   1819篇
  2011年   2294篇
  2010年   1787篇
  2009年   1687篇
  2008年   1975篇
  2007年   1919篇
  2006年   1691篇
  2005年   1536篇
  2004年   1248篇
  2003年   1190篇
  2002年   1095篇
  2001年   750篇
  2000年   595篇
  1999年   649篇
  1998年   633篇
  1997年   617篇
  1996年   600篇
  1995年   615篇
  1994年   553篇
  1993年   529篇
  1992年   524篇
  1991年   304篇
  1990年   445篇
  1989年   415篇
  1988年   337篇
  1987年   374篇
  1986年   332篇
  1985年   444篇
  1984年   432篇
  1983年   336篇
  1982年   316篇
  1981年   304篇
  1980年   294篇
  1979年   287篇
  1978年   271篇
  1977年   244篇
  1976年   225篇
  1975年   208篇
  1974年   187篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval.  相似文献   
52.
Interferon alpha-2a, which has antineoplastic, antiviral, immunomodulatory, and antiangiogenic effects, was evaluated in a prospective study, treating 10 lesions of patients with classical Kaposi's sarcoma. Ten patients received injections of interferon alpha-2a intralesionally in a dose of 3 million units three times weekly for 4 weeks, and in a variable dose for 4 more weeks. Two of the patients had a complete response, and in one of these, distant lesions also responded. Seven had a partial response, and one did not respond. The treatment was generally well tolerated. The results of our study support the use of interferon in the therapy of classical Kaposi's sarcoma, although it would appear that to achieve maximum efficacy, a longer period of treatment is needed.  相似文献   
53.
14 medicated hypertensive, 15 nonmedicated mild hypertensive, 39 normotensive, and 13 hypotensive adults participated in a 1–2 hr laboratory experiment that assessed each S's symptoms, moods, and estimates of systolic blood pressure (SBP) relative to actual SBP levels. Several self-reports and autonomic measures were collected during and after each of 22 tasks. Within-S correlations indicated that all Ss could estimate SBP at levels greater than chance. Further, 68% of the Ss evidenced at least 1 significant symptom–SBP correlation. Although medicated hypertensives believed they could estimate their BP more accurately than other groups, they were actually no more accurate than the other Ss. They also evidenced far fewer empirically derived symptom–SBP and emotion–SBP correlations than any other group. Overall, blood pressure (BP) beliefs were largely inaccurate. If these erroneous beliefs can be eliminated, Ss may be able to estimate BP fluctuations more accurately. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
54.
We report the results of the first national survey of psychologists in private practice regarding their participation in peer consultation groups. The sample (71% return) was drawn from 800 randomly selected psychologists listed in the National Register of Health Service Providers in Psychology. We found that 23% of the sample currently belonged to peer consultation groups, and 24% had belonged in the past. Of those not currently in groups, 61% expressed the desire to belong if one were available. There were virtually no significant demographic differences between current members and nonmembers. We examined the following group characteristics: formation, length of existence, size, membership, leadership, theoretical orientation, range of experience, time and place, content, and group process. Groups tended to be small, informal, and leaderless; however, we found great variation among groups on all dimensions. Findings also showed a high degree of satisfaction with membership. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
55.
56.
Control law design for rotorcraft fly-by-wire systems normally attempts to decouple the angular responses using fixed-gain crossfeeds. This approach can lead to poor decoupling over the frequency range of pilot inputs and increase the load on the feedback loops. In order to improve the decoupling performance, dynamic crossfeeds should be adopted. Moreover, because of the large changes that occur in the aircraft dynamics due to small changes about the nominal design condition, especially for near-hovering flight, the crossfeed design must be ‘robust’. A new low-order matching method is presented here to design robust crossfeed compensators for multi-input, multi-output (MIMO) systems. The technique minimizes cross-coupling given an anticipated set of parameter variations for the range of flight conditions of concern. Results are presented in this paper of an analysis of the pitch/roll coupling of the UH-60 Black Hawk helicopter in near-hovering flight. A robust crossfeed is designed that shows significant improvement in decoupling perfomance and robustness over the fixed-gain or single point dynamic compensators. The design method and results are presented in an easily used graphical format that lends significant physical insight to the design procedure. This plant precompensation technique is an appropriate preliminary step to the design of robust feedback control laws for rotorcraft.  相似文献   
57.
The realization of digital multimedia's full business potential requires networking. This article discusses the value-added benefits to the corporation of networked multimedia as well as the choice of architectures and technologies needed to deliver multimedia networking solutions.  相似文献   
58.
The aditi deductive database system   总被引:2,自引:0,他引:2  
Deductive databases generalize relational databases by providing support for recursive views and non-atomic data. Aditi is a deductive system based on the client-server model; it is inherently multi-user and capable of exploiting parallelism on shared-memory multiprocessors. The back-end uses relational technology for efficiency in the management of disk-based data and uses optimization algorithms especially developed for the bottom-up evaluation of logical queries involving recursion. The front-end interacts with the user in a logical language that has more expressive power than relational query languages. We present the structure of Aditi, discuss its components in some detail, and present performance figures.  相似文献   
59.
60.
Editorial     
  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