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   1539807篇
  免费   26261篇
  国内免费   7115篇
电工技术   34500篇
综合类   6571篇
化学工业   272383篇
金属工艺   64505篇
机械仪表   43701篇
建筑科学   47181篇
矿业工程   11506篇
能源动力   50270篇
轻工业   118503篇
水利工程   15681篇
石油天然气   37533篇
武器工业   188篇
无线电   197417篇
一般工业技术   290177篇
冶金工业   177997篇
原子能技术   33962篇
自动化技术   171108篇
  2021年   15605篇
  2020年   11918篇
  2019年   14711篇
  2018年   16023篇
  2017年   15393篇
  2016年   21571篇
  2015年   17410篇
  2014年   28774篇
  2013年   87847篇
  2012年   36525篇
  2011年   49452篇
  2010年   42950篇
  2009年   51039篇
  2008年   45962篇
  2007年   43305篇
  2006年   45863篇
  2005年   40469篇
  2004年   42461篇
  2003年   42311篇
  2002年   41185篇
  2001年   38483篇
  2000年   36590篇
  1999年   35958篇
  1998年   50387篇
  1997年   42360篇
  1996年   37289篇
  1995年   31911篇
  1994年   29765篇
  1993年   29553篇
  1992年   26543篇
  1991年   23727篇
  1990年   23944篇
  1989年   22910篇
  1988年   21548篇
  1987年   19761篇
  1986年   19214篇
  1985年   22539篇
  1984年   22595篇
  1983年   20573篇
  1982年   19417篇
  1981年   19518篇
  1980年   18119篇
  1979年   18705篇
  1978年   17889篇
  1977年   17764篇
  1976年   18842篇
  1975年   16116篇
  1974年   15661篇
  1973年   15748篇
  1972年   13164篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
This article describes the phenomenon of morphological instability in solid-solid phase transformations during thin-film interdiffusion, specifically related to the initial stages of precipitation when phase growth occurs along the interface between thin films. The experimental observations that revealed this effect will be presented, and a working hypothesis will be discussed. Experimental observations suggest that the ledge mechanism of growth is present in this system but does not inhibit the formation of interfacial instabilities. It is proposed that morphological stability for solid-phase growth occurring during thin-film interdiffusion can be treated by the inclusion of a solute-source term into the two-dimensional perturbation approach generally used to study unstable growth morphologies. Experimental observations that provide qualitative and semiquantitative support for the solute-source model are also presented.  相似文献   
993.
994.
Translated from Izmeritel'naya Tekhnika, No. 3, pp. 57–58, March, 1993.  相似文献   
995.
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   
996.
The paper proposes a structure for quality-of-service (QoS)-centered service level agreements (SLA), and a framework for their real-time management in multiservice packet networks. The SLA is structured to be fair to both parties, the service provider and their customer. The SLA considered here are for QoS assured delivery of aggregate bandwidth from ingress to egress nodes; however, the control and signaling is for the more granular flows or calls. A SLA monitoring scheme is presented in which revenue is generated by the admission of flows into the network, and penalty incurred when flows are lost in periods when the service provider is not SLA compliant. In the SLA management scheme proposed, the results of a prior off-line design are used, in conjunction with measurements taken locally at ingress nodes, to classify the loading status of routes. The routing and resource management are based on virtual partitioning and its supporting mechanism of bandwidth protection. The effectiveness of SLA management is measured by the robustness in performance in the presence of substantial diversity in actual traffic conditions. A simulation testbed called D'ARTAGNAN has been built from which we report numerical results for a case study. The results show that the SLA management scheme is robust, fair and efficient over a broad range of traffic conditions  相似文献   
997.
998.
An InAs/AlGaAs quantum-dot infrared photodetector based on bound-to-bound intraband transitions in undoped InAs quantum dots is reported. AlGaAs blocking layers were employed to achieve low dark current. The photoresponse peaked at 6.2 /spl mu/m. At 77 K and -0.7 V bias, the responsivity was 14 mA/W and the detectivity, D*, was 10/sup 10/ cm/spl middot/Hz/sup 1/2//W.  相似文献   
999.
1000.
European remote sensing (ERS) satellites synthetic aperture radar (SAR) wind retrievals using CMOD-IFR2 are, for the first time, retrieved in the marginal ice zone (MIZ) and in Arctic coastal areas and compared with in situ observations from reseach vessels (RVs) and output from a high-resolution atmospheric model. The root mean squares (rms) of the comparisons were 1.6 m s/sup -1/ and 2 m s/sup -1/, respectively. The spatial variation of the SAR wind fields established a decrease in wind speed close to the ice edge for the late summer situations where the wind was along the ice edge with the ice to the left. This decrease is believed to be due to changes in atmospheric stability, possibly through development of an internal boundary layer caused by the cold ice cover and melt water. Lower wind speed near the ice edge is confirmed by the atmospheric model and the in situ observations. Furthermore, good results are obtained from SAR wind retrieval in leads when compared with model output during a cold-air outbreak. Routine measurements in the MIZ are useful for estimating the wind stress, and therefore SAR may play an important role in this region. Finally, the identification of a jet out from Hinlopen Strait in the Svalbard region and low wind wakes along the coast in the SAR-retrieved wind field is confirmed by in situ observations as the RV moves through the region. The jet is also confirmed by the atmospheric model, which is able to reproduce the situation.  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