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   496047篇
  免费   5835篇
  国内免费   2012篇
电工技术   9056篇
综合类   844篇
化学工业   71660篇
金属工艺   19491篇
机械仪表   15337篇
建筑科学   11713篇
矿业工程   2497篇
能源动力   12337篇
轻工业   41246篇
水利工程   5144篇
石油天然气   8970篇
武器工业   108篇
无线电   61248篇
一般工业技术   97313篇
冶金工业   92215篇
原子能技术   11594篇
自动化技术   43121篇
  2021年   3844篇
  2019年   3772篇
  2018年   6419篇
  2017年   6563篇
  2016年   6914篇
  2015年   4469篇
  2014年   7619篇
  2013年   21379篇
  2012年   12394篇
  2011年   17047篇
  2010年   13322篇
  2009年   15209篇
  2008年   16173篇
  2007年   16134篇
  2006年   14259篇
  2005年   13053篇
  2004年   12812篇
  2003年   12488篇
  2002年   12029篇
  2001年   12049篇
  2000年   11481篇
  1999年   11935篇
  1998年   28494篇
  1997年   20292篇
  1996年   15822篇
  1995年   12263篇
  1994年   10816篇
  1993年   10784篇
  1992年   8244篇
  1991年   7704篇
  1990年   7441篇
  1989年   7257篇
  1988年   6779篇
  1987年   6029篇
  1986年   6009篇
  1985年   6846篇
  1984年   6342篇
  1983年   5793篇
  1982年   5495篇
  1981年   5573篇
  1980年   5450篇
  1979年   5128篇
  1978年   5024篇
  1977年   5758篇
  1976年   7351篇
  1975年   4435篇
  1974年   4325篇
  1973年   4413篇
  1972年   3610篇
  1971年   3276篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
72.
In the present study of gas–liquid contactors, mean residence/contact time was calculated from knowledge of superficial velocity and the gas phase hold-up, for various gas rates and impeller geometry and speeds, and compared with values obtained from RTD measurements. A new correlation, involving Flow Number, Froude Number, system geometry and the physical properties, is proposed. This uses the authors data and those available in literature.  相似文献   
73.
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   
74.
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   
75.
76.
This study contrasted six subscales of the Brief Psychiatric Rating Scale (BPRS) to determine their sensitivity to psychosocial treatment outcome. An expanded version of the BPRS was administered to 216 clients on admission to a day program. The subscale measuring hostility and suspiciousness discriminated at intake clients who were therapeutically discharged from clients who did not complete the program and predicted discharge status after the investigators controlled for the effects of demographic variables. Significant reductions in scores were obtained on five subscales for a subset of clients to whom the BPRS was readministered before discharge. The results support the use of the expanded BPRS as an evaluative tool in psychosocial rehabilitation programs.  相似文献   
77.
The energy expenditure and heart rate of five Shetland ponies were measured during transport and compared with the values recorded while they were at rest and walking. Secondary aims of the study were to investigate whether there was any correlation between heart rate and energy expenditure and whether different orientations affected the values to different degrees. The measurements were recorded at one-minute intervals while the ponies were at rest, walking and being transported in four different orientations, on journeys lasting 30 minutes. There were significant increases (P < 0.001) in both heart rate and energy expenditure during transport which were similar to those associated with walking, and there was a strong correlation between the two measurements. There was no conclusive evidence that orientation affected the measurements, but it appeared that rear facing transport might have had the least effect.  相似文献   
78.
79.
Purified cell-envelope polyphosphatase as well as polyphoshatase activities of cytosol and isolated vacuoles, of nuclei and mitochondria of the yeast Saccharomyces cerevisiae were compared. The polyphosphatases of cell envelope and cytosol are similar, the polyphosphatases of nuclei, vacuoles and mitochondria differ in their kinetic properties, substrate specificity, requirements in divalent cations and in some effector actions both from these and from each other.  相似文献   
80.
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