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   227328篇
  免费   20214篇
  国内免费   10101篇
电工技术   14535篇
技术理论   31篇
综合类   22880篇
化学工业   28775篇
金属工艺   9627篇
机械仪表   11556篇
建筑科学   31498篇
矿业工程   13782篇
能源动力   8818篇
轻工业   17106篇
水利工程   11322篇
石油天然气   12255篇
武器工业   3220篇
无线电   14429篇
一般工业技术   16611篇
冶金工业   12444篇
原子能技术   1699篇
自动化技术   27055篇
  2024年   1076篇
  2023年   3074篇
  2022年   5822篇
  2021年   7625篇
  2020年   7394篇
  2019年   5587篇
  2018年   5206篇
  2017年   6621篇
  2016年   7963篇
  2015年   8568篇
  2014年   15545篇
  2013年   13621篇
  2012年   16323篇
  2011年   18061篇
  2010年   13300篇
  2009年   13479篇
  2008年   12302篇
  2007年   15045篇
  2006年   13648篇
  2005年   11932篇
  2004年   9921篇
  2003年   8666篇
  2002年   7085篇
  2001年   5813篇
  2000年   4990篇
  1999年   3942篇
  1998年   2797篇
  1997年   2424篇
  1996年   1972篇
  1995年   1635篇
  1994年   1384篇
  1993年   998篇
  1992年   802篇
  1991年   561篇
  1990年   487篇
  1989年   450篇
  1988年   245篇
  1987年   192篇
  1986年   167篇
  1985年   190篇
  1984年   136篇
  1983年   113篇
  1982年   62篇
  1981年   76篇
  1980年   84篇
  1979年   38篇
  1978年   22篇
  1977年   24篇
  1975年   17篇
  1959年   25篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
This paper assesses the potential of natural zeolite utilization as a low-cost ion-exchange and sorbent material in pollution control and recovery of metals. The improvement of the purity of natural zeolites coupled with their chemical modification capabilities in order to provide specific properties may provide a cost-effective alternative for the treatment of heavy metal contaminated soil and water. The application of natural zeolites in industrial pollution control is becoming important and the level of technical effort is increasingly expanding. The extent of application is unlikely to be related solely to their low cost, but also to improved properties and performance characteristics, which will advance the practical implementation of natural zeolites' technology.  相似文献   
42.
A new principle and arrangement for directly determining the angle of incidence of an optical beam on an object are proposed and demonstrated. The novelty of the approach lies in the realization of a ‘smart object’, which extracts a portion of the incident beam's power into an optical waveguide attached to the object's surface or embedded in its body for converting the angle of incidence into the position of a guided beam with finite lateral extent. This ‘integrated optical light pointer’ beam is accomplished by means of creating additional degrees of freedom on the target in two different ways. While a first type is based on introducing spatial variations of the waveguide thickness, a second type makes use of a chirp of the grating periodicity. The feasibility for practical applications has been experimentally demonstrated by a direct comparison with a commercial high-resolution encoder, resulting in an r.m.s. error of <30′'. Measurements have been performed for chips fabricated based on replicated polycarbonate substrates and with no external optics, showing the great potential of this approach for realizing low-cost yet high-performance miniature goniometers.  相似文献   
43.
44.
本文通过焊接试验对奥氏体不锈钢绕带容器环板与绕带焊接工艺进行了研究分析,并得出了合理的焊接方法和工艺参数。  相似文献   
45.
本文就如何发挥高校教研室的职能作用记述了本教研室所采取的具体方法和措施。  相似文献   
46.
Combined shape and sizing optimization of truss structures   总被引:1,自引:0,他引:1  
 In this paper, an evolutionary optimization method is presented for weight minimum problem of a 3-dimensional truss structure in terms of nodal coordinates and element cross-sectional areas. The structure is subject to stress, local buckling and displacement constraints. Two types of design variables with different natures are optimized separately: (1) a fully stressed design (FSD) and scaling techniques are applied to sizing variables and (2) the evolutionary node shift method is applied to shape variables. Alternating procedure is utilized to couple the two types of variables and to combine the results. The optimum solution is achieved gradually from the initial configuration design. Two typical truss structures are examined to illustrate the validity of the method. Received: 22 October 2001 / Accepted: 04 June 2002 This research work is supported by the National Natural Science Foundation of China under the guarantees no. 10072050 and 10172072, respectively.  相似文献   
47.
48.
This article presents a two-dimensional transient model for gas-solids flow and heat transfer through pipes using the coupled Computational Fluid Dynamics and Discrete Element Method approach. Numerical simulations have been conducted to examine the modification of fluid thermal structure due to the presence of particles in a pneumatic transport pipeline. Modeled results have demonstrated the key role of transversal motion of rebounding particles in the pipe cross section in altering fluid temperature. Further implementation of this modeling technique in air-drying processes is discussed and possible experimental methods for the measurement of in situ particle and fluid motion and temperature profile are cited.  相似文献   
49.
Wood shaving samples were heated in both cubic baskets and in a previously described system realising the conditions of the ‘infinite slab’ in thermal ignition. Results from the two sets of experiment were found to be totally consistent with each other.  相似文献   
50.
Safe and Economic Operation of Power Plants – Research Results in the Field of Materials, Design and Maintenance Components of power plants which undergo high temperatures are subjected to complex loading situations. The requirements on the used materials result from the special operation conditions of the plants and have to be adjusted to the steadily growing requirements on higher efficiency of the complete power plant as well as to those of safe and economic operation. The expenses for control and downtimes are directly connected with economic efficiency and availability. However, in case of new procedures or components it is not possible to revert to the existing know‐how. Different failure mechanisms than known before can occur. The same goes for the load situation. Therefore the knowledge base has to be extended to in‐advance or even parallely running scientific examinations that life assessment and maintenance strategies can be applied which guarantee the operational reliability and the efficiency of the plant. The main emphasis of these F&E works has to be put on condition monitoring based on actual operational data, the standard materials’ and component’s behaviour (deformation, damage and failure behaviour) in connection with design of components and the related material laws. In the framework of applied AVIF projects, following problems are handled:. – qualification of materials by determinating parameters related to practise. – optimal design of components by making available material laws and numerical tools. – economic manufacturing of components by qualifying processing methods such as welding. – The results can be transferred to concepts for safe and economic operation of power plants, especially for newly introduced materials for which there is no operational experience available.  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