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   23293篇
  免费   795篇
  国内免费   85篇
电工技术   299篇
综合类   45篇
化学工业   5169篇
金属工艺   506篇
机械仪表   468篇
建筑科学   1747篇
矿业工程   161篇
能源动力   692篇
轻工业   2159篇
水利工程   183篇
石油天然气   57篇
武器工业   1篇
无线电   1503篇
一般工业技术   4252篇
冶金工业   2906篇
原子能技术   147篇
自动化技术   3878篇
  2023年   152篇
  2022年   310篇
  2021年   536篇
  2020年   313篇
  2019年   328篇
  2018年   497篇
  2017年   429篇
  2016年   533篇
  2015年   483篇
  2014年   696篇
  2013年   1538篇
  2012年   1088篇
  2011年   1532篇
  2010年   1106篇
  2009年   1062篇
  2008年   1277篇
  2007年   1117篇
  2006年   951篇
  2005年   874篇
  2004年   786篇
  2003年   699篇
  2002年   675篇
  2001年   400篇
  2000年   387篇
  1999年   424篇
  1998年   451篇
  1997年   389篇
  1996年   356篇
  1995年   309篇
  1994年   306篇
  1993年   308篇
  1992年   255篇
  1991年   222篇
  1990年   207篇
  1989年   232篇
  1988年   190篇
  1987年   180篇
  1986年   175篇
  1985年   244篇
  1984年   216篇
  1983年   186篇
  1982年   172篇
  1981年   201篇
  1980年   130篇
  1979年   147篇
  1978年   146篇
  1977年   132篇
  1976年   147篇
  1975年   122篇
  1974年   111篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Hydrogen free amorphous carbon coatings ‐ deposited with plasma‐activated high‐rate evaporation By using the technology of the plasmaactivated electron beam evaporation we deposited hydrogen free amorphous carbon coatings with deposition rates of up to 100 μm/h. The results of the mechanical and tribological investigations show the potential of these layers for the use in case of wear resistance. Hardnesses of up to 16GPa were proved. The actual state of the characterisation of the coatings is described and the outlook onto possibilities of further optimisation is given.  相似文献   
33.
随着移动电视在美国的开始应用,新应用逐渐站稳了脚跟,并被美国消费者的要求所推动,而消费者的这些更丰富体验的要求在以前受到过抑制。为了在卫星电信领域更好契合这一趋势,注意亚洲发展并从其经验中总结教训这一做法是有意义的。  相似文献   
34.
This paper gives a quick overview of how various scientific, operational and safety related requirements drove the development of hardware for the Bone Proteomics (BOP) experiment that was conducted on the International Space Station during the Italian Soyuz Mission in 2005. The experiment objectives will be highlighted briefly and design solutions will be presented. Comments will be given regarding the choice of a particular design solution and the impact on the complexity, cost and development time. Conclusions in this paper are based on the experience gained when developing the BOP experiment hardware and other relatively small experiment hardware packages, typical of European Soyuz Missions. The observations should not be extrapolated to large payloads. The objective of this paper is not to produce a recipe for developing experiment hardware; dedicated documents for that purpose are available elsewhere. Rather, the objective is to help others profit from experience gained in the development of relatively small experiment hardware packages, and to highlight where time and cost saving decisions can be made.  相似文献   
35.
The thermal stress on building‐integrated photovoltaic modules (BIPV) in Espoo, Finland, was studied with field‐testing of amorphous silicon modules. Based on these results, the thermal stress at two other European locations (Paris and Lisbon) was estimated. The estimation procedure entailed thermal modelling of heat transfer in the façade with meteorological data as input. The results indicate that the thermal stress on BIPV modules in Lisbon is, in this case, approximately 50% higher that in Espoo and between 80 and 200% higher than in Paris, depending on the activation energy of the degradation process. The difference in stress between a BIPV module and a free‐standing module in Espoo was 50–200%. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
36.
A test chamber has been developed in order to provide a small and simple emission testing facility capable of testing construction products in a climate where the important climatic parameters such as temperature, ventilation rate and air velocity can be varied independently around typical indoor values. The test chamber CLIMPAQ is made of panes of window glass. Other main surface materials are stainless steel and eloxated aluminium. The chamber has a volume of 50.9 litres and is designed to meet the requirements for quantifying air pollution. In this investigation human subjects acted as air pollution judges, and chemical characterization of the air pollution was carried out. Carpet, linoleum, wall paint and seal- ant were tested simultaneously in the CLIMPAQ and in four other chambers ranging from a full-scale chamber of 28 m3 to a field and laboratory emission cell of 3.5· 10?5m3. Product ranking is the same in all chambers for the sensory measurements. Emission rates based on sensory measurements differ for all products less than 100 % except for tests in a 3-litre chamber where emission rates were higher. Chemical measurements differ up to approximately 10 times for the same product in different chambers. Deviations appear to be the result of different environmental parameters in the various chambers. Low air concentrations or high specific ventilation rates seem to increase emissions, while differences in air velocities and sink properties may also be the cause of differences in emission rates.  相似文献   
37.
38.
39.
Personal exposure in a displacement ventilated room is examined. The stratified flow and the considerable concentration gradients necessitate an improvement of the widely used fully mixing compartmental approach. The exposure of a seated and a standing person in proportion to the stratification height is examined by means of full-scale measurements. A breathing thermal manikin is used to simulate a person. It is found that the flow in the boundary layer around a person is able to a great extent to entrain and transport air from below the breathing zone. In the case of non-passive, heated contaminant sources, this entrainment improves the indoor air quality. Measurements of exposure due to a passive contaminant source show a significant dependence on the flow field as well as on the contaminant source location. Poor system performance is found in the case of a passive contaminant released in the lower part of the room close to the occupant. A personal exposure model for displacement ventilated rooms is proposed. The model takes the influence of gradients and the human thermal boundary layer into account. Two new quantities describing the interaction between a person and the ventilation are defined.  相似文献   
40.
An influential and refreshingly frank report on the state of health of non-university materials research in Germany has recently been published. National Research Centers, Max Planck Institutes, and Fraunhofer Institutes are among the organizations covered. Recommendations are made on the basis of materials type, and on the performances of the individual institutes. The conclusions of this self-portrait, painted by representatives of the organizations themselves along with participants from the universities, industry, and state, will provide food for thought for both German materials scientists and those in other European countries concerned with the future development of this crucial economic sector.  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