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   59743篇
  免费   2342篇
  国内免费   1757篇
电工技术   1907篇
技术理论   3篇
综合类   1380篇
化学工业   9061篇
金属工艺   4067篇
机械仪表   2565篇
建筑科学   2422篇
矿业工程   625篇
能源动力   1900篇
轻工业   3473篇
水利工程   665篇
石油天然气   2253篇
武器工业   171篇
无线电   6092篇
一般工业技术   12688篇
冶金工业   8117篇
原子能技术   964篇
自动化技术   5489篇
  2023年   419篇
  2022年   872篇
  2021年   1237篇
  2020年   940篇
  2019年   885篇
  2018年   1186篇
  2017年   1214篇
  2016年   1292篇
  2015年   1299篇
  2014年   1712篇
  2013年   3361篇
  2012年   2474篇
  2011年   2963篇
  2010年   2496篇
  2009年   2692篇
  2008年   2611篇
  2007年   2675篇
  2006年   2274篇
  2005年   2050篇
  2004年   1846篇
  2003年   1583篇
  2002年   1589篇
  2001年   1566篇
  2000年   1398篇
  1999年   1415篇
  1998年   2464篇
  1997年   1977篇
  1996年   1736篇
  1995年   1224篇
  1994年   962篇
  1993年   950篇
  1992年   716篇
  1991年   657篇
  1990年   609篇
  1989年   563篇
  1988年   416篇
  1987年   435篇
  1986年   397篇
  1985年   395篇
  1984年   322篇
  1983年   315篇
  1982年   319篇
  1981年   304篇
  1980年   369篇
  1979年   347篇
  1978年   299篇
  1977年   428篇
  1976年   632篇
  1975年   312篇
  1973年   315篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The introduction of a 1000 Å scale corrugated structure, aligned perpendicular to the filament axis, into oriented semi-crystalline polymers on plasma etching is shown to result from restructuring of the partially etched surface and not, as has previously been proposed, to correspond to morphological detail in the unetched material. The detail exposed on plasma etching polypropylene is shown to vary extensively with the etching conditions used. The exposed surface is compared with those resulting from peeling and chromic acid etching. Plasma etching is, however, shown to be useful in exposing coarse morphological detail such as spherulites, and in providing a convenient route for rapidly stripping the polymeric sample. The restructured partially etched surface may then be removed easily by, for example, a brief chromic acid treatment, exposing the sample interior to microscopic examination.Issued as NRCC no. 16534  相似文献   
992.
Conclusions The structure created by preliminary treatment has a strong influence on the swelling, the nature of pore generation, the dislocation density, and the phase composition of 0Kh16N15M3B steel. The greatest reduction in swelling was produced by 20% cold deformation, which at a high dislocation density led to a sharp refinement of the pores and lamellar precipitations.The lamellar phases precipitated in steels of the Kh16N15 type during the irradiation after special alloying or preliminary treatment do not always determine the nature of the generation and growth of vacancy pores.At a temperature of 460 and 550°C the swelling of nickel is less by a factor of about 3, and the swelling of iron is less by a factor of about 10, than the swelling of austenized 0Kh16N15M3B steel.The least swelling was found in the Kh77TYu alloy (with 77% nickel), which before irradiation contained -phase pre-precipitations, whereas the swelling of alloys with 40 and 60% nickel is 100 times as great. From this it is clear that the nickel content is not the only factor determining the swelling.Journal version of a report delivered at the Conference on the Study of Reactor Materials (Alushta, 1978).Translated from Atomnaya Énergiya, Vol. 45, No. 6, pp. 433–439, December, 1978.  相似文献   
993.
介绍球磨机的结构和工作机理,指出球磨机存在的问题,并对其轴封、轴头、进气口、吸料口等进行了技改,以提高设备的运行周期,满足生产需求。  相似文献   
994.
Using an operator representation of the effective diffusion coefficient we obtain a hyperbolic diffusion equation in a relaxational medium.Notation Fslot return-flow slot area - F cross-sectional area of the bed in the vertical plane - G* instantaneous number of fine particles in the apparatus Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 334–338, August, 1980.  相似文献   
995.
To establish the basis of the interpretative method is congruous with finding a solid basis--epistemologically speaking--to the analytic theory. This basis would be the means to transform this theory into a real science with its necessary adecuation among method, act and object of knowledge. It is only from a scientific stand that the psychoanalytic theory will be able to face successfully the reductionisms that menace it, be it the biologist-naturalism with its explanations of the psychic phenomena by means of mechanisms and biologic models or be it the speculative ideologies with their nucleus of technical praxis which make it impossible for the social-factic sciences to become real sciences. We propose as interpretative method the union of two models: the teleologic one which makes possible the appearance of intelligible, contingent and variable explanations between an antecedent and a consequent on one side, and on the other, the analogic model with its two moments: the comparative and the symbolic one. These moments makes possible the comparison and the union between antecedent and consequent baring in mind the "natural" ambiguity of the subject-object in question. The principal objective of the method--as a regulative idea in the Kantian sense--would be the search of univocity as regards the choice of one and only one sense from all the possible senses that "explain" the motive relationship or motive-end relationship in order to make the interpretation scientific. This status of scientificity should obey the rules of explanation: that the interpretations be derived effectively from the presupposed theory, that they really explain what they claim to explain, that they are not contradictory or contrary in the same ontologic level. We postulate that the synthesis of the two mentioned models, the teleologic-explanative and the analogic one allows us to find a possibility to make clear the "dark" sense of the noun interpretation and in this way the factibility of speaking of an interpretative method that develops the real concrete object by producing the formal and abstract one--which for us is the behaviour of the subject--. In this way the interpretations come to be teleological explanations overdetermined by an analogical relationship. This means that they produce the formal and abstract object -the method--which is in itself an intelligible, continguent and variable relationship between an antecedent and a consequent permitting in this way the emergence of a symbolic comparison to explain the real concrete. The symbolic explanations and comparisons are strictly derived from the presupposed theory, the theoretical body of psychoanalysis.  相似文献   
996.
An extensive superconducting electron tunneling study of Ta, using both a proximity method and an optimized conventional spectroscopy, is reported. The results for Ta confirm the electron-phonon origin of superconductivity in this element, and provide slightly improved superconducting parameters: =0.73 and ph * = 0.11. The results from the PET and optimized conventional methods are in substantial agreement, although the proximity method appears to provide somewhat better resolution of structure in the Eliashberg function 2 F(E).Operated for the U.S. Department of Energy by Iowa State University under contract No. W-7405-Eng-82. This research was supported by the Director for Energy Research, Office of Basic Energy Sciences, WPAS-KC-02-02-02.  相似文献   
997.
Moisture Diffusivity Data Compilation in Foodstuffs   总被引:12,自引:0,他引:12  
A review of the recently reported moisture diffusivity experimental data in food materials is presented in this work. Values are classified and analysed statistically to reveal the influences of temperature and moisture content. Empirical models relating moisture diffusivity with the above variables, along with relevant graphs for various materials, are included. Other factors affecting moisture diffusivity prediction are also discussed.  相似文献   
998.
Experimentally an attempt was made to demonstrate the effects of exogenous factors on the hormonally altered laryngeal mucosa of mice. Albany mice were divided into 4 groups of 8. In the first group of males, testosterone was injected daily; in the second group of males, no testosterone was given; in the third group of females with previously removed ovaries, testosterone was given daily; and, in the fourth group of females, no testosterone was given. All 4 groups were exposed to cigarette smoke for one hour daily for six weeks. Histopathological examination of the mucosa showed that the larynx can be considered a "target" organ for male hormones and that exogenous factors produce changes that lead to malignancy.  相似文献   
999.
A 4-week UNESCO-sponsored mission to the Department of Architecture, Karadeniz Technical University in Eastern Turkey, gave an opportunity to apply ergonomics techniques to some aspects of that country's domestic washbasin design. The study was intended to provide experience in questionnaire design and administration, in the application of psycho-physical methods, and to highlight the importance of determining user characteristics and preferences with regard to the built environment. A field study elicited information on dimensions and positioning of existing wash-basins and ancillary equipment and the opinions of users as to the suitability of these features in relation to the activities performed. A laboratory study, using an adjustable rig permitting variation in the heights of basin, taps and mirror/shelf, followed. The data obtained on preferred heights of these items led to the conclusions that basin height should be increased to between 95 and 100 cm to satisfy the majority of users; tap height above the basin should be reduced to about 11 cm; the shelf and lower edge of a mirror sited above the basin should be 136 cm above the floor; and a clear space of 110 cm should be available between the front of the basin and a wall or other obstruction. Suggestions on other design aspects of the bathroom, resulting from the study, are discussed.  相似文献   
1000.
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