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   47811篇
  免费   2472篇
  国内免费   76篇
电工技术   356篇
综合类   131篇
化学工业   11447篇
金属工艺   933篇
机械仪表   929篇
建筑科学   1500篇
矿业工程   101篇
能源动力   1353篇
轻工业   8952篇
水利工程   461篇
石油天然气   275篇
武器工业   2篇
无线电   2068篇
一般工业技术   7314篇
冶金工业   7564篇
原子能技术   236篇
自动化技术   6737篇
  2024年   102篇
  2023年   442篇
  2022年   1191篇
  2021年   1683篇
  2020年   1128篇
  2019年   1242篇
  2018年   1883篇
  2017年   1826篇
  2016年   1931篇
  2015年   1377篇
  2014年   1895篇
  2013年   3620篇
  2012年   3017篇
  2011年   3115篇
  2010年   2406篇
  2009年   2259篇
  2008年   2070篇
  2007年   1842篇
  2006年   1417篇
  2005年   1188篇
  2004年   1023篇
  2003年   1006篇
  2002年   835篇
  2001年   658篇
  2000年   580篇
  1999年   614篇
  1998年   2718篇
  1997年   1755篇
  1996年   1161篇
  1995年   669篇
  1994年   544篇
  1993年   507篇
  1992年   194篇
  1991年   174篇
  1990年   138篇
  1989年   138篇
  1988年   159篇
  1987年   147篇
  1986年   123篇
  1985年   140篇
  1984年   119篇
  1983年   89篇
  1982年   90篇
  1981年   125篇
  1980年   119篇
  1979年   54篇
  1978年   61篇
  1977年   166篇
  1976年   295篇
  1973年   66篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
An evaluation of the Spanish CSIC performance in Biotechnology, as compared with those of the French CNRS and the Italian CNR, has been carried out to determine the balance between the generation of scientific knowledge and the transfer of technology. This study shows a high scientific productivity mostly in journals with moderate impact factor, a low generation of patents and an insufficient transfer of knowledge to the Spanish companies. Other indicators confirm the existence of competitive human resources in biotechnological research producing scientific knowledge of interest for the development of patents and that cooperates successfully at European level.  相似文献   
93.
We report of a theoretical study on quasi-one dimensional unconventional charge density wave (UCDW) driven by electron–phonon interaction. Within mean field theory, we find that the wavevector dependence of the coupling leads to a momentum dependent single particle gap on the Fermi surface. The presence of small energy single particle excitations around the gap nodes significantly changes the optical conductivity compared to the conventional CDW result. In addition to that, the collective phase excitation arising from fluctuation of the order parameter leads to further qualitative changes of the conductivity and results in an effective mass that is nonmonotonic in temperature.   相似文献   
94.
The fracture stress and the critical stress intensity factor of the Fe40Ni40B20 amorphous metallic ribbons 20 μm thick were measured in the temperature range 4.2–300 K and at deformation rates from 3.3×10−6 to 1.25×10−3 m−1 with the aim to obtain more information on the condition for the onset and development of the inhomogeneous plastic deformation and fracture.  相似文献   
95.
 In this paper, a new approach for powder cold compaction simulations is presented. A density-dependent plastic model within the framework of finite strain multiplicative hyperelastoplasticity is used to describe the highly nonlinear material behaviour; the Coulomb dry friction model is used to capture friction effects at die-powder contact; and an Arbitrary Lagrangian–Eulerian (ALE) formulation is used to avoid the (usual) excessive distortion of Lagrangian meshes caused by large mass fluxes. Several representative examples, involving structured and unstructured meshes are simulated. The results obtained agree with the experimental data and other numerical results reported in the literature. It is shown that, contrary to other Lagrangian and adaptive h-remeshing approaches recently reported for this type of problems, the present approach verifies the mass conservation principle with very low relative errors (less than 1% in all ALE examples and exactly in the pure Lagrangian examples). Moreover, thanks to the use of an ALE formulation and in contrast with other simulations, the presented density distributions do not present spurious oscillations. Received: 20 March 2002 / Accepted: 15 October 2002 The partial financial support of the Ministerio de Ciencia y Tecnología (grant number DPI 2001-2204) is gratefully acknowledged.  相似文献   
96.
The present paper reports the experimental results on the microstructural and textural characterization of a hot-rolled IF steel. The IF steel was hot-rolled in multiple passes in the austenitic field (1,070 °C) followed by air-cooling. SEM, TEM, and LOM were used to image the microstructure of the material. The global texture was determined by X-ray diffraction (XRD) technique. The mesotexture of selected regions was investigated by electron backscatter diffraction (EBSD). Results show the presence of a diffuse (nearly random) and weak texture in the hot-band that consists of recrystallized polygonal grains and subgrains. The fraction of boundaries with misorientations comprised in the interval 2° ≤ ψ < 15° was found to be lower than 5%. It can be concluded that these low angle boundaries and the presence of subgrains can be associated to the existence of a few areas softened by recovery during or after hot rolling in austenitic field.  相似文献   
97.
98.
The authors report one case of multiple bilateral hydatid cyst of kidney associated to brain and spleen localizations, after intra cardiac rupture. They point out the rarity of the bilateral kidney localization of hydatidosis, explain the dissemination mode, and stress the role of computed tomography for the pre-operative diagnosis. The treatment is above all surgical and adapted to each case. The post-operative results are satisfying. Complementary medical treatment could be useful.  相似文献   
99.
The transport of chromium(VI) through a flat‐sheet supported liquid membrane containing Cyanex 921 as a carrier has been investigated. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of chromium(VI) and HCl in the feed phase, carrier concentration and diluent in the membrane and strippant concentration in the stripping phase. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921‐based flat‐sheet supported liquid membrane towards different metal ions and the behaviour of the system against other carriers are presented. Copyright © 2003 Society of Chemical Industry  相似文献   
100.
We define a lexically scoped, asynchronous and distributed π-calculus, with local communication and process migration. This calculus adopts the network-awareness principle for distributed programming and follows a simple model of distribution for mobile calculi: a lexical scope discipline combines static scoping with dynamic linking, associating channels to a fixed site throughout computation. This discipline provides for both remote invocation and process migration. A simple type system is a straightforward extension of that of the π-calculus, adapted to take into account the lexical scope of channels. An equivalence law captures the essence of this model: a process behavior depends on the channels it uses, not on where it runs.  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