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   241390篇
  免费   2629篇
  国内免费   427篇
电工技术   4292篇
综合类   257篇
化学工业   39403篇
金属工艺   9379篇
机械仪表   7394篇
建筑科学   5451篇
矿业工程   1391篇
能源动力   5158篇
轻工业   24833篇
水利工程   2482篇
石油天然气   5092篇
武器工业   32篇
无线电   25045篇
一般工业技术   44800篇
冶金工业   45372篇
原子能技术   5952篇
自动化技术   18113篇
  2021年   2112篇
  2019年   2018篇
  2018年   3491篇
  2017年   3426篇
  2016年   3691篇
  2015年   2241篇
  2014年   3901篇
  2013年   10191篇
  2012年   6155篇
  2011年   8309篇
  2010年   6555篇
  2009年   7240篇
  2008年   7588篇
  2007年   7716篇
  2006年   6893篇
  2005年   6051篇
  2004年   5817篇
  2003年   5601篇
  2002年   5676篇
  2001年   5562篇
  2000年   5386篇
  1999年   5303篇
  1998年   12583篇
  1997年   8901篇
  1996年   6858篇
  1995年   5330篇
  1994年   4736篇
  1993年   4625篇
  1992年   3667篇
  1991年   3387篇
  1990年   3593篇
  1989年   3473篇
  1988年   3304篇
  1987年   2895篇
  1986年   2933篇
  1985年   3373篇
  1984年   3219篇
  1983年   2892篇
  1982年   2738篇
  1981年   2821篇
  1980年   2720篇
  1979年   2624篇
  1978年   2684篇
  1977年   2949篇
  1976年   3808篇
  1975年   2368篇
  1974年   2242篇
  1973年   2376篇
  1972年   1971篇
  1971年   1858篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Blaco CE 《Textile rental》1992,75(6):24-6, 28, 30 passim
Get ready to update and improve your company's safety program. On pages 24-38, you'll find a comprehensive guide to safe industry practices to enhance your operation and help you stay in compliance with OSHA regulations such as the General Duty Clause and the Right-to-Know law. Achieving a safe, healthy, productive, and profitable business doesn't happen by accident. It takes upper-management commitment to improve equipment, procedures, and employee training. Managers have a personal and a legal responsibility for employees' safety on the job. Don't delay safety improvements!  相似文献   
992.
Computer-assisted simulation has been used to study the effect of collagen content on the biological value of meat proteins. It has been shown that an increase in the collagen content from 2·5% to 15-20% of the total amount of proteins contained in minced meat tangibly enhances protein utilization for tissue synthesis. Hence, the above collagen content in meat products heightens their nutritional and biological value and renders them more suited for human metabolism.  相似文献   
993.
A foil of polypropylene is heat-treated in such a manner that a growing 2D cell-model is formed. A Rosiwal's line is placed into the totally primarily crystallized foil. The nucleus-coordinates of grains intercepting Rosiwal's line are measured. From these effective nuclei we determine at fraction transformedF = 1/4, 1/2 and 3/4 the distributions of grain-lengths and melt-lengths. Further we determine properties which are derived from the chord intercepts at a given F. Experimentally we find that the values (Poisson distribution of nuclei, chord intercepts, etc.) are in good agreement with the growing 2D cell-model.  相似文献   
994.
Monolayer isotherms were measured for 15, 18, and 20 K for para-hydrogen adsorbed on exfoliated graphite foam, and for the second, third, and fourth layers in the temperature interval of 8 to 20 K, using the standard volumetric method. From the data, the isosteric heat of adsorption, molar entropies and internal energies were obtained as a function of coverage. The values for coverages above the third layer were compared to those at the p-H2 bulk triple point, showing that, within our experimental uncertainty, the results are closer to the values of bulk solid para-hydrogen. Critical temperatures for the second and third layers and the triple point temperature for the second layer, were determined, yielding values of Tc2 = (10.0±0.1) K, Tc3 = (11.0±0.5) K and Tt2 = (6.5±0.1) K respectively. Features occurring along the monolayer coverages are compared to transitions which occur in the para-hydrogen phase diagrams adsorbed on graphite, obtained from heat capacity measurements by other authors. From the isotherms, compressibilities were calculated as a function of coverage for several temperatures. Whenever possible the obtained results were compared to existing data in the literature.  相似文献   
995.
Boundary conditions are discussed for spin dynamics equations in dilute spin-polarized quantum gases. The bulk equations have the macroscopic hydrodynamic form even when mean free paths of the particles are large, and the main question is whether a supplementary hydrodynamic boundary condition is valid. Different boundary processes are considered including spin-conserving and non-conserving reflections, slip, formation of adsorbed surface layers, etc. The macroscopic boundary condition fails in the cases of very effective surface processes with violation of time-reversal symmetry (e.g. spin-lattice relaxation) or very high surface-induced diffusion rates. Otherwise, the surface processes are described by a simple boundary condition or by -type singularities in bulk equations. The meaning of different macroscopic parameters is clarified. The formation of dense adsorbed boundary layers changes the frequency shifts and linewidths of spin-wave resonances because of effective exchanges between surface and bulk particles and strong interactions within the boundary layers. Here the broadening of resonances is explained not only by additional surface dissipation (diffusion), but also by dephasing processes originating from a renormalization of the molecular field in the boundary layers. The results explain recent experiments by the Cornell group.  相似文献   
996.
The empowerment of service workers: what, why, how, and when   总被引:17,自引:0,他引:17  
In recent years, businesses have rushed to adopt an empowerment approach to service delivery in which employees face customers "free of rulebooks," encouraged to do whatever is necessary to satisfy them. But that approach may not be right for everyone. Bowen and Lawler look at the benefits and costs of empowering employees, the range of management practices that empower employees to varying degrees, and key business characteristics that affect the choice of approaches. Managers need to make sure that there is a good fit between their organizational needs and their approach to frontline employees.  相似文献   
997.
The authors discuss the results of ophthalmodynamometric tests used for the assessment of cerebro-retinal vessels reactivity following carbon dioxide baths and "peat collars". An analysis of systemic and local blood pressure in the ophthalmic artery measured with Weigelin and Lobstein technique enables to assess changes in blood pressures following a/m balneologic procedures. It was found that blood pressure does not change parallelly due to the mechanism of cerebral autoregulation. Transient decrease in blood pressure in the ophthalmic artery is produced by the dilatation of the internal carotid artery indicating a potent vasodilating action of carbon dioxide.  相似文献   
998.
Scientific-Production Association "Krasnaya Zvezda." Translated from Atomnaya Énergiya, Vol. 73, No. 5, pp. 346–350, November, 1992.  相似文献   
999.
Shape optimal design is the synthesis of structural analysis and mathematical programming (MP) combined with methods of computer aided geometric design (CAGD) and behaviour sensitivity analysis (SA). The main aspect in optimal shape design is the integration of these disciplines. At the same time an efficient and well-posed model must be formulated for the overall optimization problem. The present contribution deals with the hierarchy of the different modelling levels and numerical techniques of the design process. It will be shown for the frequency tuning of a bell how the individual disciplines can be identified step by step in the optimization procedure of the program CARAT (Computer Aided Research and Analysis Tool).Presented at NATO ASI Optimization of Large Structural Systems, Berchtesgarden, Sept. 23 – Oct. 4, 1991  相似文献   
1000.
Hydrogeologic parameters evaluated for rocks investigated in deep well testing projects for nuclear waste repository feasibility are transmissivity, hydraulic conductivity and storativity. Such studies have been carried out in rock formations of different geologic types, origins and ages for nuclear waste management agencies in North America and Europe. From transient pressure testing, an assessment of static pressure in selected fracture zones was measured from which a profile with depth was developed using modelling techniques. As well, temperatures of formation fluids and hence thermal gradients have also been provided. Hydrogeologic parameters are commonly used in risk analysis for repositories with respect to the possible escape of contaminants and worst case scenarios. The parameters are related to the rate of possible radionuclide migration into the biosphere. The techniques of the investigation and analysis methods of this work have been fully described in the literature. This paper is the first to date, however, to compare results from testing in differen geologic environments. High transmissivity zones have been observed in the upper few hundred metres of granite formations. Below that depth, the rock is more competent and discrete zones of higher permeability occur less frequently. Our studies show, however, that in these rocks, zones of high hydraulic conductivity do not always correspond to zones of high fracture frequency. Most formation pressure profiles have a vertical gradient of about 10 kPa/m. In discrete zones, deviations from this trend can occur due to vertical inhomogeneity in the rock. Thermal gradients vary considerably from one investigation site to another. For example, in the Canadian Shield, gradients are of the order of 1.0 degree C per 100 m, whereas in similar rock types in Europe, the gradient is up to 4.0 degrees C per 100 m.  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