全文获取类型
收费全文 | 870885篇 |
免费 | 10771篇 |
国内免费 | 2236篇 |
专业分类
电工技术 | 16013篇 |
综合类 | 772篇 |
化学工业 | 135434篇 |
金属工艺 | 33975篇 |
机械仪表 | 26958篇 |
建筑科学 | 21485篇 |
矿业工程 | 4997篇 |
能源动力 | 22435篇 |
轻工业 | 76035篇 |
水利工程 | 9284篇 |
石油天然气 | 16410篇 |
武器工业 | 52篇 |
无线电 | 99300篇 |
一般工业技术 | 170971篇 |
冶金工业 | 155082篇 |
原子能技术 | 18481篇 |
自动化技术 | 76208篇 |
出版年
2021年 | 7472篇 |
2019年 | 7126篇 |
2018年 | 12063篇 |
2017年 | 12330篇 |
2016年 | 13013篇 |
2015年 | 8691篇 |
2014年 | 14393篇 |
2013年 | 40734篇 |
2012年 | 22937篇 |
2011年 | 31519篇 |
2010年 | 25101篇 |
2009年 | 27990篇 |
2008年 | 28977篇 |
2007年 | 28841篇 |
2006年 | 25332篇 |
2005年 | 23024篇 |
2004年 | 22250篇 |
2003年 | 21722篇 |
2002年 | 20982篇 |
2001年 | 20607篇 |
2000年 | 19449篇 |
1999年 | 19742篇 |
1998年 | 45631篇 |
1997年 | 33241篇 |
1996年 | 26013篇 |
1995年 | 20184篇 |
1994年 | 18133篇 |
1993年 | 17636篇 |
1992年 | 13528篇 |
1991年 | 12962篇 |
1990年 | 12735篇 |
1989年 | 12305篇 |
1988年 | 11817篇 |
1987年 | 10413篇 |
1986年 | 10174篇 |
1985年 | 11948篇 |
1984年 | 11029篇 |
1983年 | 10098篇 |
1982年 | 9264篇 |
1981年 | 9300篇 |
1980年 | 8888篇 |
1979年 | 8931篇 |
1978年 | 8630篇 |
1977年 | 9827篇 |
1976年 | 12704篇 |
1975年 | 7580篇 |
1974年 | 7248篇 |
1973年 | 7208篇 |
1972年 | 6116篇 |
1971年 | 5599篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Modern methods of determining fracture resistance are analyzed. The necessity of developing a crucially new method based on edge chipping of a brittle material is shown. The results of experimental studies are presented. The applicability of the method to the comparative fracture resistance evaluation of ceramics is substantiated. 相似文献
972.
A problem of deformation of a curved shell loaded by internal pressure, axial force, and temperature difference is discussed. Physical equations are derived whereby the displacements and angles of rotation of the line of centers of mass of cross sections of a shell are related to loading parameters. A general constitutive set of equations for a curved element during its deformation is given. Using a method of initial parameters, an analytical solution is obtained for the differential equations for displacements and angles of rotation of the center line allowing for the action of distributed forces and moments. 相似文献
973.
Thin hard coatings fracture propagation during the impact test 总被引:2,自引:0,他引:2
One of the most significant applications of the impact test is to investigate thin hard coatings fatigue properties. Herein the test conditions and duration up to the film damage initiation, are considered in order to determine the critical stresses associated with the coating fatigue strength. Moreover, the subsequent film damage propagation is a significant mechanism as well, since it refers to the ability of the coating to withstand loads after its fatigue damage initiation. In order to describe the film fracture propagation the failed area ratio was introduced and an algorithm to determine this magnitude developed, based on the analysis of imprint scanning electron microscopy graphs. The application of the coating failed area ratio will be demonstrated in various impact test film cases, also with superficial thin layers. The top layers do not affect, in general, the failure initiation of the basic coating. However, according to the obtained results, the superficial films influence the basic coating failure propagation rate during the impact test. 相似文献
974.
Boundary element methods (BEMs) are approved methods for an efficient numerical solution of problems, which are based on a Laplace equation. Here, the solution of electrostatic field problems, steady current flow field problems, and magnetostatic field problems is considered. Focus of this paper is on investigations of accuracy of direct formulations, which are based on Green's theorem. Different types of coupling of computational domains are examined with respect to accuracy and convergence behavior of iterative solvers of the linear system of equations. Furthermore, the influence of singular and nearly singular integrals and the influence of matrix compression techniques to the accuracy of the solution are observed 相似文献
975.
L. N. Dmitruk S. Kh. Batygov L. V. Moiseeva O. B. Petrova M. N. Brekhovskikh V. A. Fedorov 《Inorganic Materials》2007,43(7):793-796
We have studied the effect of In3+, Pb2+, Gd3+, and Cl (heavier ions) substitutions for Al3+, Ba2+, La3+, and F? on the crystallization stability and UV/IR optical properties of HBLAN fluorohafnatc glasses (HfF4-BaF2-LaF3-AlF3-NaF system). We obtained stable glasses containing InF3 and BaCl2 instead of AlF3 and BaF2, respectively, and offering increased IR transmission. The presence of CCl4 in the process atmosphere and the removal of oxygen-containing impurities via directional solidification are shown to have an advantageous effect on the optical quality of the glasses. The fluoride-chloride glasses are capable of accommodating about 1.5 times higher levels of rare-earth activators in comparison with their fluoride analogs. 相似文献
976.
977.
Colour is the most widely used attribute in image retrieval and object recognition. A technique known as histogram intersection has been widely studied and is considered to be effective for color‐image indexing. The key issue of this algorithm is the selection of an appropriate color space and optimal quantization of the selected color space. The goal of this article is to measure the model performance in predicting human judgment in similarity measurement for various images, to explore the capability of the model with a wide set of color spaces, and to find the optimal quantization of the selected color spaces. Six color spaces and twelve quantization levels are involved in evaluating the performance of histogram intersection. The categorical judgment and rank order experiments were conducted to measure image similarity. The CIELAB color space was found to perform at least as good as or better than the other color spaces tested, and the ability to predict image similarity increased with the number of bins used in the histograms, for up to 512 bins (8 per channel). With more than 512 bins, further improvement was negligible for the image datasets used in this study. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 265–274, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20122 相似文献
978.
Visualizing multivariate functions, data, and distributions 总被引:1,自引:0,他引:1
979.
The use of a sequential linear complementarity problem (SLCP) algorithm for finding a global minimum of bilinear programming problem (BLP) or a concave quadratic program (CQP) is examined. The algorithm consists of solving a sequence of linear complementarity problems (LCP). A branch-and-bound method is also considered in this study. This algorithm is based on the reformulation of a BLP into an LCP with a linear function to minimize. Computational experience with small and medium scale BLPs and CQPs indicates that the SLCP algorithm is quite efficient in finding a global minimum (or at least a solution that is quite near the optimum), but it is, in general, unable to establish that such a solution has been found. An algorithm to find a lower-bound for the BLP can overcome this drawback in some cases. Furthermore the SLCP algorithm is shown to be robust and compares favorably with the branch-and-bound method and another alternative technique. 相似文献
980.
Cinematic primitives for multimedia 总被引:5,自引:0,他引:5
The development of robust frameworks in interactive multimedia for representing story elements to the machine so that they can be retrieved in multiple contexts is addressed. Interactive multimedia is discussed as a user-directed form of storytelling, and the nature of cinematic storytelling is examined. It is proposed that content can be represented in layers. This model for layered information will allow programs to take advantage of the relation between cinematic sequences and the world they represent. The collection of content by the camera and microphone is considered in this context. The use of the methodology to build meaningful, context-rich sequences is discussed 相似文献