全文获取类型
收费全文 | 386034篇 |
免费 | 4252篇 |
国内免费 | 1712篇 |
专业分类
化学 | 205301篇 |
晶体学 | 5884篇 |
力学 | 18150篇 |
综合类 | 70篇 |
数学 | 44445篇 |
物理学 | 118148篇 |
出版年
2020年 | 3444篇 |
2019年 | 4018篇 |
2018年 | 5491篇 |
2017年 | 5522篇 |
2016年 | 7628篇 |
2015年 | 4333篇 |
2014年 | 7155篇 |
2013年 | 16146篇 |
2012年 | 13260篇 |
2011年 | 16003篇 |
2010年 | 11945篇 |
2009年 | 11909篇 |
2008年 | 15019篇 |
2007年 | 15013篇 |
2006年 | 13748篇 |
2005年 | 12381篇 |
2004年 | 11409篇 |
2003年 | 10175篇 |
2002年 | 10075篇 |
2001年 | 11224篇 |
2000年 | 8458篇 |
1999年 | 6277篇 |
1998年 | 5294篇 |
1997年 | 5327篇 |
1996年 | 5118篇 |
1995年 | 4458篇 |
1994年 | 4634篇 |
1993年 | 4468篇 |
1992年 | 4911篇 |
1991年 | 5062篇 |
1990年 | 4822篇 |
1989年 | 4782篇 |
1988年 | 4654篇 |
1987年 | 4573篇 |
1986年 | 4506篇 |
1985年 | 5803篇 |
1984年 | 5903篇 |
1983年 | 4955篇 |
1982年 | 5137篇 |
1981年 | 4902篇 |
1980年 | 4502篇 |
1979年 | 5012篇 |
1978年 | 5184篇 |
1977年 | 5336篇 |
1976年 | 5414篇 |
1975年 | 4963篇 |
1974年 | 4991篇 |
1973年 | 5137篇 |
1972年 | 3907篇 |
1971年 | 3404篇 |
排序方式: 共有10000条查询结果,搜索用时 83 毫秒
921.
922.
H. L. Skala 《Geometriae Dedicata》1992,44(3):255-272
It is shown that the Laws of Pappus and Desargues may replace the Axiom of Projectivities in Menger's development of hyperbolic geometry from axioms of alignment. 相似文献
923.
Although the most important use of nuclear magnetic resonance imaging (MRI) continues to be for diagnostic medicine, recognition is being gained for many nonmedical applications. Examples include the following areas: petrogeology, food, agriculture, polymers and polymer-composites, and pharmaceuticals. These areas all involve studies of species that have short spin-spin relaxation times, and consequently need far fast gradient switching. These technical details are discussed and typical applications given. 相似文献
924.
M. N. Davies 《The Journal of the Operational Research Society》1994,45(12):1363-1373
For the last ten years or so, developments in simulation software and methodology have been focused in two areas: (1) automating the model-building process; and (2) interfacing with other techniques and systems. That both academic and commercial research continues to be carried out in these areas is evidence of the continued popularity of the simulation technique. The most popular application areas where simulation modelling is used include manufacturing (engineering and process), warehousing and communications; not surprisingly, research and developments have therefore been concentrated in these areas. This paper describes the development of a simulation model generator for a different application area, that of clerical office processing of paper and documents for financial service companies. It outlines the reasons why there is a need for such a model generator and discusses the initial design requirements. The paper goes on to detail the developments and re-defined criteria required as the model generator brief changes as a result of practical applications. 相似文献
925.
In this paper we construct a primitive, non-symmetric 3-class association scheme with parameters v = 36, v1 = 7, p111 = 0 and p211 = 4 and show that such a scheme is determined by its parameters. 相似文献
926.
Baumgarten N. Jung H. Mehlhorn K. 《Journal of Algorithms in Cognition, Informatics and Logic》1994,17(3)
The dynamic planar point location problem is the task of maintaining a dynamic set S of n nonintersecting (except possibly at endpoints) line segments in the plane under the following operations:
- • Locate (: point): Report the segment immediately above , i.e., the first segment intersected by an upward vertical ray starting at ;
- • Insert (: segment): Add segment to the collection of segments;
- • Delete (: segment): Remove segment from the collection of segments.
927.
John L. Wood Johannes Schwarzenberg Edward F. Zganjar Dubravka Rupnik 《Hyperfine Interactions》1992,75(1-4):51-58
State-of-the-art spectroscopy of nuclei far from stability has achieved an extraordinary level of sophistication and detail
in the last ten years. In principle, if a state can be populated, it can be characterized by its energy, spin, parity, and
major decay paths. Sometimes its lifetime can be measured. In practice, one is confronted with enormous complexity. To convert
raw spectroscopic data into nuclear structure data involves a complex process of disentangling gamma rays and conversion electrons
into decay schemes. Specifically, coincidence techniques, especially coincidence intensities, play a crucial role in this
process. Recent examples and methods from work done at UNISOR are presented. 相似文献
928.
M. L. Ellzey Jr. 《Journal of mathematical chemistry》1991,8(1):333-344
TheSU(2) rotation matricesD
(j), specified in terms of axis and angle of rotation, are expressed as linear combination of normalized irreducible tensorial matricces (NITM) of rankl = 0 to 2j rotated to the polar angles of the axis. The rotated NITM are constructed from spherical harmonics of the same rank. Since this formulation requires no matrix products, it may be computationally more efficient than Euler angle formulas, particularly for largej. Rotated NITM and formulas for theD
(j) withj = 1/2 andj = 1 are written out explicitly. A formula for the structure constants of the products of conformable NITM is also given in terms of 3-j and 6-j symbols. 相似文献
929.
Silver nitrate-acetonitrile and π iodine-benzene complexes in thermotropic liquid crystals have been studied by 1H, 2H, and 13C NMR spectroscopy and by optical microscopy. Evidence for at least two silver complexes in each liquid crystal is presented. 相似文献
930.
G. V. Plyatsko V. N. Maksimovich L. V. Khomlyak 《Journal of Mathematical Sciences》1992,62(1):2518-2523
We solve the thermoplastic problem for a semi-infinite plate under local nonstationary heating by heat sources. The physical equations are taken to be the relations of the nonisothermic theory of plastic flow associated with the Mises fluidity condition. The solution of the problem is constructed by the method of integral equations and the self-correcting method of sequential loading, where time is taken as the loading parameter. We carry out numerical computations of the stresses in the case of heating a plate with heat output by normal-circular heat sources. We study the problem of optimization of heating regimes in order to introduce favorable residual compressive stresses (from the point of view of hardness) in a given region of a half-plane. Two figures.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 27, 1988, pp. 29–34. 相似文献