全文获取类型
收费全文 | 1271篇 |
免费 | 40篇 |
国内免费 | 7篇 |
专业分类
化学 | 914篇 |
晶体学 | 13篇 |
力学 | 17篇 |
数学 | 153篇 |
物理学 | 221篇 |
出版年
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 18篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 26篇 |
2013年 | 65篇 |
2012年 | 46篇 |
2011年 | 79篇 |
2010年 | 38篇 |
2009年 | 50篇 |
2008年 | 68篇 |
2007年 | 90篇 |
2006年 | 81篇 |
2005年 | 92篇 |
2004年 | 78篇 |
2003年 | 60篇 |
2002年 | 66篇 |
2001年 | 17篇 |
2000年 | 23篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1971年 | 4篇 |
排序方式: 共有1318条查询结果,搜索用时 62 毫秒
91.
Homogeneous ZnO Nanoparticles by Flame Spray Pyrolysis 总被引:2,自引:0,他引:2
Zinc oxide (ZnO) nanoparticles were made by flame spray pyrolysis (FSP) of zinc acrylate–methanol–acetic acid solution. The effect of solution feed rate on particle specific surface area (SSA) and crystalline size was examined. The average primary particle diameter can be controlled from 10 to 20nm by the solution feed rate. All powders were crystalline zincite. The primary particle diameter observed by transmission electron microscopy (TEM) was in agreement with the equivalent average primary particle diameter calculated from the SSA as well as with the crystalline size calculated from the X-ray diffraction (XRD) patterns for all powders, indicating that the primary particles were rather uniform in diameter and single crystals. Increasing the solution feed rate increases the flame height, and therefore coalescence and/or surface growth was enhanced, resulting in larger primary particles. Compared with ZnO nanoparticles made by other processes, the FSP-made powder exhibits some of the smallest and most homogeneous primary particles. Furthermore, the FSP-made powder has comparable BET equivalent primary particle diameter with but higher crystallinity than sol–gel derived ZnO powders. 相似文献
92.
The relationship between cosmological solutionsof five-dimensional Space-Time-Matter (STM) theory anda Generalized Scalar-Tensor (GST) theory is investigatedin which the cosmological term Lambda depends not only on a scalar field but also onits time derivative
.Identification of these solutions allows us to solve forthe functional form of the cosmological term, and mayhave relevance for the early Universe. 相似文献
93.
Takao Yamazaki 《Proceedings of the American Mathematical Society》1999,127(5):1269-1274
For an element of the Brauer group of a curve over a local field, we define the ``Swan conductor' of , which measures the wildness of the ramification of . We give a relation between and Swan conductors for Brauer groups of henselian discrete valuation fields defined by Kato.
94.
For a smooth projective irreducible algebraic curve C of odd gonality, the maximal possible dimension of the variety of special linear systems W
d
r
(C) is d-3r by a result of M. Coppens et al. Furthermore it is known that if the maximum dimension of W(C) for a curve C of odd gonality is attained then C is of very special type of curves by the recent progress made by G. Martens. The purpose of this paper is to chase an extension of the result of G. Martens; if dim W(C)=d-3r-1 for a curve C of odd gonality for some dg-4 and r1, then C must be either a smooth plane sextic, a pentagonal curve of bounded genus or a smooth plane octic. 相似文献
95.
Hegedus L Kirschner N Wittmann M Simon P Noszticzius Z Amemiya T Ohmori T Yamaguchi T 《Chaos (Woodbury, N.Y.)》1999,9(2):283-297
The polarization curve of an acid-base interface in a hydrogel medium has a diode characteristic. Two of each such electrolyte diodes can be combined to give an electrolyte transistor. When a salt is added to the alkaline or to the acidic part of a reverse biased electrolyte diode, the current response is highly nonlinear. If the salt is added to the acidic side, even bistability can be observed. This bistability can generate complex oscillations in a base-acid-base electrolyte transistor. These nonlinear effects are studied experimentally and theoretically. While the nonlinear salt effect can be explained with the Nernst-Planck equations, to understand the bistable behavior further investigations are necessary. (c) 1999 American Institute of Physics. 相似文献
96.
Hitoshi Suzuki Akira Ishiguro Takao Nishizeki 《Journal of Algorithms in Cognition, Informatics and Logic》1992,13(4)
This paper proposes a new data structure called a variable-priority queue. The queue supports, in addition to the ordinary queue operations, an operation MIN to find an item of minimum key and three operations to change keys of items. Any sequence of these m operations can be processed in O(m) time. Furthermore, as its application, this paper presents two efficient algorithms for network problems. The first finds multicommodity flows in cycles in linear time. The second, using the first, finds edge-disjoint paths connecting terminal pairs in a doughnut-shaped grid. The grid is bounded by two nested rectangles, and terminals are specified on the two rectangular boundaries outside the four corners. If there are k terminal pairs and all the terminals are ordered in clockwise order around rectangles, then the algorithm decides in O(k) time whether there are edge-disjoint paths connecting terminals in the grid, and actually finds edge-disjoint paths in O(k log k) time. 相似文献
97.
Takao Fukui 《General Relativity and Gravitation》1988,20(10):1037-1045
In order to study the origin of the fundamental constants and Dirac's large number, a cosmological solution in vacuum is presented in a seven-dimensional universe which is defined by adding extra three coordinates (e
2
G/c
4)1/2, (hG/c
3)1/2 and (Gm/c
2) to the four-dimensional spacetime coordinates. It has common features with Chodos-Detweiler's solution. The parameters appearing in this theory are estimated to meet the conditions required by the cosmological first-order phase transition and Dirac's large number hypothesis. 相似文献
98.
99.
Kunihiko Takabe Suguru Ohkawa Toshio Sato Gia Hien Tang Takao Katagiri 《Tetrahedron letters》1980,21(40):3883-3884
Dimerization of 3-methyl-3-butenenitrile (1) by lithium dialkylamide gave selectively 3,5,5-trimethyl-1-amino-4-cyanocyclohexa-1,3-diene (2), which was easily hydrolyzed by aqueous acid to afford 4-cyanoisophorone (3,5,5-trimethyl-4-cyano-cyclohex-2-enone) (3) quantitatively. 相似文献
100.