全文获取类型
收费全文 | 911篇 |
免费 | 17篇 |
国内免费 | 9篇 |
专业分类
化学 | 305篇 |
晶体学 | 5篇 |
力学 | 20篇 |
数学 | 335篇 |
物理学 | 272篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 14篇 |
2014年 | 13篇 |
2013年 | 45篇 |
2012年 | 35篇 |
2011年 | 32篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 33篇 |
2007年 | 42篇 |
2006年 | 50篇 |
2005年 | 44篇 |
2004年 | 38篇 |
2003年 | 27篇 |
2002年 | 28篇 |
2001年 | 12篇 |
2000年 | 24篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 23篇 |
1992年 | 28篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有937条查询结果,搜索用时 421 毫秒
81.
A new general-relativistic theory of cosmology, the dynamical variables of whichare those of Hubble's, namely distances and redshifts, is presented. The theorydescribes the universe as having a three-phase evolution with a deceleratingexpansion followed by a constant and an accelerating expansion, and it predictsthat the universe is now in the latter phase. The theory is actually a generalizationof Hubble's law taking gravity into account by means of Einstein's theory ofgeneral relativity. The equations obtained for the universe expansion are elegantand very simple. It is shown, assuming 0 = 0.24, that the time at which theuniverse goes over from a decelerating to an accelerating expansion, i.e., theconstant expansion phase, occurs at 0.03 from the big bang, where is theHubble time in vacuum. Also, at that time the cosmic radiation temperature was11 K. Recent observations of distant supernovae imply, in defiance of expectations,that the universe's growth is accelerating, contrary to what has always beenassumed, that the expansion is slowing down due to gravity. Our theory confirmsthese recent experimental results by showing that the universe now is definitelyin a stage of accelerating expansion. 相似文献
82.
Moshe Carmeli 《International Journal of Theoretical Physics》2000,39(5):1397-1404
For disk galaxies the fourth power of the circular velocity 4
c
of stars around thecore of the galaxy is proportional to the luminosity L, 4
c
L (Tully—Fisher law).Since L is proportional to the mass M of the galaxy, it follows that 4
c
M.Newtonian mechanics, however, yields 2
c
= GM/r for a circular motion. In orderto rectify this big difference, astronomers assume the existence of dark matter.We derive the equation of motion of a star moving in the central field of a galaxyand show that, for a circular motion, it yields a term of the form 4
c
GMc/,where G is Newton's gravitational constant, c is the speed of light, and is theHubble time. This puts in doubt the existence of halo dark matter for galaxies. 相似文献
83.
In this paper we investigate spectral matrices, i.e., matrices with equal spectral and numerical radii. Various characterizations and properties of these matrices are given. 相似文献
84.
We determine the smallest number f(n,k) such that every (0,1)-matrix of order n what zero main diagonal which has at least f(n,k) 1's contains an irreducible, principal submatrix of order K. We characterize those matrices with f(n,k)-1 l's having no irreducible, principal submatrix of order k 相似文献
85.
86.
87.
88.
Gy?rgy G?nd?s Gy?rgy Dombi James C. Orr 《Monatshefte für Chemie / Chemical Monthly》2000,20(3):1055-1059
The synthesis of a new chiral boroxazolidine was achieved which was used to control the stereochemistry of the borane reduction of the 20-keto group of steroids. The otherwise hardly accessible 20α-(20S)-alcohol can thus be prepared in a yield of 91%. 相似文献
89.
90.
An amended formula for the decay of radioactivematerial is presented. It is a modification of thestandard exponential formula. The new formula appliesfor long cosmic times comparable to the Hubble time. It reduces to the standard formula for shorttimes. It is shown that the material decays faster thanexpected. The application of the new formula to directmeasurements of the age of the universe and its implications are briefly discussed. 相似文献