全文获取类型
收费全文 | 26431篇 |
免费 | 614篇 |
国内免费 | 161篇 |
专业分类
化学 | 17720篇 |
晶体学 | 214篇 |
力学 | 681篇 |
综合类 | 1篇 |
数学 | 4451篇 |
物理学 | 4139篇 |
出版年
2021年 | 179篇 |
2020年 | 219篇 |
2019年 | 285篇 |
2018年 | 235篇 |
2017年 | 209篇 |
2016年 | 459篇 |
2015年 | 348篇 |
2014年 | 462篇 |
2013年 | 1335篇 |
2012年 | 1213篇 |
2011年 | 1537篇 |
2010年 | 789篇 |
2009年 | 637篇 |
2008年 | 1380篇 |
2007年 | 1432篇 |
2006年 | 1425篇 |
2005年 | 1430篇 |
2004年 | 1262篇 |
2003年 | 1057篇 |
2002年 | 1030篇 |
2001年 | 377篇 |
2000年 | 305篇 |
1999年 | 249篇 |
1998年 | 287篇 |
1997年 | 312篇 |
1996年 | 399篇 |
1995年 | 300篇 |
1994年 | 285篇 |
1993年 | 293篇 |
1992年 | 274篇 |
1991年 | 242篇 |
1990年 | 225篇 |
1989年 | 243篇 |
1988年 | 275篇 |
1987年 | 253篇 |
1986年 | 249篇 |
1985年 | 388篇 |
1984年 | 437篇 |
1983年 | 324篇 |
1982年 | 429篇 |
1981年 | 403篇 |
1980年 | 345篇 |
1979年 | 336篇 |
1978年 | 348篇 |
1977年 | 336篇 |
1976年 | 277篇 |
1975年 | 274篇 |
1974年 | 264篇 |
1973年 | 243篇 |
1972年 | 146篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
It is proved that for finite groups G, the probability thattwo randomly chosen elements of G generate a soluble subgrouptends to zero as the index of the largest soluble normal subgroupof G tends to infinity. 相似文献
73.
John C. Baez 《Foundations of Physics》1989,19(1):91-95
E. P. Wigner's argument that the probability of the existence of self-reproducing units, e.g., organisms, is zero according to standard quantum theory is stated and analyzed. Theorems are presented which indicate that Wigner's mathematical result in fact should not be interpreted as asserting the improbability of self-reproducing units. 相似文献
74.
The synthesis of the title compounds has been achieved in concise, highly regiocontrolled fashion from commercially available (+)-sclareolide. In addition, we offer evidence that the structure of a newly reported natural product from Zingiber ottensii is incorrect. 相似文献
75.
76.
John Ginsburg 《Order》1989,6(2):137-157
For a partially ordered setP and an elementx ofP, a subsetS ofP is called a cutset forx inP if every element ofS is noncomparable tox and every maximal chain ofP meets {x}∪S. We letc(P) denote the smallest integerk such that every elementx ofP has a cutsetS with ‖S‖?k: Ifc(P)?n we say thatP has then-cutset property. Our results bear on the following question: givenP, what is the smallestn such thatP can be embedded in a partially ordered set having then-cutset property? As usual, 2 n denotes the Boolean lattice of all subsets of ann-element set, andB n denotes the set of atoms and co-atoms of 2 n . We establish the following results: (i) a characterization, by means of forbidden configurations, of whichP can be embedded in a partially ordered set having the 1-cutset property; (ii) ifP contains a copy of 2 n , thenc(P)?2[n/2]?1; (iii) for everyn>3 there is a partially ordered setP containing 2 n such thatc(P)<c(2 n ); (iv) for every positive integern there is a positive integerN such that, ifB m is contained in a partially ordered set having then-cutset property, thenm?N. 相似文献
77.
An algorithm is introduced and shown to lead to a unique infinite product representation for a given formal power series A(z) with A(0) = 1. The infinite product is , where all bn ≠ 0, rn
, and rn+1 > rn. The degree of approximation by the polynomial (1 + b1zr1) · · · (1 + bnzrn) is also considered. 相似文献
78.
79.
An interesting question in symplectic geometry concerns whether or not a closed symplectic manifold can have a free symplectic circle action with orbits contractible in the manifold. Here we present a c-symplectic example, thus showing that the problem is truly geometric as opposed to topological. Furthermore, we see that our example is the only known example of a c-symplectic manifold having non-trivial fundamental group and Lusternik-Schnirelmann category precisely half its dimension.
80.