全文获取类型
收费全文 | 69786篇 |
免费 | 5137篇 |
国内免费 | 6704篇 |
专业分类
化学 | 27270篇 |
晶体学 | 324篇 |
力学 | 6460篇 |
综合类 | 1232篇 |
数学 | 24990篇 |
物理学 | 21351篇 |
出版年
2023年 | 586篇 |
2022年 | 1182篇 |
2021年 | 1300篇 |
2020年 | 1366篇 |
2019年 | 1649篇 |
2018年 | 1318篇 |
2017年 | 1560篇 |
2016年 | 1762篇 |
2015年 | 1622篇 |
2014年 | 2352篇 |
2013年 | 4426篇 |
2012年 | 2678篇 |
2011年 | 3111篇 |
2010年 | 2649篇 |
2009年 | 3758篇 |
2008年 | 4199篇 |
2007年 | 4434篇 |
2006年 | 4151篇 |
2005年 | 3523篇 |
2004年 | 3235篇 |
2003年 | 3294篇 |
2002年 | 3037篇 |
2001年 | 2550篇 |
2000年 | 2491篇 |
1999年 | 2252篇 |
1998年 | 2096篇 |
1997年 | 1722篇 |
1996年 | 1539篇 |
1995年 | 1397篇 |
1994年 | 1294篇 |
1993年 | 1100篇 |
1992年 | 1077篇 |
1991年 | 824篇 |
1990年 | 684篇 |
1989年 | 593篇 |
1988年 | 543篇 |
1987年 | 425篇 |
1986年 | 366篇 |
1985年 | 430篇 |
1984年 | 423篇 |
1983年 | 209篇 |
1982年 | 338篇 |
1981年 | 401篇 |
1980年 | 300篇 |
1979年 | 290篇 |
1978年 | 220篇 |
1977年 | 205篇 |
1976年 | 154篇 |
1974年 | 109篇 |
1973年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions. 相似文献
222.
223.
Bogdan Nita 《General Relativity and Gravitation》2003,35(10):1865-1868
Algebraically special gravitational fields are described using algebraic and differential invariants of the Weyl tensor. A type III invariant is also given and calculated for Robinson-Trautman spaces. 相似文献
224.
225.
In the present paper, Daubechies' wavelets and the computation of their scaling coefficients are briefly reviewed. Then a new method of computation is proposed. This method is based on the work [7] concerning a new orthonormality condition and relations among scaling moments, respectively. For filter lengths up to 16, the arising system can be explicitly solved with algebraic methods like Gröbner bases. Its simple structure allows one to find quickly all possible solutions. 相似文献
226.
Rafał Bocian Thorsten Holm Andrzej Skowroński 《Central European Journal of Mathematics》2004,2(1):67-75
Auslander’s representation dimension measures how far a finite dimensional algebra is away from being of finite representation
type. In [1], M. Auslander proved that a finite dimensional algebra A is of finite representation type if and only if the representation dimension of A is at most 2. Recently, R. Rouquier proved that there are finite dimensional algebras of an arbitrarily large finite representation
dimension. One of the exciting open problems is to show that all finite dimensional algebras of tame representation type have
representation dimension at most 3. We prove that this is true for all domestic weakly symmetric algebras over algebraically
closed fields having simply connected Galois coverings. 相似文献
227.
可交换随机变量序列的随机极限定理 总被引:1,自引:0,他引:1
本文讨论了可交换随机变量序列{Xn:n≥1}的极限定理,得到了可交换随机变量序列的随机强大数律及加权和定理,并推广了文[4]中的结果. 相似文献
228.
229.
We consider the problems of (1) longest common subsequence (LCS) of two given strings in the case where the first may be shifted by some constant (that is, transposed) to match the second, and (2) transposition-invariant text searching using indel distance. These problems have applications in music comparison and retrieval. We introduce two novel techniques to solve these problems efficiently. The first is based on the branch and bound method, the second on bit-parallelism. Our branch and bound algorithm computes the longest common transposition-invariant subsequence (LCTS) in time O((m2+loglogσ)logσ) in the best case and O((m2+logσ)σ) in the worst case, where m and σ, respectively, are the length of the strings and the size of the alphabet. On the other hand, we show that the same problem can be solved by using bit-parallelism and thus obtain a speedup of O(w/logm) over the classical algorithms, where the computer word has w bits. The advantage of this latter algorithm over the present bit-parallel ones is that it allows the use of more complex distances, including general integer weights. Since our branch and bound method is very flexible, it can be further improved by combining it with other efficient algorithms such as our novel bit-parallel algorithm. We experiment on several combination possibilities and discuss which are the best settings for each of those combinations. Our algorithms are easily extended to other musically relevant cases, such as δ-matching and polyphony (where there are several parallel texts to be considered). We also show how our bit-parallel algorithm is adapted to text searching and illustrate its effectiveness in complex cases where the only known competing method is the use of brute force. 相似文献
230.