全文获取类型
收费全文 | 1393篇 |
免费 | 28篇 |
国内免费 | 9篇 |
专业分类
化学 | 742篇 |
晶体学 | 3篇 |
力学 | 34篇 |
数学 | 365篇 |
物理学 | 286篇 |
出版年
2023年 | 7篇 |
2022年 | 21篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 39篇 |
2015年 | 37篇 |
2014年 | 37篇 |
2013年 | 98篇 |
2012年 | 106篇 |
2011年 | 76篇 |
2010年 | 44篇 |
2009年 | 47篇 |
2008年 | 84篇 |
2007年 | 73篇 |
2006年 | 70篇 |
2005年 | 68篇 |
2004年 | 73篇 |
2003年 | 51篇 |
2002年 | 31篇 |
2001年 | 31篇 |
2000年 | 32篇 |
1999年 | 29篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 9篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 6篇 |
1960年 | 3篇 |
排序方式: 共有1430条查询结果,搜索用时 15 毫秒
71.
72.
73.
Formation of back corona and its effect on the voltage–current characteristics, etc., have been analysed by several authors. It has also been examined how the harmful effect of back corona can be reduced, for example by the application of pulse energisation. However, to find an optimal solution, modelling of the back corona effect is necessary. Different back corona models were created to estimate the time of its development, the change in current–voltage characteristics, the decrease in particle charge and finally, the collection efficiency of the ESP with back corona. In this paper the authors present an improved numerical ESP model that is capable of determining the parameters of back corona in such cases, when pulse energisation is applied for the power supply of the electrostatic precipitator. Based on the modular structure of the model, different modules calculate the distribution of gas velocity, electric field intensity, particle charging and particle movement. All these parameters are important to determine the properties of back corona while it feeds back on these parameters; therefore iteration is necessary to obtain reliable result. The harmful effects of back corona can be characterised with the help of the evaluation of calculated results. 相似文献
74.
Tin-Yau Tam 《Proceedings of the American Mathematical Society》1999,127(1):35-44
For any , let be the following subset of :
We show that if , then is always convex. When , it is an ellipsoid, probably degenerate. The convexity result is best possible in the sense that if we have defined similarly, then there are examples which fail to be convex when and .
The set is also symmetric about the origin for all , and contains the origin when . Equivalent statements of this result are given. The convexity result for is similar to Au-Yeung and Tsing's extension of Westwick's convexity result for .
75.
Luen-fai Tam 《Proceedings of the American Mathematical Society》1998,126(10):3097-3108
In this note, we will prove that under certain conditions, the space of polynomial growth harmonic functions and harmonic forms with a fixed growth rate on manifolds which are asymptotically nonnegatively curved is finite dimensional. This is a partial generalization of the works of Li and Colding-Minicozzi. We will also give an explicit estimate for the dimension in case the manifold is a complete surface of finite total curvature. This is a generalization to harmonic forms of the work of Li and the author.
76.
77.
S.W. Tam 《Tetrahedron letters》1974,15(27):2385-2388
78.
Tamás Hausel 《Central European Journal of Mathematics》2005,3(1):26-38
Building on a recent paper [8], here we argue that the combinatorics of matroids are intimately related to the geometry and topology of toric hyperkähler varieties. We show that just like toric varieties occupy a central role in Stanley’s proof for the necessity of McMullen’s conjecture (or g-inequalities) about the classification of face vectors of simplicial polytopes, the topology of toric hyperkähler varieties leads to new restrictions on face vectors of matroid complexes. Namely in this paper we will give two proofs that the injectivity part of the Hard Lefschetz theorem survives for toric hyperkähler varieties. We explain how this implies the g-inequalities for rationally representable matroids. We show how the geometrical intuition in the first proof, coupled with results of Chari [3], leads to a proof of the g-inequalities for general matroid complexes, which is a recent result of Swartz [20]. The geometrical idea in the second proof will show that a pure O-sequence should satisfy the g-inequalities, thus showing that our result is in fact a consequence of a long-standing conjecture of Stanley. 相似文献
79.
We have demonstrated all-optical packet add-drop for all-optical packet-switched networks. Intelligent all-optical add-drop of packets is performed, based on all-optical processing of packet headers. The header and payload rates are 5 and 10 Gbits/s, respectively. 相似文献
80.
Synthesis of novel 6,11-O-bridged bicyclic ketolides via a palladium-catalyzed bis-allylation 总被引:2,自引:0,他引:2
A bridging chemistry process was developed to form an ether bridge between 6-O and 11-O of erythromycin A via a tandem or stepwise palladium-catalyzed bis-pi-allylation. By applying this bridging process, new 6,11-O-bridged bicyclic ketolides (BBKs) were synthesized. These BBKs showed good antibacterial activities against the macrolide-susceptible strains as well as mef-resistant strains and served as a good core for further modifications to study the structure-activity relationship (SAR) and to overcome bacterial resistance. [reaction: see text] 相似文献