全文获取类型
收费全文 | 160190篇 |
免费 | 14495篇 |
国内免费 | 11526篇 |
专业分类
化学 | 53815篇 |
晶体学 | 2059篇 |
力学 | 9348篇 |
综合类 | 1462篇 |
数学 | 53249篇 |
物理学 | 66278篇 |
出版年
2023年 | 1000篇 |
2022年 | 2734篇 |
2021年 | 2715篇 |
2020年 | 2851篇 |
2019年 | 3157篇 |
2018年 | 2865篇 |
2017年 | 2736篇 |
2016年 | 2938篇 |
2015年 | 2749篇 |
2014年 | 4644篇 |
2013年 | 8237篇 |
2012年 | 5046篇 |
2011年 | 6376篇 |
2010年 | 6448篇 |
2009年 | 11609篇 |
2008年 | 12747篇 |
2007年 | 11226篇 |
2006年 | 9742篇 |
2005年 | 7440篇 |
2004年 | 6857篇 |
2003年 | 6810篇 |
2002年 | 9570篇 |
2001年 | 5858篇 |
2000年 | 5429篇 |
1999年 | 4994篇 |
1998年 | 4309篇 |
1997年 | 3307篇 |
1996年 | 2919篇 |
1995年 | 3175篇 |
1994年 | 2995篇 |
1993年 | 2429篇 |
1992年 | 1946篇 |
1991年 | 1458篇 |
1990年 | 1273篇 |
1989年 | 1082篇 |
1988年 | 1047篇 |
1987年 | 814篇 |
1986年 | 618篇 |
1985年 | 1473篇 |
1984年 | 1069篇 |
1983年 | 749篇 |
1982年 | 1095篇 |
1981年 | 1233篇 |
1980年 | 1100篇 |
1979年 | 991篇 |
1978年 | 864篇 |
1977年 | 750篇 |
1976年 | 721篇 |
1974年 | 455篇 |
1973年 | 611篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Paul S. Wesson 《General Relativity and Gravitation》2003,35(1):111-119
Results from 5D induced-matter and membrane theory with null paths are extended to show that a particle obeys the 4D Klein-Gordon equation but with a variable mass. The Dirac equation also follows, but raises concerns about 4D quantization in the two natural 5D gauges, and reopens the question of a Regge-like trajectory for the spin angular momenta and squared masses of gravitationally-dominated systems. 相似文献
72.
Alexander Zeller 《Journal of organometallic chemistry》2006,691(21):4379-4385
The ethylene polymerization reaction of a neutral nickel catalyst was studied by DFT calculations at the Becke3LYP/6-31G(d) level of theory. As in related cases a β-agostic bond stabilizes the nickel alkyl ground states. Transition states for the insertion of the olefin show a distinct α-agostic interaction, which has not been observed for late metal polymerization catalysts before. An ethylene-alkyl complex was identified as the resting state of the reaction. The overall barrier height of the reaction amounts to 17.54 kcal/mol, which slightly increases to 17.60 kcal/mol for the polymerization of deuterated ethylene. Therefore, a small positive kinetic isotope effect (kH/kD = 1.09) can be calculated, which is caused by the α-agostic interaction in the transition state. A comparison to other late metal based polymerization systems reveals that the ethylene coordination step of highly active catalysts is significantly lower in energy compared to catalysts which are only moderately active. 相似文献
73.
75.
Inner derivations and norm equality 总被引:3,自引:0,他引:3
Mohamed Barraa Mohamed Boumazgour 《Proceedings of the American Mathematical Society》2002,130(2):471-476
We characterize when the norm of the sum of two bounded operators on a Hilbert space is equal to the sum of their norms.
76.
本文证明了Heisenberg群上Laplace算子的Dirichlet特征值的存在性,给出了特征值的估计 相似文献
77.
78.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
79.
P. Symonds 《Commentarii Mathematici Helvetici》1998,73(3):400-405
We show that the quotient space of the p-subgroup complex of a finite group by the action of the group is contractible. This was conjectured by Webb.
Received: June 28, 1996 相似文献
80.
Nobuaki Obata 《Acta Appl Math》1997,47(1):49-77
A general theory of operators on Boson Fock space is discussed in terms of the white noise distribution theory on Gaussian space (white noise calculus). An integral kernel operator is generalized from two aspects: (i) The use of an operator-valued distribution as an integral kernel leads us to the Fubini type theorem which allows an iterated integration in an integral kernel operator. As an application a white noise approach to quantum stochastic integrals is discussed and a quantum Hitsuda–Skorokhod integral is introduced. (ii) The use of pointwise derivatives of annihilation and creation operators assures the partial integration in an integral kernel operator. In particular, the particle flux density becomes a distribution with values in continuous operators on white noise functions and yields a representation of a Lie algebra of vector fields by means of such operators. 相似文献