全文获取类型
收费全文 | 19226篇 |
免费 | 1469篇 |
国内免费 | 5075篇 |
专业分类
化学 | 14147篇 |
晶体学 | 412篇 |
力学 | 565篇 |
综合类 | 225篇 |
数学 | 7981篇 |
物理学 | 2440篇 |
出版年
2024年 | 32篇 |
2023年 | 216篇 |
2022年 | 354篇 |
2021年 | 402篇 |
2020年 | 471篇 |
2019年 | 453篇 |
2018年 | 487篇 |
2017年 | 562篇 |
2016年 | 620篇 |
2015年 | 508篇 |
2014年 | 858篇 |
2013年 | 1513篇 |
2012年 | 1572篇 |
2011年 | 1036篇 |
2010年 | 906篇 |
2009年 | 1239篇 |
2008年 | 1414篇 |
2007年 | 1488篇 |
2006年 | 1371篇 |
2005年 | 1294篇 |
2004年 | 1151篇 |
2003年 | 993篇 |
2002年 | 881篇 |
2001年 | 680篇 |
2000年 | 697篇 |
1999年 | 656篇 |
1998年 | 572篇 |
1997年 | 521篇 |
1996年 | 451篇 |
1995年 | 397篇 |
1994年 | 349篇 |
1993年 | 239篇 |
1992年 | 291篇 |
1991年 | 217篇 |
1990年 | 172篇 |
1989年 | 124篇 |
1988年 | 104篇 |
1987年 | 69篇 |
1986年 | 77篇 |
1985年 | 66篇 |
1984年 | 55篇 |
1983年 | 31篇 |
1982年 | 39篇 |
1981年 | 22篇 |
1980年 | 29篇 |
1979年 | 20篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 8篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献
52.
Laurent Bruneau 《Reports on Mathematical Physics》2004,54(2):169-199
We study Pauli-Fierz Hamiltonians-self-adjoint operators describing a small quantum system interacting with a bosonic field. Using quadratic form techniques, we extend the results of Dereziński-Gérard and Gérard about the self-adjointness, the location of the essential spectrum and the existence of a ground state to a large class of Pauli-Fierz Hamiltonians. 相似文献
53.
S.V. Astashkin F.A. Sukochev 《Journal of Mathematical Analysis and Applications》2007,336(2):1231-1258
We catalogue all Marcinkiewicz function and sequence spaces with the Banach-Saks property and present necessary and sufficient conditions for a wide subclass of spaces to possess the p-Banach-Saks property, 1<p<∞. We apply our results to several open problems. 相似文献
54.
55.
56.
Ignacio Villanueva 《Mathematische Nachrichten》2003,250(1):98-103
We clarify and prove in a simpler way a result of Taskinen about symmetric operators on C(Kn), K an uncountable metrizable compact space. To do this we prove that, for any compact space K and any n ∈ ?, the symmetric injective n–tensor product of C(K), , is complemented in C(BC(K)*), a result of independent interest. The techniques we develop allow us to extend the result in several directions. We also show that the hypothesis of metrizability and uncountability cannot be removed. 相似文献
57.
Alexander J. Zaslavski 《Journal of Mathematical Analysis and Applications》2007,335(2):962-973
The Tonelli existence theorem in the calculus of variations and its subsequent modifications were established for integrands f which satisfy convexity and growth conditions. In this paper we consider a large class of optimal control problems which is identified with a complete metric space of integrands without convexity assumptions and show that for a generic integrand the corresponding optimal control problem possesses a unique solution and this solution is Lipschitzian. 相似文献
58.
Martin I. Karakhanyan 《Journal of Contemporary Mathematical Analysis (Armenian Academy of Sciences)》2007,42(3):146-150
The paper proves some general facts on commutators that refer to Fuglede-Putnam classical theorem in the spectral theory of not necessarily selfadjoint operators. 相似文献
59.
60.
By using the tools of statistical physics and recent investigations of the scaling properties of different complex networks,
the structural and evolving properties of the Chinese railway network (CRN) is studied. It has been verified that the CRN
has the same small-world properties of the Indian railway network (IRN). According to the class of small-world networks, we
believe the CRN is a single scale. In addition, a novel result is obtained. Measurements on the CRN indicate that the rate
at which nodes acquire links depends on the node’s degree and follows a power law.
相似文献