全文获取类型
收费全文 | 163852篇 |
免费 | 1205篇 |
国内免费 | 550篇 |
专业分类
化学 | 71359篇 |
晶体学 | 2147篇 |
力学 | 10197篇 |
综合类 | 1篇 |
数学 | 40261篇 |
物理学 | 41642篇 |
出版年
2022年 | 822篇 |
2021年 | 1105篇 |
2020年 | 1150篇 |
2019年 | 1287篇 |
2018年 | 12061篇 |
2017年 | 11951篇 |
2016年 | 8395篇 |
2015年 | 2119篇 |
2014年 | 2362篇 |
2013年 | 4176篇 |
2012年 | 7364篇 |
2011年 | 14422篇 |
2010年 | 8665篇 |
2009年 | 8965篇 |
2008年 | 10089篇 |
2007年 | 12093篇 |
2006年 | 3499篇 |
2005年 | 4176篇 |
2004年 | 4146篇 |
2003年 | 4346篇 |
2002年 | 3458篇 |
2001年 | 2683篇 |
2000年 | 2074篇 |
1999年 | 1527篇 |
1998年 | 1386篇 |
1997年 | 1257篇 |
1996年 | 1182篇 |
1995年 | 1026篇 |
1994年 | 961篇 |
1993年 | 959篇 |
1992年 | 977篇 |
1991年 | 1041篇 |
1990年 | 976篇 |
1989年 | 991篇 |
1988年 | 898篇 |
1987年 | 837篇 |
1986年 | 805篇 |
1985年 | 934篇 |
1984年 | 1024篇 |
1983年 | 869篇 |
1982年 | 899篇 |
1981年 | 802篇 |
1980年 | 758篇 |
1979年 | 829篇 |
1978年 | 943篇 |
1977年 | 943篇 |
1976年 | 838篇 |
1975年 | 801篇 |
1974年 | 804篇 |
1973年 | 794篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
81.
A modified criterion of the SM perturbative consistency is proposed. It is based on the analytic properties of the two-loop SM running couplings. Under the criterion adopted, the Higgs mass up to 380 GeV might not give rise to strong coupling prior to the Planck scale. This means that the light Higgs boson is possibly preferred for reasons other than the SM perturbative consistency, i.e., for reasons beyond the SM. 相似文献
82.
Volkan Kseli Zakir M. O. Rzaev Erhan Pikin 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1580-1593
Stimuli‐responsive poly[(N‐isopropylacrylamide‐co‐maleic anhydride)‐g‐poly(ethylene oxide)]/poly(ethylene imine) macrobranched macrocomplexes were synthesized by (1) the radical copolymerization of N‐isopropylacrylamide and maleic anhydride with α,α′‐azobisisobutyronitrile as an initiator in 1,4‐dioxane at 65 °C under a nitrogen atmosphere, (2) the polyesterification (grafting) of prepared poly(N‐isopropylacrylamide‐co‐maleic anhydride) containing less than 20 mol % anhydride units with α‐hydroxy‐ω‐methoxy‐poly(ethylene oxide)s having different number‐average molecular weights (Mn = 4000, 10,000, or 20,000), and (3) the incorporation of macrobranched copolymers with poly(ethylene imine) (Mn = 60,000). The composition and structure of the synthesized copolymer systems were determined by Fourier transform infrared, 1H and 13C NMR spectroscopy, and chemical and elemental analyses. The important properties of the copolymer systems (e.g., the viscosity, thermal and pH sensitivities, and lower critical solution temperature behavior) changed with increases in the molecular weight, composition, and length of the macrobranched hydrophobic domains. These copolymers with reactive anhydride and carboxylic groups were used for the stabilization of penicillin G acylase (PGA). The conjugation of the enzyme with the copolymers significantly increased the thermal stability of PGA (three times at 45 °C and two times at 65 °C). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1580–1593, 2003 相似文献
83.
Finite element analysis of fluid flow with moving free surface has been performed in 2‐D and 3‐D. The new VOF‐based numerical algorithm that has been proposed by the present authors (Int. J. Numer. Meth. Fluids, submitted) was applied to several 2‐D and 3‐D free surface flow problems. The proposed free surface tracking scheme is based on two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby‐cell to determine the fluid volume flux at each cell boundary. The proposed numerical algorithm has been applied to 2‐D and 3‐D cavity filling and sloshing problems in order to demonstrate the versatility and effectiveness of the scheme. The proposed numerical algorithm resolved successfully the free surfaces interacting with each other. The simulated results demonstrated applicability of the proposed numerical algorithm to the practical problems of large free surface motion. It has been also demonstrated that the proposed free surface tracking scheme can be easily implemented in any irregular non‐uniform grid systems and can be extended to 3‐D free surface flow problems without additional efforts. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
84.
The method of numerical integration of the classical equations of motion was used to study interaction of a model two-electron atom with ultrashort laser pulses. Mechanisms and specific features of the ionization process were analyzed in a broad range of laser-field parameters. 相似文献
85.
86.
A graph with n vertices that contains no triangle and no 5-cycle and minimum degree exceeding n/4 contains an independent set with at least (3n)/7 vertices. This is best possible. The proof proceeds by producing a homomorphism to the 7-cycle and invoking the No Homomorphism Lemma. For k ≥ 4, a graph with n vertices, odd girth 2k+1, and minimum degree exceeding n/(k+1) contains an independent set with at least kn/(2k+1) vertices; however, we suspect this is not best possible. © 1993 John Wiley & Sons, Inc. 相似文献
87.
In this paper, we explore a weakness of a specific implementation of the analytic center cutting plane method applied to convex optimization problems, which may lead to weaker results than Kelley's cutting plane method. Improvements to the analytic center cutting plane method are suggested, and tested on some example problems. 相似文献
88.
A. F. Blinokhvatov O. V. Markovtseva M. N. Nikolaeva 《Chemistry of Heterocyclic Compounds》1992,28(3):266-268
Substituted 4H-pyrans were obtained in high preparative yields by the reaction of 1,5-diketones with acetic anhydride and boron trifluoride etherate in diethyl ether. It is assumed that the heterocyclization of 1,5-diketones includes a step involving the formation and transformations of an acyloxy carbonium ion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 320–322, March, 1992. 相似文献
89.
V. L. Rusinov A. Yu. Petrov O. N. Chupakhin 《Chemistry of Heterocyclic Compounds》1992,28(11):1335-1339
Two variants of a synthesis for nitropyrazolopyridines from aminopyrazoles and two- or three-carbon nitrosynthons are examined.For Communication 19 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1560–1564, November, 1992. 相似文献
90.