全文获取类型
收费全文 | 286593篇 |
免费 | 3383篇 |
国内免费 | 963篇 |
专业分类
化学 | 149724篇 |
晶体学 | 4334篇 |
力学 | 11641篇 |
综合类 | 6篇 |
数学 | 35970篇 |
物理学 | 89264篇 |
出版年
2021年 | 2325篇 |
2020年 | 2586篇 |
2019年 | 2880篇 |
2018年 | 3737篇 |
2017年 | 3626篇 |
2016年 | 5739篇 |
2015年 | 3914篇 |
2014年 | 5509篇 |
2013年 | 13397篇 |
2012年 | 10746篇 |
2011年 | 12605篇 |
2010年 | 8832篇 |
2009年 | 8571篇 |
2008年 | 11513篇 |
2007年 | 11378篇 |
2006年 | 10659篇 |
2005年 | 9852篇 |
2004年 | 8836篇 |
2003年 | 7778篇 |
2002年 | 7474篇 |
2001年 | 8121篇 |
2000年 | 6360篇 |
1999年 | 4954篇 |
1998年 | 4154篇 |
1997年 | 4012篇 |
1996年 | 3985篇 |
1995年 | 3525篇 |
1994年 | 3528篇 |
1993年 | 3591篇 |
1992年 | 3707篇 |
1991年 | 3777篇 |
1990年 | 3563篇 |
1989年 | 3414篇 |
1988年 | 3442篇 |
1987年 | 3312篇 |
1986年 | 3156篇 |
1985年 | 4261篇 |
1984年 | 4442篇 |
1983年 | 3558篇 |
1982年 | 3764篇 |
1981年 | 3681篇 |
1980年 | 3539篇 |
1979年 | 3619篇 |
1978年 | 3703篇 |
1977年 | 3632篇 |
1976年 | 3732篇 |
1975年 | 3378篇 |
1974年 | 3392篇 |
1973年 | 3467篇 |
1972年 | 2391篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
P. V. Dvornikov 《Russian Physics Journal》2006,49(4):392-401
A standard model Lagrangian is constructed making the pseudo-Finsleroid generalization of the Yang-Mills field equation by
the conformal method. The Higgs field potential is suggested that ensures generation of particle masses caused by the spontaneous
symmetry breaking. After transition to the conformal coordinates, the expressions obtained assume the standard form that in
many cases allows the results of pseudo-Euclidean theory to be used in calculations of the Feynman diagrams.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 44–51, April, 2006. 相似文献
92.
A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback
circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space.
Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly
twofold. 相似文献
93.
Elena Larraz Carlos Elvira Julio San Romn 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1641-1649
This article explores the synthesis of a novel methacrylic macromonomer with an amphiphilic character derived from poly(ethylene glycol) tert‐octylphenyl ether (MT) and its respective homopolymer. To know their reactivity in radical copolymerization reactions with methyl methacrylate (MMA), a model monomer (MTm) was synthesized to determine the reactivity ratios and compare them with the low molar fractions of copolymers of MT with MMA because they were difficult to isolate. They were rMTm = 0.97 and rMMA = 0.95. The compositional diagrams when representing the weight fraction of MT and MTm in the feed and the copolymer suggested that a clear correlation exists between the experimental points of the model monomer MTm and the macromonomer MT ones, suggesting that the length of the side poly(ethylene oxide) chain does not affect the reactivity of the methacrylic double bond in the prepared monomers for this type of polymerization reaction. The reactivity ratios of the copolymers have a tendency for the formation of random or Bernoullian copolymers. The glass‐transition temperatures (Tg's) of the prepared copolymers were determined by differential scanning calorimetry, deviated from the Fox equation, and discussed on the basis of treatments that consider the influence of the monomeric units along the copolymer chains, determining the Tg of the corresponding alternating dyads. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1641–1649, 2003 相似文献
94.
L. Villa P. D' Agati C. Mansueto C. Pellerito M. Scopelliti T. Fiore L. Nagy L. Pellerito 《应用有机金属化学》2003,17(2):106-112
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
95.
María G. Armentano Ricardo G. Durn 《Numerical Methods for Partial Differential Equations》2003,19(5):653-664
In this article we analyze the effect of mass‐lumping in the linear triangular finite element approximation of second‐order elliptic eigenvalue problems. We prove that the eigenvalue obtained by using mass‐lumping is always below the one obtained with exact integration. For singular eigenfunctions, as those arising in non convex polygons, we prove that the eigenvalue obtained with mass‐lumping is above the exact eigenvalue when the mesh size is small enough. So, we conclude that the use of mass‐lumping is convenient in the singular case. When the eigenfunction is smooth several numerical experiments suggest that the eigenvalue computed with mass‐lumping is below the exact one if the mesh is not too coarse. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 653–664, 2003 相似文献
96.
97.
98.
Piryatinskiĭ Yu. P. Yaroshchuk O. V. Dolgov L. A. Bidna T. V. Enke D. 《Optics and Spectroscopy》2004,97(4):537-542
Optics and Spectroscopy - The fluorescence of the nematic liquid crystal n-butyl-n′-methoxyazoxybenzene (BMAOB) in the form of a layer and in porous glasses with pores of different diameter... 相似文献
99.
Aji P. Mathew Gabriel Groeninckx G. H. Michler H. J. Radusch Sabu Thomas 《Journal of Polymer Science.Polymer Physics》2003,41(14):1680-1696
The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (Tg's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the Tg values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003 相似文献
100.