全文获取类型
收费全文 | 648887篇 |
免费 | 7056篇 |
国内免费 | 2118篇 |
专业分类
化学 | 332792篇 |
晶体学 | 8225篇 |
力学 | 31341篇 |
综合类 | 19篇 |
数学 | 98773篇 |
物理学 | 186911篇 |
出版年
2021年 | 4822篇 |
2020年 | 5433篇 |
2019年 | 5959篇 |
2018年 | 17421篇 |
2017年 | 17105篇 |
2016年 | 17008篇 |
2015年 | 7839篇 |
2014年 | 11198篇 |
2013年 | 26690篇 |
2012年 | 23380篇 |
2011年 | 34066篇 |
2010年 | 22571篇 |
2009年 | 22680篇 |
2008年 | 28765篇 |
2007年 | 30631篇 |
2006年 | 21394篇 |
2005年 | 20253篇 |
2004年 | 18870篇 |
2003年 | 17355篇 |
2002年 | 16296篇 |
2001年 | 17163篇 |
2000年 | 13290篇 |
1999年 | 10282篇 |
1998年 | 8698篇 |
1997年 | 8453篇 |
1996年 | 8184篇 |
1995年 | 7128篇 |
1994年 | 7079篇 |
1993年 | 6972篇 |
1992年 | 7628篇 |
1991年 | 7788篇 |
1990年 | 7404篇 |
1989年 | 7226篇 |
1988年 | 7086篇 |
1987年 | 6984篇 |
1986年 | 6591篇 |
1985年 | 8641篇 |
1984年 | 8905篇 |
1983年 | 7056篇 |
1982年 | 7359篇 |
1981年 | 7243篇 |
1980年 | 6742篇 |
1979年 | 7311篇 |
1978年 | 7583篇 |
1977年 | 7448篇 |
1976年 | 7396篇 |
1975年 | 6882篇 |
1974年 | 6851篇 |
1973年 | 6982篇 |
1972年 | 4842篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献
962.
M. Ohsaki 《Archive of Applied Mechanics (Ingenieur Archiv)》2003,73(3-4):241-251
Summary Characteristics of optimal solutions under nonlinear buckling constraints are investigated by using a bar-spring model. It is demonstrated that optimization under buckling constraints of a symmetric system often leads to a structure with hill-top branching, where a limit point and bifurcation points coincide. A general formulation is derived for imperfection sensitivity of the critical load factor corresponding to a hill-top branching point. It is shown that the critical load is not imperfection-sensitive even for the case where an asymmetric bifurcation point exists at the limit point. 相似文献
963.
Florin Ambro 《manuscripta mathematica》2003,111(1):43-49
We prove a precise inversion of adjunction formula for the log variety (ℂ
d
+1,X), where X is a non-degenerate hypersurface. As a corollary, the minimal log discrepancies of non-degenerate normal hypersurface singularities
are bounded by dimension.
Received: 17 September 2002 / Revised version: 22 November 2002
Published online: 14 February 2003
Current address: DPMMS, CMS, University of Cambridge, Wilberforce Road, Cambridge CB3 0WB, England. e-mail: f.ambro@dpmms.cam.ac.uk
Mathematics Subject Classification (2000): Primary 14B05; Secondary 14M25, 52B20 相似文献
964.
In this paper, we use weighted modules ω(?)(f,t)w to study the pointwise approximation on Szasz-type operators, and obtain the direct and converse theorem, as well as characterizations of the pointwise approximation of Jacobi-weighted Szasz-type operators. 相似文献
965.
E. Rebollar M. Oujja M. Castillejo S. Georgiou 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1357-1360
Optical emission and laser-induced fluorescence spectroscopies (OES and LIF) are employed to examine the plume ejected into vacuum upon UV pulsed laser ablation (248 nm, 20 ns, and 266 nm, 5 ns) of poly(methyl methacrylate) PMMA films doped with photostable compounds naphthalene (NapH) and phenanthrene (PhenH), and their photolabile iodide derivatives iodonaphthalene (NapI) and iodophenanthrene (PhenI). Spontaneous emissions observed in the irradiation of NapI and PhenI sensitised films can be assigned to excited products resulting from photodissociation of the dopants and to excited C2, CH, and CN radicals. The presence in the plume of ground state products is revealed by LIF upon excitation at 266 nm. Measurements of the dependence of the spontaneous and LIF emissions on distance to the surface, ablation fluence, and flight velocities of species are discussed with reference to the mechanistic implications derived from the measurements. PACS 52.38.Mf; 61.82.Pv; 82.50 相似文献
966.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献
967.
E. P. Clark 《Fresenius' Journal of Analytical Chemistry》1940,120(3-4):124-125
Ohne Zusammenfassung 相似文献
968.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224
969.
970.
C. Foces‐Foces M. Lpez‐Rodríguez C. Prez 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(2):o95-o97
The title compound, C12H21NO3, crystallizes in two polymorphic forms, viz. the tetragonal form described here and the monoclinic form described previously [Foces‐Foces, López‐Rodríguez, Pérez, Martín & Pérez‐Hernández (2007). Cryst. Growth Des. 7 , 905–911]. The differences in the conformations of the hydroxymethyl and methylaminocarbonyl substituents have important consequences in the hydrogen‐bond interaction motifs and, therefore, in the packing arrangements. These forms are concomitant polymorphs with melting points differing by 3 K. 相似文献