全文获取类型
收费全文 | 290311篇 |
免费 | 3063篇 |
国内免费 | 749篇 |
专业分类
化学 | 157737篇 |
晶体学 | 4372篇 |
力学 | 12386篇 |
综合类 | 10篇 |
数学 | 33022篇 |
物理学 | 86596篇 |
出版年
2020年 | 2393篇 |
2019年 | 2606篇 |
2018年 | 3331篇 |
2017年 | 3308篇 |
2016年 | 4961篇 |
2015年 | 3077篇 |
2014年 | 4791篇 |
2013年 | 11757篇 |
2012年 | 9151篇 |
2011年 | 11219篇 |
2010年 | 7767篇 |
2009年 | 7503篇 |
2008年 | 10385篇 |
2007年 | 10667篇 |
2006年 | 10020篇 |
2005年 | 9158篇 |
2004年 | 8326篇 |
2003年 | 7547篇 |
2002年 | 7434篇 |
2001年 | 7650篇 |
2000年 | 6003篇 |
1999年 | 4639篇 |
1998年 | 4135篇 |
1997年 | 4155篇 |
1996年 | 3932篇 |
1995年 | 3613篇 |
1994年 | 3753篇 |
1993年 | 3496篇 |
1992年 | 3912篇 |
1991年 | 3883篇 |
1990年 | 3786篇 |
1989年 | 3661篇 |
1988年 | 3746篇 |
1987年 | 3673篇 |
1986年 | 3453篇 |
1985年 | 4628篇 |
1984年 | 4934篇 |
1983年 | 4097篇 |
1982年 | 4288篇 |
1981年 | 4225篇 |
1980年 | 4114篇 |
1979年 | 4108篇 |
1978年 | 4446篇 |
1977年 | 4303篇 |
1976年 | 4377篇 |
1975年 | 4056篇 |
1974年 | 4089篇 |
1973年 | 4245篇 |
1972年 | 2950篇 |
1971年 | 2484篇 |
排序方式: 共有10000条查询结果,搜索用时 495 毫秒
951.
While in the companion paper (Tonani, C. & Righetti, P. G., Electrophoresis 1991, 12, 1011-1021) we gave the general outline of our new computer program, immobilized pH gradients (IPG) simulator, able to simulate and optimize linear pH gradients for isoelectric focusing in immobilized pH gradients, in the present report we extend the application of such a program to: (i) convex exponential gradients, (ii) logarithmic and (iii) polynomial gradients. Such gradients are meant to give equal space to protein spots in complex protein mixtures (e.g., cell lysates, biological fluids) and follow the statistical distribution of protein pI values along the pH axis. They will prove of fundamental importance in two-dimensional maps, both because they optimize the spreading of spots in the two-dimensional plane and because of the excellent reproducibility of immobilized pH gradients. The following concave exponential recipes are given: pH 3-8, pH 3-9, pH 3-10, pH 3-11, pH 4-7, pH 4-8, pH 4-9, pH 4-10, pH 4-11, pH 5-8, pH 5-9, and pH 5-10, as well as the most extended pH 2.5-11 interval. Two interesting logarithmic gradients are described: pH 3-6 and pH 3-7 and one sigmoidal (derived with a polynomial of 5th degree): pH 3-11. 相似文献
952.
José A. Anquela Teresa Cortés Miguel Gómez-Lozano Mercedes Siles-Molina 《Acta Mathematica Hungarica》2004,103(3):177-196
We investigate the basic properties of the different socles that can be considered in not necessarily semiprime associative
systems. Among other things, we show that the socle defined as the sum of minimal (or minimal and trivial) inner ideals is
always an ideal. When trivial inner ideals are included, this inner socle contains the socles defined in terms of minimal
left or right ideals.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
953.
The aim of this paper is to give decompositions of some weaker forms of continuity using the concepts of classes B 1, B 2, B 3, αA and αC introduced by ourselves. 相似文献
954.
Celik Tarimci Anda? Karamustafa Kutalmi? Güven Mehmet Kabak Akgül Ye?ilada 《Analytical sciences》2003,19(9):1347-1348
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration. 相似文献
955.
Alexander G. Ramm Alexandra B. Smirnova Angelo Favini 《Annali di Matematica Pura ed Applicata》2003,182(1):37-52
A nonlinear operator equation F(x)=0, F:H→H, in a Hilbert space is considered. Continuous Newton’s-type procedures based on a construction of a dynamical system with
the trajectory starting at some initial point x
0 and becoming asymptotically close to a solution of F(x)=0 as t→+∞ are discussed. Well-posed and ill-posed problems are investigated.
Received: June 29, 2001; in final form: February 26, 2002?Published online: February 20, 2003
This paper was finished when AGR was visiting Institute for Theoretical Physics, University of Giessen. The author thanks
DAAD for support 相似文献
956.
Kentsch U. Zschornack G. Grossmann F. Ovsyannikov V. P. Ullmann F. 《Hyperfine Interactions》2003,148(1-4):237-242
Hyperfine Interactions - It is well known that many reinforced concrete structures are at risk of deterioration due to chloride ion contamination of the concrete or atmospheric carbon dioxide... 相似文献
957.
Mary E. Neubert DAVID G. ABDALLAH Jr Sandra S. Keast Julie M. Kim Soonnam Lee Ryan M. Stayshich Margaret E. Walsh Rolfe G. Petschek Shin-Tson Wu 《Liquid crystals》2003,30(6):711-731
New diphenyldiacetylenes of the type with A, B = H and/or F; m = 0, 1; n = 1-4; and X = C n H 2n + 1 , F, CF 3 or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF 3 when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices.
Four of the diacetylenes with m = 1 ( A, B = H) were also prepared ( X = C 6 H 13 , F, n = 2, 3). When X was C 6 H 13 ( n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C 6 H 13 and n = 2 had a melting temperature below room temperature. 相似文献
Four of the diacetylenes with m = 1 ( A, B = H) were also prepared ( X = C 6 H 13 , F, n = 2, 3). When X was C 6 H 13 ( n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C 6 H 13 and n = 2 had a melting temperature below room temperature. 相似文献
958.
959.
960.
Frank W. Schmidt 《Linear and Multilinear Algebra》1991,30(3):229-230
This section appears from time to time. Contributions are invited, and should be submitted to R. C. Thompson, Mathematics Department, University of California, Santa Barbara, CA 93106. 相似文献