全文获取类型
收费全文 | 10614篇 |
免费 | 905篇 |
国内免费 | 1058篇 |
专业分类
化学 | 7809篇 |
晶体学 | 144篇 |
力学 | 63篇 |
综合类 | 32篇 |
数学 | 2958篇 |
物理学 | 1044篇 |
无线电 | 527篇 |
出版年
2024年 | 18篇 |
2023年 | 128篇 |
2022年 | 125篇 |
2021年 | 157篇 |
2020年 | 247篇 |
2019年 | 298篇 |
2018年 | 221篇 |
2017年 | 260篇 |
2016年 | 272篇 |
2015年 | 395篇 |
2014年 | 469篇 |
2013年 | 910篇 |
2012年 | 629篇 |
2011年 | 604篇 |
2010年 | 551篇 |
2009年 | 593篇 |
2008年 | 696篇 |
2007年 | 654篇 |
2006年 | 540篇 |
2005年 | 516篇 |
2004年 | 480篇 |
2003年 | 431篇 |
2002年 | 611篇 |
2001年 | 330篇 |
2000年 | 322篇 |
1999年 | 263篇 |
1998年 | 255篇 |
1997年 | 206篇 |
1996年 | 164篇 |
1995年 | 136篇 |
1994年 | 135篇 |
1993年 | 103篇 |
1992年 | 94篇 |
1991年 | 76篇 |
1990年 | 77篇 |
1989年 | 86篇 |
1988年 | 60篇 |
1987年 | 44篇 |
1986年 | 44篇 |
1985年 | 53篇 |
1984年 | 46篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1979年 | 30篇 |
1978年 | 20篇 |
1974年 | 13篇 |
1973年 | 15篇 |
1971年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Igor V. Dolgachev 《Milan Journal of Mathematics》2004,72(1):163-187
We review the classical definition of the dual homogeneous form of arbitrary even degree which generalizes the well-known notion of the dual quadratic form. Following the ideas of S. Mukai we apply this construction to the study of the varieties parametrizing representations of a homogeneous polynomial as a sum of powers of linear forms.Research supported in part by NSF Grant DMS 0245203.Lecture held in the Seminario Matematico e Fisico on October 15, 2003Received: April, 2004 相似文献
92.
A ring is said to be a left essential extension of a reduced ring (domain) if it contains a left ideal which is a reduced ring (domain) and intersects nontrivially every nonzero twosided ideal of the ring. We prove that every ring which is a left essential extension of a reduced ring is a subdirect sum of rings which are essential extensions of domains, but the converse implication does not hold. We give some applications of this result and discuss several related questions.Received: 6 January 2003 相似文献
93.
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
94.
N[a,b]类中边界Nevanlinna-Pick插值(I) 总被引:1,自引:1,他引:0
用所谓的Hankel向量方法求解N[a,b]函数类中带边界插值数据的Nevanlina-Pick插值(BNP(N[a,b]))问题,并建立BNP(N[a,b])问题与[a,b]上的某种带约束条件的Hausdorff矩量问题之间等价的可解条件以及解之间明确的一一对应关系.这使得当BNP(N[a,b])问题有多解时,能通过带约束条件的矩量问题的可解性准则和解获得BNP(N[a,b])问题的可解性准则和解的参数化描述,而在唯一解的情况下,通过BNP(N[a,b])问题解的存在唯一性准则和唯一解来获得带约束条件的 相似文献
95.
Jarosł Spychała 《Research on Chemical Intermediates》2007,33(6):481-486
Evidence for a stereoinduction profile of the reaction of N-methyl-1,3-diaminopropane with acyl chlorides has been provided. A possibility to engage in intramolecular CH2⋯HN and Cl⋯H-N interactions and the proton migration process to the methylamino group leads to the E secondary amides carrying the N⋯H+⋯N or N-H⋯N bridges, that show unusual spectroscopic images. Empirical relations between the Δδ
C chemical shift differences, the polarizability of the CO(S) groups and hydrogen bonding strength have been found. Both 1H-15N-GHSQC and GHMBC experiments provide insight into the nature of hydrogen bonding and confirm the cyclic array of atoms. 相似文献
96.
Approximation of a laminated microstructure for a rotationally invariant,double well energy density 总被引:3,自引:0,他引:3
Mitchell Luskin 《Numerische Mathematik》1996,75(2):205-221
Summary. We give error estimates for the approximation of a laminated microstructure which minimizes the energy for a rotationally invariant, double well energy density . We present error estimates for the convergence of the deformation in the convergence of directional derivatives of the deformation in the “twin planes,” the weak convergence of the deformation
gradient, the convergence of the microstructure (or Young measure) of the deformation gradients, and the convergence of nonlinear
integrals of the deformation gradient.
Received July 25, 1995 / Revised version received November 20, 1995 相似文献
97.
98.
Michael Bildhauer 《manuscripta mathematica》1998,97(3):389-406
H?lder continuity up to the free boundary is proved for minimizing solutions if they meet the supporting surface in an angle
which is bounded away from zero. The problem is localized by proving the continuity of the distance function, a result which
is also true for stationary points.
Received: 14 April 1998 相似文献
99.
The hyperspaces of strongly countable dimensional compacta of positive dimension and of strongly countable dimensional continua of dimension greater than 1 in the Hilbert cube are homeomorphic to the Hurewicz set of all nonempty countable closed subsets of the unit interval [0,1]. These facts hold true, in particular, for covering dimension dim and cohomological dimension dimG, where G is any Abelian group. 相似文献
100.
The proportional hazards regression model, when subjects enter the study in a staggered fashion, is studied. A strong martingale approach is used to model the two-time parameter counting processes. It is shown that well-known univariate results such as weak convergence and martingale inequalities can be extended to this two-dimensional model. Strong martingale theory is also used to prove weight convergence of a general weighted goodness-of-fit process and its weighted bootstrap counterpart. 相似文献