全文获取类型
收费全文 | 3720篇 |
免费 | 427篇 |
国内免费 | 282篇 |
专业分类
化学 | 484篇 |
晶体学 | 11篇 |
力学 | 151篇 |
综合类 | 65篇 |
数学 | 2796篇 |
物理学 | 922篇 |
出版年
2024年 | 6篇 |
2023年 | 48篇 |
2022年 | 71篇 |
2021年 | 102篇 |
2020年 | 120篇 |
2019年 | 104篇 |
2018年 | 104篇 |
2017年 | 121篇 |
2016年 | 137篇 |
2015年 | 123篇 |
2014年 | 198篇 |
2013年 | 355篇 |
2012年 | 167篇 |
2011年 | 193篇 |
2010年 | 186篇 |
2009年 | 238篇 |
2008年 | 246篇 |
2007年 | 215篇 |
2006年 | 199篇 |
2005年 | 177篇 |
2004年 | 137篇 |
2003年 | 156篇 |
2002年 | 147篇 |
2001年 | 122篇 |
2000年 | 105篇 |
1999年 | 97篇 |
1998年 | 100篇 |
1997年 | 83篇 |
1996年 | 54篇 |
1995年 | 31篇 |
1994年 | 32篇 |
1993年 | 23篇 |
1992年 | 31篇 |
1991年 | 27篇 |
1990年 | 22篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 6篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1974年 | 1篇 |
1973年 | 5篇 |
排序方式: 共有4429条查询结果,搜索用时 172 毫秒
31.
A new sample business survey for agriculture, the REA survey, and a project of integration with the FADN network (RICA in
Italy) have significantly changed the production of statistical information nowadays available with reference to the agricultural
sector. On the basis of this relevant information, new economic analyses are being developed on farms’ performance, agricultural
households’ income and the Common Agricultural Policy (CAP). In this paper the authors estimate the relationship between the
levels of variables of interest and their sampling errors using models in order to improve the accessibility of the information
on estimates accuracy to the final users (agricultural analysts, policy makers).
The paper is the result of a joint research of the three authors. Sections 1–3 and 6 by Pizzoli, Sects. 4 and 5 by Rondinelli,
Sect. 7 by Filiberti, conclusions joint to the three authors. 相似文献
32.
We study the existence and the continuity properties of the boundary values on the real axis of the resolvent of a self-adjoint operator H in the framework of the conjugate operator method initiated by Mourre. We allow the conjugate operator A to be the generator of a C0-semigroup (finer estimates require A to be maximal symmetric) and we consider situations where the first commutator [H,iA] is not comparable to H. The applications include the spectral theory of zero mass quantum field models. 相似文献
33.
构造了第孙中禹种强度不等的非对称三态叠加多模叠加态光场|ψ1(ABC)〉q.利用多模压缩态理论研究了态|ψ1(ABC)〉q第一正交分量高次和压缩.结果发现:①当构成态|ψ1(ABC)〉q的三个多模相干态光场的强度不相等时,在一定条件下,态|ψ1(ABC)〉q的第一正交分量可出现任意幂次的高次和压缩.②当上述的三个多模相干态光场强度相等时,态|ψ1(ABC)〉q的第一正交分量的高次和压缩现象消失.在这种情况下,态|ψ1(ABC)〉q的第一正交分量恒处于NH最小测不准态. 相似文献
34.
《Magnetic resonance in chemistry : MRC》2003,41(8):585-588
A novel, radical responsive MRI contrast agent based on a gadolinium chelate conjugated to a liposome through a disulfide linker was synthesized, with the aim of pursuing the in vivo mapping of radicals. The liposome was prepared by incorporating a thiol‐activated phospholipid, which was subsequently reacted with a gadolinium chelate containing a free thiol group. The long reorientational motion of the supramolecular adduct endows the paramagnetic agent with a relaxivity significantly higher than that of the free complex. The disulfide bond represents a radical‐sensitive moiety and a large decrease in contrast efficacy (T1 relaxivity) is shown upon its cleavage. A preliminary assessment of the system was made by means of in vitro gamma‐irradiation and thiol–disulfide bond exchange with dithiothreitol. Both methods showed a clear dose‐dependent decrease in T1‐relaxivity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
35.
Nguyen Minh Chuong Bui Kien Cuong 《Proceedings of the American Mathematical Society》2004,132(12):3589-3597
A class of Cauchy problems for interesting complicated periodic pseudodifferential equations is considered. By the Galerkin-wavelet method and with weak solutions one can find sufficient conditions to establish convergence estimates of weak Galerkin-wavelet solutions to a Cauchy problem for this class of equations.
36.
37.
杨青 《高等学校计算数学学报(英文版)》2003,12(2)
The mathematical model of semiconductor devices is described by the initial boundary value problem of a system of three nonlinear partial differential equations. One equation in elliptic form is for the electrostatic potential; two equations of convection-dominated diffusion type are for the electron and hole concentrations. Finite volume element procedure are put forward for the electrostatic potential, while upwind 相似文献
38.
The main aim of this paper is to provide convergence analysis of Quasi-Wilson nonconforming finite element to Maxwell's equations under arbitrary quadrilateral meshes.The error estimates are derived,which are the same as those for conforming elements under conventional regular meshes. 相似文献
39.
40.
讨论了横向位移双曝光散斑图维纳谱的信息分布,并由此导出杨氏纹图的一般表达式。讨论了条纹可见度与应变,面内转动,照明光束直径与条纹图图空间坐标的关系,指出了在条纹可见度影响下最大可见条纹数目。还讨论了散斑衬比与衍射晕的关系。 相似文献