全文获取类型
收费全文 | 7983篇 |
免费 | 372篇 |
国内免费 | 3篇 |
专业分类
化学 | 5430篇 |
晶体学 | 69篇 |
力学 | 300篇 |
数学 | 1189篇 |
物理学 | 1370篇 |
出版年
2023年 | 58篇 |
2022年 | 75篇 |
2021年 | 104篇 |
2020年 | 160篇 |
2019年 | 139篇 |
2018年 | 197篇 |
2017年 | 152篇 |
2016年 | 314篇 |
2015年 | 254篇 |
2014年 | 261篇 |
2013年 | 579篇 |
2012年 | 533篇 |
2011年 | 603篇 |
2010年 | 325篇 |
2009年 | 284篇 |
2008年 | 556篇 |
2007年 | 557篇 |
2006年 | 494篇 |
2005年 | 460篇 |
2004年 | 339篇 |
2003年 | 315篇 |
2002年 | 261篇 |
2001年 | 107篇 |
2000年 | 95篇 |
1999年 | 77篇 |
1998年 | 63篇 |
1997年 | 44篇 |
1996年 | 77篇 |
1995年 | 60篇 |
1994年 | 52篇 |
1993年 | 51篇 |
1992年 | 42篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 49篇 |
1984年 | 36篇 |
1983年 | 17篇 |
1982年 | 51篇 |
1981年 | 37篇 |
1980年 | 50篇 |
1979年 | 40篇 |
1978年 | 30篇 |
1977年 | 29篇 |
1976年 | 40篇 |
1975年 | 37篇 |
1974年 | 26篇 |
1973年 | 25篇 |
排序方式: 共有8358条查询结果,搜索用时 15 毫秒
11.
12.
For more than 25 yearsJΨ production has helped to sharpen our understanding of QCD. In proton induced reaction some observations are rather well understood
while others are still unclear. The current status of the theory ofJΨ production will be sketched, paying special attention to the issues of formation time andJΨ re-interaction in a nuclear medium. 相似文献
13.
14.
In order to investigate the relative effects of the differences between the structures and lipophilicities of 1, 10-dioxa-4, 7, 13, 16-tetra-azacyclo-octadecane (TA-18-crown-6) and the tetrabenzyl derivative of 1,10-dioxa-4, 7, 13, 16-tetra-azacyclo-octadecane (TBTA-18-crown-6) on their extraction-abilities and -selectivities for transition metal cations, constants of the overall extraction (logK
ex) of 1:1 (M:L) complexes, the distribution (K
D) for two diluents (CH2Cl2 and CHCl3) with different dielectric constants have been determined at 25 ± 0.1 °C. The magnitude of logK
ex is largely determined by that of K
D. The equilibrium constants of TA-18-crown-6 have been compared with those of TBTA-18-crown-6. It is found that:(i) logK
ex sequences of TA-18-crown-6 and TBTA-18-crown-6 for transition metals in CH2Cl2 lie in order: Fe3+ > Cu2+ > Mn2+ > Co2+ > Cd2+ > Ni2+ > Zn2+ and Fe3+ > Cu2+ > Co2+ > Mn2+ > Ni2+ > Cd2+ > Zn2+ respectively; (ii) the stability sequences of two types of tetra-aza-crown ethers with the transition metal cations in CHCl3 are the same as follows: Fe3+ > Ni2+ > Cu2+ > Co2+ > Zn2+ > Cd2+ > Mn2+, and (iii) unusual selectivities are observed for transition metal-tetra-aza-crowns, e.g. the high Fe3+/M
n+ selectivity factors (Sf) of TA-18-crown-6, except for the competitive-extractions for the special case in CHCl3 of TBTA-18-crown-6, it was found that the Mn2+/M
n+ values were relatively higher according to the other transition metal cations. A systematic sequence in these two types of solvents is not found for a given transition metal cation in terms of the variation of selectivity with the tetra-aza-crown ethers. The results provide alternatives for the rational design of other specific ligands on the transition metal cations. 相似文献
15.
16.
This paper presents an approach based on topology for the determination of characteristics and properties of curves used in the trimming of NURBS surfaces. Through discrete subdivision and topological criteria, a method is presented to determine characteristics of the boundary; such as whether the set of trimming curves forms a set of closed loops, whether trimming curves contain singularities or self intersections, and whether the boundary is simply connected. A surface mesh partitionning the parameter space is used, formed of isoparametric lines in both parametric directions. Topological properties of the cells of this mesh and their intersections with the trimming curves allow to localize the boundary. Topological treatment of this localization allows to define the interior and exterior of the face, and to refine the boundary localization. Singularities and self intersections of the boundary as well as voids in the face are investigated through the study of topological properties of neighbors. As an application, an algorithm for point localization is presented that very rapidly allows to determine whether a given point in parameter space lies inside, on the boundary or outside of the trimmed surface. 相似文献
17.
We introduce here some Itô calculus for non-continuous Dirichlet processes. Such calculus extends what was known for continuous Dirichlet processes or for semimartingales. In particular we prove that non-continuous Dirichlet processes are stable under C
1 transformation. 相似文献
18.
Fukuji Higashi Kaori Kira 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2725-2733
The solution polyesterification of dicarboxylic acids in pyridine, the activated intermediates of which were difficult to dissolve in tosyl chloride/dimethylformamide/pyridine, was investigated in the presence of lithium chloride. The solubility of the activated dicarboxylic acids was largely improved by the presence of the salt, and the polycondensation with bisphenols was greatly facilitated. The salt was more effectively added to a pyridine solution of dicarboxylic acids than to the activated dicarboxylic acids in pyridine. The favorable additive effect on the improved solubility was attributed to a lowered degree of association of the activated dicarboxylic acids, which led to distributions of the resulting oligomers from bisphenols at an earlier stage closer to the theoretical ones and yielded better polycondensation results. The reaction, which proceeded through favorable distributions of the co‐oligomers, produced copolymers of higher inherent viscosities and slightly block sequence distributions determined by NMR. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2725–2733, 2004 相似文献
19.
François Ledrappier Mark Pollicott 《Bulletin of the Brazilian Mathematical Society》2005,36(2):143-176
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually
associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension
of the geodesic flow. 相似文献
20.