全文获取类型
收费全文 | 4444篇 |
免费 | 249篇 |
国内免费 | 6篇 |
专业分类
化学 | 3298篇 |
晶体学 | 15篇 |
力学 | 85篇 |
数学 | 672篇 |
物理学 | 629篇 |
出版年
2023年 | 54篇 |
2022年 | 37篇 |
2021年 | 85篇 |
2020年 | 109篇 |
2019年 | 122篇 |
2018年 | 64篇 |
2017年 | 45篇 |
2016年 | 165篇 |
2015年 | 142篇 |
2014年 | 154篇 |
2013年 | 211篇 |
2012年 | 282篇 |
2011年 | 297篇 |
2010年 | 173篇 |
2009年 | 117篇 |
2008年 | 214篇 |
2007年 | 182篇 |
2006年 | 193篇 |
2005年 | 185篇 |
2004年 | 142篇 |
2003年 | 104篇 |
2002年 | 122篇 |
2001年 | 74篇 |
2000年 | 60篇 |
1999年 | 49篇 |
1998年 | 61篇 |
1997年 | 53篇 |
1996年 | 69篇 |
1995年 | 60篇 |
1994年 | 50篇 |
1993年 | 68篇 |
1992年 | 57篇 |
1991年 | 44篇 |
1990年 | 35篇 |
1989年 | 35篇 |
1988年 | 49篇 |
1987年 | 52篇 |
1986年 | 46篇 |
1985年 | 56篇 |
1984年 | 43篇 |
1983年 | 40篇 |
1982年 | 31篇 |
1981年 | 32篇 |
1980年 | 32篇 |
1979年 | 20篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1976年 | 22篇 |
1975年 | 17篇 |
1974年 | 27篇 |
排序方式: 共有4699条查询结果,搜索用时 15 毫秒
1.
Synthesis of diisocyanides with phenolic groups and their polymerization to helically chiral poly(quinoxaline‐2,3‐diyl)s 下载免费PDF全文
Johannes Scholz Michael Reggelin 《Journal of polymer science. Part A, Polymer chemistry》2015,53(11):1320-1329
The development of synthetic routes which lead to five new diisocyanide monomers with one or two phenolic groups is described. Their polymerization behavior is studied with Pd‐ and Ni‐based initiators, as well as under microwave irradiation. The polymerizability is mainly dominated by steric effects as is concluded from experiments using different protecting groups. Chiroptical properties of these new polymers are studied by CD‐spectroscopy. After deprotection, helically chiral poly(quinoxalin‐2,3‐diyl)s are obtained which display a Brønsted function attached to a stereolabile biaryl axis whose configuration should be influenced by the chiral polymer backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1320–1329 相似文献
2.
3.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6. 相似文献
4.
Johannes Elschner Rainer Hinder Gunther Schmidt 《Advances in Computational Mathematics》2002,16(2-3):139-156
This paper is devoted to the numerical study of diffraction by periodic structures of plane waves under oblique incidence. For this situation Maxwell's equations can be reduced to a system of two Helmholtz equations in R
2 coupled via quasiperiodic transmission conditions on the piecewise smooth interfaces between different materials. The numerical analysis is based on a strongly elliptic variational formulation of the differential problem in a bounded periodic cell involving nonlocal boundary operators. We obtain existence and uniqueness results for discrete solutions and provide the corresponding error analysis. 相似文献
5.
Evolutionary algorithms are applied as problem-independent optimization algorithms. They are quite efficient in many situations. However, it is difficult to analyze even the behavior of simple variants of evolutionary algorithms like the (1+1) EA on rather simple functions. Nevertheless, only the analysis of the expected run time and the success probability within a given number of steps can guide the choice of the free parameters of the algorithms. Here static (1+1) EAs with a fixed mutation probability are compared with dynamic (1+1) EAs with a simple schedule for the variation of the mutation probability. The dynamic variant is first analyzed for functions typically chosen as example-functions for evolutionary algorithms. Afterwards, it is shown that it can be essential to choose the suitable variant of the (1+1) EA. More precisely, functions are presented where each static (1+1) EA has exponential expected run time while the dynamic variant has polynomial expected run time. For other functions it is shown that the dynamic (1+1) EA has exponential expected run time while a static (1+1) EA with a good choice of the mutation probability has polynomial run time with overwhelming probability. 相似文献
6.
Arno Jüschke Johannes Jahn Andreas Kirsch 《Computational Optimization and Applications》1997,7(3):261-276
In this paper we consider a special optimization problem withtwo objectives which arises in antenna theory. It is shown that thisabstract bicriterial optimization problem has at least one solution.Discretized versions of this problem are also discussed, and therelationships between these finite dimensional problems and the infinitedimensional problem are investigated. Moreover, we presentnumerical results for special parameters using a multiobjectiveoptimization method. 相似文献
7.
John L. Wood Johannes Schwarzenberg Edward F. Zganjar Dubravka Rupnik 《Hyperfine Interactions》1992,75(1-4):51-58
State-of-the-art spectroscopy of nuclei far from stability has achieved an extraordinary level of sophistication and detail
in the last ten years. In principle, if a state can be populated, it can be characterized by its energy, spin, parity, and
major decay paths. Sometimes its lifetime can be measured. In practice, one is confronted with enormous complexity. To convert
raw spectroscopic data into nuclear structure data involves a complex process of disentangling gamma rays and conversion electrons
into decay schemes. Specifically, coincidence techniques, especially coincidence intensities, play a crucial role in this
process. Recent examples and methods from work done at UNISOR are presented. 相似文献
8.
9.
Florin Radu Alexei Nefedov Johannes GrabisGregor Nowak Andre BergmannHartmut Zabel 《Journal of magnetism and magnetic materials》2006
We have used soft X-ray resonant magnetic scattering (XRMS) to search for the presence of an effective ferromagnetic moment belonging to the antiferromagnetic (AF) layer which is in close contact with a ferromagnetic (F) layer. Taking advantage of the element specificity of the XRMS technique, we have measured hysteresis loops of both Fe and CoO layers of a CoO(40 Å)/Fe (150 Å) exchange bias bilayer. From these measurements we have concluded that the proximity of the F layer induces a magnetic moment in the AF layer. The F moment of the AF layer has two components: one is frozen and does not follow the applied magnetic field and the other one follows in phase the ferromagnetic magnetization of the F layer. The temperature dependence of the F components belonging to the AF layer is shown and discussed. 相似文献
10.