全文获取类型
收费全文 | 28675篇 |
免费 | 269篇 |
国内免费 | 241篇 |
专业分类
化学 | 9641篇 |
晶体学 | 221篇 |
力学 | 1928篇 |
综合类 | 1篇 |
数学 | 8769篇 |
物理学 | 8625篇 |
出版年
2023年 | 54篇 |
2022年 | 25篇 |
2021年 | 85篇 |
2020年 | 101篇 |
2019年 | 115篇 |
2018年 | 2032篇 |
2017年 | 2275篇 |
2016年 | 1131篇 |
2015年 | 769篇 |
2014年 | 663篇 |
2013年 | 841篇 |
2012年 | 2036篇 |
2011年 | 1323篇 |
2010年 | 181篇 |
2009年 | 230篇 |
2008年 | 277篇 |
2007年 | 243篇 |
2006年 | 267篇 |
2005年 | 5952篇 |
2004年 | 5739篇 |
2003年 | 3202篇 |
2002年 | 331篇 |
2001年 | 82篇 |
2000年 | 48篇 |
1999年 | 49篇 |
1998年 | 103篇 |
1997年 | 39篇 |
1996年 | 47篇 |
1995年 | 35篇 |
1994年 | 40篇 |
1993年 | 59篇 |
1992年 | 49篇 |
1991年 | 34篇 |
1990年 | 37篇 |
1989年 | 34篇 |
1988年 | 35篇 |
1987年 | 42篇 |
1986年 | 32篇 |
1985年 | 36篇 |
1984年 | 36篇 |
1983年 | 27篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 31篇 |
1979年 | 15篇 |
1978年 | 23篇 |
1977年 | 13篇 |
1976年 | 19篇 |
1974年 | 26篇 |
1966年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 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.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 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.
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.
S. Heinze P. Kurz D. Wortmann G. Bihlmayer S. Blügel 《Applied Physics A: Materials Science & Processing》2002,75(1):25-36
In this paper we present a density functional theory investigation of complex magnetic structures in ultra-thin films. The
focus is on magnetically frustrated antiferromagnetic Cr and Mn monolayers deposited on a triangular lattice provided by a
Ag (111) substrate. This involves non-collinear magnetic structures, which we treat by first-principles calculations on the
basis of the vector spin-density formulation of the density functional theory. We find for Cr/Ag (111) a coplanar non-collinear
periodic 120° Néel structure, for Mn/Ag (111) a row-wise antiferromagnetic structure, and for Fe/Ag (111) a ferromagnetic
structure as magnetic ground states. The spin-polarized scanning tunneling microscope (SP–STM) operated in the constant-current
mode is proposed as a powerful tool to investigate complex atomic-scale magnetic structures of otherwise chemically equivalent
atoms. We discuss a recent application of this operation mode of the SP–STM on Mn/W (110), which led to the first observation
of a two-dimensional antiferromagnet on a non-magnetic metal. The future potential of this approach is demonstrated by calculating
SP–STM images for different magnetic structures of Cr/Ag (111). The results show that the predicted non-collinear magnetic
ground state structure can clearly be discriminated from competing magnetic structures. A general discussion of the application
of different operation modes of the SP–STM is presented on the basis of the model of Tersoff and Hamann.
Received: 07 May 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002 相似文献
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.
V Ravindran Pankaj Agrawal Rahul Basu Satyaki Bhattacharya J Blümlein V Del Duca R Harlander D Kosower Prakash Mathews Anurag Tripathi 《Pramana》2006,67(5):983-992
This is the report of the subgroup QCD of Working Group-4 at WHEPP-9. We present the activities that had taken place in the
subgroup and report some of the partial results arrived at following the discussion at the working group meetings. 相似文献