全文获取类型
收费全文 | 2950篇 |
免费 | 262篇 |
国内免费 | 16篇 |
专业分类
化学 | 2195篇 |
晶体学 | 11篇 |
力学 | 63篇 |
数学 | 426篇 |
物理学 | 533篇 |
出版年
2024年 | 2篇 |
2023年 | 52篇 |
2022年 | 75篇 |
2021年 | 120篇 |
2020年 | 166篇 |
2019年 | 186篇 |
2018年 | 84篇 |
2017年 | 69篇 |
2016年 | 198篇 |
2015年 | 149篇 |
2014年 | 160篇 |
2013年 | 195篇 |
2012年 | 275篇 |
2011年 | 269篇 |
2010年 | 157篇 |
2009年 | 127篇 |
2008年 | 197篇 |
2007年 | 162篇 |
2006年 | 158篇 |
2005年 | 106篇 |
2004年 | 61篇 |
2003年 | 32篇 |
2002年 | 32篇 |
2001年 | 28篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1937年 | 3篇 |
1932年 | 2篇 |
1928年 | 1篇 |
排序方式: 共有3228条查询结果,搜索用时 156 毫秒
171.
This paper describes the use of dendritic polyglycerol as a new high-loading polymeric support. The soluble polyether skeleton allows the parallel synthesis of small libraries on a large scale (1-5 mmol). Purification of polymer-bound products is easily achieved by a parallel dialysis apparatus, which was developed to separate up to 12 reaction mixtures simultaneously. The terminal 1,2-diol groups of polyglycerol (loading capacity: 4.1 mmol diol/g) can be directly coupled with carbonyl compounds without additional linker groups. At the same time the polyglycerol support acts as a polymeric ketal protecting group. The coupling of the carbonyl compounds occurs in high yields, and effective loading capacities of up to 3.5 mmol of ketone/g can be reached. The obtained polymeric acetals can easily be characterized by standard analytical techniques, such as NMR, IR, UV, and SEC. The versatility of this new polymeric support for solution-phase organic synthesis is demonstrated by two efficient polymer-supported syntheses: nucleophilic substitutions of gamma-chloroketones with amines and Suzuki-coupling on p-bromobenzaldehyde. The acid-catalyzed acetal cleavage with a solid-phase acidic ion-exchange resin in methanol demonstrates the orthogonal use of these soluble polymeric supports with conventional solid-phase reagents. Cleavage of products occurs in high yields, and almost complete recovery (>95%) of the polyglycerol support has been demonstrated after phase separation or ultrafiltration. 相似文献
172.
We study the Néel temperature of quasi-one-dimensional S = 1/2 antiferromagnets containing nonmagnetic impurities. We first consider the temperature dependence of the staggered susceptibility of finite chains with open boundary conditions, which shows an interesting difference for even and odd length chains. We then use a mean field theory treatment to incorporate the three-dimensional interchain couplings. The resulting Néel temperature shows a pronounced drop as a function of doping by up to a factor of 5. 相似文献
173.
The resonance mechanism for positive and negative ionization of an atom reflected from a metal surface is treated in the time-dependent Hartree-Fock approximation assuming that the atom moves on its classical trajectory. A simple model is parameterized to describe 30–500 eV Na atoms reflected from tungsten, and the ionization probabilities are calculated by numerical integration of the equation of motion of the time evolution operator. Significant ionization can only occur if either the ionization level, or the affinity level of the atom crosses the Fermi level beyond the range of the atom-metal hopping interaction. On clean tungsten, the former situation applies, and the probability of positive ionization is nearly unity, and of negative ionization nearly zero. 相似文献
174.
A method for the calculation of the probability of neutralisation of an ion, which is scattered from the surface of a solid is presented. It assumes the ion to move along a classical trajectory and solves for the time evolution operator for the electronic system. For one electron Hamiltonians the solution can be carried out exactly. Results are presented for scattering from a semi-infinite linear chain. 相似文献
175.
176.
We introduce a thermal conductance by using the fluctuation-dissipation theorem to analyze the heat transfer between two nanoparticles separated by a submicron distance. Using either a molecular dynamics technique or a model based on the Coulomb interaction between fluctuating dipoles, we derive the thermal conductance. Both models agree for distances larger than a few diameters. For separation distances smaller than the particle diameter, we find a transition regime characterized by a thermal conductance larger than the contact conductance. 相似文献
177.
131 W 220 fs fiber laser system 总被引:11,自引:0,他引:11
Röser F Rothhard J Ortac B Liem A Schmidt O Schreiber T Limpert J Tünnermann A 《Optics letters》2005,30(20):2754-2756
We report on an ytterbium-doped photonic-crystal-fiber-based chirped-pulse amplification system delivering 131 W average power 220 fs pulses at 1040 nm center wavelength in a diffraction-limited beam. The pulse repetition rate is 73 MHz, corresponding to a pulse energy of 1.8 microJ and a peak power as high as 8.2 MW. 相似文献
178.
Hachenberg J Streng C Süske E Vauth S Mayr SG Krebs HU Samwer K 《Physical review letters》2004,92(24):246102
The crossover in kinetic roughening of thin films from a particle-character-dominated regime to continuous growth behavior has been observed in this work. This has been accomplished by atomic force microscopy investigations of pulsed laser deposited amorphous organic films with thicknesses ranging from several nanometers to more than 4 microm. The early-stage random-deposition-like processes end once a closed layer is formed, which grows without saturation on the characteristic length scales. In addition, the influence of oblique film deposition has been examined and interpreted. 相似文献
179.
Goennenwein ST Wassner TA Huebl H Brandt MS Philipp JB Opel M Gross R Koeder A Schoch W Waag A 《Physical review letters》2004,92(22):227202
We show that upon exposure to a remote dc hydrogen plasma, the magnetic and electronic properties of the dilute magnetic semiconductor Ga1-xMnxAs change qualitatively. While the as-grown Ga1-xMnxAs thin films are ferromagnetic at temperatures T less, similar 70 K, the samples are found to be paramagnetic after the hydrogenation, with a Brillouin-type magnetization curve even at T=2 K. Comparing magnetization and electronic transport measurements, we conclude that the density of free holes p is significantly reduced by the plasma process, while the density of Mn magnetic moments does not change. 相似文献
180.
Sebastian?BreuerEmail author Katrin?Pech Armin?Buss Christoph?Spitzer Juris?Ozols Elly?M?Hol Nicole?Heussen Johannes?Noth Franz-Werner?Schwaiger Andreas?B?Schmitt 《BMC neuroscience》2004,5(1):15