全文获取类型
收费全文 | 5283篇 |
免费 | 211篇 |
国内免费 | 33篇 |
专业分类
化学 | 3716篇 |
晶体学 | 22篇 |
力学 | 130篇 |
数学 | 894篇 |
物理学 | 765篇 |
出版年
2023年 | 42篇 |
2022年 | 52篇 |
2021年 | 92篇 |
2020年 | 118篇 |
2019年 | 112篇 |
2018年 | 69篇 |
2017年 | 57篇 |
2016年 | 155篇 |
2015年 | 144篇 |
2014年 | 179篇 |
2013年 | 284篇 |
2012年 | 321篇 |
2011年 | 364篇 |
2010年 | 259篇 |
2009年 | 204篇 |
2008年 | 321篇 |
2007年 | 328篇 |
2006年 | 311篇 |
2005年 | 308篇 |
2004年 | 245篇 |
2003年 | 217篇 |
2002年 | 225篇 |
2001年 | 88篇 |
2000年 | 80篇 |
1999年 | 77篇 |
1998年 | 62篇 |
1997年 | 70篇 |
1996年 | 76篇 |
1995年 | 50篇 |
1994年 | 41篇 |
1993年 | 25篇 |
1992年 | 23篇 |
1991年 | 33篇 |
1990年 | 20篇 |
1989年 | 33篇 |
1988年 | 19篇 |
1986年 | 22篇 |
1985年 | 30篇 |
1984年 | 31篇 |
1983年 | 29篇 |
1982年 | 35篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 19篇 |
1978年 | 41篇 |
1977年 | 22篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1974年 | 23篇 |
1973年 | 12篇 |
排序方式: 共有5527条查询结果,搜索用时 0 毫秒
991.
André L. Beauchamp Stephan Latour Marc J. Olivier James D. Wuest 《Journal of organometallic chemistry》1983,254(3):283-291
The title compound, C58H52Sn3, belongs to the triclinic space group P, with a 10.165, b 13.365, c 18.670 Å, α 96.28, β 93.88, γ 103.15°, V = 2443.8 Å3, fw = 1105.1, Z = 2, Dcalc 1.501 g cm?3, m.p. 206.5–208°C, λ(Mo-K) 0.71069 Å. The structure was refined on 2684 nonzero reflections to an R factor of 0.044. The crystal contains molecules in which the (SnCH2)3CH core possesses an approximate C3 symmetry. The three SnC(H2) bonds are gauche to the C(4)-H bond. Repulsive interactions involving the bulky Ph3Sn substituents lead to large SnC(H2)C(H) angles (av. 117.3°), whereas the C(H2)C(H)C(H2) angles at the tertiary carbon average 111.3°. Little distortion of the Ph3Sn groups themselves is present, since the PhSnPh angles (av. 109.8°) are almost equal to the C(H2)SnPh angles (av. 109.9°). The molecule as a whole has no symmetry because the aromatic rings in the three Ph3Sn groups have different orientations. The phenyl groups create a pocket in the middle of the molecule which encloses and shields the tertiary hydrogen atom. The resulting inaccessibility of this hydrogen accounts in part for the low reactivity of the title compound in redox reactions. 相似文献
992.
993.
A nonlocal species concentration theory for diffusion and phase changes is introduced from a nonlocal free energy density. It can be applied, say, to electrode materials of lithium ion batteries. This theory incorporates two second-order partial differential equations involving second-order spatial derivatives of species concentration and an additional variable called nonlocal species concentration. Nonlocal species concentration theory can be interpreted as an extension of the Cahn–Hilliard theory. In principle, nonlocal effects beyond an infinitesimal neighborhood are taken into account. In this theory, the nonlocal free energy density is split into the penalty energy density and the variance energy density. The thickness of the interface between two phases in phase segregated states of a material is controlled by a normalized penalty energy coefficient and a characteristic interface length scale. We implemented the theory in COMSOL Multiphysics\(^{\circledR }\) for a spherically symmetric boundary value problem of lithium insertion into a \(\hbox {Li}_x\hbox {Mn}_2\hbox {O}_4\) cathode material particle of a lithium ion battery. The two above-mentioned material parameters controlling the interface are determined for \(\hbox {Li}_x\hbox {Mn}_2\hbox {O}_4\), and the interface evolution is studied. Comparison to the Cahn–Hilliard theory shows that nonlocal species concentration theory is superior when simulating problems where the dimensions of the microstructure such as phase boundaries are of the same order of magnitude as the problem size. This is typically the case in nanosized particles of phase-separating electrode materials. For example, the nonlocality of nonlocal species concentration theory turns out to make the interface of the local concentration field thinner than in Cahn–Hilliard theory. 相似文献
994.
Philip Coppens Mateusz Pitak Milan Gembicky Marc Messerschmidt Stephan Scheins Jason Benedict Shin‐ichi Adachi Tokushi Sato Shunsuke Nozawa Kohei Ichiyanagi Matthieu Chollet Shin‐ya Koshihara 《Journal of synchrotron radiation》2009,16(2):226-230
A RATIO method for analysis of intensity changes in time‐resolved pump–probe Laue diffraction experiments is described. The method eliminates the need for scaling the data with a wavelength curve representing the spectral distribution of the source and removes the effect of possible anisotropic absorption. It does not require relative scaling of series of frames and removes errors due to all but very short term fluctuations in the synchrotron beam. 相似文献
995.
Amin Abdolvand Robert W. Lloyd Marc J. J. Schmidt David J. Whitehead Zhu Liu Lin Li 《Applied Physics A: Materials Science & Processing》2009,95(2):447-452
We present results on the growth of highly organised, reproducible, periodic microstructure arrays on a stainless steel substrate
using multi-pulsed Nd:YAG (wavelength of 1064 nm, pulse duration of 7 ns, repetition rate of 25 kHz, beam quality factor of
M
2∼1.5) laser irradiation in standard atmospheric environment (room temperature and normal pressure) with laser spot diameter
of the target being ∼50 μm. The target surface was irradiated at laser fluence of ∼2.2 J/cm2 and intensity of ∼0.31×109 W/cm2, resulting in the controllable generation of arrays of microstructures with average periods ranging from ∼30 to ∼70 μm, depending
on the hatching overlap between the consecutive scans. The received tips of the structures were either below or at the level
of the original substrate surface, depending on the experimental conditions. The peculiarity of our work is on the utilised
approach for scanning the laser beam over the surface. A possible mechanism for the formation of the structures is proposed. 相似文献
996.
Marc Wouts 《Communications in Mathematical Physics》2009,289(1):157-204
We study the surface tension and the phenomenon of phase coexistence for the Ising model on with ferromagnetic but random couplings. We prove the convergence in probability (with respect to random couplings) of surface
tension and analyze its large deviations: upper deviations occur at volume order while lower deviations occur at surface order.
We study the asymptotics of surface tension at low temperatures and relate the quenched value τ
q
of surface tension to maximal flows (first passage times if d = 2). For a broad class of distributions of the couplings we show that the inequality –where τ
a
is the surface tension under the averaged Gibbs measure – is strict at low temperatures. We also describe the phenomenon
of phase coexistence in the dilute Ising model and discuss some of the consequences of the media randomness. All of our results
hold as well for the dilute Potts and random cluster models. 相似文献
997.
Four potential metabolites of the potassium-competitive acid blocker BYK 405879 (1) were synthesized which might be formed in vivo by enzymatic oxidation of the pyran moiety or the methyl groups attached to the (hetero) aromatic system. In all cases, the oxidation of the parent compound 1 was accompanied by a significant loss of pharmacological activity and by a decrease in lipophilicity. The target compounds 6, 14, 20, and 21 constitute valuable tool substances for the investigation of the metabolic fate of BYK 405879 (1). 相似文献
998.
The synthesis of a polypseudorotaxane, polyrotaxane, and polycatenane containing the electron-deficient cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+) subunit in the side chain is described. These interlocked supramolecular polymers have been prepared from an azide-functionalized polystyrene derivative and an acetylene-functionalized [2]rotaxane, [2]catenane and their parent tetracationic cyclophane via Cu(I)-catalyzed 1,3 dipolar cycloadditions (‘click chemistry’). The synthesis and characterization of the polymers and intermediates has been described using IR, 1H NMR, UV spectroscopies, and voltammetry. We have shown that the CBPQT4+ unit of the side chain polystyrene derivative has the ability to reversibly undergo complexation with a complementary dialkoxynaphthalene derivative. 相似文献
999.
Marc Tedetti Fabien Joux Bruno Charrière Kenneth Mopper Richard Sempéré 《Journal of photochemistry and photobiology. A, Chemistry》2009,201(2-3):243-247
We evaluated the role of nitrate (NO3?) as a potential photosensitizer and the bacterial responses to dissolved organic matter (DOM) phototransformation from coastal waters in the northwestern Mediterranean Sea. In spring, without any addition of NO3?, the exposure of 0.2 μm filtered seawater (DOM-solution) to natural solar radiation (i.e. Full Sun [FS], including photosynthetically available [PAR: 400–700 nm], ultraviolet-A [UVAR: 315–400 nm] and ultraviolet-B [UVBR: 280–315 nm] radiations) stimulated bacterial production (BP) and abundance (BA) in natural assemblages (0.8 μm filtered seawater) by 80 and 20% as compared to unexposed (Dark) DOM-solutions, respectively. This stimulation resulted primarily from the exposure to PAR. When NO3? (30 μM) was added to DOM-solution before irradiation, BP and BA increased by 150 and 65% in FS compared to Dark, respectively, due to both PAR and UVBR. By contrast, in summer, the exposure of DOM-solution caused a decrease in BP by 30% but an increase in BA by 23% in FS compared to Dark, regardless of the NO3? addition before irradiation. The inhibition of BP resulted mainly from UVAR, whereas the stimulation of BA resulted from PAR. These results suggest contrasting effects along seasons of solar radiation and NO3? on DOM bioavailability, depending on its initial chemical composition. 相似文献
1000.
Karolina Haberska Cristina Vaz-Domínguez Antonio L. De Lacey Marius Dagys Curt T. Reimann Sergey Shleev 《Bioelectrochemistry (Amsterdam, Netherlands)》2009,76(1-2):34
In an effort to find conditions favouring bioelectrocatalytic reduction of oxygen by surface-immobilised human ceruloplasmin (Cp), direct electron transfer (DET) reactions between Cp and an extended range of surfaces were considered. Exploiting advances in surface nanotechnology, bare and carbon-nanotube-modified spectrographic graphite electrodes as well as bare, thiol- and gold-nanoparticle-modified gold electrodes were considered, and ellipsometry provided clues as to the amount and form of adsorbed Cp. DET was studied under different conditions by cyclic voltammetry and chronoamperometry. Two Faradaic processes with midpoint potentials of about 400 mV and 700 mV vs. NHE, corresponding to the redox transformation of copper sites of Cp, were clearly observed. In spite of the significant amount of Cp adsorbed on the electrode surfaces, as well as the quite fast DET reactions between the redox enzyme and electrodes, bioelectrocatalytic reduction of oxygen by immobilised Cp was never registered. The bioelectrocatalytic inertness of this complex multi-functional redox enzyme interacting with a variety of surfaces might be associated with a very complex mechanism of intramolecular electron transfer involving a kinetic trapping behaviour. 相似文献