全文获取类型
收费全文 | 12492篇 |
免费 | 2397篇 |
国内免费 | 2162篇 |
专业分类
化学 | 3381篇 |
晶体学 | 233篇 |
力学 | 4179篇 |
综合类 | 162篇 |
数学 | 1396篇 |
物理学 | 7700篇 |
出版年
2024年 | 34篇 |
2023年 | 124篇 |
2022年 | 399篇 |
2021年 | 404篇 |
2020年 | 379篇 |
2019年 | 344篇 |
2018年 | 355篇 |
2017年 | 505篇 |
2016年 | 632篇 |
2015年 | 563篇 |
2014年 | 756篇 |
2013年 | 1185篇 |
2012年 | 827篇 |
2011年 | 951篇 |
2010年 | 800篇 |
2009年 | 860篇 |
2008年 | 866篇 |
2007年 | 947篇 |
2006年 | 854篇 |
2005年 | 754篇 |
2004年 | 608篇 |
2003年 | 584篇 |
2002年 | 495篇 |
2001年 | 437篇 |
2000年 | 413篇 |
1999年 | 333篇 |
1998年 | 373篇 |
1997年 | 225篇 |
1996年 | 187篇 |
1995年 | 134篇 |
1994年 | 143篇 |
1993年 | 119篇 |
1992年 | 87篇 |
1991年 | 74篇 |
1990年 | 64篇 |
1989年 | 39篇 |
1988年 | 37篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 35篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1959年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
A method is developed whereby spherical and other particles can be derivatised with electroactive species on their surface and then immobilised on the surface of an electrode. The chronoamperometric and voltammetric responses in the limit of reversible electrode kinetics are modelled using a theory of charge movement over the surface of the spheres where this movement is considered as a diffusional process. The model is extended to include different distributions of sphere radii and to model the scenario of truncated spheres resting on the electrode surface. It is found that a good estimation of the truncation angle can be found by fitting the experimental data with theoretical predictions. 相似文献
152.
A new parameter set (referred to as 45A4) is developed for the explicit-solvent simulation of hexopyranose-based carbohydrates. This set is compatible with the most recent version of the GROMOS force field for proteins, nucleic acids, and lipids, and the SPC water model. The parametrization procedure relies on: (1) reassigning the atomic partial charges based on a fit to the quantum-mechanical electrostatic potential around a trisaccharide; (2) refining the torsional potential parameters associated with the rotations of the hydroxymethyl, hydroxyl, and anomeric alkoxy groups by fitting to corresponding quantum-mechanical profiles for hexopyranosides; (3) adapting the torsional potential parameters determining the ring conformation so as to stabilize the (experimentally predominant) (4)C(1) chair conformation. The other (van der Waals and nontorsional covalent) parameters and the rules for third and excluded neighbors are taken directly from the most recent version of the GROMOS force field (except for one additional exclusion). The new set is general enough to define parameters for any (unbranched) hexopyranose-based mono-, di-, oligo- or polysaccharide. In the present article, this force field is validated for a limited set of monosaccharides (alpha- and beta-D-glucose, alpha- and beta-D-galactose) and disaccharides (trehalose, maltose, and cellobiose) in solution, by comparing the results of simulations to available experimental data. More extensive validation will be the scope of a forthcoming article. (c) 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1400-1412, 2005. 相似文献
153.
Torres-Valencia JM Meléndez-Rodríguez M Alvarez-García R Cerda-García-Rojas CM Joseph-Nathan P 《Magnetic resonance in chemistry : MRC》2004,42(10):898-902
A Monte Carlo random search using molecular mechanics, followed by geometry optimization of each minimum energy structure employing density functional theory (DFT) calculations at the B3LYP/6-31G* level and a Boltzmann analysis of the total energies, generated accurate molecular models which describe the conformational behavior of the antispasmodic bicyclic sesquiterpene valeranone (1). The theoretical H-C-C-H dihedral angles gave the corresponding 1H, 1H vicinal coupling constants using a generalized Karplus-type equation. In turn, the 3J(H,H) values were used as initial input data for the spectral simulation of 1, which after iteration provided an excellent correlation with the experimental 1H NMR spectrum. The calculated 3J(H,H) values closely predicted the experimental values, excepting the coupling constant between the axial hydrogen alpha to the carbonyl group and the equatorial hydrogen beta to the carbonyl group (J(2beta, 3beta)). The difference is explained in terms of the electron density distribution found in the highest occupied molecular orbital (HOMO) of 1. The simulated spectrum, together with 2D NMR experiments, allowed the total assignment of the 1H and 13C NMR spectra of 1. 相似文献
154.
We have shown the Lennard-Jones (LJ) phase diagram for a slit-shaped nanopore by molecular simulations and thermodynamically
predicted the results with no adjustable parameter. With this success, LJ phase diagrams are predictable. In this study, the
freezing of an LJ CH4 capillary condensate under a tensile condition in a nonstructural carbon nanopore with a cylindrical geometry was examined
using molecular dynamics (MD) simulation. We employ a unit cell in contact with a bulk vapor phase, which is useful for the
determination of the bulk vapor pressure in equilibrium with the molecules in a pore. The MD simulation results show liquid-solid
(amorphous) phase transitions with a variation in the bulk vapor pressure. The frozen particles are arranged in concentric
circular regions along the wall similar to those reported by Maddox and Gubbins. The freezing points are determined from the
variations in density, enthalpy, arrangement, and structural functions. The obtained liquid-solid coexistence points are found
to exhibit a significant dependence of the freezing point on the equilibrium bulk vapor pressure, forming an extraordinarily
skewed curve on the p-T diagram, in contrast to the bulk phase coexistence that is represented by an almost vertical line.
The origin of the significant dependence is considered to be the Laplace effect on the capillary condensate similar to the
case with a slit-shaped pore. A simple model, which the authors earlier presented for slit-shaped nanopores, successfully
predicted the p-T relation of the freezing point for cylindrical nanopores as well. 相似文献
155.
Monte Carlo studies of symmetrical polymer mixturesAB, modelled by selfavoiding walks withN
A
=N
B
=N steps on a simple cubic lattice, are presented for arbitrary concentrations of vacancies
v
in the range from
v
=0.2 to
v
=0.8 and chain lengthsN64. We obtained the phase diagrams and the equation of state for three choices of the ratio /
AB
( being the energy between monomers of the same kind,
AB
being the energy between different monomers). Flory-Huggins theory provides only a qualitative understanding of these results. If the equation of state is fitted with an effective Flory-Huggins parameter
eff
, the latter turns out to be strongly dependent on both concentration and temperature.Contributed paper delivered at the Tagung der Deutschen Physikalischen Gesellschaft, Fachausschuß Polymerphysik, Berlin, March 30–April 3, 1987. 相似文献
156.
《Arabian Journal of Chemistry》2022,15(12):104330
The present study was carried out to design and synthesize a number of novel aromatic carboxamide derivatives of dehydroabietylamine. The preliminary antifungal assay indicated that most of title compounds displayed moderate to good antifungal activity toward the six fungal strains in vitro. Compounds 3i, 3q, 4b and 4d showed significant antifungal activity against Sclerotinia sclerotiorum, with EC50 values ranging from 0.067 ~ 0.393 mg/L. Compounds 3i, 4b and 4d also showed pronounced mycelial growth inhibition activities against B. cinerea and A. solani. Furthermore, in the in vivo assay, compound 4b exhibited brilliant protective activity against S. sclerotiorum-infected rape leaves. Meanwhile, the in vivo bioassay on tomato plants infected by B. cinerea showed that compound 3i and 4d displayed excellent protective activity at 200 mg/L, which were near to boscalid. Primary mechanistic study revealed that 4b could inhibit sclerotia formation as well as reduce the exopolysaccharide level. SEM and TEM analysis indicated that 4b possessed a strong ability to destroy the surface morphology of mycelia, cell structure and seriously interfere with the growth of the fungal pathogen. In addition, 4b exhibited good inhibitory activity (IC50 = 23.3 ± 1.6 μM) toward succinate dehydrogenase (SDH). Molecular modeling study confirmed the binding modes between compound 4b and SDH. The above antifungal results and fungicidal mechanism study revealed that this class of dehydroabietylamine derivatives could be potential SDH inhibitors and lead compounds for novel fungicides development. 相似文献
157.
Yoshisuke Ueda 《Journal of statistical physics》1979,20(2):181-196
This paper deals with turbulent or chaotic phenomena which occur in the system governed by Duffing's equation, a special type of two-dimensional periodic system. By using analog and digital computers, experiments are carried out with special reference to the change of attractors and of average power spectra of the random processes under the variation of the system parameters. On the basis of the experimental results, an outline of the random process is made clear. The results obtained in this paper will be applied to various physical problems and will also serve as material for the development of a proper mathematics of this phenomenon. 相似文献
158.
159.
基于Labview的光学空间滤波远程虚拟实验 总被引:4,自引:0,他引:4
提出了一种利用Labview实现光学空间滤波模拟的新方法,并对经典的阿贝-波特实验设计了仿真程序.该程序可根据用户设置的参量生成二维网格光栅作为整个物理过程的输入物,允许用户选择多种不同的滤波方式,如低通、高通、方向滤波等,并可依次操纵成像的各个步骤.程序可脱离编程环境独立运行,具有跨平台、界面友好、易于操作等优点,并可架设基于浏览器的远程虚拟实验. 相似文献
160.