全文获取类型
收费全文 | 6587篇 |
免费 | 1173篇 |
国内免费 | 1054篇 |
专业分类
化学 | 3286篇 |
晶体学 | 35篇 |
力学 | 532篇 |
综合类 | 73篇 |
数学 | 1083篇 |
物理学 | 3805篇 |
出版年
2024年 | 7篇 |
2023年 | 80篇 |
2022年 | 133篇 |
2021年 | 172篇 |
2020年 | 242篇 |
2019年 | 214篇 |
2018年 | 183篇 |
2017年 | 198篇 |
2016年 | 224篇 |
2015年 | 222篇 |
2014年 | 320篇 |
2013年 | 588篇 |
2012年 | 418篇 |
2011年 | 419篇 |
2010年 | 337篇 |
2009年 | 433篇 |
2008年 | 475篇 |
2007年 | 478篇 |
2006年 | 459篇 |
2005年 | 393篇 |
2004年 | 362篇 |
2003年 | 331篇 |
2002年 | 284篇 |
2001年 | 219篇 |
2000年 | 230篇 |
1999年 | 191篇 |
1998年 | 191篇 |
1997年 | 165篇 |
1996年 | 107篇 |
1995年 | 101篇 |
1994年 | 86篇 |
1993年 | 75篇 |
1992年 | 77篇 |
1991年 | 60篇 |
1990年 | 45篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有8814条查询结果,搜索用时 107 毫秒
191.
Michaël Deleuze Joseph Delhalle Barry T. Pickup 《Theoretical chemistry accounts》1992,82(3-4):309-319
Summary The vertical ionization potential and the related pole strength of a model alternant chain of 14 hydrogen atoms subject to a homogeneous electric field, parallel to the chain and of increasing intensity are calculated, in the framework of a 6–31G** basis set, at the second-order level of the many-body Green's function theory. Trends observed with orbital relaxation, pair removal and pair relaxation effects are interpreted in terms of deformations of the electron density. 相似文献
192.
The relative energies of one-, two-, and three-dimensional Bravais lattice Lennard-Jones particles can be calculated by lattice sums. The expression of lattice sums over a Lennard-Jones potential can be manipulated into a form that converges rapidly. A formalism capable of calculating the lattice potential at arbitrary points of a completely general lattice has been developed. This method provides an alternative way to calculate the relative energies from the surface and the interior bulk sites of many chemical systems. The method is illustrated with application to hcp and fcc Lennard-Jonesium, both for the relative binding energy and for calculating the potential along the geometric diffusion pathway between tetrahedral and octahedral interstitial sites. Diffusion from the tetrahedral site to the octahedral site experiences a barrier of 752.600 in units of 4 epsilon. The reverse pathway experiences a barrier of 1035.614 in units of 4 epsilon. 相似文献
193.
Lü Renqing ZHANG Hongyu QIU Guangmin LIU Chenguang College of Chemistry Chemical Engineering China University of Petroleum 《Chinese Journal of Reactive Polymers》2005,(Z1)
1. INTRODUCTION Chitin, the most abundant natural amino polysaccharide and estimated to be produced annually almost as much as cellulose, is well known to consist of 2-acetamido-2-deoxy-β-D- glucose through α, β(1→4) linkage. Chitin is the major source of surface pollution in coastalareas. Chitosan is the N-deacetylated derivative of chitin and their structures are shown in Fig. 1. Fig. 1 Structures of Chitin and Chitosan Because of the excellent properties such as biocompatibility… 相似文献
194.
A straightforward discussion on how to generate molecular fields is developed within the postulates of quantum mechanics. The theoretical formalism points towards the generalization and extension of the well-known molecular field forms, associated to density function and electrostatic molecular potential (EMP), including another category of fields associated to quantum molecular similarity measures. The results show that the new formalism can be easily applied to obtain an unlimited number of new information about molecular behavior. 相似文献
195.
E. Miyoshi T. Iura Y. Sakai H. Tochihara S. Tanaka H. Mori 《Journal of Molecular Structure》2003,630(1-3):225-232
We investigated the interactions between the Si(111) surface and the Na, Mg, and Al atoms using cluster model calculations. Calculations were performed at levels of complete-active-space self-consistent-field (CASSCF) and multi-reference singly and doubly excited configuration interaction (MRSDCI) calculations using the model core potential method. Our calculations revealed that the most favorable sites of Na, Mg, and Al adsorption on Si(111) are on top (T1), bridge (B2), and 3-fold filled (T4) sites, respectively. The nature of chemical bonds between these metal atoms and the dangling bonds of the surface Si atoms are found to be essentially covalent. 相似文献
196.
采用Mishin镶嵌原子势, 通过分子动力学方法模拟了金属Cu的低指数表面在不同温度的表面熔化行为, 分析了熔化过程中系统结构组态的变化以及固-液界面迁移情况. 金属Cu的(100)和(110)表面在低于熔点发生预熔化, 而(111)表面存在明显的过热现象. 准液体层的厚度随温度升高而增加, 热稳定性与表面的密排顺序一致, 按(111)、(100)、(110)顺序增大. 当温度高于热力学熔点时, 固液界面的移动速度与温度成正比, 外推得到热力学熔点约为1360~1380 K, 与实验结果1358 K吻合良好. 动力学系数定义为界面移动速度与过热程度的比值, 表现为明显的各向异性: k100=39 cm•s−1•K−1, k110=29 cm•s−1•K−1, k111=20 cm•s−1•K−1. k100与k110之间的比例符合collision-limited理论, (111)密排面有与其它低指数表面不同的熔化方式. 相似文献
197.
A. D. Smirnov 《Journal of Structural Chemistry》2003,44(5):757-762
The vibrational, rotational, and centrifugal constants have been calculated for the ground electronic states of KRb and RbCs molecules. The calculation is performed using the semiempirical potential curves constructed in a wide range of internuclear distances. The estimated spectroscopic constants are compared with experimental data. 相似文献
198.
B. F. Myasoedov L. A. Gribov A. I. Pavlyuchko I. V. Rybalchenko G. I. Sigeikin A. F. Kireev V. N. Suvorkin 《Journal of Structural Chemistry》2006,47(3):434-441
For highly toxic organophosphorus compounds on the limiting lists of the International Chemical Weapons Ban Treaty, fragment methods may be used for calculating their IR vibrational spectra; this is shown for O-alkyl alkylfluorophosphonates used as examples. The geometrical parameters and the parameters of the potential and electrooptic functions are found for the major fragments of these compounds. Due to this, fast predictive computation of IR spectra of O-alkyl alkylfluorophosphonates is possible, the accuracy of calculation being sufficient for spectral identification of these compounds; a database of the calculated IR spectra may be created. 相似文献
199.
Electrophoretic mobilities of hexadecane/water emulsions containing dimyristoyl-phosphatidylcholine (DMPC) or egg yolk lecithin
(EYL) monolayers at the interface and those of liposomes prepared from the same lipids were measured as functions of the concentrations
of Ca2+, Mn2+, Cu2+, and Ni2+ cations in the aqueous phase. The surface potentials, surface charge densities (σ), and the Langmuir adsorption isotherms
for various distances from the charged surface to the slip plane (d) were calculated on the basis of the Gouy-Chapman theory for 1∶2 electrolytes and the values of ζ-potentials. The binding
constants (K) and parametersd were determined under the assumption that the maximum σ values correspond to one ion per phospholipid molecule at the interface.
In the case of DMPC, the ion binding constants (L mol−1) at 25°C are 230 and 87 for Ca2+, 31.5 and 21 for Mn2+, 11 and 6 for Cu2+, and 7.5 and 5.3 for Ni2+ in liposomes and emulsions, respectively. The affinities of Cu2+ and Ni2+ ions for EYL monolayers and bilayers are lower than those for DMPC mono- and bilayers. Thed parameters for all ions are smaller than the radii of the hydrated ions. In the case of Ca2+, Cu2+, and Ni2+, thed values for mono- and bilayers are different. The differences in K values between monolayers and bilayers as well as those
between DMPC and EYL mono- and bilayers can be attributed to the differences in the local environment and orientation of the
interfacial phosphate groups in these systems.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2490–2495, December, 1998. 相似文献
200.
Zeta-potentials of self-assembled surface micelles of ionic surfactants adsorbed at hydrophobic graphite surfaces 总被引:1,自引:0,他引:1
Vamsi K. Paruchuri Anh V. Nguyen Jan D. Miller 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):519-526
The zeta-potentials of the self-assembled surface ionic surfactants (sodium dodecyl sulfate—SDS and hexadecyltrimethyl ammonium bromide—CTAB) on graphite surfaces were determined both from streaming potential and electrophoretic mobility measurements. The adsorption of the surfactants at graphite–liquid interfaces has been studied using atomic force microscopy (AFM) soft-contact imaging which shows the formation of linear, parallel hemicylinders with headgroups oriented towards the solution. The magnitude of the zeta-potential increased with an increase in surfactant concentration, reaching a constant value at a concentration corresponding to the point of surface micelle formation as confirmed from AFM imaging. The streaming potential and electrophoretic mobility measurements showed that the zeta-potentials of SDS and CTAB surface micelles adsorbed at the graphite surface were about −75 and +70 mV, respectively, well in agreement with the values reported for bulk phase micelles in the literature. 相似文献