全文获取类型
收费全文 | 6547篇 |
免费 | 1162篇 |
国内免费 | 1058篇 |
专业分类
化学 | 3313篇 |
晶体学 | 35篇 |
力学 | 474篇 |
综合类 | 73篇 |
数学 | 1130篇 |
物理学 | 3742篇 |
出版年
2024年 | 6篇 |
2023年 | 81篇 |
2022年 | 170篇 |
2021年 | 170篇 |
2020年 | 241篇 |
2019年 | 217篇 |
2018年 | 181篇 |
2017年 | 197篇 |
2016年 | 219篇 |
2015年 | 217篇 |
2014年 | 309篇 |
2013年 | 584篇 |
2012年 | 407篇 |
2011年 | 411篇 |
2010年 | 334篇 |
2009年 | 422篇 |
2008年 | 472篇 |
2007年 | 462篇 |
2006年 | 457篇 |
2005年 | 387篇 |
2004年 | 367篇 |
2003年 | 332篇 |
2002年 | 285篇 |
2001年 | 220篇 |
2000年 | 231篇 |
1999年 | 190篇 |
1998年 | 192篇 |
1997年 | 167篇 |
1996年 | 106篇 |
1995年 | 99篇 |
1994年 | 85篇 |
1993年 | 74篇 |
1992年 | 77篇 |
1991年 | 60篇 |
1990年 | 46篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 27篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 25篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有8767条查询结果,搜索用时 15 毫秒
121.
M. Nagy 《Colloid and polymer science》1985,263(3):245-265
122.
摘要运用多参考微扰理论(Multireference MΦller-Plesset theory)计算了SSCH3垂直激发能及其S-C与S-S两种断键方式的绝热(Adiabatic)与非绝热(Diabatic)的基态和激发态势能曲线, 研究了在193nm激光作用下SSCH3的光解离过程, 理论计算值与实验值相符. 相似文献
123.
We developed a novel measurement method of the Donnan potential difference at a charged membrane/salt solution interface. The method can measure the potential under the condition that the membrane charge density is much lower than the KCl concentration of the salt bridge. This method is very useful for obtaining the effective charge density of each layer of a bipolar membrane. The present experiments in a system of a negatively charged poly(vinyl alcohol) membrane and a single salt solution of KCl, NaCl, LiCl, CaCl2 and LaC3 revealed that the membrane effective charged density has the same value for all the ions. The experiments in mixed KCl and CaCl2 solution revealed that the potential in the system is governed mainly by the concentration of the counterion having the highest valence in the system. 相似文献
124.
A 285-pomt multi-reference configuration-interaction involving single and double excitations ( MRS DCI) potential energy surface for the electronic ground state of L12H is determined by using 6-311G (2df,2pd)basis set.A Simons-Parr-Finlan polynomial expansion is used to fit the discrete surface with a x2 of 4.64×106 The equn librium geometry occurs at Rc=0.172 nm and,LiHL1=94.10°.The dissociation energy for reaction I2H(2A)→L12(1∑g)+H(2S) is 243.910 kJ/mol,and that for reaction L12H(2A')→HL1(1∑) + L1(2S) is 106.445 kl/mol The inversion barrier height is 50.388 kj/mol.The vibrational energy levels are calculated using the discrete variable representation (DVR) method. 相似文献
125.
The electrostatic field associated with one complete turn of B-DNA is presented. Two base sequences poly (dG) · poly (dC) and poly (dA) · poly (dT) are studied and the effects of sodium counterions bound to the nucleic acid are investigated. The contrasts between the electrostatic potential and the electrostatic field of the macromolecules are discussed and the possible applications of the field are considered. 相似文献
126.
The dialysis potentials of different collodion membranes with graded pore sizes and electrochemical activities have been measured in dilute aqueous KCl solutions as functions of concentration. It is possible to predict the value of the diffusion potential within a few millivolts on the basis of electrical conductivity data obtained with the same membranes. In general, the measured values are lower than those calculated. It is assumed that this difference is caused by the membranes having a distribution of pore sizes. 相似文献
127.
二氧化碳和氧气的快速电化学方法联合测定 总被引:4,自引:0,他引:4
根据O2和CO2在二甲亚砜(DMSO)介质中Pt电极上的伏安特性,采用微电极并结构计算机控制的电位调制技术,建立了快速联合测定CO2和O2的调制电位脉冲库仑法和调制电位脉冲电流法,取得了满意的结果。一次测量时间快达40ms。CO2检测范围0 ̄10%(体积百分比);O2检测范围不受限制。通过编程设计特定的调制电位-时间波形,可保持连续检测的长期稳定性。 相似文献
128.
Shin-ichi Naya 《Tetrahedron》2004,60(23):4953-4958
The synthesis and properties of a novel type of 7,7-bis(heteroazulen-3-yl)-8,8-dicyano-1,4-quinodimethanes (9a-c) are studied. The synthetic method is based on a TFA-catalyzed electrophilic aromatic substitution on the heteroazulenes with 4-(dicyanomethyl)benzaldehyde to afford the corresponding methane derivatives, followed by oxidative hydrogen abstraction with DDQ. The polarization of 9a-c is evaluated by the inspection of their 13C NMR and IR spectra. Based on the investigation of the UV-Vis spectra of 9a-c and protonated cations 10a-c, conformational changes of the heteroazulene-moiety and (dicyanomethyl)phenyl group are suggested. In the CV measurements of 9a-c, two reversible reduction waves are observed, indicating the stabilizing ability of heteroazulenes toward the corresponding radical and anion species. Furthermore, 9a-c exhibit two irreversible oxidation waves, which suggest a conformational change in the radical cation during the redox process. The conformational change is rationalized on the basis of the MO calculations. 相似文献
129.
UV absorption spectra of acetyl fluoride-h3 and -d3 (CH3COF and CD3COF) molecules in the region of S1S0 electronic transitions are investigated. The origins (00
0 or 140±
0) of these transitions are observed at 39912 and 39904 cm–1, respectively, and some of the fundamental frequencies of these molecules in the s0 and S1 states are determined. In particular, the systems of torsion and inversion (out-of-plane C=O vibrations) energy levels are studied. The geometric parameters of an acetyl fluoride-h3 molecule in the S1 state are estimated by the theoretical simulation of the rotational contours of the 00
0 (140±
0) band. These data are used to evaluate the potential barriers to internal rotation in the S0 and S1 states, which were found to be 360 and 560 cm–1 for acetyl fluoride-h3 and 380 and 770 cm–1 for acetyl fluoride-d3, respectively, as well as the potential barriers to inversion in the S1 states, which were found to be 2090 and 2370 cm–1 for acetyl fluoride-h3 and acetyl fluoride-d3, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1957–1964, November, 1994.In conclusion, the authors would like to acknowledge T. S. Kuznetsova for the synthesis and purification of the AF samples.The research presented here was supported in part by the International Science Foundation under grant No. MJ 1000. 相似文献
130.
Atomic chemisorption of hydrogen and oxygen on the Ni(100) surface has been studied using an Effective Core Potential (ECP) approach described in a previous paper. Clusters of up to 50 nickel atoms have been used to model the surface. The computed chemisorption energies are 62 kcal/mol (exp. 63 kcal/mol) for hydrogen and 106 kcal/mol (exp. 115–130 kcal/mol) for oxygen. Correlating the adsorbate and the cluster-adsorbate bonds is extremely important for obtaining accceptable results, particularly for oxygen. Reasonable convergence of chemisorption energies is obtained with 40–50 cluster atoms for both hydrogen and oxygen. For hydrogen the addition of a third cluster layer stabilizes the results considerably. Both hydrogen and oxygen are adsorbed at (or close to) the four-fold hollow site. The calculated barriers for surface migration are also in good agreement with the experimental estimates. The calculated equilibrium heights above the surface are on the other hand too high compared with experiments. This disagreement is believed to be due to core-valence correlation effects, which are not incorporated in the present ECP. The cluster convergence for the height above the surface is much slower than for the chemisorption energy. 相似文献