全文获取类型
收费全文 | 10139篇 |
免费 | 1431篇 |
国内免费 | 1429篇 |
专业分类
化学 | 6096篇 |
晶体学 | 101篇 |
力学 | 1387篇 |
综合类 | 66篇 |
数学 | 522篇 |
物理学 | 4827篇 |
出版年
2024年 | 28篇 |
2023年 | 121篇 |
2022年 | 277篇 |
2021年 | 291篇 |
2020年 | 390篇 |
2019年 | 342篇 |
2018年 | 307篇 |
2017年 | 408篇 |
2016年 | 426篇 |
2015年 | 396篇 |
2014年 | 526篇 |
2013年 | 854篇 |
2012年 | 641篇 |
2011年 | 726篇 |
2010年 | 559篇 |
2009年 | 616篇 |
2008年 | 584篇 |
2007年 | 638篇 |
2006年 | 557篇 |
2005年 | 571篇 |
2004年 | 479篇 |
2003年 | 412篇 |
2002年 | 346篇 |
2001年 | 346篇 |
2000年 | 283篇 |
1999年 | 242篇 |
1998年 | 222篇 |
1997年 | 178篇 |
1996年 | 159篇 |
1995年 | 161篇 |
1994年 | 133篇 |
1993年 | 98篇 |
1992年 | 94篇 |
1991年 | 82篇 |
1990年 | 68篇 |
1989年 | 48篇 |
1988年 | 51篇 |
1987年 | 36篇 |
1986年 | 36篇 |
1985年 | 41篇 |
1984年 | 34篇 |
1983年 | 13篇 |
1982年 | 30篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 15篇 |
1977年 | 24篇 |
1976年 | 13篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Dominique Dehareng Georges Dive Josette Lamotte-Brasseur Jean-Marie Ghuysen 《Theoretical chemistry accounts》1989,76(2):85-94
Summary The electrostatic interaction energy between methanol and the dyad water-imidazole has been computed numerically at three levels of approximation from 3D grids of the charge density of one partner and the electrostatic potential of the other. The minimum positions and energy values thus obtained compare well with those calculated analytically. The numerical procedure is especially interesting for the prediction of the stable conformers. 相似文献
102.
Bernards T.N.M. Huls B.G. van Bommel M.J. 《Journal of Sol-Gel Science and Technology》1997,10(2):193-202
This article describes the SmartKom Companion, one of three demonstrators developed within the SmartKom project whose goal
has been to provide an intuitive and intelligent interface for non-expert users to everyday computer-based applications in
different scenarios of use. Conceived for the SmartKom Mobile scenario, the Companion allows intuitive multimodal interaction
for drivers and pedestrians. The development of the SmartKom prototypes was constantly accompanied by Wizard-of-Oz experiments
as well as system evaluations at different stages of the project. Some usability evaluation results relative to the SmartKom
Companion will also be presented. 相似文献
103.
In this paper we present a series of work covering a range of aspects relating molecular simulation to experiment. The importance
of surface mediation type effects to the adsorption of simple and complex gases is demonstrated. Coupled with the adsorption
of simple gases is their projection area when used for surface area determination. The pressure dependence of a projection
area is demonstrated for argon at 77 and 87.3 K. A simple model is used to account for the degree of graphitisation of a surface
is demonstrated and used to account for the isosteric heat behaviour of non-graphitised carbon blacks. Turning from surfaces
to porous solids, an alternative treatment of experiment data (either sub or super critical) is presented that avoids the
ambiguity of excess amounts adsorbed. Using this method one is able to obtain pore size distributions and amounts adsorbed
without relying on such things as helium expansion volumes. Since this type of method is usually applied to composite solids
we also demonstrate the correct method for calculating the heat of adsorption using independent sets of simulations. The final
topic covered in this paper is an example of the information that can be gained from the heat capacity of an adsorbed phase. 相似文献
104.
Apparent molal heat capacities
of some piperidine, morpholine, and piperazine derivatives in aqueous solution have been determined by adiabatic calorimetry
in the temperature range 20–55°C and in the molality range 0.2–1m. Comparison of experimental
values with those calculated through group contributions, found for monofunctional compounds, indicates strong interactions
between the hydrophilic centers. An interpretation is given of the possible mechanism of this interaction. Also, values of
ΔC
p
for the addition reaction of proton to nitrogen centers of mono- and bifunctional organic compounds are examined. 相似文献
105.
通过不同阳离子和不同阴离子对唾液链球菌嗜热亚种(Streptococcus salivariussub sp.thermophilus)谷氨酸脱羧酶活性的影响以及NaNO3对不同蛋白质浓度的谷氨酸脱羧酶活性的影响进行考察,结果表明:中性盐对谷氨酸脱羧酶活性的影响不是由于增加蛋白质亚基间的疏水作用引起的,而可能是由中性盐对谷氨酸脱羧酶活性的弱抑制作用与中性盐增加了谷氨酸脱羧酶的胶体体系稳定性共同作用所致,同时还可能与中性盐降低了反应体系CO2的溶解度有关. 相似文献
106.
The energy of a disubstituted molecule has often been approximated by simple electrostatic formulas that represent the substituents as poles or dipoles. Herein, we test this approach on a new model system that is more direct and more efficient than testing on acid-base properties. The energies of 27 1,4-derivatives of bicyclo[2.2.2]octane were calculated within the framework of the density functional theory at the B3LYP/6-311+G(d,p) level; interaction of the two substituents was evaluated in terms of isodesmic homodesmotic reactions. This interaction energy, checked previously on some experimental gas-phase acidities, was considered to be accurate and served as reference to test the electrostatic approximation. This approximation works well in the qualitative sense as far as the sign and the order of magnitude are concerned: beginning with the strongest interaction between two poles, a weaker interaction between pole and dipole, and the weakest between two dipoles. However, all the electrostatic calculations yield energies that are too small, particularly for weak interaction, and this fundamental defect is not remedied by some possible improvements. In particular, variation of the effective permittivity would require a physically impossible value less than unity. The explanation must lie in a more complex distribution of electron density than anticipated in the electrostatic model. It also follows that possible conclusions about the transmission of substituent effects "through space" have little validity. 相似文献
107.
R. Winkler J. Wilhelm M. Capitelli C. Gorse 《Plasma Chemistry and Plasma Processing》1992,12(1):71-87
Calculations of the electron energy distribution and of relevant macroscopic quantities of collision-dominated, weakly ionized plasmas under rf field action have been performed with increasing degrees of ionization, and the impact of the electron-electron interaction on these quantities was determined. The investigations were performed for the gas plasmas in CO and H2 as representatives of molecular plasmas The energy distribution and macroscopic quantities are obtained by solving the nonstationary Bolizmann equation for a given rf field and degree of ionization taking into accoung and additional Fokker-Planck term besides the collision integrals for the elastic and the main inelastic collision processes. In these molecular plasmas a remarkable impact of the electron-electron interaction connected with increasing Maxwellization is observed for degrees of ionization greater than 10. 相似文献
108.
A 'H NMR signal shifted drastically to down field (δ - 10.0) at the bay area and in dose proximity to C = O group for H-1 was observed through complete assignments of 1H NMR spectra for pyridino- and benzobenzanthrones. It is concluded that this phenomenon is due not only to the anisotropy effect of C=O plus aromatic ring current effect, but also to the electrostatic attraction of C-H (δ+)…O(δ-)=C interaction. The evidence for the sp2C-H…O = C intramolecular interaction similar to hydrogen bond has also been given by EI-MS and MS/MS (CID) spectroscopy and IR spectroscopy, as well as MNDO-PM3 calculations. This new kind of interaction might be called 'quasi-hydrogen bond'. 相似文献
109.
J. Howard Rytting Danny R. McHan Takeru Higuchi David J. W. Grant 《Journal of solution chemistry》1986,15(8):693-703
Henry's law constants have been determined for -butyrolactone (BL), ethyl acetate (EA), and 2-methyl-3-pentanol (MEP) in mixtures of iso-octane (ISO) and toluene (TOL), for BL, EA, TOL, and ISO in cinnamaldehyde (CIN) and for TOL and ISO in each other and in BL. From these data and published vapor pressures, the activity coefficients at infinite dilution and the standard molar Gibbs free energy of transfer, G
2
0
of the solutes from dilute solution in ISO to dilute solution in each solvent medium have been calculated. The different behavior patterns of BL and EA are attributed to differences in their abilities to exist in different conformations possessing different dipole moments. For polar solutes, G
2
0
decreases with increasing polarizability of the solvent and with increasing dipole moment of the solute, suggesting increased contributions from dipole-induced dipole (Debye) interactions. The sigmoidal plot of G
2
0
against the change in pair potential energy calculated from the classical expressions suggests that G
2
0
seriously underestimates the strength of the Debye interactions in comparison with the London interactions. 相似文献
110.
The solid-state reactions of crystalline ferrocenyl- and ruthenocenylaldehydes with optically active primary β-hydroxyamines
were studied at ∼20 °C. The yield of the products increases substantially in the presence of K2CO3. The tautomeric equilibrium between imines and diastereomeric oxazolidines with the predominant formation of one of them
is established in solutions of the products in CDCl3.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2240–2243, December, 1997. 相似文献