全文获取类型
收费全文 | 10438篇 |
免费 | 535篇 |
国内免费 | 132篇 |
专业分类
化学 | 7294篇 |
晶体学 | 92篇 |
力学 | 530篇 |
综合类 | 6篇 |
数学 | 1367篇 |
物理学 | 1816篇 |
出版年
2024年 | 21篇 |
2023年 | 88篇 |
2022年 | 190篇 |
2021年 | 455篇 |
2020年 | 383篇 |
2019年 | 458篇 |
2018年 | 467篇 |
2017年 | 381篇 |
2016年 | 620篇 |
2015年 | 443篇 |
2014年 | 595篇 |
2013年 | 1111篇 |
2012年 | 847篇 |
2011年 | 809篇 |
2010年 | 580篇 |
2009年 | 473篇 |
2008年 | 516篇 |
2007年 | 454篇 |
2006年 | 320篇 |
2005年 | 320篇 |
2004年 | 196篇 |
2003年 | 195篇 |
2002年 | 165篇 |
2001年 | 88篇 |
2000年 | 57篇 |
1999年 | 66篇 |
1998年 | 43篇 |
1997年 | 54篇 |
1996年 | 51篇 |
1995年 | 35篇 |
1994年 | 40篇 |
1993年 | 20篇 |
1992年 | 39篇 |
1991年 | 34篇 |
1990年 | 30篇 |
1989年 | 36篇 |
1988年 | 32篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 38篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The potential between two12C nuclei in linear chain configuration has been calculated microscopically using the Ali-Bodmerα-α potential. This potential shows a pocket and compares well in the tail region with the phenomenological potential extracted
before, from the data on the quasi-molecular resonances of the12C +12C system. This provides support to the diatomic like rotation-vibration picture of quasi-molecular states. 相似文献
992.
Alkyl halides are efficiently converted to their corresponding nitroalkanes under mild and nonaqueous conditions by using polymer supported nitrites. The polymeric reagent is regenerable. 相似文献
993.
Optical shadow-casting (OSC) technique has shown excellent potential for optically implementing two-operand parallel logic gates and array logic operations. The 16 logic functions for two binary patterns (variables) are optically realizable in parallel by properly configuring an array of 2×2 light emitting diodes. In this paper, we propose an enhanced OSC technique for implementing four-operand parallel logic gates. The proposed system is capable of performing 216 logic functions by simply programming the switching mode of an array of 4×4 light emitting diodes in the input plane. This leads to an efficient and compact realization scheme when compared to the conventional two-operand OSC system. 相似文献
994.
Flow-Injection Spectrophotometric Determination of Hydrazine 总被引:1,自引:0,他引:1
A flow-injection spectrophotometric method for the determination of hydrazine is described. The method is based on the inhibitory effect of hydrazine on the reaction of thionine with nitrite in acidic media. The decolorization of thionine by the reaction with nitrite was used to monitor the reaction spectrophotometrically at 602 nm. The variables that affected the reaction rate were fully investigated and the optimum conditions were established. Hydrazine can be determined in the range 2.0–40.0 μg/ml with a limit of detection of 1.0 μg/ml. The relative standard deviation for 10 replicate determinations of 7.0 μg/ml hydrazine is 3.3%. The method is simple, rapid, and widely applicable. 相似文献
995.
Ali Ridha Mahjoub 《Discrete Mathematics》1997,170(1-3):153-172
This paper studies the graphs for which the 2-edge connected spanning subgraph polytope is completely described by the trivial inequalities and the so-called cut inequalities. These graphs are called perfectly 2-edge connected. The class of perfectly 2-edge connected graphs contains for instance the class of series-parallel graphs. We introduce a new class of perfectly 2-edge connected graphs. We discuss some structural properties of graphs which are (minimally with respect to some reduction operations) nonperfectly 2-edge connected. Using this we give sufficient conditions for a graph to be perfectly 2-edge connected. 相似文献
996.
Solid polymer electrolyte films based on poly(vinyl chloride)-lithium triflate (PVC-LiCF3SO3) have been prepared by the solution-cast technique in various concentrations. The film with the highest conductivity was
used to prepare plasticised polymer electrolyte films by using poly(ethlene glycol) (PEG) of different molecular weights,
i.e., 200, 400 and 600 gmol−1. These films were prepared to study the effects of addition of low molecular weights PEG on the lithium ionic conduction
of the PVC based polymer electrolyte. The films were characterised by electrochemical impedance spectroscopy (EIS) and Fourier
transform infrared-spectroscopy (FTIR). Results indicate that the molecular weight has an inverse effect on the conductivity
and this has been accounted for by FTIR.
Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 –
8, 2005. 相似文献
997.
Atif Fazal Sahar Al-Fayez Laila H. Abdel-Rahman Zaki S. Seddigi Abdul Rahman Al-Arfaj Bassam El Ali Mohammad A. Dastageer Mohammad A. Gondal Mohammed Fettouhi 《Polyhedron》2009,28(18):4072-4076
New copper(I) mixed-ligand complexes 1–4 of the formula Cu(N–N)PR3X, where N–N = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′dimbpy) and PR3 = tricyclohexylphosphine, tris(2-cyanoethyl)phosphine and isopropyldiphenylphosphine, have been synthesized. The complexes were characterized by EA, IR, NMR and single crystal X-ray diffraction. The solution fluorescence emission spectra were measured. The single crystal X-ray analysis showed that the copper(I) ion is four-coordinate with a distorted tetrahedral geometry. The complexes catalyze the formation of diphenylacetylene from the coupling of halobenzene with phenylacetylene. The complex Cu(5,5′-dimethylbpy)P{(cyhexyl)3}I showed the highest catalytic activity. At room temperature all four complexes exhibit, in dichloromethane, emission maxima in the 329–344 nm range, corresponding to intra-ligand excited states. 相似文献
998.
In this work we use the vapor-sorption equilibrium data to show the degree of solvent upturn in each solvent-polymer system. For this purpose, 23 isothermal data sets for four polymer + solvent binaries, one block copolymer + solvent binary and for the corresponding polymer pairs have been used in the temperature range of 25-70 °C. Solvents studied are benzene, carbon tetrachloride, chloroform and pentane. Homopolymers studied are polyisobutylene, poly(ε-caprolactone), poly(ethylene oxide), n-heptadecane, polystyrene, poly(vinyl chloride), poly(vinyl methyl ether), and n-tetracosane.According to these data sets, solvent weight fraction in the polymer is plotted against solvent-vapor activity that is calculated assuming an ideal gas phase of pure solvent vapor neglecting the vapor pressure of the polymer. We use the Flory-Huggins theory to obtain dimensionless interaction parameter, χ. Also the Zimm-Lundberg clustering theory and non-ideality thermodynamic factor, Γ are used to interpret the equilibrium data. 相似文献
999.
Barrett formula has been obtained in the framework of the effective field approach by including the zero-point energy. By fitting with experimental data of dielectric constant of SrTiO3, we find that they agree in the whole temperature range fairly well if the zero-point energy is assumed to change from a small value at low temperature to a large value at high temperature. 相似文献
1000.
Saqib Ali Syed Usman Ahmad Sadiq‐ur‐Rehman Saira Shahzadi Masood Parvez Muhammad Mazhar 《应用有机金属化学》2005,19(1):200-200
A trigonal bipyramidal C2ClS2 coordination geometry for tin is found in Ph2Sn(S2CN(CH2)5)Cl. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献