全文获取类型
收费全文 | 2796篇 |
免费 | 308篇 |
国内免费 | 348篇 |
专业分类
化学 | 732篇 |
晶体学 | 21篇 |
力学 | 341篇 |
综合类 | 76篇 |
数学 | 1339篇 |
物理学 | 943篇 |
出版年
2024年 | 9篇 |
2023年 | 28篇 |
2022年 | 53篇 |
2021年 | 59篇 |
2020年 | 54篇 |
2019年 | 64篇 |
2018年 | 60篇 |
2017年 | 91篇 |
2016年 | 92篇 |
2015年 | 97篇 |
2014年 | 174篇 |
2013年 | 238篇 |
2012年 | 173篇 |
2011年 | 191篇 |
2010年 | 133篇 |
2009年 | 186篇 |
2008年 | 198篇 |
2007年 | 201篇 |
2006年 | 158篇 |
2005年 | 163篇 |
2004年 | 127篇 |
2003年 | 125篇 |
2002年 | 116篇 |
2001年 | 97篇 |
2000年 | 75篇 |
1999年 | 85篇 |
1998年 | 68篇 |
1997年 | 67篇 |
1996年 | 53篇 |
1995年 | 34篇 |
1994年 | 34篇 |
1993年 | 14篇 |
1992年 | 28篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有3452条查询结果,搜索用时 15 毫秒
51.
52.
Summary The successful application of the formerly presented concept of diffusion-averaged molecular weight, Md, to vacuum residues of crude oils, or their fractions, is described. The samples for establishing the calibration curve, logDvs. logM, were crude oil fractions with polydispersities smaller than 1.1. In a surprisingly good approximation the calibration curve is independent of the origin of these fractions if 500<M<10000. The validity of our calibration curve was demonstrated with more than 10 crude oil residues and with some of their hydrogenation residues [2]. 相似文献
53.
The factors influencing the electrochemical behaviour of a supercapacitor have been partly examined in this work. The effects
of so-called intrinsic parameters, i.e. exchange current density, unit cell length and double layer (DL) capacitance; as well
as the so-called application parameters, i.e. cell current, on the cell potential discharge time have been considered. The
contributions of each type of capacitors, DL capacitor and faradaic supercapacitor under various states of operation and material
have been analyzed, and the competing (compensating) effects of the two types of capacitors as regards to the discharge and
power characteristics manifested by current–potential and energy–power (Ragone plots) are elucidated. 相似文献
54.
从自模式曲线分辨到渐进类因子分析法 总被引:1,自引:1,他引:1
本文对自模式曲线分辨法的发展作了简要回顾,其中特别对近来来迅速发展的一类用于色谱波谱联用仪产生的二维分析数据的渐进类分析法作了详尽的讨论。这些新化学计量学方法的涌现,对复杂的未知分析体系的定性定量分析,将带来深刻的变化。 相似文献
55.
To investigate the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine, this study uses a method based on microdialysis technique and liquid chromatography that allows continuous and concurrent in vivo monitoring of extracellular caffeine in the blood, brain and bile of anesthetized rats following the administration of caffeine (3 or 10 mg/kg, i.v.) through the femoral vein. Dialysates of the blood, brain and bile were directly injected onto the liquid chromatographic system and no further clean-up procedures were required. The study design consisted of two groups of six rats in parallel: the rats of the control group received caffeine (3 or 10 mg/kg, i.v.) alone and those of the cyclosporine treated-group were injected cyclosporine (10 mg/kg, i.v.) 10 min prior to caffeine administration (3 or 10 mg/kg, i.v.). The decline of caffeine in the blood, brain striatum and bile suggested that caffeine had rapid exchange and equilibration between the peripheral compartment and the central nervous system. In addition, the results indicated that caffeine underwent hepatobiliary excretion and was distributed into brain. When cyclosporine was co-administered, the pharmacokinetic parameters were not significantly altered. The results of this study reveal that the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine might not relate to P-glycoprotein. 相似文献
56.
The acid-catalysed esterification of myristic acid with isopropanol was studied by using near-infrared spectroscopy (NIR) in combination with soft-modeling curve resolution (MCR) methodology with a view to establishing the effect of experimental variables on the reaction kinetics. The reaction was conducted at temperatures above the boiling point of the alcohol, with continuous addition of an isopropanol/water mixture to the reactor. Spectral and concentration profiles were determined by applying soft-modeling curve resolution methodology to a column-wise augmented data matrix containing the spectra for the pure components. MCR profiles were compared with reference values and found to depart from then by less than 3% as %RSE for concentrations and to exhibit correlation above 0.999 for spectra.The reaction kinetics as estimated from the concentration profiles was found to be pseudo-first-order. Also, the pseudo-first-order rate constant was found to depend on the flow-rate of the isopropanol/water mixture and its water content; although the constant decreased with increase in the proportion of water, a content of ca. 15% could be used without important retarding effects on the kinetics. The proposed NIR-MCR method allows the rate constant and the influence of the initial water content to be determined with a view to minimizing consumption of the raw materials and optimizing the experimental conditions. 相似文献
57.
Timo O. Harju 《Journal of Molecular Structure》1996,360(1-3):135-144
Ab initio Hartree-Fock calculations utilising STO-3G, 3-21G* and 6-31G* basis sets have been performed on three neutral and highly polar molecules, (diformylmethine)borondifluoride, (acetylacetonato)borondifluoride and (dibenzylmethine) borondifluoride. The calculated and experimental structures are well correlated when using the HF/3-21G* basis set, except for the structure parameters involving the boron atom. The HF/6-31G* basis set does not improve the accuracy in structure calculations. The conformational analysis is in agreement with the experimentally observed C2v symmetrical structures, where the boron atom is tetrahedrally coordinated. The calculations support a one-dimensional ground state barrier crossing reaction for (dibenzylmethine)borondifluoride, where the phenyl torsion is the most likely reaction coordinate. Both HF/6-31G* calculations and the second-order Møller-Plesset correction with the 3-21G* basis set suggest an activation energy of the ground state reaction of about 30 kJ mol−1. The ground state barrier crossing reaction kinetics is evaluated by the Kramers theory. The calculated ground state parameters relevant to the barrier crossing reaction are compared with the experimentally observed excited state values. 相似文献
58.
59.
Tenu R. Gentil S. Baudu S. Counioux J. J. 《Journal of Thermal Analysis and Calorimetry》1999,58(1):89-101
The binary system H2O—UO2(NO3)2 was studied by solubility measurements and constant heat flow thermal analysis. Temperature and composition of the eutectic transformation between ice and uranyl nitrate hexahydrate were accurately defined. A new hydrate with 24 molecules of water decomposes at –21°C according to the peritectoid reaction<UO2(NO3)2·24H2O> <UO2(NO3)2·6H2O> + 18<H2O>The quasi-ideal model was applied to the solid—liquid equilibria, using the following reaction hypothesis:((UO
2
2+
)) + 2((NO
3
–
))+ h((H2O)) ((UO2OH+aq)) + ((H3O+aq + 2((NO
3
–
aq))A complete calculation of the binary system was carried out with a global ionic hydration number h equal to 9 in the aqueous solutions. It allowed to the melting enthalpies of uranyl nitrate hydrates.
This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
60.
J. Ghazouani 《Thermochimica Acta》2005,432(1):10-19
Volumetric properties of several low acentric factor fluids (Ar, CH4, C2H6, Kr, N2, Ne, O2, Xe) as well as CO2 are modeled using the Bender equation of state. This equation is a linear function of 19 adjustable parameters, which are evaluated from properties data, using a linear numerical procedure. The validity of the EOS is tested by calculating the Joule-Thomson inversion curve. A simple model is in particular used to correlate the inversion properties predicted by the Bender equation, expressed in term of reduced pressure as a function of reduced temperatures ranging from 0.8 to 6. The simple correlation reproduces accurately the used data. We employ data on state behaviour ρ(P,T) of homogeneous fluid phases, vapour-liquid equilibrium, second virial coefficient and the coordinates of the critical point. 相似文献