全文获取类型
收费全文 | 3810篇 |
免费 | 284篇 |
国内免费 | 368篇 |
专业分类
化学 | 1556篇 |
晶体学 | 13篇 |
力学 | 289篇 |
综合类 | 66篇 |
数学 | 1800篇 |
物理学 | 738篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 53篇 |
2021年 | 84篇 |
2020年 | 85篇 |
2019年 | 87篇 |
2018年 | 83篇 |
2017年 | 96篇 |
2016年 | 125篇 |
2015年 | 59篇 |
2014年 | 153篇 |
2013年 | 236篇 |
2012年 | 215篇 |
2011年 | 193篇 |
2010年 | 226篇 |
2009年 | 227篇 |
2008年 | 221篇 |
2007年 | 271篇 |
2006年 | 219篇 |
2005年 | 229篇 |
2004年 | 171篇 |
2003年 | 185篇 |
2002年 | 132篇 |
2001年 | 130篇 |
2000年 | 116篇 |
1999年 | 94篇 |
1998年 | 77篇 |
1997年 | 70篇 |
1996年 | 66篇 |
1995年 | 45篇 |
1994年 | 82篇 |
1993年 | 52篇 |
1992年 | 56篇 |
1991年 | 35篇 |
1990年 | 33篇 |
1989年 | 30篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 27篇 |
1985年 | 29篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 19篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1969年 | 3篇 |
排序方式: 共有4462条查询结果,搜索用时 312 毫秒
161.
162.
163.
Attila R. Imre W. Alexander Van Hook Bong Ho Chang Young Chan Bae 《Monatshefte für Chemie / Chemical Monthly》2003,134(12):1529-1539
Summary. Upper critical solution temperatures (UCSTs) for liquid–liquid demixing in a set of mixtures of linear alkanes (pentane (N
1=5) to pentacontane (N
1=50)) with an oligostyrene (1241amu, N
2=12) are reported. We find strong correlation between the Hildebrand solubility parameters of the alkanes and the UCST. Correlations are developed which enable predictions concerning the miscibility of mixtures of compounds with longer chains. 相似文献
164.
The thermodynamic aspects of adsorption equilibrium in systems with crystalline, liquid, and dense gas phases have been considered. The heats of phase transition and corresponding directions of mass transfer from the adsorbed phase into crystalline and liquid phases at different temperatures have been determined. The general equilibrium diagram in the coordinates Inp-T
–1 has been given with indication of the equilibrium lines of three-phase systems and characteristic points on the isosteres of adsorption,viz., the Gurvitsch and quasicritical points.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1480–1485, August, 1995. 相似文献
165.
Measurements of the equilibrium degree of swelling and of the equilibrium modulus were performed on poly(dimethylsiloxane) networks (PDMS) and on polyisoprene vulcanizates. The results support the concept that topological interactions between network chains, e.g. entanglements or the like, have a large influence on the rubber elastic behavior, at least within a certain range of network densities.PDMS networks having network chains of different lengths and varying functionlities of the crosslinks were prepared in bulk by endlinking fractionated ,-divinyl PDMS via multifunctional hydrogen-siloxanes (f=3 to 22). Natural rubber (NR) and synthetic liquid polyisoprene (IR) were cured in bulk with various amounts of dicumyl peroxide to give randomly crosslinked samples.The experimentally determined moduli and degrees of swelling were compared with theoretical predictions based on the phantom network theory and affine network theory, taking into account only chemical crosslinks. The observed discrepancies can be traced back to a contribution of topological interactions (trapped entanglements) to the total effective network density. The modulus and swelling data are consistent, thus ruling out non-equilibrium effects. 相似文献
166.
测定了四元体系ErCl3-CdCl2-HCl-H2O(298.15K)的相平衡溶度数据, 绘制了相应的溶度图. 该四元体系是由4 个固相区CdCl2·H2O(原始盐)、9CdCl2·2ErCl3·29H2O、CdCl2·7ErCl3·42H2O、ErCl3·6H2O(原始盐)组成的复杂
体系. 对两个新物相化合物9CdCl2·2ErCl3·29H2O 和CdCl2·7ErCl3·42H2O 进行了XRD、TG-DTG 和荧光光谱研究.结果表明, 两个新物相化合物均具有荧光和上转换发光性能; 化合物9CdCl2·2ErCl3·29H2O通过3 步失去其结晶水, CdCl2·7ErCl3·42H2O 则1 步失去其结晶水. 相似文献
167.
Norman O. Smith 《Journal of solution chemistry》1994,23(4):521-539
A method of finding the activity coefficients of salts, anhydrous or hydrated, in binary solid solutions, described in an earlier paper as it applies to continuous series, has been applied to discontinuous series. The salts must differ with respect to only one ion. The method requires isothermal distribution data for equilibria between liquid (aqueous) and solid solutions in the ternary system consisting of the two salts and water. The following salt pairs were used for illustration: K(I/Br) at 0, 15, 25, 35, and 50°C., (NH4/K)SCN at 0, 30, 60, and 90°C., (K/Tl)C103 at 10°C., and (NH4/K)SO3NH2, (NH4/K)Br, (Mg/Co)SO4-7H2O, and (Mn/Cu) SO4.n H2O-all at 25°C. Two kinds of behavior were noted and treated differently: systems in which the two series have the same, and those in which they have different crystal lattices. For two salts, A and B, which have the same lattice, and whose rational activity coefficients, f
A
and f
B
, can be described by 2-suffix Margules equations (regular solutions), lnf
A
=Bsx
B
2
and lnf
B
=Bsx
A
2
to be partially miscible, Bs>2, but this requirement does not apply if the lattices are different. In each series, distribution constants for the equilibria were also determined. Where possible, the calculated activities of the salts or the Gibbs excess energies of the solid solutions were compared with values reported by others who determined them by other methods. All the salt pairs studied show slight or strong positive deviations from ideality. 相似文献
168.
Michael C. Bhm Joachim Schulte Rafael Ramírez 《International journal of quantum chemistry》2002,86(3):280-296
The absolute magnetic shieldings of benzene and ethylene have been theoretically studied under the conditions of thermal equilibrium, i.e., under explicit consideration of the nuclear degrees of freedom. For this purpose we have combined the Feynman path integral quantum Monte Carlo (PIMC) formalism with the gauge‐including atomic orbital (GIAO) approach in the Hartree–Fock (HF) approximation. The HF operator has been employed to derive the NMR parameters of the two hydrocarbons via an ensemble averaging over large sets of molecular configurations that are populated in thermal equilibrium. The nuclear fluctuations are responsible for a deshielding of the nuclei relative to the shieldings at the vibrationless minimum of the potential energy surface (PES). The influence of the nuclear degrees of freedom is largest for the isotropic part of the 13C shielding tensor. The theoretical results can be explained on the basis of simple geometrical considerations. The bond lengths in thermal equilibrium are larger than the bond lengths at the minimum of the PES. This length enhancement is the prerequisite for a deshielding of the nuclei in thermal equilibrium. The vibrational corrections of the nuclear magnetic resonance (NMR) parameters of benzene and ethylene are quantum driven; classical thermal degrees of freedom of the nuclei are of minor importance. Conceptual problems of theoretical studies of NMR parameters on the basis of a single molecular geometry are emphasized. The influence of the spatial uncertainty of the nuclei becomes decisive in molecules with light atoms. It is pointed out that the combination of the PIMC formalism with electronic Hamiltonians of state‐of‐the‐art quality renders possible accurate determinations of NMR parameters. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem 86: 280–296, 2002 相似文献
169.
Comparison of equilibrium and nonequilibrium models of a CSTR with total condenser focused on the multiple steady states and
dynamic behaviour was carried out. The steady-state behaviour of the model system, MTBE synthesis from methanol and isobutene
in a reactive distillation column, was studied in terms of the input parameters, i. e. feed flow rate of methanol or butenes, reflux ratio, and mass of catalyst. The dynamic behaviour of the system during the
start-up was investigated and perturbations of manipulated variables were found to cause transitions between the parallel
steady states.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
170.
C. Marhag H. Said P. Satre C. Favotto J. Rogez 《Journal of Thermal Analysis and Calorimetry》2003,74(1):275-285
Study of solid-liquid phase diagram of LiPO3-Pb(PO3)2 binary system, in certain calcination conditions, shows the existence of several metastable phasis. When heated at a temperature
of 723 K the binary mixtures lead uncompletely to a defined compound Pb2Li(PO3). On heating these ternary solid mixtures, three eutectic reactions have been observed: LiPO3+Pb(PO3)2→Liquid at a temperature of 793 K(1) LiPO3+Pb2Li(PO3)5→Liquid at a temperature of 843 K (2) Pb2Li(PO3)5+Pb(PO3)2→Liquid at a temperature of 891 K (3) The metastable liquid phase appears in the system at temperature of 793 K. DTA experiments
performed on the binary LiPO3-Pb(PO3)2 mixtures, show a superposition of two diagrams. The first one is metastable and the second represents the stable equilibrium
phase diagram. Measurements of liquid enthalpy of binary LiPO3-Pb(PO3)2 system at temperature of 979.65 K were reported. The corresponding values were very small and so the binary system can be
considered as athermal. Assuming an ideal behaviour, the liquidus curves in the metastable diagram were calculated and the
eutectic reaction (LiPO3-Pb(PO3)2→Liquid) was confirmed at 793 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献