全文获取类型
收费全文 | 1855篇 |
免费 | 37篇 |
国内免费 | 220篇 |
专业分类
化学 | 863篇 |
晶体学 | 7篇 |
力学 | 61篇 |
综合类 | 2篇 |
数学 | 590篇 |
物理学 | 589篇 |
出版年
2024年 | 2篇 |
2023年 | 24篇 |
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 23篇 |
2019年 | 22篇 |
2018年 | 26篇 |
2017年 | 42篇 |
2016年 | 39篇 |
2015年 | 65篇 |
2014年 | 76篇 |
2013年 | 140篇 |
2012年 | 154篇 |
2011年 | 149篇 |
2010年 | 87篇 |
2009年 | 134篇 |
2008年 | 111篇 |
2007年 | 100篇 |
2006年 | 105篇 |
2005年 | 85篇 |
2004年 | 85篇 |
2003年 | 79篇 |
2002年 | 57篇 |
2001年 | 51篇 |
2000年 | 45篇 |
1999年 | 52篇 |
1998年 | 40篇 |
1997年 | 39篇 |
1996年 | 35篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1974年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有2112条查询结果,搜索用时 24 毫秒
51.
Fatma M. Elzawawy 《Monatshefte für Chemie / Chemical Monthly》1991,122(11):921-925
Summary The stoichiometric stability constants for La(III) and Y(III)L-serine complexes were determined by potentiometric methods at different ionic strengths adjusted with NaClO4 and at different temperatures. The overall changes in free energy (G
o), enthalpy (H
o), and entropy (S
o) during the protonation ofL-serine and that accompanying the complex formation with the metal ions have been evaluated.
Komplexbildungskonstanten und thermodynamische Parameter für La(III)- und Y(III)-L-Serin-Komplexe
Zusammenfassung Die stöchiometrischen Komplexbildungskonstanten für La(III)- und Y(III)-L-Serin-Komplexe wurden mittels potentiometrischer Methoden bei verschiedenen Ionenstärken (mit NaClO4 adjustiert) und bei verschiedenen Temperaturen bestimmt. Die Änderungen in der freien Energie (G o), Enthalpie (H o) und Entropie (S o) während der Protonierung und der Komplexbildung mit den Metallionen wurden ermittelt.相似文献
52.
By high-precision dynamic calorimetry the temperature dependences of heat capacity of dimethylene urethane (DMU) between 320 and 370 K and partially crystalline poly(dimethylene urethane) (PDMU) in the range 326-490 K at standard pressure have been determined within ±1.5%. The thermodynamic characteristics of fusion of the substances, namely the temperature interval of melting, temperature, enthalpy and entropy of fusion, as well as the characteristics of devitrification and glassy state for poly(dimethylene urethane) have been estimated. The first and the second cryoscopic constants have been calculated for dimethylene urethane. The experimental data obtained in the present work and literature findings on the heat capacity of the substances were used to calculate their thermodynamic functions: the heat capacity C°p (T), enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from T→0 to (370-480) K. Based on the data, the thermodynamic characteristics of polymerization process with five-membered ring opening ΔpolH°, ΔpolS° and ΔpolG° of dimethylene urethane with the formation of linear partially crystalline poly(dimethylene urethane) have been evaluated. 相似文献
53.
Low-temperature heat capacities of the compound Na(C4H7O5)·H2O(s) have been measured with an automated adiabatic calorimeter. A solid-solid phase transition and dehydration occur at 290-318 K and 367-373 K, respectively. The enthalpy and entropy of the solid-solid transition are ΔtransHm = (5.75 ± 0.01) kJ mol−1 and ΔtransSm = (18.47 ± 0.02) J K−1 mol−1. The enthalpy and entropy of the dehydration are ΔdHm = (15.35 ± 0.03) kJ mol−1 and ΔdSm = (41.35 ± 0.08) J K−1 mol−1. Experimental values of heat capacities for the solids (I and II) and the solid-liquid mixture (III) have been fitted to polynomial equations. 相似文献
54.
Dhanpat Rai Yuanxian Xia Linfeng Rao Nancy J. Hess Andrew R. Felmy Dean A. Moore David E. McCready 《Journal of solution chemistry》2005,34(4):469-498
The objectives of this study were to address uncertainties in the solubility product of (UO2)3(PO4)2⋅4H2O(c) and in the phosphate complexes of U(VI), and more importantly to develop needed thermodynamic data for the Pu(VI)-phosphate system in order to ascertain the extent to which U(VI) and Pu(VI) behave in an analogous fashion. Thus studies were conducted on (UO2)3(PO4)2⋅4H2O(c) and (PuO2)3(PO4)2⋅4H2O(am) solubilities for long-equilibration periods (up to 870 days) in a wide range of pH values (2.5 to 10.5) at fixed phosphate concentrations of 0.001 and 0.01 M, and in a range of phosphate concentrations (0.0001–1.0 M) at fixed pH values of about 3.5. A combination of techniques (XRD, DTA/TG, XAS, and thermodynamic analyses) was used to characterize the reaction products. The U(VI)-phosphate data for the most part agree closely with thermodynamic data presented in Guillaumont et al.,(1) although we cannot verify the existence of several U(VI) hydrolyses and phosphate species and we find the reported value for formation constant of UO2PO−4 is in error by more than two orders of magnitude. A comprehensive thermodynamic model for (PuO2)3(PO4)2⋅4H2O(am) solubility in the H+-Na+-OH−-Cl−-H2PO−4-HPO2−4-PO3−4-H2O system, previously unavailable, is presented and the data shows that the U(VI)-phosphate system is an excellent analog for the Pu(VI)-phosphate system. 相似文献
55.
Luiza N.H. Arakaki Maria G. da Fonseca Edson C. da Silva Filho Ana Paula de M. Alves Kaline S. de Sousa Andr Leonardo P. Silva 《Thermochimica Acta》2006,450(1-2):12-15
The reaction of ethylene sulfide with 3-aminopropyltrimethoxysilane gave a new silylating agent, which was anchored onto a silica surface via the sol–gel procedure. This surface displayed a chelating moiety containing nitrogen and two sulfur basic centers potentially capable of extracting cations from aqueous solutions. The process of metal extraction was followed by a batch method, and fitted to a modified Langmuir equation. The maximum adsorption capacities found were: 2.06 ± 0.01, 3.72 ± 0.02, and 5.14 ± 0.02 mmol g−1 for Pb(II), Cd(II), and Hg(II), respectively. The enthalpies of bending are: −1.16 ± 0.04, −3.60 ± 0.10, and −8.94 ± 0.03 kJ mol−1 for Cd(II), Pb(II), and Hg(II), respectively. The Gibbs free energies of binding agree with the spontaneity of the proposed reactions between cations and basic centers. 相似文献
56.
S.I. Lopatin S.M. Shugurov Z.G. Turnina 《The Journal of chemical thermodynamics》2006,38(12):1706-1710
In the present study, the stability of gaseous barium silicates was confirmed by the high temperature mass spectrometry. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined for gaseous barium silicates as (−510 ± 15) kJ · mol−1 and (−884 ± 18) kJ · mol−1 at 298 K; standard atomization enthalpies as (1637 ± 17) kJ · mol−1 and (2318 ± 20) kJ · mol−1 at 298 K for BaSiO2 and BaSiO3, respectively. Based on the results obtained the critical analysis of the literature data was carried out. 相似文献
57.
硝酸甲酯分子间相互作用的DFT和ab initio比较 总被引:5,自引:0,他引:5
用密度泛函理论(DFT)和从头算(ab initio)方法,分别在B3LYP/6 31G和HF/6 31G水平上求得硝酸甲酯三种二聚体的全优化几何构型和电子结构,并用6 311G和6 311++G基组进行总能量计算.对HF/6 31G计算结果进行MP4SDTQ电子相关校正.在各基组下均进行基组叠加误差(BSSE)和零点能(ZPE)校正求得结合能.对6 31G优化构型作振动分析并基于统计热力学求得200~600 K温度下单体和二聚体的热力学性质.详细比较两种方法的相应计算结果,发现DFT求得的分子间距离较短,分子内键长较长,所得结合能均小于相应ab initio计算值. 相似文献
58.
David MacGowan 《Journal of statistical physics》1983,32(1):123-139
The consequences of choosing the adjustable hard-core diameter in the mean spherical approximation for the one-component plasma so as to achieve thermodynamic consistency between the energy and compressibility equations are investigated. Such a choice is found to be possible only for >8.5 and, although the resulting correlation functions are discontinuous, the height of the main peak in the static structure factor is remarkably accurate. Two especially noteworthy aspects of the thermodynamic results are that the compressibility equation is much more accurate than in any previous approximation free of input from computer simulations and that the nonstatic part of the internal energy has a 1/4 dependence in the strong coupling limit in agreement with Monte Carlo data. 相似文献
59.
信息拓扑指数与烷烃分子热力学性质的关系 总被引:13,自引:0,他引:13
Two topological information indices were constructed based on Randic and Wiener indices, and the values of topological information indices for 85 alkanes were calculated. The thermodynamic properties such as the standard enthalpies of formation, the standard entropies and the standard free energies of formation for these alkanes were also correlated with these topological and information indices. It is found that the thermodynamic properties calculated for both gaseous and liquid states of the 85 alkanes are in excellent agreement with the experimental values through the regression analysis. 相似文献
60.