全文获取类型
收费全文 | 7014篇 |
免费 | 1198篇 |
国内免费 | 1064篇 |
专业分类
化学 | 3328篇 |
晶体学 | 35篇 |
力学 | 521篇 |
综合类 | 77篇 |
数学 | 1201篇 |
物理学 | 4114篇 |
出版年
2024年 | 7篇 |
2023年 | 88篇 |
2022年 | 177篇 |
2021年 | 180篇 |
2020年 | 259篇 |
2019年 | 231篇 |
2018年 | 195篇 |
2017年 | 206篇 |
2016年 | 226篇 |
2015年 | 235篇 |
2014年 | 332篇 |
2013年 | 610篇 |
2012年 | 425篇 |
2011年 | 423篇 |
2010年 | 352篇 |
2009年 | 448篇 |
2008年 | 487篇 |
2007年 | 502篇 |
2006年 | 482篇 |
2005年 | 420篇 |
2004年 | 390篇 |
2003年 | 359篇 |
2002年 | 318篇 |
2001年 | 234篇 |
2000年 | 245篇 |
1999年 | 204篇 |
1998年 | 201篇 |
1997年 | 173篇 |
1996年 | 110篇 |
1995年 | 101篇 |
1994年 | 85篇 |
1993年 | 76篇 |
1992年 | 79篇 |
1991年 | 61篇 |
1990年 | 45篇 |
1989年 | 38篇 |
1988年 | 36篇 |
1987年 | 33篇 |
1986年 | 27篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 26篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有9276条查询结果,搜索用时 15 毫秒
921.
UV absorption spectra of acetyl fluoride-h3 and -d3 (CH3COF and CD3COF) molecules in the region of S1S0 electronic transitions are investigated. The origins (00
0 or 140±
0) of these transitions are observed at 39912 and 39904 cm–1, respectively, and some of the fundamental frequencies of these molecules in the s0 and S1 states are determined. In particular, the systems of torsion and inversion (out-of-plane C=O vibrations) energy levels are studied. The geometric parameters of an acetyl fluoride-h3 molecule in the S1 state are estimated by the theoretical simulation of the rotational contours of the 00
0 (140±
0) band. These data are used to evaluate the potential barriers to internal rotation in the S0 and S1 states, which were found to be 360 and 560 cm–1 for acetyl fluoride-h3 and 380 and 770 cm–1 for acetyl fluoride-d3, respectively, as well as the potential barriers to inversion in the S1 states, which were found to be 2090 and 2370 cm–1 for acetyl fluoride-h3 and acetyl fluoride-d3, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1957–1964, November, 1994.In conclusion, the authors would like to acknowledge T. S. Kuznetsova for the synthesis and purification of the AF samples.The research presented here was supported in part by the International Science Foundation under grant No. MJ 1000. 相似文献
922.
923.
From the measurements of surface potentials of quartz capillaries before and after adsorption of poly(ethylene oxides) (PEO) of various molecular mass, an assessment of the equilibrium hydrodynamic thickness of the adsorption layers has been obtained. The results have been compared with those of independent measurements of . The flow of the polymer solution under increasing pressure drops at the ends of a capillary, which causes the corresponding shear stress () on the surface of adsorbed PEO layers, results in the deformation of the latter, which manifests itself in decreasing 5. The values decrease by several times when the shear stress rises to 2×102 N m–2. Such values of have been obtained using thin capillaries (r = 5÷6 mm) and by application of the capillary electrokinetic method with pressure drops up to 5÷6 MPa.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 31–37, January, 1994. 相似文献
924.
CHANG Kai-Guo LU Xiang-Ping DU Fu-Ying ZHAO Min-ShouChangchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun Jilin China 《中国化学》1994,(6)
The apparent standard potential of Dy/Dy(III) system in the LiCl-KCl eutectic has been determined by the logarithmic analysis of the semi-integrals of voltammograms, logarithmic analysis of chronopotentiograms and the open circuit potentiometry. The dysprosium equilibrium potentiab for various concentration of dysprosium chloride in the LiCl-KCl eutectic melt between 400-500℃ were first determined experimentally, and the apparent standard potential of this system and its temperature dependance have been calculated. 相似文献
925.
In order to systematically investigate the effects of simulated weightlessness on thefunction state of human brain, 15° head-down tilt (HDT) was used to simulate weightless-ness, and the response changes of event-related EEG power spectra, medium-frequencysynchronous potentials and slow-waves were examined in the present study. It was foundthat HDT had characteristic effects on the above EEG responses, suggesting that the ef-fects mainly occurred in the brain's regulatory system, therefore, resulting in changes ofthe brain function state. 相似文献
926.
Maksymilian Ignaczak Andrzej Grzejdziak Barbara Olejniczak 《Monatshefte für Chemie / Chemical Monthly》1989,120(6-7):515-527
Summary The conditional protonation constants (=0.1) for 2,2:6,2-terpyridine, logK
1=4.93, logK
2=3.69, were determined by thepH-metric method. The compositions of complexes of Ag2+ and Ag+ ions with 2,2:6,2-terpyridine (tp) were studied and equilibria of the complex formation process were described. The values of conditional complex formation constants are as follows: for Ag(tp)
2
+
:log01=5.79, log02=9.68, for Ag(tp)
2
2+
:log02=25.31, while the conditional constant of the Ag(tp)NO3 precipitate formation is:K
SO=2.45·104. Using coulometric and chronovoltamperometric measurements, the redox systems being formed in the complex solutions of Ag(II) and Ag(I) were determined and described including their formal potentials.
Komplexibildungsgleichgewichte und Redoxpotentiale des Systems Ag(II)/Ag(I) in Gegenwart von 2,2:6,2-Terpyridin in Wasser
Zusammenfassung Mit Hilfe derpH-metrischen Methode wurden die konditionalen Protonationskonstanten (=0.1) von 2,2:6,2-Terpyridin bestimmt: logK 1=4.93, logK 2=3.69. Es wurde auch die Zusammensetzung der Komplexe von Ag(II) und Ag(I) mit 2,2:6,2-Terpyridin(tp) bestimmt sowie die Gleichgewichte der komplexbildung beschrieben. Die Werte der Konditionalkomplexbildungskonstanten sind: für Ag(tp) 2 + :log01=5.79, log02=9.68, für Ag(tp) 2 2+ :log02=25.31 und für das Löslichkeitsprodukt Ag(tp)NO3:K SO –1 =4.08·10–5. Die in Komplexlösungen von Ag(II) und Ag(I) vorliegenden Redoxsysteme wurden mittels cyclischer Voltametrie und Coulometrie untersucht und die Formalpotentialwerte dieser Systeme in Wasser bestimmt.相似文献
927.
A new experimental approach is proposed for the evaluation of liquid junction potentials and single ion activities. Neither of these quantities can be experimentally measured without assumption. Furthermore, they are concentration dependent but without clearly defined functional relationships. Thus, a given assumption may be satisfactory to obtain these quantities at a given concentration, but will fail at another concentration. It is the intent of this paper to establish a functional relationship between the ratio of activity coefficients and the ionic strength, through which the liquid junction potentials may be computed, as well as the pH values at moderate ionic strengths (<1.0 m). Experimental results are presented and uncertainties are discussed. 相似文献
928.
Maksymilian Ignaczak Andrzej Grzejdziak Ewa Degen-Piotrowska 《Monatshefte für Chemie / Chemical Monthly》1989,120(6-7):529-537
Summary Composition of complexes of Ag(II) and Ag(I) ions with 2,2:6,2-terpyridine (tp) have been established. It has been found that the Ag+ ion forms only one complex Ag(tp)+ withtp in acetonitrile; its conditional formation constant: 01=6.6·104 has been determined by the potentiometric method. Equilibria and redox systems formed in solutions due to the complexation of Ag+ and Ag2+ and oxidation of Ag(II) complexes are described. Their formal potentials have been found by coulometric and voltamperometric examinations. The presence of the Ag(tp)
2
3+
ion in the anodic oxidized solutions of the complexes Ag(tp)(NO3)2 and Ag(tp)2(NO3)2 has been proved. Properties of the system Ag(II)/Ag(I) in the presence of terpyridine in water and in acetonitrile have been compared.
Charakteristik der Systeme Ag(II)/Ag(I) in Gegenwart von 2,2:6,2-Terpyridin in Acetonitril
Zusammenfassung Die Zusammensetzung der Komplexe von Ag(I)- und Ag(II)-Ionen mit 2,2:6,2-Terpyridin (tp) wurde bestimmt. Das Ag+-Ion bildet mittp in Acetonitril nur einen Komplex-Ag(tp)+. Seine Konditionalbildungskonstante 01=6.6·104 wurde mit Hilfe der potentiometrischen Methode bestimmt. Es wurden die Gleichgewichte und Redoxsysteme als Resultat der Komplexbildung von Ag(II)- und Ag(I)-Ionen und der Ag(II)-Komplexoxidation charakterisiert und die Formalpotentiale mittels Voltametrie und Coulometrie bestimmt. Die Gegenwart der Ag(tp) 2 3+ -Ionen wurde in anodisch oxydierten Lösungen der Komplexe Ag(tp)(NO3)2 und Ag(tp)2(NO3)2 nachgewiesen. Die Eigenschaften des Systems Ag(II)/Ag(I) in Gegenwart von 2,2:6,2-Terpyridin in Wasser und in Acetonitril wurden verglichen.相似文献
929.
Jian Wang Xing‐You Xu Lu‐De Lu Xu‐Jie Yang Wei‐Xing Ma Xiang‐Ning Cui 《Surface and interface analysis : SIA》2007,39(6):482-486
The streaming potential of supersaturated solution of binary carboxylic acids, which have even carbon atoms, was determined to characterize crystallization under different temperatures. The value of the streaming potential was related to the type and solubility of the acids and the starting temperature of crystallization, and was easily influenced by the pressure difference of the liquid or the rate of temperature decline. When the temperature was declined to the point where a crystal nucleus appeared, the streaming potential reached the minimum. Thereafter, as the temperature was sequentially lowered, some minicrystals grew, and the streaming potential presented an ascendant tendency. The higher the starting temperature of the acids saturated solution, the higher is the temperature corresponding to the streaming potential minimum. The less the carbon atoms in the acids and the greater the solubility of the acids are, the higher is the temperature of the streaming potential minimum. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
930.
Xiu Hui Lu Hai Bin Yu Wei Rong Wu Yue Hua Xu 《International journal of quantum chemistry》2007,107(2):451-457
Mechanisms of the cycloaddition reaction between singlet difluoromethylene carbene and acetone have been investigated with the second‐order Møller–Plesset (MP2)/6‐31G* method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface (PES) are corrected by zero‐point energy (ZPE) and CCSD(T)/6‐31G* single‐point calculations. From the PES obtained with the CCSD(T)//MP2/6‐31G* method for the cycloaddition reaction between singlet difluoromethylene carbene and acetone, it can be predicted that path B of reactions 2 and 3 should be two competitive leading channels of the cycloaddition reaction between difluoromethylene carbene and acetone. The former consists of two steps: (i) the two reactants first form a four‐membered ring intermediate, INT2, which is a barrier‐free exothermic reaction of 97.8 kJ/mol; (ii) the intermediate INT2 isomerizes to a four‐membered product P2b via a transition state TS2b with an energy barrier of 24.9 kJ/mol, which results from the methyl group transfer. The latter proceeds in three steps: (i) the two reactants first form an intermediate, INT1c, through a barrier‐free exothermic reaction of 199.4 kJ/mol; (ii) the intermediate INT1c further reacts with acetone to form a polycyclic intermediate, INT3, which is also a barrier‐free exothermic reaction of 27.4 kJ/mol; and (iii) INT3 isomerizes to a polycyclic product P3 via a transition state TS3 with an energy barrier of 25.8 kJ/mol. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献