全文获取类型
收费全文 | 6223篇 |
免费 | 161篇 |
国内免费 | 18篇 |
专业分类
化学 | 4540篇 |
晶体学 | 20篇 |
力学 | 72篇 |
数学 | 983篇 |
物理学 | 787篇 |
出版年
2020年 | 54篇 |
2019年 | 63篇 |
2016年 | 106篇 |
2015年 | 98篇 |
2014年 | 108篇 |
2013年 | 199篇 |
2012年 | 186篇 |
2011年 | 256篇 |
2010年 | 132篇 |
2009年 | 123篇 |
2008年 | 251篇 |
2007年 | 236篇 |
2006年 | 234篇 |
2005年 | 262篇 |
2004年 | 210篇 |
2003年 | 181篇 |
2002年 | 185篇 |
2001年 | 93篇 |
2000年 | 81篇 |
1999年 | 73篇 |
1998年 | 61篇 |
1997年 | 89篇 |
1996年 | 77篇 |
1995年 | 90篇 |
1994年 | 61篇 |
1993年 | 65篇 |
1992年 | 94篇 |
1991年 | 60篇 |
1990年 | 82篇 |
1989年 | 46篇 |
1988年 | 77篇 |
1987年 | 78篇 |
1986年 | 50篇 |
1985年 | 106篇 |
1984年 | 63篇 |
1983年 | 64篇 |
1982年 | 80篇 |
1981年 | 71篇 |
1980年 | 59篇 |
1979年 | 74篇 |
1978年 | 70篇 |
1977年 | 58篇 |
1976年 | 81篇 |
1975年 | 81篇 |
1974年 | 68篇 |
1973年 | 55篇 |
1972年 | 46篇 |
1970年 | 51篇 |
1967年 | 44篇 |
1966年 | 47篇 |
排序方式: 共有6402条查询结果,搜索用时 0 毫秒
31.
Karl Jug 《Theoretical chemistry accounts》1970,19(4):301-309
The operator relationship p=[r, h] between linear momentum, position vector and Hamiltonian is the basis for an investigation of formulas for
¦ atomic orbitals is discussed. Formulas for
parameters useful in extended Hückel methods are presented.
Zusammenfassung Die Operatorengleichung p=[r, h] zwischen Impuls, Ortsvektor und Hamiltonoperator ist die Grundlage für eine Untersuchung von Formeln für -Parameter in der erweiterten Hückel[1]- und CNDO [2]-Methode. Das Eichproblem dieser Gleichung in Verbindung mit abgebrochenen Entwicklungen für Matrixelemente ¦P¦ über Atomfunktionen wird diskutiert. Nützliche Formeln für die erweiterte Hückel-Methode werden abgeleitet.
Résumé La relation entre opérateurs moment linéaire, position et hamiltonien: p=[r, h] sert de base à une étude de formules pour les paramètres dans les méthodes de type Hückel étendu [1] et CNDO [2]. Le problème de jauge de cette équation est discuté par rapport au développement limité des éléments de matrice ¦P¦ dans une base d'orbitales atomiques. Présentation de formules pour les paramètres utiles dans les méthodes Hückel étendu.相似文献
32.
33.
34.
35.
The complexes [Te(etu)4][SiF6] (1), [Te(etu)4][SiF6] · H2O (2), [Te(trtu)4][SiF6] (3), [Te(etu)4][GeF6] · H2O (4), [Te(trtu)4][GeF6] (5) and [Te(etu)4][SnF6] (6) (etu = ethylenethiourea, trtu = trimethylenethiourea) have been prepared and their crystal structures determined by X-ray crystallographic methods. The crystals of 1, 3 and 5 are tetragonal; space groups P4cc (No. 103) with Z = 4 for 1, P4nc (No. 104) with Z = 2 for 3, and I4 (No. 79) with Z = 2 for 5. The crystals of 2, 4 and 6 are orthorhombic, space group Pccn (No. 56) with Z = 8 for 2 and 4 and Z = 4 for 6; those of 2 and 4 being isomorphous. The cations contain square planar or slightly distorted square planar TeS4 coordination groups. In 1, 3 and 5 the Te atoms are located on fourfold rotation axes; the cations have fourfold rotational symmetry and the four thiourea ligands extend to the same side of the TeS4 plane. These are the first examples of [TeL4]2+ conformers of this type. In 2 and 4 the Te atoms lie on general positions; the cations are distorted versions of those in 1, and also in these the four ligands extend to the same side of the TeS4 plane. In 6 the Te atoms are located on twofold rotation axes, the conformation of the cations corresponds to the point group C2 with two neighbouring ligands extending to one side of the coordination plane and the remaining two to the opposite side. In 1–5 each of the four ligands forms a N–HF bond to the same F atom in the counter ion. The crystals of 1–5 are red, and those of 6 are yellow. The red colour is attributed to interactions of Te and S lone electron pairs caused by ligand TeS4/TeSC tilt angles markedly different from 90°. 相似文献
36.
Iodine monofluorosulfate has been found to react with fluoroolefins in the absence of a solvent to give the corresponding iodo alkyl fluorosulfates by addition of ?l and ?OSO2F across the double bond. The observed products were ICF2CF2SO3F, CF3CFlCF2SO3F, and the isomer mixture ICF2CFClSO3F and ICFClCF2SO3F. Perfluorocyclobutene was unreactive. The iodine fluorosulfate used for this study was synthesized from the reactions of either I2 or RfI with ClSO3F, with both reactions being new routes to this compound. These iodo fluorocarbon fluorosulfates are novel compounds and were characterized by spectroscopy and by formation of the derivatives CF3CFICFO and ICF2CFO. 相似文献
37.
Vladimir Rapić Prof. Dr. Karl Schlögl Brigitte Steinitz 《Monatshefte für Chemie / Chemical Monthly》1977,108(4):767-780
Starting from optically active methylferrocene-- and--carboxylic acids (1 a and1 b) of known absolute configuration and enantiomeric purity about 15 chiral ferrocenes (of each isomeric series— and ) were obtained by suitable ligand transformations. Thereby (almost) all possible chiral combinations of the ligands CH3, COOH (COO–), COOCH3, CN and NH2 (NH3
+) were accessible which are necessary for a potential test of approximations of chirality functions for compounds with basic symmetry C5v. The chiroptical properties of these disubstituted ferrocenes are recorded.Preliminary tests using a shortened Ansatz revealed large discrepancies between calculated () and found [M]D-values. Possible reasons for this failure are discussed.
61. Mitt. über Ferrocenderivate
39. Mitt.:A. Meyer, H. Neudeck undK. Schlögl, Chem. Ber.110, 1403 (1977).
60. Mitt.:V. Rapi, K. Schlögl undB. Steinitz, J. Organometal. Chem.94, 87 (1975). 相似文献
61. Mitt. über Ferrocenderivate
39. Mitt.:A. Meyer, H. Neudeck undK. Schlögl, Chem. Ber.110, 1403 (1977).
60. Mitt.:V. Rapi, K. Schlögl undB. Steinitz, J. Organometal. Chem.94, 87 (1975). 相似文献
38.
39.
There is a need to develop reliable portable analytical systems for on-site and real-time biomonitoring of lead (Pb) from both occupational and environmental exposures. Saliva is an appealing matrix since it is easily obtainable, and therefore a potential substitute for blood due to existing reasonably good correlation between Pb levels in blood and saliva. The microanalytical system is based on flow-injection/stripping voltammetry with a wall-jet (flow-onto) microelectrochemical cell. Samples that contain as little as 1% saliva can cause electrode fouling, resulting in significantly reduced responsiveness and irreproducible quantitations. In addition, incomplete Pb release from salivary protein can also yield a lower Pb response than expected. This paper evaluates the extent of in vitro Pb-protein binding and the optimal pretreatment for releasing Pb from the saliva samples. Even in 50% by volume of rat saliva, the electrode fouling was not observed, due to the appropriate sample pretreatment and the constant flow of the sample and acidic carrier that prevented passivation by the protein. The system offered a linear response over a low Pb range of 1-10 ppb, low detection limit of 1 ppb, excellent reproducibility, and reliability. It also yielded the same Pb concentrations in unknown samples as did the ICP-MS. These encouraging results suggest that the microanalytical system represents an important analytical advancement for real-time non-invasive biomonitoring of Pb. 相似文献