全文获取类型
收费全文 | 2686篇 |
免费 | 47篇 |
国内免费 | 3篇 |
专业分类
化学 | 1773篇 |
晶体学 | 17篇 |
力学 | 39篇 |
数学 | 354篇 |
物理学 | 553篇 |
出版年
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 21篇 |
2016年 | 38篇 |
2015年 | 28篇 |
2014年 | 40篇 |
2013年 | 90篇 |
2012年 | 80篇 |
2011年 | 87篇 |
2010年 | 60篇 |
2009年 | 46篇 |
2008年 | 94篇 |
2007年 | 93篇 |
2006年 | 93篇 |
2005年 | 74篇 |
2004年 | 66篇 |
2003年 | 54篇 |
2002年 | 62篇 |
2001年 | 46篇 |
2000年 | 49篇 |
1999年 | 31篇 |
1998年 | 28篇 |
1997年 | 36篇 |
1996年 | 44篇 |
1995年 | 38篇 |
1994年 | 57篇 |
1993年 | 33篇 |
1992年 | 26篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 29篇 |
1988年 | 34篇 |
1987年 | 30篇 |
1986年 | 40篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 30篇 |
1982年 | 44篇 |
1981年 | 49篇 |
1980年 | 49篇 |
1979年 | 39篇 |
1978年 | 48篇 |
1977年 | 39篇 |
1976年 | 33篇 |
1975年 | 25篇 |
1974年 | 20篇 |
1973年 | 22篇 |
1972年 | 25篇 |
1968年 | 46篇 |
1967年 | 26篇 |
排序方式: 共有2736条查询结果,搜索用时 46 毫秒
61.
62.
The eigenfunctions and energies of general dilated Hamiltonians are expanded in powers of the dilatation parameter. These expansions, augmented by stationarity and stability conditions, are used to derive exact sum rules for bound and resonance states. Particular attention is paid to Hamiltonians with potentials which depend on external parameters, such as the nuclear coordinates in molecules, and to self-consistent potentials. The sum rules can be employed in practical computations to improve the quality of the results and may also serve in analyzing the results from approximate calculations. 相似文献
63.
Hans Beat Bürgi Hermann Gehrer Peter Strickler Fritz Karl Winkler 《Helvetica chimica acta》1976,59(7):2558-2565
Crystals of the title compound are triclinic, a = 27.87 Å, b = 10.77 Å, c = 12.94 Å, α 73.1°, β 116.1°, γ 120.0°, space group P1 . The structure consists of octanuclear ions: Eight Cd(II) ions are found at the corners of a distorted cube, the center of the cube is occupied by an iodide, the twelve thioglycolate sulfur atoms bridge the twelve edges of the cube thereby forming a distorted icosahedron. Cadmium ions are either five or seven coordinate. The phase problem for this structure was solved using a combination of very high and very low E-values. 相似文献
64.
Peter Ettmayer Johann Waldhart Alfred Vendl 《Monatshefte für Chemie / Chemical Monthly》1979,110(5):1109-1112
X-Ray studies of the mixed nitride phases indicate complete miscibility in all cases. Lattice parameters generally showed negative deviations from the additivity rule.
Teilauszug aus der Dissertation des Dipl.-Ing.J. Waldhart an der Technischen Universität Wien, Österreich. 相似文献
65.
A new photoaldol route to alpha-amino-beta-hydroxy carboxylic acid esters is initiated by the photocycloaddition of aromatic or aliphatic aldehydes to 5-methoxyoxazoles. The 4-unsubstituted 5-methyloxazole 1 gave the cycloadducts 8a-f in high yields and excellent exo-diastereoselectivities. Hydrolysis of 8a-f gives the N-acetyl alpha-amino-beta-hydroxy esters 9a-f, which could be subsequently converted into the corresponding Z-didehydro alpha-amino acids 10a-f. Quartenary alpha-amino-beta-hydroxy esters 12, 14, 16, 18, and 20, which are stable against dehydration, were obtained from the 4-alkylated 5-methoxyoxazoles 2-6, in most cases highly erythro-selective due to the high degree of stereocontrol (exo) at the photocycloaddition (to give 11, 13, 15, 17, and 19) level. The relative configurations of the N-acetyl alpha-amino-beta-hydroxy esters were determined by NMR spectroscopy and comparison with chiral pool-derived compounds as well as by X-ray structure determination of the ester 23, formed by hydrolysis of the cycloadduct 22, derived from photocycloaddition of propionaldehyde to the isoleucine-derived oxazole 21. 相似文献
66.
Griesbeck AG Heinrich T Oelgemöller M Lex J Molis A 《Journal of the American Chemical Society》2002,124(37):10972-10973
An elaborated protocol is described which allows the efficient transformation of di-, tri-, and tetrapeptides into cyclopeptides with a minimum of protection and activation chemistry using the photoinduced electron transfer initiated decarboxylation of N-phthaloyl peptides resulting in C-C coupling between the initially formed carbon radicals. 相似文献
67.
On addition, at neutral reaction, of increasing amounts of AlCl3 solutions to 0.005 m Na-silicate solutions, in which the silicate anions are monomeric, amorphous, almost Na+-free precipitates are formed being at first characterised by a higher atomic Al:Si ratio than the total Al:Si mixing ratio. With increasing Al:Si addition, the Al:Si ratio of the precipitates increases until — at a 3:1 ratio in both the liquid and the solid phase — a definite, “saturated” compound, {[(OH)2AlO]3SiOH · aq}, is formed. In this compound the silicate anions are monomeric and not condensable at room temperature. This is valid, too, for precipitates from Al:Si > 3 which contain, besides the “saturated” compound, free Al hydroxide. The first-mentioned precipitates with Al:Si < 3, however, contain polymeric Si units which easily condense to more high-polymeric silicate anions. 相似文献
68.
We evaluate the force-length relation for short model chains. It is shown that this relation is markedly different when evaluated for static and dynamic model chains with rigid segments. The relation also differs for chains with rigid segments when they are isolated and coupled to a canonical heatbath, respectively. Furthermore, it is derived that the variation of the masses along the chain only has a small influence on the force-length relation. On the other hand, restricting the motion of the chain by walls perpendicular to the chain extension has a pronounced effect. We especially find that in this situation the chain has a finite equilibrium length.Dedicated to Professor W. Pechhold on the occasion of his 60th birthday 相似文献
69.
Will S Lex J Vogel E Adamian VA Van Caemelbecke E Kadish KM 《Inorganic chemistry》1996,35(19):5577-5583
The synthesis, electrochemistry, spectroscopy, and structural characterization of two high-valent phenyl sigma-bonded cobalt corroles containing a central cobalt ion in formal +IV and +V oxidation states is presented. The characterized compounds are represented as phenyl sigma-bonded cobalt corroles, (OEC)Co(C(6)H(5)) and [(OEC)Co(C(6)H(5))]ClO(4), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. The electronic distribution in both molecules is discussed in terms of their NMR and EPR spectroscopic data, magnetic susceptibility, and electrochemistry. 相似文献
70.
Hans-Joachim Schulz Jürgen Liebscher Peter Luger Minxie Quian Johann Mulzer 《Journal of heterocyclic chemistry》1992,29(5):1125-1132
2,4,6-Trialkyl-1,3,5-triazines 1 can selectively be mono, bis or trisiminoformylated by reaction with trismorpholinomethane 2 or chloromethylene iminium salts 3 (Vilsmeier reagents), with each alkyl substituent reacting with only one molecule of the electrophile. The resulting aminoalkenyltriazines 4, 5 and 6 are partially or fully hydrolysed to corresponding formylation products. The latter exist either in enol or in unusual acylenamine tautomeric structures 10, 12 , and 13 , depending on the number of enamine or enol units found in the molecule. Reaction of triazines 1 with chlorobenzylidene iminium salts 16 gives monoiminobenzoylation to enaminotriazines 17 . 相似文献