全文获取类型
收费全文 | 5827篇 |
免费 | 154篇 |
国内免费 | 18篇 |
专业分类
化学 | 4241篇 |
晶体学 | 18篇 |
力学 | 66篇 |
数学 | 1034篇 |
物理学 | 640篇 |
出版年
2020年 | 52篇 |
2019年 | 54篇 |
2016年 | 94篇 |
2015年 | 92篇 |
2014年 | 104篇 |
2013年 | 167篇 |
2012年 | 170篇 |
2011年 | 241篇 |
2010年 | 118篇 |
2009年 | 107篇 |
2008年 | 217篇 |
2007年 | 223篇 |
2006年 | 217篇 |
2005年 | 246篇 |
2004年 | 192篇 |
2003年 | 167篇 |
2002年 | 165篇 |
2001年 | 77篇 |
2000年 | 74篇 |
1999年 | 74篇 |
1998年 | 52篇 |
1997年 | 74篇 |
1996年 | 73篇 |
1995年 | 73篇 |
1994年 | 52篇 |
1993年 | 53篇 |
1992年 | 68篇 |
1991年 | 50篇 |
1990年 | 71篇 |
1989年 | 44篇 |
1988年 | 67篇 |
1987年 | 68篇 |
1986年 | 47篇 |
1985年 | 100篇 |
1984年 | 61篇 |
1983年 | 63篇 |
1982年 | 70篇 |
1981年 | 67篇 |
1980年 | 53篇 |
1979年 | 72篇 |
1978年 | 71篇 |
1977年 | 58篇 |
1976年 | 80篇 |
1975年 | 79篇 |
1974年 | 54篇 |
1973年 | 50篇 |
1971年 | 41篇 |
1970年 | 49篇 |
1967年 | 41篇 |
1966年 | 42篇 |
排序方式: 共有5999条查询结果,搜索用时 15 毫秒
141.
Zusammenfassung Es werden Hückel-MO-Rechnungen am Borazol und den B-Trihalogenoborazolen durchgeführt und die entsprechenden Parameter an den teils bekannten und teils gemessenen UV-Spektren geeicht. Die für diese Verbindungen bestimmten chemischen Verschiebungen der 11B- und 14N-Kernresonanz lassen sich mit den berechneten -Elektronendichten erklären.
Herrn Professor Dr. H. Hartmann danken wir für sein stetes Interesse und die wohlwollende Förderung dieser Arbeit. Für die Hilfe bei der Aufnahme des Vakuum-UV-Spektrums von Fluoroborazol danken wir Herrn Diplom-Physiker E. Mohler. 相似文献
Hückel-MO calculations are performed for Borazine and the B-Trihalogenoborazines; the parameters used are calibrated with the UV-spectra, which had either been measured here or obtained from the literature. The calculated -electron densities compare favorably well with the 11B- and 14N-nuclear magnetic resonances determined for the above mentioned compounds.
Résumé Le borazole et les B-trihalogenoborazoles sont calculés par la méthode de Hückel en utilisant des paramètres calibrés sur les spectres U.V. mesurés ou obtenus dans la littérature. Les densités électroniques sont en bon accord avec le déplacement chimique de N.M.R. de 11B et 14N déterminé pour les composés cidessus.
Herrn Professor Dr. H. Hartmann danken wir für sein stetes Interesse und die wohlwollende Förderung dieser Arbeit. Für die Hilfe bei der Aufnahme des Vakuum-UV-Spektrums von Fluoroborazol danken wir Herrn Diplom-Physiker E. Mohler. 相似文献
142.
Peter Graf Ekkehard Kaempf Klaus Reichlmeier Karl Bernhard 《Helvetica chimica acta》1977,60(7):2151-2154
Metabolism of Acetylenic Monocarboxylic and Dicarboxylic Acids Feeding of acetylenic monoacids with chain length of 11 to 18 C-atoms to rats led to excretion of dicarboxylic acids with retained triple bonds. 10-Octadecynoic acid led to the formation of metabolites with even and odd number of C-atoms, suggesting in addition to established ω- and β-oxidation an α-oxidative pathway. 相似文献
143.
Karl S. Coleman Simon Turberville Malcolm L.H. Green 《Journal of organometallic chemistry》2005,690(3):653-658
A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe3)2 and reacted with [PdCl2 (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl2(C∧fc∧C)], where (cod) = 1,5-cyclooctadiene and (C∧fc∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene. 相似文献
144.
Heinz-Peter Klein Ulf Thewalt Karl Döppert Roberto Sanchez-Delgado 《Journal of organometallic chemistry》1982,236(2):189-195
The trinuclear titanium(IV) complex (π-C5H5)2TiClOTi(π-C5H5)ClOTiCl(π-C5H5)2 · CHCl3 is formed by hydrolysis of (π-C5H5)2TiCl2 at pH > 3.5 and can be isolated in the crystalline state from the reaction of (π-C5H5)2TiCl2 with Ag2O and water in chloroform. Its structure is determined by X-ray analysis. 相似文献
145.
Abstract— Photolysis of ethidium azide ( lb ) and proflavine azide ( 2b ) immobilized in glassy media at 77 K produces triplet EPR spectra of the corresponding triplet nitrenes lc and 2c . The resonance field positions of the nitrenes are shifted by the presence of self-complementary dinucleotides. Control experiments indicated that the interaction of lc and 2c with CP G mini-duplexes is consistent with intercalation. 相似文献
146.
Karl Jug 《Theoretical chemistry accounts》1973,31(1):63-73
A new definition of atomic charges in molecules is presented which conserves charge and dipole moment. It contains the Mulliken and Löwdin definitions as special cases of zero and first order truncations of commutator expansions. The definition allows for a systematic improvement of charges paralleling the improvement of the basis set in the LCAO approximation. We have tested the definition in thirteen selected diatomics and polyatomics in optimal minimal Slater basis set SCF calculations by means of 4G-level Gaussian expansions. The results suggest that the proposed definition is better than either Mulliken's or Löwdin's definition.Presented in part at the E. U. Condon Symposium, Sanibel Island, Florida, 21–27 January 1973. 相似文献
147.
The brown crystals of [NEt4]2[Se3Br8(Se2Br2)] ( 1 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of tetraethylammonium bromide. The crystal structure of 1 has been determined by the X‐ray methods and refined to R = 0.0308 for 10433 reflections. The crystals are monoclinic, space group P21 with Z = 2 and a = 12.0393(3) Å, b = 11.8746(3) Å, c = 13.1946(3) Å, β = 96.561(1)° (123 K). In the solid state structure the anion of 1 is built up of Se3Br8 unit which consists of a triangular arrangement of three planar SeBr4 units sharing a common edge through two μ3‐bridging Br atoms, and one Se2Br2 molecule which is linked to one of μ3‐bridging Br atoms. The three SeII atoms form a triangle which is almost perpendicular to the planes given by three SeBr4 moieties. The contact between the μ3Br and the SeI atom of the Se2Br2 molecule is 3.1711(8) Å and can be interpreted as a bond of the donor‐acceptor type with the μ3Br as donor and the Se2Br2 molecule as acceptor. The terminal SeII‐Br and μ3Br‐SeII bond lengths are in the ranges 2.3537(7)–2.4737(7) Å and 2.7628(7)–3.1701(7) Å, respectively. The bond lengths in coordinated Se2Br2 molecule are: SeI‐SeI = 2.2636(9) Å, SeI‐Br = 2.3387(11) and 2.3936(8) Å. 相似文献
148.
Kadish KM Phan TD Wang LL Giribabu L Thuriere A Wellhoff J Huang S Caemelbecke EV Bear JL 《Inorganic chemistry》2004,43(16):4825-4832
Six Ru2(6+) derivatives of the form Ru2(L)4(C[triple bond]CC6H5)(2), where L = 2-Fap, 2,3-F(2)ap, 2,4-F(2)ap, 2,5-F(2)ap, 3,4-F(2)ap, or 2,4,6-F(3)ap, are synthesized and characterized as to their electrochemical, spectroscopic, and/or structural properties. These compounds are synthesized from a reaction between LiC[triple bond]CC6H5 and Ru2(L)4Cl. Two of the investigated complexes exist in a (4,0) isomeric form while four adopt a (3,1) geometric conformation. These two series of geometric isomers are compared with previously characterized (4,0) Ru2(ap)4(C[triple bond]CC6H5)(2), (4,0) Ru2(F5ap)4(C[triple bond]CC6H5)(2), and (3,1) Ru2(F5ap)4(C[triple bond]CC6H5)(2). The overall data on the nine compounds thus provide an opportunity to systematically examine how the electrochemical and structural properties of these Ru2(6+) complexes vary with respect to isomer type and electronic properties of the bridging ligands. 相似文献
149.
Oxygen vacancy diffusion in rutile was studied by Born-Oppenheimer molecular dynamics techniques in the framework of the semiempirical molecular orbital method MSINDO. Migration of an oxygen vacancy from the rutile (110) surface towards the bulk was simulated. The metadynamics technique was employed to accelerate the diffusion processes. In this way, transition state structures and activation energies for the diffusion processes were obtained. Rate constants and the time scale of diffusion processes were estimated for different temperatures using the calculated activation energy. It was found that the vacancies in the bulk are less stable than on the surface. The feasibility of oxygen vacancy diffusion under experimental conditions is discussed. 相似文献
150.
David G. Morris Kenneth W. Muir Karl S. Ryder 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(10):o615-o618
Crystals of 9‐methylfluoren‐9‐ol, C14H12O, undergo a reversible phase transition at 176 (2) K. The structure of the high‐temperature α form at 200 K is compared with that of the low‐temperature β form at 100 K. Both polymorphs crystallize in space group P with Z = 4 and contain discrete hydrogen‐bonded R(8) ring tetramers arranged around crystallographic inversion centres. The most obvious changes observed on cooling the crystals to below 176 K are an abrupt increase of ca 0.5 Å in the shortest lattice translation, and a thermal transition with ΔH = 1 kJ mol?1. 相似文献