全文获取类型
收费全文 | 3992篇 |
免费 | 85篇 |
国内免费 | 11篇 |
专业分类
化学 | 2602篇 |
晶体学 | 11篇 |
力学 | 59篇 |
数学 | 623篇 |
物理学 | 793篇 |
出版年
2021年 | 28篇 |
2019年 | 35篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 69篇 |
2015年 | 59篇 |
2014年 | 60篇 |
2013年 | 123篇 |
2012年 | 113篇 |
2011年 | 156篇 |
2010年 | 86篇 |
2009年 | 77篇 |
2008年 | 121篇 |
2007年 | 134篇 |
2006年 | 124篇 |
2005年 | 99篇 |
2004年 | 114篇 |
2003年 | 66篇 |
2002年 | 87篇 |
2001年 | 78篇 |
2000年 | 70篇 |
1999年 | 40篇 |
1998年 | 42篇 |
1997年 | 51篇 |
1996年 | 72篇 |
1995年 | 60篇 |
1994年 | 69篇 |
1993年 | 58篇 |
1992年 | 58篇 |
1991年 | 52篇 |
1990年 | 57篇 |
1989年 | 63篇 |
1988年 | 45篇 |
1987年 | 53篇 |
1986年 | 31篇 |
1985年 | 77篇 |
1984年 | 72篇 |
1983年 | 63篇 |
1982年 | 37篇 |
1981年 | 62篇 |
1980年 | 68篇 |
1979年 | 46篇 |
1978年 | 83篇 |
1977年 | 63篇 |
1976年 | 54篇 |
1975年 | 64篇 |
1974年 | 53篇 |
1973年 | 48篇 |
1972年 | 31篇 |
1971年 | 25篇 |
排序方式: 共有4088条查询结果,搜索用时 218 毫秒
101.
Two methods based on gel permeation chromatography (GPC) [size exclusion chromatography] for the analysis of traces (ng/kg)
of nitrogen and phosphorus containing pesticides (like triazines or phosphothionates) from marine sediment samples are compared:
A macro GPC with Biobeads SX-3 and a chromatography on a high-performance (HP-GPC) column with UV-detection. Results for eight
triazine herbicides, two triazine metabolites, the phenylurea derivative linuron, two acetanilides and two organophosphorus
compounds are given. Concentrations obtained with the HP-GPC are compared with those obtained with a macro GPC approach in
an earlier study.
Received: 4 October 1996/Revised: 20 December 1996/Accepted: 24 December 1996 相似文献
102.
Heinrich Wefelscheid 《Journal of Geometry》1977,9(1-2):127-133
A characterisation of those (B*G)-Geometries (in the sense of Benz) is given, which can be constructed with the help of nearfields F, char F 2, in which the multiplicative group F*(·) has a subgroup A with index [F*:A]=2.
Werner Burau zum 70. Geburtstag gewidmet 相似文献
Werner Burau zum 70. Geburtstag gewidmet 相似文献
103.
For classicalN-particle systems with pair interactionN
–1
ø(q
i–q
i) the Vlasov dynamics is shown to be thew*-limit asN. Propagation of molecular chaos holds in this limit, and the fluctuations of intensive observables converge to a Gaussian stochastic process. 相似文献
104.
105.
The S1 ← S0 absorption spectra of 2,1,3-benzothiadiazole (BTD) have been measured at 4.2 K in four different host crystals: naphthalene, durene, p-dichlorobenzene (DCB) and p-dibromobenzene. Detailed vibrational analyses are given for BTD imbedded in napthalene and DCB. The polarization measurements show that the S1 state has B2 symmetry, like its selenium analogue (BSD). The transition is dominated by a single totally symmetric mode - 484 cm?1. The Herzberg-Teller coupling contributes only a very small fraction of the total intensity. The Stark measurements of a DCB sample containing both BTD and BSD enabled us to compare the charge distribution of BTD and BSD in the state S1. The Stark splittings of BTD are 17% greater than the splittings of BSD. Reorganization of the σ-core during the excitation is used to explain the difference. The drastic change in dipole moment upon excitation implies that the S1←S0 transitions of BTD and BSD are not localized in the six-membered ring as suggested by previous workers. Weak phosphorescence of BTD in napthalene and DCB and singlet-triplet absorption spectrum of neat BTD have been observed. The heavy atom effect of spin-orbit coupling is to explain the ST absorption intensity of BTD and BSD. 相似文献
106.
107.
108.
Braun T Steffen A Schorlemer V Neumann B Stammler HG 《Dalton transactions (Cambridge, England : 2003)》2005,(20):3331-3336
Treatment of a toluene solution of [PdMe(2)(Cy(2)PCH(2)PCy(2))](1) with pentafluoropyridine in the presence of traces of water affords the generation of the A-frame complexes [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][SiMeF(4)]() and [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][OC(5)NF(4)](2b). If the reaction is performed in an NMR tube equipped with a PFA inliner, complex 2b is produced, only. Treatment of 1 with pentafluoropyridine in the presence of an excess water yields the pyridyloxy complex [PdMe(OC(5)NF(4))(Cy(2)PCH(2)PCy(2))](3). Compound [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][FHF](2c) bearing a bifluoride anion instead of SiMeF(4)(-) or OC(5)NF(4)(-) can be generated by reaction of 1 with substoichiometric amounts of Et(3)N.3HF. The analogous complex [(PdMe)(2){mu-kappa(2)(P,P)Ph(2)PCH(2)PPh(2)}(2)(mu-F)][FHF] (5c) has been synthesized by addition of Ph(2)PCH(2)PPh(2) to a solution of [PdMe(2)(Me(2)NCH(2)CH(2)NMe(2))](4) in THF and subsequent treatment of the reaction mixture with Et(3)N.3HF. The structure of the A-frame complex 5c has been determined by X-ray crystallography. 相似文献
109.
On Oxostannates(II). III. K2Sn203, Rb2Sn203, and Cs2Sn2O3 – a Comparison Hitherto unknown Rb2Sn2O3 has been obtained by heating of mixtures of binary oxides [RbO0.48 + SnO, Rb:Sn = 1.1:1, Al2O3?cylinders, Ar] as deep yellow powder or deep yellow single crystals. It is isotypic to K2Sn2O3, R3 m-D with a = 6.086 Å, c = 15.101 Å, Z = 3, dcalc = 4.69, dobs = 4.64 g X cm?3. For 260 hkl it is R = 5.27% and Rw = 5.09% (MoKα, 4-circle diffractometer data). The structure of K2Sn2O3 and Rb2Sn2O3 is compared with that of Cs2Sn2O3. For both types Effektive Coordination Numbers, ECoN, and the Madelung Part of Lattice Energy, MAPLE, have been calculated. 相似文献
110.
Mohamed El-Sayed Hardy Müller Gerd Rheinwald Heinrich Lang Stefan Spange 《Monatshefte für Chemie / Chemical Monthly》2003,50(11):361-370
N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments
by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of νmax is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is
described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel
entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular
hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing
an unprecedented bathochromic shift. 相似文献