全文获取类型
收费全文 | 13091篇 |
免费 | 560篇 |
国内免费 | 192篇 |
专业分类
化学 | 9266篇 |
晶体学 | 104篇 |
力学 | 669篇 |
综合类 | 3篇 |
数学 | 1602篇 |
物理学 | 2199篇 |
出版年
2024年 | 25篇 |
2023年 | 104篇 |
2022年 | 527篇 |
2021年 | 502篇 |
2020年 | 451篇 |
2019年 | 560篇 |
2018年 | 610篇 |
2017年 | 493篇 |
2016年 | 813篇 |
2015年 | 551篇 |
2014年 | 762篇 |
2013年 | 1419篇 |
2012年 | 1023篇 |
2011年 | 988篇 |
2010年 | 717篇 |
2009年 | 586篇 |
2008年 | 630篇 |
2007年 | 546篇 |
2006年 | 369篇 |
2005年 | 368篇 |
2004年 | 254篇 |
2003年 | 231篇 |
2002年 | 198篇 |
2001年 | 96篇 |
2000年 | 69篇 |
1999年 | 80篇 |
1998年 | 50篇 |
1997年 | 55篇 |
1996年 | 54篇 |
1995年 | 42篇 |
1994年 | 40篇 |
1993年 | 24篇 |
1992年 | 42篇 |
1991年 | 34篇 |
1990年 | 33篇 |
1989年 | 38篇 |
1988年 | 35篇 |
1987年 | 35篇 |
1986年 | 31篇 |
1985年 | 42篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 20篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1975年 | 15篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
We report a novel dimeric boradiazaindacene dye which can be converted in one step to an efficient resonance energy transfer (RET) dyad. In addition, if this modification is done with appropriate ligands, RET can be coupled to ion sensing. The utility of this approach is demonstrated in a highly selective, emission ratiometric chemosensor for Ag(I). 相似文献
82.
Shamsipur M Chaichi MJ Karami AR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(3):511-517
The chemiluminescence arising from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of acriflavine has been studied. The relationship between the chemiluminescence intensity and concentrations of TCPO, H2O2, acriflavine and the base sodium salicylate are reported. The kinetic parameters for the peroxyoxalate-chemiluminescence (PO-CL) of acriflavine were evaluated from the computer fitting of the corresponding chemiluminescence intensity-time plots. 相似文献
83.
H. Ali Dondas 《Tetrahedron letters》2005,46(24):4179-4182
Alkenylsulfinimines and alkenylsulfinamides underwent electrophile induced cyclisation reactions with phenylselenyl bromide, iodine and bromine to cyclic and spirocyclic imines, pyrrolidines and piperidines with spontaneous cleavage of the protective group at nitrogen in good to excellent yield. 相似文献
84.
In this study, the functionality of maleic anhydride was utilized in the maleic anhydride-styrene-methyl metacrylate (MAStMMA) terpolymer. First, the polyester of poly(ethylene adipate), PEA, polycondensation copolymer was synthesized from ethylene glycol and adipic acid monomers. PEA was then modified on its maleic anhydride units in the MAStMMA terpolymer which has been synthesized previously. This modified copolymer was characterized by FTIR (Fourier Transform Infrared spectroscopy). The viscosimetric and thermomechanical characterization of MAStMMA terpolymer and its modified copolymer were also performed and the results were compared. The modified copolymer obtained was found to be more elastic and more soluble, and had lower viscosity and density. 相似文献
85.
Icbudak H. Heren Z. Kose D. Ali Necefoglu H. 《Journal of Thermal Analysis and Calorimetry》2004,76(3):837-851
The mixed-ligand p-hydroxybenzoate complexes of Ni(II), Cu(II) and Zn(II) with nicotinamide and N,N-diethylnicotinamide were synthesized and
characterized by elemental analysis, magnetic susceptibility measurements and mass spectrometry. The thermal behavior of the
complexes was studied by simultaneous TG, DTG and DTA methods in static air atmosphere. The infrared spectral characteristics
of the complexes are also discussed. The complexes contain two water molecules, two p-hydroxybenzoato (p-hba) and two nicotinamide (na) (or diethylnicotinamide (dena)) ligands per formula unit. In these complexes,
all ligands are coordinated to the metal ion as monodendate ligands. In Zn(II)-na and Cu(II)-dena complexes, thep-hydroxybenzoate behaves as bidentate chelating ligand through carboxylic oxygen atoms. The decomposition pathways and the
stability of the complexes are interpreted in the terms of the structural data. The final decomposition products were found
to be the respective metal oxides.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
86.
Esahak Ali Ajit K. Chakravarty Satyesh C. Pakrashi Klaus Biemann Charles E. Hignite 《Tetrahedron》1977,33(11):1371-1377
The structure of solanoforthine, m.p. 208–10°, [α]D- 26.6°, a new steroidal alkaloid isolated from Solanum seaforthianum Andr., has been established as 3β-amino-22,26-epimino-16α,23-epoxy-22αH,25βH-cholest- 5- en -23β - ol 3, based on chemical and spectroscopic evidence and by its reduction to solanocapsine 2, another steroidal alkaloid encountered in the same species. The mass spectra of2 and 3 are discussed. 相似文献
87.
Ali Hashem Essa 《Journal of organometallic chemistry》2007,692(22):4917-4920
The correlation analysis of Mulliken charge (QM) calculated by using density functional theory (B3LYP/STO-3G) calculations of 1-(4-azido-5-hydroxymethyl-tetrahydro-selenophen-2-ylmethyl)-5-substituted-1H-pyrimidine-2,4-dione, were done by using mono substituent parameter (Hammett’s model), and dual substituent parameter (Taft’s, Reynolds’, and Swain’s models). The dual substituent parameter correlations of the QM data gave no significant improvement over single parameter correlations, the best correlation observed with the Taft’s Model as compared with the Swain’s and Reynolds’ Models, respectively. The correlation analysis of Mulliken charge can be used successfully to demonstrate the existence or absence of the interaction between the oxygen of the carbonyl group and selenium atom. 相似文献
88.
Sharpless asymmetric dihydroxylation and aminohydroxylation of (E)-dimethyl-2-alkylidene glutarates 2 were shown to afford enantio-enriched or enantiopure highly functionalized γ-butyrolactones 3 and 7. 相似文献
89.
Single nanocrystal arrays on patterned poly(ethylene glycol) copolymer microstructures using selective wetting and drying 总被引:1,自引:0,他引:1
Suh KY Khademhosseini A Eng G Langer R 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6080-6084
Single nanocrystal arrays were fabricated on sub-microwells of poly(ethylene glycol) (PEG) copolymer using selective wetting on the hydrophilic regions of the exposed substrate surface and subsequent drying. Templates were produced by molding a thin film of a PEG-based random copolymer on hydrophilic substrates such as glass or silicon dioxide. The polymeric microstructures provide a topographical barrier around the well, which makes it possible to create nanocrystal arrays with controlled geometrical features. The size of the nanocrystal was found to decrease with decreasing well size and also decrease with decreasing topological height. A simple empirical equation was derived to predict the size of the crystal as a function of the pattern size and height, which is in good agreement with the experimental data. 相似文献
90.
Densities,ρ, ultrasonic speeds, u, viscosities,η, and refractive indices, n, of pure benzene, benzyl alcohol (BA), benzonitrile (BN), benzoyl chloride (BC), chlorobenzene (CB) and their thirty six binary mixtures, with benzene as common component, were measured at 303.15 K over the entire mole fraction range. From these experimental data the values of deviations in ultrasonic speed, △u, isentropic compressibility, △ks,excess acoustic impedance, ZE, deviation in viscosity, Dh, and excess Gibbs free energy of activation of viscous flow, G*E, and partial molar isentropic compressibility, Kφ,20 of BA, BN, BC and CB in benzene were computed. The variation of these derived functions with composition of the mixtures suggested the increased cohesion
(molecular order) in the solution and that interaction (A-B)>(A-A) or (B-B).Moreover, theoretical prediction of ultrasonic speed, viscosity and refractive index of all the four binary mixtures was made on the basis of empirical and semi-empirical relations by using the experimental values of the pure components. Comparison of theoretical results with the experimental values was made in order to assess the suitability of these relations in reproducing the
experimental values of u, η and n. Also, molecular radii of pure liquids and the average molecular radii of binary mixtures were evaluated using the corresponding refractive indices of pure liquids and binary mixtures. The average molecular radii of binary mixtures were found to be additive with respect to mole fraction of the pure component. 相似文献