全文获取类型
收费全文 | 4141篇 |
免费 | 87篇 |
国内免费 | 22篇 |
专业分类
化学 | 2705篇 |
晶体学 | 25篇 |
力学 | 161篇 |
数学 | 651篇 |
物理学 | 708篇 |
出版年
2021年 | 27篇 |
2020年 | 31篇 |
2019年 | 33篇 |
2018年 | 39篇 |
2017年 | 38篇 |
2016年 | 61篇 |
2015年 | 74篇 |
2014年 | 86篇 |
2013年 | 229篇 |
2012年 | 170篇 |
2011年 | 199篇 |
2010年 | 124篇 |
2009年 | 116篇 |
2008年 | 171篇 |
2007年 | 165篇 |
2006年 | 177篇 |
2005年 | 196篇 |
2004年 | 158篇 |
2003年 | 145篇 |
2002年 | 157篇 |
2001年 | 61篇 |
2000年 | 70篇 |
1999年 | 65篇 |
1998年 | 47篇 |
1997年 | 73篇 |
1996年 | 75篇 |
1995年 | 65篇 |
1994年 | 55篇 |
1993年 | 59篇 |
1992年 | 50篇 |
1991年 | 54篇 |
1990年 | 40篇 |
1989年 | 44篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1985年 | 80篇 |
1984年 | 62篇 |
1983年 | 50篇 |
1982年 | 66篇 |
1981年 | 72篇 |
1980年 | 53篇 |
1979年 | 66篇 |
1978年 | 68篇 |
1977年 | 78篇 |
1976年 | 53篇 |
1975年 | 53篇 |
1974年 | 50篇 |
1973年 | 38篇 |
1971年 | 36篇 |
1968年 | 27篇 |
排序方式: 共有4250条查询结果,搜索用时 15 毫秒
131.
132.
133.
Dickson JL Binks BP Johnston KP 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):7976-7983
Stable carbon dioxide-in-water emulsions were formed with silica nanoparticles adsorbed at the interface. The emulsion stability and droplet size were characterized with optical microscopy, turbidimetry, and measurements of creaming rates. The increase in the emulsion stability as the silica particle hydrophilicity was decreased from 100% SiOH to 76% SiOH is described in terms of the contact angles and the resulting energies of attachment for the silica particles at the water-CO(2) interface. The emulsion stability also increased with an increase in the particle concentration, CO(2) density, and shear rate. The dominant destabilization mechanism was creaming, whereas flocculation, coalescence, and Ostwald ripening played only a minor role over the CO(2) densities investigated. The ability to stabilize these emulsions with solid particles at CO(2) densities as low as 0.739 g/mL is particularly relevant in practical applications, given the difficulty in stabilizing these emulsions with surfactants, because of the unusually weak solvation of the surfactant tails by CO(2). 相似文献
134.
Jean-Marie Bessiere Bernard Boutevin Lena Sarraf 《Journal of polymer science. Part A, Polymer chemistry》1988,26(12):3275-3295
The stereoselectivity of the addition step and the transfer step of the radical telomerization of methyl methacrylate with thiophenol has been studied by determining the structure and the amount of each isomer by 1H-NMR. We found, in this case, that the addition step gave preferentially a diad r and that the transfer step gave preferentially a diad m. On the other hand, the tacticity observed for higher telomers is preferentially syndiotactic, similar to that of the poly(methyl methacrylate) prepared by radical initiation. The propagation process for radical telomerization obeys, as for the radical polymerization, Bernoulli's statistics. 相似文献
135.
Diels-Alder adducts were formed in the lead tetraacetate oxidations of substituted cyclic hydrazides of furan, pyridazine and pyrrole dicarboxylic acids in the presence of 1,3-cyclo-hexadiene or 1,3-cyclopentadiene. The products resulting were furo[3,4-g]pyridazino[1,2-a]-pyridazine-6,10-diones, pyridazino[4,5-g]pyridazino[1,2-a]pyridazine-6,11-diones, and pyrrolo-[3,4-g]pyridazino[1,2-a]pyridazine-6,10-diones, respectively. Some hydrogenations and ring opening reactions were studied. 相似文献
136.
Emmanuel Beyou Pierre Babin Bernard Bennetau Jacques Dunogues Dominique Teyssie Sylvie Boileau 《Journal of polymer science. Part A, Polymer chemistry》1994,32(9):1673-1681
Unsaturated perfluoroalkyl esters derived from undecylenic acid: CH2?CH? (CH2)8? COO? CH2? CH2? RF (with RF?C6F13, 2a and RF?C8F17, 2b ) and C8F17? (CH2)10? COO? CH2? CH?CH2, 2c were prepared with excellent yields. Their hydrosilylation by methylhydrodimethylsiloxane copolymers of various Si? H contents gives new fluorinated polysiloxanes which were examined by 1H- and 13C-NMR, GPC, differential scanning calorimetry, and optical polarizing microscopy. Polymers derived from compounds 2a and 2b exhibit mesomorphic structures. © 1994 John Wiley & Sons, Inc. 相似文献
137.
Sylvie Corbin Richard Lavery Bernard Pullman 《International journal of quantum chemistry》1983,23(4):1451-1461
The molecular electrostatic potential of the triple helix poly(dT)·tpoly(dA)·poly(dT) is calculated, and the results are examined in relation to those obtained for its component double and single helical parts. For the double helix presenting the standard Watson–Crick hydrogen bonds, the deepest potentials are formed on the side of the major groove, a situation similar to that observed in the A-DNA duplex. For the double helix presenting Hoogsteen-type hydrogen bonds the deepest potentials lie in the major groove, on the side of the pyrimidine strand. In the triple helix the deepest potentials are located in the major groove in a narrow zone over the thymine bases of the Watson–Crick pair. 相似文献
138.
Bernard Spiess Franoise Arnaud-Neu Marie-Jos Schwing-Weill 《Helvetica chimica acta》1979,62(5):1531-1542
Complexation in anhydrous methanol of Cu (II) and Zn (II) with diaza-polyoxamacrocyclic ligands Protonation of five diaza-polyoxamacrocyclic ligands, (L = [2.1], [2.2], [2.1.1.], [2.2.1], [2.2.2]), and their complexing properties towards Cu2+ and Zn2+ cations have been studied in anhydrous methanolic solutions. Potentiometric measurements have been carried out at 25°, using 5 · 10?2MEt4N+ClO as support-electrolyte, in order to determine the nature of the species formed upon complexation and their stability constants. The results were confirmed by spectrophotometry, for the cupric complexes of [2.1] and [2.2.2], and the electronic spectra of the different complexes were calculated. Comparison between complexation in aqueous and methanolic solutions have been made: as in water, ML2+ species and sometimes protonated MHL3+ species, with higher stability constants, are present in methanol; but the main difference is the formation of dinuclear complexes M2L4+, between Cu2+ and all ligands except [2.1]. In these complexes the Cu2+ cations cannot be both ‘encaged’ in the ligand cavity because of its small size. The different possible structures are discussed in terms of the stability constants values. The protonation constants values and the existence of the binuclear complexes may indicate a possible conformational change in the complexing ligand on changing the solvent from water to methanol. 相似文献
139.
Bernard Dietrich Jean Guilhem Jean-Marie Lehn Claudine Pascard Etienne Sonveaux 《Helvetica chimica acta》1984,67(1):91-104
The crystal structures of four anion cryptates [X? ? BT -6H+] formed by the protonated macrobicyclic receptor BT -6H+ with F?, Cl?, Br? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F?-ion is tetracoordinated, while Cl? and Br? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H+ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H+ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP2?, ADP3?, ATP4?, P2O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F?, Cl?, Br?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H+ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered. 相似文献
140.
Quéméner B Cabrera Pino JC Ralet MC Bonnin E Thibault JF 《Journal of mass spectrometry : JMS》2003,38(6):641-648
Partially acetylated and methylated oligogalacturonides produced by enzymatic hydrolysis of sugar beet pectin were analysed by negative electrospray ionization ion trap mass spectrometry (ESI-ITMS). The (18)O labelling of the oligomer reducing end allowed the precise assignment of the fragments resulting from glycosidic bond and cross-ring cleavages. The collisional-induced dissociation of the C(i) and Z(j) fragment ions through sequential MS(n) experiments always displayed (0, 2)A-type cross-ring cleavage ions which were related to C(2)H(4)O(2) losses. These (0, 2)A ions appeared to be highly diagnostic ions allowing the precise location of the acetyl groups to the O-2 and/or O-3 of the acetylated galacturonic acid residues. 相似文献