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991.
The properties of an excess electron interacting with a monovalent cation in bulk water are studied by molecular dynamics simulations. Sodium and silver cations are chosen as prototypical cases because of their very different redox properties. In both cases, mixed quantum classical molecular dynamics simulations reproduce the experimental UV-Vis spectra. In the case of silver, we observe a highly polarized neutral atom, corresponding to a dipolar excitonic state. For sodium a contact cation/electron pair is observed. Free energy curves along the cation electron coordinate are calculated using quantum Umbrella Sampling technique. The relative stability of the different chemical species is discussed. 相似文献
992.
Jordan Geller Ivor Wharf Francine Blanger‐Garipy Anne‐Marie Lebuis Ian S. Butler Denis F. R. Gilson 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):m466-m468
Chlorotris(2,4,6‐trimethylphenyl)tin(IV), crystallizes from ethanol as solvent‐free needles, [Sn(C9H11)3Cl], (I), and as the hemisolvate, [Sn(C9H11)3Cl]·0.5C2H6O, (II). The asymmetric unit in (I) has three independent molecules, whereas in (II), there are two [Sn(C9H11)3Cl] molecules together with one ethanol molecule. In the unit cell of (II), the ethanol molecules lie in channels between stacks of (Mes)3SnCl molecules (Mes is 2,4,6‐trimethylphenyl) and each ethanol molecule is disordered (0.50:0.50) over two positions. A comparison of the structures of the title compounds and other (Mes)3SnX (X = F, Br or I) systems with those of the triphenyltin analogues shows that the steric requirements of the o‐CH3 groups are met by a flattening of the SnC3 skeleton and increases in the average Sn—X and Sn—C values. Comparing Sn—X data for (Mes)3SnX (X = F, Cl, Br or I) systems with values for the tris(o‐methoxyphenyl)tin analogues suggests that the Sn—F distance of 1.961 Å in (Mes)3SnF may well be characteristic of sterically unhindered four‐coordinate Ar3SnF systems. 相似文献
993.
Alison T Ung Karl Schafer Karl B Lindsay Stephen G Pyne Kitti Amornraksa Ria Wouters Ilse Van der Linden Ilse Biesmans Anne S J Lesage Brian W Skelton Allan H White 《The Journal of organic chemistry》2002,67(1):227-233
An efficient method for preparing conformationally restricted cyclopentenyl-glutamate analogues in a regioselective and diastereoselective manner has been developed using a formal [3 + 2] cycloaddition reaction of dehydroamino acids. Methods for preparing optically active versions of these compounds have also been devised. Of these compounds, (S)-2 is an agonist at the mGlu5 (EC(50) 18 microM) and mGlu2 (EC(50) 45 microM) receptors. 相似文献
994.
Stadler C de Lacey AL Montet Y Volbeda A Fontecilla-Camps JC Conesa JC Fernández VM 《Inorganic chemistry》2002,41(17):4424-4434
ZORA relativistic DFT calculations are presented which aim to model the geometric and electronic structure of the active site of NiFe hydrogenases in its EPR-active oxidized states Ni-A (unready state) and Ni-B (ready state). Starting coordinates are taken from the X-ray structure of a mutant of Desulfovibrio fructosovorans hydrogenase refined at 1.81 A resolution. Nine possible candidates for Ni-A and Ni-B are analyzed in terms of their geometric and electronic structure. Comparison of calculated geometric and magnetic resonance parameters with available experimental data indicates that both oxidized states have a micro-hydroxo bridge between the two metal centers. The different electronic structures of both forms can be explained by a modification of a terminal cysteine in Ni-B, best modeled by protonation of the sulfur atom. A possible mechanism for the activation of both oxidized forms is presented. 相似文献
995.
Anne Eisenberg 《Trends in analytical chemistry : TRAC》1984,3(6):IV-VI
Scientists spend a good part of their working day writing, yet few have formal training in the techniques of technical writing, particularly in ways to address an interdisciplinary audience. One useful technique is to take the traditional mould of the academic report, with its dense abstract, curt introduction, and compressed discussion, and refocus it bearing in mind the background and expectations of the audience. A direct writing style that avoids negatives, nominalizations and wordiness will increase a report's readability, as will an informative abstract, an introduction that includes the theoretical background, and an emphasis on implications in the conclusion. 相似文献
996.
Irving J. Borowitz Whei-Oh Lin Tze-Chein Wun Robert Bittman Louis Weiss Vladimir Diakiw Grace B. Borowitz 《Tetrahedron》1977,33(14):1697-1705
The preparation of a series of neutral ligands featuring ether and N-methyl-N-carbethoxypentylamide groups is described. These ligands as well as related ones bearing other diamide groups are shown to selectively chelate Group IIA cations by picrate extraction from water to methylene chloride. The changes in UV absorption of aromatic rings and amide groups in the ligands upon titration with metal salts in methanol allow the estimation of the stoichiometry of complexation and the ordering of cation binding. The observed selectivity sequences of cation extraction and binding are briefly discussed. Preliminary proton and 13C NMR studies on the effect of addition of Group IIA cation salts to several of the ligands in methanol suggest that most of the complexation occurs at the central ether and amide groups. 13C NMR T1 changes by the Inversion Recovery Fourier Transform method are in agreement with the cation-induced shift data. 相似文献
997.
The synthesis of a library of N-alkylated O-arylated hydroxyproline derivatives has been achieved on solid phase. The choice of O-protection and the optimization of the Mitsunobu reaction involving a secondary alcohol were key to the success of this synthesis. First, acylation of resin-bound amines with N-Fmoc-O-THP-hydroxyproline was accomplished readily. Subsequent deprotection of the Fmoc and reductive amination with different aldehydes resulted in the tertiary amine intermediate. The deprotection of the THP group by p-toluenesulfonic acid was followed by a Mitsunobu reaction with a series of phenols. Finally, the products were cleaved from the resin using trifluoroacetic acid to produce a 10 200 member library. 相似文献
998.
Pennequin-Cardinal A Plaisance H Locoge N Ramalho O Kirchner S Galloo JC 《Talanta》2005,65(5):1233-1240
Radiello® diffusive samplers filled with a thermally desorbable adsorbent (graphitised charcoal Carbograph 4) have been tested for the monitoring of BTEX. The sampling rates have been estimated under various controlled atmospheres in order to evaluate the effects of two factors (exposure time, concentration levels and their interaction) on the performances of the Radiello® sampler. Experiments have been carried out under various atmospheres in exposure chamber. A total of 174 Radiello® samplers were exposed while varying two conditions: exposure time (1, 3, 7 and 14 days) and BTEX concentrations (low, medium and high levels). The results show that the sampling rates of benzene and toluene decrease for exposure of 14 days and especially for high concentration levels: decrease of 30% at 10 μg m−3 for benzene and 14% at 30 μg m−3 for toluene.
To try to explain the variations of these sampling rates, the breakthrough volumes (VB) of BTEX on Carbograph 4 have been determined at different temperature and concentration conditions in order to evaluate the Langmuir parameters and their adsorption enthalpy (−ΔHads) using the Van’t Hoff equation. With regard to these adsorption characteristics, the dependence of sampling rates with concentration level and exposure time were analysed and discussed. 相似文献
999.
New chiral Schiff base complexes have been obtained by condensation of 2,2'-diamino-1,1'-binaphthalene or 1,2-diaminocyclohexane and various salicylaldehydes and by subsequent metalation with manganese, iron, cobalt, nickel, copper, or zinc. The complete (1)H and (13)C NMR characterization of the ligands is reported, as are the X-ray crystal structures of (1R,2R)-(-)-N,N'-bis[3-(N,N-dimethylamino)salicylidene]-trans-1,2-cyclohexanediimine and [(1R,2R)-(-)-N,N'-bis(salicylidene)-trans-1,2-cyclohexanediiminato]copper(II). The new chiral manganese complexes have been evaluated in the oxygenation of prochiral olefins and sulfides using sodium hypochlorite, hydrogen peroxide, or N-methylmorpholine N-oxide/m-chloroperbenzoic acid as oxidant. 相似文献
1000.
Karl Schnafinger Christine M. Yasenchak Anne Vollman Helen H. Ong 《Journal of heterocyclic chemistry》1988,25(2):535-537
A series of structurally novel 7,8,9,10-tetrahydropyrido[3′,4′:4,5]pyrrolo[2,3-c,]quinolines, 4a-c , were synthesized via a facile Fischer indole cyclization from the appropriately substituted hydrazinoquinolines 2a-c . Acetamides 4a,c were hydrolyzed to 5a,b and further converted to tertiary amines 6a-c . Potent antihypertensive activity has been observed with a number of the title compounds as well as the intermediate 3a . 相似文献