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71.
The rotational potential around the interannular bond in 2,2-bipyrrole has been calculated making use of standard minimal STO-3G and split valence 4-31G basis sets. Geometrical optimization concerning the most significant interannular internal parameters has been performed with both basis sets. The trans conformer is predicted to be more stable than the cis. The minimal basis set predicts the existence of a cisoid-gauche minimum which after limited optimization becomes very shallow and it seems to be an artifact of the rigid rotor approximation. At 4-31G level, both the trans and cis conformers represent maxima in the potential curve and two gauche minima appear at =46.0° and =147.6°, the latter being the absolute minimum. The absolute maximum of the potential curve corresponds to the cis conformer. 相似文献
72.
Bartolom Vilanova Francisco Muoz Josefa Donoso Francisco Garcia-Blanco 《Helvetica chimica acta》1993,76(4):1619-1625
A kinetic study on the alkaline hydrolysis of cephaloridine ( 1 ) at pH 10.5 and 37° was carried out using ion-pair reversed-phase HPLC. The main resulting degradation products, the 7-epimer 2 of 1 , the Δ2-isomer 3 of 1 , and the 3-methylidene compound 4 were identified. The presence of a pyridinio group at C(31) results in a slightly increased formation constant for the 3-methylidene compound 4 and the 7-epimer 2, and introduces a new reaction: the isomerization of the double bond at C(3) in the dihydrothiazine ring to C(2). 相似文献
73.
Crowe MC Kapoor RN Cervantes-Lee F Párkányí L Schulte L Pannell KH Brodbelt JS 《Inorganic chemistry》2005,44(18):6415-6424
Electrospray ionization (ESI) quadrupole ion trap mass spectrometry (QIT-MS) and collisionally activated dissociation (CAD) were used to evaluate the rare-earth binding properties of two hydrophobic carbamoylmethylphosphine oxide (CMPO) ligands, the normal bidentate variety, (t-BuC6H4)2P(O)CH2C(O)N(i-Bu)2 (A), a new potentially tridentate extractant, (t-BuC6H4)2P(O)CH[CH2C(O)N(i-Bu)2]C(O)N(i-Bu)2 (B), and tributyl phosphate. The mass spectral results obtained from analysis of 1% HNO3/methanol solution containing the ligands and dissolved lanthanide salts reveal that the favorable stoichiometries of the ligand/metal/nitrate complexes are 2:1:2 for the bidentate ligand A, 1:1:2 for the tridentate ligand B, and 3:1:2 for the monodentate tributyl phosphate. These observed stoichiometries correlate with the number of available binding sites on each ligand as well as with potential steric effects. Energy-variable collisionally activated dissociation experiments showed that for the 2:1:2 complexes involving ligand A or B, as the ionic radius of the bound metal decreased, the removal of nitric acid required less energy and resulted in less extensive spontaneous solvent coordination. This experimental trend suggests that, as the ionic radius of the lanthanide ion decreases, a pair of the carbamoylmethylphosphine ligands is able to more completely solvate the bound metal ion thereby weakening the nitrate-metal interaction. 相似文献
74.
3-Methoxy[2, 1]benzisoxazole-4, 7-quinones 1 and naphth[2,3-c]isoxazole-4,9-quinone 4 react with dimethyl sulfoxides to give sulfoximidoquinones 2 and 5 , sulfimidoquinones 8 and 11 respectively as major products. 相似文献
75.
Montserrat Barquín María J. Gonzlez Garmendia Liher Larrínaga Elena Pinilla María R. Torres 《无机化学与普通化学杂志》2005,631(11):2210-2214
The complexes of copper formato with pyrazine and dimethylpyrazines: Cu(HCOO)2(pyrz) ( 1 ), Cu2(HCOO)4(pyrz) ( 2 ), Cu2(HCOO)4(2,3‐Me2pyrz) ( 3 ), Cu2(HCOO)4(2,5‐Me2pyrz) ( 4 ), and Cu2(HCOO)4(2,6‐Me2pyrz)2 ( 5 ) have been synthesized and characterized by chemical analysis and IR and electronic spectro scopies. The three‐dimensional structure of compound 1 consists of –Cu–pyrz–Cu–pyrz– chains joined by bridging formate groups coordinated, in configuration syn‐anti, to two copper atoms. The coordination around the copper atom is orthorhombic with two Cu–O distances of 2.374(1) Å, two Cu–O of 1.952 Å and two Cu–N of 2.080 Å. Compound 5 is formed by molecular dimers with the [Cu2(μ‐HCOO)4] unit, two copper atoms and four syn‐syn fomate groups, and two ligands coordinated to the copper atoms in the axial positions. In compounds 2 and 3 chains of [Cu2(μ‐HCOO)4] dimers with pyrz or 2,3‐Me2pyrz as bridging ligands are formed. The EPR signal of 1 is orthorhombic (g = 2.23, 2.20 and 2.06). In the EPR spectra of 2 – 5 compounds the triplet (S = 1) signals are observed. The g?, g∥ and D values are been calculated. 相似文献
76.
Francisco M. Ferndez Eduardo A. Castro 《International journal of quantum chemistry》1982,21(5):875-884
New formal results regarding the hypervirial analysis of enclosed systems are given. Novel applications are presented and several previous equations are reformulated in a more appropriate form. 相似文献
77.
Lhiaubet-Vallet V Sarabia Z Boscá F Miranda MA 《Journal of the American Chemical Society》2004,126(31):9538-9539
A remarkable stereodifferentiation has been observed in the interaction between the excited triplet state of carprofen (CP) and human serum albumin (HSA). Time-resolved measurements using laser flash photolysis reveal the presence of two components with different lifetimes in triplet decay. This is explained by complexation of CP to the two possible HSA binding sites. The shorter-lived components are ascribed to the CP/HSA complexes in site I, where stereodifferentiation is more important (tauR/tauS ca. 4). This is correlated with formation of a dehalogenated photoproduct upon steady-state photolysis. 相似文献
78.
Susana Marques Luís Alves Sandra Ribeiro Francisco M. Gírio M. T. Amaral-Collaço 《Applied biochemistry and biotechnology》1998,73(2-3):159-172
In a recent screening for thermophilic bacteria from Azores hot springs, a Bacillus sp strain 3M, exhibiting cellulase-free extracellular xylanolitic activity, was isolated. Further enzyme characterization from liquid cultures grown on birchwood xylan revealed that the endo-l,4-βxylanase retains 100% of activity for at least 3 d at 55°C. At 80°C, it retains 47% of its maximal activity, and the enzyme is still active at 90°C. The optimum pH of the enzyme has a broad pH range, between 6.0 and 7.5, and it is remarkably active for the alkaline region, exhibiting 89% of relative activity at pH 9.O. The enzyme was partially inactivated by different divalent metal ions. Because of its tolerance for high temperature and pH conditions, and the absence of contaminating cellulase activity, the xylanase produced byBacillus sp 3M appears to be attractive for use in the pulp and paper industry. Indeed, the efficiency of the enzyme application to the kraftEucalyptus pulp was studied for bleaching pretreatment, resulting in a moderate increase of pulp bleachability. 相似文献
79.
The simultaneous determination of gallium and aluminium by using conventional fluorimetry and derivative synchronous fluorescence spectrometry has been studied. These determinations are based on the formation of fluorescent complexes of gallium and aluminium with salicylaldehyde carbohydrazone (SACH). In the conventional method, two samples are analysed under different analytical conditions, and the results are evaluated by solving a system of two simultaneous equations. In the derivative synchronous method (at pH = 2.6, in an ethanol-water medium containing 72% of ethanol), the following conditions are used: a constant wavelength difference of 20 nm between the monochromator settings, a time-constant of 1.5 sec, a scan-speed of 120 nm/min, and a derivative wavelength difference of 10 nm; gallium can be determined in the range 7-38 ng/ml, and aluminium between 6 and 45 ng/ml. The synchronous method shows more advantages, and has been used in the determination of both metal ions in diverse biological samples (animal tissues and human serum) with good results. 相似文献
80.
The reaction of mono-enolate anions with O2NCMe2X where X = Cl, NO2, p-MePhSO2 yield coupling (RCOCH(R′)(CMe2NO2) and enolate dimerization products (RCOCH(R′)CH(R′)COR) by free radical chain mechanisms involving bimolecular substitution or electron transfer reactions between the enolate anion and the intermediate nitro alkane radical anion (XCMe2NO2?). 相似文献