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31.
Ângela F. S. S. Mendonça Dina T. R. Formigo Isabel M. S. Lampreia 《Journal of solution chemistry》2002,31(8):653-670
Solubilities of triethylamine in aqueous tetraethylammonium chloride solutions were measured at 20, 25, and 35°C. The molalities in Et4NCl of the aqueous solvents ranged from 0.03 to 1 mol-kg–1. The data were evaluated from density measurements using a vibrating-tube densimeter. At each temperature, least-squares method was used to fit experimental density data points to double polynomial equations of various degrees. Triethylamine molalities of the saturated aqueous phases were estimated by extrapolation from those equations. Experimental data were interpreted in terms of hydrophobic and electrostatic perturbed domains in the hydration shells of the noneleceory and of the cation of the salt, as a function of temperature and salt concentration. The conclusions obtained are consistent with previous volumetric studies. 相似文献
32.
The effect of the bifunctional crosslinking reagent glutaraldehyde on the activity of the restriction enzymes Bam HI,Hind III, EcoRI, and Tthlll I was investigated. The four enzymes exhibited differential sensitivity to inactivation. Tthlll I
was the most sensitive, with activity losses occurring at levels of 0.0025% and above.Hind III was the most stable of the four and remained fully active at concentrations as high as 0.075%. Addition of BSA to incubation
mixtures generally had a stabilizing effect. Implications of these results for the design of glutaraldehyde-based methods
for the immobilization of restriction endonucleases are discussed. 相似文献
33.
J. Zsakó 《Journal of Thermal Analysis and Calorimetry》1996,46(6):1845-1864
Four many curves methods, viz. calculation techniques based on Eqs (30), (31), (34) and (36), respectively, for deriving kinetic parameters from several TG curves recorded with different heating rates are tested on two sets of theoretical TG curves. The maximum reaction rate temperature and conversion, as well as the approximate formulae used for their calculation are discussed. Some aspects of the kinetic compensation effect are analysed. The final conclusion is that the use of the many curves methods is not reasonable. 相似文献
34.
High-resolution solid-state 29Si NMR has been applied to the study of partially exchanged Li, K, and Cs NaY zeolites. The order of the 29Si chemical shifts of dehydrated samples is Li, Na-Y < Na-Y < K, Na-Y. The correlation between the 29Si chemical shift and the Li or K loading on Li, Na-Y or K, Na-Y was rationalized in terms of the interaction between the framework and the cations inside the small cages. Because of the restrictive migration of large Cs+ ions from the supercages to the small cages, the 29Si chemical shift of Cs, Na-Y was found to be similar to that of Na-Y. 相似文献
35.
The π-π stacking interactions between maleimide's and nitrone's aromatic rings during the 1,3-dipolar cycloaddition were assumed to control the exo-endo selectivity of the reaction. The exo-endo ratios change during the reactions until they reach a constant value, which depends on the substituent. Electron-withdrawing groups favour the exo adduct while electron-donating groups favour the endo adduct. The nitrone ZnBr2 complexes react much more slowly than the free nitrone and the cycloaddition is exo selective in all cases independent of the substituents on the maleimide's aromatic ring. Thermal retrocycloaddition of the cycloadducts produce the corresponding nitrones. The ring opening in the presence of secondary amines did not induce imine formation. endo Adducts were shown for the first time to be the stable paramagnetic compounds. 相似文献
36.
The relaxation field for solutions of mixed electrolytes of any type is calculated. the calculation is based on the well-known
treatment due to Fuoss-Onsager with the same distance parameter for all the ions in solution. A general conductance-continuity
equation has been established and an improved iterative method of calculation, using Laplace transforms, is proposed. The
relaxation-field results are derived to the second iteration in the perturbation method of integration. 相似文献
37.
It follows from an analysis of the error levels of TG evaluation methods that it is a conceptual error to disregard the analogies
of mass, energy and momentum streams of subordinate partial processes. This error is bypassed by means of the introduced method
of dimensionless analysis and by determining the characteristic, constants-like data of thermal processes by using the measured
data directly. These methods are very suitable for increasing the consistency of the calculated results by seeking for similarity,
even in comparisons of measurements made under very different conditions and for emphasizing the differences too, quantitatively.
With this new interpretation of TG processes, the idea of the kinetic compensation effect becomes only a consequence of the
discussed conceptual error.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
The rate of electron transfer from organic sulfides to [CrV(ehba)2]− (ehba-2-ethyl-2-hydroxy butyric acid) decreases with a decrease in the polarity of the medium. The anionic surfactant, SDS and the cationic surfactant, CTAB have different effects on the kinetics of this reaction. The micellar inhibition observed in the presence of SDS is probably due to the decrease in the polarity and the electrostatic repulsion faced by the anionic oxidant from the anionic micelle and the partition of the hydrophobic substrate between the aqueous and micellar phases. The micellar catalysis in the presence of CTAB is attributed to the increase in the concentration of both reactants in the micellar phase. This micellar catalysis is observed to offset the retarding effects of the less polar micellar medium and the unfavorable charge-charge interaction between the + charge developed on S center in the transition state and the cationic micelle. This catalysis is contrary to the enormous micellar inhibition observed with IO4−, HSO5− and HCO4− oxidation of organic sulfides. 相似文献
39.
1INTRODUCTIONRecentlyorganicnonlinearoptical(NLO)materialsarebeingdevelopedforfre-quencyconversionoflaserinopto-electrics-Especiallybluelightisrequiredforopti-calmemoryofhighdensityrecording.Becauseadiodelaserisusedasalightsource,thenonlinearmaterialswhichhaveextremelyhighvalueofNLOcoefficientsandthetransmissionofblueregionarenecessary.Sincethesecond-orderNLOpropertyoforganiccompoundisderivedfromconjugateddelocalizedrrelectrons,thecompoundswhichhavebeenreportedhavefocusedonthenitroanil… 相似文献
40.
Paul Ruelle Michel Buchmann Hô Nam-Tran Ulrich W. Kesselring 《Journal of computer-aided molecular design》1992,6(5):431-448
Summary The thermodynamics of mobile order is applied to predict the aqueous solubility of liquid and solid aliphatic and polycyclic aromatic hydrocarbons. The solubility values are mainly determined by the magnitude of the hydrophobic effect. However, contrary to the solubilities of the alkanes, the solubilities of polycyclic aromatic hydrocarbons in water predicted in absence of solute-solvent hydrogen (H) bonds are systematically too low. This shows the contribution of weak specific interactions between the OH groups and the electrons of the aromatic substances. According to the theory, these interactions are characterized by a stability bility constant Ko which can be derived from solubility data. At 25°C, this constant amounts to 80 cm3/mol, the order of magnitude of which can be explained by the competition of these intermolecular bonds with the rather weak self-association bonds in the secondary chains of water. 相似文献