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991.
We describe the development of empirical potential functions for the study of the excited state intramolecular proton transfer
reaction in 1-(trifuloroacetylamino)-naphtaquinone (TFNQ). The potential is a combination of the standard CHARMM27 force field
for the backbone structure of TFNQ and an empirical valence bond formalism for the proton transfer reaction. The latter is
parameterized to reproduce the potential energies both in the ground and the excited state, determined at the CASPT2 level
of theory. Parameters describing intermolecular interactions are fitted to reproduce molecular dipole moments computed at
the CASSCF level of theory and to reproduce ab initio hydrogen bonding energies and geometries for TFNQ-water bimolecular
complexes. The utility of this potential energy function was examined by computing the potentials of mean force for the proton
transfer reactions in the gas phase and in water, in both electronic states. The ground state PMF exhibits little solvent
effects, whereas computed potential of mean force shows a solvent stabilization of 2.5 kcal mol−1 in the product state region, suggesting proton transfer is more pronounced in polar solvents, consistent with experimental
findings.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Contribution to the Fernando Bernardi Memorial Issue. 相似文献
992.
Alessandro Marcuzzi Anthony Linden Wolfgang von Philipsborn 《Helvetica chimica acta》1993,76(2):976-987
A variety of [Ru(CO)2L(η4enone)] complexes (L = phosphines, phosphites, and arsines, enone = (E)-4-phenylbut-3-en-2-one) have been synthesized. 1H-, 13C-, and 31P-NMR spectra are reported and the X-ray structures of two Ru complexes with L ? Ph3P(7), Et3P ( 10 ) and one Fe complex with L ? Ph3P ( 14 ) are presented. All three compounds crystallize in the same monoclinic space group P21/n with a = 10.575(2) Å, b =9.213(2) Å, and c = 27.608(5) Å, β = 100.04(2)°, Z = 4 for 7 , a = 10.276(3) Å, b = 12.935(3) Å, and c = 14.854(2) Å, β = 96.96(2)°, Z = 4 for 10 , and a = 10.492(2) Å, b = 9.232(3) Å, and c = 27.129(3) Å, β = 98.67(2)°, Z = 4 for 14 . The structures of the Ru complexes are compared with the Fe analogues. In the case of M ? Ru and L ? (EtO)3P, (MeO)3P, and (i-PrO)3P ( 9 , 11 , and 13 , respectively) stereoisomers could be detected by 31P-NMR at room temperature, wich arise from rotation at the coordinated metal centre. 相似文献
993.
Pursuing our previous research on azaquinoxalinones (1,2-dihydropyrido[2,3-b]/[3,4-b]pyrazinones) we prepared, through a reductive cyclization of N-(3′-nitropyridin-2′-yl)piperidine-2-carboxylic acids 3a-c , a set of derivatives of a new tricyclic structure, 7,8,9,10-tetrahydro-5H-dipyrido[1,2-a:3′,2′-e]pyrazin-6(6aH)-ones 4a-c. Starting from these compounds we obtained substituted amides 5a-c and, from 4a , the amidines 6a-c. In the synthesis of 6 , a dehydrogenation reaction occurred giving rise to 7. The compounds 9 and 10 , characterized by a different ring-fusion between the pyridine and pyrazine rings, were synthesized in a similar manner. 相似文献
994.
Cocchi M Hidalgo-Hidalgo-de-Cisneros JL Naranjo-Rodríguez I Palacios-Santander JM Seeber R Ulrici A 《Talanta》2003,59(4):735-749
Successful applications of multivariate calibration in the field of electrochemistry have been recently reported, using various approaches such as multilinear regression (MLR), continuum regression, partial least squares regression (PLS) and artificial neural networks (ANN). Despite the good performance of these methods, it is nowadays accepted that they can benefit from data transformations aiming at removing baseline effects, reducing noise and compressing the data. In this context the wavelet transform seems a very promising tool. Here, we propose a methodology, based on the fast wavelet transform, for feature selection prior to calibration. As a benchmark, a data set consisting of lead and thallium mixtures measured by differential pulse anodic stripping voltammetry and giving seriously overlapped responses has been used. Three regression techniques are compared: MLR, PLS and ANN. Good predictive and effective models are obtained. Through inspection of the reconstructed signals, identification and interpretation of significant regions in the voltammograms are possible. 相似文献
995.
Alessandro de Robertis Concetta de Stefano Rosario Scarcella Carmelo Rigano 《Thermochimica Acta》1984,80(2):197-208
The formation constants for the complexes Mg2+ -, Ca2+ -, Sr2+ - and Ba2+ - succinate (succ2−) have been determined by potentiometric measurements, in aqueous solution, at different temperatures and ionic strengths. The species [M(succ)]0 and [M(succ)H]+ were found for all systems. For the stability constant the ionic strength dependence has been found, and general parameters for the relation log β = f(I) have been obtained. From the temperature dependence of stability constants ΔH values have been deduced. The procedure adopted in calculating all the thermodynamic parameters for the systems under study, where weak complexes are formed, is discussed. The stability of the complexes follows the order Mg < Ca Sr ≈ Ba. 相似文献
996.
M. P. F. Graça M. G. Ferreira da Silva M. A. Valente 《Journal of Sol-Gel Science and Technology》2007,42(1):1-8
The glass composition 88SiO2-6Li2O-6Nb2O5 (mole %) was successfully prepared by the sol-gel technique. The dried and translucent gel was heat-treated at temperatures
between 500°C and 800°C. Lithium niobate crystallites, an important ferroelectric material, were detected in the gel derived
glass-ceramics treated above 650°C. In the samples treated at 700 and 800°C the Li2Si2O5 crystalline phase is present. The 800°C treated sample also presents the Li3NbO4 phase.
The structure and morphology of the samples were studied by X-ray powder diffraction (XRD), Raman spectroscopy and scanning
electron microscopy (SEM). The SEM revealed that all the samples, heat-treated above 650°C, present crystallites embedded
in the glass matrix. The particles detected in the 600°C treated sample are essentially amorphous, or with an incipient structure.
The temperature dependence of the dc electrical conductivity (σ
dc
) shows two regions with different activation energies. The conductivity behaviour of the sample is mainly due to the mobile
ion number. The ac conductivity (σ
ac
), measured at 1 kHz decreases with the rise of the treatment temperature due to the increase of the LiNbO3 crystallites amount.
The electrical behavior of the glass and glass-ceramics reflects the important role carried out by the treatment temperature
in the gel-glass structure. 相似文献
997.
Cocchi M Foca G Marchetti A Sighinolfi S Lorenzo T Ulrici A 《Annali di chimica》2005,95(9-10):657-666
Different kinds of bread, stored at constant temperature and at controlled humidity conditions for a week since their manufacturing date, were analysed by Attenuated Total Reflectance-Fourier Transform InfraRed (ATR-FTIR) spectroscopy. The collected spectra were processed by Principal Component Analysis (PCA), in order to evaluate the changes occurring during bread ageing. For the sake of comparison, the 1060-950 cm spectral window has been also investigated by curve-fitting methods. It was observed that the first PC increases monotonically with ageing of samples. Furthermore, the more influential variables on PC1 correspond to spectral regions where are located stretching and bending bands, which are mainly attributed to typical starch bonds vibrations. 相似文献
998.
Charles Brown Brian T. Heaton Anthony D.C. Towl Paolo Chini Alessandro Fumagalli Giuliano Longoni 《Journal of organometallic chemistry》1979,181(1):233-254
Platinum-195 spectra are reported for [Ptn(CO)2n]2- (n = 3, 6, 9, 12 and 15) and carbon-13 spectra are reported for n = 6, 9 and 12 over a range of temperatures. The spectra provide evidence for (a) intramolecular rotation of the Pt3-triangles about the principal three-fold axis, (b) inter-exchange of Pt3-triangles, (c) lack of terminal/edge carbonyl exchange within the Pt3(CO)3(μ-CO)3 group. Evidence is also presented for the formation of [Ni3Pt3(CO)12]2- on mixing [Pt6(CO)12]2- [Ni6(CO)12]2-. 相似文献
999.
C. H. Collins C. A. Bertran A. L. Pires Valente Priscila de A. Leone A. L. M. Murta K. E. Collins 《Chromatographia》1988,26(1):168-170
Summary Separation of perhalogenated compounds resulting from thermolysis, photolysis or radiolysis of mixtures of halogens in carbon tetrachloride was carried out by programmed temperature gas chromatography. Plots of relative retentions (to CBr4) vs the number of bromine atoms present for known compounds of the general formula CxBryClz (x=1 and 2; y+z=4 or 6) gave three linear correlations (all with r>0.99). These correlations permitted projections of the identities of reaction products for which no standards were available. These projections were later confirmed by CG-MS. *** DIRECT SUPPORT *** A0732166 00010 相似文献
1000.
Starting from racemic 4-hydroxy-4-methyl-2-cyclopentenone, a family of enantiopure carbanucleosides locked in the northern conformation has been synthesized. The use of ionic liquids was determinant in the last step resulting in a tangible increase of the yields and dramatic reduction of reaction times and volumes of organic solvents. To our knowledge, this is the first example of the use of ionic liquids in the coupling of carbasugars with heterocyclic bases. 相似文献