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301.
Kenta Hongo Yoshiyuki Kawazoe Hiroshi Yasuhara 《International journal of quantum chemistry》2007,107(6):1459-1467
The diffusion Monte Carlo (DMC) method shows that correlation in H2 produces a set of three spatial changes: (i) an enhancement in the electron density distribution n( r ) in the left and right anti‐binding regions that include separately the immediate vicinity of each of the two nuclei, (ii) a reduction in n( r ) in the binding region intervening between the two nuclei as a counterbalance, and (iii) a concomitant increase in the equilibrium internuclear separation. It is stressed that the correlation energy Ec (= Tc + Vc) for diatomic molecules be defined by the difference in the total energy between the exact and the Hartree–Fock (HF) variational calculations that are performed at individually optimized internuclear separations. It is this definition that makes it possible to involve a significant contribution from a correlation‐induced change in the equilibrium internuclear separation as part of the correlation energy and to relate (i) and (ii) to (iii) in consistency with the electrostatic theorem. The present calculations fulfill the virial theorem to an accuracy of ?V/T = 2.00 for DMC and ?VHF/THF = 2.000 for HF. The present correlation energy Ec = ?0.0408 hartree is not only in good agreement with the most accurate value previously reported, but also can be analyzed into all its components in accordance with the correlational virial theorem 2Tc + Vc = 0. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
302.
Two groups of polymer networks (polymer resins) are investigated by selective liquid sorption fromn-propanol-water mixtures. Group 1 consists of gel polymerized polar (hydrophilic) ion exchangers which swell in the binary liquid mixture. Group 2 consists of non-polar, non-swelling, macroporous resins. The free energy isotherms accompanying the sorption processes are calculated from the excess isotherms and the bulk activities. The adsorption excess free energies reveal the differences in polarity of the polymer network. 相似文献
303.
Olga N. Kataeva Aidar T. Gubaidullin Igor A. Litvinov Olga A. Lodochnikova Lenar R. Islamov Alexander I. Movchan Galina A. Chmutova 《Journal of Molecular Structure》2002,610(1-3):175-179
Crystal and molecular structure of 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one as a product of the benzoylation of 1-phenyl-3-benzoylaminopyrazol-2-in-5-one was characterised by X-ray single crystal diffraction. It is shown that 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one exists in the solid phase in an NH-tautomeric form, which is stabilised by two intramolecular hydrogen bonds and one intermolecular bond with the solvate dioxane molecule, the latter being used as a solvent for recrystallisation. 相似文献
304.
Safoklov B. B. Atovmyan E. G. Nikonova L. A. Tkachev V. V. Aldoshin S. M. 《Russian Chemical Bulletin》2002,51(12):2224-2229
Pyrrole-2-carbaldehyde isonicotinoylhydrazone (1) and its hydrate [1·H2O] (2) were studied by single-crystal X-ray diffraction analysis. The introduction of the pyrrole substituent into N"-substituted isonicotinic hydrazide (INH) causes the intramolecular redistribution of the electron density compared to those in INHs studied earlier, which increases the basicity of the hydrazone nitrogen atom (N") involved in intermolecular hydrogen bonding. This effect has not been observed in the structures of N"-substituted INHs and benzhydrazides studied previously. Intermolecular hydrogen bonds play a decisive role in the formation of the crystal structures of 1 and 2. 相似文献
305.
An intelligent, automatic system based on an array of non-specific-response chemical sensors was developed. As a great amount of information is required for its correct modelling, we propose a system generating it itself. The sequential injection analysis (SIA) technique was chosen as it enables the processes of training, calibration, validation and operation to be automated simply. Detection was carried out using an array of potentiometric sensors based on PVC membranes of different selectivity. The diluted standard solutions needed for system learning and response modelling are automatically prepared from more concentrated standards. The electrodes used were characterised with respect to one and two analytes, by means of high-dimensionality calibrations, and the response surface of each was represented; this characterisation enabled an interference study of great practical utility. The combined response was modelled by means of artificial neural networks (ANNs), and thus it was possible to obtain an automated electronic tongue based on SIA. In order to identify the ANN which provided the best model of the electrode responses, some of the network's parameters were optimised and its usefulness in determining NH4+, K+ and Na+ ions in synthetic samples was then tested. Finally, it was used to determine these ions in commercial fertilisers, the obtained results being compared with reference methods. 相似文献
306.
Summary Chirally substituted Si–H-containing polysiloxanes were synthesized, which can be immobilized on small particle silica gel as well as on the smooth surfaces of fused silica capillaries. Immobilization is achieved either by crosslinking or by chemical bonding to the surfaces via silanol groups; both reactions can only be performed by addition of H2PtCl6, which acts as catalyst for hydrosilylation and as stoichiometric reagent for crosslinking. Chiral substituents of systematically varied chemical structure were introduced into the polysiloxanes by hydrosilylation. The mechanism of immobilization was investigated by spectroscopic methods, notably29Si-NMR. Homogenous stationary-phase coatings of variable film thickness and corresponding retentivity can easily be achieved. The enantioselectivity of the phase systems was characterized in dependency on the chemical structure of the chiral selectors attached to the polysiloxane chain of the chiral stationary phases and also in terms of the functional groups introduced into the solutes by derivatisation. 相似文献
307.
New experimental data of the molar excess volume V
E
of the mixtures ethanol/n-butylamine, heptanol/n-butylamine, n-propanol/dibutylamine have been obtained using the technique of the vibrating tube densitometer. Together with the data for the molar excess enthalpy H
E
from the literature, the V
E
data have been used for testing the applicability of the socalled ERAS model which accounts for hydrogen bonding effects as well as for free volume effects in associating mixtures. The results obtained by adjusting the model parameters reveal a strong cross association between the unlike molecules in the mixture resulting from strong negative values for the hydrogen bonding energy and the hydrogen bonding volume.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60th birthday, Clermont-Ferrand, France, 17–18 May 1990. 相似文献
308.
Variations of densities and viscosities with temperature and composition are reported for binary liquid mixtures containing propionic acid+aniline (I),+o-toluidine (II),+o-anisidine (III), and+o-chloroaniline (IV). Entropies S
m and enthalpies H
m of activation as functions of the composition of the mixtures, as well as free energies of activation G
m at 10, 20, 30, 40, and 50°C and different compositions were calculated by means of Eyring's equation. The formation of activated complexes between the components of these binary mixtures is postulated and claimed to result from acid-base and hydrogen bonding exchange interactions. 相似文献
309.
Tarek M. Madkour Rasha A. Azzam 《Journal of polymer science. Part A, Polymer chemistry》2002,40(14):2526-2536
Polyurethane elastomers of a controlled molecular architecture were synthesized using a two‐step polymerization technique. The building blocks of the elastomeric materials included urea–urethane prepolymers end‐capped with diisocyanate groups and had an exact number of urea groups at both ends. Two‐dimensional bifurcated hydrogen‐bonding networks incorporating the urea groups were, with differential scanning calorimetric and dynamic mechanical thermal analyzer techniques, responsible for the increase in the glass‐transition temperature (Tg) of the hard block and sharp interface morphology between the pure “hard” domains and pure “soft” domains. The higher extent of the phase separation between the two phases contributed to higher elastic moduli for the hard blocks and higher tensile strength for the elastomeric samples. Higher elongation values were attributed to the liberation of the elastomeric chain ends that otherwise would have been constrained in the interface region. The higher Tg values of the hard blocks corresponded to an increase in the hardness values and a decrease in the tear‐strength values. The increase in the amount of urea groups within the hard segments, as a result of the increased amount of water and blowing catalyst, resulted in elastomeric foams with higher open‐cell content. This resulted in lower resilience values as measured using the pendulum rebound test and was attributed to the ability of the open cells to absorb and dissipate energy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2526–2536, 2002 相似文献
310.
The reaction of Co(NO3)2·6H2O with two equivalents of PPz (PPz = piperazine hexahydrate) and two equivalents of NH4SCN in CH3OH afforded the complex [Co(NCS)2(PPz)2(CH3OH)2]. The reaction of Ni(NO3)2·6H2O with two equivalents of PPz and four equivalents of NH4SCN in CH3OH afforded the complex [Ni(NCS)4(PPz)2]. Their IR spectra have been recorded and the structures have been determined. Crystal data for 1 : space group P&1bar;, a = 6.7208(6) Å, b = 8.4310(8) Å, c = 8.5923(8) Å, a = 77.881(2)°, β = 76.342(2)°, γ = 83.936(2)°, V = 461.75(1) Å3, Z = 1 with final residuals R1 = 0.0650 and wR2 = 0.1725. Crystal data for 2 : space group P2(1)/n, a = 7.4209(6) Å, b = 11.0231(9) Å, c = 12.317(1) Å, β = 96.642(9)°, V = 1000.9(2) Å3, Z = 2 with final residuals R1 = 0.0378 and wR2 = 0.0809. Important NCS—H‐N and O‐H—N(PPz) hydrogen‐bonding interactions in compound 1 and NCS···H‐N hydrogen‐bonding interactions and NCS—SCN interactions in compound 2 play a significant role in aligning the polymer strands in crystalline solids. 相似文献