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941.
942.
AFMR experiments in the frequency range 77<v<600 GHz and in the magnetic field range 0<H<75 kG on antiferromagnetic CoCl2 and CoBr2 single crystals at 4.2 K are reported. The waves propagate along the c axis of the crystals and the steady magnetic field is in the plane of the layers, which is also the easy plane of the spins.The influence of a rotation of the field in the easy magnetization plane is investigated, showing the existence of antiferromagnetic domains.The results of the field dependence of uniform magnon energies are reported in detail for the two compounds CoCl2 and CoBr2. In CoBr2, the two magnon modes at zero field are non degenerate, their frequencies are v1(0) = 60 GHzandv2(0) = 675 GHz, and the field required for saturation is Hs⊥ = 74.2 kG. 相似文献
943.
Sans résuméTravail subventionné par Dirección de Investigación, Universidad de La Frontera, Temuco. Chile et CONICYT. 相似文献
944.
Summary Relationships derived from the thermodynamic formulation of TLC with a binary mobile phase are discussed. The adsorption equilibrium
constant is determined from the linear form of a basic equation considering the adsorption process. This linear relationship
is examined with help of TLC data obtained by using six different chromatographic systems. The adsorption equilibrium constant
obtained from the TLC data is compared to the equilibrium constant determined from adsorption measurements.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
945.
o. Prof. Dr.-Ing. habil. S. Traustel 《Heat and Mass Transfer》1970,3(3):153-155
Zusammenfassung Es wird dargelegt, wie man nach Einführung des bekannten Begriffes Übertragungseinheit und mit Hilfe eines Vierfelderdiagramms zu einer relativ einfachen und durchsichtigen Berechnung von Gleich- und Gegenstrom-Wärmeübertragern gelangt.
On transfer units and a four-quadrant-diagram for the calculation of heat exchangers
It is shown that the introduction of the known concept of a transfer unit and the use of a four-quadrant diagram leads to a relatively simple and clear computation method for co-current and counter-current heat exchangers.相似文献
946.
[reaction: see text] A systematic study of dimethyl cuprate conjugate additions to diastereoisomeric ethyl gamma-hydroxy (or tert-butyldimethylsilyloxy)-delta-p-tolylsulfinyl-2-pentenoates and the analoguous sulfones showed mainly 3,4-anti diastereoselectivity when the reaction occurred in the presence of TMSCl. The pi-facial diastereoselection is mainly governed by the gamma-hydroxy or silyloxy group, whereas the role of the sulfur functionality is to increase the reactivity of the pentenoate system, probably by assisting the transfer of the alkyl group from the cuprate. This was evidenced by the reactions on similar systems that lack the sulfur functions. The appropriate choice of NH4OH or HCl hydrolysis in the workup allowed direct access to the open chain products or the lactones. 相似文献
947.
[reaction: see text] A study of published crystal structures (of O-acetylated sugars for the most part) suggests that the exocyclic C-O bond in acetate esters of cyclic alcohols intrinsically prefers a staggered conformation, although the eclipsed conformation is only slightly less stable. When the acetate is flanked by two equatorial substituents the preferred conformation is close to eclipsed. Over 1500 C-OAc bonds have been analyzed. Diagnostic NMR criteria for torsion angles and MM3 calculations are reported and confirm these conclusions. 相似文献
948.
The rate of S-nitrosocysteine decomposition in a pH range between 0.7 < pH < 13 exhibits first- and second-order dependence on total cysteine concentration. The second-order term is only observed for pH values between 6.9 < pH < 12. Both first- and second-order terms show a complex dependence on the acidity of the medium. They increase with increasing pH, reaching a maximum value around pH = 8 and then decrease with further increase in pH. An analysis of the reaction products reveals the absence of nitrite ion and ammonia. No evidence of catalysis by copper ions is observed. These results suggest the existence of a new decomposition pathway for S-nitrosocysteine, which proceeds via an intramolecular nitroso group transfer producing a primary N-nitrosamine that decomposes rapidly to give the corresponding diazonium salt. The nitroso group transfer reaction occurs intermolecularly for the decomposition pathway exhibiting a quadratic dependence on cysteine concentration. Both nitroso group transfer pathways are subject to acid catalysis by cysteine. Kinetic results indicate that the extent of S...NO bond cleavage in the transition state is ahead of protonation of the AH...S sulfur atom. The results obtained show the existence of a new decomposition pathway for the S-nitrosocysteine where NO is not released, and hence, it has a significant biological impact due to the potential use of nitrosothiols as NO donors. 相似文献
949.
In this work the separation of eighteen flavonoids was attempted using reduced-flow micellar elektrokinetic chromatography (RF-MEKC) electrolytes modified by selected solvents with differing properties: methanol (MeOH), acetonitrile (ACN) and tetrahydrofuran (THF). Structural aspects such as unsaturation of the C ring, number and position of OH groups, methylation and glycosylation as well as solvent effects and their impact on the electrophoretic behavior of flavonoids were addressed. By evaluating the electropherograms obtained from mixture-designed electrolytes and searching for changes in the critical pairs, a favorable separation condition was achieved using 20 mmol/L phosphate buffer at pH 2.5 containing 50 mmol/L sodium dodecyl sulfate (SDS), 15% ACN and 5% THF (one critical pair) in less than 12 min with 1.5% coefficient of variation (CV) for retention factor and 3% CV for peak area (n = 5). The applicability of the proposed separation condition was demonstrated by the inspection of flavonoids in herbal extracts of Neem. 相似文献
950.
Ferreira da Silva P Lima JC Freitas AA Shimizu K Maçanita AL Quina FH 《The journal of physical chemistry. A》2005,109(32):7329-7338
Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E(red) approximately -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA(Anthoc) - IP(Cop), the difference between the electron affinity of the anthocyanin, EA(Anthoc), and the ionization potential of the copigment, IP(Cop). Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted. 相似文献