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961.
Ippolito Antonini Francesco Claudi Gloria Cristalli Mario Grifantini Sante Martelli 《Journal of heterocyclic chemistry》1981,18(2):399-404
The course of the thermal decomposition of various 2-amino-3-substituted aziridino-1,4-naphthoquinones (Ia-g) was investigated. In all the cases, the thermal decomposition gave variable amounts of 2,3-diamino-1,4-naphthoquinone (II) and of substituted 1,2,3,4,5,10-hexahydrobenzo[g]quinoxaline-5,10-diones (IIIa-g) with complete stereospecificity. The decomposition of the aziridines Ib,f also gave significative amounts of 2-amino-3-allylamino-1,4-naphthoquinones (IVb,f). In the case of 2-amino-3-(2′-phenyl-3′-ethylaziridino)-1,4-naphthoquinone (Ig), the formation of trans-1-phenyl-1-butene (V), 2-(1-phenylpropyl)-1H-naphtho-imidazole-4,9-dione (VI), 2-phenyl-3-ethyl-3,4,5,10-tetrahydrobenzo[g]quinoxaline-5,10-dione (VII), 2-phenyl-3-ethyl-5,10-dihydrobenzo[g]quinoxaline-5,10-dione (VIII), and a mixture of cis- and trans-4H-2,3,5,6-tetra-hydro-2-phenyl-3-ethyl-5-iminonaphtho[1,2-b]oxazin-6-one (IX) also occurred. Hypotheses concerning the mechanism and the steric course of this reaction are given. The reaction is a general method for the stereospecific synthesis of 2,3-disubstituted 1,2,3,4,5,10-hexahydrobenzo[g]quinoxalines. 相似文献
962.
Optimization of virtual orbitals in the framework of a multiconfiguration spin-coupled wave function
Nick J. Clarke Mario Raimondi Maurizio Sironi Joseph Gerratt David L. Cooper 《Theoretical chemistry accounts》1998,99(1):8-17
A new method is introduced for the optimization of nonorthogonal virtual orbitals for use in general multiconfiguration spin-coupled wave functions. The use of a number of highly effective approximations greatly reduces the computational effort
involved, the most important being the use of a second-order perturbation expression for the energy and an approximate expression
for the elements of the Hessian. As a result, the overall scheme scales very favourably with respect to the numbers of active
electrons and of basis functions, making it suitable for the accurate study of large systems. Benchmark calculations are presented
for the dissociation of LiH(X1Σ+) and Li2(X1Σ+
g
) using a highly compact four-configuration wave function. Standard spin-coupled valence bond expansions in the same virtual
space are required to be significantly larger before equivalent results are obtained. The results are shown to compare very
favourably with full valence complete active space self-consistent field calculations using an identical basis, and binding
energies are within 4% of the values obtained from full configuration interaction calculations in the same basis set.
Received: 10 June 1997 / Accepted: 7 October 1997 相似文献
963.
Multireference configuration interaction with singles and doubles (MR-CISD) calculations has been performed for the optimization of conical intersections and stationary points on the fluoroethylene excited-state energy surfaces. For the planar ground state geometry, the vertical spectrum including 3s and 3p Rydberg states was calculated. From this geometry, a rigid torsion around the CC bond strongly reduces the energy gap between S0 and S1 states. Furthermore, a search for the minimum of the crossing seam shows that there exists a conical intersection close to the twisted structure and two additional ones for cis and trans pyramidalized structures. These three intersections are connected by the same seam. We have shown that the Hula-Twist process is an alternative way to the direct CC twisting in order to reach this part of the seam. Other conical intersections were also located in the CH3CF and CH2FCH, H-migration, and C(3v) structures. The photodynamics of the system is discussed based on topological features of these intersections. 相似文献
964.
Holger Braunschweig Frank M. Breitling Katharina Kraft Mario Kraft Fabian Seeler Sascha Stellwag Krzysztof Radacki 《无机化学与普通化学杂志》2006,632(2):269-278
A wide range of potential ligand precursors and related compounds have been synthesized from ferrocenyldibromoborane and ferrocenylenebis(dibromoborane) via salt elimination reactions. These comprise ligand precursors suitable for the preparation of (i) ansa‐metallocenes such as [FcB(η1‐C5H5)2] ( 2 ), [FcB(1‐C9H7)2] ( 3 ), [FcB(3‐C9H7)2] ( 4 ) and [1,1′‐fc{B(3‐C9H7)2}2] ( 11 ), (ii) constrained geometry complexes such as [FcB(1‐C9H7)N(H)Ph] ( 7 ) and [FcB(3‐C9H7)N(H)Ph] ( 8 ), (iii) ansa‐diamido complexes such as [FcB(N(H)Ph)2] ( 9 ) as well as (iv) the related compounds [FcB(Br)N(H)tBu] ( 5 ), [FcB(Br)N(H)Ph] ( 6 ), [1,1′‐fc{B(Br)N(SiMe3)2}2] ( 12 ) and [1,1′‐fc{B(Br)NiPr2}2] ( 13 ) (Fc = ferrocenyl, fc = ferrocenylene, C5H5 = cyclopentadienyl, C9H7 = indenyl). All new compounds have been characterised by multinuclear NMR spectroscopic techniques and in the case of 7 and 12 by X‐ray diffraction methods. 相似文献
965.
Luciano Farias Almeida Edvan Cirino Silva Mario Cesar Ugulino Araujo 《Analytica chimica acta》2003,486(1):143-148
A novel strategy for implementing the automatic standard addition method (SAM) is described. By using a flow-batch system that presents the intrinsic favourable characteristics of the flow and batch techniques, the proposed strategy performs fast standard additions with sufficient flexibility and versatility and employs only one standard solution per analyte. To calculate the analyte concentration, a mathematical model based on a classical SAM and flow variables of the system was developed. The proposed flow-batch SAM was applied to copper determination by flame atomic absorption spectrometry (AAS) in sugar cane-made alcoholic beverages, known as “Cachaça”, available in Brazil. A SAM has been recommended for these analyses because “Cachaças” presents a significantly different composition causing matrix effects and copper determination by calibration using matrix-matching standards can yield inaccurate results. The results show good agreement between the obtained values with the proposed flow-batch SAM and a manual SAM. The mean relative errors and overall standard deviations were always <1.0% (n=6) and 0.2 mg l−1, respectively, for 1.0-7.0 mg l−1 Cu. By using five standard addition levels, the sample throughput was 70 h−1 and the consumption of sample and standard solution were 1.5 and 0.5 ml per analysis, respectively. 相似文献
966.
967.
Atom-atom, atom-bond and bond-bond polarizabilities are calculated with a previously used LCAO approximation. Some properties of naphtalene, assumed as general for alternant hydrocarbons, seem to depend on the approximation employed. Atom-atom polarizabilities in azines are related to other theoretical and experimental quantities. In all the molecules studied, the part played by formal bonds is highly stressed.
With a fellowship from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.
With a fellowship from the Centro Latino Amerioano de Física.
The authors gratefully acknowledge the helpful discussions with Dr. J. Brieux and Lic. H. C. González, who has besides collaborated in part of the calculations. 相似文献
Zusammenfassung Atom-Atom-, Atom-Bindungs- und Bindungs-Bindungs-Polarisierbarkeiten werden mit einem schon früher benutzten LCAO-Verfahren berechnet. Einige Eigenschaften von Naphthalin, die für alternierende Kohlenwasserstoffe als charakteristisch angesehen werden, scheinen von der benutzten Näherung abzuhängen. Atom-Atom-Polarisierbarkeiten in Azinen werden auf andere theoretische und experimentelle Größen zurückgeführt. In allen betrachteten Molekülen spielen formale Bindungen eine bedeutende Rolle.
Résumé Calcul des polarisabilités atome-atome, atome-liaison et liaison-liaison dans une approximation LCAO utilisée auparavant. Certaines propriétés du naphtalène, supposées générales pour les hydrocarbures alternants, semblent dépendre de l'approximation employée. Les polarisabilités atome-atome des azines sont reliées à d'autres grandeurs théoriques et expérimentales. Dans toutes les molécules étudiées, le rôle joué par les liaisons formelles est mis en relief.
With a fellowship from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.
With a fellowship from the Centro Latino Amerioano de Física.
The authors gratefully acknowledge the helpful discussions with Dr. J. Brieux and Lic. H. C. González, who has besides collaborated in part of the calculations. 相似文献
968.
The rates of intramolecular condensation of a series of monoesters of dicarboxylic acids have been shown to be highly dependent on the nature of the intervening groups. To understand the origin of this effect, we estimated DeltaS(NAC,S), the entropy difference between the ensemble of accessible ground state conformers and a single ground state conformer having transition-state-like geometry. DeltaS(NAC,S) differs from the activation entropy for the reaction by DeltaS(TS,NAC), the difference in vibrational entropy between the selected ground state conformer and the transition state. The estimated values of DeltaS(NAC,S) correlate well (R(2) = 0.96 and 0.73 using dielectric constant values of 80 and 1, respectively) with experimentally determined reaction rate constants. Normal-mode analysis performed on minimized ground state conformations of each molecule suggests that the change in vibrational entropy makes only a small contribution to the total activation entropy. These results indicate that the conformational entropy difference between the transition and the ground states contributes significantly to the free energy of activation. 相似文献
969.
Jan C. J. Bart Mario Calcaterra Walter Cavigiolo Pietro Massardo 《Journal of chemical crystallography》1989,19(1):99-108
Mw=403,2 amu,P21/c,a 18.944(8) Å,b=8.540(4) Å,c=10.794(7) Å,=98.11(4)°,V=1729(2) Å3,Z=4,D
x=1.548 g·cm–3, (MoK)=4.26 cm–1; m.p. 202–204°C. FinalR=0.083 for 1632 independent observed reflections having 2 (Mo K)<50° andI>2 (I). The molecule has an extended overall nonplanar conformation with onecis and twotrans-C(O)-NH- units and intramolecular hydrogen bridges. The relatively highR factor is on account of conformational disorder of the trifluoromethyl and chloro substituents of the 2-chloro-3,3,3-trifluoropropenyl moiety. 相似文献
970.
Numerical Algorithms - Quasi-Newton methods for solving nonlinear systems of equations are generally defined in order to satisfy a “direct secant equation” or an “inverse secant... 相似文献