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861.
862.
Volker Bhmer Walter Vogt Salah Chafaa Jean Meullemeestre Marie-Jos Schwing Franois Vierling 《Helvetica chimica acta》1993,76(1):139-149
(o-Hydroxyphenyl)methylphosphonic acids are readily obtained from o-(bromomethyl)- or o-(hydroxymethyl)phenols and trialkyl phosphites. Subsequent hydrolysis leads to the corresponding phosphonic acids. For a series of such compounds, the pKa values have been determined by potentiometry. Their dependence on additional substituents in the aromatic ring is discussed in terms of electronic and steric effects. 相似文献
863.
Summary Methods for preparation of copper phosphides at ambient temperatures by electrodeposition are presented. From P4/PCl3/Acetonitrile/TBA-BF4/Cu+ (solvated) Cu3P and Cu3P2 can be obtained at different deposition potentials.
Elektrochemische Abscheidung von Kupferphosphiden
Zusammenfassung Es werden Verfahren zur Herstellung von Kupferphosphiden bei ambienten Temperaturen beschrieben. Aus der Anordnung P4/PCl3/Acetonitril/TBA-BF4/Cu+ (solvatisiert) können Cu3P und Cu3P2 bei verschiedenen Abscheidungspotentialen erhalten werden.相似文献
864.
865.
866.
867.
To supplement previous studies of polyesters with laterally attached and cross-shaped mesogens the influence of molecular weight and molecular weight distribution on the phase behaviour has been investigated. For that purpose two polyesters have been fractionated by preparative gel permeation chromatography under high pressure and observed by polarizing microscopy and DSC measurements. A monotropic nematic polyester with laterally attached mesogens shows changing phase transitions up to a molecular weight of 10 000 (Mw); at higher molecular weight only the clearing transition is still slightly influenced. The molecular weight distribution at an average molecular weight of 15 000 (Mw) has no influence on the melting and clearing temperatures, but does effect recrystallization. The tendency to recrystallize decreases with increasing polydispersity, with increasing aberration from a monomodal molecular weight distribution. The recrystallization and the melting enthalpy are most distinguished at molecular weights around 12 000 (Mw) and crystallization disappears at molecular weights under about 5000 (Mw). In this way, fractions with stable nematic phases are obtained. Additionally, the broadness of the biphasic region shows a distinct dependence on molecular weight. Clearing temperatures show the most significant dependence on the molecular weight of an enantiotropic polyester with crossshaped mesogens dropping significantly below a molecular weight of about 20 000 (Mw). Oligomers with molecular weights below 10 000 (Mw) do not exhibit a mesophase. Polyesters with laterally attached mesogens as well as with crossshaped mesogens show no new liquid-crystalline phases by varying the molecular weight or the molecular weight distribution. 相似文献
868.
869.
Numerical computation of an analytic singular value decomposition of a matrix valued function 总被引:1,自引:0,他引:1
Angelika Bunse-Gerstner Ralph Byers Volker Mehrmann Nancy K. Nichols 《Numerische Mathematik》1991,60(1):1-39
Summary This paper extends the singular value decomposition to a path of matricesE(t). An analytic singular value decomposition of a path of matricesE(t) is an analytic path of factorizationsE(t)=X(t)S(t)Y(t)
T whereX(t) andY(t) are orthogonal andS(t) is diagonal. To maintain differentiability the diagonal entries ofS(t) are allowed to be either positive or negative and to appear in any order. This paper investigates existence and uniqueness of analytic SVD's and develops an algorithm for computing them. We show that a real analytic pathE(t) always admits a real analytic SVD, a full-rank, smooth pathE(t) with distinct singular values admits a smooth SVD. We derive a differential equation for the left factor, develop Euler-like and extrapolated Euler-like numerical methods for approximating an analytic SVD and prove that the Euler-like method converges.Partial support received from SFB 343, Diskrete Strukturen in der Mathematik, Universität BielefeldPartial support received from FSP Mathematisierung, Universität BielefeldPartial support received from FSP Mathematisierung, Universität BielefeldPartial support received from National Science Foundation grant CCR-8820882. Some support was also received from the University of Kansas through International Travel Fund 560478 and General Research Allocations # 3758-20-0038 and #3692-20-0038. 相似文献
870.
Summary In this paper we study the numerical factorization of matrix valued functions in order to apply them in the numerical solution of differential algebraic equations with time varying coefficients. The main difficulty is to obtain smoothness of the factors and a numerically accessible form of their derivatives. We show how this can be achieved without numerical differentiation if the derivative of the given matrix valued function is known. These results are then applied in the numerical solution of differential algebraic Riccati equations. For this a numerical algorithm is given and its properties are demonstrated by a numerical example. 相似文献