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排序方式: 共有646条查询结果,搜索用时 15 毫秒
1.
A short introduction of Hamilton, Cartan and Generalized Hamilton spaces is provided. The Hamilton--Jacobi equations are deduced by variational calculus. 相似文献
2.
This paper addresses the natural question: “How should frames be compared?” We answer this question by quantifying the overcompleteness of all frames with the same index set. We introduce the concept of a frame measure function: a function which maps each frame to a continuous function. The comparison of these functions induces an equivalence and partial order that allows for a meaningful comparison of frames indexed by the same set. We define the ultrafilter measure function, an explicit frame measure function that we show is contained both algebraically and topologically inside all frame measure functions. We explore additional properties of frame measure functions, showing that they are additive on a large class of supersets—those that come from so called non-expansive frames. We apply our results to the Gabor setting, computing the frame measure function of Gabor frames and establishing a new result about supersets of Gabor frames. 相似文献
3.
Florin Radu Alexei Nefedov Johannes GrabisGregor Nowak Andre BergmannHartmut Zabel 《Journal of magnetism and magnetic materials》2006
We have used soft X-ray resonant magnetic scattering (XRMS) to search for the presence of an effective ferromagnetic moment belonging to the antiferromagnetic (AF) layer which is in close contact with a ferromagnetic (F) layer. Taking advantage of the element specificity of the XRMS technique, we have measured hysteresis loops of both Fe and CoO layers of a CoO(40 Å)/Fe (150 Å) exchange bias bilayer. From these measurements we have concluded that the proximity of the F layer induces a magnetic moment in the AF layer. The F moment of the AF layer has two components: one is frozen and does not follow the applied magnetic field and the other one follows in phase the ferromagnetic magnetization of the F layer. The temperature dependence of the F components belonging to the AF layer is shown and discussed. 相似文献
4.
Radu Miron 《Reports on Mathematical Physics》2004,54(2):131-147
The Randers spaces RFn were introduced by R. S. Ingarden. They are considered as Finsler spaces Fn = (M, α + β) equipped with the Cartan nonlinear connection. In the present paper we define and study what we call the Ingarden spaces, I Fn, as Finsler spaces I Fn = (M, α + β) equipped with the Lorentz nonlinear connection. The spaces R Fn and I Fn are completely different. For I Fn we discuss: the variational problem, Lorentz nonlinear connection, canonical N-metrical connection and its structure equations, the Cartan 1-form ω, the electromagnetic 2-form tF and the almost symplectic 2-form 0. The formula dω = F+θ is established. It has as a consequence the generalized Maxwell equations. Finally, the almost Hermitian model of I Fn is constructed. 相似文献
5.
V. Badescu M. Radu M. Zaharescu A. Vasilescu 《Journal of Sol-Gel Science and Technology》1994,2(1-3):43-49
Gas-chromatography coupled with mass spectrometry was used to investigate the hydrolysis and condensation of tetra-ethoxysilane (TEOS) in nonparental solvents (MeOH and nPrOH). In the presence of nonparental solvents, the reaction that advanced at highest rate is alkoxy group scrambling, that changes the precursor at the molecular level. Subsequent stages of hydrolysis-polycondensation process are essentially determined by the reactivity of the new molecular species formed. 相似文献
6.
Radu Ioan Boţ Ioan Bogdan Hodrea Gert Wanka 《Nonlinear Analysis: Theory, Methods & Applications》2007
Considering a constrained fractional programming problem, within the present paper we present some necessary and sufficient conditions, which ensure that the optimal objective value of the considered problem is greater than or equal to a given real constant. The desired results are obtained using the Fenchel–Lagrange duality approach applied to an optimization problem with convex or difference of convex (DC) objective functions and finitely many convex constraints. These are obtained from the initial fractional programming problem using an idea due to Dinkelbach. We also show that our general results encompass as special cases some recently obtained Farkas-type results. 相似文献
7.
8.
Custelcean R Gorbunova MG Bonnesen PV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(5):1459-1466
Hydrogen bonding in crystalline N,N'-dialkylthioureas was examined with the help of single-crystal X-ray diffraction, DFT calculations, and Cambridge Structural Database (CSD) analysis. A CSD survey indicated that unlike the related urea derivatives, which persistently self-assemble into one-dimensional hydrogen-bonded chains, the analogous thioureas can form two different hydrogen-bonding motifs in the solid state: chains, structurally similar with those found in ureas, and dimers, that further associate into hydrogen-bonded layers. The formation of one motif or another can be manipulated by the bulkiness of the organic substituents on the thiourea group, which provides a clear example of steric control over the hydrogen bonding arrangement in crystalline organic solids. 相似文献
9.
One considers m-dimensional Riemannian manifoldsM with tangent spaces Tp(M), p M that are a direct sum of a spacelike m-2 planeR
p and a 2-planeH
p. It is supposed that onM there exists a connection whose space-like components are parallel conformal flat (pkf). These components are generated by a vector field X. Assuming that X belongs to a pair X,Y of reciprocal quasi-cocircular vector fields and that the Pfaffian of this pair is the 1-form associated with the connection, the following results are derived: 1. X and Y are of equal constant length (This is true for all Riemannian manifolds). 2. The immersion of the integral manifold ofH
p intoM is cylindrical and the normal connection is flat. 3. The immersion of any space-like submanifold intoM is cylindrical with respect to the sections inH
p and umbilical with respect to all spacelike sections. 4. If m 4, the integral manifoldP
p is flat.
Herrn Prof. Dr. WERNER BURAU zum 70.Geburtstag Klaus Buchner und Radu Rosca 相似文献
Herrn Prof. Dr. WERNER BURAU zum 70.Geburtstag Klaus Buchner und Radu Rosca 相似文献
10.
The reactions between silver tetrafluoroborate and the ligands 1,2,4,5-C(6)H(2)[CH(2)OCH(2)C(pz)(3)](4) (L1, pz = pyrazolyl ring), o-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L2), and m-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L3) yield coordination polymers of the formula (C(6)H(6)(-)(n)[CH(2)OCH(2)C(pz)(3)](n)(AgBF4)(m))( infinity ) (n = 4, m = 2, 1; n = 2, ortho substitution, m = 1, 2; meta substitution, m = 2, 3). In the solid state, L2 molecules dimerize by a pair of C-H.pi interactions, forming an arrangement that resembles the tetratopic ligand L1. In the solid-state structure of 1, each silver atom is kappa(2)-bonded to two tris(pyrazolyl)methane units from different ligands with the overall structure a polymer made up from 32-atom macrocyclic rings formed by bonding tris(pyrazolyl)methane groups from nonadjacent positions on the central arene rings to the same two silver atoms. In 2, each silver is bonded to two tris(pyrazolyl)methane units in the same kappa(2)-kappa(2) fashion as with 1, forming a polymer chain. The chains are organized into dimeric units by strong face-to-face pi-pi stacking between the central arene rings making bitopic L2 act as half of tetratopic L1. The chains in both structures are organized by weak C-H.F hydrogen bonds and pi-pi stacking interactions into very similar 3D supramolecular architectures. The structure of 3 contains three types of silvers with the overall 3D supramolecular sinusoidal structure comprised of 32-atom macrocycles. Infrared studies confirm the importance of the noncovalent interactions. Calculations at the DFT (B3LYP/6-31G) level of theory have been carried out on L2 and also support C-H.pi interactions. Electrospray mass spectral data collected from acetone or acetonitrile show the presence of aggregated species such as [(L)Ag(2)(BF(4))](+) and [(L)Ag(2)](2+), despite the fact that (1)H NMR spectra of all compounds show that acetonitrile completely displaces the ligand whereas acetone does not. 相似文献