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991.
Claudio Somaini 《代数通讯》2013,41(11):4104-4115
Let d be a prehomogeneous dimension vector for a connected quiver Q with the property that c ? d has a negative entry for some ? ∈ ? where c is the Coxeter transformation corresponding to an admissible numbering of the vertices Q 0 of Q. Denote by rep(Q, d) the variety of d-dimensional representations of Q and by Sl(d) the product of the special linear groups at all vertices Q 0. We show how to find the irreducible components of the null cone of the algebraic quotient rep(Q, d)//Sl(d). 相似文献
992.
We prove optimal high-frequency resolvent estimates for self-adjoint operators of the form ${G=\left(i\nabla+b(x)\right)^2+V(x)}$ on ${L^2({\bf R}^n), n\ge 3}$ , where the magnetic potential b(x) and the electric potential V(x) are long-range and large. As an application, we prove dispersive estimates for the wave group ${{\rm e}^{it\sqrt{G}}}$ in the case n = 3 for potentials b(x), V(x) = O(|x|?2-δ ) for ${|x|\gg 1}$ , where δ > 0. 相似文献
993.
994.
In this paper we analyze in a general and pure algebraic way imaging systems characterized by shift-variant integral kernels which hide some intrinsic shift-invariance, related to an appropriate coordinate change; we call as structured shift-variant these kinds of imaging systems. In this respect, we propose an algorithm for finding a coordinate transformation which allows a structured shift-variant PSF to become explicitly shift-invariant. The usage of the computed coordinate transformation will highly reduce the numerical complexity of the imaging system, providing a real time deblurring in some real applications. Some preliminary numerical results show the effectiveness of the proposal. 相似文献
995.
Baggiani C Giovannoli C Anfossi L Passini C Baravalle P Giraudi G 《Journal of the American Chemical Society》2012,134(3):1513-1518
In the current paradigm for molecular imprinting, the imprinted binding sites exist as a consequence of the polymerization process around templates, and the properties of nonimprinted polymers (NIPs) have largely been overlooked. Thus, nothing can be affirmed a priori concerning the binding properties of NIPs. We propose an alternative view where the imprinting effect is due to the presence of a template molecule that enhances the pre-existing binding properties of a polymer. If a NIP shows no binding properties toward a target molecule, the corresponding imprinted polymer (MIP) will show a weak imprinting effect. On the other hand, if a NIP shows binding properties toward a target molecule, the corresponding MIP will show a significant imprinting effect. To verify this hypothesis, we prepared a 96-member combinatorial polymeric library in the absence of any template molecule. This library was screened for several potential ligands, and with no exceptions, the composition of the best-binding NIP produced a MIP with excellent binding properties, whereas a low-binding NIP formulation produced a MIP with comparable low binding. To validate these results, the binding properties toward naproxen and ibuprofen were measured for two combinatorial libraries of polymers prepared in the presence (MIP library) and the absence (NIP library) of the template molecule. The experiment's results showed a correlation between the apparent affinity constants measured for the NIP and MIP libraries, confirming the proposed hypothesis. Moreover, for closely related molecules, it was shown that binding selectivity is an emergent property derived from the imprinting process and not a property of NIPs. 相似文献
996.
Rojas A Martínez-Morales E Zicovich-Wilson CM Camblor MA 《Journal of the American Chemical Society》2012,134(4):2255-2263
Pure silica ITW zeolite can be synthesized using 1,2,3-trimethylimidazolium and 1,3-dimethylimidazolium cations and fluoride anions as structure-directing agents (SDAs). Similarly to the previously reported 1,3,4-trimethylimidazolium, the dimethyl cation can also produce the zeolite TON, but this higher framework density phase finally transforms in situ into ITW. The structures of the as-made and calcined phases prepared with the new cations show a unit cell doubling along z, and the refined structures are reported. Periodic Density Functional Theory calculations provide the energies of the six SDA-ITW and SDA-TON zeolites, and their relative stabilities fully agree with the experimental observations. Structure-direction in this system is discussed from experimental and theoretical results that give strong support to the idea that strained silica frameworks are made possible in fluoride media by decreasing the covalent character of the Si-O bond. This decreased covalency is enhanced with the 1,2,3-trimethyl isomer, which is shown to be the strongest SDA for ITW and, at the same time, is the more hydrophilic of the three SDAs tested. Our observations with the three SDAs agree with the so-called Villaescusa's rule, i.e., the low framework density phase is favored at higher concentrations, but at the same time question the supersaturation hypothesis that has been proposed to explain this rule, since here the low-density phase is the most stable one. 相似文献
997.
RM Maria TB Moraes CJ Magon T Venâncio WF Altei AD Andricopulo LA Colnago 《The Analyst》2012,137(19):4546-4551
Proton nuclear magnetic resonance ((1)H NMR) spectroscopy for detection of biochemical changes in biological samples is a successful technique. However, the achieved NMR resolution is not sufficiently high when the analysis is performed with intact cells. To improve spectral resolution, high resolution magic angle spinning (HR-MAS) is used and the broad signals are separated by a T(2) filter based on the CPMG pulse sequence. Additionally, HR-MAS experiments with a T(2) filter are preceded by a water suppression procedure. The goal of this work is to demonstrate that the experimental procedures of water suppression and T(2) or diffusing filters are unnecessary steps when the filter diagonalization method (FDM) is used to process the time domain HR-MAS signals. Manipulation of the FDM results, represented as a tabular list of peak positions, widths, amplitudes and phases, allows the removal of water signals without the disturbing overlapping or nearby signals. Additionally, the FDM can also be used for phase correction and noise suppression, and to discriminate between sharp and broad lines. Results demonstrate the applicability of the FDM post-acquisition processing to obtain high quality HR-MAS spectra of heterogeneous biological materials. 相似文献
998.
Claudio Gorodski 《Transformation Groups》2012,17(1):143-156
We consider a generalized discriminant associated to a symmetric space which generalizes the discriminant of real symmetric
matrices, and note that it can be written as a sum of squares of real polynomials. A method to estimate the minimum number
of squares required to represent the discrimininant is developed and applied in examples. 相似文献
999.
1000.
Silveira PC da Silva LA Tromm PT Scheffer Dda L de Souza CT Pinho RA 《Ultrasonics》2012,52(5):650-654