全文获取类型
收费全文 | 322篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 178篇 |
晶体学 | 1篇 |
力学 | 10篇 |
数学 | 66篇 |
物理学 | 79篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 20篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 18篇 |
2013年 | 15篇 |
2012年 | 12篇 |
2011年 | 21篇 |
2010年 | 23篇 |
2009年 | 13篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 19篇 |
2005年 | 27篇 |
2004年 | 15篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1966年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 15 毫秒
91.
Steady free surface flows are of interest in the fields of marine and hydraulic engineering. Fitting methods are generally used to represent the free surface position with a deforming grid. Existing fitting methods tend to use time-stepping schemes, which is inefficient for steady flows. There also exists a steady iterative method, but that one needs to be implemented with a dedicated solver. Therefore a new method is proposed to efficiently simulate two-dimensional (2D) steady free surface flows, suitable for use in conjunction with black-box flow solvers. The free surface position is calculated with a quasi-Newton method, where the approximate Jacobian is constructed in a novel way by combining data from past iterations with an analytical model based on a perturbation analysis of a potential flow. The method is tested on two 2D cases: the flow over a bottom topography and the flow over a hydrofoil. For all simulations the new method converges exponentially and in few iterations. Furthermore, convergence is independent of the free surface mesh size for all tests. 相似文献
92.
93.
The anisotropic feature of most crystals, involves a direction dependent wave velocity for each of the possible modes. Paratellurite (Tellurium dioxide) is extraordinary because, for one of the propagation modes, i.e. the quasi shear horizontal (QSH) mode, the anisotropy is exceptional. This results, on the one hand in a very strong directional dependent sound velocity and on the other hand, in a low wave velocity in certain directions, resulting in a high figure of merit for the acousto-optical interaction. In the case of inhomogeneous waves, the slowness surfaces change their shape and magnitude, for all crystals. However, for paratellurite, this effect is again extraordinary. As soon as a relatively small inhomogeneity is considered, the sound velocity for the QSH mode becomes really exceptionally anisotropic, resulting in a slowness surface that is almost spherical, covered by pins. The velocity corresponding to those 'pins', is much lower than in the case of homogeneous plane waves, which is very promising for the future development of acousto-optic cells involving an even higher figure of merit. 相似文献
94.
To describe the full spectrum of surface fluctuations of the interface between phase-separated colloid-polymer mixtures from low scattering vector q (classical capillary wave theory) to high q (bulklike fluctuations), one must take account of the interface's bending rigidity. We find that the bending rigidity is negative and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations. 相似文献
95.
The development of model systems that mimic biological interactions and allow the control of both receptor and ligand densities, is essential for a better understanding of biomolecular processes, such as the recruitment of receptors at interfaces, at the molecular level. Here we report a model system based on supported lipid bilayers (SLBs) for the investigation of the clustering of receptors at their interface. Biotinylated SLBs, used as cell membrane mimics, were functionalized with streptavidin (SAv), used here as receptor. Subsequently, biotinylated small (SUVs) and giant (GUVs) unilamellar vesicles were bound to the SAv-functionalized SLBs by multivalent interactions and found to induce the recruitment of both SAv on the SLB surface and the biotin moieties in the vesicles. The recruitment of receptors was investigated with quartz crystal microbalance with dissipation monitoring (QCM-D), which allowed the identification of the biotin and SAv densities necessary to obtain receptor recruitment. At approx. 0.6% of biotin in the vesicles, a transition between dense and low vesicle packing was observed, which coincided with the transitions between recruitment in the vesicles vs. recruitment in the SLB and between full and partial use of the biotin moieties in the vesicle. Direct optical visualization of the clustering at the interface of individual GUVs with the SLB platform was achieved with fluorescence microscopy, showing recruitment of SAv at the contact area as well as the deformation of the vesicles upon binding. Different vesicle binding regimes were observed for lower and higher biotin densities in the vesicles and at the SLBs. A more quantitative analysis of the molecular parameters implied in the interaction, indicated that approx. 10% of the vesicle area constitutes the contact area. Moreover, the SUV binding and recruitment appeared to be fast on the analysis time scale, whereas the binding of GUVs is slower due to the larger SLB area over which SAv recruitment needs to occur. The mechanisms revealed in this study may provide insight in biological processes in which recruitment occurs.The development of model systems that mimic biological interactions and allow the control of both receptor and ligand densities, is essential for a molecular understanding of biomolecular processes, such as the recruitment of receptors at interfaces. 相似文献
96.
Müller A Todea AM Bögge H van Slageren J Dressel M Stammler A Rusu M 《Chemical communications (Cambridge, England)》2006,(29):3066-3068
The spherical capsule skeleton of the host-guest system [{Mo6O19}2- subset {Mo(VI)72Fe(III)30O252(CH3COO)20(H2O)92}]4- 1a--built up by 12 {(Mo(VI))Mo(VI)5} type pentagonal units linked by 30 Fe(III) centers which span the unique icosahedral Archimedean solid, the icosidodecahedron--can now be constructed deliberately and with a simpler composition than before from an acidified aqueous molybdate solution containing the mentioned (virtual) pentagonal units; the encapsulated hexamolybdate--normally not formed in water--is built up in an unprecedented way concomitant with capsule growth, while being directed by the corresponding internal electrophilic surface functionalities. 相似文献
97.
van Slageren J Piligkos S Neese F 《Dalton transactions (Cambridge, England : 2003)》2010,39(20):4999-5004
A Magnetic Circular Dichroism (MCD) spectroscopic study of the antiferromagnetic ring [Cr?F?Piv??] (Piv = pivalate) is reported. From the splitting of the MCD bands, the single ion anisotropy parameters in the cluster spin ground state at different fields were determined to be d(Cr) = -0.33 ± 0.02 cm?1, e(Cr) = 0.11 ± 0.01 cm?1. Analysis of the MCD intensity as a function of field and temperature revealed the influence of spin mixing effects and yielded independent estimates of the single ion anisotropies (d(Cr) = -0.19 cm?1, e(Cr) = 4.3 × 10-4 cm?1), as well as yielding the isotropic exchange interaction strength (J = -6.00 cm?1). Thus it is shown that MCD is a powerful method to unravel the relation between single-ion and cluster anisotropy, furthering the design of molecular magnets with desired properties. 相似文献
98.
Quentin Van Overmeere Frédéric Blaffart Joris Proost 《Electrochemistry communications》2010,12(9):1174-1176
In this paper, we use energy-based perturbation criteria to examine whether strain or electrostatic energy acts as a driving force for porosity initiation in anodic oxides. By doing so, we also succeeded to rationalise the dependence of pore spacing on anodising conditions. Our experimental approach consists of measuring in-situ the internal stress in anodic oxide films grown galvanostatically on aluminium in phosphoric acid, and to correlate these data with the measured pore spacing of the obtained porous films. Our results indicate that the possibility of a strain energy-induced surface instability is unlikely, as for this case the constitutive dependence of pore spacing on internal stress was not verified. Instead, the measured pore spacing, electric field and barrier oxide thickness obtained on our anodic alumina films indicate that electrostatic energy is the main driving force for pore initiation, as well as the factor controlling the pore spacing. Corroborative quantitative evidence for this novel electrostatic-based scaling law is provided by data compiled from the literature for a range of other anodic oxide systems, including nanoporous alumina and nanotubular titania films. 相似文献
99.
Derivatives of 5-Aminolevulinic Acid for Photodynamic Therapy: Enzymatic Conversion into Protoporphyrin 总被引:6,自引:0,他引:6
Joris Kloek Willem Akkermans Gerard M. J. Beijersbergen van Henegouwen 《Photochemistry and photobiology》1998,67(1):150-154
In recent years, 5-aminolevulinic acid (ALA) has become a widespread agent for photodynamic therapy (PDT). In nucleated cells, ALA is converted into the endogenous photosensitizer protoporphyrin IX (PpIX). A major drawback of ALA is its low bioavailability. As a result, high doses of ALA must be administered in order to reach clinically relevant levels of PpIX. Moreover, only superficially located lesions can be treated as a result of the poor penetration of ALA into tissues. A possible solution for this problem may be provided by the prod rug concept. In the present study, prodrugs of ALA have been synthesized. These ALA prodrugs are shown to result in higher PpIX levels in cells than does ALA itself. Of a range of ester prodrugs of ALA, the ALA-pentyl ester elicits the highest fluorescence. Further-more, the enzymatic conversion of the derivatives into ALA and PpIX has been studied in lysed cells. Under these circumstances, the esters with the shorter alkyl chains induce the highest fluorescence. The alcohols that arise as side products from enzymatic conversion of the prodrugs are shown to have no influence on the experiments. 相似文献
100.
Batchelor LJ Sander M Tuna F Helliwell M Moro F van Slageren J Burzurí E Montero O Evangelisti M Luis F McInnes EJ 《Dalton transactions (Cambridge, England : 2003)》2011,40(19):5278-5284
We report the synthesis, structures and magnetic properties of a series of chromium(III) metal-centered triangle (or "star") clusters, [Cr(4){RC(CH(2)O)(3)}(2)(4,4'-R'(2)-bipy)(3)Cl(6)] [R = Et, R' = H (2); R = HOCH(2), R' = H (3); R = Et, R' = (t)Bu (4)], prepared by two-step solvothermal reactions starting from [CrCl(3)(thf)(3)]. The product of the first stage of this reaction is the salt [Cr(bipy)(2)Cl(2)](2)[Cr(2)Cl(8)(MeCN)(2)] (1). In the absence of the diimine, a different family of tetrametallics is isolated: the butterfly complexes [Cr(4){EtC(CH(2)O)(3)}(2){NH(C(R)NH)(2)}(2)Cl(6)] (R = Me (5), Et (6), Ph (7)] where the chelating N-acetimidoylacetamidine NH(C(R)=NH)(2) ligands are formed in situ via condensation of the nitrile solvents (RCN) under solvothermal conditions. Magnetic measurements show the chromium stars to have an isolated S = 3 ground state, arising from antiferromagnetic coupling between the central and peripheral metal ions, analogous to the well-known Fe(III) stars. Bulk antiferromagnetic ordering is observed at 0.6 K. The butterfly complexes have a singlet ground state, with a low-lying S = 1 first excited state, due to dominant wing-body antiferromagnetic coupling. 相似文献