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601.
Christopher Middlebrook Michael Roggemann Glenn Boreman Nikola Subotic Kyle Cooper William Buller Weidong Yang Javier Alda 《International Journal of Infrared and Millimeter Waves》2008,29(2):179-187
The first direct measurement of the mutual coherence function of a spatially incoherent infrared beam was performed at 10.6 μm
using a pair of infrared dipole nano-wire antennas that were connected to a common bolometer in the center of the pair by
short lengths of coplanar strip transmission line. A spatially incoherent source was constructed by dithering a BaF2 diffuser
near the focus of a CO2 laser beam. The distance from the diffuser to the nano-wire antenna pair was held constant while the
distance from the focus of the laser beam to the diffuser was varied to control the effective diameter of the source. The
measured bolometer signal was proportional to the magnitude of the mutual coherence function at the plane of the antennas.
The experimental results were found to match the predicted performance closely. If this technology can be extended to large
arrays, a form of synthetic aperture optical imaging based on the Van Cittert-Zernike theorem is possible, similar to that
performed at microwave frequencies now by astronomers. This has the potential to greatly increase the angular resolution attainable
with optical instruments. 相似文献
602.
Kyle A. Powers David K. Geiger 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(3):329-335
The isostructural salts benzene‐1,2‐diaminium bis(pyridine‐2‐carboxylate), 0.5C6H10N22+·C6H4NO2?, (1), and 4,5‐dimethylbenzene‐1,2‐diaminium bis(pyridine‐2‐carboxylate), 0.5C8H14N22+·C6H4NO2?, (2), and the 1:2 benzene‐1,2‐diamine–benzoic acid cocrystal, 0.5C6H8N2·C7H6O2, (3), are reported. All of the compounds exhibit extensive N—H…O hydrogen bonding that results in interconnected rings. O—H…N hydrogen bonding is observed in (3). Additional π–π and C—H…π interactions are found in each compound. Hirshfeld and fingerprint plot analyses reveal the primary intermolecular interactions and density functional theory was used to calculate their strengths. Salt formation by (1) and (2), and cocrystallization by (3) are rationalized by examining pKa differences. The R22(9) hydrogen‐bonding motif is common to each of these structures. 相似文献
603.
Xiang-Fa Wu Yuris A. Dzenis Kyle W. Strabala 《International Journal of Solids and Structures》2008,45(7-8):2251-2264
This paper considers the explicit solutions of free-edge stresses near circumferential cracks in surface coatings of circular torsion bars and their application in determining the progressive cracking density in the coating layers. The problem was formulated within the framework of linear elastic fracture mechanics (LEFM). The free-edge stresses near crack tip and the shear stresses in the cross-section of the torsion bar were approached in explicit forms based on the variational principle of complementary strain energy. Criterion for progressive cracking in the coating layer was established in sense of strain energy conservation, and the crack density is thereby estimated. Effects of external torque, aspect ratio, and elastic properties on the density of progressive cracking were examined numerically. The present study shows that, in the sense of inducing a given crack density, compliant coating layer with lower modulus has much higher critical torque than that of a stiffer one with the same geometries and substrate material, i.e., compliant coating layer has greater cracking tolerance. Meanwhile, the study also indicates that thicker surface coating layer is more pliant to cracking than the thinner ones. The present model can be used for analyzing the damage mechanism and cracking tolerance of surface coatings of torsion shafts and for data reduction of torsional fracture test of brittle surface coatings, etc. 相似文献
604.
605.
The goal of artificial photosynthesis is to use the energy of the sun to make high-energy chemicals for energy production. One approach, described here, is to use light absorption and excited-state electron transfer to create oxidative and reductive equivalents for driving relevant fuel-forming half-reactions such as the oxidation of water to O2 and its reduction to H2. In this "integrated modular assembly" approach, separate components for light absorption, energy transfer, and long-range electron transfer by use of free-energy gradients are integrated with oxidative and reductive catalysts into single molecular assemblies or on separate electrodes in photelectrochemical cells. Derivatized porphyrins and metalloporphyrins and metal polypyridyl complexes have been most commonly used in these assemblies, with the latter the focus of the current account. The underlying physical principles--light absorption, energy transfer, radiative and nonradiative excited-state decay, electron transfer, proton-coupled electron transfer, and catalysis--are outlined with an eye toward their roles in molecular assemblies for energy conversion. Synthetic approaches based on sequential covalent bond formation, derivatization of preformed polymers, and stepwise polypeptide synthesis have been used to prepare molecular assemblies. A higher level hierarchial "assembly of assemblies" strategy is required for a working device, and progress has been made for metal polypyridyl complex assemblies based on sol-gels, electropolymerized thin films, and chemical adsorption to thin films of metal oxide nanoparticles. 相似文献
606.
A novel Zn2+-selective visible wavelength fluoroionophore (FluoZin-3, 9) was synthesized. The chelating portion of the molecule resembles known EGTA-based Ca2+-selective fluoroionophores, except that one of the N-acetic acid moieties has been deleted in 9. FluoZin-3 is virtually non-fluorescent in the absence of Zn2+, and exhibits a several hundred-fold fluorescence increase upon saturation with Zn2+( approximately 100 nM), with a Kd = 15 +/- 2 nM. A 1:1 binding stoichiometry of 9:Zn2+ was determined, and the fluorescence of the complex is pH-independent at pH > 6. FluoZin-3 was used to monitor Zn2+ that was co-secreted with insulin from pancreatic beta-cells by exocytosis following stimulation with glucose. The total Zn2+ concentration near the cells reached 600 nM, and Zn2+ was detectable at least 15 mum away from secreting cells. Heterogeneity in secretion among cells was indicated in that some cells in a cluster did not release Zn2+. Also, within secreting cells some regions of the cell membrane gave rise to secretion while others did not, suggesting active zones of secretion on the cell surface. 相似文献
607.
Capsazepine (CPZ, 1) is a well-known vanilloid receptor (VR1) antagonist that has been cited widely used in the literature. However the current synthetic methods used for the total synthesis of CPZ are lengthy, involve multiple purification steps, and produce low yields. Here we describe a new and highly efficient synthesis of benzazepine 3, a synthetic precursor of CPZ, in only two steps and 59% overall yield from a commercially available tetralone 2 via a Schmidt reaction as a key step. Moreover, we apply parallel synthesis techniques to prepare CPZ and CPZ analogs. Our approach enables the possibility of preparing larger, and more diverse libraries of CPZ analogs. 相似文献
608.
Ye JY Chang G Norris TB Tse C Zohdy MJ Hollman KW O'Donnell M Baker JR 《Optics letters》2004,29(18):2136-2138
We observed that laser-induced cavitation bubbles in water can be trapped in a self-focused laser beam. Both optical imaging and acoustic detection have been utilized to confirm bubble trapping. Transverse and longitudinal trapping forces were measured to be as large as 87 and 11 pN, respectively. This result is contrary to conventional wisdom, since the mechanism of trapping in conventional optical tweezers implies that a low-index particle (a bubble being the limiting case) should be antitrapped. 相似文献
609.
Fujdala KL Drake IJ Bell AT Tilley TD 《Journal of the American Chemical Society》2004,126(35):10864-10866
A nonaqueous molecular precursor grafting approach was employed for the generation of well-defined surface structures featuring Cu on a mesoporous silica support. X-ray absorption measurements (XANES and EXAFS) were used to determine that [CuOSi(OtBu)3]4 provided 100% isolated Cu(I) sites upon grafting (without thermal treatment), whereas [CuOtBu]4 gave isolated species with most of the original Cu-O-Cu linkages intact, but in a more relaxed straight chain form. Upon heating under inert conditions, the vast majority of Cu in the materials from [CuOSi(OtBu)3]4 remained as isolated Cu(I) sites (up to 88% isolation), with significant stabilization provided from the -OSi(OtBu)3 ligands. In stark contrast, approximately 100% of the Cu in the materials generated from [CuOtBu]4 was readily reduced upon heating, forming isolated Cu metal particles with an average diameter of 0.7 nm. 相似文献
610.
Kyle S. Hickmann 《Applicable analysis》2013,92(9):1675-1690
The interior transmission eigenvalue problem for scalar acoustics is studied for a new class of refractive index. Existence of an infinite discrete set of transmission eigenvalues in the case that the acoustic properties of a domain D???? n are allowed to have a C 2-transition to the homogeneous background medium is established. It is shown that the transmission problem has a weak formulation on certain weighted Sobolev spaces for this class of refractive index. The weak formulation and the discreteness of the spectrum is justified by using the Hardy inequality to prove compact imbedding theorems. Existence of transmission eigenvalues is demonstrated by investigating a generalized eigenvalue problem associated with the weak formulation. 相似文献