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121.
Chu-Chi Ting Yi-Shan Chiu Chia-Wei Chang Liang-Chih Chuang 《Journal of solid state chemistry》2011,184(3):563-9
Er3+-doped Y2Ti2O7 nanocrystals were fabricated by the sol-gel method. While the annealing temperature exceeds 757 °C, amorphous pyrochlore phase ErxY2−xTi2O7 transfers to well-crystallized nanocrystals, and the average crystal size increases from ∼70 to ∼180 nm under 800-1000 °C/1 h annealing. ErxY2−xTi2O7 nanocrystals absorbing 980 nm photons can produce the upconversion (526, 547, and 660 nm; 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2, respectively) and Stokes (1528 nm; 4I13/2→4I15/2) photoluminescence (PL). The infrared PL decay curve is single-exponential for Er3+ (5 mol%)-doped Y2Ti2O7 nanocrystals but slightly nonexponential for Er3+ (10 mol%)-doped Y2Ti2O7 nanocrystals. For 5 and 10 mol% doping concentrations, the mechanism of up-converted green light is the two-photon excited-state absorption. Much stronger intensity of red light relative to green light was observed for the sample with 10 mol% dopant. This phenomenon can be attributed to the reduced distance between Er3+-Er3+ ions, resulting in the enhancement of the energy-transfer upconversion and cross-relaxation mechanisms. 相似文献
122.
Droplet microfluidics has attracted much attention in recent years. For many droplet-based applications, researchers want to predict the size of the droplets in a certain experimental condition. To meet this need, van Steijn and colleagues proposed an elegant theoretical model that predicts the volume of droplets generated in a common channel configuration for forming a steady-state, continuous stream of droplets, the T-junction geometry. To determine the accuracy of this model in predicting droplet volume, we performed a systematic experimental study over two orders of magnitude in capillary number. We found that this model, albeit elegant, has a limited range of interfacial tension over which it can predict accurately the droplet volume. Our experimental results, together with fluid dynamic simulations, allowed us to highlight the importance of physical fluid properties when employing theoretical models. 相似文献
123.
Carboxyl groups of surface-tethered poly(acrylic acid) (PAA) brushes should be able to serve as versatile moieties for a wide range of chemical modifications, including an attachment of bioactive species that can act as sensing probes for biosensors. In this research, poly(tert-butyl acrylate) (Pt-BA) brushes were prepared by surface-initiated atom transfer radical polymerization of tert-butyl acrylate. PAA brushes were then obtained after removal of the tert-butyl groups from the Pt-BA brushes by acid hydrolysis. The carboxyl group density of the PAA brushes can be varied as a function of chain length or molecular weight. The reactivity of the carboxyl groups of PAA brushes towards the immobilization of biotin, a frequently used model bioactive probe in biosensing applications, was evaluated. Qualitative determination of streptavidin (SA) binding to the biotin-attached PAA brushes was verified by fluorescence microscopy. The efficiency of the PAA brushes to act as a three dimensional (3D) precursor layer for biosensing applications was further demonstrated using surface plasmon resonance (SPR), where the biotin-attached PAA brushes showed an enhanced signal for the biospecific binding of SA in comparison with a self-assembled monolayer (SAM) of a carboxyl-terminated alkanethiol, used as a model two-dimensional (2D) conventional precursor layer. The PAA brushes showed very low non-specific interactions with two other tested proteins of a similar pI but different sizes. This desirable feature should be highly beneficial for the development of biosensors. 相似文献
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125.
Tang X Houchins C Lau KC Ng CY Dressler RA Chiu YH Chu TS Han KL 《The Journal of chemical physics》2007,127(16):164318
Time-dependent wave packet quantum scattering (TWQS) calculations are presented for HD(+) (v = 0 - 3;j(0)=1) + He collisions in the center-of-mass collision energy (E(T)) range of 0.0-2.0 eV. The present TWQS approach accounts for Coriolis coupling and uses the ab initio potential energy surface of Palmieri et al. [Mol. Phys. 98, 1839 (2000)]. For a fixed total angular momentum J, the energy dependence of reaction probabilities exhibits quantum resonance structure. The resonances are more pronounced for low J values and for the HeH(+) + D channel than for the HeD(+) + H channel and are particularly prominent near threshold. The quantum effects are no longer discernable in the integral cross sections, which compare closely to quasiclassical trajectory calculations conducted on the same potential energy surface. The integral cross sections also compare well to recent state-selected experimental values over the same reactant and translational energy range. Classical impulsive dynamics and steric arguments can account for the significant isotope effect in favor of the deuteron transfer channel observed for HD(+)(v<3) and low translational energies. At higher reactant energies, angular momentum constraints favor the proton-transfer channel, and isotopic differences in the integral cross sections are no longer significant. The integral cross sections as well as the J dependence of partial cross sections exhibit a significant alignment effect in favor of collisions with the HD(+) rotational angular momentum vector perpendicular to the Jacobi R coordinate. This effect is most pronounced for the proton-transfer channel at low vibrational and translational energies. 相似文献
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128.
Addison N. Desnoyer Florian W. Friese Weiling Chiu Marcus W. Drover Dr. Brian O. Patrick Prof. Dr. Jennifer A. Love 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):4070-4077
Recently, esters have received much attention as transmetalation partners for cross‐coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}2(μ‐η2:η2‐C6H6)] (dtbpe=1,2‐bis(di‐tert‐butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η2‐carbonyl complexes. In contrast, acetylthioesters underwent rapid Cacyl?S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross‐coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η2‐carbonyl complex, phenyl esters were found to predominantly undergo Caryl?O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2‐naphthyl acetate was also found to undergo clean Caryl?O bond cleavage, and although stoichiometric cross‐coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive. 相似文献
129.
Synthesis of nano-sized TiO(2)/poly(AA-co-MMA) composites by heterocoagulation and blending with PET
Nano-sized TiO(2) or SiO(2)/TiO(2) particles were prepared by hydrolysis and condensation reactions in aqueous media, followed by mixing with poly(AA-co-MMA) latex to form different composites, then blending with poly(ethylene terephthalate), PET. The TGA results of composites indicated that negative charged latexes had greater interaction with TiO(2)/ or SiO(2)/TiO(2) particles through strong electrostatic forces, while cationic latexes incorporated with TiO(2) or SiO(2)/TiO(2) particles by pH induced coagulation, carbonyl group chelation and hydrogen bonding. The soapless latex polymer particles showed lower ability of adsorption to TiO(2) particles due to the decrease of total surface area of these larger particles. If SiO(2)/TiO(2) particles were used instead of TiO(2) particles, unexpected high adsorption result was observed. Morphology results observed by SEM showed that PET blended with positive charged composites was more homogeneous than PET blended with negative charged composites. DSC results also indicated that the T(g) of PET was increased, melting temperatures (T(m) or T(m)(')) were increased, and the temperature range of crystallization was narrowed after blending with the composites. The presence of composites affected the mobility and packing of PET molecular chains therefore changing the thermal properties of PET. 相似文献
130.
A series of lithium europium double tungsto-molybdate phosphors LiEu(WO4)2−x(MoO4)x (x=0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the 5D0→7F2 emission of Eu3+ activated at wavelength of 396 nm was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the 5D0→7F2 transition. As the molybdate content increases the emission intensity of the 615 nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photoluminescent properties of LiEu(WO4)2−x(MoO4)x is investigated and discussed. 相似文献