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71.
ABSTRACTA widely used method for obtaining silver nanoparticles uses plant extracts for reduction because of the presence of phytochemicals such as terpenoids, tannins, and flavonoids. Extracts of Flores sambuci, Hypericum perforatum, Lavandula angustifolia, Origanum vulgare, Rosmarinus officinalis, and Salvia officinalis were used for generating silver nanoparticles. The ultraviolet–visible spectra of silver nanoparticle solutions were correlated with variations of phytochemical characteristics to evaluate the plant extracts. These parameters were the antioxidant activity, total flavonoids, total tannins, total terpenoids, and total phenolics. Correlations between measurements of extracts’ phytoreductive characteristics were explained using Pearson coefficients. The results showed medium linear positive correlations for total tannins with the spectra of silver nanoparticle solutions. The antioxidant activity and total terpenoids presented medium linear negative correlations. Pearson coefficients between total phenolics and relative areas from ultraviolet–visible spectra from 350 to 600?nm were close to zero indicating no linear correlation. 相似文献
72.
A metal-free protocol for the selective cleavage of unstrained C–C single bonds was developed. Under the catalysis of KI and in the presence of NaHCO3, the readily available α-chloro-β-hydroxy ketones underwent bond breaking and sulfonylation smoothly to afford β-ketosulfones with high efficiency and broad substrate scope. Mechanism investigations, both experimental and theoretical, showed that a retro-aldol cleavage/nucleophilic substitution sequence might be involved. 相似文献
73.
Six new coordination complexes, Ln2(2,2′-oba)2(phen)2(ox)(H2O)2 (Ln = Eu 1, Tb 2), Ln4(2,2′-oba)6(phen)2 (Ln = Eu 3, Tb 4), Eu4(2,2′-oba)6(phen)2(H2O) (5), and K[Eu(2,2′-oba)2(phen)2] (6) [2,2′-H2oba = 2,2′-oxybis(benzoic acid), phen = 1,10-phenanthroline, H2ox = oxalic acid] were synthesized by hydrothermal reactions with the same compound molar ratios but different modulatory reagents (MRs). Complexes 1–5 have different 1-D chain structures and 6 shows a mononuclear structure. These complexes form diverse 3-D supramolecular networks through hydrogen bonds. The interaction between these complexes and hippuric acid (HA) or bovine serum albumin (BSA) was investigated by fluorescence spectral analysis. Interestingly, the hippuric acid could quench the luminescence of these complexes while the fluorescence of BSA could be quenched by these complexes. Results suggested that the complexes may be potential luminescent testing reagents for HA or BSA by significant fluorescence quenching of Ln3+ or BSA, respectively, through a static and dynamic quenching process. 相似文献
74.
Jian Dong Yun Wang Xu Tang Wenli Zhang 《Journal of Dispersion Science and Technology》2017,38(10):1388-1395
The cloud points (CPs) of the copolymers 17R4 and L64 were first measured, and then the effects of salts ((NH4)3C6H5O7, K3C6H5O7) on 17R4 and L64 were researched. After finishing the work described above, the temperature (278.15, 283.15, and 288.15) K of aqueous two-phase systems was determined, which consist of 17R4-(NH4)3C6H5O7, 17R4-K3C6H5O7, L64-(NH4)3C6H5O7, and L64-K3C6H5O7. Finally, the liquid–liquid equilibrium (LLE) data of binodal curve and the tie line for 17R4-(NH4)3C6H5O7 aqueous two- phase systems (ATPSs) 17R4-K3C6H5O7 ATPSs, L64-(NH4)3C6H5O7 ATPSs, and L64-K3C6H5O7 ATPSs were obtained. Nonlinear fitting of the empirical equation was used for making the diagram. The results showed that the change in the size of the two-phase areas increases with the increase of temperature. The capacity of the salts to induce phase segregation follows the Hofmeister series, that is, K3C6H5O7?>?(NH4)3C6H5O7. In addition, the findings also showed that the phase separation ability of 17R4 is better than that of L64. 相似文献
75.
The use of liquid crystals (LCs) as anisotropic solvents is desired for various potential applications and usually for other organic and inorganic compounds. In this work, solvent polarity parameters are obtained using a spectroscopic method for four LCs with a range of high and low dielectric anisotropy (?ε). Solvatochromic polarity parameters for these LCs were defined via Kamlet–Abboud–Taft polarity functions characterizing different temperatures and phases, isotropic and anisotropic, and using the Reichardt’s dye and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio) phenolate standard probe. The investigated polarity parameters reveal the effects of LC media on the photo-physical behaviour of solute molecules in isotropic and anisotropic media. Subsequently, a new LC polarity parameter (Zo) is introduced as an overall matrix anisotropy polarity parameter to characterize variation between isotropic and anisotropic phases. The values of Zo are sorted from higher to lower dielectric anisotropies (?ε). 相似文献
76.
The Langmuir monolayer at an air–water interface shows remarkably different surface pressure (π)–area (A) isotherm, when measured with the surface normal of a Wilhelmy plate parallel or perpendicular to the direction of compression of the monolayer. Such difference arises due to difference in stress exerted by the monolayer on the plate in different direction. In this article, we report the effect of changing the direction of substrate normal with respect to the compression of the monolayer during Langmuir–Blodgett (LB) film deposition on the morphology of the films. The morphology of the LB film of stearic acid is studied using an atomic force microscope. The morphology of the LB films is found to be different due to difference in the stress in different directions. The role of such surface morphology on the alignment of a nematic liquid crystal (LC) in LC cells is studied. The granular texture of LB films of stearic acid supports the homogeneous alignment of the LC whereas the uniform texture supports the homeotropic alignment of the LC. 相似文献
77.
《Comptes Rendus Chimie》2017,20(3):230-236
Long-range electron transfer reactions play a key role in biological photosynthesis, and they are likely to play an important role for future artificial photosynthetic endeavors as well. The possibility to control the rates for long-range electron transfer with external stimuli is of particular interest in this context. In the work presented herein, we explored a donor–bridge–acceptor compound in which intramolecular electron transfer from a triarylamine donor to a photoexcited Ru(bpy)32+ (bpy = 2,2′-bipyridine) acceptor occurs across an organoboron bridge over a distance of approximately 22 Å. Fluoride has a high binding affinity to the organoboron bridge in apolar solutions, and the resulting organofluoroborate has a significantly different electronic structure. We explored to what extent the change from an electron-deficient organoboron wire to an electron-rich organofluoroborate bridge affects long-range electron transfer between the distant triarylamine donor and the Ru(bpy)32+ acceptor. 相似文献
78.
Dr. Walter T. Ralston Dr. Gérôme Melaet Tommy Saephan Prof. Gabor A. Somorjai 《Angewandte Chemie (International ed. in English)》2017,56(26):7415-7419
The Fischer–Tropsch process, or the catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks. The observed size dependence of cobalt (Co) catalysts for the Fischer–Tropsch reaction was studied with colloidally prepared Co nanoparticles and a chemical transient kinetics reactor capable of measurements under non-steady-state conditions. Co nanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H2/CO=2. Large differences in carbon coverage (ΘC) were observed for the two catalysts: the 4.3 nm Co catalyst has a ΘC less than one while the 9.5 nm Co catalyst supports a ΘC greater than two. The monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles, and the major CO dissociation site is identified as the B5-B geometry. The difference in activity of Co nanoparticles was found to be a result of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes. 相似文献
79.
The iodine/DMAP-mediated intramolecular tandem C–C/C–O bond forming reaction of malonate bearing alkene moiety proceeded to give bicyclic lactones with good diastereoselectivity in good yield. The mechanistic investigation was also discussed on the basis of various control experimental results. 相似文献
80.
Yingting Wang Jiangfeng Huang Xiaomeng Xia Xinhua Peng 《Journal of Saudi Chemical Society》2018,22(2):129-135
A highly efficient catalyst Fe–Co/sulfonated polystyrene (Fe–Co/SPS) was introduced and synthesized, which catalyzed BV oxidation of ketones with aqueous hydrogen peroxide to give the corresponding lactones in high yield and selectivity. Solid acid catalyst of Fe–Co/SPS has been prepared by using the 98-wt% sulfuric acid as the sulfonating agent and CoCl2 combined FeCl3 as sources of metal ions. Various physical–chemical characterizations including FT-IR, XRD, SEM and TGA, revealed that bimetallic ions Fe3+–Co2+ species in the sulfonated polystyrene framework were responsible for the catalytic activities. The BV reaction catalyzed by Fe–Co/SPS highlighted the special effects between metal ions and protonic acids as well as solvent-free heterogeneous catalytic oxidation with excellent conversion. 相似文献