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931.
取代γ-丁内酯是一类非常重要的精细化学品。N-杂环卡宾(NHC)催化α,β-不饱和醛发生共轭极性反转后,与芳香醛、三氟甲基酮、酮酸酯或邻二酮等发生环化反应可一步生成不同取代的γ-丁内酯化合物。该方法具有原子经济性高、路径简捷、反应条件温和等明显的优势。本文主要结合笔者课题组的研究方向,从不同催化剂前体和不同反应底物两方面进行分类,介绍近年来NHC催化合成取代γ-丁内酯的方法及其研究进展,归纳总结了不同催化体系的优缺点,并在此基础上展望了NHC催化合成取代γ-丁内酯反应的发展趋势和应用前景。 相似文献
932.
Xiaodong Wen Shengchun Yang Haizhu Zhang Xia Zhao Jie Guo 《International journal of environmental analytical chemistry》2013,93(12):1243-1253
As a new developed instrument, a portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) was first coupled with surfactant assisted dispersive liquid–liquid microextraction (SA-DLLME) to improve its analytical performance and expand its applications in this work. SA-DLLME was very simple, rapid and the extraction efficiency was considerably improved by the effect of surfactant, which was suitable to be coupled with the portable instrument in field analysis. After SA-DLLME, concentrated chromium in organic phase was directly determined on W-coil atomiser. The influence factors relevant to SA-DLLME and instrumental conditions were studied systematically. Under the optimal conditions, the limit of detection (LOD) for Cr(VI) was 0.016 µg L?1, with sensitivity enhancement factor (EF) of 107. The relative standard deviation (RSD) for seven replicate measurements of 0.5 µg L?1 of Cr(VI) was 4.6%. The recoveries for the spiked samples were in the acceptable range of 96.8–104%. The rapid, simple and high effective method greatly improved the sensitivity of this portable spectrometer for the determination of Cr(VI) and was applied to the analysis of ultra-trace Cr(VI) in real and certified water samples with satisfactory results. 相似文献
933.
Two concise routes toward betulin-3-yl-β-D-glucopyranoside, being different in the protection of primary alcohol of betulin, were developed. The synthesis adopted a stepwise glycosidation method employing glycosyl trichloroacetimidate as donor. 相似文献
934.
Jin-Qiang Liu Xin-Zhi Chen Baoming Ji Bang-Tun Zhao 《Research on Chemical Intermediates》2013,39(3):1143-1152
(S)-Indoline-2-carboxylic acid was synthesized by use of a nitro amination approach with l-phenylalanine as chiral pool. The first step of the synthesis was nitration of l-phenylalanine, with urea nitrate (UN)/H2SO4 as nitrating reagent, to give 2,4-dinitro-l-phenylalanine in 75.7 % yield in one-pot synthesis and 69.1 % yield by step-wise nitration. Intramolecular nitro amination of 2,4-dinitro-l-phenylalanine gave (S)-6-nitro-indoline-2-carboxylic acid in 65.7 % yield and more than 99.5 % enantiomeric excess (ee). The title compound, (S)-indoline-2-carboxylic acid, was obtained in 85.9 % yield and high ee by one-pot transformation of (S)-6-nitroindoline-2-carboxylic acid. The total synthesis consisted of three operations and gave the title compound in 42 % yield and more than 99.5 % ee. 相似文献
935.
Hongtao Cui Minmin Wang Wanzhong Ren Yan Liu Yunan Zhao 《Journal of Sol-Gel Science and Technology》2013,66(3):512-517
Silica monoliths embedded with high concentration of γ-Fe2O3 or TiO2 nanoparticles were prepared by a sol–gel procedure designed according to the inherent properties of oxide colloids. In the first step, highly dispersible oxide nanoparticles were produced using an in situ modification sol–gel strategy. Then, these particles were re-dispersed in silicon alkoxide-containing solution to form a stable colloidal solution. The hydrolysis and condensation reactions of alkoxide were catalyzed by an organic base (morpholine). Due to the large molecule size of morpholine, the electric double layer on the surface of colloidal particles was not compressed by the ionized morpholine molecules. The colloidal solution thus remained stable during the gelation process. Through this procedure, oxide nanoparticles could be immobilized homogeneously in the pores of a silica matrix, forming highly transparent and crack-free monoliths. 相似文献
936.
Yuxia Sun Yong Zhou Hongri Liu Zhao Xia Man Luo Kai Wan Chengyan Wang 《Journal of Sol-Gel Science and Technology》2013,66(3):429-433
Highly preferentially oriented polycrystalline BiFeO3 thin film was grown on FTO/glass substrate by a sol–gel method annealed at 500 °C. XRD result showed that the film adopts highly (100) preferential orientation. SEM results indicate that the film is composed of large grains of 40–200 nm and the thickness is about 320 nm. Room temperature saturated polarization and large Pr ~55 μC/cm2 were obtained. Leakage current was substantially reduced by the controlling of ferroelectric polarization. Polarization-modulated conduction mechanism was studied. Moreover, substantial photovoltaic effect was observed. 相似文献
937.
Yong Li Xia Wen Lei Li Feng Wang Ning Zhao Fukui Xiao Wei Wei Yuhan Sun 《Journal of Sol-Gel Science and Technology》2013,66(3):353-362
A one-pot template-free route was developed for the synthesis of novel tetraethylenepentamine modified porous silica as CO2 adsorbents, the obtained materials were characterized by N2 adsorption/desorption, thermogravimetry, elemental analysis, Fourier transform infrared spectrometry,scanning electron microscopy and transmission electron microscopy. It was found that the amine species were inserted into the silica skeleton, which considerably enhanced their dispersion. Compared with similar materials derived from impregnation, the porous structure of the silica can be better reserved, leading to a promising CO2 adsorption capacity of 3.98 mmol CO2/g-adsorbent and a fast adsorption kinetic in simulated flue gas at 348 K. The resulted adsorbents could also be easily regenerated and showed a good durability in multiple adsorption–desorption cycles. All these features make this method a promising option for the preparation of CO2 adsorbents. 相似文献
938.
In this paper, a simple sol–gel route has been adopted in developing substrate surface for the first time. Only by adjusting the concentration of precursor solution, LaAlO3 (LAO) nanodot arrays were directly obtained on LAO single crystal substrate, without incorporating additional processing steps. Subsequently, YBa2Cu3O7?x (YBCO) superconducting films were prepared on the nanodot arrays using a low-fluorine solution process. In contrast, J c of YBCO films grown on the substrate developed with nanodot arrays is almost three times as large as that of YBCO films grown on undeveloped substrate in an applied magnetic field with the strength of 3 Tesla. The pinning force density (F p ) of YBCO film on the nanodot arrays developed substrate is 2.7 GN/m3 which exceeds that (1.8 GN/m3) of YBCO films on undeveloped substrate. The results of cross-section transmission electron microscope (TEM) images show that the extended defects along the a–b planes of YBCO, induced by the developed substrate with nanodot arrays, should be the origin of the J c enhancement. 相似文献
939.
Li‐Wei Zhao Hui‐Min Shi Zhe An Jiu‐Zhao Wang Prof. Jing He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12350-12355
Effectively enhancing the enantioselectivity is a persistent challenge in heterogeneous asymmetric catalysis. Here, the validity of a layered double hydroxides (LDH) nanosheet as an efficient planar substituent to enhance the enantioselectivity has been investigated theoretically; first in vanadium‐catalyzed asymmetric epoxidation of allylic alcohols, and then in zinc‐catalyzed direct asymmetric aldol addition. The computational predication is further confirmed experimentally in zinc‐catalyzed direct asymmetric aldol addition by controlling the location of catalytic sites. 相似文献
940.
Dr. Cunku Dong Prof. Xin Li Wei Zhao Pengfei Jin Xiujuan Fan Prof. Jingyao Qi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(30):10046-10056
A unique one‐dimensional (1D) sandwich single‐walled TiO2 nanotube (STNT) is proposed as a photoanode nanomaterial with perfect morphology and large specific surface area. We have thoroughly examined the elementary photoelectronic processes occurring at the porphyrin dye/STNT hetero‐interface in dye‐sensitized solar cells (DSSCs) by theoretical simulation. It is desirable to investigate the interfacial photoelectronic processes to elucidate the electron transfer and transport mechanism in 1D STNT‐based DSSCs. We have found that the photoexcitation and interfacial charge separation mechanism can be described as follows. A ground‐state electron of the dye molecule (localized around the electron donor) is first promoted to the excited state (distributed electron donor), and then undergoes ultrafast injection into the conduction band of the STNT, leaving a hole around the oxidized dye. Significantly, the injected electron in the conduction band is transported along the STNT by means of Ti 3d orbitals, offering a unidirectional electron pathway toward the electrode for massive collection without the observation of trap states. Our study not only provides theoretical guidelines for the modification of TiO2 nanotubes as a photoanode material, but also opens a new perspective for the development of a novel class of TiO2 nanotubes with high power‐generation efficiency. 相似文献