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991.
Chun‐Wei Chang Chia‐Hui Wu Mei‐Huei Lin Pin‐Hsuan Liao Chun‐Chi Chang Hsiao‐Han Chuang Su‐Ching Lin Sarah Lam Ved Prakash Verma Chao‐Ping Hsu Cheng‐Chung Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(47):16931-16935
Stereocontrolled chemical glycosylation remains a major challenge despite vast efforts reported over many decades and so far still mainly relies on trial and error. Now it is shown that the relative reactivity value (RRV) of thioglycosides is an indicator for revealing stereoselectivities according to four types of acceptors. Mechanistic studies show that the reaction is dominated by two distinct intermediates: glycosyl triflates and glycosyl halides from N‐halosuccinimide (NXS)/TfOH. The formation of glycosyl halide is highly correlated with the production of α‐glycoside. These findings enable glycosylation reactions to be foreseen by using RRVs as an α/β‐selectivity indicator and guidelines and rules to be developed for stereocontrolled glycosylation. 相似文献
992.
993.
Nancy C. Forero-Martinez Ha-Linh Thi Le Holger Vach 《Plasma Chemistry and Plasma Processing》2014,34(3):535-543
We theoretically predict that low pressure silane/hydrogen plasmas may present the ideal venue for the fabrication of a new nanostructured silicon material with strong aromatic properties. Precisely controlling the ratio of atomic and molecular hydrogen concentrations during the growth of hydrogenated silicon clusters in a pulsed plasma enhanced chemical vapor deposition reactor will allow us to “steer” the growth toward over-coordinated silicon nanocrystals that reveal aromatic properties as strong as those of benzene. In addition, those pure silicon nanocrystals demonstrate optical, electrical, and mechanical characteristics that could so far only be obtained by adding toxic or expensive elements (as PbS, PbSe, CdS, CdSe, or Au) in the cluster structure. Due to their light absorption not only in the ultraviolet, but also in the visible and the infrared spectrum, they might, for instance, play a major role for photovoltaic devices or in the hyperthermal treatment of cancer. 相似文献
994.
Shaobin Miao Dr. Anthony L. Appleton Nancy Berger Stephen Barlow Dr. Seth R. Marder Prof. Kenneth I. Hardcastle Dr. Uwe H. F. Bunz Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(20):4990-4993
A new relative of pentacene : The dialkynylated tetraazapentacene (see figure) was prepared by a two‐step synthesis from the corresponding quinone derivative. The heteroacene is an air‐stable, dark‐blue, crystalline material and is of great interest as a potential organic n‐electron‐transport material.
995.
Shern‐Long Lee Dr. Nai‐Ti Lin Dr. Wei‐Chih Liao Chun‐hsien Chen Prof. Hsiao‐Ching Yang Prof. Tien‐Yau Luh Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11594-11600
Self‐assembly at the molecular level in solutions or on a surface is a subject of current interest. Herein we describe the tailoring of oligobisnorbornene 1 , which represents an innovative concept of a preorganized building block on the tens of nanometer scale. The rodlike 1 has vinyl and styrenyl end groups. Scanning tunneling microscopy (STM) reveals that the oligomers aggregate anisotropically along the long axis and form a one‐dimensional assembly in which, remarkably, no interstitial gap appears between neighboring oligomers. Dynamic light‐scattering (DLS) measurements indicate that the assembly develops in solution. With a shear treatment for dropcast films, a unidirectionally ordered domain with a defect density less than 0.5 % can be prepared. Simulation results by molecular dynamics suggest that there may be multiple interactions such as π–π stacking and dipolar attractions taking place between the termini of the oligomers. To demonstrate the importance of double bonds in the oligomeric backbones and termini towards the tectonic assembly, a hydrogenated analogue was synthesized; π–π interactions are thus less significant and the film morphology is completely different from that of 1 . This work extends the concept of molecular tectonics to preorganized oligomers and opens up a new avenue of nanopatterning toward nanodevices. 相似文献
996.
Wen‐Ping Su Yu‐Hsuen Lee Ching‐Tien Hsieh Hwo‐Shuenn Sheu Jyh‐Fu Lee Yong‐Ping Chiang H.‐C. I. Kao 《中国化学会会志》2009,56(6):1112-1117
A new series of (Y2‐yLiy)Ti2O7‐y having an ordered pyrochlore phase was prepared by a solid state reaction method with a solid solution range of 0.05 ≥ y ≥ 0.10. Unit cell parameters obtained by the Rietveld refinement method shows that the a‐axis decreases linearly with increasing the amount of Li ion addition, indicating the successful incorporation of the Li ion into unit cell. The average x‐fractional coordinate of the O(1) site depends on the ionic radius ratio of r(A3+)/r(Ti4+) in the A2Ti2O7 with a pyrochlore phase. The Ti K‐edge XANES spectra of the (Y2‐yLiy)Ti2O7‐y show that the valence of the Ti ions is slightly less than 4 so that Ti is in the mixed valence state. Average particle size increases with increasing the amount of extra Li ion addition, which acts as a flux to lower the melting point of the materials. 相似文献
997.
Gold-catalyzed isomerization of 2-alkynyl-1-tetralones afforded the corresponding 2-naphthylmethyl ketones in good to high yields. For example, the reaction of 2-{4-(methoxyphenyl)methyl}-2-(phenylethynyl)-3,4-dihydronaphthalen-1(2H)-one and 2-benzyl-2-(phenylethynyl)-3,4-dihydronaphthalen-1(2H)-one in the presence of 5 mol % of (Ph3P)AuCl and 5 mol % of AgOTf in THF at 50 °C gave 2-{1-(4-methoxyphenylmethyl)naphthalen-2-yl}-1-(4-methoxyphenyl)ethanone and 2-(1-benzylnaphthalen-2-yl)-1-phenylethanone in 85% and 96% yields, respectively. The present reaction proceeds through [1,2] alkyl migration followed by oxygen transfer. 相似文献
998.
Manju Rajeswaran Thomas N. Blanton Ching W. Tang William C. Lenhart Steven C. Switalski David J. Giesen Brian J. Antalek Thomas D. Pawlik Denis Y. Kondakov Nicholas Zumbulyadis Ralph H. Young 《Polyhedron》2009
The interest in organic materials for use in organic light-emitting diodes (OLEDs) began with the pioneering report of efficient green electroluminescence from Alq3, tris(quinolin-8-olato)aluminum(III), by Tang and Van Slyke [C.W. Tang, S.A. Van Slyke, Appl. Phys. Lett. 51 (1987) 913]. After more than 20 years of intense research and development in OLEDs, Alq3 continues to be a widely used electroluminescent material in OLED technology. Alq3 is used in the electron-transport and/or electron-injecting layer in multilayer device structures and also as an effective host material for various dyes. Much is known about the properties of this metal chelate complex, yet much remains unknown despite numerous studies. In recent years, five crystalline phases (α, β, γ, δ, and ε) of Alq3 have been identified. In the present report, a combined structural, thermal, and spectroscopic (Raman, fluorescence, and nuclear magnetic resonance) analysis of different crystalline phases of Alq3 is presented. 相似文献
999.
Polyacrylonitrile (PAN) was blended with polyvinylidine fluoride (PVDF) at various ratios and made into membranes. The hemocompatibility of the resulting membranes was evaluated based on human plasma proteins adsorption, platelet adhesion, thrombus formation, and blood coagulation time. The PAN/PVDF blends exhibited partial miscibility according to the inward shifting of their two glass transition temperatures. The microstructures of blend membranes examined using atomic force microscopy (AFM) indicated that the roughness increased with the PVDF content, and the phase separation was too severe to form a membrane when the PVDF content was more than 30%. The water contact angle of PAN/PVDF blend membranes increased with the PVDF content. By blending with 20 wt% apolar PVDF the adsorption of blood proteins could be reduced, and hence the platelet adhesion and thrombus formation was also reduced. However, when the PVDF content was 30 wt%, severe thrombogenicity was observed due probably to the more porous structure of blend membrane. These results demonstrated that the hemocompatibility would be improved for PAN/PVDF blend membranes with appropriate hydrophilicity and roughness. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
1000.