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51.
Cooperative Bond Activation and Catalytic Reduction of Carbon Dioxide at a Group 13 Metal Center 下载免费PDF全文
Joseph A. B. Abdalla Dr. Ian M. Riddlestone Rémi Tirfoin Prof. Simon Aldridge 《Angewandte Chemie (International ed. in English)》2015,54(17):5098-5102
A single‐component ambiphilic system capable of the cooperative activation of protic, hydridic and apolar H? X bonds across a Group 13 metal/activated β‐diketiminato (Nacnac) ligand framework is reported. The hydride complex derived from the activation of H2 is shown to be a competent catalyst for the highly selective reduction of CO2 to a methanol derivative. To our knowledge, this process represents the first example of a reduction process of this type catalyzed by a molecular gallium complex. 相似文献
52.
Isolation and Total Synthesis of Kirkamide,an Aminocyclitol from an Obligate Leaf Nodule Symbiont 下载免费PDF全文
Simon Sieber Dr. Aurélien Carlier Dr. Markus Neuburger Dr. Giselher Grabenweger Prof. Leo Eberl Prof. Dr. Karl Gademann 《Angewandte Chemie (International ed. in English)》2015,54(27):7968-7970
The new C7N aminocyclitol kirkamide ( 1 ) was isolated from leaf nodules of the plant Psychotria kirkii by using a genome‐driven 1H NMR‐guided fractionation approach. The structure and absolute configuration were elucidated by HRMS, NMR, and single‐crystal X‐ray crystallography. An enantioselective total synthesis was developed, which delivered kirkamide ( 1 ) on a gram scale in 11 steps and features a Ferrier carbocyclization and a Pd‐mediated hydroxymethylation. We propose that kirkamide is synthesized by Candidatus Burkholderia kirkii, the obligate leaf symbiont of Psychotria kirkii. Kirkamide ( 1 ) was shown to be toxic to aquatic arthropods and insects, thus suggesting that bacterial secondary metabolites play a protective role in the Psychotria/Burkholderia leaf nodule symbiosis. 相似文献
53.
Simon Wübbolt Prof. Dr. Martin Oestreich 《Angewandte Chemie (International ed. in English)》2015,54(52):15876-15879
A C? H silylation of pyridines that seemingly proceeds through electrophilic aromatic substitution (SEAr) is reported. Reactions of 2‐ and 3‐substituted pyridines with hydrosilanes in the presence of a catalyst that splits the Si? H bond into a hydride and a silicon electrophile yield the corresponding 5‐silylated pyridines. This formal silylation of an aromatic C? H bond is the result of a three‐step sequence, consisting of a pyridine hydrosilylation, a dehydrogenative C? H silylation of the intermediate enamine, and a 1,4‐dihydropyridine retro‐hydrosilylation. The key intermediates were detected by 1H NMR spectroscopy and prepared through the individual steps. This complex interplay of electrophilic silylation, hydride transfer, and proton abstraction is promoted by a single catalyst. 相似文献
54.
Hanna Luhavaya Dr. Marcio V. B. Dias Simon R. Williams Dr. Hui Hong Prof. Luciana G. de Oliveira Prof. Peter F. Leadlay 《Angewandte Chemie (International ed. in English)》2015,54(46):13622-13625
Tetrahydropyran rings are a common feature of complex polyketide natural products, but much remains to be learned about the enzymology of their formation. The enzyme SalBIII from the salinomycin biosynthetic pathway resembles other polyether epoxide hydrolases/cyclases of the MonB family, but SalBIII plays no role in the conventional cascade of ring opening/closing. Mutation in the salBIII gene gave a metabolite in which ring A is not formed. Using this metabolite in vitro as a substrate analogue, SalBIII has been shown to form pyran ring A. We have determined the X‐ray crystal structure of SalBIII, and structure‐guided mutagenesis of putative active‐site residues has identified Asp38 and Asp104 as an essential catalytic dyad. The demonstrated pyran synthase activity of SalBIII further extends the impressive catalytic versatility of α+β barrel fold proteins. 相似文献
55.
Catalytic Borylation using an Air‐Stable Zinc Boryl Reagent: Systematic Access to Elusive Acylboranes 下载免费PDF全文
Dr. Jesús Campos Prof. Dr. Simon Aldridge 《Angewandte Chemie (International ed. in English)》2015,54(47):14159-14163
The use of borylzinc reagents in palladium‐catalyzed borylation chemistry is described (i.e. a boron analogue of the Negishi coupling), including a one‐pot bench‐top protocol using an air‐ and moisture‐stable bis(boryl)zinc reagent. The steric/electronic properties of the boryl fragment employed enable a systematic method for accessing acylboranes, a rare class of organoboron species with great potential in chemical synthesis. The reactions proceed under mild conditions, use inexpensive commercial sources of palladium, and demonstrate a remarkable functional‐group tolerance. 相似文献
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Electro‐oxidation and reduction of H2 on platinum studied by scanning electrochemical microscopy for the purpose of local detection of H2 evolution 下载免费PDF全文
Sina S. Jamali Simon E. Moulton Dennis E. Tallman Jan Weber Gordon G. Wallace 《Surface and interface analysis : SIA》2015,47(13):1187-1191
Electrochemical detection of H2 using scanning electrochemical microscopy (SECM) has shown to hold great promise as a sensitive characterization method with high spatial resolution for active surfaces generating H2. Herein, the factors contributing to the current that is measured by SECM in generation/collection mode for H2 detection are studied. In particular, the concentration gradient of H2 at the substrate, the H2/H+ recycling between the SECM tip and substrate and hemispherical profile of H2 diffusion has been discussed. It was postulated that H2/H+ recycling plays a dominant role in the oxidative current measured in generation/collection mode of SECM when the microelectrode is positioned in close vicinity of substrate. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
59.
Lithium‐Salt‐Containing High‐Molecular‐Weight Polystyrene‐block‐Polyethylene Oxide Block Copolymer Films 下载免费PDF全文
Dr. Ezzeldin Metwalli Majid Rasool Simon Brunner Prof. Dr. Peter Müller‐Buschbaum 《Chemphyschem》2015,16(13):2882-2889
Ionic conductivity in relation to the morphology of lithium‐doped high‐molecular‐weight polystyrene‐block‐polyethylene oxide (PS‐b‐PEO) diblock copolymer films was investigated as solid‐state membranes for lithium‐ion batteries. The tendency of the polyethylene (PEO) block to crystallize was highly suppressed by increasing both the salt‐doping level and the temperature. The PEO crystallites completely vanished at a salt‐doping ratio of Li/EO>0.08, at which the PEO segments were hindered from entering the crystalline unit of the PEO chain. A kinetically trapped lamella morphology of PS‐b‐PEO was observed, due to PEO crystallization. The increase in the lamella spacing with increasing salt concentration was attributed to the conformation of the PEO chain rather than the volume contribution of the salt or the previously reported increase in the effective interaction parameter. Upon loading the salt, the PEO chains changed from a compact/highly folded conformation to an amorphous/expanded‐like conformation. The ionic conductivity was enhanced by amorphization of PEO and thereby the mobility of the PEO blocks increased upon increasing the salt‐doping level. 相似文献
60.
Scalar coupling in proton NMR spectra provides important information for the structural analysis. However, the low resolution due to the resulting signal splitting, together with the rather narrow spectral range of hydrogen, often prevents the extraction of J‐coupling information. Here we present a method to achieve real‐time homonuclear J‐downscaling. Thereby, all J‐values are uniformly reduced by an arbitrary scaling factor. In the resulting one‐dimensional spectra, signal overlap is reduced, while scalar coupling information is still available. 相似文献