全文获取类型
收费全文 | 39963篇 |
免费 | 15776篇 |
国内免费 | 52篇 |
专业分类
化学 | 53020篇 |
晶体学 | 22篇 |
力学 | 1086篇 |
数学 | 1168篇 |
物理学 | 495篇 |
出版年
2024年 | 423篇 |
2023年 | 4250篇 |
2022年 | 1426篇 |
2021年 | 2425篇 |
2020年 | 4685篇 |
2019年 | 2229篇 |
2018年 | 2374篇 |
2017年 | 601篇 |
2016年 | 5552篇 |
2015年 | 5511篇 |
2014年 | 4927篇 |
2013年 | 5057篇 |
2012年 | 3061篇 |
2011年 | 1007篇 |
2010年 | 3334篇 |
2009年 | 3267篇 |
2008年 | 1013篇 |
2007年 | 699篇 |
2006年 | 127篇 |
2005年 | 87篇 |
2004年 | 68篇 |
2003年 | 70篇 |
1996年 | 58篇 |
1995年 | 110篇 |
1994年 | 71篇 |
1993年 | 187篇 |
1992年 | 67篇 |
1991年 | 58篇 |
1989年 | 48篇 |
1988年 | 75篇 |
1987年 | 60篇 |
1986年 | 45篇 |
1985年 | 51篇 |
1984年 | 59篇 |
1983年 | 64篇 |
1982年 | 74篇 |
1981年 | 85篇 |
1980年 | 104篇 |
1979年 | 94篇 |
1978年 | 95篇 |
1977年 | 162篇 |
1976年 | 181篇 |
1975年 | 187篇 |
1974年 | 195篇 |
1973年 | 111篇 |
1972年 | 153篇 |
1971年 | 122篇 |
1970年 | 207篇 |
1969年 | 126篇 |
1968年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Catalytic Desymmetrizing Dehydrogenation of 4‐Substituted Cyclohexanones through Enamine Oxidation 下载免费PDF全文
Lihui Zhu Dr. Long Zhang Prof. Dr. Sanzhong Luo 《Angewandte Chemie (International ed. in English)》2018,57(8):2253-2258
A desymmetrizing dehydrogenation process catalyzed by a chiral primary amine is described herein. The reaction proceeds through the oxidation of a ketone enamine by IBX and enables the highly enantioselective desymmetrization of 4‐substituted cyclohexanones with the generation of chiral 4‐substituted cyclohexenones containing a remote γ‐stereocenter. 相似文献
932.
Copper‐Catalyzed Enantioselective Arylative Desymmetrization of Prochiral Cyclopentenes with Diaryliodonium Salts 下载免费PDF全文
Dr. Hua Wu Dr. Qian Wang Prof. Dr. Jieping Zhu 《Angewandte Chemie (International ed. in English)》2018,57(10):2721-2725
A copper‐catalyzed enantioselective arylative desymmetrization of prochiral cyclopentenes with diaryliodonium salts was developed. In the presence of a catalytic amount of a chiral copper–bisoxazoline complex, which was generated in situ, the reaction of 4‐substituted or 4,4‐disubstituted cyclopent‐1‐enes with diaryliodonium hexafluoroarsenates afforded the chiral arylated products in good yields with excellent enantioselectivity. A cyclohexyl‐containing Box ligand was essential for the high enantioselectivity. Transformation of the enantiomerically enriched adducts into other chiral building blocks is also documented. 相似文献
933.
Thermally Rearranged Polymer Membranes Containing Tröger's Base Units Have Exceptional Performance for Air Separations 下载免费PDF全文
Stephen M. Meckler Dr. Jonathan E. Bachman Benjamin P. Robertson Chenhui Zhu Prof. Jeffrey R. Long Dr. Brett A. Helms 《Angewandte Chemie (International ed. in English)》2018,57(18):4912-4916
The influence of segmental chain motion on the gas separation performance of thermally rearranged (TR) polymer membranes is established for TR polybenzoxazoles featuring Tröger's base (TB) monomer subunits as exceptionally rigid sites of contortion along the polymer backbone. These polymers are accessed from solution‐processable ortho‐acetate functionalized polyimides, which are readily synthesized as high‐molecular‐weight polymers for membrane casting. We find that thermal rearrangement leads to a small increase in d‐spacing between polymer chains and a dramatic pore‐network reconfiguration that increases both membrane permeability and O2/N2 selectivity, putting its performance above the 2015 upper bound. 相似文献
934.
Ana Sánchez‐Iglesias Nathalie Claes Dr. Diego M. Solís Dr. Jose M. Taboada Prof. Sara Bals Prof. Luis M. Liz‐Marzán Dr. Marek Grzelczak 《Angewandte Chemie (International ed. in English)》2018,57(12):3183-3186
A limiting factor of solvent‐induced nanoparticle self‐assembly is the need for constant sample dilution in assembly/disassembly cycles. Changes in the nanoparticle concentration alter the kinetics of the subsequent assembly process, limiting optical signal recovery. Herein, we show that upon confining hydrophobic nanoparticles in permeable silica nanocapsules, the number of nanoparticles participating in cyclic aggregation remains constant despite bulk changes in solution, leading to highly reproducible plasmon band shifts at different solvent compositions. 相似文献
935.
Helicenophyrins: Expanded Carbaporphyrins Incorporating Aza[5]helicene and Heptacyclic S‐Shaped Aza[5]helicene Motifs 下载免费PDF全文
Dr. Bartosz Szyszko Monika Przewoźnik Dr. Michał J. Białek Dr. Agata Białońska Prof. Dr. Piotr J. Chmielewski Dr. Jakub Cichos Prof. Dr. Lechosław Latos‐Grażyński 《Angewandte Chemie (International ed. in English)》2018,57(15):4030-4034
Incorporation of phenanthrene into a hexaphyrin(1.1.1.1.1.0) frame resulted in intramolecular ring fusion, thus giving rise to chiral helicenophyrins. These molecules contain helicene and porphyrin features by incorporating either an aza[5]helicene or heptacyclic S‐shaped aza[5]helicene. 相似文献
936.
Synthesis of (−)‐Hebelophyllene E: An Entry to Geminal Dimethyl‐Cyclobutanes by [2+2] Cycloaddition of Alkenes and Allenoates 下载免费PDF全文
Dr. Johannes M. Wiest Dr. Michael L. Conner Prof. M. Kevin Brown 《Angewandte Chemie (International ed. in English)》2018,57(17):4647-4651
The first synthesis of hebelophyllene E is presented, along with assignment of its previously unknown relative configuration through synthesis of epi‐ent‐hebelophyllene E. Development of a catalytic enantioselective [2+2] cycloaddition of alkenes and allenoates provides access to the required chiral geminal dimethylcyclobutanes. Key to its success is the identification of a novel oxazaborolidine catalyst which promotes the cycloaddition in high enantioselectivities with good functional‐group tolerance (9 examples, up to 97:3 e.r.). Thus, a late‐stage cycloaddition using a fully functionalized alkene, followed by a diastereoselective reduction allows a concise entry to this class of natural products. 相似文献
937.
Copper‐Catalyzed Heteroarylboration of 1,3‐Dienes with 3‐Bromopyridines: A cine Substitution 下载免费PDF全文
Kevin B. Smith Dr. Yuan Huang Prof. M. Kevin Brown 《Angewandte Chemie (International ed. in English)》2018,57(21):6146-6149
A method for the heteroarylboration of 1,3‐dienes is presented. The process involves an unusual cine substitution of 3‐bromopyridine derivatives to deliver highly functionalized heterocyclic products. Mechanistic studies are included that clarify the details of this unusual process. 相似文献
938.
Bottleable Neutral Analogues of [B2H5]− as Versatile and Strongly Binding η2 Donor Ligands 下载免费PDF全文
Dr. Sunewang R. Wang Dominic Prieschl James D. Mattock Dr. Merle Arrowsmith Dr. Conor Pranckevicius Dr. Tom E. Stennett Dr. Rian D. Dewhurst Dr. Alfredo Vargas Prof. Dr. Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2018,57(21):6347-6351
Herein we report the discovery that two bottleable, neutral, base‐stabilized diborane(5) compounds are able to bind strongly to a number of copper(I) complexes exclusively through their B?B bond. The resulting complexes represent the first known complexes containing unsupported, neutral σB?B diborane ligands. Single‐crystal X‐ray analyses of these complexes show that the X?Cu moiety (X=Cl, OTf, C6F5) lies opposite the bridging hydrogen atom of the diborane and is near perpendicular to the B?B bond, interacting almost equally with both boron atoms and causing a B?B bond elongation. DFT studies show that σ donation from and π backdonation to the pseudo‐π‐like B?B bond account for their formation. Astoundingly, these copper σB?B complexes are inert to ligand exchange with pyridine under either heating or photoirradiation. 相似文献
939.
Nicolas Sauermann Dr. Ruhuai Mei Prof. Dr. Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2018,57(18):5090-5094
Syntheses of substituted anilines primarily rely on palladium‐catalyzed coupling chemistry with prefunctionalized aryl electrophiles. While oxidative aminations have emerged as powerful alternatives, they largely produce undesired metal‐containing by‐products in stoichiometric quantities. In contrast, described herein is the unprecedented electrochemical C?H amination by cobalt‐catalyzed C?H activation. The environmentally benign electrocatalysis avoids stoichiometric metal oxidants, can be conducted under ambient air, and employs a biomass‐derived, renewable solvent for sustainable aminations in an atom‐ and step‐economical manner with H2 as the sole byproduct. 相似文献
940.
Optically Matched Semiconductor Quantum Dots Improve Photophosphorylation Performed by Chloroplasts 下载免费PDF全文
Youqian Xu Dr. Jinbo Fei Guangle Li Tingting Yuan Xia Xu Chenlei Wang Prof. Dr. Junbai Li 《Angewandte Chemie (International ed. in English)》2018,57(22):6532-6535
A natural–artificial hybrid system was constructed to enhance photophosphorylation. The system comprises chloroplasts modified with optically matched quantum dots (chloroplast–QD) with a large Stokes shift. The QDs possess a unique optical property and transform ultraviolet light into available and highly effective red light for use by chloroplasts. This favorable feature enables photosystem II contained within the hybrid system to split more water and produce more protons than chloroplasts would otherwise do on their own. Consequently, a larger proton gradient is generated and photophosphorylation is improved. At optimal efficiency activity increased by up to 2.3 times compared to pristine chloroplasts. Importantly, the degree of overlap between emission of the QDs and absorption of chloroplasts exerts a strong influence on the photophosphorylation efficiency. The chloroplast–QD hybrid presents an efficient solar energy conversion route, which involves a rational combination of a natural system and an artificial light‐harvesting nanomaterial. 相似文献