全文获取类型
收费全文 | 215240篇 |
免费 | 1761篇 |
国内免费 | 627篇 |
专业分类
化学 | 117921篇 |
晶体学 | 3270篇 |
力学 | 8349篇 |
综合类 | 6篇 |
数学 | 23305篇 |
物理学 | 64777篇 |
出版年
2020年 | 1970篇 |
2019年 | 2263篇 |
2018年 | 3205篇 |
2017年 | 3113篇 |
2016年 | 4267篇 |
2015年 | 2371篇 |
2014年 | 3818篇 |
2013年 | 9260篇 |
2012年 | 6893篇 |
2011年 | 8434篇 |
2010年 | 6072篇 |
2009年 | 5921篇 |
2008年 | 8136篇 |
2007年 | 8206篇 |
2006年 | 7629篇 |
2005年 | 6936篇 |
2004年 | 6166篇 |
2003年 | 5641篇 |
2002年 | 5497篇 |
2001年 | 5939篇 |
2000年 | 4684篇 |
1999年 | 3470篇 |
1998年 | 3007篇 |
1997年 | 3033篇 |
1996年 | 2823篇 |
1995年 | 2319篇 |
1994年 | 2419篇 |
1993年 | 2450篇 |
1992年 | 2595篇 |
1991年 | 2657篇 |
1990年 | 2559篇 |
1989年 | 2533篇 |
1988年 | 2463篇 |
1987年 | 2434篇 |
1986年 | 2357篇 |
1985年 | 3037篇 |
1984年 | 3194篇 |
1983年 | 2559篇 |
1982年 | 2827篇 |
1981年 | 2703篇 |
1980年 | 2503篇 |
1979年 | 2718篇 |
1978年 | 2833篇 |
1977年 | 2856篇 |
1976年 | 2832篇 |
1975年 | 2687篇 |
1974年 | 2665篇 |
1973年 | 2810篇 |
1972年 | 1875篇 |
1967年 | 1830篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Kinetics and Catalysis - Boron and barium were employed as dopants for the VMgO system. The catalysts were characterized by ICP-OES, BET, IR, powder XRD, EDX, TPR-H2, TPD-NH3, XPS, and 51V MAS NMR.... 相似文献
42.
Chris H. Hill Agnete H. Viuff Samantha J. Spratley Stéphane Salamone Stig H. Christensen Randy J. Read Nigel W. Moriarty Henrik H. Jensen Janet E. Deane 《Chemical science》2015,6(5):3075-3086
Krabbe disease is a devastating neurodegenerative disorder characterized by rapid demyelination of nerve fibers. This disease is caused by defects in the lysosomal enzyme β-galactocerebrosidase (GALC), which hydrolyzes the terminal galactose from glycosphingolipids. These lipids are essential components of eukaryotic cell membranes: substrates of GALC include galactocerebroside, the primary lipid component of myelin, and psychosine, a cytotoxic metabolite. Mutations of GALC that cause misfolding of the protein may be responsive to pharmacological chaperone therapy (PCT), whereby small molecules are used to stabilize these mutant proteins, thus correcting trafficking defects and increasing residual catabolic activity in cells. Here we describe a new approach for the synthesis of galacto-configured azasugars and the characterization of their interaction with GALC using biophysical, biochemical and crystallographic methods. We identify that the global stabilization of GALC conferred by azasugar derivatives, measured by fluorescence-based thermal shift assays, is directly related to their binding affinity, measured by enzyme inhibition. X-ray crystal structures of these molecules bound in the GALC active site reveal which residues participate in stabilizing interactions, show how potency is achieved and illustrate the penalties of aza/iminosugar ring distortion. The structure–activity relationships described here identify the key physical properties required of pharmacological chaperones for Krabbe disease and highlight the potential of azasugars as stabilizing agents for future enzyme replacement therapies. This work lays the foundation for new drug-based treatments of Krabbe disease. 相似文献
43.
44.
45.
46.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
47.
Michiel Janssen Prof. Dirk E. De Vos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10724-10734
The practical application of Shilov-type Pt catalysis to the selective hydroxylation of terminal aliphatic C−H bonds remains a formidable challenge, due to difficulties in replacing PtIV with a more economically viable oxidant, particularly O2. We report the potential of employing FeCl2 as a suitable redox mediator to overcome the kinetic hurdles related to the direct use of O2 in the Pt reoxidation. For the selective conversion of butyric acid to γ-hydroxybutyric acid (GHB), a significantly enhanced catalyst activity and stability (turnover numbers (TON)>30) were achieved under 20 bar O2 in comparison to current state-of-the-art systems (TON<10). In this regard, essential reaction parameters affecting the overall activity were identified, along with specific additives to attain catalyst stability at longer reaction times. Notably, deactivation by reduction to Pt0 was prevented by the addition of monodentate pyridine derivatives, such as 2-fluoropyridine, but also by introducing varying partial pressures of N2 in the gaseous atmosphere. Finally, stability tests revealed the involvement of PtII and FeCl2 in catalyzing the non-selective overoxidation of GHB. Accordingly, in situ esterification with boric acid proved to be a suitable strategy to maintain enhanced selectivities at much higher conversions (TON>60). Altogether, a useful catalytic system for the selective hydroxylation of primary aliphatic C−H bonds with O2 is presented. 相似文献
48.
Norbornene derivatives from a metal‐free,strain‐promoted cycloaddition reaction: New building blocks for ring‐opening metathesis polymerization reactions 下载免费PDF全文
Christopher E. Hobbs Binhong Lin Thomas Malinski 《Journal of polymer science. Part A, Polymer chemistry》2015,53(20):2357-2362
The preparation of new ring opening metathesis polymerization (ROMP) monomers using a 1,3‐dipolar cycloaddition between aryl azides and norbornadiene is described. Various norbornenetriazolines, obtained through a solvent‐and catalyst‐free reaction, can subsequently be incorporated into polymer backbones through ROMP reactions. Furthermore, thermal decomposition of the triazoline moiety can allow for further polymer functionalization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2357–2362 相似文献
49.
50.
Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and... 相似文献