全文获取类型
收费全文 | 860篇 |
免费 | 17篇 |
国内免费 | 4篇 |
专业分类
化学 | 648篇 |
晶体学 | 8篇 |
力学 | 6篇 |
数学 | 72篇 |
物理学 | 147篇 |
出版年
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 28篇 |
2012年 | 26篇 |
2011年 | 34篇 |
2010年 | 25篇 |
2009年 | 33篇 |
2008年 | 65篇 |
2007年 | 45篇 |
2006年 | 47篇 |
2005年 | 52篇 |
2004年 | 48篇 |
2003年 | 45篇 |
2002年 | 41篇 |
2001年 | 14篇 |
2000年 | 22篇 |
1999年 | 17篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 29篇 |
1983年 | 8篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1969年 | 4篇 |
1968年 | 6篇 |
1967年 | 4篇 |
排序方式: 共有881条查询结果,搜索用时 18 毫秒
851.
Tanaka SY Tagashira N Chiba K Yasuda M Baba A 《The Journal of organic chemistry》2008,73(16):6312-6320
A highly practical reductive cross-aldol reaction of alpha-bromoaldehydes with various aldehydes has been developed using Ge(II)Cl 2 to produce aldehyde germanium(IV) aldolates, which were directly transformed to various multifunctionalized compounds. A remarkable change in stereoselectivity depended on the alpha-bromoaldehydes employed; secondary alpha-bromoaldehydes gave syn selectivities, while tertiary alpha-bromoaldehydes accomplished the synthesis of anti-selective aldol products with a quaternary carbon center. NMR studies and X-ray analysis strongly suggested the formation of germanium enolate in the reaction of alpha-bromoaldehyde 2h with GeCl 2-dioxane. Detailed mechanistic studies, including NMR analysis and ab initio calculations, revealed the generation of stable germanium aldolates, which was due to the remarkably low Lewis acidity of the germanium(IV). 相似文献
852.
Structural characterization of a procyanidin tetramer and pentamer from the apple by low-temperature NMR analysis 总被引:1,自引:0,他引:1
The structures of a procyanidin tetramer and pentamer from unripe apple (Malus pumila) were elucidated by low-temperature NMR analysis at −34 °C. These structures were [epicatechin-(4β→6)-epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin (1)] and [epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin (2)]. 相似文献
853.
854.
Hu L Ma R Ozawa TC Geng F Iyi N Sasaki T 《Chemical communications (Cambridge, England)》2008,(40):4897-4899
Layered rare-earth hydroxide crystallites self-assembled at the hexane/water interface were transferred to various substrates to form a monolayer film, which exhibited photoluminescence properties and ion-exchange ability. 相似文献
855.
We studied the thermodynamic stability of interfacial gaseous states on atomically smooth highly ordered pyrolytic graphite (HOPG) in water using atomic force microscopy. Quasi-two-dimensional gas layers (micropancakes) required a higher supersaturation of gas than spherical-cap-shaped nanobubbles. The two forms of gas coexisted at a sufficiently high supersaturation of gas where one or more of the nanobubbles may sit on top of a micropancake. The micropancakes spontaneously coalesced with each other over time. After the coalescence of two neighboring micropancakes which each had had a nanobubble on top, one nanobubble grew at the expense of the other. We analyzed these results assuming temporal and local quasi-equilibrium conditions. 相似文献
856.
Manda S Nakanishi I Ohkubo K Uto Y Kawashima T Hori H Fukuhara K Okuda H Ozawa T Ikota N Fukuzumi S Anzai K 《Chemical communications (Cambridge, England)》2008,(5):626-628
More than two-fold augmentation in the radical-scavenging activity of artepillin C could be achieved via altering the O-H bond dissociation enthalpy of artepillin C by means of structural modifications. 相似文献
857.
Okazaki K Kiyama T Hirahara K Tanaka N Kuwabata S Torimoto T 《Chemical communications (Cambridge, England)》2008,(6):691-693
The simultaneous sputter deposition of gold and silver onto ionic liquids formed bimetallic alloy nanoparticles, which exhibited composition-sensitive surface plasmon resonance, the peak wavelength being red-shifted with an increase in the surface area of the gold foil targets sputtered. 相似文献
858.
Mori T Kodera T Yoshimine H Kakuta Y Sugiura N Kimata K Okahata Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(24):7388-7393
Using a highly sensitive flow-type 27?MHz quartz crystal microbalance, we could detect a small mass change during stepwise and alternating one-sugar transfer of glucuronic acid (GlcA) and N-acetylgalactosamine (GalNAc) to an acceptor, catalyzed by chondroitin polymerase from Escherichia coli strain K4 (K4CP), and analyze the elongation mechanism of K4CP. K4CP was found to bind strongly to a chondroitin acceptor (K(d)=0.97?μM). Although the binding affinity and the catalytic rate constant for each monomer were considerably different, the apparent catalytic efficiency (k(cat)/K(m)) was similar (6.3×10(4) M(-1) s(-1) for GlcA transfer and 3.4×10(4) M(-1) s(-1) for the GalNAc transfer). This is reasonable for the smooth alternating elongation of GlcA and GalNAc on the acceptor. This is the first study to report the determination of kinetic parameters for enzymatic, alternated, sugar elongation. 相似文献
859.
Synthetic layered silicate saponite was modified with dodecyltrimethylammonium (C12), octadecyltrimethylammonium (C18), and dioctadecyldimethylammonium (2C18) cations for use as sorbents of the laser dye, rhodamine 6G (R6G). Via solvent exchange, transparent colloids in xylene were prepared and investigated using absorption and fluorescence spectroscopies. Molecular aggregation and partial quenching of the fluorescence were observed for the colloids based on 2C18 cations. Maximal fluorescence yields were observed for the colloids with C12 and C18 cations. Transparent gels without an apparent loss of luminescent efficiency could be prepared by concentrating the colloids. These highly fluorescent colloids and gels represent new types of materials with interesting optical properties. 相似文献
860.
Israelachvili J Maeda N Akbulut M 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2397-8; discussion 2399-401