全文获取类型
收费全文 | 12301篇 |
免费 | 246篇 |
国内免费 | 95篇 |
专业分类
化学 | 8569篇 |
晶体学 | 226篇 |
力学 | 263篇 |
综合类 | 1篇 |
数学 | 2066篇 |
物理学 | 1517篇 |
出版年
2022年 | 83篇 |
2021年 | 109篇 |
2020年 | 126篇 |
2019年 | 125篇 |
2018年 | 99篇 |
2017年 | 102篇 |
2016年 | 232篇 |
2015年 | 202篇 |
2014年 | 207篇 |
2013年 | 577篇 |
2012年 | 567篇 |
2011年 | 654篇 |
2010年 | 338篇 |
2009年 | 291篇 |
2008年 | 626篇 |
2007年 | 655篇 |
2006年 | 622篇 |
2005年 | 586篇 |
2004年 | 531篇 |
2003年 | 426篇 |
2002年 | 482篇 |
2001年 | 143篇 |
2000年 | 144篇 |
1999年 | 126篇 |
1998年 | 140篇 |
1997年 | 165篇 |
1996年 | 217篇 |
1995年 | 144篇 |
1994年 | 131篇 |
1993年 | 138篇 |
1992年 | 138篇 |
1991年 | 119篇 |
1990年 | 141篇 |
1989年 | 117篇 |
1988年 | 121篇 |
1987年 | 101篇 |
1986年 | 103篇 |
1985年 | 183篇 |
1984年 | 195篇 |
1983年 | 141篇 |
1982年 | 233篇 |
1981年 | 195篇 |
1980年 | 172篇 |
1979年 | 156篇 |
1978年 | 152篇 |
1977年 | 137篇 |
1976年 | 147篇 |
1975年 | 129篇 |
1974年 | 149篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Martic G Gentner F Seveno D De Coninck J Blake TD 《Journal of colloid and interface science》2004,270(1):171-179
To model the imbibition of liquids into porous solids, use is often made of the Lucas-Washburn equation, which relates the distance of penetration of a liquid at a given time to the pore radius, the viscosity and surface tension of the liquid, and the effective contact angle between the liquid and the solid. In this paper, we extend previous large-scale molecular dynamics simulations to show how this tool can be used to study the details of liquid imbibition, including the impact of the contact angle on the dynamics of penetration and the evolution of the internal flow field. In particular, we show that the asymptotic behavior of the contact angle versus time for a completely wetting liquid is given by approximately t(-1/4). 相似文献
62.
For couplings and mass ratios appropriate to molecules such as H2O, D2O, and CH2 large volumes of the classical vibrational phase space are found to be non-dissociating even well above threshold. Fully quantum calculations yield families of exceptionally long-lived quantum states corresponding to these trapped volumes. 相似文献
63.
J.William Suggs S.D. Cox Robert H. Crabtree Jennifer M. Quirk 《Tetrahedron letters》1981,22(4):303-306
The title complex readily hydrogenates a number of hindered steroidal olefin groups from the α face, without reducing ketone carbonyl groups, carbon—halogen bonds or cyclopropane rings. 相似文献
64.
William B. Smith 《Journal of heterocyclic chemistry》1987,24(3):745-748
The reduction of aryl nitro groups by the palladium-sodium borohydride system can be controlled in some instances to give products differing from those of catalytic hydrogenation. With six equivalents of borohydride added to the catalyst 2,2′-dinitrobiphenyl formed only 2,2′-diaminobiphenyl. With added sodium hydroxide and varying amounts of borohydride and catalyst, the reduction can be controlled to give benzo[c]cinnoline, benzo[c]cinnoline 5-oxide or benzo[c]cinnoline 5,6-dioxide. In a closed system, the reagents reduce both the nitro and olefin functional groups in 6-nitro-5,8-dimethoxy-1,4-dihydro-1,4-ethano-naphthalene. In an open flask flushed with argon, the reduction is confirmed to the nitro group. Reduction of 2-chloro and 4-chloronitrobenzene with palladium-borohydride gives substantial yields of the appropriate chloroanilines. In contrast, hydrogen and palladium give aniline as the major product from each of these. These results suggest that the addition of sodium borohydride to palladium on carbon produces a reductive entity differing from that of catalytic hydrogenation. 相似文献
65.
Jensen TR Breyfogle LE Hillmyer MA Tolman WB 《Chemical communications (Cambridge, England)》2004,(21):2504-2505
A new Zn alkoxide catalyst supported by an N-heterocyclic carbene rapidly polymerizes D,L-lactide (D,L-LA) to heterotactic enriched poly(lactide)(PLA), while the free carbene and analogs instead yield highly isotactic enriched PLA. 相似文献
66.
67.
The Curtin-Hammett (C-H) principle and the Winstein-Holness (W-H) equation approximate the product ratio and overall rate constant of reaction for systems involving a starting material which exists in two forms, each of which reacts via first-order kinetics to give a different product. The C-H/W-H approximations are valid when the rates of isomer interconversion are significantly faster than the rates of product formation. The present treatment encompasses non-first-order reactions to product. A numerical predictor-corrector technique is used to show (1) that relative reagent concentration can affect both the product ratio and the observed rates of product formation; (2) that the absolute concentration of reagent and substrate can affect the kinetics; and (3) that factors (1) and (2) above can affect the validity of the C-H/W-H approximations for non-first-order C-H/W-H schemes. 相似文献
68.
A new short synthesis of 3-substituted 5-amino-1-(chloromethyl)-1,2-dihydro-3H-benzo[e]indoles from Martius Yellow is disclosed. The key steps of the synthesis were three efficient regioselective reactions (iodination, 5-exo-trig aryl radical-alkene cyclization and carboxylation). 相似文献
69.
A route to the doubly unsaturated bridgehead sultam 12 has been developed. When irradiated at 350 nm, this conjugated diene is isomerized via a two-photon process to the structurally novel spiro heterocycle 17 constituted of cyclobutene, thietane dioxide, and pyrrolidine rings. A probable mechanism for the generation of 17 and select reactions thereof are reported. [reaction: see text] 相似文献
70.
Although the arsenic containing analogue of triptycene, 5,10--benzenoarsanthrene (E=As) was isolated some time ago [1] the related derivatives of antimony and bismuth are unknown. We now find that when 1,2-diiodotetrafluorobenzene is treated with methyllithium at -78/dg, to afford the little studied dilithiotetrafluorobenzene [2], and the appropriate metal chloride is added to the resulting solution, perfluorinated analogues of (E = As, Sb, or Bi) are obtained in good yield. These are stable volatile solids. 相似文献