全文获取类型
收费全文 | 795篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 581篇 |
晶体学 | 5篇 |
力学 | 17篇 |
数学 | 80篇 |
物理学 | 134篇 |
出版年
2020年 | 8篇 |
2019年 | 15篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 11篇 |
2013年 | 20篇 |
2012年 | 24篇 |
2011年 | 44篇 |
2010年 | 16篇 |
2009年 | 17篇 |
2008年 | 38篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 26篇 |
2004年 | 18篇 |
2003年 | 22篇 |
2002年 | 34篇 |
2001年 | 25篇 |
2000年 | 23篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 19篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 14篇 |
1973年 | 9篇 |
1972年 | 9篇 |
1971年 | 9篇 |
1970年 | 9篇 |
1969年 | 11篇 |
1967年 | 8篇 |
排序方式: 共有817条查询结果,搜索用时 31 毫秒
51.
Catalytic 1,4‐Rhodium(III) Migration Enables 1,3‐Enynes to Function as One‐Carbon Oxidative Annulation Partners in CH Functionalizations
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. David J. Burns Prof. Hon Wai Lam 《Angewandte Chemie (International ed. in English)》2014,53(37):9931-9935
1,3‐Enynes containing allylic hydrogens cis to the alkyne are shown to act as one‐carbon partners, rather than two‐carbon partners, in various rhodium‐catalyzed oxidative annulations. The mechanism of these unexpected transformations is proposed to occur through double C? H activation, involving a hitherto rare example of the 1,4‐migration of a RhIII species. This phenomenon is general across a variety of substrates, and provides a diverse range of heterocyclic products. 相似文献
52.
Libo Li Ken A. Dill Christopher J. Fennell 《Journal of computer-aided molecular design》2014,28(3):259-264
Here, we test a method, called semi-explicit assembly (SEA), that computes the solvation free energies of molecules in water in the SAMPL4 blind test challenge. SEA was developed with the intention of being as accurate as explicit-solvent models, but much faster to compute. It is accurate because it uses pre-simulations of simple spheres in explicit solvent to obtain structural and thermodynamic quantities, and it is fast because it parses solute free energies into regionally additive quantities. SAMPL4 provided us the opportunity to make new tests of SEA. Our tests here lead us to the following conclusions: (1) The newest version, called Field-SEA, which gives improved predictions for highly charged ions, is shown here to perform as well as the earlier versions (dipolar and quadrupolar SEA) on this broad blind SAMPL4 test set. (2) We find that both the past and present SEA models give solvation free energies that are as accurate as TIP3P. (3) Using a new approach for force field parameter optimization, we developed improved hydroxyl parameters that ensure consistency with neat-solvent dielectric constants, and found that they led to improved solvation free energies for hydroxyl-containing compounds in SAMPL4. We also learned that these hydroxyl parameters are not just fixing solvent exposed oxygens in a general sense, and therefore do not improve predictions for carbonyl or carboxylic-acid groups. Other such functional groups will need their own independent optimizations for potential improvements. Overall, these tests in SAMPL4 indicate that SEA is an accurate, general and fast new approach to computing solvation free energies. 相似文献
53.
David A. Burns Eric M. Press M. A. Siegler Rebekka S. Klausen V. Sara Thoi 《Angewandte Chemie (International ed. in English)》2020,59(2):763-768
We report the synthesis of a set of 2D metal–organic frameworks (MOFs) constructed with organosilicon‐based linkers. These oligosilyl MOFs feature linear SinMe2n(C6H4CO2H)2 ligands (lin‐Sin, n=2, 4) connected by Cu paddlewheels. The stacking arrangement of the 2D sheets is dictated by van der Waals interactions and is tunable by solvent exchange, leading to reversible structural transformations between many crystalline and amorphous phases. 相似文献
54.
William N. Setzer Shahrara Afshar Norman L. Burns Lucille A. Ferrante Amy M. Hester Edward J. Meehan Gregory J. Grant Saju M. Isaac Christopher P. Laudeman Charles M. Lewis Donald G. VanDerveer 《Heteroatom Chemistry》1990,1(5):375-387
The mesocyclic trithioethers, 1,4,7-trithiacyclodecane, 1,4,7-trithiacycloundecane, 1,4,8-trithiacycloundecane, and 1,5,9-trithiacyclododecane; the mesocyclic trithioether ketones, 1,4,7-trithiacyclodecan-9-one; 1,4,8-trithiacycloundecan-6-one, and 1,5,9-trithiacyclododecan-3-one; and the mesocyclic trithioether alcohols, 1,4,7-trithiacyclodecan-9-ol, 1,4,8-trithiacycloundecan-6-ol, and 1,5,9-trithiacyclododecan-3-ol, have been synthesized using the cesium dithiolate technique. In some cases, the corresponding macrocyclic hexathioether was isolated from the reaction mixture in addition to the mesocyclic trithioether; 1,4,7,11,14,17-hexathiacycloeicosane, 1,4,7,11,14,17-hexathiacycloeicosan-9,19-dione, 1,4,7,12,15,18-hexathiacyclodocosane, and 1,5,9,13,17,21-hexathiacyclotetracosane. Single-crystal X-ray structures have been determined for 1,5,9-trithiacyclododecan-3-ol and 1,4,7,12,15,18-hexathiacyclodocosane. For 1,5,9-trithiacyclododecane-3-ol, the compound crystallizes in the monoclinic space group, C2/c, with a = 10.5926( 9 ) Å, b = 15.582(2) Å, c = 13.6015(8) Å, β = 98.186(6)0, Z = 8, and R = 0.038. The macrocycle, 1,4,7,12,15,18-hexathiacyclodocosane, crystallizes in the orthorhombic space group, Pbca, with a = 21.406(5) Å, b = 9.810(2) Å, c = 10.225(2) Å, Z = 4, and R = 0.020. 相似文献
55.
研究了Er∶Yb∶YCa4O(BO3)3(简称Er∶Yb∶YCOB)的多晶制备和单晶生长,用提拉法生长出光学质量优良的Er∶Yb∶YCOB单晶,测量了其吸收光谱和荧光光谱,分析了其能级和泵浦原理,并进行了以激光二极管为抽运源的激光试验,实现了Er∶Yb∶YCOB晶体的在1.55μm附近110mW的激光输出,且斜效率达18.9;. 相似文献
56.
Dr. Pere Miró Dr. Bess Vlaisavljevich Dr. Adria Gil Dr. Peter C. Burns Dr. May Nyman Dr. Carles Bo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8571-8578
A wide range of uranyl–peroxide nanocapsules have been synthesized using very simple reactants in basic media; however, little is known about the process to form these species. We have performed a density functional theory study of the speciation of the uranyl ions under different experimental conditions and explored the formation of dimeric species via a ligand exchange mechanism. We shed some light onto the importance of the excess of peroxide and alkali counterions as a thermodynamic driving force towards the formation of larger uranyl–peroxide species. 相似文献
57.
58.
Synthesis of a new fluorescent probe specific for catechols 总被引:1,自引:0,他引:1
[reaction: see text] The synthesis of a new fluorescent probe, specific for the catechol moiety, has been conducted by preparation of alpha,alpha-dibromomalonamides containing an appropriate fluorophore. N,N'-Bis-anthracen-9-ylmethyl-2,2-dibromomalonamide reacted with various catechols in the presence of cesium carbonate to generate highly fluorescent derivatives. 相似文献
59.
60.
We prove that a diffeomorphism possessing a homoclinic point with a topological crossing (possibly with infinite order contact) has positive topological entropy, along with an analogous statement for heteroclinic points. We apply these results to study area-preserving perturbations of area-preserving surface diffeomorphisms possessing homoclinic and double heteroclinic connections. In the heteroclinic case, the perturbed map can fail to have positive topological entropy only if the perturbation preserves the double heteroclinic connection or if it creates a homoclinic connection. In the homoclinic case, the perturbed map can fail to have positive topological entropy only if the perturbation preserves the connection. These results significantly simplify the application of the Poincaré-Arnold-Melnikov-Sotomayor method. The results apply even when the contraction and expansion at the fixed point is subexponential.The first author was partially supported by a Sloan Foundation Fellowship and an N.S.F. grant. The second author was partially supported by a National Science Foundation Postdoctoral Research Fellowship. Both authors would like to thank MSRI for their support during the period that much of this paper was written. 相似文献