全文获取类型
收费全文 | 4136篇 |
免费 | 134篇 |
国内免费 | 35篇 |
专业分类
化学 | 3072篇 |
晶体学 | 33篇 |
力学 | 93篇 |
综合类 | 1篇 |
数学 | 571篇 |
物理学 | 535篇 |
出版年
2023年 | 14篇 |
2022年 | 18篇 |
2021年 | 35篇 |
2020年 | 57篇 |
2019年 | 56篇 |
2018年 | 36篇 |
2017年 | 43篇 |
2016年 | 96篇 |
2015年 | 93篇 |
2014年 | 102篇 |
2013年 | 219篇 |
2012年 | 217篇 |
2011年 | 337篇 |
2010年 | 125篇 |
2009年 | 128篇 |
2008年 | 269篇 |
2007年 | 270篇 |
2006年 | 266篇 |
2005年 | 256篇 |
2004年 | 229篇 |
2003年 | 169篇 |
2002年 | 161篇 |
2001年 | 49篇 |
2000年 | 54篇 |
1999年 | 44篇 |
1998年 | 38篇 |
1997年 | 45篇 |
1996年 | 64篇 |
1995年 | 40篇 |
1994年 | 44篇 |
1993年 | 47篇 |
1992年 | 35篇 |
1991年 | 36篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 28篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 48篇 |
1984年 | 43篇 |
1983年 | 33篇 |
1982年 | 57篇 |
1981年 | 45篇 |
1980年 | 42篇 |
1979年 | 32篇 |
1978年 | 41篇 |
1977年 | 35篇 |
1976年 | 25篇 |
1975年 | 31篇 |
1974年 | 22篇 |
排序方式: 共有4305条查询结果,搜索用时 15 毫秒
991.
Previously, it was found that extruded (200 nm) polymer vesicles are capable of fusion into giant polymersomes using agitation in the presence of salt. In this study, several factors contributing to this phenomenon, including the effects of (i) polymer vesicle concentration, (ii) agitation speed and duration, and (iii) variation of the salt and its concentration are investigated. To accomplish these goals dynamic light scattering is used in conjunction with fluorescence microscopy, which provides insight into vesicles above the practical limit for DLS characterization. Increasing the concentration of the polymer dramatically increases the production of giant vesicles through the increased collisions of polymersomes. Likewise, increasing the frequency of agitation increases the efficiency of fusion, although ultimately the size of vesicle that could be produced is limited due to the high shear involved. Finally, salt‐mediation of the fusion process was not limited to NaCl, but is instead a general effect facilitated by the presence of solvated ionic compounds, albeit with different salts initiating fusion at different concentrations. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 297–303 相似文献
992.
Malcolm R. Banks J. I. G. Cadogan Ian Gosney Philip K.G. Hodgson David R. Rodger 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):381-384
Abstract Whereas arylmetaphosphates (ArOPO2) tend to cyclise by intramolecular C-H insertion (phosphorylation) when generated in the gas phase, their alkyl-substituted counterparts exhibit non-electrophilic behaviour and give rise to alkenes by an unusual 1,2-methyl shift induced by a combination of hydrogen abstraction with concomitant elimination of metaphosphoric acid (HOPO2). 相似文献
993.
994.
Ian C. Watson André Schumann Haoyang Yu Prof. Dr. Emma C. Davy Dr. Robert McDonald Dr. Michael J. Ferguson Prof. Dr. Christian Hering-Junghans Prof. Dr. Eric Rivard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(41):9678-9690
New N-heterocyclic olefins (NHOs) are described with functionalization on the ligand heterocyclic backbone and terminal alkylidene positions. Various PdII–NHO complexes have been formed and their use as pre-catalysts in Buchwald–Hartwig aminations was explored. The most active system for catalytic C−N bond formation between hindered arylamine and arylhalide substrates was accessed by combining a backbone methylated NHO with [Pd(cinnamyl)Cl]2 in the presence of NaOtBu as a base. In these active systems evidence suggests that catalysis is mediated by colloidal palladium metal, highlighting a different coordination ability of NHOs in comparison with commonly used N-heterocyclic carbene co-ligands. 相似文献
995.
996.
997.
998.
Peyton W. Roth Ahlam M. Armaly Ian McCraw James H. Tryon Hayden M. Rudd Brian C. Goess 《Tetrahedron letters》2018,59(39):3586-3588
The first total syntheses of the furanosesquiterpenoids hibiscone B and acyl hibiscone B are reported. The chemistry used to prepare hibiscone B solves an important challenge to the synthesis of other members of the furanosesquiterpenoid family of natural products, for which the parent molecule, hibiscone C, has shown promising biological activity. 相似文献
999.
Lee R. Collins Gabriele Hierlmeier Dr. Mary F. Mahon Dr. Ian M. Riddlestone Prof. Michael K. Whittlesey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3215-3218
The electrophilic character of free diamidocarbenes (DACs) allows them to activate inert bonds in small molecules, such as NH3 and P4. Herein, we report that metal coordinated DACs also exhibit electrophilic reactivity, undergoing attack by Zn and Cd dialkyl precursors to afford the migratory insertion products [(6‐MesDAC‐R)MR] (M=Zn, Cd; R=Et, Me; Mes=mesityl). These species were formed via the spectroscopically characterised intermediates [(6‐MesDAC)MR2], exhibiting barriers to migratory insertion which increase in the order MR2 = ZnEt2 < ZnMe2 < CdMe2. Compound [(6‐MesDAC‐Me)CdMe] showed limited stability, undergoing deposition of Cd metal, by an apparent β‐H elimination pathway. These results raise doubts about the suitability of diamidocarbenes as ligands in catalytic reactions involving metal species bearing nucleophilic ligands (M‐R, M‐H). 相似文献
1000.
Eleven members of the homologous series of liquid crystal dimers, the α,ω-bis(4-cyanobiphenyl-4′-yl) alkanedioates, have been synthesised and their transitional properties characterised. These dimers consist of two cyanobiphenyl units connected by an alkyl spacer attached via ester linkages. All eleven members exhibit exclusively nematic behaviour. The nematic–isotropic transition temperatures, TNI, and associated entropy changes, ?SNI/R, exhibit pronounced alternations as the length and parity of the spacer is varied; this is characteristic behaviour of liquid crystal dimers. The transitional properties of the ester-linked dimers are compared with the corresponding materials having either ether, methylene or carbonate linkages between the spacer and mesogenic units. For short spacer lengths and both odd- and even-membered dimers, the ester-linked materials show the highest values of TNI and the methylene-linked the lowest. For longer spacer lengths, TNI of the carbonate-linked dimers fall between those of the corresponding ester- and ether-linked dimers. The ether-linked materials show the largest alternation in ?SNI/R on varying spacer length and the carbonate-linked dimers the lowest. This behaviour is interpreted in terms of the molecular geometry and it is suggested that the ether- and ester-linked odd-membered dimers have rather similar shapes. A phase diagram constructed using binary mixtures of the pentyl member of this ester-linked series and the known twist-bend nematogen, 1,7-bis(4-cyanobiphenyl-4′-yl)heptane (CB7CB), is presented. The twist-bend nematic–nematic transition temperature of the mixtures shows a striking convex curvature as the concentration of CB7CB is decreased, and so it is not possible to estimate a virtual twist-bend nematic–nematic transition temperature for the ester-linked material. 相似文献