全文获取类型
收费全文 | 3462篇 |
免费 | 123篇 |
国内免费 | 22篇 |
专业分类
化学 | 2450篇 |
晶体学 | 25篇 |
力学 | 81篇 |
数学 | 440篇 |
物理学 | 611篇 |
出版年
2023年 | 21篇 |
2022年 | 32篇 |
2021年 | 87篇 |
2020年 | 85篇 |
2019年 | 72篇 |
2018年 | 57篇 |
2017年 | 51篇 |
2016年 | 105篇 |
2015年 | 67篇 |
2014年 | 76篇 |
2013年 | 196篇 |
2012年 | 182篇 |
2011年 | 254篇 |
2010年 | 153篇 |
2009年 | 109篇 |
2008年 | 178篇 |
2007年 | 202篇 |
2006年 | 217篇 |
2005年 | 160篇 |
2004年 | 127篇 |
2003年 | 86篇 |
2002年 | 111篇 |
2001年 | 62篇 |
2000年 | 65篇 |
1999年 | 39篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 32篇 |
1995年 | 41篇 |
1994年 | 34篇 |
1993年 | 35篇 |
1992年 | 23篇 |
1991年 | 33篇 |
1990年 | 22篇 |
1989年 | 18篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 25篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 32篇 |
1981年 | 18篇 |
1980年 | 33篇 |
1979年 | 33篇 |
1978年 | 21篇 |
1977年 | 30篇 |
1975年 | 22篇 |
1974年 | 24篇 |
1973年 | 18篇 |
排序方式: 共有3607条查询结果,搜索用时 218 毫秒
1.
2.
Crosslinked poly(ethylene oxide) containing siloxanes fabricated through thiol‐ene photochemistry 下载免费PDF全文
Victor A. Kusuma Elliot A. Roth William P. Clafshenkel Steven S. Klara Xu Zhou Surendar R. Venna Erik Albenze David R. Luebke Meagan S. Mauter Richard R. Koepsel Alan J. Russell David Hopkinson Hunaid B. Nulwala 《Journal of polymer science. Part A, Polymer chemistry》2015,53(13):1548-1557
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557 相似文献
3.
Chromatographia - The reversed phase behaviour of high molecular mass polystyrenes was investigated on C18 bonded phase columns with ethyl acetate-methanol and ethyl acetateacetonitrile mobile... 相似文献
4.
Ohne Zusammenfassung 相似文献
5.
Rodrigo París José Luis de la Fuente 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3538-3549
Different diblock copolymers constituted by one segment of a monomer supporting a reactive functional group, like allyl methacrylate (AMA), were synthesized by atom transfer radical polymerization (ATRP). Bromo‐terminated polymers, like polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) were employed as macroinitiators to form the other blocks. Copolymerizations were carried out using copper chloride with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as the catalyst system in benzonitrile solution at 70 °C. At the early stage, the ATRP copolymerizations yielded well‐defined linear block copolymers. However, with the polymerization progress a change in the macromolecular architecture takes place due to the secondary reactions caused by the allylic groups, passing to a branched and/or star‐shaped structure until finally yielding gel at monomer conversion around 40% or higher. The block copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy, and differential scanning calorimetry (DSC). In addition, one of these copolymers, specifically P(BA‐b‐AMA), was satisfactorily modified through osmylation reaction to obtain the subsequent amphiphilic diblock copolymer of P(BA‐b‐DHPMA), where DHPMA is 2,3‐dihydroxypropyl methacrylate; demonstrating the feasibility of side‐chain modification of the functional obtained copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3538–3549, 2007 相似文献
6.
Humberto César Chaves Fernandes Arthur Rodrigo Barros da Rocha 《International Journal of Infrared and Millimeter Waves》2003,24(7):1171-1176
The use of photonic materials has been used in the theory of optical waves. The PBG (Photonic Band Gap) theory and material, was developed recently for optical frequencies and can be easily applied to millimeter waves, microwaves and planar antenna frequencies. The presence of photonic materials as substrate in antennas has some good characteristics such as, supression of light spontaneous emission and suppression of surface waves, allowing the application in planar antenna array. In this work an elaborate analysis using the full wave Transverse Transmission Line - TTL method, that provides efficient and concise results is applied to the planar antennas array with PBG substrate. 相似文献
7.
This work presents a formulation based on UPML for truncating conductive media by using a local and non-orthogonal coordinate
system to solve Maxwell’s equations by the FDTD method. The detailed procedure for obtaining the UPML equations for this case
is shown and the complete equation set is provided. 相似文献
8.
Gianluigi Luppi Rodrigo J. Corrêa Angelo C. Pinto Quirinus B. Broxterman Claudia Tomasini 《Tetrahedron》2006,62(51):12017-12024
The first total synthesis of (R)-convolutamydine A has been achieved by the organocatalytic addition of acetone to 4,6-dibromoisatin. The absolute configuration was determined by single crystal X-ray diffraction. DFT studies were used to model the transition states for the aldol reaction and equilibrium geometries of the post-aldol reaction intermediates. The DFT study revealed that the aldol bond forming reaction was considerably endothermic. 相似文献
9.
F. C. ten Doornkaat Koolman J. Traube Jandell Henderson Donald G. Russell und H. Bunzel 《Fresenius' Journal of Analytical Chemistry》1914,53(6):404
Ohne Zusammenfassung 相似文献
10.
Jos Luis Rodrigo 《纯数学与应用数学通讯》2005,58(6):821-866
We consider the problem of the evolution of sharp fronts for the surface quasi‐geostrophic (QG) equation. This problem is the analogue to the vortex patch problem for the two‐dimensional Euler equation. The special interest of the quasi‐geostrophic equation lies in its strong similarities with the three‐dimensional Euler equation, while being a two‐dimen‐sional model. In particular, an analogue of the problem considered here, the evolution of sharp fronts for QG, is the evolution of a vortex line for the three‐dimensional Euler equation. The rigorous derivation of an equation for the evolution of a vortex line is still an open problem. The influence of the singularity appearing in the velocity when using the Biot‐Savart law still needs to be understood. We present two derivations for the evolution of a periodic sharp front. The first one, heuristic, shows the presence of a logarithmic singularity in the velocity, while the second, making use of weak solutions, obtains a rigorous equation for the evolution explaining the influence of that term in the evolution of the curve. Finally, using a Nash‐Moser argument as the main tool, we obtain local existence and uniqueness of a solution for the derived equation in the C∞ case. © 2004 Wiley Periodicals, Inc. 相似文献