全文获取类型
收费全文 | 1505篇 |
免费 | 15篇 |
国内免费 | 5篇 |
专业分类
化学 | 1099篇 |
晶体学 | 18篇 |
力学 | 10篇 |
数学 | 121篇 |
物理学 | 277篇 |
出版年
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 20篇 |
2014年 | 13篇 |
2013年 | 71篇 |
2012年 | 40篇 |
2011年 | 72篇 |
2010年 | 38篇 |
2009年 | 47篇 |
2008年 | 65篇 |
2007年 | 83篇 |
2006年 | 76篇 |
2005年 | 77篇 |
2004年 | 67篇 |
2003年 | 75篇 |
2002年 | 75篇 |
2001年 | 40篇 |
2000年 | 27篇 |
1999年 | 18篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 24篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 23篇 |
1985年 | 22篇 |
1984年 | 36篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 21篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 21篇 |
1974年 | 14篇 |
1972年 | 9篇 |
1970年 | 7篇 |
排序方式: 共有1525条查询结果,搜索用时 46 毫秒
961.
962.
This paper presents a simple and practical scheme for capturing moving interfaces or free boundaries in multi‐fluid simulations. The scheme, which is called THINC (tangent of hyperbola for interface capturing), makes use of the hyperbolic tangent function to compute the numerical flux for the fluid fraction function, and gives a conservative, oscillation‐less and smearing‐less solution to the fluid fraction function even for the extremely distorted interfaces of arbitrary complexity. The numerical results from the THINC scheme possess adequate quality for practical applications, which make the extra geometric reconstruction, such as those in most of the volume of fluid (VOF) methods unnecessary. Thus the scheme is quite simple. The numerical tests show that the THINC scheme has competitive accuracy compared to most exiting methods. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
963.
Yasutaka Kamei Atsushi Sudo Haruo Nishida Kiyoshi Kikukawa Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》2008,46(7):2525-2535
A series of activated urethane‐type derivatives of α‐amino acids were synthesized and applied to polypeptide synthesis. The urethane used herein, N‐(4‐nitrophenoxycarbonyl)‐α‐amino acids 1 , were synthesized by N‐carbamoylation of γ‐benzyl‐L ‐glutamate, β‐benzyl‐L ‐aspartate, L ‐leucine, L ‐phenylalanine, and L ‐proline, with 4‐nitrophenyl chloroformate. When 1 was dissolved in N,N‐dimethylacetamide (DMAc) and heated at 60 °C, it was smoothly converted into the corresponding polypeptides with releasing 4‐nitrophenol and carbon dioxide. Spectroscopic analyses of the obtained polypeptides revealed that they were comparable with the authentic polypeptides synthesized by the ring‐opening polymerizations of amino acid N‐carboxyanhydrides (NCAs). Besides the successful polycondensations of a series of 1 , their polycondensations of 1a and other 1 were also successfully carried out to obtain the corresponding statistic copolypeptides. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2525–2535, 2008 相似文献
964.
965.
Shunji Kono Yu Jiang Wang Li Ming Tang 《中国化学快报》2007,18(12):1548-1550
A supramolecular hydrogel(defined as G1) formed from 1,2,4,5-benzene tetracarboxylic acid (BTCA) and 2-amino-3- hydroxypyridine possessed higher T_(gel) than that of another hydrogel(defined as G2) formed from BTCA and 3-hydroxypyridine. Based on the analysis of their xerogels by ~1H NMR,IR and XRD,the higher stability of G1 was attributed to the formation of stronger hydrogen binding enhanced by the ortho amino group of 2-amino-3-hydroxypyridine. 相似文献
966.
Yasutaka Kamei Atsushi Nagai Atsushi Sudo Haruo Nishida Kiyoshi Kikukawa Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》2008,46(8):2649-2657
A series of activated urethane‐type derivatives of γ‐benzyl‐L ‐glutamate were synthesized, and their potential as monomers for polypeptide synthesis was investigated. The derivatives of the focus of this work were a series of N‐aryloxycarbonyl‐γ‐benzyl‐L ‐glutamate 1 , of which aryl groups were phenyl, 4‐chlorophenyl, and 4‐nitrophenyl. These urethanes 1 were reactive in polar solvents such as dimethylsulfoxide, N,N‐dimethylformamide (DMF), and N,N‐dimethylacetamide (DMAc), and were efficiently converted into poly(γ‐benzyl‐L ‐glutamate) (poly(BLG)) under mild conditions; at 60 °C without addition of any catalyst. Among the three urethanes, that having 4‐nitrophenoxycarbonyl group 1c was the most reactive to give poly(BLG) efficiently, as was expected from the highly electron deficient nature of the nitrophenoxycarbonyl group. On the other hand, the urethane 1a having phenoxycarbonyl group was also efficiently converted into poly(BLG), in spite of the intrinsically less electrophilicity of the phenoxycarbonyl group. In addition, the successful formation of poly(BLG) by the reaction of 1a favored its diluted concentration (0.1 M) much more than 2.0 M, the optimum initial concentration for 1c . 1H NMR spectroscopic analyses of the reactions in situ revealed that the predominant pathway from 1 to poly(BLG) involved the intramolecular cyclization of 1 into the corresponding N‐carboxyanhydride, with release of phenol and its successive ring‐opening polymerization with release of carbon dioxide. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2649–2657, 2008 相似文献
967.
Yuki Matsunaga Kiyoshi Fujisawa Nagina Amir Yoshitaro Miyashita Ken‐ichi Okamoto 《应用有机金属化学》2005,19(1):208-208
The Zn center in [ZnCl2(L‐S‐S‐L)], where L‐S‐S‐L = bis(1‐methylimidazole‐2)disulfide, adopts a tetrahedral configuration defined by two Cl atoms and two N atoms from L‐S‐S‐L, which was obtained by in situ oxidation of 1‐methylimidazole‐2‐thione. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
968.
Tran Thi Ngoc Lan Rokuro Nishimura Yoshio Tsujino Kiyoshi Imamura Munehiro Warashina Nguyen Thai Hoang Yasuaki Maeda 《Analytical sciences》2004,20(1):213-217
A passive sampling method was applied to measure the concentrations of air pollutants, such as sulfur dioxide, nitrogen oxides, ammonia, hydrogen chloride, and nitric, formic and acetic acids, in the ambient air at four test sites in the southern region of Vietnam. The monthly averages and the average concentrations of air pollutants during the period from July 2001 to September 2002 are reported here. The concentrations of air pollutants varied widely, depending on the test sites and the sampling periods. The average concentrations of sulfur dioxide in the air during the period from July 2001 to September 2002 at the four test sites were 3.3-16.9 ppb, and those of nitrogen dioxide were 5.4-12.8 ppb. The concentrations of nitrogen monoxide and hydrogen chloride were very low at all of the test sites. The observed concentrations of all of the above-mentioned pollutants were lower than those of the Vietnamese standards of air pollutants. 相似文献
969.
A weighted graph is one in which every edge e is assigned a nonnegative number, called the weight of e. The sum of the weights of the edges incident with a vertex υ is called the weighted degree of υ. The weight of a cycle is defined as the sum of the weights of its edges. In this paper, we prove that: (1) if G is a 2‐connected weighted graph such that the minimum weighted degree of G is at least d, then for every given vertices x and y, either G contains a cycle of weight at least 2d passing through both of x and y or every heaviest cycle in G is a hamiltonian cycle, and (2) if G is a 2‐connected weighted graph such that the weighted degree sum of every pair of nonadjacent vertices is at least s, then for every vertex y, G contains either a cycle of weight at least s passing through y or a hamiltonian cycle. AMS classification: 05C45 05C38 05C35. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
970.
We propose a technique for chromatic dispersion monitoring based on optical time domain level monitoring.Experimental and simulation results show that the technique is effective for the monitoring of dispersion in 42.7-Gbps CS-RZ signals for dynamic dispersion compensation. 相似文献