全文获取类型
收费全文 | 2250篇 |
免费 | 59篇 |
专业分类
化学 | 1265篇 |
晶体学 | 42篇 |
力学 | 77篇 |
数学 | 540篇 |
物理学 | 385篇 |
出版年
2023年 | 12篇 |
2022年 | 29篇 |
2021年 | 37篇 |
2020年 | 49篇 |
2019年 | 65篇 |
2018年 | 97篇 |
2017年 | 101篇 |
2016年 | 104篇 |
2015年 | 78篇 |
2014年 | 121篇 |
2013年 | 332篇 |
2012年 | 124篇 |
2011年 | 140篇 |
2010年 | 150篇 |
2009年 | 96篇 |
2008年 | 131篇 |
2007年 | 116篇 |
2006年 | 75篇 |
2005年 | 47篇 |
2004年 | 46篇 |
2003年 | 33篇 |
2002年 | 36篇 |
2001年 | 23篇 |
2000年 | 20篇 |
1999年 | 18篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1968年 | 9篇 |
排序方式: 共有2309条查询结果,搜索用时 343 毫秒
1.
2.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
3.
Suppose there exists a global solution u to the incompressible Navier–Stokes equations, such that . We prove that its norm goes to 0 at infinity. We next use this fact to control the norm of u, and finally we prove that such a solution is stable. To cite this article: I. Gallagher et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 289–292. 相似文献
4.
Stefan Cobzaş 《Acta Appl Math》2004,80(3):363-363
5.
Mustafa Çelebier Ertan Şahin Nilgün Ancın Nurşen Altuntaş Öztaş Selma Gül Öztaş 《应用有机金属化学》2007,21(10):viii-viii
The article referenced above was first published online on 30 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
We continue the studies on the so–called genuine Bernstein–Durrmeyer operators U
n
by establishing a recurrence formula for the moments and by investigating the semigroup T(t) approximated by U
n
. Moreover, for sufficiently smooth functions the degree of this convergence is estimated. We also determine the eigenstructure
of U
n
, compute the moments of T(t) and establish asymptotic formulas.
Received: January 26, 2007. 相似文献
7.
We give a concise review and extension of S-procedure that is an instrumental tool in control theory and robust optimization analysis. We also discuss the approximate S-Lemma as well as its applications in robust optimization.The many suggestions and detailed corrections of an anonymous referee are gratefully acknowledged. 相似文献
8.
Duygu Avci Aylin Ziylan Albayrak 《Journal of polymer science. Part A, Polymer chemistry》2003,41(14):2207-2217
Two phosphorus‐containing acrylate monomers were synthesized from the reaction of ethyl α‐chloromethyl acrylate and t‐butyl α‐bromomethyl acrylate with triethyl phosphite. The selective hydrolysis of the ethyl ester monomer with trimethylsilyl bromide (TMSBr) gave a phosphonic acid monomer. The attempted bulk polymerizations of the monomers at 57–60 °C with 2,2′‐azobisisobutyronitrile (AIBN) were unsuccessful; however, the monomers were copolymerized with methyl methacrylate (MMA) in bulk at 60 °C with AIBN. The resulting copolymers produced chars on burning, showing potential as flame‐retardant materials. Additionally, α‐(chloromethyl)acryloyl chloride (CMAC) was reacted with diethyl (hydroxymethyl)phosphonate to obtain a new monomer with identical ester and ether moieties. This monomer was hydrolyzed with TMSBr, homopolymerized, and copolymerized with MMA. The thermal stabilities of the copolymers increased with increasing amounts of the phosphonate monomer in the copolymers. A new route to highly reactive phosphorus‐containing acrylate monomers was developed. A new derivative of CMAC with mixed ester and ether groups was synthesized by substitution, first with diethyl (hydroxymethyl)phosphonate and then with sodium acetate. This monomer showed the highest reactivity and gave a crosslinked polymer. The incorporation of an ester group increased the rate of polymerization. The relative reactivities of the synthesized monomers in photopolymerizations were determined and compared with those of the other phosphorous‐containing acrylate monomers. Changing the monomer structure allowed control of the polymerization reactivity so that new phosphorus‐containing polymers with desirable properties could be obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2207–2217, 2003 相似文献
9.
Adsorption of the copper ions from aqueous solutions, benzene, and water on the active carbon obtained by chemical activation
from walnut shells was studied. The active carbon was additionally oxidized with hydrogen peroxide and then impregnated with
nitrogen-containing compounds. As a result of impregnation with melamine, a secondary porosity is formed within the oxidized
active carbon, leading to an increase in the specific surface of the sorbent. A modified carbon surface is heterogeneous,
and the carbons themselves exhibit catalytic activity in the oxidation of luminol and decomposition of hydrogen peroxide. 相似文献
10.