全文获取类型
收费全文 | 927篇 |
免费 | 10篇 |
国内免费 | 10篇 |
专业分类
化学 | 322篇 |
晶体学 | 12篇 |
力学 | 15篇 |
数学 | 317篇 |
物理学 | 281篇 |
出版年
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 17篇 |
2016年 | 26篇 |
2015年 | 19篇 |
2014年 | 30篇 |
2013年 | 58篇 |
2012年 | 50篇 |
2011年 | 44篇 |
2010年 | 37篇 |
2009年 | 39篇 |
2008年 | 59篇 |
2007年 | 46篇 |
2006年 | 50篇 |
2005年 | 35篇 |
2004年 | 33篇 |
2003年 | 27篇 |
2002年 | 27篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 22篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1969年 | 4篇 |
排序方式: 共有947条查询结果,搜索用时 15 毫秒
141.
Liviu Horia Popescu 《Integral Equations and Operator Theory》2014,79(3):355-375
The present paper is devoted to the study of some qualitative properties of C 0-groups via topological equivalence, also called conjugacy. The special case of the evolution groups is analysed. We show that hyperbolicity implies structural stability. Our constructions improve existing similar results for groups with bounded generators, and apply to linear differential equations with unbounded coefficient operator. 相似文献
142.
Sorin G. Gal 《Results in Mathematics》2014,65(3-4):453-462
By analogy with the probabilistic approach of the classical Bernstein polynomials, in this paper firstly we give the proof for the uniform convergence of the nonlinear max-product Bernstein operator by using the theory of possibility. This new approach, which interprets the max-product Bernstein operator as a possibilistic expectation of a particular fuzzy variable having a possibilistic Bernoulli distribution, does not only offer a good justification for the max-product Bernstein operator, but also allows to extend the method to other discrete max-product Bernstein type operators. 相似文献
143.
Catalytic and Atom‐Economic C
−C
Bond Formation: Alkyl Tantalum Ureates for Hydroaminoalkylation
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)
Rebecca C. DiPucchio Dr. Sorin‐Claudiu Roşca Prof. Laurel L. Schafer 《Angewandte Chemie (International ed. in English)》2018,57(13):3469-3472
Atom‐economic and regioselective C ?C bond formation has been achieved by rapid C?H alkylation of unprotected secondary arylamines with unactivated alkenes. The combination of Ta(CH2SiMe3)3Cl2, and a ureate N,O‐chelating‐ligand salt gives catalytic systems prepared in situ that can realize high yields of β‐alkylated aniline derivatives from either terminal or internal alkene substrates. These new catalyst systems realize C?H alkylation in as little as one hour and for the first time a 1:1 stoichiometry of alkene and amine substrates results in high yielding syntheses of isolated amine products by simple filtration and concentration. 相似文献
144.
Leulescu Marian Rotaru Andrei Pălărie Ion Moanţă Anca Cioateră Nicoleta Popescu Mariana Morîntale Emilian Bubulică Maria Viorica Florian Gabriel Hărăbor Ana Rotaru Petre 《Journal of Thermal Analysis and Calorimetry》2018,134(1):209-231
Journal of Thermal Analysis and Calorimetry - The food-colouring dye tartrazine is a significant additive and in the same time a biologically active material. Thermal behaviour of trisodium... 相似文献
145.
A theoretical study of the solvation of ( R)- N-(3,5-dinitrobenzoyl)phenylglycine- and ( R)- N-(3,5-dinitrobenzoyl)leucine-derived chiral stationary phases (CSPs) is presented. Semiflexible models of the chiral selectors are prepared from B3LYP/6-311G** calculations, and these are used in the molecular dynamics simulations of the corresponding interface. The chiral interface is examined for four solvents: 100% hexane, 90:10 hexane:2-propanol, 80:20 hexane:2-propanol, and 100% 2-propanol. Despite the similarities between phenylglycine and leucine, the interfaces are distinct both in terms of the selector orientations at the surface and in the number of hydrogen bonds formed with 2-propanol. We also find that an increase in alcohol concentration alters the preferred orientations of the selectors. 相似文献
146.
We consider amalgamated free product II1 factors M = M
1*B
M
2*B
… and use “deformation/rigidity” and “intertwining” techniques to prove that any relatively rigid von Neumann subalgebra Q ⊂ M can be unitarily conjugated into one of the M
i
’s. We apply this to the case where the M
i
’s are w-rigid II1 factors, with B equal to either C, to a Cartan subalgebra A in M
i
, or to a regular hyperfinite II1 subfactor R in M
i
, to obtain the following type of unique decomposition results, àla Bass–Serre: If M = (N
1 * CN2*C
…)
t
, for some t > 0 and some other similar inclusions of algebras C ⊂ N
i
then, after a permutation of indices, (B ⊂ M
i
) is inner conjugate to (C ⊂ N
i
)
t
, for all i. Taking B = C and , with {t
i
}
i⩾1 = S a given countable subgroup of R
+
*, we obtain continuously many non-stably isomorphic factors M with fundamental group equal to S. For B = A, we obtain a new class of factors M with unique Cartan subalgebra decomposition, with a large subclass satisfying and Out(M) abelian and calculable. Taking B = R, we get examples of factors with , Out(M) = K, for any given separable compact abelian group K. 相似文献
147.
Gelu Popescu 《Journal of Functional Analysis》2008,254(4):1003-1057
In this paper, we initiate the study of a class of noncommutative domains of n-tuples of bounded linear operators on a Hilbert space H, where m?2, n?2, and p is a positive regular polynomial in n noncommutative indeterminates. These domains are defined by certain positivity conditions on p, i.e.,
148.
M. D. Stanescu C. Popescu A. Rus C. Guran 《Journal of Thermal Analysis and Calorimetry》2008,94(2):535-538
A number of dibenzobicyclo[2.2.2]octane derivatives have been studied due to the interest of such compounds as ligands for
coordination compounds with potential biological activity. Their thermal behaviour has been analyzed in order to find out
more information about their fragmentation. A connection between the bridge substituents and the fragmentation process has
been observed. 相似文献
149.
Laura Mureşan Ruben Ronda Valera Ivo Frébort Ionel Catalin Popescu Elisabeth Csöregi Mihaela Nistor 《Mikrochimica acta》2008,163(3-4):219-225
A selective and sensitive method is presented for biogenic amines (BA) determination. The novelty consists in coupling a highly selective electrochemical biosensor to a weak acid cation-exchange column for online detection of amines. A bienzyme design, based on a recently isolated amine oxidase from grass pea and commercial horseradish peroxidase, was used for the biosensor construction. The enzymes were co-immobilized on the surface of a graphite electrode together with the electrochemical mediator (Os-redox polymer). The electrochemical detection was performed at a low applied potential (?50 mV vs. Ag/AgCl, KCl0.1 M), where biases from interferences are minimal. The separation and determination of six BA, with relevance in food analysis (tyramine, putrescine, cadaverine, histamine, agmatine and spermidine), were investigated. Irrespective of the BA nature, the amine oxidase-based biosensor showed a linear response up to 5 mM, and its sensitivity decreases in the following order: cadaverine, putrescine, spermidine, agmatine, histamine and tyramine. The approach was used to estimate the BA content in fish samples, after their extraction with methanesulfonic acid. 相似文献
150.
C. Popescu P. Budrugeac F.-J. Wortmann L. Miu D.E. Demco M. Baias 《Polymer Degradation and Stability》2008,93(5):976-982
The thermal degradation of collagen-based materials, viz. collagen, recently manufactured parchments and tanned leathers, a heritage parchment and patrimonial (historical) leathers, was investigated by thermal analysis methods. With progressive heating, all these materials exhibit three main successive processes, associated with dehydration, protein denaturation and pyrolysis/oxidation. The analysis of both denaturation and thermo-oxidation revealed significant differences between aged leather, collagen, recently manufactured parchments and tanned leathers in terms of the number of overlapping processes (reflected in the number of peaks recorded at denaturation) and of the oxidative degradation rates, given by the normalised curves of differential thermal gravimetry (DTG). The various observations are proposed as qualitative indices for assessing the age and storage conditions of leather. A three-phase model was used for explaining the results. This consists of crystalline collagen filaments that are embedded in an amorphous matrix with an interface zone between the crystalline and amorphous regions. Solid-state 1H NMR investigations corroborate the thermal analysis results and enhance the understanding of the ageing processes. 相似文献