全文获取类型
收费全文 | 10058篇 |
免费 | 705篇 |
国内免费 | 226篇 |
专业分类
化学 | 7190篇 |
晶体学 | 108篇 |
力学 | 249篇 |
综合类 | 8篇 |
数学 | 1267篇 |
物理学 | 2167篇 |
出版年
2023年 | 101篇 |
2022年 | 107篇 |
2021年 | 183篇 |
2020年 | 232篇 |
2019年 | 226篇 |
2018年 | 224篇 |
2017年 | 204篇 |
2016年 | 397篇 |
2015年 | 359篇 |
2014年 | 367篇 |
2013年 | 746篇 |
2012年 | 717篇 |
2011年 | 799篇 |
2010年 | 406篇 |
2009年 | 378篇 |
2008年 | 671篇 |
2007年 | 658篇 |
2006年 | 528篇 |
2005年 | 501篇 |
2004年 | 372篇 |
2003年 | 375篇 |
2002年 | 346篇 |
2001年 | 243篇 |
2000年 | 232篇 |
1999年 | 155篇 |
1998年 | 122篇 |
1997年 | 116篇 |
1996年 | 138篇 |
1995年 | 90篇 |
1994年 | 99篇 |
1993年 | 124篇 |
1992年 | 86篇 |
1991年 | 55篇 |
1990年 | 45篇 |
1989年 | 54篇 |
1988年 | 38篇 |
1987年 | 31篇 |
1986年 | 41篇 |
1985年 | 66篇 |
1984年 | 65篇 |
1983年 | 38篇 |
1982年 | 39篇 |
1981年 | 28篇 |
1980年 | 23篇 |
1979年 | 13篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1976年 | 13篇 |
1975年 | 17篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
961.
José A. de la Peña 《Algebras and Representation Theory》2014,17(3):905-930
Let A be a finite dimensional algebra over an algebraically closed field k. Assume A is basic connected with n pairwise non-isomorphic simple modules. We consider the Coxeter transformation ? A as the automorphism of the Grothendieck group K 0(A) induced by the Auslander-Reiten translation τ in the derived category Der(modA) of the module category modA of finite dimensional left A-modules. We say that A is an algebra of cyclotomic type if the characteristic polynomial χ A of ? A is a product of cyclotomic polynomials. There are many examples of algebras of cyclotomic type in the representaton theory literature: hereditary algebras of Dynkin and extended Dynkin types, canonical algebras, some supercanonical and extended canonical algebras. Among other results, we show that: (a) algebras satisfying the fractional Calabi-Yau property have periodic Coxeter transformation and are, therefore, of cyclotomic type, and (b) algebras whose homological form h A is non-negative are of cyclotomic type. For an algebra A of cyclotomic type we describe the shape of the Auslander-Reiten components of Der(modA). 相似文献
962.
Carmen Coll Elena Aznar Ramón Martínez‐Máñez Prof. M. Dolores Marcos Dr. Félix Sancenón Dr. Juan Soto Dr. Pedro Amorós Joan Cano Dr. Eliseo Ruiz Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(33):10048-10061
We report the preparation of a MCM‐41 mesoporous material that contains the dye [Ru(bipy)3]Cl2 (bipy=bipyridine) inside the mesopores and functionalised with suitable binding groups at the entrance of the pores. Solids S1 – S3 were obtained by the reaction of the mesoporous material with N‐methyl‐N′‐propyltrimethoxysilylimidazolium chloride, N‐phenyl‐N′‐[3‐(trimethoxysilyl)propyl]thiourea, or N‐phenyl‐N′‐[3‐(trimethoxysilyl)propyl]urea, respectively. A study of the dye delivery of these systems in buffered water (pH 7.0, 2‐[4‐(2‐hydroxyethyl)piperazin‐1‐yl]ethanesulfonic acid (HEPES), 10?3 mol dm?3) in the presence of a family of carboxylate ions was carried out. In the interaction of the anions with the surface of the solids, the response depends on the characteristics of the binding groups (i.e., imidazolium, urea and thiourea) at the pore outlets and their specific interaction with the corresponding anion. The interaction of long‐chain carboxylate ions with the binding sites at the surface of the solids resulted in a remarkable inhibition of the delivery of the dye. This inhibition was observed clearly for the dodecanoate anion, whereas the octanoate, decanoate, cholate, deoxycholate, glycodeoxycholate and taurocholate anions induced a certain pore blockage that varied according to the solid studied. The interaction of smaller anions, such as acetate, butanoate, hexanoate and octanoate, with the solids had no effect on the dye release process. The possible use of the gating system for the chromo‐fluorogenic detection of anionic surfactants through selective dye delivery inhibition was also explored. Molecular dynamic simulations that use force‐field methods have been made to theoretically study the capping carboxylate mechanism. The calculations are in agreement with the experimental results, thus allowing a representation of the dye delivery inhibition in the presence of long‐chain carboxylate ions. 相似文献
963.
Margareth S. Alves Jaime E. Muñoz Rivera Mauricio Sepúlveda Octavio P. Vera Villagrán 《Applied Mathematics Letters》2012,25(5):884-889
In this paper we investigate the asymptotic behavior of solutions to the initial boundary value problem for a mixture of two rigid solids modeling temperature and porosity. Our main result is to establish conditions which ensure the analyticity and the exponential stability of the corresponding semigroup. 相似文献
964.
965.
Albert Compta Josep Ferrer Marta Peña 《Mathematical Methods in the Applied Sciences》2011,34(3):309-314
Given ?? an (A,B)‐invariant subspace, we prove that the set of friend feedbacks is a linear variety, which can be considered as the direct sum of the feedbacks of the restriction to ?? and the co‐restriction to ??⊥. In particular, when the natural controllability hypothesis hold, both pole assignments are simultaneously possible by means of a convenient friend feedback. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
966.
Raquel Múrtula M. Adela Yáñez Elena Soria Vicente Catalán 《Accreditation and quality assurance》2010,15(4):217-221
The standard methodology used for the detection of bacteria in environmental samples and food is primarily based on bacterial
growth on specific culture media and confirmation by biochemical and/or immunological tests of all presumptive colonies. However,
this methodology presents a number of drawbacks, such as low sensitivity and specificity, and the long time needed to obtain
results. For this reason, the implementation of molecular methods in diagnostic laboratories has increased over the past several
years. Nevertheless, most of these newer methods have not been included in current legislation, and, in most of cases, they
have not yet been normalized. In this sense, the availability of appropriate reference materials (RMs) can help to overcome
these deficiencies. The aim of this study was to develop and validate, following ISO Guide 34, a new RM, in a tablet format,
for the quantification of Legionella pneumophila and Salmonella spp. by quantitative PCR (qPCR). This new RM can be used as a work reference sample in internal quality control, in the organization
of proficiency testing schemes (PTS), as well as for the validation of molecular methods based on qPCR. 相似文献
967.
968.
L. Escuder-Gilabert Y. Martín-Biosca R. M. Villanueva-Camañas M. J. Medina-Hernández S. Sagrado 《Chromatographia》1999,50(5-6):325-332
Summary In micellar liquid chromatography (MLC), the hydrophobicity of a compound is the predominant factor in its retention and interaction
with micelles. A non-linear empirical model can describe the dependence between the retention factor (logk) in MLC and the logarithm of partition coefficients octanol-water (logP). An algorithm based on such a model has been used to makelogP predictions. Retention data for series of neutral compounds eluted with different mobile phases and alkyl-bonded stationary
phases have been used to test the predictive ability of the algorithm. The results of this approach are compared with those
obtained from automatic computational software packages. 相似文献
969.
V. Rodríguez-Lugo L. Ortiz-Velázquez J. Miranda M. Ortiz-Rojas V. M. Castaño 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(2):561-569
The characterization of samples of painted plasters obtained from the archaeological site of Xochicalco, in Central Mexico,
is presented. Elemental concentrations of the painted layers were obtained by using proton induced X-ray emission (PIXE).
The main crystalline structures of the samples are identified with the help of X-ray diffraction (XRD), while the microstructure
is studied by scanning electron microscopy (SEM). The information resulting from the application of these three techniques
is used to achieve more accurate values for the elemental concentrations. Additional data regarding organic components of
the paintings was obtained through Fourier transform infrared spectrometry (FTIR). Although the latter results only provided
reliable data on inorganic components, they help to clarify the results from XRD and confirm those of SEM. 相似文献
970.
Jorge J. Betancor Juan C. Fariña Eleonor Harboure Lourdes Rodríguez-Mesa 《Potential Analysis》2013,38(3):711-739
In this paper we prove that the variation operators of the heat semigroup and the truncations of Riesz transforms associated to the Schrödinger operator are bounded on a suitable BMO type space. 相似文献