全文获取类型
收费全文 | 1279篇 |
免费 | 39篇 |
国内免费 | 5篇 |
专业分类
化学 | 822篇 |
晶体学 | 14篇 |
力学 | 46篇 |
数学 | 140篇 |
物理学 | 301篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 36篇 |
2021年 | 47篇 |
2020年 | 29篇 |
2019年 | 34篇 |
2018年 | 40篇 |
2017年 | 24篇 |
2016年 | 38篇 |
2015年 | 46篇 |
2014年 | 40篇 |
2013年 | 100篇 |
2012年 | 105篇 |
2011年 | 101篇 |
2010年 | 64篇 |
2009年 | 66篇 |
2008年 | 73篇 |
2007年 | 72篇 |
2006年 | 50篇 |
2005年 | 42篇 |
2004年 | 46篇 |
2003年 | 32篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有1323条查询结果,搜索用时 15 毫秒
161.
Residual stress field and reduction of stress intensity factors in cold-worked holes 总被引:1,自引:0,他引:1
S.T. Pinho H.B. Martins P.P. Camanho M.H. Santare P.M.S.T. de Castro 《Theoretical and Applied Fracture Mechanics》2005,44(2):168-177
Closed-form and semi-analytical solutions are obtained for the residual stress distributions in a plate caused by pressure acting on a central circular hole, representing the cold-work process. The material is elastic–perfectly plastic. Both Tresca and von Mises yield criteria are used and the corresponding residual stress distributions are compared. The relation between the dimension of the plastic zone and the value of internal pressure is presented. The relation between the magnitude of the residual stresses and the remote uniform tensile stress required to open symmetrical radial cracks is also presented. The reduction of the stress intensity factors of cracked open and riveted holes as a function of the internal pressure applied (or mandrel radial displacement) is investigated using numerical models for both an elastic–perfectly plastic material and for an Al 2024-T3 Alclad aluminum alloy. 相似文献
162.
Liliana Costa C.M. da Fonseca Enide Andrade Martins 《Linear algebra and its applications》2008,428(7):1524-1537
In this work we give an interpretation of vertices and edges of the acyclic Birkhoff polytope, Tn=Ωn(T), where T is a tree with n vertices, in terms of graph theory. We generalize a recent result relatively to the diameter of the graph G(Tn). 相似文献
163.
Martins Bruveris 《Annals of Global Analysis and Geometry》2017,51(1):11-20
In this paper, we introduce the twistor space of a Riemannian manifold with an even Clifford structure. This notion generalizes the twistor space of quaternion-Hermitian manifolds and weak-\(\mathrm {Spin}(9)\) structures. We also construct almost complex structures on the twistor space for parallel even Clifford structures and check their integrability. Moreover, we prove that in some cases one can give Kähler and nearly Kähler metrics to these spaces. 相似文献
164.
This paper considers the issues related to uniqueness and existence of a finite deformation generated by prescribed right or left Cauchy-Green strain tensor field in the plane. First, the questions of uniqueness and existence to a pre-assigned right strain field C are discussed. It is shown that the existence condition, in the context of continuum mechanics, are naturally posed using the field corresponding to the square root of C instead of C, the latter a classical approach. Then, the corresponding questions for the left strain field are considered, which is more involved. The analysis of uniqueness gives rise to an appropriate classification of the deformation fields. The question of existence is discussed and a complete solution is presented. In both the right and left cases, we stress the techniques for obtaining the corresponding deformation fields. 相似文献
165.
Martins GV Mano JF Alves NM 《Langmuir : the ACS journal of surfaces and colloids》2011,27(13):8415-8423
In this paper, we describe the construction and characteristics of thermoresponsive, thin nanostructured films prepared by layer-by-layer sequential assembly of chitosan-graft-NIPAAm and alginate. FTIR and (1)H NMR spectra have confirmed the introduction of NIPAAm moieties onto the chitosan backbone. The LCST of the synthesized copolymer was found to be around 31-33 °C. The formation of the polyelectrolyte multilayers containing the copolymer and alginate was followed in situ by quartz crystal microbalance with dissipation monitoring technique and ex situ by UV-vis measurements. Our results revealed the linear increase of the multilayer film growth and the influence of the presence of salt. Moreover, AFM analysis has confirmed that PNIPAAm is able to reconform upon temperature swaps even when combined with other layers in a polyelectrolyte multilayer, demonstrating that the nanoassemblies are thermoresponsive. Preliminary results showed that, upon reducing culture temperature below PNIPAAm LCST, a gradual detachment of cell sheets from these PNIPAAm-based coatings has occurred. 相似文献
166.
Martins LA Meneghini LZ Junqueira CA Ceni DC Bergold AM 《Journal of chromatographic science》2011,49(10):796-800
A simple stability indicating high-performance liquid chromatography method for the analysis of adapalene in pharmaceutical gel formulation is developed and validated. An isocratic separation is performed using a Merck RP-8 (150 mm × 4.6 mm i.d., particle size 5 m) column and a mixture of acetonitrile water (67:33, v/v, pH adjusted to 2.5 with phosphoric acid) as the mobile phase. The detection is achieved with a photodiode array detector at 321 nm. The specificity of the method is verified by subjecting both the reference substance and the pharmaceutical form to hydrolytic, oxidative, photolytic, and thermal stress conditions. There is no interference from the excipients of the formulation on the determination of adapalene in gel. The response is linear over the concentration range of 8.0-16.0 μg/mL (r > 0.999) with a limit of detection and quantification of 0.04 and 0.14 μg/mL, respectively. The mean recovery is 100.8%. The RSD values for the intra- and inter-day precision studies are < 1.2%. The method is validated by reaching satisfactory results for linearity, selectivity, specificity, precision, accuracy, robustness, and system suitability. 相似文献
167.
Soni R Cheung FK Clarkson GC Martins JE Graham MA Wills M 《Organic & biomolecular chemistry》2011,9(9):3290-3294
Ru(II) complexes of TsDPEN containing two alkyl groups on the non-tosylated nitrogen atom are poor catalysts for asymmetric transfer hydrogenation of ketones and imines; this observation provides direct evidence for the importance of the N-H interaction in the transition state for ketone reduction. 相似文献
168.
Reis FS Pereira E Barros L Sousa MJ Martins A Ferreira IC 《Molecules (Basel, Switzerland)》2011,16(6):4328-4338
The use of natural products isolated from mushrooms, included inedible species, against infection, cancer diseases and other oxidative-stress related diseases is one of the cornerstones of modern medicine. In the present work, the antioxidant molecule profiles of inedible mushroom species were evaluated and compared with those of edible species. The order of antioxidant abundance found in inedible wild mushrooms was: phenolics > flavonoids > ascorbic acid > tocopherols > carotenoids, similar to that of edible species. Furthermore the same energetic biomolecules were found including the disaccharide trehalose, the monosaccharide alcohol derivative mannitol and the fatty acids palmitic, oleic and linoleic acids. Fomitopsis pinicola revealed a very high phenolics concentration (388 mg GAE/g extract) and powerful antioxidant properties, mainly reducing power (EC??) value 60 μg/mL similar to the standard Trolox?). It could find applications in the prevention of free radical-related diseases as a source of bioactive compounds. 相似文献
169.
We study iteration of polynomials on symmetric stochastic matrices. In particular, we focus on a certain one-parameter family
of quadratic maps which exhibits chaotic behavior for a wide range of the parameters. The well-known dynamical behavior of
the quadratic family on the interval, and its dependence on the parameter, is reproduced on the spectrum of the stochastic
matrices. For certain subclasses of stochastic matrices the referred dynamical behavior is also obtained in the matrix entries.
Since a stochastic matrix characterizes a Markov chain, we obtain a discrete dynamical system on the space of reversible Markov
chains. Therefore, depending on the parameter, there are initial conditions for which the corresponding reversible Markov
chains will lead under iteration to a fixed point, to a periodic point, or to an aperiodic point. Moreover, there are sensitivity
to initial conditions and the coexistence of infinite repulsive periodic orbits, both features of chaos. 相似文献
170.
In the context of non-abelian gerbes, we define a cubical version of categorical group 2-bundles with connection over a smooth manifold. We address their two-dimensional parallel transport, study its properties, and construct non-abelian Wilson surface functionals. 相似文献