全文获取类型
收费全文 | 1174篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 908篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 169篇 |
物理学 | 118篇 |
出版年
2023年 | 9篇 |
2022年 | 55篇 |
2021年 | 62篇 |
2020年 | 54篇 |
2019年 | 33篇 |
2018年 | 34篇 |
2017年 | 26篇 |
2016年 | 54篇 |
2015年 | 54篇 |
2014年 | 48篇 |
2013年 | 83篇 |
2012年 | 71篇 |
2011年 | 85篇 |
2010年 | 62篇 |
2009年 | 55篇 |
2008年 | 71篇 |
2007年 | 58篇 |
2006年 | 51篇 |
2005年 | 41篇 |
2004年 | 44篇 |
2003年 | 32篇 |
2002年 | 27篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1992年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1936年 | 2篇 |
1927年 | 2篇 |
1924年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有1208条查询结果,搜索用时 31 毫秒
101.
Gabriela Wallova Norbert Kandler Gabriele Wallner 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(2):429-433
This work describes a procedure for the isolation of 90Sr and 210Pb from deer bones by anion exchange methods and their sequential measurement by LSC. To prevent collection of Pb on the Sr·Spec® resin we first separated Pb on a Dowex anion exchange column. Sr, which is not held back on the Dowex column, was then purified using Sr·Spec® resin: first Ca and the Ra isotopes were eluted with 3 M HNO3 and then Sr was eluted with distilled water. With this 2-steps procedure pure 210Pb and 90Sr spectra can be achieved. The chemical yield of both steps was determined by ICP-MS. Our 90Sr results show satisfying agreement with data obtained by a shorter Sr·Spec® method and also by the “classical” 90Sr determination using fuming nitric acid. Also 210Pb results were checked by re-measuring bone samples with already known 210Pb activities. Further our method was verified on the reference sample IAEA-A-12. 相似文献
102.
In this paper we are concerned with solutions, in particular with univalent solutions, of the Loewner differential equation
associated with non-normalized subordination chains on the Euclidean unit ball B
n
in
\mathbbCn{\mathbb{C}^n}. The main result is a generalization to higher dimensions of a well known result due to Becker. Various particular cases
of this result have been recently obtained for subordination chains with normalization Df(0,t)=etIn{Df(0,t)=e^tI_n} or Df(0, t) = e
tA
, t ≥ 0, where
A ? L(\mathbbCn,\mathbbCn){A\in L(\mathbb{C}^n,\mathbb{C}^n)}. We also determine the form of the standard solutions to the Loewner differential equation associated with generalized spirallike
mappings. In the last section we obtain the form of the solution in the presence of coefficient bounds. 相似文献
103.
Magdalena Ulmeanu Iuliana Iordache Mihaela Filipescu Valentin Craciun Simona Cinta Pinzaru Andreas Hörner 《Central European Journal of Physics》2011,9(5):1280-1287
Experimental studies on patterning hexagonal Ge nanostructures have been conducted on Si substrates through deposition of
Ge with colloidal particles as a mask. The deposited Ge thin film possesses, according to the X-ray diffraction measurements,
in plane texture, being epitaxial and aligned with the (111) Si substrate. The size distribution of the patterned Ge nanostructures
is narrow, as indicated by the atomic force microscopy and scanning electron microscopy measurements. We have obtained Ge
nanostructures with lateral dimension of 490 nm (height 12 nm), 200 nm (height 6 nm) and 82 nm (height 6 nm) by using different
sizes of polystyrene spheres. We have performed in depth studies of the Ge nanostructures’ behavior due to thermal and rapid
thermal post-annealing processes. FT micro-Raman spectroscopy shows that there is no Si intermixing during the annealing process.
In order to quantify the changes in the height and lateral dimension, we have performed atomic force microscopy and white
light interferometry analysis. The changes in shape and the decrease in the area of a cross-section of Ge nanostructure will
be discussed in respect to similar results shown in the literature for Ge thin films during the annealing process. 相似文献
104.
105.
In this paper we consider the motion of a rigid body in a viscous incompressible fluid when some Navier slip conditions are prescribed on the body's boundary. The whole system “viscous incompressible fluid + rigid body” is assumed to occupy the full space R3. We start by proving the existence of global weak solutions to the Cauchy problem. Then, we exhibit several properties of these solutions. First, we show that the added-mass effect can be computed which yields better-than-expected regularity (in time) of the solid velocity-field. More precisely we prove that the solid translation and rotation velocities are in the Sobolev space H1. Second, we show that the case with the body fixed can be thought as the limit of infinite inertia of this system, that is when the solid density is multiplied by a factor converging to +∞. Finally we prove the convergence in the energy space of weak solutions “à la Leray” to smooth solutions of the system “inviscid incompressible fluid + rigid body” as the viscosity goes to zero, till the lifetime T of the smooth solution of the inviscid system. Moreover we show that the rate of convergence is optimal with respect to the viscosity and that the solid translation and rotation velocities converge in H1(0,T). 相似文献
106.
Jorge A. Soria-Alcaraz Gabriela Ochoa Jerry Swan Martin Carpio Hector Puga Edmund K. Burke 《European Journal of Operational Research》2014
Course timetabling is an important and recurring administrative activity in most educational institutions. This article combines a general modeling methodology with effective learning hyper-heuristics to solve this problem. The proposed hyper-heuristics are based on an iterated local search procedure that autonomously combines a set of move operators. Two types of learning for operator selection are contrasted: a static (offline) approach, with a clear distinction between training and execution phases; and a dynamic approach that learns on the fly. The resulting algorithms are tested over the set of real-world instances collected by the first and second International Timetabling competitions. The dynamic scheme statistically outperforms the static counterpart, and produces competitive results when compared to the state-of-the-art, even producing a new best-known solution. Importantly, our study illustrates that algorithms with increased autonomy and generality can outperform human designed problem-specific algorithms. 相似文献
107.
Gabriela Marinoschi 《Journal of Optimization Theory and Applications》2014,161(2):430-445
We provide existence results for nonlinear diffusion equations with multivalued time-dependent nonlinearities related to convex continuous not coercive potentials. The results in this paper, following a variational principle, state that a generalized solution of the nonlinear equation can be retrieved as a solution of an appropriate minimization problem for a convex functional involving the potential and its conjugate. In the not coercive case, this assertion is conditioned by the validity of a relation between the solution and the nonlinearity. A sufficient condition, under which this relation is true, is given. At the end, we present a discussion on the solution existence for a particular equation describing a self-organized criticality model. 相似文献
108.
109.
110.
Ohne Zusammenfassung 相似文献