全文获取类型
收费全文 | 2414篇 |
免费 | 314篇 |
国内免费 | 320篇 |
专业分类
化学 | 168篇 |
晶体学 | 2篇 |
力学 | 150篇 |
综合类 | 86篇 |
数学 | 1935篇 |
物理学 | 707篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 47篇 |
2021年 | 52篇 |
2020年 | 54篇 |
2019年 | 62篇 |
2018年 | 71篇 |
2017年 | 78篇 |
2016年 | 77篇 |
2015年 | 63篇 |
2014年 | 100篇 |
2013年 | 237篇 |
2012年 | 115篇 |
2011年 | 133篇 |
2010年 | 144篇 |
2009年 | 139篇 |
2008年 | 183篇 |
2007年 | 186篇 |
2006年 | 158篇 |
2005年 | 143篇 |
2004年 | 116篇 |
2003年 | 120篇 |
2002年 | 118篇 |
2001年 | 94篇 |
2000年 | 108篇 |
1999年 | 94篇 |
1998年 | 53篇 |
1997年 | 57篇 |
1996年 | 53篇 |
1995年 | 36篇 |
1994年 | 22篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有3048条查询结果,搜索用时 15 毫秒
991.
In this paper, we study a two-dimensional piecewise smooth map arising in ecology. Such map, containing two parameters d and β, is derived from a model describing how masting of a mature forest happens and synchronizes. Here d is the energy depletion quantity and β is the coupling strength. Our main results are the following. First, we obtain a “weak” Sharkovskii ordering for the map on its nondiagonal invariant region for a certain set of parameters. In particular, we show that its Sharkovskii ordering is the natural number (resp., the positive even number) for β>1 (resp., 0<β<1). Second, we obtain a region of parameter space for which its corresponding global dynamics can be completely characterized. 相似文献
992.
993.
R. Casadio M. Compiani P. Fariselli I. Jacoboni P. L. Martelli 《SAR and QSAR in environmental research》2013,24(2):149-182
Abstract In the genomic era DNA sequencing is increasing our knowledge of the molecular structure of genetic codes from bacteria to man at a hyperbolic rate. Billions of nucleotides and millions of aminoacids are already filling the electronic files of the data bases presently available, which contain a tremendous amount of information on the most biologically relevant macromolecules, such as DNA. RNA and proteins. The most urgent problem originates from the need to single out the relevant information amidst a wealth of general features. Intelligent tools are therefore needed to optimise the search. Data mining for sequence analysis in biotechnology has been substantially aided by the development of new powerful methods borrowed from the machine learning approach. In this paper we discuss the application of artificial feedforward neural networks to deal with some fundamental problems tied with the folding process and the structure-function relationship in proteins. 相似文献
994.
SSThread: Template‐free protein structure prediction by threading pairs of contacting secondary structures followed by assembly of overlapping pairs
下载免费PDF全文
![点击此处可从《Journal of computational chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kevin J. Maurice 《Journal of computational chemistry》2014,35(8):644-656
Acquiring the three‐dimensional structure of a protein from its amino acid sequence alone, despite a great deal of work and significant progress on the subject, is still an unsolved problem. SSThread, a new template‐free algorithm is described here that consists of making several predictions of contacting pairs of α‐helices and β‐strands derived from a database of experimental structures using a knowledge‐based potential, secondary structure prediction, and contact map prediction followed by assembly of overlapping pair predictions to create an ensemble of core structure predictions whose loops are then predicted. In a set of seven CASP10 targets SSThread outperformed the two leading methods for two targets each. The targets were all β‐strand containing structures and most of them have a high relative contact order which demonstrates the advantages of SSThread. The primary bottlenecks based on sets of 74 and 21 test cases are the pair prediction and loop prediction stages. © 2014 Wiley Periodicals, Inc. 相似文献
995.
For finite semidistributive lattices the map κ gives a bijection between the sets of completely join-irreducible elements and completely meet-irreducible elements.Here we study the κ-map in the context of torsion classes. It is well-known that the lattice of torsion classes for an artin algebra is semidistributive, but in general it is far from finite. We show the κ-map is well-defined on the set of completely join-irreducible elements, even when the lattice of torsion classes is infinite. We then extend κ to a map on torsion classes which have canonical join representations given by the special torsion classes associated to the minimal extending modules introduced by the first and third authors and A. Carroll in 2019.For hereditary algebras, we show that the extended κ-map on torsion classes is essentially the same as Ringel's ?-map on wide subcategories. Also in the hereditary case, we relate the square of κ to the Auslander-Reiten translation. 相似文献
996.
The secant caustic of a planar curve M is the image of the singular set of the secant map of M. We analyze the geometrical properties of the secant caustic of a planar curve, i.e. the number of branches of the secant caustic, the parity of the number of cusps and the number of inflexion points in each branch of this set. In particular, we investigate in detail some of the geometrical properties of the secant caustic of a rosette, i.e. a smooth regular oriented closed curve with non-vanishing curvature. 相似文献
997.
In this paper, we propose a new method to study intermittent behaviors of coupled piecewise-expanding map lattices. We show that the successive transition between ordered and disordered phases occurs for almost every orbit when the coupling is small. That is,where $x_i(n)$ correspond to the coordinates of $m$ nodes at the iterative step $n$. Moreover, when the uncoupled system is generated by the tent map and the lattice consists of two nodes, we prove a phase transition occurs between synchronization and intermittent behaviors. That is, $$\lim_{n\rightarrow \infty}| x_1(n)-x_2(n)|=0\quad\text{for }\ \ \Big|c-\frac12\Big|<\frac14$$ and intermittent behaviors occur for $|c-\frac12|>\frac14$, where $0\le c\le 1$ is the coupling. 相似文献
998.
利用已知的KKM型定理,在广义空间上得到若干个新的重合点定理和推广的Fan-Browder型不动点定理,并且讨论了Von Newmann-Sion型极大极小不等式.主要结果改进和推广了文献中的相应结论. 相似文献
999.
设E是一致凸Banach空间,K是E中非空闭凸集且是一个非扩张收缩核,T:K→E是具非空不动点集F(T):={x∈K:Tx=x}的非扩张映像.设{α_n},{β_n},{γ_n},{α′_n},{β′_n},{γ′_n}是[0,1]中实数列满足α_n+β_n+γ_n=α′_n+γ′_n+γ′_n=1,对任意初值x_1∈K,定义{x_n}如下(ⅰ)如果对偶空间E*具有Kadec-Klee性质,那么{x_n}弱收敛于T的某不动点x*∈F(T);(ⅱ)若T满足(A)条件,那么{x_n}强收敛于T的某不动点x*∈F(T). 相似文献
1000.
In this paper, we introduce a new notion named as Schrödinger soliton. The so-called Schrödinger solitons are a class of solitary wave solutions to the Schrödinger flow equation from a Riemannian manifold or a Lorentzian manifold M into a Kähler manifold N. If the target manifold N admits a Killing potential, then the Schrödinger soliton reduces to a harmonic map with potential from M into N. Especially, when the domain manifold M is a Lorentzian manifold, the Schrödinger soliton is a wave map with potential into N. Then we apply the geometric energy method to this wave map system, and obtain the local well-posedness of the corresponding Cauchy problem as well as global existence in 1+1 dimension. As an application, we obtain the existence of Schrödinger soliton solution to the hyperbolic Ishimori system. 相似文献