全文获取类型
收费全文 | 1062篇 |
免费 | 33篇 |
国内免费 | 12篇 |
专业分类
化学 | 664篇 |
晶体学 | 11篇 |
力学 | 36篇 |
数学 | 258篇 |
物理学 | 138篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 45篇 |
2020年 | 36篇 |
2019年 | 20篇 |
2018年 | 31篇 |
2017年 | 22篇 |
2016年 | 54篇 |
2015年 | 33篇 |
2014年 | 43篇 |
2013年 | 86篇 |
2012年 | 78篇 |
2011年 | 73篇 |
2010年 | 62篇 |
2009年 | 55篇 |
2008年 | 57篇 |
2007年 | 69篇 |
2006年 | 44篇 |
2005年 | 42篇 |
2004年 | 49篇 |
2003年 | 28篇 |
2002年 | 35篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
排序方式: 共有1107条查询结果,搜索用时 18 毫秒
81.
Let T
n
be the complete binary tree of height n considered as the Hasse-diagram of a poset with its root 1
n
as the maximum element. For a rooted tree T, define two functions counting the embeddings of T into T
n
as follows A(n;T)=|{S
T
n
: 1
n
∈S, S≅T}|, and B(n;T)=|{S
T
n
:1
n
∉S, S≅T}|. In this paper we investigate the asymptotic behavior of the ratio A(n;T)/B(n;T), and we show that lim
n→∞[A(n;T)/B(n;T)]=2ℓ;−1−1, for any tree T with ℓ leaves.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
82.
83.
Grzegorz Stepniak Lukasz Maksymiuk Jerzy Siuzdak 《Optical and Quantum Electronics》2007,39(15):1281-1288
Frequency response of passive optical network (PON) based on multimode fibers is investigated. The network comprises fibers,
connectors and splitters/couplers. It is shown that due to mode filtering at splitters, the frequency response is different
for different network nodes in otherwise symmetrical network. 相似文献
84.
85.
It is known that the orbit closures for the representations of the equioriented Dynkin quivers ?
n
are normal and Cohen–Macaulay varieties with rational singularities. In the paper we prove the same for the Dynkin quivers
?
n
with arbitrary orientation.
Received: 25 October 2000 / Revised version: 28 February 2001 相似文献
86.
Frances Y. Kuo Grzegorz W. Wasilkowski Henryk Wo
niakowski 《Journal of Approximation Theory》2008,152(2):135-160
We study the worst case setting for approximation of d variate functions from a general reproducing kernel Hilbert space with the error measured in the L∞ norm. We mainly consider algorithms that use n arbitrary continuous linear functionals. We look for algorithms with the minimal worst case errors and for their rates of convergence as n goes to infinity. Algorithms using n function values will be analyzed in a forthcoming paper.We show that the L∞ approximation problem in the worst case setting is related to the weighted L2 approximation problem in the average case setting with respect to a zero-mean Gaussian stochastic process whose covariance function is the same as the reproducing kernel of the Hilbert space. This relation enables us to find optimal algorithms and their rates of convergence for the weighted Korobov space with an arbitrary smoothness parameter α>1, and for the weighted Sobolev space whose reproducing kernel corresponds to the Wiener sheet measure. The optimal convergence rates are n-(α-1)/2 and n-1/2, respectively.We also study tractability of L∞ approximation for the absolute and normalized error criteria, i.e., how the minimal worst case errors depend on the number of variables, d, especially when d is arbitrarily large. We provide necessary and sufficient conditions on tractability of L∞ approximation in terms of tractability conditions of the weighted L2 approximation in the average case setting. In particular, tractability holds in weighted Korobov and Sobolev spaces only for weights tending sufficiently fast to zero and does not hold for the classical unweighted spaces. 相似文献
87.
In this paper we discuss a minmax regret version of the single-machine scheduling problem with the total flow time criterion. Uncertain processing times are modeled by closed intervals. We show that if the deterministic problem is polynomially solvable, then its minmax regret version is approximable within 2. 相似文献
88.
Tomasz Smolinski Danuta Wawszczak Andrzej Deptula Wieslawa Lada Tadeusz Olczak Marcin Rogowski Marta Pyszynska Andrzej Grzegorz Chmielewski 《Journal of Radioanalytical and Nuclear Chemistry》2017,313(1):69-77
A micro-cloud point extraction method was discussed for preconcentration and spectrophotometric quantification of U(VI). The method depends on complex formation between U(VI) and 2-(4-sulphophenyloazo)-1,8-dihydroxy-3,6-naphtalenedisulphonic acid (SPADNS) at pH 7.0 and subsequent extraction of the complex in a mixed surfactant medium (cethyltrimethyl ammonium bromide and Triton X-114). The separation was carried out in the presence of 1% Na2SO4 at room temperature. The calibration curve was linear up to 3000 µg L?1. The enrichment factor, detection limit and precision were 16.0, 1.05 µg L?1, and 2.3%, respectively. The method was employed for the determination of U(VI) in real samples with different matrices. 相似文献
89.
McIntosh JA Robertson CR Agarwal V Nair SK Bulaj GW Schmidt EW 《Journal of the American Chemical Society》2010,132(44):15499-15501
A protease from ribosomal peptide biosynthesis macrocyclizes diverse substrates, including those resembling nonribosomal peptide and hybrid polyketide-peptide products. The proposed mechanism is analogous to thioesterase-catalyzed chemistry, but the substrates are amide bonds rather than thioesters. 相似文献
90.
A series of vanadium(V) complexes with unsymmetrical tridentate Schiff base ligands, obtained by the single condensation of R(−)-1,2-diaminopropane with salicylaldehyde and its derivatives, 2-hydroxy-1-naphthaldehyde, 2-hydroxyacetophenone, 1-hydroxy-2-acetonaphthone and 2-hydroxybenzophenone, were prepared. The complexes were characterized by elemental analysis and by their IR, CD, UV–Vis, 1D (1H, 51V) and 2D (COSY, NOESY, gHSQC) NMR spectra. Crystal structures of the mononuclear complex {R(−)-2-amino-1-N-[(2′-oxido-κO-4′,6′-dimethoxyphenyl)methylene]aminopropane-κ2N}dioxidovanadium(V), VO2(C12H17N2O3), 4, and of the dinuclear complex, di-μ-oxido-bis({R(−)-2-[1-(2-aminopropylimino)ethyl]-4-methylphenolato-κ3N,N′,O}oxidovanadium(V)), V2O4(C11H15N2O)2, 5, have been obtained by X-ray diffraction studies. The structure of 4 was revealed to be a distorted trigonal–bipyramidal coordination geometry, rarely encountered in VO2(tridentate Schiff base) complexes. Complexes 2 and 3 have the ability to catalyze the oxidation of prochiral sulfide substrates PhSR (R = Me, Bz) utilizing hydrogen peroxide or cumene hydroperoxide (CHPO) as the oxidant. 相似文献