首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2095篇
  免费   226篇
  国内免费   173篇
化学   203篇
晶体学   1篇
力学   166篇
综合类   43篇
数学   1684篇
物理学   397篇
  2023年   14篇
  2022年   29篇
  2021年   61篇
  2020年   50篇
  2019年   47篇
  2018年   56篇
  2017年   71篇
  2016年   58篇
  2015年   55篇
  2014年   87篇
  2013年   149篇
  2012年   84篇
  2011年   104篇
  2010年   95篇
  2009年   113篇
  2008年   133篇
  2007年   117篇
  2006年   108篇
  2005年   123篇
  2004年   89篇
  2003年   95篇
  2002年   90篇
  2001年   80篇
  2000年   65篇
  1999年   60篇
  1998年   56篇
  1997年   55篇
  1996年   40篇
  1995年   35篇
  1994年   39篇
  1993年   21篇
  1992年   13篇
  1991年   21篇
  1990年   14篇
  1989年   14篇
  1988年   13篇
  1987年   10篇
  1986年   11篇
  1985年   17篇
  1984年   15篇
  1983年   5篇
  1982年   10篇
  1981年   8篇
  1980年   11篇
  1979年   16篇
  1978年   12篇
  1977年   6篇
  1976年   7篇
  1975年   5篇
  1974年   6篇
排序方式: 共有2494条查询结果,搜索用时 31 毫秒
1.
2.
3.
We investigate cosmological dark energy models where the accelerated expansion of the universe is driven by a field with an anisotropic universe. The constraints on the parameters are obtained by maximum likelihood analysis using observational of 194 Type Ia supernovae(SNIa) and the most recent joint light-curve analysis(JLA) sample. In particular we reconstruct the dark energy equation of state parameter w(z) and the deceleration parameter q(z). We find that the best fit dynamical w(z) obtained from the 194 SNIa dataset does not cross the phantom divide line w(z) =-1 and remains above and close to w(z)≈-0.92 line for the whole redshift range 0 ≤ z ≤ 1.75 showing no evidence for phantom behavior. By applying the anisotropy effect on the ΛCDM model, the joint analysis indicates that ?_(σ0)= 0.0163 ± 0.03,with 194 SNIa, ?_(σ0)=-0.0032 ± 0.032 with 238 the SiFTO sample of JLA and ?_(σ0)= 0.011 ± 0.0117 with 1048 the SALT2 sample of Pantheon at 1σ′confidence interval. The analysis shows that by considering the anisotropy, it leads to more best fit parameters in all models with JLA SNe datasets. Furthermore, we use two statistical tests such as the usual χ_(min)~2/dof and p-test to compare two dark energy models with ΛCDM model. Finally we show that the presence of anisotropy is confirmed in mentioned models via SNIa dataset.  相似文献   
4.
A clique (resp, independent set) in a graph is strong if it intersects every maximal independent set (resp, every maximal clique). A graph is clique intersect stable set (CIS) if all of its maximal cliques are strong and localizable if it admits a partition of its vertex set into strong cliques. In this paper we prove that a clique C in a vertex-transitive graph Γ is strong if and only if ◂=▸◂⋅▸CI=V(Γ) for every maximal independent set I of Γ. On the basis of this result we prove that a vertex-transitive graph is CIS if and only if it admits a strong clique and a strong independent set. We classify all vertex-transitive graphs of valency at most 4 admitting a strong clique, and give a partial characterization of 5-valent vertex-transitive graphs admitting a strong clique. Our results imply that every vertex-transitive graph of valency at most 5 that admits a strong clique is localizable. We answer an open question by providing an example of a vertex-transitive CIS graph which is not localizable.  相似文献   
5.
6.
In the United States, the NATO Reference Mobility Model (NRMM) has been used for evaluating military ground vehicle mobility and the Vehicle Cone Index (VCI) has been selected as a mobility metric. VCI represents the minimum soil strength required for a vehicle to consistently make a specific number of passes, usually one or fifty passes. In the United Kingdom, the Mean Maximum Pressure (MMP) has been adopted as a metric for assessing military vehicle cross-country mobility. MMP is the mean value of the maxima occurring under all the wheel stations of a vehicle. Both VCI and MMP are empirically based. This paper presents a review of the basis upon which VCI and MMP were developed, as well as their applications to evaluating vehicle mobility in practice. With the progress in terramechanics and in modelling and simulation techniques in recent years, there is a growing desire to develop physics-based mobility metrics for next generation vehicle mobility models. Based on the review, criteria for selecting physics-based mobility metrics are proposed. Following these criteria, metrics for characterizing military vehicle traction limits and traversability on a given operating area are recommended.  相似文献   
7.
8.
It is considered the class of Riemann surfaces with dimT1 = 0, where T1 is a subclass of exact harmonic forms which is one of the factors in the orthogonal decomposition of the spaceΩH of harmonic forms of the surface, namely The surfaces in the class OHD and the class of planar surfaces satisfy dimT1 = 0. A.Pfluger posed the question whether there might exist other surfaces outside those two classes. Here it is shown that in the case of finite genus g, we should look for a surface S with dimT1 = 0 among the surfaces of the form Sg\K , where Sg is a closed surface of genus g and K a compact set of positive harmonic measure with perfect components and very irregular boundary.  相似文献   
9.
Aromatic components are important functional products during the wine fermentation process. In the current study, nine strains (Y10, Y5, Y21, Y2, Y19, Y16, Y3, Y13 and Y4) of non-Saccharomyces were isolated from Cabernet Sauvignon grape wine. Aromatic components from Cabernet sauvignon-fermented wine were determined the phylogenetic evolution status of different non-Saccharomyces based on 26S rDNA and D1/D2 sequence analysis and analysed by a gas chromatography–mass spectrometry analysis, and they were grouped into one category with four different yeast genus which were Meyerozyma guilliermondii, Brettanomyces naardenensis, Pichia guilliermondi and Candida fermentati. A total of 102 kinds of aroma components were detected, including 39 kinds of esters, 31 kinds of alcohols, 8 kinds of ketones, 10 kinds of alkanes, 15 kinds of acids and 4 kinds of other aroma substances.  相似文献   
10.
This paper analyzes data from experiments on simple polymer chains. It measures the extent to which a particular monomer prefers to link with another of the same type. To analyze the data, it derives the likelihood function for a two‐state Markov model in which only the number in each state, but not the order, is observed. This technology is applied to a data set on which experimenters mixed lactic‐glycolic monomers with a known proportion of a contaminant consisting of an extra lactic acid. The resulting copolymers were subjected to matrix‐assisted laser desorption ionization mass spectrometry. This records the number of copolymers at each atomic weight, which can be associated with a given length of copolymer and number of contaminant monomers. Analysis of the data shows that the proportion of contaminant monomers exceeded the proportion of experimentally induced contaminant. Maximum likelihood estimates using the data show that lactic‐glycolic monomers show a positive affinity for the contaminant. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号