全文获取类型
收费全文 | 10012篇 |
免费 | 972篇 |
国内免费 | 861篇 |
专业分类
化学 | 1388篇 |
晶体学 | 92篇 |
力学 | 994篇 |
综合类 | 165篇 |
数学 | 6974篇 |
物理学 | 2232篇 |
出版年
2024年 | 19篇 |
2023年 | 92篇 |
2022年 | 124篇 |
2021年 | 165篇 |
2020年 | 255篇 |
2019年 | 297篇 |
2018年 | 266篇 |
2017年 | 301篇 |
2016年 | 326篇 |
2015年 | 267篇 |
2014年 | 466篇 |
2013年 | 823篇 |
2012年 | 445篇 |
2011年 | 556篇 |
2010年 | 463篇 |
2009年 | 568篇 |
2008年 | 616篇 |
2007年 | 619篇 |
2006年 | 533篇 |
2005年 | 515篇 |
2004年 | 446篇 |
2003年 | 426篇 |
2002年 | 446篇 |
2001年 | 367篇 |
2000年 | 337篇 |
1999年 | 320篇 |
1998年 | 273篇 |
1997年 | 252篇 |
1996年 | 185篇 |
1995年 | 134篇 |
1994年 | 118篇 |
1993年 | 87篇 |
1992年 | 72篇 |
1991年 | 80篇 |
1990年 | 54篇 |
1989年 | 65篇 |
1988年 | 52篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 52篇 |
1984年 | 53篇 |
1983年 | 33篇 |
1982年 | 38篇 |
1981年 | 27篇 |
1980年 | 21篇 |
1979年 | 39篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1976年 | 15篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Chemical bonding in representative astrophysically relevant neutral,cation, and anion HCnH chains
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ioan Baldea 《中国物理 B》2022,31(12):123101-123101
Most existing studies assign a polyynic and cumulenic character of chemical bonding in carbon-based chains relying on values of the bond lengths. Building on our recent work, in this paper we add further evidence on the limitations of such an analysis and demonstrate the significant insight gained via natural bond analysis. Presently reported results include atomic charges, natural bond order and valence indices obtained from ab initio computations for representative members of the astrophysically relevant neutral and charged HC2k/2k+1H chain family. They unravel a series of counter-intuitive aspects and/or help naive intuition in properly understanding microscopic processes, e.g., electron removal from or electron attachment to a neutral chain. Demonstrating that the Wiberg indices adequately quantify the chemical bonding structure of the HC2k/2k+1H chains—while the often heavily advertised Mayer indices do not—represents an important message conveyed by the present study. 相似文献
3.
We describe a unified approach for studying book, point-set, and simultaneous embeddability problems of upward planar digraphs. The approach is based on a linear time strategy to compute an upward planar drawing of an upward planar digraph such that all vertices are collinear. Besides having impact in relevant application domains of graph drawing and computational geometry, the presented results open new research directions in the area of upward planarity with constraints of the positions of the vertices. 相似文献
4.
Thalia Tsiaka Panagiotis Zoumpoulakis Vassilia J. Sinanoglou Constantinos Makris Georgios A. Heropoulos Antony C. Calokerinos 《Analytica chimica acta》2015
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE. 相似文献
5.
Nitin P. Lobo K.V. Ramanathan T. Narasimhaswamy 《Magnetic resonance in chemistry : MRC》2020,58(11):988-1009
In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one- and two-dimensional (2D) solid-state 13C nuclear magnetic resonance (NMR) spectroscopy are described. Besides 13C chemical shifts, the 13C─1H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the 13C─1H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B1 and B2 mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state 13C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed. 相似文献
6.
The zero dissipation limit of the one-dimensional non-isentropic micropolar equations is studied in this paper. If the given rarefaction wave which connects to vacuum at one side, a sequence of solution to the micropolar equations can be constructed which converge to the above rarefaction wave with vacuum as the viscosity and the heat conduction coefficient tend to zero. Moreover, the uniform convergence rate is obtained. The key point in our analysis is how to control the degeneracies in the vacuum region in the zero dissipation limit process. 相似文献
7.
8.
9.
Lin Surong 《Annals of Differential Equations》2006,22(4):517-523
The singularly perturbed boundary value problem for nonlinear higher order ordinary differential equation involving two small parameters has been considered. Under appropriate assumptions, for the three cases:ε/μ2→0(μ→0),μ2/ε→0 (ε→0) andε=μ2, the uniformly valid asymptotic solution is obtained by using the expansion method of two small parameters and the theory of differential inequality. 相似文献
10.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献