全文获取类型
收费全文 | 4405篇 |
免费 | 1177篇 |
国内免费 | 321篇 |
专业分类
化学 | 1125篇 |
晶体学 | 22篇 |
力学 | 862篇 |
综合类 | 59篇 |
数学 | 420篇 |
物理学 | 3415篇 |
出版年
2024年 | 12篇 |
2023年 | 40篇 |
2022年 | 129篇 |
2021年 | 152篇 |
2020年 | 142篇 |
2019年 | 134篇 |
2018年 | 135篇 |
2017年 | 193篇 |
2016年 | 250篇 |
2015年 | 185篇 |
2014年 | 335篇 |
2013年 | 325篇 |
2012年 | 317篇 |
2011年 | 328篇 |
2010年 | 214篇 |
2009年 | 249篇 |
2008年 | 289篇 |
2007年 | 275篇 |
2006年 | 258篇 |
2005年 | 232篇 |
2004年 | 177篇 |
2003年 | 190篇 |
2002年 | 165篇 |
2001年 | 153篇 |
2000年 | 141篇 |
1999年 | 133篇 |
1998年 | 101篇 |
1997年 | 91篇 |
1996年 | 98篇 |
1995年 | 70篇 |
1994年 | 57篇 |
1993年 | 48篇 |
1992年 | 42篇 |
1991年 | 37篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 18篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有5903条查询结果,搜索用时 328 毫秒
121.
出行者的选择行为分析是交通系统中的一项重要内容,随着城市的发展,交通出行方式大体分为三大类:公共交通出行、辅助公共交通出行和私人交通出行。本文在以往的研究基础上,采用演化博弈的方法研究公共交通、共享汽车以及私家车三者之间的博弈关系,模拟出行者的选择行为,分析博弈均衡点稳定性及参数条件。通过模型仿真实验,演化结果中各项比例大小取决于各项收益、补贴、损失以及额外收益,要增加公共交通的配套设施,增收拥堵费以及增加对共享汽车的补贴及配套服务。 相似文献
122.
123.
An improved algorithm for the shallow water equations model reduction: Dynamic Mode Decomposition vs POD 下载免费PDF全文
We propose an improved framework for dynamic mode decomposition (DMD) of 2‐D flows for problems originating from meteorology when a large time step acts like a filter in obtaining the significant Koopman modes, therefore, the classic DMD method is not effective. This study is motivated by the need to further clarify the connection between Koopman modes and proper orthogonal decomposition (POD) dynamic modes. We apply DMD and POD to derive reduced order models (ROM) of the shallow water equations. Key innovations for the DMD‐based ROM introduced in this paper are the use of the Moore–Penrose pseudoinverse in the DMD computation that produced an accurate result and a novel selection method for the DMD modes and associated amplitudes and Ritz values. A quantitative comparison of the spatial modes computed from the two decompositions is performed, and a rigorous error analysis for the ROM models obtained is presented. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
124.
In this paper an inclined edge cracked short beam specimen subjected to symmetric three-point bend loading was designed and examined for conducting mixed-mode I/II fracture toughness experiments. The aspect ratio (i.e. length to width ratio) and the loading span distance are considered much lower than the other conventional cracked bend beam samples. Crack tip parameters such as stress intensity factors and T-stress were computed numerically for this specimen by several finite element analyses and it was demonstrated that the specimen is able to produce full combinations of mode I and II including pure mode II. The practical capability of the short bend beam specimen was studied experimentally by conducting a set of mixed-mode fracture tests on PolymethylMethacrylate (PMMA) as a well-known model brittle material. The critical stress intensity factors, the direction of fracture kinking and the path of fracture trajectory were investigated both experimentally and theoretically using two stress and strain-based fracture criteria. The fracture toughness of tested PMMA was decreased by moving towards mode II case due to the effect of T-stress on the fracture mechanism of the short bend beam specimen. 相似文献
125.
126.
Mohammad Pourmahmood Aghababa 《Communications in Nonlinear Science & Numerical Simulation》2012,17(3):1489-1492
The aim of this note is to point out some comments to the article [Delavari H, Ghaderi R, Ranjbar A, Momani S. Fuzzy fractional order sliding mode controller for nonlinear systems, Commun Nonlinear Sci Numer Simulat 15 (2010) 963-978]. 相似文献
127.
The quantum dynamics of carriers bound to helical tube surfaces is investigated in a thin-layer quantization scheme. By numerically solving the open-boundary Schrödinger equation in curvilinear coordinates, geometric effect on the coherent transmission spectra is analysed in the case of single propagating mode as well as multimode. It is shown that, the coiling endows the helical nanotube with different transport properties from a bent cylindrical surface. Fano resonance appears as a purely geometric effect in the conductance, the corresponding energy of quasibound state is obviously influenced by the torsion and length of the nanotube. We also find new plateaus in the conductance. The transport of double-degenerate mode in this geometry is reminiscent of the Zeeman coupling between the magnetic field and spin angular momentum in quasi-one-dimensional structure. 相似文献
128.
Lidiya I. Kursheva Olga N. Kataeva Dmitrii B. Krivolapov Elvira S. Batyeva Oleg G. Sinyashin 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1425-1426
Abstract The synthesis and coordination chemistry of ligands bearing PS donor groups in complexes with copper(I) halides, in particular thiophosphites, thiophosphonites, and thiophosphinites, are described. 相似文献
129.
《化学:亚洲杂志》2017,12(3):324-331
This work illustrates several theoretical fundamentals for the application of THz vibrational spectroscopy to molecular characterization in the solid state using two different types of saccharide systems as examples. Four subjects have been specifically addressed: (1) the qualitative differences in the molecular vibrational signatures monitored by THz and mid‐IR vibrational spectroscopy; (2) the selection rules for THz vibrational spectroscopy as applied to crystalline and amorphous systems; (3) a normal mode simulation, using α‐l ‐xylose as an example; and (4) a rigorous mode analysis to quantify the percentage contributions of the intermolecular and intramolecular vibrations to the normal mode of interest. 相似文献
130.
“奇妙的化学世界”是天津师范大学面向全校非化学专业的本科生开设的一门通识选修课。课程主要采用启发式教学模式、案例式教学模式、互动式教学模式等相结合的混合式教学模式,涉及当今活跃的科研领域和生活实际。课程采用多种方式如图片展示、教学辅助视频、小组讨论、调查问卷等,调动学生的积极性和主动性,使学生在较为轻松的状态下掌握课程内容。此外,力求做到集知识性、实用性、趣味性于一体,避免了化学专业课程中的复杂多变的化学结构描述。 相似文献