全文获取类型
收费全文 | 39941篇 |
免费 | 7167篇 |
国内免费 | 5341篇 |
专业分类
化学 | 28976篇 |
晶体学 | 539篇 |
力学 | 2493篇 |
综合类 | 484篇 |
数学 | 4608篇 |
物理学 | 15349篇 |
出版年
2024年 | 65篇 |
2023年 | 785篇 |
2022年 | 899篇 |
2021年 | 1278篇 |
2020年 | 1634篇 |
2019年 | 1594篇 |
2018年 | 1314篇 |
2017年 | 1282篇 |
2016年 | 1859篇 |
2015年 | 1900篇 |
2014年 | 2272篇 |
2013年 | 2887篇 |
2012年 | 3612篇 |
2011年 | 3842篇 |
2010年 | 2670篇 |
2009年 | 2539篇 |
2008年 | 2834篇 |
2007年 | 2606篇 |
2006年 | 2389篇 |
2005年 | 2046篇 |
2004年 | 1580篇 |
2003年 | 1281篇 |
2002年 | 1251篇 |
2001年 | 1013篇 |
2000年 | 861篇 |
1999年 | 874篇 |
1998年 | 682篇 |
1997年 | 696篇 |
1996年 | 593篇 |
1995年 | 534篇 |
1994年 | 520篇 |
1993年 | 401篇 |
1992年 | 304篇 |
1991年 | 323篇 |
1990年 | 276篇 |
1989年 | 184篇 |
1988年 | 156篇 |
1987年 | 149篇 |
1986年 | 104篇 |
1985年 | 77篇 |
1984年 | 70篇 |
1983年 | 50篇 |
1982年 | 50篇 |
1981年 | 35篇 |
1980年 | 29篇 |
1979年 | 6篇 |
1976年 | 6篇 |
1975年 | 10篇 |
1959年 | 5篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
从现行典型园区网络安全设计方案入手,结合其在安全防范解决方案上存在的问题,提出了一种网络主动安全模型;在全局网络安全认识的基础上.阐述了模型组成部件的功能定义和网络主动安全实现流程;采用统一网络入口认证、网络知识发现及资源有效控制、沟通等手段,解决了现行网络安全设计中存在的恶意攻击行为源头定位困难,以及信息安全司法取证不准、网络资源安全被动防护、网络灾难快速反映能力差等问题.实验结果表明,该设计方案具有较好的可行性和实用性. 相似文献
92.
Resistivity-temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere 下载免费PDF全文
The relationship of resistivity versus synthesizing temperature of sol gel YBa_2Cu_3O_y samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ-T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ_{300}=9.83×10^{-3 }Ω·cm at room temperature. The ρ-T curve also showed that the orthorhombic-tetragonal phase transformation of sol-gel YBa_2Cu_3O_y sample occurred at 581℃ for the sample in the rising temperature process, but at 613℃ in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods. 相似文献
93.
Yang Dai Faquan Li Xuewu Cheng Zhiling Jiang Shunsheng Gong 《Optics & Laser Technology》2007,39(7):1374-1379
In Shack–Hartmann wavefront sensor (SHWS), the behavior of the irradiance pattern produced by the micro-lens array is important for an accurate centroid estimation. In this paper, the behavior of a micro-lens array in SHWS is analyzed using Fourier optics, and reveals that in addition to the main, expected spots, secondary spots with smaller intensities also appeared as a result of diffraction by the small dimensions of the micro-lens and interference from the different micro-lenses. This result is confirmed by comparing with a irradiance pattern taken from an actual SHWS. The additional error in centroid estimation caused by these secondary spots is discussed and relationship to the parameters of the micro-lens of SHWS is analyzed. 相似文献
94.
多年来人们对实验教学加以重视的同时却陷入了一个误区:只重视做好课堂演示实验和学生分组实验,而忽视了课外小实验的作用.其实,经常性地引导学生自己动手,就地取材,开展课外小实验、小制作,对加强物理实验教学,加深对物理知识的理解,提高学生的分析解决问题的能力,将会起到重要的作用. 相似文献
95.
96.
In this paper, we use weighted modules ω(?)(f,t)w to study the pointwise approximation on Szasz-type operators, and obtain the direct and converse theorem, as well as characterizations of the pointwise approximation of Jacobi-weighted Szasz-type operators. 相似文献
97.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献
98.
Current methodologies used for the inference of thin film stress through curvature measurement are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to a single layer of thin film deposited on a substrate subjected to the non-uniform misfit strain in the thin film. Such methodologies are further extended to multi-layer thin films deposited on a substrate in the present study. Each thin film may have its own non-uniform misfit strain. We derive relations between the stresses in each thin film and the change of system curvatures due to the deposition of each thin film. The interface shear stresses between the adjacent films and between the thin film and the substrate are also obtained from the system curvatures. This provides the basis for the experimental determination of thin film stresses in multi-layer thin films on a substrate. 相似文献
99.
Pengbo Jiang Tiexin Cheng Yan Liu Xianghao Cui Yingli Bi Kaiji Zhen 《Reaction Kinetics and Catalysis Letters》2004,82(1):49-56
The novel phase transfer catalysts S-8 [4-(dimethyloctylammonium) propansultan] and DB-X [1,4-bis(triethylmethylammonium)benzene dibromide] were synthesized and employed for high conversion synthesis of dichlorocyclopropane from various olefins.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
100.
ZhenFengZHANG 《数学学报(英文版)》2005,21(1):155-168
In this paper, we extend a classical result of Hua to arithmetic progressions with large moduli. The result implies the Linnik Theorem on the least prime in an arithmetic progression. 相似文献