全文获取类型
收费全文 | 38014篇 |
免费 | 6281篇 |
国内免费 | 5901篇 |
专业分类
化学 | 28791篇 |
晶体学 | 577篇 |
力学 | 2026篇 |
综合类 | 559篇 |
数学 | 4512篇 |
物理学 | 13731篇 |
出版年
2024年 | 51篇 |
2023年 | 516篇 |
2022年 | 788篇 |
2021年 | 1078篇 |
2020年 | 1331篇 |
2019年 | 1369篇 |
2018年 | 1157篇 |
2017年 | 1102篇 |
2016年 | 1615篇 |
2015年 | 1755篇 |
2014年 | 2136篇 |
2013年 | 2825篇 |
2012年 | 3314篇 |
2011年 | 3505篇 |
2010年 | 2598篇 |
2009年 | 2565篇 |
2008年 | 2929篇 |
2007年 | 2613篇 |
2006年 | 2425篇 |
2005年 | 2027篇 |
2004年 | 1783篇 |
2003年 | 1478篇 |
2002年 | 1594篇 |
2001年 | 1317篇 |
2000年 | 1021篇 |
1999年 | 847篇 |
1998年 | 591篇 |
1997年 | 611篇 |
1996年 | 514篇 |
1995年 | 443篇 |
1994年 | 405篇 |
1993年 | 330篇 |
1992年 | 268篇 |
1991年 | 238篇 |
1990年 | 211篇 |
1989年 | 161篇 |
1988年 | 121篇 |
1987年 | 114篇 |
1986年 | 87篇 |
1985年 | 69篇 |
1984年 | 55篇 |
1983年 | 46篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 25篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
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
82.
Resistivity-temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
83.
84.
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
85.
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
86.
恩格尔系数衡量城镇居民生活水平适用性 总被引:2,自引:0,他引:2
根据我固1980年和2000年恩格尔系数所反映的各省(市)居民生活水平资料,发现两个不同时期其真实性有很大差异,分析了造成这种差别的原因:(1)职工非现金福利收入的增加;(2)少数职工的非法收入的大量增加;(3)居民饮食结构的改变;(4)物价上涨的影响;(5)恩格尔系数本身存在技术问题;(6)抽样调查本身存在问题,提出用一种“新系数”来衡量城镇居民生活水平,其优点是:(1)不受各地区实际支出,即人为控制调节的影响;(2)不需用其他指标作解释,直观性强;(3)因可以扣除物价因素,它不受物价波动的影响;(4)调查户填报和计算简易方便。可扩大样本调查量,提高反映住户总量可靠性。 相似文献
87.
We investigate the two methods of defining the surface gravity ,κ on the horizon, which are the metric definition and the definition given by the spacetime conformal method. It is found that the latter is of greater generality. By this method, we find that ,κ of η- ξ spacetime is equal to the exponent factor α in the coordinate transformation, which confirms the argument that η- ξ spacetime can be considered as the background spacetime for finitetemperature field theories. The reasons why the metric definition of ,κ can not be applied in η- ξ spacetime are presented. 相似文献
88.
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
89.
Based on the algebraic entanglement measure proposed [G. Vidal et al., Phys. Rev. A 65 (2002) 032314],we study the entanglement evolution of both pure quantum states and mixed ones of 2-qutrit system in a symmetrybroken environment consisting of a fermionic bath. Entanglement of states will decrease or remain constant under the influence of environment, and the class of states which remain unchanged has been found out. 相似文献
90.
XiWenHE HongShengGUO YuMeiJIA 《中国化学快报》2003,14(9):979-982
In order to obtain mechanically stable membrane for practical application, the imprinted polymer was synthesized in the pores of polyfluoromembrane, the binding and transport ability of the membrane were studied. 相似文献