全文获取类型
收费全文 | 592篇 |
免费 | 62篇 |
国内免费 | 140篇 |
专业分类
化学 | 425篇 |
晶体学 | 20篇 |
力学 | 34篇 |
综合类 | 23篇 |
数学 | 83篇 |
物理学 | 209篇 |
出版年
2023年 | 3篇 |
2022年 | 17篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 13篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 32篇 |
2012年 | 43篇 |
2011年 | 49篇 |
2010年 | 45篇 |
2009年 | 30篇 |
2008年 | 55篇 |
2007年 | 50篇 |
2006年 | 57篇 |
2005年 | 44篇 |
2004年 | 28篇 |
2003年 | 22篇 |
2002年 | 22篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1981年 | 4篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有794条查询结果,搜索用时 484 毫秒
81.
Jaap F. Vente Steven McIntosh Wim G. Haije Henny J. M. Bouwmeester 《Journal of Solid State Electrochemistry》2006,10(8):581-588
The present paper discusses the oxygen transport properties, oxygen stoichiometry, phase stability, and chemical and mechanical
stability of the perovskites (BSCF) and (SCF) for air separation applications. The low oxygen conductive brownmillerite phase in SCF is characterized using in-situ
neutron diffraction, thermographic analysis and temperature programmed desorption but this phase is not present for BSCF under
the conditions studied. Although both materials show oxygen fluxes well above 10 ml/cm2·min at T=1,273 K and pO2=1 bar for self-supporting, 200 μm-thick membranes, BSCF is preferred as a membrane material due to its phase stability. However,
BSCF’s long-term stable performance remains to be confirmed. The deviation from ideal oxygen stoichiometry for both materials
is high: δ>0.6. The thermal expansion coefficients of BSCF and SCF are 24×10−6 and 30×10−6 K−1, respectively, as determined from neutron diffraction data. The phenomenon of kinetic demixing has been observed at pO2<10−5 bar, resulting in roughening of the surface and enrichment with alkaline earth metals. Stress–strain curves were determined
and indicated creep behavior that induces undesired ductility at T=1,073 K for SCF. Remedies for mechanical and chemical instabilities are discussed. 相似文献
82.
In this paper, we study a quantum anti-Zeno effect (QAZE) purely induced by repetitive measurements for an artificial atom interacting with a structured bath. This bath can be artificially realized with coupled resonators in one dimension and possesses photonic band structure like Bloeh electron in a periodic potential. In the presence of repetitive measurements, the pure QAZE is discovered as the observable decay is not negligible even for the atomic energy level spacing outside of the energy band of the artificial bath. If there were no measurements, the decay would not happen outside of the band. In this sense, the enhanced decay is completely induced by measurements through the relaxation channels provided by the bath. Besides, we also discuss the controversial golden rule decay rates originated from the van Hove's singularities and the effects of the counter-rotating terms. 相似文献
83.
水上交通事故严重程度影响因素的识别对从根本上减少严重事故件数、降低事故危害和损失具有重要意义。在历史事故报告的基础上,构建并量化事故影响因素集,提出以极限学习机(ELM)为一般事故、严重事故的二分类器,以遗传算法(GA)为因素搜索算法的GA-ELM因素识别模型。对发生在我国水域的737件水上交通事故进行实证研究,并与以支持向量机(SVM)为分类器的GA-SVM模型进行对比分析。结果表明,GA-ELM模型识别出时段、人为致因、环境致因等9个事故严重程度影响因素,较GA-SVM模型结果更为精简,且分类精度较不做因素识别时分别提高8.2%、7.1%。此外,GA-ELM大大缩短运算时间。由此可见,GA-ELM可为水上交通事故严重程度影响因素识别提供一个较好的方法。 相似文献
84.
Richard J. McIntosh 《The Ramanujan Journal》2018,46(2):593-604
In their paper “A survey of classical mock theta functions”, Gordon and McIntosh observed that the classical mock \(\theta \)-functions, including those found by Ramanujan, can be expressed in terms of two ‘universal’ mock \(\theta \)-functions denoted by \(g_{2}\) and \(g_{3}\). These identities are known as mock \(\theta \)-conjectures. The fifth- and seventh-order mock \(\theta \)-conjectures were proved by Dean Hickerson. In the survey paper the authors gave mock \(\theta \)-conjectures for the other mock \(\theta \)-functions and referred the proofs to a future paper with this title, listed in their references as [GM4]. The purpose of this paper is to prove these identities for the functions of orders 2 and 3. 相似文献
85.
86.
87.
88.
We consider the propagation of a combustion front resulting from the gasless combustion of a condensed state fuel. The propagation of the front, essentially a premixed laminar flame, is supported by an exothermic reaction subject to possible heat loss through a competitive endothermic reaction. The dynamics of the endothermic process inducing the heat loss strongly depend on the temperature and the local fuel concentration. Through an analysis based on high activation energy, the steady-state values of the final burnt temperature as well as the burning velocity are obtained, and the control parameters are identified. Using a linear perturbation method, we assess the stability of the propagating front and obtain a condition for oscillatory behaviour. The critical parameter values for the transition from steady to oscillatory burning speeds are identified. The results represent a generalization of those obtained by Matkowsky and Sivashinsky to include the effects of heat loss induced by a competitive endothermic reaction. 相似文献
89.
采用两步法合成了γ-Fe2O3/Ag/TiO2复合光催化剂, 以大肠埃希氏菌(E. coli)为目标菌, 对数去除率为评价指标评价了催化剂的抗菌性能, 优化了催化剂的最佳制备参数. 通过X射线衍射、 扫描电子显微镜、 X射线光电子能谱和紫外-可见漫反射光谱等手段对催化剂进行了表征. 结果表明, 当Ti/Ag摩尔比为1:0.05, 煅烧时间为3 h, 煅烧温度为350 ℃时, γ-Fe2O3/Ag/TiO2表现出最佳抗菌活性. 复合催化剂具有介孔结构, 比表面积为89.1 m2/g; 光吸收边界达690 nm, 有良好的可见光响应能力; 磁性较强, 在水处理应用中可有效分离和重复使用. 反应条件不受光源限制, 在有/无光照下均具有良好的抗菌活性, 且太阳光辐照下对E. coli的对数去除率可达6.28. 相似文献
90.
一种新的空间域图像错误掩盖方法 总被引:2,自引:1,他引:1
提出了空间域图像错误掩盖方法.在信道丢包率较高时,采用场编码交织技术将图像按像素行分为两个场,并分别独立编码和传输.当某个场中的图像数据在网络传输过程中丢失时,用相邻场的像素值通过插值的方法恢复丢失数据.实验结果表明,掩盖效果明显优于现有的空间域错误掩盖方法,即使在图像数据丢失一半的情况下,恢复图像主观上仍可接受,测试图像的PSNR增益可达2.77~7.24 dB. 相似文献