全文获取类型
收费全文 | 9342篇 |
免费 | 3859篇 |
国内免费 | 3919篇 |
专业分类
化学 | 4261篇 |
晶体学 | 288篇 |
力学 | 2037篇 |
综合类 | 253篇 |
数学 | 1067篇 |
物理学 | 9214篇 |
出版年
2024年 | 100篇 |
2023年 | 405篇 |
2022年 | 525篇 |
2021年 | 503篇 |
2020年 | 418篇 |
2019年 | 402篇 |
2018年 | 282篇 |
2017年 | 365篇 |
2016年 | 391篇 |
2015年 | 447篇 |
2014年 | 752篇 |
2013年 | 620篇 |
2012年 | 656篇 |
2011年 | 665篇 |
2010年 | 693篇 |
2009年 | 734篇 |
2008年 | 775篇 |
2007年 | 716篇 |
2006年 | 784篇 |
2005年 | 625篇 |
2004年 | 638篇 |
2003年 | 618篇 |
2002年 | 593篇 |
2001年 | 577篇 |
2000年 | 424篇 |
1999年 | 346篇 |
1998年 | 349篇 |
1997年 | 389篇 |
1996年 | 328篇 |
1995年 | 304篇 |
1994年 | 304篇 |
1993年 | 251篇 |
1992年 | 263篇 |
1991年 | 242篇 |
1990年 | 194篇 |
1989年 | 197篇 |
1988年 | 79篇 |
1987年 | 65篇 |
1986年 | 41篇 |
1985年 | 28篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1979年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
DENG Kai WU Yunfei LI Hua FANG Deming ZHONG Yingjie 《声学学报:英文版》2011,(4):417-426
Based on the energy conservation relationship,nonlinear thermo-acoustic effects of Rijke tube including instability range,saturation processes and higher harmonics modes were investigated.With coupling between the external flow and the inner space of a Rijke tube, the acoustic characteristics of self-excited oscillation were simulated.The experimental study was also carried out and the results were compared with those from simulation.The nonlinear factors which distort the acoustic waveform distortion were analyzed.From the results,it is seen that varying size of the nozzle outlet changes the acoustic impedance in the boundary, and leads to reduction of the nonlinear effects.The results show that the modes of self-excited oscillation could be influenced by the position of higher harmonics.In the large amplitude oscillation,the distortion of pressure wave within Rijke tube could be induced by the acoustic losses due to vortices on nozzle.It is found that the waveform distortion could be avoided by the shrinkage of nozzle. 相似文献
992.
993.
994.
995.
996.
997.
Homogeneous interface-type resistance switching in Au/La0.67Ca0.33MnO3/SrTiO3/F:SnO2 heterojunction memories 下载免费PDF全文
La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the heterojunetions exhibit an asymmetric and resistance switching behaviour. A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy. The spatial homogeneity of the charge carrier distribution leads to field- induced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect. The ratio of the high resistance state to the low resistance state is found to be as high as 1.3 x 10^4% by simulating the AC electric field. This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications. 相似文献
998.
Sm~(3+),Sr~(2+)共掺杂CeO_2的离子电导率被证实可高达Sm~(3+)掺杂CeO_2离子电导率的近两倍,然而,共掺杂对CeO_2电导率的作用机理尚不明确.本文利用第一性原理计算的密度泛函理论+U方法,对Sm~(3+)和Sr~(2+)共掺杂的CeO_2进行了系统的研究,对比Sm~(3+)或Sr~(2+)单掺杂的CeO_2体系,计算并分析了共掺杂体系的电子态密度、能带结构、氧空位形成能以及氧空位迁移能等微观属性.计算结果表明,Sm~(3+),Sr~(2+)的共掺杂对CeO_2基电解质性能的提高具有协同效应,二者的共掺杂不仅能协同抑制CeO_2体系的电子电导率,还能在单掺杂CeO_2的基础上进一步降低氧空位形成能,Sm~(3+)的存在还有助于降低Sr~(2+)对氧空位的俘获作用,而Sr~(2+)的加入则能够在Sm~(3+)掺杂CeO_2的基础上进一步降低最低氧空位迁移能,爬坡式弹性能带方法计算表明共掺杂体系的氧空位迁移能最低可达0.314/0.295 eV,低于Sm~(3+)掺杂CeO_2的最低氧空位迁移能.研究揭示了Sm~(3+),Sr~(2+)共掺杂对CeO_2电导率的协同作用机理,对进一步研发其他高性能的共掺杂电解质材料具有重要的指导意义. 相似文献
999.
双连续型结构是指同一体系中存在两种连续态,这在刚体中很容易实现,但对于流体却十分困难.要使两种流体同时保持连续态,不仅对它们的相容性、密度、极性等方面要求极高,还需要稳定剂来牢牢稳定住液-液界面.最早的双连续型凝胶是在对高聚物进行研究时发现的,后来英国爱丁堡大学软物质课题组进行了一系列研究,最终在低分子量液体体系中实现了重大突破,制备出本文所要讨论的bicontinuous interfacially jammed emulsion gel(Bijel).这种结构可以被称作"双连续型乳液凝胶",它兼有乳液(emulsion)和凝胶(gel)的物理性质,独特的双连续结构使它拥有更为广阔的应用空间.本文简短地回顾了Bijel的研发过程,总结近年来的研究进展,指出它在工业应用中受到的限制,并对室温下通过直接搅拌制备Bijel的方法做重点介绍. 相似文献
1000.
辐照诱导的人正常肝细胞系HL-7702细胞延迟效应 总被引:1,自引:0,他引:1
利用X射线辐照人正常肝细胞系HL-7702细胞, 运用胞质分离阻滞微核法实验检测细胞微核率,AnnexinV FITC细胞凋亡检测试剂盒检测细胞凋亡率, 细胞微核率和凋亡率随着辐照剂量的增加而显著增加。X射线照射后细胞传代培养, 第7代时不同剂量辐照后子代细胞微核率和凋亡率同未辐照细胞相比已无明显区别。 对不同剂量辐照后传代7代的细胞再次照射2.5 Gy的相同剂量,发现它们细胞微核率和凋亡率存在明显差异,即初次受辐照剂量高的细胞, 再次以相同剂量辐照后的微核率和凋亡率也高. 这些结果表明,X射线辐照导致了HL-7702细胞基因组不稳定性这一辐射延迟效应,再次辐照使得辐射的延迟效应得以明显的表现。 Human normal liver cell line HL-7702 cells were irradiated with different doses of X rays. Micronucleus and apoptosis rates in the irradiated cells were measured with cytokinesis block micronucleus method and Annexin V FITC apoptosis detection kit, respectively. Experimental data showed that the micronucleus and apoptosis rates increased obviously with increasing irradiation dose. After seven population doublings, the micronucleus and apoptosis rates of the cells surviving exposure to the X rays reduced to the same levels as non irradiated control cells; the progenies of the cells were secondly exposed to X rays at the same dose of 2.5 Gy. We found that the progenies of the cells surviving the first irradiations of the various doses showed markedly differential micronucleus frequencies and apoptotic rates. Although the same dose of 2.5 Gy was applied in the second irradiations, the micronucleus frequencies and apoptotic rates of the progenies of the cells initially exposed at higher doses were significantly higher than the others. These results indicate that X rays lead to genomic instability in HL 7702 cells, which is an important manifestation of radiation induced delayed effect, and a second radiation stimulus makes the delayed effect in the progeny of the previously irradiated cells be expressed obviously. 相似文献