全文获取类型
收费全文 | 2710篇 |
免费 | 639篇 |
国内免费 | 1092篇 |
专业分类
化学 | 1987篇 |
晶体学 | 130篇 |
力学 | 148篇 |
综合类 | 97篇 |
数学 | 494篇 |
物理学 | 1585篇 |
出版年
2024年 | 11篇 |
2023年 | 32篇 |
2022年 | 99篇 |
2021年 | 103篇 |
2020年 | 96篇 |
2019年 | 102篇 |
2018年 | 90篇 |
2017年 | 148篇 |
2016年 | 77篇 |
2015年 | 148篇 |
2014年 | 162篇 |
2013年 | 214篇 |
2012年 | 210篇 |
2011年 | 252篇 |
2010年 | 225篇 |
2009年 | 267篇 |
2008年 | 313篇 |
2007年 | 301篇 |
2006年 | 265篇 |
2005年 | 219篇 |
2004年 | 151篇 |
2003年 | 113篇 |
2002年 | 131篇 |
2001年 | 124篇 |
2000年 | 158篇 |
1999年 | 79篇 |
1998年 | 56篇 |
1997年 | 34篇 |
1996年 | 21篇 |
1995年 | 32篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有4441条查询结果,搜索用时 328 毫秒
971.
972.
含联萘基团的旋光性聚喹啉的合成与性质 总被引:7,自引:0,他引:7
由2,2′-二甲氧基-1,1′-联萘 了旋光活性的2,2′-二甲氧基-6,6′-二乙酰基-1,1′-联萘(DMDABN),经元素分析,NRM,IR和MS等方法对其进行结构表征,DMDABN与3,3′-二苯甲酰基-4,4′二氨基-二苯基醚通过Friedlander反应合成了旋光性聚喹啉,所制备的聚喹啉具有较高的玻璃化转变温度(474-578K),热分解温度(703-770K),很好的耐溶性能和较强的旋光活性。 相似文献
973.
Highly dispersed Ni catalysts on spherical SiO2 were prepared by simple impregnation of Ni(acac)2, [Ni-(NH3)6-n(H2O)n]^2+, [Ni(en)3]^2+ and [Ni(EDTA)]^2-. Pulse adsorption of H2 and TEM analysis results confirmed that Ni was dispersed very well on the surface of SiO2 even after calcination (4 h) and reduction (1 h) at high temperature of 800 ℃. These highly dispersed and uniquely sized Ni crystallites were more stable and more reactive for both autothermal reforming and partial oxidation of methane in fluidized reactor. 相似文献
974.
LV Peng ZHANG ZaiQiang GUAN JinTong WANG XiaoDong HOU XiuLi ZHANG LingYan WANG JiJun CHEN Bo GUAN QingFeng 《中国科学:物理学 力学 天文学(英文版)》2013,(9):1689-1693
Mo/Si multilayers were fabricated by using magnetron sputtering method at different background pressures:6×10-5 Torr,3×10-5 Torr,and 3×10-6 Torr.The reflectivity of the Mo/Si multilayers increased from 1.93% to 16.63%,and the center wavelength revealed a blue shift to 0.12 nm with the decrease of background pressure.Grazing incident X-ray diffraction(GIXRD) indicated that multilayers fabricated at high background pressure possessed better periodic structure and thinner Mo-on-Si interlayers.Low crystallization degree in(110) preferred the orientation of Mo layers and serious interdiffusion in the Mo/Si multilayers fabricated at low background pressure were observed by transmission electron microscopy(TEM).According to quantitative analysis of microstructural parameters,the Mo layers thickness and thickness ratio of Mo/Si multilayers both decreased and approached the design value gradually by the decrease of background pressure.In addition,the thicknesses of Mo-on-Si and Si-on-Mo interlayers were 1.17 nm and 0.85 nm respectively.It is suggested that the influence of background pressures on the microstructure has a critical role in determining the optical properties of Mo/Si multilayers. 相似文献
975.
描述了中国聚变工程实验堆(CFETR)磁体支撑系统的初步工程概念设计,介绍了纵场(TF)磁体支撑
和极向场(PF)磁体支撑的结构设计。用解析法和有限元法对磁体支撑进行了初步的分析。分析结果表明,该设计基本满足磁体支撑的要求。 相似文献
976.
通过高温碳化聚吡咯纳米管制备了氮掺杂碳纳米管(N-CNTs), 并采用共沉淀法将镍钴层状双氢氧化物(NiCo-LDH)原位生长在N-CNTs上, 制备出具有三维互联网状结构的N-CNTs/NiCo-LDH复合材料. 研究了镍钴摩尔比对N-CNTs/NiCo-LDH复合材料形貌结构和电化学性能的影响. 结果表明, 当镍钴摩尔比为1∶2时, N-CNTs/Ni1Co2-LDH具有最佳的电化学性能. 在1 A/g电流密度下, 其比电容可达1311.8 F/g; 当电流密度为 10 A/g时, 电容保持率高达88.3%, 展现出优异的倍率性; 在经过2500次循环后, 电容保持率仍可达76.4%, 具有良好的循环稳定性.由N-CNTs/Ni1Co2-LDH与活性炭(AC)电极所构建的N-CNTs/Ni1Co2-LDH//AC水系混合型超级电容器, 在750 W/kg功率密度下, 具有27.19 W·h/kg的高能量密度. 相似文献
977.
In a unified algebraic scheme,we investigate the relation between the E(5) symmetry and the interacting boson model beyond the mean-field level.The results indicate that the E(5) symmetry is actually in between the critical point of the U(5)-O(6) transition and the O(6) limit but it is fairly close to the former based on the phase diagram of the interacting boson model at the large boson number limit.In addition,an algebraic Hamiltonian of the E(5)-β2n model is proposed. 相似文献
978.
979.
The biodegradation rate and biocompatibility of poly(d, l -lactide) (PDLLA) in vivo were evaluated. The aim of this study was to establish a nerve guide constructed by the PDLLA with 3-D microenvironment and to repair a 10 mm of sciatic nerve gap in rats. The process of the nerve regeneration was investigated by histological assessment, electrophysiological examination, and determination of wet weight recovery rate of the gastrocnemius muscle. After 3 weeks, the nerve guide had changed from a transparent to an opaque status. The conduit was degraded and absorbed partly and had lost their strength with breakage at the 9th week of postoperation. At the conclusion of 12 weeks, proximal and distal end of nerves were anastomosed by nerve regeneration and the conduit vanished completely. The results suggest that PDLLA conduits may serve for peripheral nerve regeneration and PDLLA is a sort of hopeful candidate for tissue engineering. 相似文献