全文获取类型
收费全文 | 9377篇 |
免费 | 1793篇 |
国内免费 | 1317篇 |
专业分类
化学 | 5382篇 |
晶体学 | 380篇 |
力学 | 920篇 |
综合类 | 136篇 |
数学 | 185篇 |
物理学 | 5484篇 |
出版年
2024年 | 15篇 |
2023年 | 58篇 |
2022年 | 246篇 |
2021年 | 282篇 |
2020年 | 252篇 |
2019年 | 244篇 |
2018年 | 277篇 |
2017年 | 384篇 |
2016年 | 447篇 |
2015年 | 349篇 |
2014年 | 474篇 |
2013年 | 868篇 |
2012年 | 663篇 |
2011年 | 609篇 |
2010年 | 565篇 |
2009年 | 595篇 |
2008年 | 552篇 |
2007年 | 625篇 |
2006年 | 554篇 |
2005年 | 506篇 |
2004年 | 480篇 |
2003年 | 421篇 |
2002年 | 354篇 |
2001年 | 309篇 |
2000年 | 312篇 |
1999年 | 303篇 |
1998年 | 233篇 |
1997年 | 196篇 |
1996年 | 182篇 |
1995年 | 154篇 |
1994年 | 132篇 |
1993年 | 153篇 |
1992年 | 124篇 |
1991年 | 72篇 |
1990年 | 71篇 |
1989年 | 66篇 |
1988年 | 86篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 28篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
YBa2Fe3O8(YBFO)是具有三方钙钛矿结构的反铁磁(AFM)体,研究它的结构和磁性质对于我们认识三方钙钛矿结构具有重要作用.目前,关于固相法制备YBFO中退火温度方面的研究并不多,而控制退火温度是这种工艺中的重要环节.为制备高含量的YBa2Fe3O8,本文分别在760℃、950℃和1100℃退火温度下,采用固相... 相似文献
992.
本文基于OH自由基所固有的分子结构特征,通过分子光谱理论系统地分析和计算了OH自由基A2Σ + →X2Πr 电子带系发射光谱的谱线跃迁频率、能级分布以及爱因斯坦自发发射跃迁概率等重要参数.同时结合实际的光谱实验,分析了谱线的自然展宽、碰撞展宽、多普勒展宽以及仪器展宽等各种展宽因素对谱线线型的影响,从理论上计算了任意转动温度、振动温度以及谱线展宽条件下OH自由基A2Σ 关键词:
发射光谱
转动温度
振动温度
自发发射爱因斯坦跃迁概率 相似文献
993.
Ce0.8Gd0.05Y0.15O1.9 (GYDC) electrolyte was prepared by a carbonate co-precipitation method. Lithium nitrate at 1, 1.5, 2 and 3 mol% was added to GYDC as sintering additive. 96% relative density was achieved for GYDC at sintering temperature of 800 °C with addition of 1.5 mol% LiNO3. The conductivities of GYDC with sintering aids LiNO3 were measured by a.c. impedance spectroscopy and showed comparable values to that of pure GYDC sample sintered at 1400 °C. A single cell with 1.5 mol% LiNO3 infiltrated GYDC electrolyte was fabricated by sintering at 800 °C for only 2 h. Lithiated NiO was synthesized by the glycine-nitrate combustion method and employed as cathode material. The cell was tested at temperatures from 500 to 575 °C and a maximum power density of 73 mW cm− 2 was obtained at 575 °C. These preliminary results indicate that LiNO3 is a very effective sintering additive for intermediate temperature solid oxide fuel cell fabrication. 相似文献
994.
Palash SetuaRajib Pramanik Souravi SarkarChiranjib Ghatak Vishal Gobind RaoNilmoni Sarkar Satyen Kumar Das 《Journal of Molecular Liquids》2011,162(1):33-37
Two silver salts, silver tetrafluoroborate and silver trifluoromethanesulfonate were dissolved in two different room temperature ionic liquids (RTILs), 1-Butyl-3 methyl imidazolium tetrafluoroborate ([Bmim][BF4]) and 1-Butyl-1 methyl pyrrolidinium trifluoromethanesulfonate ([Bmpy][Tfms]). Triton x-100 (TX-100) surfactant and cyclohexane as nonpolar medium are used to dissolve these RTILs to create reverse micellar system. Pure reverse micellar system is characterized by dynamic light scattering (DLS) measurement. These pure RTIL reverse micellar systems are used to prepare stable silver nanoparticle solution without using any other auxiliary solvent in the whole process. 相似文献
995.
Ibtissem Ben AssakerMahmoud Dhahbi 《Journal of Molecular Liquids》2011,161(1):13-18
The electrodeposition of metallic Copper in binary mixture ionic liquid/organic solvent (tri-n-octylmethylammonium chloride (TOMAC))/chloroform (CHCl3) was investigated. The electrochemical behavior of Cu(II) in TOMAC/CHCl3 at glassy carbon working electrode at room temperature was studied by cyclic voltammetry and spectroscopy impedance. The results from the cyclic voltammetry showed that the electrodeposition of metallic Cu in the binary mixture ionic liquid/organic solvent was an irreversible process and was controlled by the diffusion of Cu(II) on a glassy carbon working electrode. The average value of αnα was found to be 0.23 at 25 °C and the diffusion coefficient (D0) of Cu(II) was calculated to be 7.12 10− 9 cm2/s at room temperature. The performance of TOMAC ionic liquid such as internal resistance has been investigated with electrochemical impedance spectroscopy (EIS). The scanning electron microscopy (SEM) micrographs was used to observe that the copper plating was moderately dense and contains fine crystallites with average sizes of about 1 μm at room temperature. Energy dispersive X-ray analysis (EDAX) profile showed that the obtained film was copper. 相似文献
996.
Low temperature synthesis of iodine-doped TiO2 nanocrystallites with enhanced visible-induced photocatalytic activity 总被引:1,自引:0,他引:1
Iodine-doped TiO2 nanocrystallites (denoted as I-TNCs) were prepared via a newly developed triblock copolymer-mediated sol-gel method at a temperature of 393 K. I-doping, crystallization and the formation of porous structure have been simultaneously achieved. The obtained particles were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV-vis spectrophotometer. The results indicated that the as-prepared I-TNCs possessed a diameter of ca. 5 nm with anatase crystalline structure and a specific surface area of over 200 m2 g−1. The presence of iodine expanded the photoresponse in visible light range, and led to enrich in surface hydroxyl group on the TiO2 surface. Compared with the commercial photocatalyst P25, the I-TNCs significantly enhanced the photocatalytic efficiency in the degradation of rhodamine B and 2,4-dichlorophenol, and the I-TNCs with 2.5 mol% doping ratio exhibited the best photocatalytic activity. 相似文献
997.
S. PatilVijaya Puri 《Applied Surface Science》2011,258(4):1535-1540
The magnesium oxide thin films were prepared by thermal oxidation (in air) of vacuum evaporated magnesium thin film on alumina. It was found that oxidation temperature (623 K, 675 K and 723 K) and thickness (103 nm and 546 nm) dependent effects were prominently manifested in the surface morphology. Electrical and microwave properties (8-12 GHz) of the MgO thin films were also carried out. X-ray diffraction showed orientation along (2 0 0) and (2 2 0) directions. Flowerlike morphology was observed from SEM and flake like morphology for films of higher thickness oxidized at higher temperatures. The magnesium oxide thin film showed NTC behavior. Microwave transmittance was found to increase with increase in oxidation temperature but was lower than alumina. Frequency and oxidation temperature dependent microwave permittivity was obtained. The microwave dielectric constant varied in the range 8.3-15.3. 相似文献
998.
We present a simple, low-cost and high-effective method for synthesizing high-quality, large-area graphene using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) on SiO2/Si substrate covered with Ni thin film at relatively low temperatures (650 °C). During deposition, the trace amount of carbon (CH4 gas flow rate of 2 sccm) is introduced into PECVD chamber and the deposition time is only 30 s, in which the carbon atoms diffuse into the Ni film and then segregate on its surface, forming single-layer or few-layer graphene. After deposition, Ni is removed by wet etching, and the obtained single continuous graphene film can easily be transferred to other substrates. This investigation provides a large-area, low temperature and low-cost synthesis method for graphene as a practical electronic material. 相似文献
999.
This paper presents the investigation of the properties of GaN nanowires synthesized from Ni-catalyzed chemical vapour deposition method under various growth temperatures. The influence of the growth temperatures on the morphological, structural and optical characteristics of the synthesized GaN nanowires was investigated in this work. Field-emission scanning electron microscopy images revealed that the 950 °C was the optimal growth temperature for synthesizing uniform, straight and smooth morphology of GaN nanowires. X-ray diffraction results demonstrated that the synthesized low dimensional GaN structures have the hexagonal wurtzite structure. Ultraviolet and blue emissions were detected from photoluminescence measurements. In addition, phonon replicas with the energy separation of 90 meV have been observed at the lower energy of the blue emission region in photoluminescence spectra. 相似文献
1000.
抑制损伤发展的CO_2激光修复技术及机理研究 总被引:1,自引:1,他引:0
熔石英表面激光损伤发展问题一直制约着激光器的运行通量。采用CO2激光在线熔融修复损伤点,修复后形成一个光滑的高斯坑,去除了损伤点中的裂纹,平滑了凹凸不平的表面,并且在紫外脉冲激光作用下,修复斑再次产生损伤的阈值高于熔石英元件的损伤生长阈值。因此CO2熔融修复技术能有效地抑制损伤发展。通过分析CO2激光作用下熔石英表面的温度分布,讨论修复坑的形成过程,确定激光参数对修复效果的影响,为寻找最佳修复参数提供理论基础。同时利用原子力显微镜(AFM)、轮廓仪细致分析损伤点和修复斑的微细结构,采用有限差分时域方法计算损伤点和修复斑周围的光强分布,探索消除裂纹和平滑表面对抑制损伤生长的作用。 相似文献