首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1037篇
  免费   174篇
  国内免费   124篇
化学   550篇
晶体学   44篇
力学   3篇
综合类   4篇
数学   2篇
物理学   645篇
无线电   87篇
  2024年   2篇
  2023年   5篇
  2022年   18篇
  2021年   24篇
  2020年   14篇
  2019年   11篇
  2018年   18篇
  2017年   17篇
  2016年   24篇
  2015年   18篇
  2014年   21篇
  2013年   51篇
  2012年   74篇
  2011年   42篇
  2010年   52篇
  2009年   137篇
  2008年   136篇
  2007年   113篇
  2006年   86篇
  2005年   50篇
  2004年   77篇
  2003年   50篇
  2002年   75篇
  2001年   56篇
  2000年   22篇
  1999年   18篇
  1998年   13篇
  1997年   21篇
  1996年   15篇
  1995年   10篇
  1994年   12篇
  1993年   13篇
  1992年   12篇
  1991年   7篇
  1990年   5篇
  1989年   5篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1982年   1篇
  1981年   1篇
  1979年   2篇
  1975年   1篇
排序方式: 共有1335条查询结果,搜索用时 171 毫秒
1.
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   
2.
获得了一种研究碲镉汞深能级的方法。通过分析迁移率 载子浓度与温度的关系,可以得到关于深能级的重要依据。  相似文献   
3.
该文对Cd-HEDTA(N-(2-羟基乙基)乙二胺-N',N',N'-三乙酸),Cd-PDTA(1,2丙二胺四乙酸)和Cd-DTPA(二乙三胺五乙酸)的113Cd NMR谱和自旋晶格弛豫时间T1,及NOE因子进行了研究.结果表明,Cd-HEDTA和Cd-PDTA结构与Cd-EDTA类似,Cd-PDTA双线归因于其可能的两种异构体.Cd-DTPA大的化学位移表明其具有七配位的五角双锥结构.在这种结构中DTPA可用三个氮原子参加配位.对113Cd自旋晶格弛豫时间分析表明,Cd-DTPA配合物中质子偶极作用机理的贡献较大,这归因于Cd DTPA有更多的乙酸根亚甲基质子参与偶极作用.  相似文献   
4.
微波消解ICP-AES法同时测定花岗石中铜、镉、铬和砷   总被引:9,自引:3,他引:6  
张萍 《光谱实验室》2002,19(3):338-340
本文采用微波消解和ICP-AES法,同时测定花岗石样品的铅、镉、铬、砷4有害元素,检出限分别为0.0008、0.0007、0.0018、0.0012μg.mL^-1,回收率为93.4%-102.5%,RSD为1.3%-3.6%,该法准确、快速、简便,结果令人满意。  相似文献   
5.
Helium-charged nanocrystalline titanium films have been deposited by HeAr magnetron co-sputtering. The effects of substrate temperature on the helium content and microstructure of the nanocrystalline titanium films have been studied. The results indicate that helium atoms with a high concentration are evenly incorporated in the deposited titanium films. When the substrate temperature increases from 60℃ to 350℃ while the other deposition'parameters are fixed, the helium content decreases gradually from 38.6 at.% to 9.2at.%, which proves that nanocrystalline Ti films have a great helium storage capacity. The 20 angle of the Bragg peak of (002) crystal planes of the He-charged Ti film shifts to a lower angle and that of (100) crystal plane is unchanged as compared with that of the pure Ti film, which indicates that the lattice parameter c increases and a keeps at the primitive value. The grain refining and helium damage result in the diffraction peak broadening.  相似文献   
6.
The magnetic properties of annealed Fe-Pt multilayer thin films with a broad composition range were investigated in order to identify the effects of composition and annealing temperature on the achievable coercive field, and to identify its maximum at low processing temperatures. Two types of multilayer systems were deposited as materials libraries to vary the composition from Fe20Pt80 to Fe75Pt25. The first type of multilayer was comprised of alternating opposing wedges, whereas the second type consisted of repeated uniform Fe and Pt layers interspersed periodically with Fe wedge layers. It was found that coercive fields μ0HC > 0.7 T can be achieved at an annealing temperature of about 300 °C (60 min) for both types of multilayers as long as the composition is close to 50:50. Higher annealing temperatures are needed for films, which deviate from this composition. Increasing the annealing temperature up to 700 °C leads to increased coercivity values. Multilayers with additional Fe layers showed increased remanence but reduced coercive fields.  相似文献   
7.
The dependence of structural properties and surface morphology of Cu-In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn2 phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu-In/In/Glass). This permitted the fabrication of a homogeneous Cu-In alloy layer, which was not possible through the simple co-sputtering.  相似文献   
8.
通过适当的工艺措施,采用Bridgman法生长了直径为30mm的X射线及γ射线探测器级的Cd.9Zn0.1Te晶锭.测试结果表明:该晶锭结晶质量良好,位错密度低,成分均匀,杂质含量低,红外透过率和电阻率都十分接近本征Cd.9Zn0.1Te的值.并从晶体的生长特性、缺陷和杂质的角度,分析了生长高性能晶体的条件,研究了生长Cdl-xZnxTe晶体的x值与缺陷和杂质浓度之间的关系.  相似文献   
9.
火焰原子吸收光谱法测定磁化杯中铅、镉和铁   总被引:1,自引:0,他引:1  
本文研究了火焰原子吸收光谱法测定磁化杯陶瓷内胆中Ph、Cd和Fe含量的方法。样品经粉碎,用硝酸-高氯酸混合液进行消解后测定。本法灵敏度高,干扰少,简单,快速,具有良好的精密度和准确度,其相对标准偏差分别为Pb3.99%,Cd10.7%,Fe0.9%。回收率Pb100.61%,Cd101.18%,Fe102.4%。  相似文献   
10.
Cr1−xAlxC films were deposited on high-speed steel by RF reactive magnetron sputtering. In this study, we aimed to identify the effect of the Al content on the properties of Cr1−xAlxC films. We found that Cr1−xAlxC films exhibited a fine columnar grain microstructure with some special characteristics, such as high hardness of Hv 1426, a low friction coefficient of 0.29, and a large contact angle of 90° for x = 0.18. Furthermore, an increase in Al content resulted in a decrease in film hardness and an increase in contact angle. Moreover, on annealing at 923 K, the mechanical properties of the films improved and a dense protective film of complex Cr2O3 and Al2O3 oxides was formed on the surface for better wear resistance, which will ultimately increase the lifetime of the high-speed steel substrate.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号