全文获取类型
收费全文 | 4363篇 |
免费 | 825篇 |
国内免费 | 401篇 |
专业分类
化学 | 2968篇 |
晶体学 | 39篇 |
力学 | 288篇 |
综合类 | 57篇 |
数学 | 503篇 |
物理学 | 1734篇 |
出版年
2024年 | 17篇 |
2023年 | 95篇 |
2022年 | 175篇 |
2021年 | 198篇 |
2020年 | 212篇 |
2019年 | 192篇 |
2018年 | 177篇 |
2017年 | 138篇 |
2016年 | 228篇 |
2015年 | 231篇 |
2014年 | 283篇 |
2013年 | 369篇 |
2012年 | 395篇 |
2011年 | 361篇 |
2010年 | 281篇 |
2009年 | 210篇 |
2008年 | 254篇 |
2007年 | 243篇 |
2006年 | 203篇 |
2005年 | 169篇 |
2004年 | 112篇 |
2003年 | 115篇 |
2002年 | 103篇 |
2001年 | 98篇 |
2000年 | 86篇 |
1999年 | 122篇 |
1998年 | 74篇 |
1997年 | 90篇 |
1996年 | 69篇 |
1995年 | 66篇 |
1994年 | 53篇 |
1993年 | 46篇 |
1992年 | 27篇 |
1991年 | 28篇 |
1990年 | 19篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 13篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有5589条查询结果,搜索用时 15 毫秒
151.
采用真空熔融缓冷方法制备了单相β-Zn4Sb3以及含有过量Zn的β-Zn4Sb3块体热电材料.在300—700K的温度范围内测试了材料的电导率、Seebeck系数和热导率,研究了β-Zn4Sb3化合物中过量Zn的分布状态及其对材料热电性能的影响规律.结果表明:过量的Zn作为第二相较均匀的分布在β-Zn4Sb3的晶界上,随着Zn含量增加,材料电导率和热导率上升,Seebeck系数下降,Zn第二相的引入能有效提高材料的功率因子,Zn过量2at%的材料在700K时其ZT值达到1.10. 相似文献
152.
用Origin软件处理物理实验数据 总被引:10,自引:1,他引:10
用Origin软件对物理实验数据进行处理,简单易行、方便可靠。 相似文献
153.
左手介质椭圆光波导基模传播特性 总被引:1,自引:0,他引:1
在椭圆柱坐标系中,采用分离变量方法,得出了左手介质椭圆光波导本征方程的近似解,通过数值计算,分析了椭圆波导偏心率、左手介质的电容率、磁导率对椭圆光波导基模传播特性的影响,并将左介质光波导与右手介质光波导基模特性进行对比,得出左手介质光波导的基模特性与右手介质光波导基模特性差别不大的结论. 相似文献
154.
This paper studies the light scattering and adsorption of nanocrystalline TiO2 porous films used in dye-sensitized solar cells composed of anatase and/or rutile particles by using an optical four-flux radiative transfer model. These light properties are difficult to measure directly on the functioning solar cells and they can not be calculated easily from the first-principle computational or quantitative theoretical evaluations. These simulation results indicate that the light scattering of 1 25 nm TiO2 particles is negligible, but it is effective in the range of 80 and 180 nm. A suitable mixture of small particles (10 nm radius), which are resulted in a large effective surface, and of larger particles (150 nm radius), which are effective light scatterers, have the potential to enhance solar absorption significantly. The futile crystals have a larger refractive index and thus the light harvest of the mixtures of such larger rutile and relatively small anatase particles is improved in comparison with that of pure anatase films. The light absorption of the 10μm double-layered films is also examined. A maximal light absorption of double-layered film is gotten when the thickness of the first layer of 10 urn-sized anatase particles is comparable to that of the second larger rutile layer. 相似文献
155.
156.
采用甚高频等离子体增强化学气相沉积技术制备了系列微晶硅薄膜太阳电池,指出了气体总流量和背反射电极的类型对电池性能参数的影响.电池的I-V测试结果表明:随反应气体总流量的增加,对应电池的短路电流密度、开路电压和填充因子都有很大程度的提高,结果使得电池的光电转换效率得以提高.另外,ZnO/Ag/Al背反射电极能明显提高电池的短路电流密度,进而也提高了电池的光电转换效率.对气体总流量和背反射电极类型影响电池效率的原因进行了分析.
关键词:
微晶硅薄膜太阳电池
气体流量
ZnO/Ag/Al背反射电极 相似文献
157.
以商用金红石相TiO2粉末为原料,通过在碱性溶液中150℃水热48h的方法合成TiO2纳米管.采用SEM,TEM,XRD分析手段对TiO2纳米管的形貌和结构演变进行了表征.制成的TiO2纳米管与TritonX-100,乙酰丙酮混合后,通过丝网印刷的方法涂敷到ITO导电玻璃衬底上,并且在450℃下烧结30min后得到可应用于染料敏化太阳电池的多孔光阳极.将此光阳极浸泡于N719染料敏化后,与镀铂对电极组装电池,两者之间灌
关键词:
2纳米管')" href="#">TiO2纳米管
染料敏化太阳电池
水热法 相似文献
158.
Xinhuan Feng Lei Sun Yange Liu Lingyun Xiong Shuzhong Yuan Guiyun Kai Xiaoyi Dong 《Optical and Quantum Electronics》2004,36(10):919-926
A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated. 相似文献
159.
We have calculated the transport properties of electron through an
artificial quantum dot by using the numerical renormalization group
technique in this paper. We obtain the conductance for the system of
a quantum dot which is embedded in a one-dimensional chain in zero
and finite temperature cases. The external magnetic field gives rise
to a negative magnetoconductance in the zero temperature case. It
increases as the external magnetic field increases. We obtain the
relation between the coupling coefficient and conductance. If the
interaction is big enough to prevent conduction electrons from
tunnelling through the dot, the dispersion effect is dominant in this
case. In the Kondo temperature regime, we obtain the conductivity of
a quantum dot system with Kondo correlation. 相似文献
160.
Charge coupled devices (CCD) photometry and long-term optical variability of gamma-ray-loud BL Lacertae object Mkn 421 下载免费PDF全文
Evidence for the long-term optical curve variability and colour behaviour of the BL
Lac object Mkn 421 is presented. Our results show that the amplitude of the optical
variations of Mkn 421 is only about {\Delta} B=4.7 magnitude in the B-band for
its photometric history from 1899 to 2002. The results of optical photometric
monitoring of the Mkn 421 from April 2000 to Jan 2002 are provided. During our
observation, Mkn 421 shows significant rapid variations and exhibits short time
variability of 2.42 hours in the B band. A strong correlation between the B-V
colour index and the magnitude in the B band is found. Our charge coupled device
(CCD) photometry of Mkn 421 shows that the measured results are in good agreement
with the predicted optical variability period of about 23 years. 相似文献