全文获取类型
收费全文 | 110642篇 |
免费 | 28785篇 |
国内免费 | 25172篇 |
专业分类
化学 | 73861篇 |
晶体学 | 2064篇 |
力学 | 7008篇 |
综合类 | 833篇 |
数学 | 14274篇 |
物理学 | 66559篇 |
出版年
2023年 | 1199篇 |
2022年 | 1698篇 |
2021年 | 1843篇 |
2020年 | 2216篇 |
2019年 | 2755篇 |
2018年 | 2526篇 |
2017年 | 3413篇 |
2016年 | 3582篇 |
2015年 | 3995篇 |
2014年 | 4349篇 |
2013年 | 6619篇 |
2012年 | 7343篇 |
2011年 | 9159篇 |
2010年 | 12088篇 |
2009年 | 12299篇 |
2008年 | 6395篇 |
2007年 | 5690篇 |
2006年 | 5245篇 |
2005年 | 5066篇 |
2004年 | 5347篇 |
2003年 | 4219篇 |
2002年 | 4015篇 |
2001年 | 4218篇 |
2000年 | 3531篇 |
1999年 | 3257篇 |
1998年 | 2592篇 |
1997年 | 2344篇 |
1996年 | 2609篇 |
1995年 | 3008篇 |
1994年 | 3063篇 |
1993年 | 3083篇 |
1992年 | 2642篇 |
1991年 | 2271篇 |
1990年 | 1921篇 |
1989年 | 1976篇 |
1988年 | 1948篇 |
1987年 | 1220篇 |
1986年 | 1268篇 |
1985年 | 909篇 |
1984年 | 1000篇 |
1982年 | 920篇 |
1981年 | 754篇 |
1980年 | 788篇 |
1979年 | 541篇 |
1978年 | 544篇 |
1977年 | 637篇 |
1976年 | 1046篇 |
1973年 | 442篇 |
1972年 | 533篇 |
1971年 | 440篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Summary Wet-chemical cleaning procedures of Si(100) wafers are surface analytically characterized and compared. Hydrophobic surfaces show considerably less native oxides in comparison to hydrophilic surfaces.The growth of the oxide is determined as a function of exposure to air by means of XPS measurements. The chemically shifted Si2p XPS signal is utilized for the quantification of the growth kinetics.One hour after cleaning no chemically shifted Si2p XPS peak is discernible on the hydrophobic surfaces. Assuming homogeneous oxide growth, the detection limit of native oxides is estimated to be below 0.05 nm using an emission angle of 18° with respect to the wafer surface. The calculation of the oxide thickness from the chemically shifted and nonchemically shifted Si2p XPS peak intensities is carried out according to Finster and Schulze [1]. For more than a day after cleaning no surface oxides can be identified on the hydrophobic surfaces. The oxide growth kinetics is logarithmic. The very slow oxidation rate cannot be attributed to fluorine residues since no fluorine is seen by XPS. We explain the slow oxidation rate by a homogeneous hydrogen saturated Si(100) wafer surface.
Oberflächenanalytische Charakterisierung oxidfreier Si(100)-Waferoberflächen相似文献
972.
Effects of Nb2O5 on thermal stability and optical properties of Er3+-doped tellurite glasses 下载免费PDF全文
Er3+-doped tellurite glasses with molar compositions of
xNb2O5-(14.7-x)Na2O--10ZnO--5K2O--10GeO2--
60TeO2--0.3Er2O3
(x=0, 3, 5, 7 and 9) have been investigated for developing 1.5~μm
fibre and planar amplifiers. The effects of Nb2O5 on the thermal stability
and optical properties of Er3+-doped tellurite glasses have been discussed.
It is noted that the incorporation of Nb2O5 (x=5) increases the thermal
stability of tellurite glasses significantly. Er3+-doped niobium tellurite
glasses exhibit a large stimulated emission cross-section (7.2\times 10-21-
10.7×10-21~cm2 and the gain bandwidth, FWHM×\sigmae^{\rm peak} (274\times 10-28 - 480×10-28~cm3), which are
significantly higher than that of silicate and phosphate glasses. In addition, the
intensity of upconversion luminescence of the Er3+-doped niobium tellurite
glasses decreases rapidly with increasing Nb2O5 content. As a result,
Er3+-doped niobium tellurite glasses might be a potential candidate for
developing laser or optical amplifier devices. 相似文献
973.
提出了一种基于微悬臂梁传感技术研究大分子折叠/构象转变的新方法.通过分子自组装的方法将热敏性的聚N-异丙基丙烯酰胺(PNIPAM)分子链修饰到微悬臂梁的单侧表面,用光杠杆技术检测温度在20—40℃之间变化时由于微悬臂梁上的PNIPAM分子在水中的构象转变所引起的微悬臂梁变形.实验结果显示:在升温过程中,微悬臂梁的表面应力发生了变化并且导致微悬臂梁产生了弯曲变形,这个过程对应着微悬臂梁上的PNIPAM分子从无规线团构象到塌缩小球构象的构象转变.在降温过程中,微悬臂梁发生了反方向的弯曲变形,这对应着PNIPA
关键词:
构象转变
聚N-异丙基丙烯酰胺分子链
表面应力
微悬臂梁 相似文献
974.
采用Cr4 ∶YAG晶体作为可饱和吸收体,实现连续激光二极管(LD)端面抽运的Nd∶YVO4激光器的高重复率被动调Q·在注入抽运功率为8.8W时,得到重复频率23.8kHz、平均功率1.21W的调Q脉冲序列;每个脉冲能量为51μJ、脉宽为25ns、峰值功率达到2.03kW·实验上研究了脉冲重复频率、平均输出功率、脉冲宽度、单脉冲能量与抽运功率、输出镜透过率的关系·实验结果表明,当抽运功率较大时,脉冲重复频率和输出平均功率随着抽运功率的增加而减小,对此进行了合理的理论解释· 相似文献
975.
976.
977.
Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the material's structure. There appears a relatively large change in structure of the material at about 273K, The anharmonic potential of the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes at around 312 cm^-1 and 464cm^-1 indicate that the latter phonon mode is more anharmonic than the former one. 相似文献
978.
979.
DIELECTRIC EFFECT ON THE RADIO-FREQUENCY CHARACTERISTICS OF A RECTANGULAR WAVEGUIDE GRATING TRAVELING WAVE TUBE 总被引:2,自引:0,他引:2
Zhigang Lu Yubin Gong Yanyu Wei Wenxiang Wang 《International Journal of Infrared and Millimeter Waves》2006,27(8):1095-1108
A new type of partial-dielectric-loaded rectangular waveguide grating slow-wave structure (SWS) for millimeter wave traveling
wave tube (TWT) is presented in this paper. The radio-frequency characteristics including the dispersion properties, the longitudinal
electric field distribution and the beam-wave coupling impedance of this structure are analyzed. The results show that the
dispersion of the rectangular waveguide grating circuit is weakened, the phase velocity is reduced and the position of the
maximum E
z
is basically invariant after partially filling the dielectric materials in the rectangular waveguide grating SWS. Although
the coupling impedance decreases a little, it still keeps above 40 Ω. 相似文献
980.
ZONG Hong-Shi SUN Wei-Min 《理论物理通讯》2006,46(11)
By differentiating the inverse dressed quark propagator at finite chemical potential μ with respect to μ, the linear response of the dressed quark propagator to the chemical potential can be obtained. From this we extract a modelindependent formula for the linear chemical potential dependence of the in-medium two-quark condensate and show by two independent methods (explicit calculation and Lorentz covariance arguments) that the first-order contribution in μto the in-medium two-quark condensate vanishes identically. Therefore if one wants to study the in-medium two-quark condensate one should expand to at least the second order in the chemical potential μ. 相似文献