全文获取类型
收费全文 | 2237篇 |
免费 | 91篇 |
国内免费 | 25篇 |
专业分类
化学 | 1417篇 |
晶体学 | 21篇 |
力学 | 112篇 |
数学 | 206篇 |
物理学 | 597篇 |
出版年
2023年 | 19篇 |
2022年 | 24篇 |
2021年 | 37篇 |
2020年 | 29篇 |
2019年 | 27篇 |
2018年 | 37篇 |
2017年 | 30篇 |
2016年 | 57篇 |
2015年 | 64篇 |
2014年 | 91篇 |
2013年 | 103篇 |
2012年 | 173篇 |
2011年 | 194篇 |
2010年 | 123篇 |
2009年 | 127篇 |
2008年 | 135篇 |
2007年 | 127篇 |
2006年 | 123篇 |
2005年 | 103篇 |
2004年 | 74篇 |
2003年 | 77篇 |
2002年 | 48篇 |
2001年 | 47篇 |
2000年 | 45篇 |
1999年 | 28篇 |
1998年 | 25篇 |
1997年 | 22篇 |
1996年 | 29篇 |
1995年 | 31篇 |
1994年 | 16篇 |
1993年 | 26篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 15篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有2353条查询结果,搜索用时 15 毫秒
51.
An efficiency of 8.2% is demonstrated for a diode-pumped passively Q-switched self-stimulated Raman laser with an a-cut mixed vanadate crystal, Nd:Gd0.8Y0.2VO4. At 2.2 W of incident pump power, the self-stimulated Raman laser produces pulses as short as 660 ps at a Stokes wavelength of 1175 nm with 2.7 microJ of energy per pulse at a 66-kHz repetition rate. 相似文献
52.
In this study, the axial flow cyclone used in Tsai et al. (2004) was further tested for the collection efficiency of both
solid (NaCl) and liquid (OA, oleic acid) nanoparticles. The results showed that the smallest cutoff aerodynamic diameters
achieved for OA and NaCl nanoparticles were 21.7 nm (cyclone inlet pressure: 4.3 Torr, flow rate: 0.351 slpm) and 21.2 nm
(5.4 Torr, 0.454 slpm), respectively. The collection efficiencies for NaCl and OA particles were close to each other for the
aerodynamic diameter ranging from 25 to 180 nm indicating there was almost no solid particle bounce in the cyclone. The 3-D
numerical simulation was conducted to calculate the flow field in the cyclone and the flow was found to be nearly paraboloid.
Numerical simulation of the particle collection efficiency based on the paraboloid flow assumption showed that the collection
efficiency was in good agreement with the experimental data with less than 15% of error. A semi-empirical equation for predicting
the cutoff aerodynamic diameter at different inlet pressures and flow rates was also obtained. The semi-empirical equation
is able to predict the cutoff aerodynamic diameter accurately within 9% of error. From the empirical cutoff aerodynamic diameter,
a semi-empirical square root of the cutoff Stokes number, , was calculated and found to be a constant value of 0.241. This value is useful to the design of the cyclone operating in
vacuum to remove nanoparticles. 相似文献
53.
Chien-Cheng Tsai 《Applied Surface Science》2006,253(4):1898-1902
Nanotube aggregates with high porosity were prepared from hydrothermal treatment of TiO2 particles in NaOH at 130 °C, followed by HCl rinsing to different pH values. Pore structure of the aggregates, which were mainly mesoporous, was characterized by analyzing the N2 sorption isotherm with different methods including the t-plot and density function theory. The surface area, pore volume and mean pore size of the aggregates increased with the rinsing acidity to reach a maximum (e.g. 400 m2/g in surface area) at pH 1.6 and then decreased with further increase of the acidity. The crystalline phase and composition of the aggregates were, as well, significantly affected by the acidity of the post-treatment rinsing. Large-surface area aggregates were of loosely-attached nanotubes, composed of both anatase TiO2 and H2Ti2O5·H2O, obtained under a mildly acidic rinsing condition, while basic or highly acidic conditions resulted in the formation of closely coagulated dense structures consisting of different crystalline phases. 相似文献
54.
Y.T. Chen S.U. Jen Y.D. Yao J.M. Wu G.H. Hwang T.L. Tsai Y.C. Chang A.C. Sun 《Journal of magnetism and magnetic materials》2006
Co50Fe50 films with thickness varying from 100 to 500 Å were deposited on a glass substrate by sputtering process, respectively. Two kinds of CoFe films were studied: one was the as-deposited film, and the other the annealed film. The annealing procedure was to keep the films at 400 °C for 5 h in a vacuum of 5×10−6 mbar. From the X-ray study, we find that the as-deposited film prefers the CoFe(1 1 0) orientation. Moreover, the body-centered cubic (bcc) CoFe(1 1 0) line is split into two peaks: one corresponding to the ordered body-centered tetragonal (bct) phase, and the other, the disordered bcc phase. After annealing, the peak intensity of the ordered bct phase becomes much stronger, while that of the disordered bcc phase disappears. The annealing has also caused the ordered CoFe(2 0 0) line to appear. When the amount of the ordered bct phase in Co50Fe50 is increased, the saturation magnetization (Ms) and coercivity (Hc) become larger, but the electrical resistivity (ρ) decreases. From the temperature coefficient of resistance (TCR) measurement, we learn that the bct grains in the CoFe film start to grow at temperature 82 °C. 相似文献
55.
56.
A Revisit on the Derivation of the Particular Solution for the Differential Operator ∆2 ± λ2 下载免费PDF全文
Guangming Yao C. S. Chen & Chia Cheng Tsai 《advances in applied mathematics and mechanics.》2009,1(6):750-768
In this paper, we applied the polyharmonic splines as the basis functions
to derive particular solutions for the differential operator ∆2 ± λ2. Similar to the
derivation of fundamental solutions, it is non-trivial to derive particular solutions
for higher order differential operators. In this paper, we provide a simple algebraic
factorization approach to derive particular solutions for these types of differential
operators in 2D and 3D. The main focus of this paper is its simplicity in the sense
that minimal mathematical background is required for numerically solving higher
order partial differential equations such as thin plate vibration. Three numerical
examples in both 2D and 3D are given to validate particular solutions we derived. 相似文献
57.
Jen-Hwan Tsai 《Journal of luminescence》2010,130(10):1680-1686
In this paper, a shift in the photoluminescence (PL) peak from blue to near-infrared region was observed in the Si+-implanted 400-nm-thick SiO2 films with the rapid thermal annealing (RTA) method only. As the Si+-fluence was 1×1016 ions/cm2, a blue band was observed in the films after RTA at 1050 °C for 5 s in dry-N2 atmosphere; then, the band shifted from blue to orange upon increasing the holding temperature of RTA to 1250 °C in the films after the isochronal RTA in dry N2. Furthermore, while the fluence was increased to 3×11016 ions/cm2 and the holding temperature was at the same range between 1050 and 1250 °C, the PL peak occurred between red and near-infrared regions. Although the RTA and conventional thermal annealing (CTA) methods produce a similar mechanism, the CTA method needs a much longer annealing-time and a higher Si+-implanted dose than the RTA method for producing the same shift and intensity of PL peak from the as-implanted sample. Therefore, the RTA method can produce the mechanism in the Si+-implanted sample with the PL energy between blue and near-infrared band in place of the CTA method. 相似文献
58.
Y. Hwu W. L. Tsai B. Lai J. H. Je G. H. Fecher M. Bertolo G. Margaritondo 《Surface science》2001,480(3):188-195
We present several successful test cases of using photoelectron emission microscopy (PEEM) for photon energy up to 25 keV. First, the full extended X-ray absorption fine structure analysis was implemented in areas as small as 100 μm2 for transition-metal K edge absorption spectra and, therefore, demonstrated the feasibility of combining structural and chemical analysis with hard-X-ray absorption spectroscopy with high lateral resolution. We also show that PEEM can be used in a transmission (radiography) mode as an imaging detector for hard-X-ray. This approach again leads to the unprecedented 0.3 μm lateral resolution, particularly critical for the use of coherence-based phase contrast techniques in real time X-ray radiology. 相似文献
59.
This study examines the use of stationary Cartesian mesh for steady and unsteady flow computations. The surface boundary conditions are imposed by reflected points. A cloud of nodes in the vicinity of the surface is used to get a weighted average of the flow properties via a gridless least-squares technique. If the displacement of the moving surface from the original position is typically small, a small-perturbation boundary condition method can be used. To ensure computational efficiency, multigrid solution is made via a framework of embedded grids for local grid refinement. Computations of airfoil wing and wing-body test cases show the practical usefulness of the embedded Cartesian grids with the small-perturbation boundary conditions approach. 相似文献
60.
应用分子动力学方法,模拟了298 K下,密度为1.0 g/cm~3的水溶液中Ca2+,Mg2+,Cl~-的水化现象,得到了相应离子周围水分子的微观分布情况.发现在钙离子周围,水分子以其氧离子去靠近中心离子;而在氯离子周围,水分子则以其中的一个氢原子去靠近中心离子.通过分析三种离子的径向分布函数、配位数曲线、水化数、水化半径,发现Ca2+的水化数和水化半径均大于Mg2+,即Ca2+的水合能力比Mg2+强.与以往研究结果相比,本文计算所得的自扩散系数更接近实验所得结果.为了使模型更好的代表真实水溶液体系,本文还应用分子动力学和拉曼光谱法研究了不同浓度的CaCl2水溶液.分子动力学研究发现随着浓度的升高,CaCl2溶液中Ca2+,Cl~-的配位数分别呈降低趋势.同时,随着浓度的升高,Ca2+,Cl~-的自扩散系数也呈现降低的趋势.作者推断这是由于浓度的升高,加剧了离子的微观反... 相似文献