全文获取类型
收费全文 | 5044篇 |
免费 | 318篇 |
国内免费 | 413篇 |
专业分类
化学 | 1230篇 |
晶体学 | 15篇 |
力学 | 347篇 |
综合类 | 32篇 |
数学 | 693篇 |
物理学 | 1501篇 |
无线电 | 1957篇 |
出版年
2024年 | 36篇 |
2023年 | 181篇 |
2022年 | 151篇 |
2021年 | 167篇 |
2020年 | 204篇 |
2019年 | 150篇 |
2018年 | 151篇 |
2017年 | 230篇 |
2016年 | 214篇 |
2015年 | 214篇 |
2014年 | 332篇 |
2013年 | 358篇 |
2012年 | 300篇 |
2011年 | 377篇 |
2010年 | 301篇 |
2009年 | 328篇 |
2008年 | 318篇 |
2007年 | 262篇 |
2006年 | 262篇 |
2005年 | 176篇 |
2004年 | 152篇 |
2003年 | 140篇 |
2002年 | 114篇 |
2001年 | 99篇 |
2000年 | 68篇 |
1999年 | 61篇 |
1998年 | 61篇 |
1997年 | 45篇 |
1996年 | 33篇 |
1995年 | 36篇 |
1994年 | 32篇 |
1993年 | 25篇 |
1992年 | 29篇 |
1991年 | 28篇 |
1990年 | 17篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1973年 | 6篇 |
1957年 | 2篇 |
排序方式: 共有5775条查询结果,搜索用时 0 毫秒
991.
The interaction and coupling between the electrical, mechanical properties and formation energy for SW defective (10,0) carbon nanotube is studied in density functional theory. The investigated configurations include the axial and circumferential orientations for single defect as well as four distribution types for double ones. The more stable defective configurations, namely, SW-I configurations for single SW defective carbon nanotube and II–II-(2) and I–I ones for double SW defective tubes are related to high symmetry distribution of the defects. Moreover, we found that the σ?–π* hybridization induced by curvature effect causes the semiconductor to metal transition for double axial SW defects case. Young's modulus reduction of SW defective carbon nanotube with respect to defect-free one is less than 8%. The energy bands and Young's moduli of double SW defective tubes are mostly affected by the defect distribution and concentration but insensitive to the circumferential distance between the double defects. 相似文献
992.
We investigate theoretically the dependence of energy transfer rate in Double-Quantum-Well system on the well thickness by using the balance equation formalism. Also, by including the local field correction in our calculations through the zero- and finite-temperature Hubbard approximations, we study the effect of the short-range interactions on the energy transfer phenomenon. Calculations consider both the static and dynamic screening approximations. Our numerical results predict that the energy transfer rate increases considerably by increasing the layers' thicknesses and by taking into account the short-range interactions, as well. 相似文献
993.
In this paper a detailed mathematical model for an electromagnetic energy harvesting architecture based on a semi-analytical approach is introduced. This model estimates the generated energy of the architecture by computing the static and dynamic magnetic and electric fields that describe its dynamics. A comparison of the static fields with the results of a Finite Element Analysis simulation in COMSOL Multiphysics shows good agreement. The model also features increased accuracy and numerical stability. In the model the semi-analytical solutions for the electromagnetic damping force exerted by the induced current coil and the induced electromotive force on the coil provide additional insight into the interactions of electromagnetic induction and damping. Additionally, the energy estimation could be used as a figure of merit in an maximization process to identify the optimal dimensions of the energy harvester. 相似文献
994.
朱艳科 《数学的实践与认识》2012,42(3):14-18
对1985-2008年广东省能源消费总量数据序列进行分析,建立了ARIMA(2,2,2)模型,检验结果表明,该模型对原始数据序列有较好的拟合效果,模型的预测效果良好,可用于短期外推预测. 相似文献
995.
对浙江省城乡居民消费能力的重要指标应用计量经济学,建立城乡居民的消费函数模型,并用定性分析与定量研究相结合的方法,就城乡居民消费能力与趋势进行计量经济的实证分析.进而探讨城乡居民消费水平的差距,寻求持续稳定提高城乡居民消费水平的主要途径.研究表明所建消费函数模型具有较高的拟合精度,且很好的反映了城乡居民消费能力的发展现状和趋势.对促进城乡居民消费能力的协调发展,缩小城乡居民消费水平差距等具有一定的现实意义. 相似文献
996.
硅通孔(TSV)是三维集成电路的一种主流技术.基于TSV寄生参数提取模型,对不同物理尺寸的TSV电阻-电容(RC)参数进行提取,采用Q3D仿真结果验证了模型精度.分析TSVRC效应对片上系统的性能及功耗影响,推导了插入缓冲器的三维互连线延时与功耗的解析模型.在45nm互补金属氧化物半导体工艺下,对不同规模的互连电路进行了比较分析.模拟结果显示,TSVRC效应导致互连延时平均增加10%,互连功耗密度平均提高21%;电路规模越小,TSV影响愈加显著.在三维片上系统前端设计中,包含TSV寄生参数的互连模型将有助于设计者更加精确地预测片上互连性能. 相似文献
997.
998.
Weerapong Chewpraditkul Krittiya SreebunpengMartin Nikl Jiri A. MaresKarel Nejezchleb Akapong PhunpueokChalerm Wanarak 《Radiation measurements》2012,47(1):1-5
The scintillation properties of Lu3Al5O12:Pr3+ (LuAG:Pr) single crystal grown by the Czochralski method with praseodymium concentration of 0.19 mol% were investigated. For a comparison, a good quality Bi4Ge3O12 (BGO) single crystal grown by Bridgman method was also studied. The light yield and energy resolution were measured using photomultiplier tube (XP5200B PMT) readout. Moderate light yield of 15,900 photons per MeV was measured for the LuAG:Pr(0.19%) crystal. For 662 keV gamma rays (137Cs source), an energy resolution of 6.5% obtained for LuAG:Pr(0.19%) is much better than that of 9.0% obtained for BGO. The light yield non-proportionality and energy resolution versus energy of gamma rays were measured and the intrinsic resolution of the crystals was determined after correcting the measured energy resolution for PMT statistics. The LuAG:Pr(0.19%) showed a good proportionality of the light yield within 5% over the energy range from 1274.5 keV down to 32 keV, which is much better than that of 14% for BGO. The photofraction was determined at 320 and 662 keV for both crystals and compared with the ratio of the cross-sections for the photoelectric effect to the total one calculated using WinXCOM program. 相似文献
999.
Ce3+ and Tb3+ co-doped Sr2B5O9Cl phosphors with intense green emission were prepared by the conventional high-temperature solid-state reaction technique. A broad band centered at about 315 nm was found in phosphor Sr2B5O9Cl: Ce3+, Tb3+ excitation spectrum, which was attributed to the 4f-5d transition of Ce3+. The typical sharp line emissions ranging from 450 to 650 nm were originated from the 5D4 → 7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions. The photoluminescence (PL) intensity of green emission from Tb3+ was enhanced remarkably by co-doping Ce3+ in the Tb3+ solely doped Sr2B5O9Cl phosphor because of the dipole-dipole mechanism resonant energy transfer from Ce3+ to Tb3+ ions. The energy transfer process was investigated in detail. In light of the energy transfer principles, the optimal composition of phosphor with the maximum green light output was established to be Sr1.64Ce0.08Tb0.1Li0.18B5O9Cl by the appropriate adjustment of dopant concentrations. The PL intensity of Tb3+ in the phosphor was enhanced about 40 times than that of the Tb3+ single doped phosphor under the excitation of their optimal excitation wavelengths. 相似文献
1000.