全文获取类型
收费全文 | 186011篇 |
免费 | 38361篇 |
国内免费 | 27063篇 |
专业分类
化学 | 123162篇 |
晶体学 | 2281篇 |
力学 | 12513篇 |
综合类 | 727篇 |
数学 | 22968篇 |
物理学 | 89784篇 |
出版年
2024年 | 580篇 |
2023年 | 2818篇 |
2022年 | 3155篇 |
2021年 | 4315篇 |
2020年 | 5331篇 |
2019年 | 5594篇 |
2018年 | 4992篇 |
2017年 | 5217篇 |
2016年 | 7389篇 |
2015年 | 7357篇 |
2014年 | 8387篇 |
2013年 | 12057篇 |
2012年 | 13934篇 |
2011年 | 15875篇 |
2010年 | 15734篇 |
2009年 | 15655篇 |
2008年 | 10255篇 |
2007年 | 9257篇 |
2006年 | 8407篇 |
2005年 | 7785篇 |
2004年 | 7173篇 |
2003年 | 5736篇 |
2002年 | 5355篇 |
2001年 | 5276篇 |
2000年 | 4249篇 |
1999年 | 4750篇 |
1998年 | 4030篇 |
1997年 | 3745篇 |
1996年 | 4240篇 |
1995年 | 4214篇 |
1994年 | 4205篇 |
1993年 | 3966篇 |
1992年 | 3481篇 |
1991年 | 3045篇 |
1990年 | 2529篇 |
1989年 | 2442篇 |
1988年 | 2286篇 |
1987年 | 1534篇 |
1986年 | 1569篇 |
1985年 | 1197篇 |
1984年 | 1235篇 |
1983年 | 528篇 |
1982年 | 1032篇 |
1981年 | 851篇 |
1980年 | 852篇 |
1979年 | 577篇 |
1978年 | 568篇 |
1977年 | 661篇 |
1976年 | 1082篇 |
1972年 | 554篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
利用一维辐射流体力学程序MULTI数值模拟研究了功率为1014Wcm2、脉冲宽度为300ps、波长为0.44μm的强激光辐照平面Au靶时产生X射线的过程,给出了X射线转换效率和能谱分布.通过将靶物质划分为对所产生的X射线光学薄的转化区和光学厚的再发射区,得到了作为黑体辐射热源的最佳靶厚度,并给出了辐射加热靶所产生的等离子体的密度和温度的空间分布.
关键词:
辐射流体力学
激光等离子体
X射线转换
辐射热波 相似文献
993.
放射源的辐射指纹能起到标识和鉴别放射性物体的作用.在涉及核弹头不可逆销毁过程的深度核裁军核查中,核弹头的辐射指纹对标识和鉴别裁减下来的核弹头将起到关键作用.预先研究辐射指纹的有关技术,如识别机理的研究,将有助于深度核裁军的核弹头核查技术发展.以实验室放射源为研究对象,探索了类型γ射线能谱指纹的同一性识别机理.类型γ射线指纹识别机理的研究,就是要找出一种合适的方法,以较高的置信度,描述两个正在进行比较的γ射线指纹是否为同一放射源的指纹.采用了谱形比较法,并用谱相似度概念来描述两个指纹的相似程度.在谱形比较思想的指导下,编制了放射源类型指纹识别软件,并通过放射源同一性的识别实验验证了软件的有效性,同时研究了谱相似度随统计涨落和测量条件,如时间、源强和本底等因素的变化情况.研究结果表明:1)用相似度概念来描述两个指纹的相似程度,回答两个待比较的γ射线能谱是否代表同一类型放射源,是切实可行的;2)该识别机理只具备识别放射源类型的能力,而对同一类型、差异甚微的放射源个体还不能识别
关键词:
γ射线能谱指纹
辐射指纹
识别机理
核查技术 相似文献
994.
995.
Chongyu Mei Junqiao Ding Bing Yao Yanxiang Cheng Zhiyuan Xie Yanhou Geng Lixiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1746-1757
Two orange phosphorescent iridium complex monomers, 9‐hexyl‐9‐(iridium (III)bis(2‐(4′‐fluorophenyl)‐4‐phenylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐PIr) and 9‐hexyl‐9‐(iridium(III)bis(2‐(4′‐fluorophenyl)‐4‐methylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐MIr), were successfully synthesized. The Suzuki polycondensation of 2,7‐bis(trimethylene boronate)‐9,9‐dioctylfluorene with 2,7‐dibromo‐9,9‐dioctylfluorene and Br‐PIr or Br‐MIr afforded two series of copolymers, PIrPFs and MIrPFs, in good yields, in which the concentrations of the phosphorescent moieties were kept small (0.5–3 mol % feed ratio) to realize incomplete energy transfer. The photoluminescence (PL) of the copolymers showed blue‐ and orange‐emission peaks. A white‐light‐emitting diode with a configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/PIr05PF (0.5 mol % feed ratio of Br‐PIr)/Ca/Al exhibited a luminous efficiency of 4.49 cd/A and a power efficiency of 2.35 lm/W at 6.0 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.46, 0.33). The CIE coordinates were improved to (0.34, 0.33) when copolymer MIr10PF (1.0 mol % feed ratio of Br‐MIr) was employed as the white‐emissive layer. The strong orange emission in the electroluminescence spectra in comparison with PL for these kinds of polymers was attributed to the additional contribution of charge trapping in the phosphorescent dopants. © 2007 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 45: 1746–1757, 2007 相似文献
996.
Li-Min Wang 《Semigroup Forum》1995,50(1):141-160
Communicated by F. Pastijn 相似文献
997.
To satisfy the volatile nature of today’s markets, businesses require a significant reduction in product development lead times. Consequently, the ability to develop precise product sales forecasts is of fundamental importance to decision-makers. Over the years, many forecasting techniques of varying capabilities have been introduced. The precise extent of their influences, and the interactions between them, has never been fully clarified, although various forecasting factors have been explored in previous studies. Accordingly, this study adopts the Taguchi method to calibrate the controllable factors of a forecasting model. An L9(34) inner orthogonal array is constructed for the controllable factors of data period, horizon length, and number of observations required. An experimental design is then performed to establish the appropriate levels for each factor. At the same time, an L4(23) outer orthogonal array is used to consider the inherited parameters of forecasting method as the noise factors of Taguchi method simultaneously. An illustrated example, employing data from a power company, serves to demonstrate the thesis. The results show that the proposed model permits the construction of a highly efficient forecasting model through the suggested data collection method. 相似文献
998.
本文在经典风险模型的基础上,将索赔到达过程推广为更新过程,索赔可以批量到达,且带有常数利息力和Brown运动干扰项,得到一个新的风险模型,运用Markov骨架过程的方法,得出盈余过程的瞬时分布和生存概率. 相似文献
999.
Humberto César Chaves Fernandes Arthur Rodrigo Barros da Rocha 《International Journal of Infrared and Millimeter Waves》2003,24(7):1171-1176
The use of photonic materials has been used in the theory of optical waves. The PBG (Photonic Band Gap) theory and material, was developed recently for optical frequencies and can be easily applied to millimeter waves, microwaves and planar antenna frequencies. The presence of photonic materials as substrate in antennas has some good characteristics such as, supression of light spontaneous emission and suppression of surface waves, allowing the application in planar antenna array. In this work an elaborate analysis using the full wave Transverse Transmission Line - TTL method, that provides efficient and concise results is applied to the planar antennas array with PBG substrate. 相似文献
1000.