全文获取类型
收费全文 | 3001篇 |
免费 | 615篇 |
国内免费 | 192篇 |
专业分类
化学 | 579篇 |
晶体学 | 9篇 |
力学 | 295篇 |
综合类 | 54篇 |
数学 | 896篇 |
物理学 | 1975篇 |
出版年
2024年 | 5篇 |
2023年 | 22篇 |
2022年 | 72篇 |
2021年 | 52篇 |
2020年 | 51篇 |
2019年 | 54篇 |
2018年 | 84篇 |
2017年 | 100篇 |
2016年 | 110篇 |
2015年 | 86篇 |
2014年 | 188篇 |
2013年 | 229篇 |
2012年 | 189篇 |
2011年 | 232篇 |
2010年 | 197篇 |
2009年 | 226篇 |
2008年 | 210篇 |
2007年 | 203篇 |
2006年 | 177篇 |
2005年 | 156篇 |
2004年 | 148篇 |
2003年 | 123篇 |
2002年 | 123篇 |
2001年 | 111篇 |
2000年 | 103篇 |
1999年 | 79篇 |
1998年 | 98篇 |
1997年 | 66篇 |
1996年 | 64篇 |
1995年 | 47篇 |
1994年 | 24篇 |
1993年 | 29篇 |
1992年 | 23篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有3808条查询结果,搜索用时 15 毫秒
131.
B. Barret D. Hurtmans M. De Mazière P.-F. Coheur 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,95(4):499-519
Collision-induced line narrowing, which has been discovered in the 1950s and investigated thoroughly in the laboratory since then, has yet never been taken into account in the spectroscopic remote sensing of the atmosphere. This work investigates the effect of collision-induced line narrowing onto the retrieval of HCl and HF vertical profiles from ground-based solar absorption FTIR measurements made at the NDSC station of the Jungfraujoch (46.5°N, 8°E and 3580 m above see level). The retrievals are performed with the Atmosphit software, recently developed at the Université Libre de Bruxelles. It is presented in this paper for the first time and is validated against the widely used SFIT2 software. The impact of the line narrowing onto the retrieval of HCl and HF vertical profiles is examined relying on careful information content and error budget analyses. We report that the effect is relatively weak for HCl but significant for HF. Confirmation of the need to take the line narrowing into account for the retrieval of vertical profiles from ground-based FTIR spectra is given by comparison with data from the HALOE space borne instrument, rather insensitive to this spectroscopic effect. 相似文献
132.
David Jacquemart Robert Gamache 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,96(2):205-239
This paper describes a semi-empirical calculation of the air-broadened half-widths and the air pressure-induced frequency shifts for the H216O isotopologue. This semi-empirical calculation is based on fits of several recent high-quality measurements and theoretical calculations to the first-order terms in the expansion of the complex Robert-Bonamy (CRB) equations, which yields a second- and first-order polynomial function of the differences in the upper- and lower-state vibrational quantum numbers for the half-width and line shift, respectively. The aim of this work was to obtain a complete set of air-broadened half-widths and air pressure-induced frequency shifts for transitions of H216O present in the HITRAN database from microwave to the visible in order to supplement the observed and calculated values. For around 700 sets of rotational quantum numbers (), semi-empirical coefficients describing the vibrational dependence of the air-broadened half-widths and the air pressure-induced frequency shifts have been obtained directly from the fit of experimental and/or theoretical data. The accuracy of the parameters deduced from this calculation is estimated to be between 5% and 10% for the air-broadened half-widths and between 0.001 and for the air pressure-induced frequency shifts. For sets of rotational quantum numbers for which either none or insufficient experimental/theoretical data were available to deduce a vibrational dependence, further approximations have been used to obtain a complete set of semi-empirical coefficients. 相似文献
133.
提出了两种适用于光突发交换网的可编程光缓存器结构:交叉型和多端口开关型.两种结构都能满足突发包缓存的超长性和可变性的要求,且结构简单紧凑,成本低,可扩展.交叉型缓存器通过指定信号在每个子缓存模块的光纤环中的循环次数即能实现可变时间的延迟.多端口开关型缓存器通过指定信号在两个多端口开关相应端口与所接光纤延迟线组成的光纤环中的循环次数实现可变时间的延迟.仿真结果表明,两种可编程光缓存器都能对光突发包实现ns级指定时间延迟,可用于解决光突发交换网突发包的冲突问题. 相似文献
134.
S. A. Kirillov A. Morresi M. Paolantoni P. Sassi 《Journal of Physical Organic Chemistry》2007,20(8):568-573
The most obvious consequence of the concept of aromaticity is the common confidence that in aromatic compounds, bond lengths do not alternate and are between typical to the single and double ones. However, in 1994, performing crystal structure investigations of substituted pyridines and their salts, Krygowski and co‐workers have discovered a very surprising angular group induced bond alteration (AGIBA) effect: It appears that some angular substituents, like methoxy or nitrozo groups, can induce bond alternation in aromatic rings. Crystal studies do not allow one to operate with liquids that are more common in organic chemistry. This paper presents the first possible evidence of spectroscopic manifestations of the AGIBA effect. Raman spectra of the liquid toluene are analyzed. It is found that instead of being single, the line corresponding to the ring breathing vibrations is clearly split by 1.0–1.4 cm?1, thus indicating the presence of two (cis‐ and trans‐) AGIBA isomers. The energy difference between these isomers estimated in temperature dependent Raman studies is found equal to 6.68 kJ mol?1. The low‐wavenumber line therefore corresponds to the cis‐AGIBA isomer and the high‐wavenumber line to the trans‐AGIBA isomer stabilized by the AGIBA effect. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
135.
介绍了时域传输线和时域有限差分两种计算电缆X射线瞬态响应的方法,并利用电缆芯线总电荷以及介质层的电荷分布,结合实验结果,分别给出了时域传输线模型中的电流源和时域有限差分模型中电流密度的计算方法。作为例子,在60 keV单能X射线垂直于电缆轴向辐照的条件下,采用两种方法计算了电缆两端接匹配负载时负载上的电流响应;采用传输线方法计算了不同能量X射线辐照电缆时的芯线负载电流响应。计算结果表明,两种方法计算的电缆X射线瞬态响应是一致的;电缆介质层中存在静电场;X射线能量不同时,电缆芯线负载电流存在最大值。计算中,电缆与X射线的作用采用蒙特卡罗方法计算。 相似文献
136.
137.
研究了有界波电磁脉冲模拟器下短线缆效应的理论建模和实验方法。基于传输线模型计算了线缆在有界波电磁脉冲模拟器辐照下的电流响应。建立了有界波电磁脉冲模拟试验环境,其前沿时间小于5 ns,脉冲半高宽约200 ns。开展了短线缆的效应实验验证研究,短线缆负载端响应电流的测量和计算结果吻合得很好,表明应用改型有界波电磁脉冲模拟器开展短线缆效应实验在理论和实验上都是可行的。这种线缆实验方法具有效应实验空间电磁场分布规范均匀、参数指标可控、监测技术成熟等优点。 相似文献
138.
139.
140.
针对光纤光栅应变传感器接收信号弱且信噪比低这一问题,提出了应用DSP技术来抑制噪声,提高Bragg峰值波长检测精度的方法.实验结果表明所设计的498阶Kaiser窗低通FIR数字滤波器能够显著提高光纤光栅应变传感器的信号检测精度.采用DSP技术可以较好地解决光纤光栅传感器的波长解调这一技术难题. 相似文献