全文获取类型
收费全文 | 6375篇 |
免费 | 717篇 |
国内免费 | 472篇 |
专业分类
化学 | 1449篇 |
晶体学 | 59篇 |
力学 | 547篇 |
综合类 | 39篇 |
数学 | 354篇 |
物理学 | 2038篇 |
综合类 | 3078篇 |
出版年
2024年 | 20篇 |
2023年 | 55篇 |
2022年 | 109篇 |
2021年 | 101篇 |
2020年 | 147篇 |
2019年 | 150篇 |
2018年 | 126篇 |
2017年 | 176篇 |
2016年 | 265篇 |
2015年 | 242篇 |
2014年 | 307篇 |
2013年 | 400篇 |
2012年 | 364篇 |
2011年 | 390篇 |
2010年 | 304篇 |
2009年 | 378篇 |
2008年 | 356篇 |
2007年 | 410篇 |
2006年 | 400篇 |
2005年 | 302篇 |
2004年 | 305篇 |
2003年 | 251篇 |
2002年 | 229篇 |
2001年 | 211篇 |
2000年 | 213篇 |
1999年 | 183篇 |
1998年 | 166篇 |
1997年 | 146篇 |
1996年 | 117篇 |
1995年 | 116篇 |
1994年 | 93篇 |
1993年 | 89篇 |
1992年 | 87篇 |
1991年 | 70篇 |
1990年 | 64篇 |
1989年 | 56篇 |
1988年 | 58篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7564条查询结果,搜索用时 31 毫秒
931.
932.
采用斜投影-子空间夹角算法快速分析农药中阿维菌素的含量。用斜投影算法从阿维菌素对照品中提取阿维菌素B_(1a)纯光谱数据,用子空间夹角判据计算农药中阿维菌素的含量。阿维菌素的质量浓度在4~14μg/mL范围内与用斜投影法提取的阿维菌素B_(1a)纯光谱吸光度呈良好的线性关系,相关系数r=0.9994。斜投影-子空间夹角算法加标回收率在98.80%~101.67%之间,测定结果的相对标准偏差小于2%(n=6)。用该方法与高效液相色谱法对同一样品进行测定,两种方法测定结果相接近,相对误差小于2.20%。该方法满足快速检测农药中阿维菌素含量的分析要求。 相似文献
933.
Cover Picture: On The Potential of Dynamic Nuclear Polarization Enhanced Diamonds in Solid‐State and Dissolution 13C NMR Spectroscopy (ChemPhysChem 17/2016)
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
934.
V. S. Bezruchenko A. A. Muravsky A. A. Murauski A. I. Stankevich U. V. Mahilny 《Molecular Crystals and Liquid Crystals》2016,626(1):222-228
The new method of LC lenses fabrication based on innovative alignment material for pretilt angle gradient generation is developed. The alignment layer provides LC lens pretilt angle gradient via two-step treatment: uniform rubbing and gradient nonpolarized UV exposure. LC lens has uniform cell-gap, 2–10 V tunable voltage range. The fabrication method is scalable for lens arrays for two-dimensional/three-dimensional autostereoscopic and light-field displays. 相似文献
935.
In the paper we consider the Bessel differential operator in half‐line , , and its Dirichlet heat kernel . For , by combining analytical and probabilistic methods, we provide sharp two‐sided estimates of the heat kernel for the whole range of the space parameters and every , which complements the recent results given in 1 , where the case was considered. 相似文献
936.
应用场光线传递方程,从鱼眼镜头的孔径光阑处,逆向追迹场光线传递方程,确定任意视场角场光线的初始位置,即光阑球差.正向追迹场光线计算鱼眼镜头系统物、像空间视场角之间的关系曲线;用多项式拟合求出关系曲线的解析表达式.通过反演运算,根据畸变图像复原物的图像分布,达到消除鱼眼镜头成像系统畸变的目的.最后,计算了一个160°鱼眼镜头光学系统的光阑球差和图像的畸变,并应用本文方法复原物的图像分布.计算结果表明:光阑球差的计算结果与真值的相对误差小于1%;复原的物方图像径向高度相对误差小于0.25%,说明本文计算鱼眼镜头像场像差的方法是可行的. 相似文献
937.
研究了部分相干高斯谢尔光束在大气湍流中的到达角起伏.主要采用湍流内外尺度的修正Von Karmon谱模型及广义惠更斯-菲涅尔原理和交叉谱密度函数推导出了部分相干光在大气湍流中的到达角起伏表达式.对比分析了湍流内外尺度、湍流强度、传输距离、源相干参数以及波长等参数对部分相干光在大气湍流水平路径上传输时的到达角起伏的影响.结果表明:随着传输距离的增加,到达角起伏越来越小;随着大气湍流内外尺度和源相干参数的增加,到达角起伏也越来越大;与部分相干光相比,完全相干光的到达角起伏受湍流影响很小;随着波长和湍流强度的减小,到达角起伏越来越小. 相似文献
938.
939.
940.
Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems. 相似文献