全文获取类型
收费全文 | 1003篇 |
免费 | 271篇 |
国内免费 | 189篇 |
专业分类
化学 | 594篇 |
晶体学 | 82篇 |
力学 | 85篇 |
综合类 | 26篇 |
数学 | 273篇 |
物理学 | 403篇 |
出版年
2023年 | 8篇 |
2022年 | 39篇 |
2021年 | 28篇 |
2020年 | 35篇 |
2019年 | 30篇 |
2018年 | 30篇 |
2017年 | 51篇 |
2016年 | 35篇 |
2015年 | 63篇 |
2014年 | 84篇 |
2013年 | 108篇 |
2012年 | 138篇 |
2011年 | 161篇 |
2010年 | 139篇 |
2009年 | 120篇 |
2008年 | 101篇 |
2007年 | 74篇 |
2006年 | 34篇 |
2005年 | 31篇 |
2004年 | 16篇 |
2003年 | 3篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1971年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1463条查询结果,搜索用时 15 毫秒
1.
2.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions. 相似文献
3.
4.
采用浮床黑麦草(Lolium multi florum)对畜禽养殖富营养水体氨氮的净化效应及动态过程进行了研究.结果表明:浮床黑麦草对富营养水体中的氨氮具有明显的净化效果.当覆盖率30%时,对氨氮的去除率最高可达到95.89%.对其去除水体氨氮的动态过程拟合表明符合三次方程曲线.该研究为冬季陆生植物修复富营养水体提供重要依据. 相似文献
5.
We report a new approach for the self-assembly of cuboid micro-parts onto Si substrates to construct three-dimensional microstructures. To perform assembly, the Si substrates are prepared with a deep cavity array as binding sites. An aggregate composed of hundreds of uniformly aligned micro-parts is formed at the C10F18-H2O interface. The micro-parts are arranged by passing the substrate through the aggregate of micro-parts, thus the micro-parts are left on the substrate, and then the substrate is vibrated ultrasonically in the solution, making it possible for the micro-parts to fall into the cavities on the substrate. Finally the substrate is pulled out of the solution after assembly. This technique could give a high yield of up to 70%, providing a new method for micro-assembly. 相似文献
6.
Effect of Molecular Weight on Liquid Crystal Photoalignment by Photosensitive Polyester Containing Thrifluoromethyl Moieties
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigate the liquid-crystal (LC) alignment direction on photoalignment films formed from photosensitive polyester containing thrifluoromethyl moieties (PPDA) with various molecular weights by crossed polarized optical microscopy. It is found that LC alignment behaviour changes with molecular weight of PPDA. The LC alignment on PPDA irradiated films with the highest molecular weight is homogeneous, while those with low and intermediate molecular weights are homeotropic. However, surface morphologies show weak dependence on molecular weight. The surfaces are smooth and there is no clear morphological anisotropy on these aligned films observed by an atomic force microscope. The surface energies of the irradiated films are also measured by using an indirect contact-angle method where both surface energy and its polar component, increase with increasing molecular weight. Different polar surface energies can be considered as a main reason for different alignment characteristics. 相似文献
7.
A gravimetric method for determination of rhenium is based on formation of sparingly soluble 2,4,6-triphenylpyrylium perrhenate. The conditional solubility product in O.1N sulphuric acid medium was found to be (3.72 +/- 0.08) x 10(-9). The interference of foreign anions (simple or complex) is eliminated by preliminary extraction of perrhenate with acetone from strongly alkaline medium. The method is applied to the determination of rhenium in perrhenates and rhenium alloys. 相似文献
8.
J. N. Kotzev M. I. Aroyo M. N. Angelova 《International journal of quantum chemistry》1985,27(1):45-58
The relations between isoscalar factors for corepresentations of antiunitary magnetic point groups are discussed in the case of associated corepresentations. The tables of the isoscalar factors for the single- and double-valued corepresentations of all tetragonal, orthorhombic, monoclinic, and triclinic Shubnikov point groups are given. Some peculiarities of the calculation method of the isoscalar factors for corepresentations are considered. 相似文献
9.
采用XRD表征了水蒸气和磷联合改性的HZSM-5沸石分子筛的结构.通过NH3-TPD和N2吸附脱附研究了样品的酸性和比表面.采用正庚烷的裂化反应研究了样品的裂化活性,研究结果表明,磷改性样品与母体样品相比,经过水蒸气处理后显示出较高的酸量和正庚烷裂化活性.上述结果首次用模型簇和计算量子化学方法进行了解释.采用Gaussian94软件包和PM3半经验量子化学方法对模型簇进行了全优化和频率分析.计算结果显示磷改性后样品的脱铝补硅反应热大于母体样品脱铝补硅反应热,从而显示出磷对骨架的稳定化作用. 相似文献
10.
Dolashka-Angelova P Angelova M Genova L Stoeva S Voelter W 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1999,(11):2249-2260
The fungal strain Humicola lutea 110 produces a mangan- and a copper zinc-containing superoxide dismutases (SOD). In this study, the purification, N-terminal sequence and spectroscopic properties of the new Cu,Zn SOD are described. The preparation of the pure metalloenzyme was achieved via treatment of the strain with acetone followed by gel and ion exchange chromatography. The protein consists of 302 amino acid residues and has a molecular mass of approximately 32 kDa, as determined by PAG electrophoresis and 3100 U mg-1 protein-specific activity. It is a dimeric enzyme with two identical subunits of 15,950 Da, as indicated by SDS-PAGE, mass spectroscopic and amino acid analysis. The N-terminal sequence analysis of the Cu,Zn SOD from the fungal strain revealed a high degree of structural homology with enzymes from other eukaryotic sources. Conformational stability and reversibility of unfolding of the dimeric enzyme were determined by fluorescence and circular dichroism (CD) spectroscopy. The critical temperature of deviation from linearity (Tc) of the Arrhenius plot ln (Q-1(-1)) vs. 1/T was calculated to be 68 degrees C and the respective activation energy for the thermal deactivation of the excited indole chromophores is 42 kcal mol-1. The melting temperatures (Tm) were determined by CD measurements to be 69 degrees C for the holo- and 61 degrees C for the apo-enzyme. The fluorescence emission of the Cu,Zn SOD is dominated by 'buried' tryptophyl chromophores. Removal of the copper-dioxygen system from the active site caused a 4-fold increase of the fluorescence quantum yield and a 10 nm shift of the emission maximum position towards higher wavelength. 相似文献