全文获取类型
收费全文 | 4566篇 |
免费 | 213篇 |
国内免费 | 518篇 |
专业分类
化学 | 3269篇 |
晶体学 | 57篇 |
力学 | 97篇 |
综合类 | 6篇 |
数学 | 69篇 |
物理学 | 1799篇 |
出版年
2024年 | 11篇 |
2023年 | 124篇 |
2022年 | 109篇 |
2021年 | 73篇 |
2020年 | 127篇 |
2019年 | 146篇 |
2018年 | 103篇 |
2017年 | 120篇 |
2016年 | 151篇 |
2015年 | 178篇 |
2014年 | 196篇 |
2013年 | 232篇 |
2012年 | 202篇 |
2011年 | 373篇 |
2010年 | 325篇 |
2009年 | 342篇 |
2008年 | 316篇 |
2007年 | 339篇 |
2006年 | 242篇 |
2005年 | 195篇 |
2004年 | 195篇 |
2003年 | 165篇 |
2002年 | 126篇 |
2001年 | 93篇 |
2000年 | 101篇 |
1999年 | 82篇 |
1998年 | 94篇 |
1997年 | 64篇 |
1996年 | 64篇 |
1995年 | 52篇 |
1994年 | 53篇 |
1993年 | 32篇 |
1992年 | 41篇 |
1991年 | 44篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1986年 | 17篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 6篇 |
排序方式: 共有5297条查询结果,搜索用时 15 毫秒
81.
82.
Chemistry is a central science. However, the public's recognition of chemistry needs to be promoted, and the prejudice needs to be reduced. Chemical science popularization is a long-term, complex and arduous social education project, which is of great significance to promote social harmony and improve people's quality of life. This paper summarizes the current status of chemical science popularization in China, and puts forward the innovative development countermeasures which focus on improving public participation, training popular science talents, carrying out popular science popularization education at different levels, creating high-quality science popularization works and opening up new positions and approaches of chemical science popularization. This paper has the reference value for the science popularization colleagues. 相似文献
83.
84.
A novel approach to the fabrication of metal ring-disk (RD) microelectrodes is presented that employs flexible chemical vapor deposition (CVD) and electrode modification techniques. Specifically, the development of a copper ring-disk microelectrode is described utilizing a combination of CVD coating, electroetching, and electroplating. Initially, a 25 μm diameter tungsten wire is concentrically coated by CVD with an insulating layer of silica, a layer of tungsten metal, and finally, a second outer layer of silica. The copper surface was prepared by first creating micrometer cavities by electrochemical etching the tungsten in hydroxide solutions followed by electrodeposition of copper from aqueous solutions of Cu(II). Each step of the process was characterized by scanning electron microscopy, optical microscopy, and cyclic voltammetry, demonstrating the preparation of a viable metal-based dual ring-disk microelectrode system. For the purpose of demonstrating the concept of introducing specific selectivity into the device, amperometric detection of galactose in 0.1 M NaOH was performed at +0.60 V in bulk solution and after flow injection analysis in a capillary column. 相似文献
85.
高温超导体的Cu-O键型和氧上的部分电荷 总被引:2,自引:0,他引:2
多数钙钛矿型化合物是离子型绝缘体,而高温超导化合物则有金属电性,它们是以什么键型为主?对此等人[1]认为用共价或金属成键图像描述高温超导体在化学上更合理,Nepela等人[2]指出超导体临界温度(Tc)随阴离子平均电负性与阳离子平均电负性之差增大而升高.这意味着离子性较强的超导体有较高的人.杨频等问运用晶型键参数方法估算结果表明高温超导体属干部分离子性与部分共价性键.以上不同的结果都是基丁理论处理或估算得到的·本文试图在实验上通过比较不同成键特征的铜化合物的x光电子能潜(*P8)来估计对高温超导性起重要作用的C… 相似文献
86.
The chemical fixation of CO2 with mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under the ZnCl2/[BMIm]Br catalyst system without using additional organic solvents was achieved in excellent selectivity (>98%) and TOF (5410 h−1) and the catalyst could be used six times almost without losing its catalytic activity and selectivity. Besides, the pure cis-cyclic carbonate of cyclohexene oxide was obtained in this catalyst system. 相似文献
87.
Ivan Gutman 《Monatshefte für Chemie / Chemical Monthly》2005,136(6):1055-1069
Summary. The fact that cyclic arrangements of double bonds have a dramatic effect on the behavior of conjugated organic molecules is known since the 19th century. The fact that in monocyclic conjugated systems the size of the cycle and the number of -electrons involved is decisive for their stability (aromaticity) or lack of stability (antiaromaticity) is known since the 1930s. In polycyclic -electron systems several cyclic effects are present simultaneously and their separation became possible only recently. A molecular orbital method has been elaborated, by means of which the energy effects of individual cycles in polycyclic -electron systems can be estimated. This method is briefly outlined and illustrated by pertinent examples. An exhaustive bibliography of the topic considered is given. 相似文献
88.
89.
Oxidative cyclization of 2-pyrrolidinyl-acetamide and 2-pyrrolidinyl-propionamide local anaesthetics
2 - Pyrrolidinyl - acetamide and -propionamide local anaesthetics (1a–d) on oxidation with mercuric acetate, potassium hexacyanoferrate(III) and potassium permanganate underwent oxidative cyclization to give new bicyclic compounds, hexahydro - 1H - pyrrolo[1,2 - a]imidazolin - 2 - ones (2a–d). The propionamides (1c–d) yielded mixtures of the two possible diastereoisomers of 2c and 2d. These were separated; in solution and above their melting points they epimerized via ring opening and reclosure between the 7a-carbon and 1-nitrogen atoms. 相似文献
90.
用ICP-AES法测定了东太平洋深海锰结核样品中二十多种主,次及微量元素,结果表明,表面瘤状和表面光滑两种类型锰结核的化学元素含量有较明显的区别,如表面光滑的锰结核TiO2含较高,而表面瘤状的锰结核Mn/Fe之值较高等。 相似文献