全文获取类型
收费全文 | 3023篇 |
免费 | 87篇 |
国内免费 | 74篇 |
专业分类
化学 | 2467篇 |
晶体学 | 12篇 |
力学 | 88篇 |
综合类 | 25篇 |
数学 | 347篇 |
物理学 | 245篇 |
出版年
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 21篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 23篇 |
2017年 | 24篇 |
2016年 | 24篇 |
2015年 | 24篇 |
2014年 | 61篇 |
2013年 | 61篇 |
2012年 | 59篇 |
2011年 | 77篇 |
2010年 | 74篇 |
2009年 | 93篇 |
2008年 | 139篇 |
2007年 | 194篇 |
2006年 | 125篇 |
2005年 | 109篇 |
2004年 | 138篇 |
2003年 | 112篇 |
2002年 | 130篇 |
2001年 | 97篇 |
2000年 | 130篇 |
1999年 | 91篇 |
1998年 | 87篇 |
1997年 | 105篇 |
1996年 | 78篇 |
1995年 | 109篇 |
1994年 | 79篇 |
1993年 | 100篇 |
1992年 | 65篇 |
1991年 | 74篇 |
1990年 | 91篇 |
1989年 | 71篇 |
1988年 | 104篇 |
1987年 | 127篇 |
1986年 | 63篇 |
1985年 | 40篇 |
1984年 | 52篇 |
1983年 | 7篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有3184条查询结果,搜索用时 15 毫秒
1.
溴酸钾-亚甲蓝催化光度法测定硝酸盐和亚硝酸盐 总被引:16,自引:1,他引:15
用镉柱将NO-3 还原为NO-2 ,利用在磷酸介质中NO-2 对溴酸钾氧化亚甲蓝这一褪色反应具有强烈的催化作用而建立了同时测定痕量硝酸盐和亚硝酸盐的新方法。本方法简便、快速、灵敏 ,对亚硝酸盐和硝酸盐测定的线性范围分别为 0~ 2 0 0 μg·L-1和 0 0 0 3~ 310 μg·L-1,用于测定各种水样中痕量NO-2 和NO-3 的含量均获得满意结果 相似文献
2.
3.
4.
Summary Excessive breakdown of elastin, a structural protein, may be related to aortic disease and emphysema. Since L-valyl-L-proline occurs in high concentrations in elastin, a rapid and sensitive method using HPLC with post-column on-line derivatization was used to measure the dipeptide from swine aortic tissue, and the amount of elastin present was determined. Elastin was extracted by alkaline hydrolysis. After neutralization and filtration, the sample was injected onto a ODS-2 gel column, and the dipeptide was eluted by a linear gradient of 0 to 10% of 1-propanol in 50 mM heptafluorobutyrate, pH 3, at a flow rate of 1 ml/min. The eluent was reacted with fluorescamine at pH 8.6, and fluorescence was detected at an excitation wavelength of 395 nm and a 455 nm cutoff emission filter.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria. 相似文献
5.
通过用毛细管测量纯水表面张力系数实验,得到管内径d与接触角θ的相对误差之间的关系曲线,由此说明实验测得的表面张力系数α和理论公式相比呈现一定的偏差,并简单地讨论了实验的理想状态与实际情况的差别. 相似文献
6.
7.
A method employing a wide pore polymeric reversed phase column has been developed for the separation of most of the chlorophylls and related compounds previously described as occurring in marine microalgae. The high selectivity toward molecular shape of this kind of stationary phase has enabled compounds of very similar structure, such as chlorophylls c1, c2 and Mg-divinylpheoporphyrin a5 monomethyl ester, and chlorophyll a and the phytol-substituted chlorophyll c-like pigments, which commonly coelute on monomeric bonded phases, to be resolved in a single run. Some of these pigments, formerly thought to be a single compound, have, in fact, been demonstrated to be groups of two or more. The method has been successfully applied to both algal cultures and natural sea water samples. When visible light absorbance detection was used, the method proved suitable for separation of various carotenoids. 相似文献
8.
The Dantzig-Wolfe reformulation principle is presented based on the concept of generating sets. The use of generating sets allows for an easy extension to mixed integer programming. Moreover, it provides a unifying framework for viewing various column generation practices, such as relaxing or tightening the column generation subproblem and introducing stabilization techniques. 相似文献
9.
A new method for constructing infinite families of k-tight optimal double loop networks 总被引:2,自引:0,他引:2
CHEN Xiebin Department of Mathematics Information Science Zhangzhou Teachers College Zhangzhou China 《中国科学A辑(英文版)》2006,49(4)
The double loop network (DLN) is a circulant digraph with n nodes and outdegree 2. DLN has been widely used in the designing of local area networks and distributed systems. In this paper, a new method for constructing infinite families of k-tight optimal DLN is presented. For k = 0,1,…,40, the infinite families of k-tight optimal DLN can be constructed by the new method, where the number nk(t,a) of their nodes is a polynomial of degree 2 in t and contains a parameter a. And a conjecture is proposed. 相似文献
10.
G. Gargaro F. Gasparrini D. Misiti G. Palmieri M. Pierini C. Villani 《Chromatographia》1987,24(1):505-509
Summary Enantiomers of several sulfoxides and some selenoxides can be easily separated by using a new chiral stationary phase (CSP-DACH-DNB)
containing the 3,5-dinitrobenzoyl derivative of R,R-(-)1,2-diamino-cyclohexane as selector, covalently bonded to the siliceous
matrix. The easy operative conditions and the high enantioselectivity values (α) allow a direct transfer of the analytical
separations to a semi-preparative and preparative scale. 相似文献