全文获取类型
收费全文 | 4030篇 |
免费 | 280篇 |
国内免费 | 545篇 |
专业分类
化学 | 3356篇 |
晶体学 | 22篇 |
力学 | 94篇 |
综合类 | 38篇 |
数学 | 283篇 |
物理学 | 1062篇 |
出版年
2024年 | 13篇 |
2023年 | 33篇 |
2022年 | 54篇 |
2021年 | 27篇 |
2020年 | 30篇 |
2019年 | 43篇 |
2018年 | 48篇 |
2017年 | 38篇 |
2016年 | 44篇 |
2015年 | 35篇 |
2014年 | 76篇 |
2013年 | 46篇 |
2012年 | 316篇 |
2011年 | 388篇 |
2010年 | 95篇 |
2009年 | 168篇 |
2008年 | 488篇 |
2007年 | 353篇 |
2006年 | 399篇 |
2005年 | 422篇 |
2004年 | 313篇 |
2003年 | 247篇 |
2002年 | 191篇 |
2001年 | 118篇 |
2000年 | 135篇 |
1999年 | 71篇 |
1998年 | 45篇 |
1997年 | 52篇 |
1996年 | 76篇 |
1995年 | 61篇 |
1994年 | 62篇 |
1993年 | 82篇 |
1992年 | 51篇 |
1991年 | 41篇 |
1990年 | 25篇 |
1989年 | 30篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 21篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1963年 | 3篇 |
1962年 | 4篇 |
1961年 | 3篇 |
排序方式: 共有4855条查询结果,搜索用时 179 毫秒
31.
32.
1 INTRODUCTION donor due to the presence of the protonated carboxyl group; (d) it can form short bridges via one car- Coordination polymers are of great interest due to boxylato end or long bridges via the benzene ring[7]. their physical properties and potential applications in We believe that coordination functionality of isoph- functional materials[1~3]. Aromatic polycarboxylic acids thalate can lead to interesting structures. In this com- such as 1,2,4,5-benzenetetracarboxylic acid[4],… 相似文献
33.
一水草酸铵(简称AOM)是一种优良的电光晶体 ̄[1]。文献 ̄[1,2]报道了该晶体的晶体结构,化学式为(NH_4)_2C_2O_2·H_2O,属正交晶系,P222空间群,晶胞参数a=0.8035nm,b=1。031nm,c=0.3801nm,z=2。本文拟报道AOM单晶生长,热化学分析,透过波段以及非线性光学性质的初步研究。 相似文献
34.
35.
36.
LIU Langa JI Ya-Lia JIA Dian-Zenga② YU Kai-Beib a 《结构化学》2003,22(5):568-572
1 INTRODUCTION In recent years, investigations on the com- pounds containing hydrazide or hydrazone moieties have been increased considerably because of their potentially biological activities, especially as poten- tial inhibitors for many enzymes[1~5]. The presence of weak molecular interactions such as hydrogen- bonding controls the conformational and structural features which are important to the drug action[6, 7]. We have synthesized the photochromic compounds of pyrazolone thiosemi… 相似文献
37.
1 INTRODUCTION 2-Aminochromene is an important class of com- pounds found as the main compounds of many natu- rally occurring products employed as cosmetics and pigments and utilized as potential biodegradeable agro- chemicals[1~3]. In recent years, montmorillonite in natural and ex- changed forms has received considerable attention in different organic syntheses because of its environ- mental compatibility, low cost, high selectivity, reusa- bility and operational simplicity[4], such as … 相似文献
38.
XU Xing-Youa MA Wei-Xinga GAO Jiana LIU Qing-Liangb a 《结构化学》2002,21(5):473-476
1 INTRODUCTION Macrocyclic ligands and their metal complexes have received much attention due to their applications in ion transport, ion separation and as models in biomimic researches[1~7]. The synthetic methods of macrocyclic ligands and their metal complexes are mainly divided into three kinds[8]. The first one is synthesizing free ligand, then forming the metal complexes; the second is template synthesis; and the third is synthesizing the end-off or side-off precursor ligand, then c… 相似文献
39.
A simple technique is described for the routine simultaneous capillary electrophoretic determination of 6 cations in wine. Separation was achieved on a fused silica capillary column with a UV-Cat-1, alpha-hydroxysobutyric acid and 18-crown-6-ether buffer at pH 4.5 and indirect UV detection at 214 nm. The content of magnesium, sodium, potassium, calcium, manganese, and lithium was determined. The method is quantitative, with recoveries in the 92-102% range, and linear over more than one order of magnitude. The precision is better than 2.5-3.4%. The method is sensible, with detection limits between 0.01 and 0.06 mg/L. Twenty-five red wines with a Certified Brand of Origin from Galicia (north-western Spain) were analyzed by the proposed method. Various wines showed very similar electrophoretic profiles, but significant quantitative differences were observed. 相似文献
40.
脱乙酰甲壳质是甲壳质衍生物中最重要,用途最为广泛的一种,属阳离子性聚电解质,可以溶于多种稀酸溶液中,本文从脱乙酰甲壳质在甲酸、乙酸和丁酸溶液中的粘度变化,研究其稀溶液性质。分別考察了脱乙酰甲壳质在8×10~(71)~3×10~(72)/1,酸浓度在5×10~(-1)~1×10~(-1)mol范围内溶液ηsp/c-c的关系。实验结果表明,作为脱乙酰甲壳质溶剂的酸,在溶液稀释时对溶液ηsp/c的影响,在不同的阶段可以是完全不同的。当溶液中可离解的酸还未能完全满足游离氨基成盐要求时,酸溶液的增加将导致溶液的ηsp/c的增加,而一旦游离氨都已成盐,过量酸的增加都会导致溶液粘度的下降。而在一般情况下,酸的酸性越强,酸的浓度越大,都会使溶液得到较低的粘度值。 相似文献