全文获取类型
收费全文 | 18350篇 |
免费 | 2626篇 |
国内免费 | 885篇 |
专业分类
化学 | 20158篇 |
晶体学 | 60篇 |
力学 | 91篇 |
综合类 | 22篇 |
数学 | 41篇 |
物理学 | 1489篇 |
出版年
2024年 | 32篇 |
2023年 | 257篇 |
2022年 | 648篇 |
2021年 | 694篇 |
2020年 | 1256篇 |
2019年 | 962篇 |
2018年 | 781篇 |
2017年 | 653篇 |
2016年 | 1259篇 |
2015年 | 1118篇 |
2014年 | 1125篇 |
2013年 | 1350篇 |
2012年 | 1052篇 |
2011年 | 1102篇 |
2010年 | 938篇 |
2009年 | 977篇 |
2008年 | 923篇 |
2007年 | 851篇 |
2006年 | 795篇 |
2005年 | 715篇 |
2004年 | 725篇 |
2003年 | 579篇 |
2002年 | 1238篇 |
2001年 | 278篇 |
2000年 | 194篇 |
1999年 | 207篇 |
1998年 | 236篇 |
1997年 | 165篇 |
1996年 | 110篇 |
1995年 | 122篇 |
1994年 | 66篇 |
1993年 | 42篇 |
1992年 | 38篇 |
1991年 | 42篇 |
1990年 | 41篇 |
1989年 | 24篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 70篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 11篇 |
1970年 | 7篇 |
1966年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
M. Matschke 《Tetrahedron letters》2005,46(47):8249-8251
Syntheses and redox chemistry of the nearly unknown 4,4′,5,5′-tetraamino derivatives of 2,2′-biimidazole are studied. These cyclic versions of electron-rich ethenes are only stable under strictly anaerobic conditions. In the presence of oxygen, a fast oxidation reaction occurs to form stable, deeply coloured tetraazafulvalenes. Leuco-forms, however, can be stabilized towards air by acylation reactions. This accounts for the hexa-Boc derivative 6. Based on these findings, we present the first synthesis of tetraazafulvalenes, which possess four peripheric secondary amine functions. 相似文献
92.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(1):160-163
This paper describes the preparation of uniform silver nanowires by reducing freshly prepared silver chloride with glucose at 180 °C for 18 hours in the absence of any surfactants or polymers. Scanning electron microscopy studies indicated that the silver nanowires are about 100 nm in diameter and up to 500 μm in length. High‐resolution transmission electron microscopy analyses showed that the silver nanowires grow perpendicularly to the Ag(200) plane. The silver nanowires are believed to grow through a solid–solution–solid process. Some influential factors on the growth of silver nanowires are also discussed. 相似文献
93.
David Gerristma 《Tetrahedron letters》2004,45(45):8319-8321
The use of Pd2dba3·CHCl3 and 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phospha-adamantane has been shown to facilitate the effective amination of aryl halides with aromatic or aliphatic amines in high yields. 相似文献
94.
The laccase catalyzed oxidative dimerization of salicylic esters, a rare example of a laccase-catalyzed carbon-carbon bond formation, was studied. This reaction allows the use of air as stoichiometric oxidant and proceeds in aqueous solution. The preparative scope and the mechanism of the method, which provides a new and convenient access to functionalized biaryls under mild conditions, were investigated. 相似文献
95.
The crystal-chemical structure of the minerals and inorganic compounds kuznetsovite [Hg3](AsO4)Cl and terlinguaite [Hg3][HgO2]Cl2, as well as [Hg3]3(AsO4)4 and [Hg3]2[HgO2](PO2 and their analogs, is considered from the viewpoint of the packing of large supramolecular atomic groups. The cationic layer of polyhedra around the large [Hg3]4+ cations, alternating with the anionic layer of [HgO2]2-, (AsO4)3-, (PO4)3-, Cl-, plays the major role in structure formation. Segregation of mercury cations of different valences possibly reflects the solid-state transformations occurring in nature and accompanied by mercury liberation. 相似文献
96.
元素无机化学是大学化学及相关专业无机化学课程的核心内容。如何教好、学好元素无机化学的知识一直是教学工作者研究的课题。为改变教学现状,提高教学效果,培养学生的逻辑思维和科学创新能力,提出一种整合元素无机化学知识的思路,即:以化合物类型为主线对元素无机化学知识进行系统化整合,并以氧化物部分为例加以说明。 相似文献
97.
茂基稀土胺化物(MeCp)2YbNPh2(THF)与异氰酸正己酯(n-HexylNCO)按11摩尔比反应, 分离出产物{(MeC5H4)2Yb[OC(NPh2)N(n-hexyl)]}2. 产物经元素分析和核磁共振表征, 并测定了其晶体结构. 配合物属三斜晶系, R-3空间群, 晶胞参数为a=2.9533(11) nm, b=2.9533(11) nm, c=1.5873(6) nm, V=11.9896(80) nm3, Z=9, Dc=1.562 mg·m-3, μ=3.536 mm-1 (Mo Kα), F(000)=5670, R=0.034, Rw=0.064. 该化合物具有二个对称氧桥的双分子结构, 并存在着由氮原子向中心金属镱分子内配位而形成的三环骨架, 中心金属镱的配位数是九, 整个分子呈中心对称. 相似文献
98.
"Energy chemistry" was approved as one of the chemistry majors for undergraduate by the Ministry of Education in 2015. Based on the ideas and ways of emerging engineering education, this paper hereby proposed some of constructive suggestions on the training objectives, graduation requirements, curriculum system, teaching contents, teaching staff and conditions for development of "energy chemistry" major. 相似文献
99.
Yuming Dong Yuqiang Ding Weifu Dong Cheng Yang Xuefeng Liu Ye Fan Jing Wang Qingwei Pan 《大学化学》1986,35(10):71-76
Based on the development prospect of cosmetics industry, the advantage of light industry characteristic and the foundation of applied chemistry in Jiangnan University, a systematic upgrading of applied chemistry was carried out through "emerging engineering education (3E)" project "upgrade and practice of chemistry-related majors of local and/or trade university responding to the social developments" supported by the Ministry of Education. On the basis of investigation and analysis, the orientation and training goal of applied chemistry were updated first, and then the curriculum system was determined and the curriculum construction is strengthened, so as to achieve more distinctive characteristics, more solid foundation and more comprehensive quality. In view of the new requirements of the 3E for talent training, some practices have been formed in the aspects of multi-disciplinary integration, multi-angle coordination and close integration to industry. Contributing the development of cosmetics industry and seizing the commanding point of science and technology from the perspective of talent training, will play a unique role in human social progress. 相似文献
100.
有机化学,特别是天然有机化学,是和医学科学密切相关的,有机化学的成就在许多方面促进了医学科学的进步,反过来医学科学中提出的课题也推动了有机化学的发展。本文以抗疟药等天然药物和廿碳酸类等生理活性物质为例讨论了这两门学科间的一些关系。 相似文献