全文获取类型
收费全文 | 43647篇 |
免费 | 18132篇 |
国内免费 | 57篇 |
专业分类
化学 | 55390篇 |
晶体学 | 53篇 |
力学 | 2050篇 |
综合类 | 2篇 |
数学 | 3103篇 |
物理学 | 1238篇 |
出版年
2024年 | 158篇 |
2023年 | 4086篇 |
2022年 | 1427篇 |
2021年 | 2481篇 |
2020年 | 4639篇 |
2019年 | 2322篇 |
2018年 | 2303篇 |
2017年 | 641篇 |
2016年 | 5603篇 |
2015年 | 5554篇 |
2014年 | 4996篇 |
2013年 | 5248篇 |
2012年 | 3227篇 |
2011年 | 1073篇 |
2010年 | 3450篇 |
2009年 | 3385篇 |
2008年 | 1059篇 |
2007年 | 776篇 |
2006年 | 130篇 |
2005年 | 90篇 |
1997年 | 86篇 |
1995年 | 144篇 |
1994年 | 90篇 |
1993年 | 213篇 |
1992年 | 98篇 |
1988年 | 120篇 |
1987年 | 102篇 |
1986年 | 81篇 |
1985年 | 106篇 |
1984年 | 110篇 |
1983年 | 107篇 |
1982年 | 132篇 |
1981年 | 162篇 |
1980年 | 197篇 |
1979年 | 189篇 |
1978年 | 196篇 |
1977年 | 317篇 |
1976年 | 368篇 |
1975年 | 459篇 |
1974年 | 476篇 |
1973年 | 291篇 |
1972年 | 372篇 |
1971年 | 357篇 |
1970年 | 542篇 |
1969年 | 417篇 |
1968年 | 457篇 |
1967年 | 116篇 |
1966年 | 89篇 |
1965年 | 83篇 |
1963年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
A 2D HgII coordination polymer containing ligands 1,2,4‐triazole (Htrz) and thiocyanate, [Hg(μ3‐trz)(SCN)]n ( 1 ) has been synthesized and characterized by elemental analysis and IR spectroscopy. The single‐crystal X‐ray data show the coordination number of Hg atoms is four and the ligand trz? acts as a three‐fold donor. The thermal stability of compound 1 was studied by thermal gravimetric and differential thermal analyses. The composition and formation of the complex in methanol solution were found to be in support of its solid state structure. 相似文献
142.
Ohne Zusammenfassung 相似文献
143.
144.
145.
146.
147.
Akira Yanagisawa Prof. Dr. Takahiro Suzuki Takanori Koide Shogo Okitsu Takayoshi Arai Prof. Dr. 《化学:亚洲杂志》2008,3(10):1793-1800
A Barbier‐type regioselective propargylation of aldehydes and ketones with (3‐bromobut‐1‐ynyl)trimethylsilane has been achieved using reactive barium as a low‐valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of α,β‐unsaturated carbonyl compounds, only 1,2‐adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13. 相似文献
148.
Silica@copper (SiO2@Cu) core–shell nanoparticles were synthesized and well characterized by XRD, TEM, AFM, XPS, UV/Vis, TGA–MS, and ICP–AES techniques. The synthesized SiO2@Cu core–shell nanoparticles were employed as catalysts for the conjugate addition of amines to α,β‐unsaturated compounds in water to obtain β‐amino carbonyl compounds in excellent yields in shorter reaction times. Furthermore, the catalyst works well for hetero‐Michael addition reactions of heteroatom nucleophiles such as thiols to α,β‐unsaturated compounds. As the reaction is performed in water, it allows for easy recycling of the catalyst with consistent activity. 相似文献
149.
150.
In this article, we present results of an empirical study with 500 German students of grades 7 and 8. The study focussed on students' mathematics achievement and their interest in mathematics as well as on the relation between these two constructs. In particular, the results show that the development of an individual student's achievement between grade 7 and grade 8 depends on the achievement level of the specific classroom and therefore on the specific mathematics instruction Interest in mathematics could be regarded a predictor for mathematics achievement Moreover, our findings suggest that the students show hardly any fear of mathematics independent of their achievement level. 相似文献