全文获取类型
收费全文 | 4654篇 |
免费 | 615篇 |
国内免费 | 458篇 |
专业分类
化学 | 3453篇 |
晶体学 | 51篇 |
力学 | 258篇 |
综合类 | 39篇 |
数学 | 510篇 |
物理学 | 1416篇 |
出版年
2023年 | 71篇 |
2022年 | 76篇 |
2021年 | 142篇 |
2020年 | 157篇 |
2019年 | 176篇 |
2018年 | 155篇 |
2017年 | 129篇 |
2016年 | 223篇 |
2015年 | 187篇 |
2014年 | 231篇 |
2013年 | 325篇 |
2012年 | 329篇 |
2011年 | 378篇 |
2010年 | 259篇 |
2009年 | 254篇 |
2008年 | 289篇 |
2007年 | 260篇 |
2006年 | 263篇 |
2005年 | 183篇 |
2004年 | 175篇 |
2003年 | 159篇 |
2002年 | 182篇 |
2001年 | 138篇 |
2000年 | 108篇 |
1999年 | 115篇 |
1998年 | 99篇 |
1997年 | 86篇 |
1996年 | 52篇 |
1995年 | 74篇 |
1994年 | 61篇 |
1993年 | 51篇 |
1992年 | 54篇 |
1991年 | 35篇 |
1990年 | 37篇 |
1989年 | 16篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1969年 | 4篇 |
排序方式: 共有5727条查询结果,搜索用时 125 毫秒
101.
Cecilia Wan Ying Chung 《Tetrahedron》2005,61(3):709-715
An insoluble polystyrene-supported triflating reagent has been prepared by suspension co-polymerization of N-(4-vinylphenyl)trifluoromethanesulphonimide, styrene and the JandaJel® cross-linker. This reagent, in the presence of triethylamine, allows for the efficient synthesis of aryl triflates from a wide range of phenols in a process that permits the desired product to be isolated from the reaction mixture in essentially pure form via several filtration and concentration operations. Adding to the utility of this reagent is its ability to be easily recovered, regenerated and reused. Both soluble and insoluble bifunctional polymers containing trialkylamine moieties in addition to triflimide groups were also prepared and examined as triflating reagents. Unfortunately these reagents afforded only modest yields of the desired products in representative reactions. 相似文献
102.
LeiLi Xiao-dongZhao Jing-lunZhou Xing-heFan Xiao-fangChen Xin-huaWan Qi-fengZhou 《高分子科学》2004,(4):349-353
Aromatic polybenzoxazole (PBO) precursor, hydroxy-substituted polyenaminonitrile, was prepared by direct polycondensation of 1,4-bis(l-chloro-2,2-dicyanovinyl)benzene (CCB) and 4,6-diaminoresorcinol dihydrochloride (DAR) using pyridine and N,N-dimethylacetamide as condensing agent and solvent. The precursor has good solubility in polar aprotic solvent which is due to the strong dipolar nature of the main chain. The soluble precursor was subjected to thermal cyclization in an inert atmosphere to convert it into the corresponding PBO, which has its 5% weight loss temperature at 540℃ The fully cyclized PBO were characterized by FT-IR and TGA. The introduction of 10% mol 1,3,5-benzenetricarboxylic chloride (BTC) into the main chain not only has little effect on the solubility of PBO precursor but also raises its 5% weight loss temperature to 552℃ and char yield at 700℃ for the cyclized PBO with BTC. 相似文献
103.
The time-resolved ESR signal of a triplet radical pair was detected upon excitation of a solid mixture of acridine and acridan at room temperature. The ZFS parameters of the triplet radical pair were determined to be D=−0.0100 cm−1 and E=0.00053 cm−1. The structure of the radical pair is discussed on the basis of the data. 相似文献
104.
The sorption and desorption characteristics of gold and silver on a polyhydroxamic acid chelating resin are described. Gold is quantitatively sorbed from 0.5 M nitric acid or neutral solutions, and readily eluted with 0.5% () potassium cyanide solution. Silver is removed from 0.05 M nitric acid or neutral solutions, and can be eluted with the cyanide solution or with 0.5 M nitric acid. Gold can be quantitatively separated from copper, iron and silver; gold and silver are sorbed from dilute cyanide solutions. Tests with river water and other eluting systems are reported. 相似文献
105.
106.
107.
This paper proves that circular vortex patches in the plane are stable for the nonlinear dynamical system generated by the Euler equations of incompressible fluids. This is achieved by establishing a relative variational principle in terms of either energy or angular momentum. Thus, we exploit and extend Arnold's idea in (1965, 1969) to a nonsmooth setting as well.Research partially supported by DOE contract DE-AT03-82ER12097 to the University of California, Berkeley 相似文献
108.
单胺类神经递质,多巴胺(DA)、去甲肾上腺素(NA)和肾上腺素(A)是哺乳动物和人类中枢重要的信息传递物质。了解脑组织中各部位单胺类神经递质的含量对于研究其生理功能、有关疾病的诊断和药物及手术疗效的评价均有重要的意义。 相似文献
109.
110.
氧化物、盐类在氧化物载体表面的自发分散是一种广泛存在的现象,文献中已报导过大量氧化物和盐类在高比表面载体上分散的研究结果['-3]TIO。作为一种较新型的载体,与Y-AI。O。、硅胶等传统载体相比,有许多不同特性.活性组分在TIO。表面的分散状态及所得催化剂的性能已有不少报导['-'],但所用的TIOZ主要是较高比表面的锐钛矿型TIOZ(刘金红石型TIO。(r)和锐钛矿型TIOZ(a)的结构不同,它是高温生成相,比表面较小['].氧化物在金红石上的分散行为仍未见报导.我们制备了三种具有不同比表面的TIO水),系统地研… 相似文献