全文获取类型
收费全文 | 12479篇 |
免费 | 2585篇 |
国内免费 | 5309篇 |
专业分类
化学 | 9623篇 |
晶体学 | 624篇 |
力学 | 913篇 |
综合类 | 391篇 |
数学 | 1853篇 |
物理学 | 6969篇 |
出版年
2024年 | 36篇 |
2023年 | 143篇 |
2022年 | 448篇 |
2021年 | 444篇 |
2020年 | 434篇 |
2019年 | 447篇 |
2018年 | 384篇 |
2017年 | 606篇 |
2016年 | 403篇 |
2015年 | 594篇 |
2014年 | 775篇 |
2013年 | 1081篇 |
2012年 | 1008篇 |
2011年 | 1153篇 |
2010年 | 1201篇 |
2009年 | 1260篇 |
2008年 | 1352篇 |
2007年 | 1260篇 |
2006年 | 1236篇 |
2005年 | 1003篇 |
2004年 | 815篇 |
2003年 | 580篇 |
2002年 | 568篇 |
2001年 | 552篇 |
2000年 | 683篇 |
1999年 | 346篇 |
1998年 | 193篇 |
1997年 | 151篇 |
1996年 | 159篇 |
1995年 | 112篇 |
1994年 | 132篇 |
1993年 | 134篇 |
1992年 | 101篇 |
1991年 | 70篇 |
1990年 | 85篇 |
1989年 | 83篇 |
1988年 | 70篇 |
1987年 | 55篇 |
1986年 | 38篇 |
1985年 | 22篇 |
1984年 | 26篇 |
1983年 | 22篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1971年 | 5篇 |
1965年 | 11篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
功能化基团对C60-β-丙氨酸衍生物清除超氧阴离子自由基O-2·能力的影响 总被引:4,自引:0,他引:4
自Chiang等[1]发现富勒醇可以清除*OH以来, C60衍生物作为自由基清除剂的研究备受关注[2,3]. 超氧阴离子自由基O-*2是生物体内一类重要的氧自由基, 可以经过一系列反应生成其它自由基, 从而引发一系列疾病[4]. 及时清除过剩的O-*2具有重要意义. 相似文献
62.
63.
A new element tracer technique has firstly been established to estimate the contributions of mineral aerosols from both inside and outside Beijing. The ratio of Mg/Al in aerosol is a feasible element tracer to distinguish between the sources of inside and outside Beijing. Mineral aerosol, inorganic pollution aerosol mainly as sulfate and nitrate, and organic aerosol are the major components of airborne particulates in Beijing, of which mineral aerosol accounted for 32%―67% of total suspended particles (TSP), 10%―70% of fine particles (PM2.5), and as high as 74% and 90% of TSP and PM2.5, respectively, in dust storm. The sources from outside Beijing contributed 62% (38%―86%) of the total mineral aerosols in TSP, 69% (52%―90%) in PM10, and 76% (59%―93%) in PM2.5 in spring, and 69% (52%―83%), 79% (52%―93%), and 45% (7%―79%) in TSP, PM10, and PM2.5, respectively, in winter, while only ~20% in summer and autumn. The sources from outside Beijing contributed as high as 97% during dust storm and were the dominant source of airborne particulates in Beijing. The contributions from outside Beijing in spring and winter are higher than those in summer, indicating clearly that it was related to the various meteorological factors. 相似文献
64.
In the degassing process of transformer oil with ultrasonic waves ,decompostition of the oil was observed.Light hydrocarbons,including methane,ethane,ethylene ,aceylene,propane etc,were found to be released continuously from the oil into headspace within a closed vial placed in an ultrasonic field ,The gases came from decomposition of hydrocarbon molecules under cavitation effect. 相似文献
65.
AlkylationofBenzenewithPropeneoverHβZeolite──TheEffectofReactionConditionsontheDistributionofProductsMAJun,SHENJian-ping,SUNT... 相似文献
66.
67.
68.
IntroductionInthepastseveralyears ,considerableprogresshasbeenachievedincontrollingtheassemblyofindividualbuildingblocksintostructureswithspecifictopologiesandinterestingpropertiessuchasmolecularrecognition ,ionexchangeandselectiveguestinclusion .1 3 Itis… 相似文献
69.
The polystyrene supported phenylalanine Schiff base complex of Mn(Ⅱ)(PS-Sal-Phe-Mn)was prepared with chloromethylated styrene polymer beads, 2,4-dihydroxybenzaldehyde,L-phenylalanine and manganese(Ⅱ)acetate tetrahyrate., The polymeric ligand and the complex were characterized by FT-IR,, small area X-ray photoelectron spectroscopy(XPS), and ICP-AES. In the presence of the manganese complex, cyclohexene(1)was effectively oxidized by molecular oxygen without reductant. The major products of the reaction were 2-cyclohexen-1-ol(2),2-cyclohexen-1-one(3)and 2-cyclohexen-1- hydroperoxide(4), which was different with typical oxidation of cyclohexene. The influence of reaction temperature and additive for oxidation had been studied. The selectivity of 2-cyclohexen-l-hydroperoxide varied with reaction time and different additives. The mechanism of cyclohexene oxidation had also been discussed. 相似文献
70.