全文获取类型
收费全文 | 1491篇 |
免费 | 337篇 |
国内免费 | 247篇 |
专业分类
化学 | 948篇 |
晶体学 | 57篇 |
力学 | 47篇 |
综合类 | 21篇 |
数学 | 121篇 |
物理学 | 881篇 |
出版年
2024年 | 11篇 |
2023年 | 25篇 |
2022年 | 46篇 |
2021年 | 62篇 |
2020年 | 70篇 |
2019年 | 60篇 |
2018年 | 38篇 |
2017年 | 54篇 |
2016年 | 68篇 |
2015年 | 90篇 |
2014年 | 99篇 |
2013年 | 116篇 |
2012年 | 116篇 |
2011年 | 116篇 |
2010年 | 109篇 |
2009年 | 83篇 |
2008年 | 94篇 |
2007年 | 78篇 |
2006年 | 80篇 |
2005年 | 86篇 |
2004年 | 66篇 |
2003年 | 73篇 |
2002年 | 103篇 |
2001年 | 58篇 |
2000年 | 48篇 |
1999年 | 44篇 |
1998年 | 32篇 |
1997年 | 30篇 |
1996年 | 26篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有2075条查询结果,搜索用时 0 毫秒
951.
Zhang C Albermann C Fu X Thorson JS 《Journal of the American Chemical Society》2006,128(51):16420-16421
The glycosyltransferase AveBI, which is involved in the biosynthesis of the macrolide antihelmintic avermectin (AVM), was characterized in vitro. AveBI was confirmed to catalyze two separate iterative additions of l-oleandrose, and the reversibility of AveBI-catalyzed reaction was also demonstrated. Investigation of sugar nucleotide specificity revealed 10 unique sugar nucleotide substrates which, in combination with five distinct aglycones, led to the production of 50 differentially glycosylated AVM variants. 相似文献
952.
通过对竖直放置直接甲醇燃料电池水平流道内扩散层壁面上CO_2气泡的受力分析,建立描述气泡生长动力学方程,获得CO_2气泡生长速率和气泡脱离直径的计算方法。计算结果表明:CO_2气泡生长和脱离主要受浮力、曳力、剪切升力和表面张力的控制;气泡生长速率随电流密度和接触环直径的增大而增大;甲醇溶液流速增加,气泡脱离直径变小,且流速对气泡脱离直径的影响随接触环直径减小而变大;电池放电电流密度的变化对气泡脱离直径几乎没有影响;温度和甲醇浓度增加,均使气泡脱离直径略有减小;扩散层表面润湿性越好,气泡的脱离直径越小。 相似文献
953.
通过对2007年10月-2008年4月经停厦门港的不同航线9条国际船舶29个压舱水中有色溶解有机物(CDOM)的三维荧光光谱和吸收光谱分析,探讨了利用CDOM光谱参数检验进出我国港口的国际船舶是否进行了远洋压舱水交换(BWE)国际公约规定的可行性.利用平行因子分析(PARAFAC)对三维荧光光谱进行解潜,共鉴别出压舱水CDOM具有2个类腐殖质及2个类蛋白质荧光组分,其中长波类腐殖质组分C2(250,345/458 nm)可作为判断压舱水是否进行BWE的合适指标.压载舱中各荧光组分垂直分布基本均匀.利用C2组分结合吸收光谱斜率比值SR、盐度等指标.对七述船舶是否进行BWE作出了准确判断.研究结果表明,3类指标的综合应用将能更有效地对国际船舶是否进行BWE进行可靠的检验,对今后在厦门港乃至国内其他港口开展压舱水水源的快速检测提供了技术支撑. 相似文献
954.
We investigated solution-processed films of 4,4′-bis(2,2-diphenylvinyl)-1,1′-bibenyl (DPVBi) and its blends with N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) by atomic force microscopy (AFM). The AFM result shows that the solution-processed films are pin-free and their morphology is smooth enough to be used in OLEDs. We have developed a solution-processed white organic light-emitting device (WOLEDs) based on small-molecules, in which the light-emitting layer (EML) was formed by spin-coating the solution of small-molecules on top of the solution-processed hole-transporting layer. This WOLEDs, in which the EML consists of co-host (DPVBi and TPD), the blue dopant (4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) and the yellow dye (5,6,11,12-tetraphenylnaphtacene), has a current efficiency of 6.0 cd/A at a practical luminance of 1000 cd/m2, a maximum luminance of 22500 cd/m2, and its color coordinates are quite stable. Our research shows a possible approach to achieve efficient and low-cost small-molecule-based WOLEDs, which avoids the complexities of the co-evaporation process of multiple dopants and host materials in vacuum depositions. 相似文献
955.
Yao T Zhang X Sun Z Liu S Huang Y Xie Y Wu C Yuan X Zhang W Wu Z Pan G Hu F Wu L Liu Q Wei S 《Physical review letters》2010,105(22):226405
Understanding the kinetics during the metal-insulator transition process is crucial to sort out the underlying physical nature of electron-lattice interactions in correlated materials. Here, based on the temperature-dependent in situ x-ray absorption fine structure measurement and density-functional theory calculations, we have revealed that the monoclinic-to-tetragonal phase transition of VO2 near the critical temperature is characterized by a sharp decrease of the twisting angle δ of the nearest V-V coordination. The VO2 metallization occurs in the intermediate monoclinic like structure with a large twist of V-V pairs when the δ angle is smaller than 1.4°. The correlation between structural kinetics and electronic structure points out that the structural rearrangement is a key factor to narrow the insulating band gap. 相似文献
956.
957.
Jian Xun ZHANG Chen Chen LI Zheng CHEN Zhi Hua RAO Da Wei WEN Ke An LI Hu Wei LIU 《中国化学快报》2005,16(12):1633-1636
Metabolism of four tobacco-specific N-nitrosamines (TSNAs), N'-nitrosonornicotine (NNN), N'-nitrosoanatabine (NAT), N'-nitrosoanabasine (NAB) and 4-(methyl nitrosamino)-1- (3-pyridyl)-1-butanone (NNK) was studied by solid-phase extraction (SPE) and liquid chromato- graphy-electrospray ionization-mass spectrometry (LC-ESI-MS). SPE and LC-ESI-MS method was evaluated to be rapid, simple, sensitive and selective for analysis of TSNAs in rabbit serum. The doses of TSNAs administrated were 4.666 μg/kg and 11.665 μg/kg according to different levels in cigarettes. Metabolic curves of four TSNAs and 4-(methyl nitrosamino)-1-(3-pyridyl)- 1-butanone (NNAL), the metabolite of NNK, were obtained. 相似文献
958.
Xun Tian JIANG Li Gong OU Dong Mei HAN Yu Feng ZHAI Dong Lu BAI* Shanghai Institute of Materia Medica Chinese Academy of Sciences Taiyuan Road Shanghai 《中国化学快报》2001,(2)
Pseudolaric acid A (1), which exhibits antifungal activity, cytotoxicity against several tumor cell lines in vitro, as well as contraceptive effects in mice, is a diterpenoid compound isolated from Pseudolarix Kaemferi1. The unusual structural feature in this molecule is a trans arrangement of the lactone and acetoxy group at the fused junction of 5, 7-fused ring skeleton bearing four contiguous stereogenic centers. The synthetic challenges posed by these structural elements in a rather compa… 相似文献
959.
960.
电子俘获型红外上转换屏 总被引:5,自引:1,他引:4
利用溶液悬浮分层提取技术获得粒度较为一致的电子俘获材料(ETM)粉末,考虑ETM屏空间分辨率、红外→可见发光亮度、ETM化学稳定性和膜层均匀性等主要因素,采用不同方法制作了ETM屏,较好地解决了ETM膜层均匀性及器件封装后的化学稳定性等问题,并通过测试比较,提出了一种兼顾空间分辨率和红外上转换发光亮度的微镶嵌屏制作技术方案. 相似文献