全文获取类型
收费全文 | 132885篇 |
免费 | 23300篇 |
国内免费 | 14914篇 |
专业分类
化学 | 92419篇 |
晶体学 | 1460篇 |
力学 | 8503篇 |
综合类 | 1020篇 |
数学 | 16134篇 |
物理学 | 51563篇 |
出版年
2024年 | 136篇 |
2023年 | 2689篇 |
2022年 | 2941篇 |
2021年 | 4303篇 |
2020年 | 5419篇 |
2019年 | 5077篇 |
2018年 | 4501篇 |
2017年 | 4093篇 |
2016年 | 6423篇 |
2015年 | 6117篇 |
2014年 | 7457篇 |
2013年 | 9818篇 |
2012年 | 12095篇 |
2011年 | 12705篇 |
2010年 | 8483篇 |
2009年 | 8234篇 |
2008年 | 8956篇 |
2007年 | 8046篇 |
2006年 | 7467篇 |
2005年 | 6254篇 |
2004年 | 4756篇 |
2003年 | 3858篇 |
2002年 | 3597篇 |
2001年 | 2967篇 |
2000年 | 2686篇 |
1999年 | 2944篇 |
1998年 | 2400篇 |
1997年 | 2348篇 |
1996年 | 2226篇 |
1995年 | 1969篇 |
1994年 | 1754篇 |
1993年 | 1471篇 |
1992年 | 1289篇 |
1991年 | 1157篇 |
1990年 | 965篇 |
1989年 | 742篇 |
1988年 | 554篇 |
1987年 | 494篇 |
1986年 | 460篇 |
1985年 | 385篇 |
1984年 | 236篇 |
1983年 | 182篇 |
1982年 | 154篇 |
1981年 | 92篇 |
1980年 | 69篇 |
1979年 | 22篇 |
1976年 | 9篇 |
1975年 | 16篇 |
1973年 | 7篇 |
1957年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
The biodegradability of phtalic acid esters in marine and freshwater environments was characterized by their binding free energy with corresponding degrading enzymes. According to comprehensive biodegradation effects weights, the binding free energy values were converted into dimensionless efficacy coefficient using ratio normalization method. Then, considering comprehensive dual biodegradation effects value and the structural parameters of PAEs in both marine and freshwater environments, a 3D-QSAR pharmacophore model was constructed, five PAE derivatives (DBP−COOH, DBP−CHO, DBP−OH, DINP−NH2, and DINP−NO2) were screened out based on their environmental friendliness, functionality and stability. The prediction of biodegradation effects on five PAE derivatives by biodegradation models in marine and freshwater environment increased by 15.90 %, 15.84 %, 27.21 %, 12.33 %, and 8.32 %, and 21.57 %, 15.21 %, 20.99 %, 15.10 %, and 9.74 %, respectively. By simulating the photodegradation path of the PAE derivative molecular, it was found that DBP−OH can generate .OH and provides free radicals for the photodegradation of microplastics in the environment. 相似文献
82.
This minireview describes the strategies for synthesis of fiuorinated surfactants potentially nonbioaccumulable.Various strategies have been focused on(Ⅰ) reducing the length of the perfluorocarbon chain,(Ⅱ) introducing hetero atoms into the fluorocarbon chain,(Ⅲ) introducing branch(herein and after branch means the fluoro-carbon chain section is not straight).In most cases,the surface tensions versus the surfactant concentrations have been assessed.These above strategies led to various highly fiuorinated(perfluorinated or not perfluorinated) surfactants whose chemical changes enabled to obtain novel alternatives to perfluorooctanoic acid(PFOA) and perfluorooctane sulphonate(PFOS). 相似文献
83.
84.
85.
86.
87.
88.
89.
90.
CongZhan Liu YiFei Zhang XuFang Li XueFeng Lu Zhi Chang ZhengWei Li AiMei Zhang YongJie Jin HuiMing Yu Zhao Zhang MinXue Fu YiBao Chen JianFeng Ji YuPeng Xu JingKang Deng RenCheng Shang GuoQing Liu FangJun Lu ShuangNan Zhang YongWei Dong TiPei Li Mei Wu YanGuo Li HuanYu Wang BoBing Wu YongJie Zhang Zhi Zhang ShaoLin Xiong Yuan Liu Shu Zhang HongWei Liu YiJung Yang Fan Zhang 《中国科学:物理学 力学 天文学(英文版)》2020,(4):20-34
The Insight-Hard X-ray Modulation Telescope(Insight-HXMT) is a broadband X-ray and γ-ray(1-3000 ke V) astronomy satellite. One of its three main telescopes is the High Energy X-ray telescope(HE). The main detector plane of HE comprises 18 Na I(Tl)/Cs I(Na) phoswich detectors, where Na I(Tl) is used as the primary detector to measure ~ 20-250 ke V photons incident from the field of view(FOV) defined by collimators, and Cs I(Na) is used as the active shielding detector to Na I(Tl) by pulse shape discrimination. Additionally, Cs I(Na) is used as an omnidirectional γ-ray monitor. The HE collimators have a diverse FOV,i.e. 1.1°×5.7°(15 units), 5.7°×5.7°(2 units), and blocked(1 unit). Therefore, the combined FOV of HE is approximately5.7°×5.7°. Each HE detector has a diameter of 190 mm resulting in a total geometrical area of approximately 5100 cm2, and the energy resolution is ~15% at 60 ke V. For each recorded X-ray event by HE, the timing accuracy is less than 10 μs and the deadtime is less than 10 μs. HE is used for observing spectra and temporal variability of X-ray sources in the 20-250 ke V band either by pointing observations for known sources or scanning observations to unveil new sources. Additionally, HE is used for monitoring the γ-ray burst in 0.2-3 Me V band. This paper not only presents the design and performance of HE instruments but also reports results of the on-ground calibration experiments. 相似文献