全文获取类型
收费全文 | 1806篇 |
免费 | 78篇 |
国内免费 | 7篇 |
专业分类
化学 | 1424篇 |
晶体学 | 6篇 |
力学 | 12篇 |
数学 | 119篇 |
物理学 | 330篇 |
出版年
2023年 | 5篇 |
2022年 | 34篇 |
2021年 | 42篇 |
2020年 | 33篇 |
2019年 | 37篇 |
2018年 | 18篇 |
2017年 | 22篇 |
2016年 | 52篇 |
2015年 | 58篇 |
2014年 | 47篇 |
2013年 | 103篇 |
2012年 | 108篇 |
2011年 | 142篇 |
2010年 | 92篇 |
2009年 | 69篇 |
2008年 | 121篇 |
2007年 | 117篇 |
2006年 | 112篇 |
2005年 | 115篇 |
2004年 | 71篇 |
2003年 | 63篇 |
2002年 | 53篇 |
2001年 | 22篇 |
2000年 | 30篇 |
1999年 | 23篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有1891条查询结果,搜索用时 31 毫秒
71.
Domínguez-González R Moreda-Piñeiro A Bermejo-Barrera A Bermejo-Barrera P 《Talanta》2005,66(4):937-942
A new method using diluted reagents (nitric and hydrochloric acids and oxygen peroxide) and ultrasound energy to assist metals acid leaching with from edible seaweed was optimized. The method uses a first sonication at high temperature with hydrochloric acid as a previous stage to an ultrasound-assisted acid leaching with 7 ml of an acid solution containing nitric acid, hydrochloric acid and hydrogen peroxide at concentrations of 3.7, 3.0 and 3.0 M, respectively. Optimum conditions for the first sonication step were ultrasound energy at 17 kHz, sonication temperature at 65 °C, an acid volume of 2 ml, an hydrochloric acid concentration of 6.0 M and a sonication time of 10 min. It has been found that the first sonication stage at high temperature with hydrochloric acid is necessary to obtain quantitative recoveries for As, Ba, Fe and V. Otherwise quantitative recoveries were reached for the other elements investigated (Ca, K, Na, Mg, Cd, Cr, Cu, Mn, Ni, Pb and Zn). The repeatability of the ultrasound-assisted acid leaching method was around 10% for all elements. Adequate limit of detection and limit of quantification were reached by using inductively coupled plasma-optical emission spectrometry (ICP-OES) for measurements. The method resulted accurate after analysing several seaweed certified reference materials (IAEA-140/TM, NIES-03 and NIES-09). The method was finally applied to the multi-element determination in edible seaweed samples. 相似文献
72.
C. Cruces Blanco F. Garcia Sanchez 《International journal of environmental analytical chemistry》2013,93(4):513-523
Abstract A simple kinetic-spectrophotometric method for the analysis of the organophosphate insecticide methyl parathien is presented. The method is based on the alkaline hydrolysis of the insecticide into its main metabolite p-nitrophenol. The influence of reaction variables (pH and temperature), and the effect of other pesticides, are discussed. The calibration graphs (initial rate, fixed time, fixed absorbance) were linear from 2 to 30μg/ml. The precision was calculated for the different methods applied, the relative standard deviation being 6.25% for 4μg/ml. The proposed kinetic method can be applied directly to synthetic mixtures, commercial formulations and different aqueous environment, with recoveries close to 100%. 相似文献
73.
Stella M. Zabala R.M. Torres Sanchez 《Journal of Dispersion Science and Technology》2013,34(7):957-968
The movement of water originated by the spreading of two surfactants was analyzed in glass beads as well as on soil systems, both of particles of nonuniform size The higher difference of surface tension produced in the system by 1 -hexadecanol compared to that of 1-tetradecanol led therefore to a higher amount of water moved. Decreased proportion of the smaller sized particles in glass beads system produced a decrease in the total water moved by both surfactants. Organic matter acted in soil as a second surfactant in glass beads. This effect was compared in glass beads systems once 1-hexadecanol was evenly distributed among the particles as continuous film, which played a role alike that of organic matter in soil and then a second surfactant 1-tetradecanol was added. These additional surfactant effect diminished the difference between initial and final surface tension (surface tension depression) of the system and so the total water moved. The soil organic matter (1.7%) modified the water movement curve in the presence of low (0.2g) content of 1-hexadecanol, whereas for high content of either alcohol (0.4g) or low content of 1-tetradecanol content (0.2g) the water movement curves were the same 相似文献
74.
Katherine M. Byrd Chitra Subramanian Jacqueline Sanchez Hashim F. Motiwala Weiya Liu Prof. Mark S. Cohen Prof. Jeffrey Holzbeierlein Prof. Brian S. J. Blagg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6921-6931
Development of heat shock protein 90 (Hsp90) C‐terminal inhibitors has emerged as an exciting strategy for the treatment of cancer. Previous efforts have focused on modifications to the natural products novobiocin and coumermycin. Moreover, variations in both the sugar and amide moieties have been extensively studied, whereas replacements for the coumarin core have received less attention. Herein, 24 cores were synthesized with varying distances and angles between the sugar and amide moieties. Compounds that exhibited good anti‐proliferative activity against multiple cancer cell lines and Hsp90 inhibitory activity, were those that placed the sugar and amide moieties between 7.7 and 12.1 Å apart along with angles of 180°. 相似文献
75.
76.
Adrian Tlahuext‐Aca Dr. Matthew N. Hopkinson R. Aleyda Garza‐Sanchez Prof. Dr. Frank Glorius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(17):5909-5913
Highly selective tandem nucleophilic addition/cross‐coupling reactions of alkynes have been developed using visible‐light‐promoted dual gold/photoredox catalysis. The simultaneous oxidation of AuI and coordination of the coupling partner by photo‐generated aryl radicals, and the use of catalytically inactive gold precatalysts allows for high levels of selectivity for the cross‐coupled products without competing hydrofunctionalization or homocoupling. As demonstrated in representative arylative Meyer–Schuster and hydration reactions, this work expands the scope of dual gold/photoredox catalysis to the largest class of substrates for gold catalysts and benefits from the mild and environmentally attractive nature of visible‐light activation. 相似文献
77.
78.
79.
Patrick Achenbach Sebastian Bleser Josef Pochodzalla Alicia Sanchez Lorente Marcel Steinen 《Hyperfine Interactions》2012,208(1-3):99-104
Samples obtained as a result of the valleriite synthesis process under different conditions (temperature and proportion Cu:Fe:Mg in the initial mixture) were investigated by 57Fe M?ssbauer spectroscopy with attraction data of X-ray diffraction. Parameters of hyperfine interactions for valleriite were determined and crystal chemical identification of 57Fe subspectra was carried out. It was found that valleriite was formed in samples synthesized at 150°C and 180°C and not formed in samples synthesized at 250°C. 相似文献
80.