全文获取类型
收费全文 | 1365篇 |
免费 | 37篇 |
国内免费 | 223篇 |
专业分类
化学 | 1197篇 |
晶体学 | 2篇 |
力学 | 1篇 |
综合类 | 12篇 |
数学 | 1篇 |
物理学 | 44篇 |
综合类 | 368篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 20篇 |
2021年 | 14篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 18篇 |
2017年 | 33篇 |
2016年 | 28篇 |
2015年 | 31篇 |
2014年 | 33篇 |
2013年 | 117篇 |
2012年 | 73篇 |
2011年 | 82篇 |
2010年 | 66篇 |
2009年 | 70篇 |
2008年 | 71篇 |
2007年 | 110篇 |
2006年 | 86篇 |
2005年 | 87篇 |
2004年 | 66篇 |
2003年 | 73篇 |
2002年 | 66篇 |
2001年 | 52篇 |
2000年 | 43篇 |
1999年 | 42篇 |
1998年 | 47篇 |
1997年 | 44篇 |
1996年 | 35篇 |
1995年 | 23篇 |
1994年 | 26篇 |
1993年 | 24篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1625条查询结果,搜索用时 15 毫秒
101.
102.
Y2O3涂层负载Pd整体式催化剂的制备和催化性能 总被引:5,自引:0,他引:5
以Y(NO3)3为前驱体制备了Y2O3涂层的堇青石蜂窝陶瓷载体.扫描电子显微镜、X射线能谱和超声波振荡等表征结果表明,Y2O3涂层不但具有良好的抗振荡性和粘结强度,而且具有很强的吸附催化剂活性组分(H2PdCl4)的能力,适合制备负载型Pd催化剂.以甲苯和乙酸乙酯完全燃烧为模型反应考察了催化剂的活性,发现以Y2O3涂层堇青石蜂窝陶瓷为载体的整体式Pd/Y2O3催化剂具有良好的催化活性和热稳定性,甲苯和乙酸乙酯催化燃烧的T99分别为210和300℃;催化剂经900℃焙烧4 h后,T99仅提高20℃,表明催化剂具有很高的热稳定性.催化剂的X射线衍射、拉曼光谱和程序升温还原结果表明,Pd/Y2O3催化剂经低温焙烧时,Y2O3和PdO均高度分散在堇青石蜂窝陶瓷的表面,而高温焙烧使催化剂活性组分PdO晶粒增大,从而导致催化剂活性下降. 相似文献
103.
Mojtahedi MM Chalavi S Ghassempour A Tabar-Heydar K Sharif SJ Malekzadeh M Aboul-Enein HY 《Biomedical chromatography : BMC》2007,21(3):234-240
This work aims to evaluate for the enantiomeric separations of three agrochemical toxins: haloxyfop-methyl, fenoxaprop-p-ethyl and indoxacarb on crystalline degradation products-chiral stationary phase (CDP-CSP) of high-performance liquid chromatography (HPLC) under normal and polar organic phases. In the normal phase, the mobile phase was n-hexane with alcohols including methanol and isopropanol as polar modifiers. In the polar organic phase mode, the mobile phase was methanol with different percentages of triethylammunium acetate. The influence of flow rate (0.3-0.9 mL/min), analyte concentration and silica gel particle sizes (10, 15 and 30 microm) was investigated. This new chiral stationary phase showed excellent stereoselectivity for the two enantiomers of haloxyfop-methyl and fenoxaprop-p-ethyl and chiral recognition for indoxacarb under normal-phase mode. However, under polar organic phase, only indoxacarb was separated (alpha < 1.5). The chromatographic results were compared with commercial chiral columns. 相似文献
104.
Nickel acetate promoted reaction of diethyl acetone-1,3-dicarboxylate with N-cyanobenzamidine led to ethyl 4-amino-6-ethoxycarbonylmethyl-2-phenylpyrimidine-5-carboxylate, upon treatment of which with
RNH2, the corresponding 6-(carbamoylmethyl)pyrimidines were obtained. Cyclization of the latter upon treatment with MeONa afforded
6-R-4-amino-7-hydroxy-2-phenylpyrido[4,3-d]pyrimidin-5(6H)-ones.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2212–2214, November, 2007. 相似文献
105.
Zhenbin Niu Xingyuan Zhang Jiabing Dai Heping Zhang 《Frontiers of Chemistry in China》2007,2(2):151-155
A new kind of ultraviolet (UV) curable waterborne polyurethane acrylate dispersion was synthesized based on hydroxyl-terminated
polybutadiene (HTPB), poly-(propylene glycol) (PPG), isophorene diisocyanate (IPDI), 2-hydroxy ethyl acrylate (HEA) and dimethylol
propionic acid (DMPA) after neutralizing by triethylamine (TEA). 2-Hydroxy-1-[4-2-hydroxyethoxy) phenyl]-2-methyl-1-propanone
(Irgacure 2959) was used as a photoinitiator and deionized water as a diluent. Fourier transform infrared (FTIR) analysis
was used to identify the chain structure of the UV-curable polyurethane prepolymer based on HTPB and the curing process. Effects
of relative content of HTPB and PPG on emulsion stability, resistance to water and ethanol, thermal stability, compatibility
of soft and hard segment, as well as the mechanical property of the cured film were investigated.
Translated from Polymer Materials Science and Engineering, 2006, 22(3): 199–203 (in Chinese) 相似文献
106.
Hélène Pellissier Author Vitae 《Tetrahedron》2007,63(16):3235-3285
107.
108.
以草酰乙酸和D-阿拉伯糖为原料,经缩合-脱羧,乙酰化,甲酯化和乙硫苷化等4步反应合成了β-Kdo乙硫苷供体,总收率24%,立体选择性单一,其结构经~1H NMR和~(13)C NMR确证。 相似文献
109.
After mixing a methylbenzene 4 with “magic blue” solution in F113 (CClF2CCl2F) containing bis{perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide 2 and perfluoro-1-nitroso-1-[1-(2-fluorosulfonyl)ethoxy]ethane 3 at room temperature, benzylic H-atom of 4 could be selectively abstracted by 2, and benzyl radical 5 thus generated was immediately trapped by 3. Based on hyper-fine splitting constants (hfsc), the structure of the spin adducts perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl benzyl nitroxides 6 derived from seven methylbenzenes have been identified. The mechanism of the H-abstraction/spin trapping process is also discussed. 相似文献
110.
Poojali P. Warekar Priyanka T. Patil Kirti T. Patil Dattatraya K. Jamale Govind B. Kolekar 《合成通讯》2016,46(24):2022-2030
An ecofriendly route has been investigated for the synthesis of 4-(4-nitro-phenyl)-2-phenyl-1,4-dihydro-benzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylic acid ethyl ester derivatives by one-pot, three-component condensation of ethyl benzoylacetate, aromatic aldehydes, and 2-amino benzimidazole using 260?mol% of citric acid as reaction mediator. Citric acid is an inexpensive, nontoxic, and green medium with smoothly activates the rate of reaction. The synthesized compounds were assessed for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37RV strain using the microplate alamar blue assay (MABA). The results indicate that among all the synthesized compound series, P-4 and P-9 compounds illustrate effective activity with a minimum inhibitory concentration of 25?µg/ml. 相似文献