全文获取类型
收费全文 | 391篇 |
免费 | 12篇 |
国内免费 | 79篇 |
专业分类
化学 | 424篇 |
晶体学 | 3篇 |
力学 | 2篇 |
综合类 | 1篇 |
数学 | 5篇 |
物理学 | 47篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 28篇 |
2021年 | 16篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 12篇 |
2013年 | 21篇 |
2012年 | 15篇 |
2011年 | 14篇 |
2010年 | 12篇 |
2009年 | 20篇 |
2008年 | 15篇 |
2007年 | 20篇 |
2006年 | 19篇 |
2005年 | 16篇 |
2004年 | 26篇 |
2003年 | 18篇 |
2002年 | 16篇 |
2001年 | 20篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有482条查询结果,搜索用时 15 毫秒
471.
472.
474.
A highly stereoselective method for achieving the anti-Mannich reaction of aldehydes and ketones with ethyl (4-methoxyphenylimino)acetate was realized using the modularly designed organocatalysts (MDOs) self-assembled from cinchona alkaloid derivatives and (R)-pyrrolidien-3-carboxylic acid in the reaction media. The desired anti-Mannich products were obtained in good to excellent yields (up to 93%), excellent diastereoselectivities (up to 99:1 dr), and good to high enantioselectivities (up to 99% ee). 相似文献
475.
利用奎宁能与贵金属的络阴离子发生络合作用的性质,将其负载到阳离子交换树脂上,制得奎宁负载树脂( Q C R) .以 I C P A E S为检测手段,详细考察了吸附材料在静态吸附条件下对贵金属络阴离子的富集分离性能.结果表明, 在盐酸(0.1~3.0 m ol/ L) 溶液中,负载奎宁树脂的化学稳定性好.以0.1 m ol/ L的 H Cl为吸附介质,贵金属 Au、 Pd、 Pt可实现定量分离富集,吸附于奎宁树脂上的贵金属可用0.1 m ol/ L 的 H Cl- 2 g/ L 硫脲混合淋洗液完全解脱.方法用于抗癌药物及催化剂中 Pt、 Pd 的富集分离与测定,分析结果满意 相似文献
476.
摘要:应用聚合电介质吸附的定标理论,根据介质和表面电介质常数的比率,考虑多化合价吸附电介质之间强相关性作用,我们提出一种表面排斥电荷的近似定标理论方法,根据这种方法把电介质表面吸附层的相图分为本质上不同的两大类。从相图可知:当表面电荷密度低(或体带相反电荷离子密度高),这时表面和体带相反电荷离子密度几乎相同;一旦表面电荷密度足够高,就使带相反电荷的离子在表面上浓缩。据此,可确定在这个区域内,低化合价聚合电介质形成一个相关的多链状态,当化合价足够高时,由于近邻链之间的更强排斥增强,使状态转变成单链。 相似文献
477.
XU Mancai WANG Cairong SHI Zuoqing XU Mingcheng ZHANG Shang LI Haitao. FAN Yunge HE Binglin. 《Chinese Journal of Reactive Polymers》2000,(1)
1 INTRODUCTIONHydrogen-bonding adsorbents are functional polymers for adsorption and separation via theformation of hydrogen bond between the adsorbentS and adsorbates. Because hydrogen bond is astrong intermolecular (or intramolecular) force, hydrogen-bonding adsorbents have strong potentto adsorbing adsorbates with which can form hydrogen bond. In our previous work, three seriesof hydrogen-bonding adsorbents have been studied, which were adsorbents with hydrogendonator, adsorbentS with … 相似文献
478.
Zhang Q Kusunoki T Xu Q Wang H Kobayashi T 《Analytical and bioanalytical chemistry》2007,388(3):665-673
Phase separation of poly(acrylonitrile–co-methacrylic acid) in compressed liquid CO2 resulted in formation of a porous imprinted membrane which preferentially adsorbed uracil (URA). The cross-section of the
membrane was observed by SEM, which revealed its porous structure. The mechanical strength of the membrane indicated formation
of a rigid matrix with high tensile strength (4.4 N mm−2). The imprinted membranes bound highly selectively to URA (12.8 μmol g−1) but binding to dimethyluracil (DMURA), thymine, and cytosine was less (0.7, 0.8, and 0.9 μmol g−1, respectively). When DMURA was similarly used to prepare an imprinted membrane in liquid CO2 there was less binding of DMURA to the imprinted membrane obtained. The URA-imprinted membranes were evaluated by IR spectroscopy
before and after URA extraction. The results indicated that hydrogen bonding was the mechanism of binding of URA to the imprinted
membrane. Competitive binding studies were performed with binary mixtures of URA and its analogues. The URA-imprinted membrane
enabled good separation of URA from cytosine, DMURA, and thymine, with separation factors of 3.0, 3.8, and 2.5, respectively.
It was confirmed that the compressed liquid CO2 contributed to efficient formation of template substrate sites in the URA-imprinted membrane. 相似文献
479.
Gojić M. Črnko J. Sućeska M. Rajić M. 《Journal of Thermal Analysis and Calorimetry》2000,62(3):703-710
Heat treatment of pipes was performed under industrial conditions at 580°C in a dry protective gas containing a CO2–CO–H2–N2 mixture. A commercial adsorbent (733 kg) used for production ofthe gas removed 52.7 l of water in five h and 22.5 min. During
the annealing of pipesoxidation and decarburization were not observed. The results were confirmed bymetallographic analysis.
The values of enthalpy of water desorption (36.4–40.5 kJ mol–1) obtained by DSC and TG measurements were close to those of water evaporation(44.1 kJ mol–1). This suggests that the bonds between the water molecules andadsorbents were not of chemical but of physical nature.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
480.
《Mendeleev Communications》2022,32(6):825-827
Composites containing a metal–organic framework of copper(ii) 1,3,5-benzenetricarboxylate with activated carbons from pyrolysis of the coffee bean as well as green and black tea waste have been found suitable for recovery of the organic dyes Congo red and methylene blue from their aqueous solutions with a maximum adsorption of 180 mg g–1 相似文献