全文获取类型
收费全文 | 355篇 |
免费 | 16篇 |
国内免费 | 28篇 |
专业分类
化学 | 277篇 |
晶体学 | 7篇 |
力学 | 2篇 |
综合类 | 24篇 |
物理学 | 89篇 |
出版年
2023年 | 3篇 |
2022年 | 23篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 14篇 |
2012年 | 19篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 18篇 |
2007年 | 18篇 |
2006年 | 17篇 |
2005年 | 12篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有399条查询结果,搜索用时 15 毫秒
71.
拉曼微区分析技术在古颜料研究中的应用 总被引:2,自引:0,他引:2
拉曼微区分析技术可进行空间分辨的原位无损检测,为其他现代分析技术所不及,文章介绍了这一分析技术在古代文稿、油画、水彩画、壁画、陶等颜料分析中的应用。 相似文献
72.
以氯氧化锆、正硅酸乙酯为主要原料,氧化镨作为着色剂,采用溶剂热法制备镨锆黄陶瓷颜料前驱体,经1050℃煅烧得到镨锆黄陶瓷颜料,考察镨掺杂量对该颜料呈色的影响.采用扫描电镜和X射线衍射仪对样品的显微结构进行分析,样品性能采用色度分析、粒度分析和紫外-可见光光谱分析仪测试.实验结果表明:相对于其它掺镨样品,当镨掺杂含量为0.15 g,样品的ZrSiO4结晶度较高且Pr4+固溶到ZrSiO4晶格中,颗粒尺寸分布较小且较均匀,使样品在400~480 nm对蓝紫光有非常强的吸收,样品呈现较纯正的黄色色调. 相似文献
73.
Robert Huber 《Angewandte Chemie (International ed. in English)》1988,27(1):79-88
Proteins may be rigid or flexible to various degrees as required for optimal function. Flexibility of large parts of a protein, which rearrange or move, is particularly interesting and will be discussed in this article. We differentiate between several categories, although the boundaries between them are diffuse: flexibility of peptide segments, order–disorder transitions of spatially contiguous regions, and domain motions. The domains may be flexibly linked to allow rather unrestricted motions or the motions may be constrained to certain modes. The various categories of large-scale flexibility will be illustrated with the following examples: (1) Small protein proteinase inhibitors are rather rigid molecules which provide binding surfaces complementary to their cognate proteases but show also limited segmental flexibility and adaptation. (2) Large plasma proteinase inhibitors exhibit large conformational changes after interaction with proteases probably for regulatory purposes. (3) Pancreatic serine proteases employ a disorder–order transition of their activation domain as a means to regulate enzymic activity. (4) Immunoglobulins show rather unrestricted and also hinged domain motions in different parts of the molecule probably to allow binding to antigens in different arrangements. (5) Citrate synthase adopts open and closed forms by a hinged domain motion to bind substrates and release products and to perform the catalytic condensation reaction, respectively. (6) Riboflavin synthase, a bifunctional multienzyme complex, catalyzes two consecutive reactions by means of two subunits, α and β. The β-subunits form a shell, in which the α-subunits are enclosed. Diffusional motion of the catalytic intermediates is therefore restricted. In addition, rearrangement of the N-terminal segment occurs during the assembly of the β-subunit. In contrast, rigidity is dominant in the structures of the light-harvesting complexes and the photosynthetic reaction centers involved in photosynthetic light reactions. These are large protein–pigment complexes in which the proteins serve as matrices to hold the pigments in the appropriate conformation and relative arrangement. Since motion would contribute to deactivation of the photoexcited states of the pigments and diminish the efficiency of light-energy and electron transfer, the functional role of rigidity is easy to rationalize for these proteins. 相似文献
74.
环境因子对东湖几种沉水植物生理的影响研究 总被引:2,自引:0,他引:2
报道了光照强度、水体温度及水体pH值对东湖5种沉水植物生理的影响.实验结果表明,在一定温度范围内,5种植物的光补偿点均随温度的升高而上升,且种间有较大的差异.各植物光合色素的含量,受生态因子的影响,表现出一定的适应性.5种植物对水体高pH值耐受能力有明显的差异.探讨了富营养化湖泊沉水植物消亡的原因及生态分布的规律,提出了富营养化湖泊水生植被的恢复及水生生态系统重建中的植物选种原则. 相似文献
75.
以碱提取、酸沉淀和silicagel、Al2O3及sephadexG-25柱层析分离纯化等步骤,从悬铃木落叶中制备得到一种暗棕色化合物,经PAGE、PLC及TLC检测均为单一谱带或单一斑点;该有色化合物熔点282.59~283.29℃,λKOHmax:215nm,E1%1cm:348.7,肩峰:256nm,pI:3.5,对大肠杆菌、金黄葡萄球菌、巨大芽孢杆菌及枯草杆菌有较强的抑菌活性 相似文献
76.
对食用合成色素日落黄的荧光光谱进行了研究,发现在310~400nm紫外光的激励下,日落黄溶液发出强荧光,峰值荧光强度随浓度的增加先增强后减弱,且荧光谱峰位置出现明显红移。经分析认为,日落黄溶液能产生荧光是因为分子中偶氮键将一个苯环和一个萘环连接在一起,形成大共轭结构,并且取代基-SO3Na与-OH处于萘环的对位,大大增强了日落黄分子的共轭程度,使其具有强的吸光功能,发出强荧光。另外,结合BP神经网络,通过训练好的网络对4种不同浓度的样本进行浓度预测,结果表明相对误差分别为4.269%,6.078%,4.977%和5.308%,相对标准偏差分别为0.448%,0.375%,0.419%和0.414%。实验表明,该方法具有训练速度快、预测结果准确度高等特点,有望成为一种对食用合成色素进行高效、痕量检测的有效方法。 相似文献
77.
78.
Milad Javanmard Hossein Ali Asadi-Gharneh Pejman Nikneshan 《Natural product research》2018,32(14):1738-1743
Dog rose (Rosa canina L.) is a wild native species in Iran, with a significant genetic diversity. This plant serves as a rich source of vitamin C, anthocyanins, phenolic contents and carotenoids. Rose hips have been used in several food products, as well as perfumery and cosmetics industries. In this research, we investigate biochemical characteristics of five dog rose ecotypes (Kopehjamshid, Zarneh, Miyankish, Aghcheh and Sadeghiyeh), that were collected from the central part of Iran (Isfahan province). Amounts of vitamin C, total carotenoids, total phenolic contents, total anthocyanins, macro and micro minerals were measured. Seed oil are extracted by soxhlet method and analysed by gas chromatography. The macro and micro minerals levels in the fruit vary significantly among these regions. The results of this study demonstrate that dog rose have great diversity and can be used in breeding programmes in order to increase nutrient values as a food resource additive. 相似文献
79.
枸杞子中红色素的提取及稳定性 总被引:10,自引:0,他引:10
枸杞子中红色素的提取及稳定性伍明,王杰,闪春霞,任仲皎,宋锡瑾,詹国庆(中南民族学院化学系武汉430074)关键词枸杞,色素,液泛提取法枸杞子为茄科枸杞属植物的果实,具有补肾养肝,润肺明目以及调节机体免疫力,抑制肿瘤生长和细胞突变,延缓衰老及抗脂肪肝... 相似文献
80.
G. Monrós M. A. Tena P. Escribano V. Cantavella J. Carda 《Journal of Sol-Gel Science and Technology》1994,2(1-3):377-380
Classical ceramic pigments are manufactured through the traditional method of firing a mixture of oxides previously mechanical homogeneized in a mill. From industrial overview sol-gel applied in ceramic pigments manufacture is more expensive than ceramic method because the high price of raw materials. However in some classical pigments it would be economically interesting to use a sol-gel route because raw materials in ceramic route are as well expensive and gel route give the pigment at lower firing temperature and soaking time. In this paper a discussion for several pigments is presented. 相似文献