全文获取类型
收费全文 | 709篇 |
免费 | 24篇 |
国内免费 | 38篇 |
专业分类
化学 | 215篇 |
晶体学 | 7篇 |
力学 | 2篇 |
综合类 | 16篇 |
物理学 | 74篇 |
综合类 | 457篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 22篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 18篇 |
2014年 | 23篇 |
2013年 | 18篇 |
2012年 | 26篇 |
2011年 | 32篇 |
2010年 | 18篇 |
2009年 | 34篇 |
2008年 | 31篇 |
2007年 | 38篇 |
2006年 | 36篇 |
2005年 | 29篇 |
2004年 | 59篇 |
2003年 | 42篇 |
2002年 | 34篇 |
2001年 | 24篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有771条查询结果,搜索用时 8 毫秒
1.
2.
亚硝基血红色素食品着色剂的研究 总被引:7,自引:0,他引:7
本文以健康的猪、牛、羊的新鲜牲血为原料,经化学提取、合成及酶解等简单步骤、研制成了亚硝基血红色素食品着色剂。该产品可替代具有毒性作用的亚硝酸盐而直接加入食品着色,是一种无毒副作用的理想的调味食品着色剂,同时也增强了食品的营成份。 相似文献
3.
曾昭琪 《南京大学学报(自然科学版)》1988,(2)
本文报告了在南京发现的蓝色裸甲藻,测定了它的藻胆色素。证明蓝色藻胆蛋白不是山“胞内蓝藻”(Cyanellen)所提供。电子显微镜的扫描表明细胞表面有众多的突起,不是光滑的;横沟内的鞭毛不是“带状”而是由细纤维丝膜状物拉着的螺旋形。透视电子显微镜观察表明,该藻有两个类型的细胞核,即“甲藻核结构”(Dinocaryotic structure)和“真核结构”,(Eucaryotic Structure),真核与叶绿体有一个共同的膜的包被,有一个与原生动物相近似的伸缩泡系统。叶绿体是分枝状,在细胞的边缘位,但也有其它形态。有淀粉颗粒而无“造粉核”或称”“蛋白核”(Pyrenoid),多数位于叶绿体外或之间,类囊体与一般甲藻不同,不是三个排成一条“带”而是两个排列成“带”。有发达的线粒体,和高尔基体;鞭毛不论纵沟内的或横沟内的,其横切面,均为9+2的形式,其纵切面是由纤维丝成束的结构。蓝色色素提取物,可见光最大吸收峰为456nm,与隐藻藻胆色素十分相似。从细胞亚微结构及其色素性质,作者认为它是藻类演化过程中的一个中间类型的甲藻共生体。 相似文献
4.
The light-scattering properties of coatings based on monodisperse polymeric spheres of two different diameters (ca 0.5 and 1 m) were evaluated from reflectance measurements as a function of the wavelength from 400 to 700 nm. Some of these plastic pigments were hollow and it was noted that these particles gave coatings with a greater light-scattering ability than coatings based on solid particles of a similar size. It was possible to estimate the contribution of the internal pores to the scattering ability of the coating layers by saturating the layers with an oil of a refractive index similar to that of the polymeric pigment particles. A simple model accounting for the scattering provided by the internal pores of the hollow particles is suggested. The agreement between the experimental results and the prediction of the model is fair. It was noted that the light scattering coefficient of the coatings increased when the external diameter of their constituent hollow particles increased from ca 0.5 to 1 m. 相似文献
5.
微波萃取花生壳天然黄色素及其稳定性研究 总被引:19,自引:0,他引:19
对福建产花生壳进行了微波萃取天然黄色素及其稳定性的研究 .研究表明微波萃取的工艺条件是 :以pH =3,体积分数 70 %的乙醇水溶液作提取剂 ,原料与提取剂配比为 1g∶5mL ,微波辐射功率为 12 0W ,辐射时间2 4 0s.对该色素稳定性研究结果表明 ,该色素为水溶性色素 ,属黄酮类色素 ,适用pH值范围比较宽 ,尤其碱性状态效果最佳 ,对光、热稳定性好 ,大多数食品添加剂对色素稳定性影响不大 ,对氧化剂H2 O2 的耐受能力较差 ,对还原剂Na2 SO3 的耐受能力强 相似文献
6.
紫荆花红色素开发利用的研究 总被引:9,自引:0,他引:9
首次报道紫荆花红色素的提取纯化方法及红色素的理化性质,并与玫瑰茄红色素作对比研究,证实同属于花青甙类化合物,又经急性毒性试验证明其毒性极低,故紫荆花天然红色素具有开发利用的价值。 相似文献
7.
Three novel perylene polyimides (PPIs) containing p‐n diblock units were designed and synthesized for use in dye‐sensitized mesoporous TiO2 solar cells. They all dissolve in m‐cresol and N‐methyl‐2‐pyrrolidone (NMP). Their visible light absorption, electrochemical and photoelectrochemical properties were systematically studied. The polyimides have band gap energies of 2.16, 2.19 and 2.25 eV deduced from ultraviolet–visible absorption spectra, and electron affinity (Ea) and ionization potential (IP) of ?3.93 and 6.10 eV for PPI1, ?3.94 and 6.13 eV for PPI2, ?3.93 and 6.59 eV for PPI3, respectively, deduced from cyclic voltammogram. Experimental data show that introduction of 4,4′‐bisaminetriphenylamine cannot only greatly enhance optic‐electro conversion efficiency, but also enhance the dissolubility which in favorable for making the devices. The relationship of structure and properties of PPI is discussed and the mechanism of photocurrent generation is explained. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
8.
介绍了以鸡冠花为原料,提取其红色素的方法及工艺流程。通过光谱分析的手段,研究了酸度、温度、光、时间、金属离子等因素对色素稳定性的影响。 相似文献
9.
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
10.
Burchard Franck 《Angewandte Chemie (International ed. in English)》1982,21(5):343-353
Uroporphyrinogen III plays a key role in the biosynthesis of heme, the red pigment of blood. In vivo studies with specifically 14C- and 3H-labeled precursors have revealed that the formation uroporphyrinogen III in the organism follows several primary and subsidiary pathways. Model experiments on the pattern of biosynthesis have led to simple and effective methods of synthesizing uroporphyrin analogs and have shown that their production is strongly favored thermodynamically. The biologically porphyrins important thus available permit a mechanistic explanation of the light-induced dermatoses in porphyria diseases and suggest promising medical applications in diagnosis and therapy. 相似文献