全文获取类型
收费全文 | 158篇 |
免费 | 22篇 |
国内免费 | 30篇 |
专业分类
化学 | 113篇 |
力学 | 10篇 |
综合类 | 7篇 |
数学 | 34篇 |
物理学 | 46篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 4篇 |
2013年 | 6篇 |
2012年 | 22篇 |
2011年 | 17篇 |
2010年 | 12篇 |
2009年 | 6篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
排序方式: 共有210条查询结果,搜索用时 31 毫秒
91.
Wenguang Jing Xiaoliang Zhao Minghua Li Xiaowen Hu Xianlong Cheng Shuangcheng Ma Feng Wei 《Molecules (Basel, Switzerland)》2022,27(12)
Magnolia officinalis Rehd. et Wils. and Magnolia officinalis Rehd. et Wils. var. biloba Rehd. et Wils, as the legal botanical origins of Magnoliae Officinalis Cortex, are almost impossible to distinguish according to their appearance traits with respect to medicinal bark. The application of AFLP molecular markers for differentiating the two origins has not yet been successful. In this study, a combination of e-nose measurements, e-tongue measurements, and chemical analyses coupled with multiple-source data fusion was used to differentiate the two origins. Linear discriminant analysis (LDA) and quadratic discriminant analysis (QDA) were applied to compare the discrimination results. It was shown that the e-nose system presented a good discriminant ability with a low classification error for both LDA and QDA compared with e-tongue measurements and chemical analyses. In addition, the discriminating capacity of LDA for low-level fusion with original data, similar to a combined system, was superior or equal to that acquired individually with the three approaches. For mid-level fusion, the combination of different principals extracted by PCA and variables obtained on the basis of PLS-VIP exhibited an analogous discrimination ability for LDA (classification error 0.0%) and was significantly superior to QDA (classification error 1.67–3.33%). As a result, the combined e-nose, e-tongue, and chemical analysis approach proved to be a powerful tool for differentiating the two origins of Magnoliae Officinalis Cortex. 相似文献
92.
93.
常见的阳离子聚合物能够通过静电作用有效缩合DNA,形成聚电解质复合物(PECs)。这些复合物易于细胞内在化,从内涵体中逃逸,并能保护DNA免受DNA酶的降解。但是,强烈的静电作用也限制了基因进入细胞核之后从复合物中的释放,限制了基因的表达。鉴于此,科学家们设计了一类“智能”高分子载体,这些智能高分子载体能够响应外界微环境温度、pH值和氧化还原环境变化的刺激,其自身大分子构象发生改变,进而促进DNA从复合物中逃逸,提高了转染率。本文介绍了近年来有关聚异丙基丙烯酰胺基温度响应性载体以及光、pH和响应胞内谷胱甘肽(GSH)等氧化还原反应的非病毒转基因载体的研究进展。 相似文献
94.
Sophisticated Design of Covalent Organic Frameworks with Controllable Bimetallic Docking for a Cascade Reaction
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Wenguang Leng Yongsheng Peng Jianqiang Zhang Dr. Hui Lu Dr. Xiao Feng Dr. Rile Ge Dr. Bin Dong Prof. Bo Wang Prof. Xiangping Hu Prof. Yanan Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9087-9091
Precise control of the number and position of the catalytic metal ions in heterogeneous catalysts remains a big challenge. Here we synthesized a series of two‐dimensional (2D) covalent organic frameworks (COFs) containing two different types of nitrogen ligands, namely imine and bipyridine, with controllable contents. For the first time, the selective coordination of the two nitrogen ligands of the 2D COFs to two different metal complexes, chloro(1,5‐cyclooctadiene)rhodium(I) (Rh(COD)Cl) and palladium(II) acetate (Pd(OAc)2), has been realized using a programmed synthetic procedure. The bimetallically docked COFs showed excellent catalytic activity in a one‐pot addition–oxidation cascade reaction. The high surface area, controllable metal‐loading content, and predesigned active sites make them ideal candidates for their use as heterogeneous catalysts in a wide range of chemical reactions. 相似文献
95.
96.
补硒对预防原发性肝癌的作用 总被引:2,自引:2,他引:2
原发性肝癌病因为多因素协同作用的结果,我国肝癌病因以乙型肝炎病毒(HBV)、黄曲霉毒(AFB1)、饮水污染和遗传等因素为主。某些微量元素缺乏,促进了肝癌的发生、发展。科学工作者针对肝癌病因采取以“防治肝炎、管粮防霉、改良饮水、适量补硒”为中心的综合防治措施,已取得初步成效,本硒进一步阐明在肝癌高发现场应用补硒肝癌的作用。通过四年前瞻研究结果表明,食硒盐补硒组较对照组血硒GSH-px升高,UDS、微 相似文献
97.
A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O2 atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO2nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during nanowire formation, is discussed. 相似文献
98.
PET表面接枝偶氮聚合物和光致取向研究 总被引:2,自引:0,他引:2
合成了一种丙烯酸酯类含芳香族偶氮生色团的单体ANB .以二苯甲酮为引发剂 ,采用固相紫外光接枝方法将上述单体接枝到聚酯 (PET)膜的表面 ,得到了一种具有光响应性的接枝膜 .通过SEM研究了接枝膜的表面和断面的形貌 ,观察到偶氮接枝层均匀地覆盖了PET表面 ,接枝层厚度约 0 4μm .研究发现 ,当使用488nm的线偏振激光照射接枝膜时 ,偶氮生色团通过快速的顺反异构化反应在垂直于偏振光极化方向上发生取向 ,得到了具有光学各向异性表面的PET接枝膜 .接枝膜的取向是一个快速过程 ,取向有序度参数在 2min时即达到最大值 ,为 0 0 6左右 相似文献
99.
Kuan Wang Danyang Chen Zhuoya Wang Jianhai Yang Wenguang Liu 《Macromolecular bioscience》2023,23(10):2300142
The imbalance of extrinsic and intrinsic healing of tendon is thought to be the main cause of peritendinous adhesions. In this work, an injectable supramolecular poly(N-(2-hydroxypropyl) acrylamide) (PHPAm) hydrogel is prepared merely via side chain hydrogen-bonding crosslinks. This PHPAm exhibits good antifouling and self-healing properties. The supramolecular hydrogel simultaneously loaded with Prussian blue (PB) nanoparticles and platelet lysate (PL) is explored as a functional physical barrier, which can significantly resist the adhesion of fibrin and fibroblasts, attenuate the local inflammatory response, and enhance the tenocytes activity, thus balancing extrinsic and intrinsic healing. The PHPAm hydrogel is shown to prevent peritendinous adhesions considerably by inhibiting NF-κB inflammatory pathway and TGF-β1/Smad3-mediated fibrosis pathway, thereby significantly improving tendon repair by releasing bioactive factors to regulate the tenocytes behavior. This work provides a new strategy for developing physical barriers to prevent peritendinous adhesions and promote tissue repair effectively. 相似文献
100.
A Closed Cavity measuring platform is built on the basis of a 1000 W-class direct current(DC)-discharge drived continuous-wave(CW) HF/DF chemical laser. On this platform, the absorption coefficients of optical thin films coated on the surfaces of monocrystalline silicon substrates, at the wavelength of 3.6–4.1 μm, is measured, when the power density on the surfaces of optical thin films reaches about 3.16 kW ∕cm2. The measuring principle and structure of the Closed Cavity is introduced. The temperature curves and balanced temperature rises of the film-substrate systems under test measured through the experiment is presented in this Letter. The experiments show high reliability, good repeatability and strong practicality. The Closed Cavity measuring platform is applicable for not only absorption measurement but other performance measurement of optical thin films under high power density. 相似文献