全文获取类型
收费全文 | 1084篇 |
免费 | 40篇 |
国内免费 | 112篇 |
专业分类
化学 | 1116篇 |
晶体学 | 9篇 |
力学 | 2篇 |
综合类 | 12篇 |
数学 | 44篇 |
物理学 | 53篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 106篇 |
2021年 | 76篇 |
2020年 | 67篇 |
2019年 | 60篇 |
2018年 | 71篇 |
2017年 | 40篇 |
2016年 | 55篇 |
2015年 | 32篇 |
2014年 | 48篇 |
2013年 | 99篇 |
2012年 | 111篇 |
2011年 | 40篇 |
2010年 | 37篇 |
2009年 | 58篇 |
2008年 | 50篇 |
2007年 | 37篇 |
2006年 | 35篇 |
2005年 | 26篇 |
2004年 | 18篇 |
2003年 | 19篇 |
2002年 | 19篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1236条查询结果,搜索用时 15 毫秒
991.
Vera A. Alferova Roman A. Novikov Olga P. Bychkova Eugene A. Rogozhin Maxim V. Shuvalov Igor A. Prokhorenko Vera S. Sadykova Alexander B. Kulko Lyubov G. Dezhenkova Elena A. Stepashkina Mikhail A. Efremov Olga N. Sineva Gulnara Kh. Kudryakova Aleksander S. Peregudov Pavel N. Solyev Yaroslav V. Tkachev Galina B. Fedorova Larisa P. Terekhova Vladimir A. Korshun 《Tetrahedron》2018,74(52):7442-7449
Two new natural compounds, astolides A,B, were isolated from Streptomyces hygroscopicus collected from the alkaline soil obtained from Saratov region, Russia. The structures were elucidated by interpretation of UV spectroscopic, MS, 1D and 2D NMR data. The relative configurations were determined by analysis of NOESY/ROESY spectra and coupling constants. The isolated compounds were evaluated for their inhibitory activity against bacteria, fungi and yeasts and showed pronounced antifungal activity. Both compounds are noticeably cytotoxic, being active against doxorubicin-resistant human leukemia cell line. 相似文献
992.
Thamere Cheriet Ines Mancini Ramdane Seghiri Fadila Benayache Samir Benayache 《Natural product research》2015,29(17):1589-1613
This is a review on 95 references dealing with the genus Linaria (Scrophularioideae-Antirrhineae tribe), a known genus of the Scrophulariaceae family, which comprises about 200 species mainly distributed in Europe, Asia and North Africa. The use of some Linaria species in folk medicine has attracted the attention for chemical and biological studies. This report is aimed to be a comprehensive overview on the isolated or identified known and often new metabolites from the 41 Linaria species so far cited. It is organised presenting first the phytochemical classes of alkaloids, polyphenols including flavonoids, the latter being quite diffused and mostly present as flavones, flavonols and their glycosides, and terpenoids including iridoids and steroids. Second, the results from biological investigation on plant extracts, pure natural products isolated from Linaria species and some synthetic derivatives are reported, with antitumour, anti-acetylcholinesterase, anti-inflammatory and analgesic, antioxidant and antibacterial activities. 相似文献
993.
1,3-方酸衍生物亲电作用的理论研究 总被引:4,自引:1,他引:3
设计了负离子与2,4-二苯基-1,3-环丁烯二酮(Sq)的作用模型,用AM1方法研究了F-,Cl-,Br-,O2-,S2-等负离子与Sq的相互作用.结果表明,负离子对体系具有稳定化作用,离子电荷、离子极化性和取代基效应等对亲电作用有显著的影响. 相似文献
994.
Hideo Tanaka Tomoharu Ebata Isamu Kuwahara Masaru Matsuo James C. Ogbonna 《Applied biochemistry and biotechnology》1999,80(1):51-64
Development and application of a system for real-time quantitative assessment of individual cell activities in a mixed culture
system was investigated. This was based on a concept that the activities of individual cells in a mixed culture can be assessed
if the cells are physically separated (in separate compartments) in a vessel while the culture conditions, including the broth
components, are maintained the same in all the compartments during the cultivation. On this basis, three different apparatus
(M-1, M-2, and M-3) were constructed using various types of membranes. In terms of mass transfer characteristics and membrane
fouling, the M-3 apparatus was the most effective system for analysis of mixed cultures at high cell densities. With the M-3
apparatus, the interrelationships between two alcohol-producing strains (Saccharomyces cerevisiae and Zymomonas mobilis) under anaerobic and aerobic conditions were studied. Under anaerobic condition, except for possible competition for nutrients,
there were no significant effects of the activities of one microorganism on the other. However, under aerobic condition, amensalism
was observed because acetaldehyde that was produced by Z. mobilis inhibited the growth of S. cerevisiae. 相似文献
995.
利用二(2,4-二氯苄基)二氯化锡分别与对甲基苯甲酰肼或对叔丁基苯甲酰肼、丙酮酸钠在甲醇中发生反应,合成了2个二(2,4-二氯苄基)锡配合物(C1、C2),通过元素分析、IR、1H NMR、13C NMR、119Sn NMR、HRMS以及X射线单晶衍射表征了配合物结构。测试了配合物C1、C2的热稳定性以及配合物对NCI-H460(人肺癌细胞)、HepG2(人肝癌细胞)和MCF7(人乳腺癌细胞)的体外抑制活性,发现配合物C1对癌细胞均表现较好的抑制作用。利用UV-Vis光谱、荧光光谱以及黏度法研究了2个配合物与ct-DNA之间的相互作用,结果表明配合物是以经典的嵌入模式与DNA结合。 相似文献
996.
用烯基膦亚胺与4-甲苯基异氰酸酯、对甲硫苯酚的串联aza-Wittig反应合成了2-(4-甲硫基苯氧基)-3-(4-甲苯基)-4H-咪唑啉-4-酮衍生物.探讨了反应进行的条件和产物的波谱性质,提出了可能的环化反应机理.生成的环化产物均为新的化合物,其结构经元素分析、IR、1H NMR和MS确证.并探讨了所合成的新型杂环化合物的生物活性,结果表明部分化合物表现出良好的抑菌活性,其中3f的活性最好,在质量分数为5×10-5浓度时,对稻瘟菌和苹果轮纹菌的抑制率均达到100%. 相似文献
997.
Rong Dong Li Xin Zhai Yan Fang Zhao Ping Gong 《中国化学快报》2007,18(10):1191-1194
A novel series of 5H-pyridazino[4,5-b]indoles were designed and synthesized in order to find novel potent anticancer compounds.The structures were confirmed by ~1H NMR and MS.Their antiproliferative activities against two cancer cell lines were tested by the MTT method in vitro.Three of compounds (1e,1g,and 1h) exhibited potent antiproliferative activities,especially compound 1h (with IC_(50) values of 5.2μmol/L and 1.9μmol/L against Bel-7402 and HT-1080,respectively).The preliminary structure-activity relationships of 5H-pyridazino[4,5-b]indole derivatives were discussed. 相似文献
998.
浙东南山门地区早白垩世同源岩浆活动的稀土元素制约 总被引:1,自引:0,他引:1
对浙东南山门地区早白垩世中酸性火山-侵入杂岩进行了稀土元素含量的ICP-MS分析,对比研究了其稀土元素地球化学特征。不同类型岩浆岩的稀土元素除Eu外具有基本一致的轻稀土富集的右倾配分模式,以及稳定的Sm/Nd,La/Nd和La/Sm比值,表明它们具有一致的岩浆源区,只是分异演化程度不同。Eu/Sm比值(0.02~0.09和0.15~0.21)及一致的Nb/Ta比值(13.9~16.9),介于地壳和地幔值之间,表明其为壳幔岩浆混合作用的产物。稀土元素协变关系显示成岩过程可能以部分熔融作用为主。结合微量元素研究,山门地区早白垩世同源岩浆活动可能与古太平洋板块俯冲碰撞后岩石圈伸展引起的弧后引张构造有关。 相似文献
999.
1000.
Maheswari Chinnapaiyan Yashika Selvam Fatma Bassyouni Mathammal Ramu Chandrasekar Sakkaraiveeranan Aravindan Samickannian Gobi Govindan Matheswaran Palaniswamy Uthrakumar Ramamurthy Mohamed Abdel-Rehim 《Molecules (Basel, Switzerland)》2022,27(5)
Nanomaterial is a rapidly growing area that is used to create a variety of new materials and nanotechnology applications from medical, pharmaceuticals, chemical, mechanical, electronics and several environmental industries including physical, chemical and biological nanoparticles are very important in our daily life. Nanoparticles with leaf extract from the healthy plant are important in the area of research using biosynthesis methods. Because of it’s used as an environmentally ecofriendly, other than traditional physical and chemical strategies. In particular, biologically synthesized nanoparticles have become a key branch of nanotechnology. The present work presents a synthesis of zinc oxide nanoparticles using an extract from the Argemone leaf Mexicana. Biosynthetic nanoparticles are characterized by X-ray diffraction (XRD), Ultraviolet visible (UV-vis) spectroscopy analysis, a Fourier Transform Infrared Spectroscopy analysis (FTIR) and a scanning electron microcopy (SEM), X-ray analysis with dispersive energy (EDAX). XRD is used to examine the crystalline size of zinc oxide nanoparticles. The FTIR test consists in providing evidence of the presence of targeted teams. UV is used for optical properties and calculates the energy of the bandwidth slot. The scanning microscope emission reveals the morphology of the surface and the energy dispersive X-ray analysis confirms the basic composition of zinc oxide nanoparticles. It is found that zinc nanoparticles are capable of achieving high anti-fungal efficacy and therefore have a high potential antimicrobial activity of ZnO NPs, like antibacterial and high antioxidant. Zinc Oxide nanoparticles from the Argemone Mexicana leaf extract have several antimicrobial applications, such as medical specialty, cosmetics, food, biotechnology, nano medicine and drug delivery system. ZnO nanoparticles are important because they provide many practical applications in industry. The most important use of nanoparticles of ZnO would be strong antibacterial and antioxidant activity with a simple and efficient biosynthesis method may be used for future work applications. 相似文献