全文获取类型
收费全文 | 270篇 |
免费 | 13篇 |
国内免费 | 11篇 |
专业分类
化学 | 239篇 |
力学 | 1篇 |
综合类 | 19篇 |
数学 | 6篇 |
物理学 | 29篇 |
出版年
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 5篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 3篇 |
2013年 | 11篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 25篇 |
2008年 | 19篇 |
2007年 | 20篇 |
2006年 | 11篇 |
2005年 | 8篇 |
2004年 | 10篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有294条查询结果,搜索用时 140 毫秒
41.
Zhao Y Kang LP Liu YX Zhao Y Xiong CQ Ma BP Dong FT 《Magnetic resonance in chemistry : MRC》2007,45(9):739-744
A mixture of a pair of stereoisomeric new spirostanol saponins (1a and 1b) and a new cholestane saponin (2) were isolated from the rhizome of Paris pollyphylla Smith var. yunnanensis. Their structures were elucidated as (25R)-spirost-5-en-3beta, 7beta-diol-3-O-alpha-L-arabinofuranosyl-(1 --> 4)-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (1a), (25R)-spirost-5-en-3beta, 7alpha-diol-3-O-alpha-L-arabinofuranosyl-(1 --> 4)-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (1b) and 26-O-beta-D-glucopyranosyl-(25R)-Delta(5(6), 17(20))-dien-16, 22-dione-cholestan-3beta, 26-diol-3-O-alpha-L-arabinofuranosyl-(1 --> 4)-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (2) by a combination of HR-ESI-MS, FAB-MS, 1D and 2D NMR techniques (including (1)H-NMR, (13)C-NMR, (1)H--(1)H COSY, HSQC, HMBC and NOESY). 相似文献
42.
The green method of nanoparticle synthesis, which is an environment and living-friendly method, is an updated subject that has appeared as an alternative to conventional methods such as physical and chemical synthesis. In this presented study, the green synthesis of magnetic iron oxide nanoparticles (IONPs) from iron (III) chloride by using Brassica oleracea var. capitata sub.var. rubra aqueous peel extract has been reported. The prepared IONPs were characterized with fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-VIS), zeta potential, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The cytotoxic effects of IONPs on MCF-7 breast cancer cell line were studied by MTT assay, and migrative effect of its were carried out by the wound healing assay. It was found that the mean particle size of IONPs was 675 ± 25 nm, and the polydispersity index was 0.265 PDI. It was also determined that these nanoparticles had an anti-proliferative impact on the MCF-7 breast cancer cell line depending on the dosage. Characterization results support the successful synthesis of nanoparticles, and the dose-dependent cytotoxic effects of nanoparticles on MCF-7 cells also make it a potential chemotherapeutic agent for breast cancer treatment. 相似文献
43.
应用均匀设计法对深山草莓花瓣诱导愈伤组织和愈伤组织再分化芽苗的主要因子和水平进行了探讨.结果表明,深山草莓花瓣愈伤组织诱导的适宜培养基为LS+TDZ 2.06 mg.L-1+2,4-D 0.60 mg.L-1,诱导率为98%;愈伤组织再分化芽苗的适宜培养基为1/2 LS+TDZ 2.30 mg.L-1+NAA 0.10 mg.L-1+KT1.30 mg.L-1,分化率为96.3%.炼苗移栽后观察植株的形态、花、果及生长等特征,以筛选具有优良性状的株系. 相似文献
44.
从滇重楼中分离得到2个甾体皂苷,利用1H NMR、13C NMR、1H-1H COSY、HSQC、HMBC、1D和2D TOCSY等多种核磁共振方法鉴定其结构分别为(25R)-26-O-β-D-吡喃葡萄糖基-3β,22α,26-三羟基-呋甾-5-烯-3-O-α-L-吡喃鼠李糖基-(1→2)-[α-L-呋喃阿拉伯糖基-(1→4)]-β-D-吡喃葡萄糖苷(1,Parisaponin I)和(25R)-3β,5α,6β-三羟基-△7-螺甾烯-3-O-β-D-吡喃葡萄糖基-(1→3)-[α-L-吡喃鼠李糖基-(1→2)]-β-D-吡喃葡萄糖苷(2,paris-vietnaside A).对化合物1和2的1H NMR和13C NMR信号分别进行了归属和详细分析,并纠正了文献中的核磁数据归属错误.化合物2为首次从滇重楼中分离得到. 相似文献
45.
P.D.S.C. Mariani K. Allganer F.B. Oliveira E.J.B.N. Cardoso L.H. Innocentini-Mei 《Polymer Testing》2009,28(8):824-829
The development of biodegradable polymers is considered to be a good alternative to decrease the volume of the plastic waste disposed into the environment every year. The use of natural polymers as raw materials to develop polymer blends and composites has increased the demand for renewable sources such as starch and soy protein.In this work, the authors prepared and characterized the thermal, mechanical and morphological properties of blends based on poly (-caprolactone) and modified corn starch, with added soy protein isolate (SPI) and sorbitol. All samples were processed by extrusion in a single-screw extruder and hot pressing. It was observed that the addition of modified corn starch and SPI were responsible for the reduction of thermal and mechanical properties of the materials, compared to pristine PCL. However, with increasing amounts of SPI and the reduction of starch incorporated into the samples, their properties tend to recover. The insertion of soy protein isolate in the formulations was done with the aim of balancing the C/N ratio of the blend, which plays a key role in the biodegradation process of these materials. 相似文献
46.
Camila Y. Henrique Camila S. Bertanha Tavane A. Alvarenga Márcio L. A. Silva Wilson R. Cunha Ana H. Januário 《液相色谱法及相关技术杂志》2016,39(2):65-69
Zanthoxylum naranjillo and Z. tingoassuiba (Rutaceae) are traditional herbal medicines with various biological activities including anti-inflammatory, analgesic, and antimalarial action. In this work, we have developed a simple HPLC-DAD method to quantify sesamin, a bioactive lignan present in Z. naranjillo and Z. tingoassuiba; egonol was the internal standard. According to the developed method, 11.07 ± 1.66, 8.69 ± 0.95, and 15.11 ± 0.72 µg/mL sesamin was present in the ethanol extract of Z. naranjillo leaves, in the methanol extract of Z. naranjillo leaves, and in the methanol extract of Z. tingoassuiba bark, respectively. The limits of detection and quantification were 0.32 and 1.06 µg/mL, respectively. The developed method can be easily applied during routine analysis of sesamin in these medicinal plants. 相似文献
47.
48.
一阶混合型积分微分方程的周期边值问题 总被引:1,自引:0,他引:1
在有一般化的上下解的条件下,研究了一阶混合型积分微分方程的周期边值问题的可解性和最小最大解的存在性。讨论基于迭合度方法,单调迭代方法和新的比较定理。 相似文献
49.
Two new compounds,oleanolic acid 28-O- β-D-glucopyranosyl-3-O-α-L-arabinopyranosyl-(1→3)-(6′-butyl ester)-β-D-glucuropyranoside 1,oleanolic acid 28-O-β-D-glucopyranosyl(1→6)-β-D-glucopyranoside 2 have been isolated from the roots of Hemsleya penxianensis var.gulinensis.Their structures were determined on the bases of the spectral and chemical evidences. 相似文献
50.
The chemical constituents of the roots of Zizyphus jujuba Mill. var. spinosa were investigated with a combination of Sephadex LH-20 column, centrifugal partition chromatography and RP-18 low pressure liquid chromatography. We isolated seven flavonoids-quercetin ( 1 ), (+)-dihydroquercetin ( 2 ), (+)-dihydrokaempferol ( 7 ), quercetin-3-0-β-glucoside ( 8 ), 2-hydroxynaringenin ( 11 ), rutin ( 12 ), and quercetin 3-0-(2G-β-D-xylopyranosylrutinoside) ( 13 ); four catechins-(-)-gallocatechin ( 3 ), (-)-epigallocatechin ( 4 ), (-)-catechin ( 5 ), and (-)-epicatechin ( 6 ); and two phenolic carboxylic acids-p-hydroxybenzoic acid ( 9 ) and protocatechuic acid ( 10 ) from the water soluble fraction of the ethanolic extract NMR date of 13 were assigned by 2D NMR techniques. 相似文献