全文获取类型
收费全文 | 800篇 |
免费 | 30篇 |
国内免费 | 35篇 |
专业分类
化学 | 774篇 |
晶体学 | 1篇 |
力学 | 3篇 |
综合类 | 13篇 |
数学 | 1篇 |
物理学 | 73篇 |
出版年
2023年 | 22篇 |
2022年 | 131篇 |
2021年 | 91篇 |
2020年 | 44篇 |
2019年 | 32篇 |
2018年 | 32篇 |
2017年 | 20篇 |
2016年 | 31篇 |
2015年 | 32篇 |
2014年 | 26篇 |
2013年 | 23篇 |
2012年 | 33篇 |
2011年 | 35篇 |
2010年 | 22篇 |
2009年 | 33篇 |
2008年 | 31篇 |
2007年 | 37篇 |
2006年 | 29篇 |
2005年 | 22篇 |
2004年 | 26篇 |
2003年 | 22篇 |
2002年 | 11篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1981年 | 2篇 |
1979年 | 2篇 |
排序方式: 共有865条查询结果,搜索用时 250 毫秒
801.
本文采用傅立叶变换红外光谱(吸收光谱、二阶导数谱及差谱)法对经不同剂量核辐照的人参粉进行了对比研究.辐照剂量不高于9 kGy时,人参粉样品的化学成分几乎没有发生变化;人参粉样品经15kGy及以上的辐照剂量辐照后,可能产生新的化学成分,表明采用辐照剂量不高于9 kGy的核辐照杀灭人参粉污染的微生物和各种寄生虫卵是可行的;... 相似文献
802.
Ginsenosides exhibit diverse biological activities and are major well-known components isolated from the radix of Panax ginseng C.A. Meyer. In the present work, a rapid and facile method for the separation and purification of eight ginsenosides from P. ginseng by high-speed counter-current chromatography coupled with evaporative light scattering detector (HSCCC-ELSD) was successfully developed. The crude samples for HSCCC separation were first purified from ginseng extract using a macroporous resin; the extract was loaded onto a Diaion-HP20 column and fractionated by methanol and water gradient elution. The ginsenosides-protopanaxadiol (PPD) and protopanaxatriol (PPT) fractions were subsequently eluted with 65 and 80% methanol and water gradient elution, respectively. Furthermore, these two fractions were separated by HSCCC-ELSD. The two-phase solvent system used for separation was composed of chloroform/methanol/water/isopropanol at a volume ratio of 4:3:2:1. Each fraction obtained was collected and dried, yielding the following eight ginsenosides: Rg(1), Re, Rf, Rh(1), Rb(1), Rc Rb(2) and Rd. The purity of these ginsenosides was greater than 97% as assessed by HPLC-ELSD, and their structures were characterized by electrospray-ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance spectroscopy. This is the first report regarding the separation of the ginsenosides Rh(1), Rb(2) and Rc from P. ginseng by HSCCC. 相似文献
803.
804.
采用傅里叶变换红外光谱结合二阶导数谱和二维相关红外光谱的三级鉴定技术对肉苁蓉的不同浓度醇提物药液和相应的药渣由表及里地进行了分析与评价研究.结果表明,用乙醇提取肉苁蓉活性成分的加工过程使苯乙醇苷类等活性物质在红外光谱上得以明显体现,并发现70%乙醇提取物中苯乙醇苷类等物质均高于其他浓度提取物.该技术从整体上揭示了乙醇萃... 相似文献
805.
建立氢化物发生-原子荧光光谱法(HG-AFS)测定铀钼矿钼反萃取液、净化液中砷含量的分析方法。仪器主要工作条件:负高压280 V,灯电流60 mA,原子化器高度9 mm,载气流量400 mL/min,屏蔽气流量1000 mL/min。砷的质量浓度在0~40μg/L范围内与荧光强度呈良好的线性,线性相关系数r=0.9998。方法测定砷的检出限为0.037μg/L,测定结果的相对标准偏差小于5%(n=6),加标回收率为90.5%~102.5%。针对溶液中的钼同多酸和杂多酸以及存在的其它氧化物,采取抗坏血酸-硫脲混合溶液进行预还原,溶液中铀含量约为0.1 g/L时,对砷的测定无影响。该法能满足铀钼矿钼反萃取液、净化液中砷含量0.005~4 g/L的测定要求。 相似文献
806.
Partially purified ginsenoside extract (PGE) and compound K enriched extract (CKE) were prepared from ginseng sprouts, and their antioxidant, anti-inflammatory and antithrombotic effects were investigated. Compared to the 6-year-old ginseng roots, ginseng sprouts were found to have a higher content of phenolic compounds, saponin and protopanaxadiol-type ginsenoside by about 56%, 36% and 43%, respectively. PGE was prepared using a macroporous adsorption resin, and compound K(CK) was converted and enriched from the PGE by enzymatic hydrolysis with a conversion rate of 75%. PGE showed higher effects than CKE on radical scavenging activity in antioxidant assays. On the other hand, CKE reduced nitric oxide levels more effectively than PGE in RAW 264.7 cells. CKE also reduced pro-inflammatory cytokines, such as tumor necrosis factor-α, interleukin (IL)-1β and IL-6 than PGE. Tail bleeding time and volume were investigated after administration of CKE at 70–150 mg/kg/day to mice. CKE administered group showed a significant increase or increased tendency in bleeding time than the control group. Bleeding volume in the CKE group increased than the control group, but not as much as in the aspirin group. In conclusion, ginseng sprouts could be an efficient source of ginsenoside, and CKE converted from the ginsenosides showed antioxidant, anti-inflammatory and antithrombotic effects. However, it was estimated that the CKE might play an essential role in anti-inflammatory effects rather than antioxidant effects. 相似文献
807.
Fatty acid content and lipid oxidation products were compared in chicken breast and leg meats derived from birds fed on animal-fat- and vegetable-oil-based diets, supplemented with ginseng prong powder. The first experiment examined polyunsaturated fatty acid (PUFA) content and the formation of primary and secondary lipid oxidation products in meats stored at refrigeration temperatures (4 °C) for up to 10 days, while the second experiment examined similar changes in the poultry meats when frozen stored at −18 °C, for up to six months. Results showed that initial lipid hydroperoxide concentrations increased in both breast and leg meat within the first week of refrigerated storage and also was ongoing during the first three to four months of frozen storage. A higher (p < 0.05) PUFA content in leg meat, especially in broilers fed a vegetable-oil-blended diet, corresponded to greater tendency for generation of primary lipid oxidation products after refrigerated and frozen storage (p < 0.05). The inclusion of powdered ginseng prong in broiler diets significantly inhibited (p < 0.05) secondary lipid oxidation products (e.g., malonaldehyde [MDA]) formation in both stored leg and breast meat, compared to controls. Significant interactions (p < 0.05) were obtained for storage time and inclusion of ginseng against production of primary and secondary lipid oxidation in broiler breast and leg meats from broilers fed PUFA-containing diets. We conclude that including ginseng prong in broiler growing diets represents a viable strategy to control lipid oxidation in refrigerated/cold-stored meat products. 相似文献
808.
《Comptes Rendus Chimie》2014,17(3):218-231
Herbal ingredients for use in the food, cosmetic and pharmaceutical industry are mainly gained from plant extracts. The challenge of producing these ingredients is the economic optimization of the design for the corresponding technical processes. To achieve this goal, a systematic, model-based approach is necessary, which is not yet available for complex mixtures (Bart and Pilz, 2010 [11]). The general basis for modeling and simulation of industrial processes is the knowledge of the physical properties of the system. A cost-effective option to get hold of separation factors of mixtures is the direct characterization of the multicomponent system, which has been the subject of earlier publications (Josch et al., 2012 [2]; Josch and Strube, 2012 [3]; Bart and Pilz, 2010 [11]). In this work, a systematic approach is illustrated on how to effectively characterize complex mixtures for a first process design. In addition, physical properties for individual plant components can be determined for modeling to optimize industrial processes. For this purpose, those processes which are well established in the chemical industry, including the use of substance databases and calculation of properties by means of thermodynamic theories, will be discussed. In addition, limitations of these approaches and resulting research requirements are shown. 相似文献
809.
Energy crisis is what being faced by every country today. Many efforts have been devoted to overcome the problems. One of several offered solutions is to develop solar cells (SCs) since solar energy is abundant and free to use. Especially in a tropical country like Indonesia, solar energy is available a whole year with quite high power 450 mWcm-2. Several types of SCs, especially silicon-based, have been mass-produced and applied in our daily life. Silicon-based SC has high efficiency yet has high price. Dye Sensitized Solar Cell is an inexpensive type of SC. The natural ingredients could be utilized as dyes for DSSC. In this research, tamarillo extract was employed as the dye for TiO2-based DSSC. TiO2 powder was spin-coated on top of Fluorine- Doped Tin Oxide (FTO) conductive glass and calcined at 550 ̊C, 650 ̊C and 750 ̊C each for 60 and 120 min. Scanning ElectronMicroscope (SEM) and X-Ray Diffractometer (XRD) were used to characterize the morphology and structure of the material. Brunauer-Emmet-Teller (BET) analysis was utilized to measure the material active surface area. As the result, the sample calcined at 650 ̊C for 60 minutes showed the highest electrical performance of 542.5 mV and 0.356 mAcm-2 which corresponded to an SC efficiency of 0.043%. This result was supported by the BET analysis showing the sample calcined at 650 ̊C for 60 min had the largest active surface area of 9.3 m2g-1. A large active surface area enabled more dye and electrolyte to be stored inside the material so that photon adsorptions from solar energy became more effective and resulting in higher efficiency. Despite of the small efficiency, this work demonstrated the opportunities of tamarillo and TiO2 to be applied as a DSSC. 相似文献
810.
The analgetic activity of Carica papaya leaves (CPL) extracts (n-hexane, ethyl acetate, ethanol) was investigated in mice model using acetic acid induced pain (Siegmund method). Experimental animals were divided into 11 groups and received n-hexane, ethyl acetate, and ethanol extracts at doses of 0.175, 0.35, 0.70 mg/kg bw orally; CMC-Na 0.5% (control group); 50 mg/ kg bw of aspirin. The results showed that all extracts at the doses of 0.175, 0.35 and 0.70 mg/kg bw gave significant analgetic activity (p<0.05) compared to control group. Ethanol extract of CPL dose of 0.70 mg/kg bw showed the best analgetic activity that was comparable to aspirin. 相似文献