全文获取类型
收费全文 | 1380篇 |
免费 | 92篇 |
国内免费 | 187篇 |
专业分类
化学 | 939篇 |
晶体学 | 3篇 |
力学 | 153篇 |
综合类 | 37篇 |
数学 | 134篇 |
物理学 | 393篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 34篇 |
2021年 | 39篇 |
2020年 | 49篇 |
2019年 | 52篇 |
2018年 | 41篇 |
2017年 | 26篇 |
2016年 | 58篇 |
2015年 | 62篇 |
2014年 | 64篇 |
2013年 | 71篇 |
2012年 | 100篇 |
2011年 | 100篇 |
2010年 | 71篇 |
2009年 | 76篇 |
2008年 | 73篇 |
2007年 | 71篇 |
2006年 | 79篇 |
2005年 | 67篇 |
2004年 | 55篇 |
2003年 | 51篇 |
2002年 | 44篇 |
2001年 | 33篇 |
2000年 | 46篇 |
1999年 | 53篇 |
1998年 | 47篇 |
1997年 | 28篇 |
1996年 | 37篇 |
1995年 | 24篇 |
1994年 | 21篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 1篇 |
排序方式: 共有1659条查询结果,搜索用时 109 毫秒
941.
Liquid chromatography/ultraviolet (LC/UV) and mass spectrometry/mass spectrometry (MS/MS) libraries containing 39 phenolic compounds were established by coupling a LC and an ion trap MS with an electrospray ionization (ESI) source, operated in negative ion mode. As a result, the deprotonated [M-H]- molecule was observed for all the analyzed compounds. Using MS/MS hydroxybenzoic acid and hydroxycinnamic acids showed a loss of CO2 and production of a [M-H-44]- fragment and as expected, the UV spectra of these two compounds were affected by their chemical structures. For flavonol and flavonol glycosides, the spectra of their glycosides and aglycones produced deprotonated [M-H]- and [A-H]- species, respectively, and their UV spectra each presented two major absorption peaks. The UV spectra and MS/MS data of flavan-3-ols and stilbenes were also investigated. Using the optimized LC/MS/MS analytical conditions, the phenolic extracts from six representative wine samples were analyzed and 31 phenolic compounds were detected, 26 of which were identified by searching the LC/UV and MS/MS libraries. Finally, the presence of phenolic compounds was confirmed in different wine samples using the LC/UV and LC/MS/MS libraries. 相似文献
942.
Xiangyang X Ling L Jianping Z Shiyue L Jie Y Xiaojin Y Jinsheng R 《Colloids and surfaces. B, Biointerfaces》2007,55(2):222-228
N-Succinyl-N′-octyl chitosan (SOC) was prepared and characterized by elemental analysis, FTIR, 1H NMR, WAXD and TG. An anticancer drug, doxorubicin (DOX), was incorporated into polymeric micelles forming by SOC in aqueous solutions. Critical micelle concentrations (CMC) of SOC were determined by fluorescence spectroscopy. The DOX-loaded SOC micelles were characterized by measurement of size and drug loading. The loading content of DOX increased with increasing drug-to-carrier ratio, and the more amount of the octyl chain, the higher the drug loading content. The average size, which was affected by the amount of octyl chain and drug loading content, was in the range of 100–200 nm. The polymeric micelles containing doxorubicin in the core region exhibited a sustained release and more cytotoxic activity against HepG2, A549, BGC and K562 than doxorubicin alone, this can be attributed to an endocytosis mechanism rather than passive diffusion. 相似文献
943.
To enhance the binding ability of β-cyclodextrin with naphthalene derivatives,a hydrophobic group to the rim of β-cyclodextrin was added and the new β-cyclodextrin compound—mono-6-p-nitrobenzoyl-β-cyclodextrin was synthesized. Its binding ability for 1: 1 inclusion complexation with 1-naphthoic acid was evaluated in the KCl/HCl buffer solution(pH=1.5,0.1 mol/dm3)at 15℃ by the spectrofluormetric titration. The results obtained indicated that mono-6-p-nitrobenzoyl-β-cyclodextrin could strongly include 1-naphthoic acid in aqueous solution;the modification dramatically enhanced the original binding ability of native β-cyclodextrin by a factor 9. The binding constants of mono-6-p-nitrobenzoyl-β-cyclodextrin and other naphthalenes such as 1-methoxynaphthalene,2-methoxynaphthalene,1-N,N-dimethylaminonaphthalene and 1-N,N-dimethylaminonaphthalene were obtained from the time-resolved fluorescence. The high binging ability of naphthalenes with NBCD make it is possible to assemble stable host-guest complexes. 相似文献
944.
藻胆蛋白是一组同源捕光色素蛋白,由多肽链及相连的开链四吡咯环色团构成。多肽链对色团的调控形成不同藻胆蛋白的特征吸收及荧光光谱。这些色团是藻蓝胆素(吸收带590~670 nm)、藻红胆素(吸收带530~570 nm)和藻尿胆素(吸收带490~500nm)。藻尿胆素由于在共轭体系中含有较少的双键,所以与前二者比,在较短波长有吸收。它们总是与藻红胆素伴生,在藻胆蛋白中作为敏化基团存在。 相似文献
945.
946.
醇对水中DDAHPS分子聚集行为的影响 总被引:1,自引:0,他引:1
分别用稳态荧光猝灭技术和时间分辨荧光方法研究醇对两性表面活性剂 (十二烷基羟基磺化甜菜碱 ,DDAHPS)在水中聚集行为的影响 .结果表明 :在 4.0 0× 1 0 - 2 mol·L- 1DDAHPS水溶液中 ,随着正丁醇浓度的逐渐增大 ,表面活性剂的聚集数 (N)逐渐降低 .恒定醇的浓度为 2 .1 4× 1 0 - 2mol·L- 1时 ,醇碳链越长 ,N值越大 .与无醇体系相比 ,正丙醇和正丁醇使N值变小 ,正戊醇、正己醇和正庚醇使N值变大 .本文同时还测定了醇对微环境的极性 ,芘的荧光寿命及胶束内芘的激基缔合物形成效率的影响 . 相似文献
947.
The discrepancies of the spectral behavior for the C-H stretching band between some long chain hydrocarbon compounds and steroids were investigated. At low temperature, the C-H stretching bands exhibit complex fine structure in steroids but remain simple in long chain hydrocarbon compounds. MM3 molecular mechanics calculation indicates that, for long chain hydrocarbon compounds, the C-H groups vibrate with large scale coupling. There exist a few bands where the C-H groups vibrate in synchronous and inphase mode. Thus the variations of dipole moment for these bands are enhanced and the intensities are obviously stronger than others and cover other band in the spectra. This is just the reason why the C-H stretching bands are simple even at low temperature environment. Nevertheless, for the steroids, the C-H stretching bands vibrate with local coupling mode. The synchronous enhancement effect does not occur, the differences of intensities for various modes are not as large as those in long chain hydrocarbo 相似文献
948.
合成了一种新的环糊精衍生物单 6 氧 (对硝基苯甲酰基 ) β 环糊精 (NBCD) .该化合物与 1 萘甲酸(NA)在KCl/HCl缓冲水溶液 (pH =1.5,0 .1mol/dm3)中形成 1∶1包合物 ,15℃时的包合常数由稳态荧光测定 ,结果表明 ,NBCD可以和 1 萘甲酸形成稳定的包合物 ,与 β 环糊精相比 ,稳定常数增加 9倍左右 .同时 ,时间分辨荧光得到了NBCD与其它给电子的萘的衍生物的包合常数 .结果表明 ,在 β 环糊精的 6位引进对硝基苯甲酰基能够显著增强其包合能力 ,使NBCD能够与萘的衍生物形成稳定的主 客体包合物 相似文献
949.
新型固体汞电极在仪器分析实验中的应用 总被引:1,自引:0,他引:1
介绍了仪器分析实验中阳极溶出伏安法的改进方法。利用银汞固体电极阳极溶出伏安法连续测定痕量铜、铅、镉、锌。在pH=4.7的HAc-NH4Ac缓冲液中,富集电位为-1.3V,Cu2 、Pb2 、Cd2 、Zn2 在固体汞电极表面分别还原成金属,并沉积在工作电极上。溶出时电极上沉积的金属分别于-0.13、-0.45、-0.63和-1.00V产生4个灵敏的溶出峰,灵敏度与传统的液态汞电极相当。避免了汞电极使用中的不方便性和毒性。用于大学生实验可得到较好的实验效果。 相似文献
950.