全文获取类型
收费全文 | 925篇 |
免费 | 140篇 |
国内免费 | 65篇 |
专业分类
化学 | 851篇 |
力学 | 1篇 |
综合类 | 7篇 |
数学 | 178篇 |
物理学 | 93篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 23篇 |
2021年 | 40篇 |
2020年 | 60篇 |
2019年 | 34篇 |
2018年 | 39篇 |
2017年 | 32篇 |
2016年 | 57篇 |
2015年 | 57篇 |
2014年 | 59篇 |
2013年 | 69篇 |
2012年 | 75篇 |
2011年 | 67篇 |
2010年 | 68篇 |
2009年 | 67篇 |
2008年 | 62篇 |
2007年 | 54篇 |
2006年 | 45篇 |
2005年 | 41篇 |
2004年 | 39篇 |
2003年 | 30篇 |
2002年 | 22篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 4篇 |
1987年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1130条查询结果,搜索用时 0 毫秒
991.
DBD-d(and l)-beta-proline, new fluorescent chiral derivatization reagents, were synthesized from the reaction of 4-(N,N-dimethylaminosulfonyl)-7- fl uoro-2,1,3-benzoxadiazole (DBD-F) with beta-proline. The racemic mixture synthesized was separated by a chiral stationary phase (CSP) column, Chiralpak AD-H, with n-hexane-EtOH-TFA-diethylamine (70:30:0.1:0.1) as the mobile phase. The dl-forms were decided according to the results obtained from a circular dichroism (CD) detector after separation by the CSP column. The fractionated enantiomers reacted with chiral amine to produce a couple of diastereomers. The labeling proceeded in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and pyridine as the activation reagents. The reaction conditions were mild and no racemization occurred during the diastereomer formation. The resulting diastereomers fluoresced at around 570 nm (excitation at around 460 nm). Good linearity of the calibration curves was obtained in the range 1-75 pmol and the detection limits on chromatogram were less than 1 pmol. The separability of the diastereomers was compared with the diastereomers derived from DBD-d(or l)-proline. The resolution values (Rs) obtained from the diastereomers of three chiral amines with DBD-d(or l)-beta-proline were higher than those derived from DBD-d(or l)-proline, e.g. dl-phenylalanine methylester (dl-PAME), 2.23 vs 1.37; (R)(S)-1-phenylethylamine [(R)(S)-PEA], 2.09 vs 1.13; and (R)(S)-1-(1-naphthyl)ethylamines [(R)(S)-NEA], 5.19 vs 1.23. The results suggest that the position of COOH group on pyrrolidine moiety in the structures is one of the important factors for the efficient separation of a couple of the diastereomers. 相似文献
992.
William R. Dolbier Jr. Emilie Gautriaud Xiaohong Cai 《Journal of fluorine chemistry》2005,126(3):339-343
The synthesis of 1,1-difluoro-2-(dideuteriomethylene)-cyclopropane is reported along with the kinetics of its competing, reversible, first order rearrangements: (a) the degenerate rearrangement to 1,1-difluoro-3,3-dideuterio-2-methylene-cyclopropane, and (b) its rearrangement to 2,2-dideuterio-1-(difluoromethylene)-cyclopropane. The observed experimental ratio of these two rate constants, 2.3, is consistent with Borden's theoretically predicted ratio of 3. 相似文献
993.
Fredrik LakeChristian Linde 《Tetrahedron letters》2012,53(30):3927-3929
A high yielding gram-scale synthesis of [13C4] N-benzylpiperazine for use as a convenient and versatile building block in isotope labeling studies of clinical drug candidates is reported. 相似文献
994.
995.
996.
纳米粒子是当今最受关注也是最常报道的一类纳米材料,尺寸处于纳米级别是纳米粒子的突出特点,这赋予其在化学、光学、电学和磁学等方面优于传统块体材料的独特性能,因而纳米粒子越来越受到人们的重视,并广泛应用于很多领域,尤其是生物医药领域。本文围绕可生物应用的纳米粒子,从组成以及结构的角度着手,将纳米粒子分为有机纳米粒子、无机纳米粒子以及有机/无机杂化纳米粒子。同时结合近三年国内外关于各类纳米粒子新颖的合成报道,分别阐述了上述不同种类纳米粒子所具有的适合生物应用的物理和化学方面的特征,并针对不同类别的新型纳米粒子,着重描述了其具体合成方法和潜在的生物应用。最后,简单介绍了纳米粒子在生命科学这一领域的具体应用实例,如刺激响应感应器、生物特异性标记及基因药物载体等,并展望了纳米粒子在该领域的长远发展。 相似文献
997.
998.
分泌蛋白质是调控细胞间信号转导的重要生物大分子。由于分泌蛋白的丰度相比于胞内蛋白以及培养基添加剂更低,因此分泌蛋白的高通量鉴定是目前蛋白质组学界研究的热点和难点。目前,基于生物质谱的分泌蛋白质组学分析一般均需要从无血清的条件培养基中获得分泌蛋白质,再对其进行富集和分析。该流程操作步骤繁琐,易造成分泌蛋白质的损失和降解。本工作采用基于生物正交化学生物学技术实现对分泌蛋白质的高选择性标记和高效富集。通过结合点击化学技术,综合评估了分泌蛋白质分析中用于代谢标记的不同糖类似物。采用3种最常用的商品化糖类似物,N-叠氮乙酰甘露糖胺(ManNAz)、N-叠氮乙酰半乳糖胺(GalNAz)和N-叠氮乙酰葡萄糖胺(GlcNAz)分别对HeLa细胞进行代谢标记,之后通过炔基生物素探针对条件培养基中的分泌蛋白进行富集,结合质谱分析来对比3种糖类似物对分泌蛋白的标记效率。最后通过无标定量蛋白质组学分析,系统评估了3种糖类似物用于分泌蛋白质组分析的性能。结果表明,基于ManNAz的分泌蛋白标记方法鉴定到了282个分泌蛋白、224个细胞质膜蛋白以及846个N-糖基化位点;对分泌蛋白的富集效率分别较GalNAz和GlcNAz提高了130%和67.2%;对细胞质膜蛋白的富集效率较GalNAz和GlcNAz分别提高了273.3%和148.7%,体现出了明显的优势。本研究的实验结果为分泌蛋白高选择性富集和系统分析提供了有益的对比分析和新技术策略。 相似文献
999.
A novel isotope labeling reagent d0-/d6-2, 4-dimethoxy-6-piperazin-1-yl pyrimidine (DMPP) has been developed for derivatization toward the carboxyl group based on carbodiimide chemistry for mass spectrometry (MS) analysis. The strengths of this derivatization strategy involve fast labeling (15 s), low chemical background and general access to most carboxylic analytes. This has been demonstrated using a series of compounds containing carboxylic acids, including peptides and proteins. To enhance the MS response of the derivatized analytes, the design of DMPP has been based on integration of the theoretical consideration of high gas-phase hydrogenation capacity and hydrophobicity. In addition, the high abundance product ions at m/z 225 and m/z 231 from d0-/d6-DMPP labeled carboxylic acids indicate high efficiency of the gas-phase cleavage induced by the labeling reagent. Quantitative determination of these ions can also be used in single reaction monitoring to achieve extremely high sensitivity toward the target analytes. This has subsequently been used to determine trace free fatty acids in human urine. Furthermore, the DMPP labeled peptides also provide additional sequence information in MALDI–MS/MS because of the formation of sequence-related isotope fragment ions. This DMPP-oriented labeling technique is expected to be a promising tool for the MS detection of many varieties of compounds containing carboxyl groups. 相似文献
1000.
SUI Yu-jie ZHANG Gui-zhen WANG Qian WANG Ya-li WU Mei DU Zhen-wu ZHANG Jie JIANG Ri-hua . Central Laboratory China-Japan Union Hospital of Jilin University Changchun P. R. China . Central Laboratory the Second Hospital of Jilin University Changchun 《高等学校化学研究》2011,(2):277-281
A relatively sensitive, specific, and photostable method for the detection of cytokeratin of cancer cells via conjugation with cadmium telluride quantum dots(CdTe QDs) was described. Water soluble CdTe QDs were conjugated to anti-pan-cytokeratin(CK) monoclonal antibody(MAb) through coupling reagent [1-ethyl-3-(3-dimethyla- mino propyl)carbodiimide, EDC] and the conjugates were purified by dialysis. The expression of pan CK protein in HepG2 cells was observed by immunocytochemistry and direct immunofluoresce... 相似文献