全文获取类型
收费全文 | 3112篇 |
免费 | 693篇 |
国内免费 | 243篇 |
专业分类
化学 | 2643篇 |
晶体学 | 4篇 |
力学 | 64篇 |
综合类 | 46篇 |
数学 | 653篇 |
物理学 | 638篇 |
出版年
2024年 | 3篇 |
2023年 | 35篇 |
2022年 | 87篇 |
2021年 | 97篇 |
2020年 | 155篇 |
2019年 | 96篇 |
2018年 | 107篇 |
2017年 | 107篇 |
2016年 | 194篇 |
2015年 | 190篇 |
2014年 | 240篇 |
2013年 | 277篇 |
2012年 | 239篇 |
2011年 | 229篇 |
2010年 | 170篇 |
2009年 | 199篇 |
2008年 | 203篇 |
2007年 | 248篇 |
2006年 | 182篇 |
2005年 | 177篇 |
2004年 | 151篇 |
2003年 | 138篇 |
2002年 | 82篇 |
2001年 | 70篇 |
2000年 | 64篇 |
1999年 | 48篇 |
1998年 | 44篇 |
1997年 | 46篇 |
1996年 | 36篇 |
1995年 | 27篇 |
1994年 | 16篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 15篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有4048条查询结果,搜索用时 796 毫秒
71.
72.
《Arabian Journal of Chemistry》2022,15(12):104368
Protein hydrolysates have the potential to be natural and safer sources of bioactive peptides. In this study, two proteases were used to hydrolyze Chinese sturgeon (Acipenser sinensis) protein, and the hydrolysates were then purified to yield antioxidant peptides. The degree of hydrolysis of 23.56 % and 18.14 % was obtained using papain and alcalase 2.4L, respectivly, and hydrolysates had 96.80 % and 87.24 % total amino acid content, respectivly. The papain hydrolysate (PH) and alcalase 2.4L hydrolysate (AH) showed good antioxidant activity against DPPH? (IC50 of 3.64 and 3.15 mg/mL) and ABTS?+ (IC50 of 1.92 and 1.58 mg/mL), respectively. The low-molecular-weight (<1000 Da) fraction of both hydrolysates demonstrated the highest antiradical activity (IC50 of 2.59 and 2.31 mg/mL, DPPH) and (IC50 of 1.54 and 1.36 mg/mL, ABTS), respectively. Nine peptides were separated from both hydrolysates using reverse phase high performance liquid chromatography (RP-HPLC). The IC50 for ABTS?+ scavenging activity of peptide P5 with valine, glycine and asparagine (MW of 282.13 Da) from PH, and peptide P3 with histidine, glycine and alanine (MW of 302.74 Da) from AH was 0.89 and 0.72 mg/mL, respectively. The fractions and purified peptides obtained from Chinese sturgeon hydrolysates could be utilized as natural antioxidant substitutes in pharmaceuticals and food products. 相似文献
73.
The influence of CCl4 on the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), the value of the
total antioxidant status (TAS), and the concentration of malonic dialdehyde (MDA) and glutathione (GSH) was monitored in plasma
or whole blood of rabbits. The administration of CCl4 caused the increase of the SOD activity to approximately 150 % and the decrease in the activity of GPx and GR by about 50
%. These changes were accompanied with the increase in TAS value and MDA concentration and the decrease of GSH concentration.
The effect of CCl4 was suppressed by the previous 7 days lasting or simultaneous administration of vitamin E. Oxidative stress caused by CCl4 was accompanied by the development of reactive oxygen forms, especially superoxide radical anion. 相似文献
74.
Mariko Kitajima 《Tetrahedron letters》2006,47(19):3199-3202
A new pyrrolidinoindoline-type alkaloid, CPC-1, and a new tryptamine-derived dimeric alkaloid, CPC-2, were isolated from the seeds and rinds of Chimonanthus praecox f. concolor. The structure including the absolute configuration of CPC-1 was determined by chiral total synthesis. CPC-2 has a unique hexahydropyrroloquinoline skeleton. 相似文献
75.
A new synthetic method for the preparation of allyl amines has been developed. The key steps of this method are enantioselective addition of diethylzinc and [1,3]-chirality transfer through the [3.3] sigmatropic rearrangement of allyl cyanates. Stereocontrolled syntheses of lentiginosine (1) and polyoxamic acid derivative 2 from a common intermediate 7 derived from D-tartaric acid (8), have been accomplished. 相似文献
76.
77.
Shinya Nakashima Dr. Hiromune Ando Risa Saito Hideki Tamai Dr. Hideharu Ishida Dr. Makoto Kiso 《化学:亚洲杂志》2012,7(5):1041-1051
The first total synthesis of the hybrid ganglioside X2, which consisted of a highly branched octasaccharide and ceramide moieties, was accomplished by using a glucosyl ceramide cassette approach. With a disaccharyl donor, the heptasaccharide could not be constructed by glycosylation of the C4 hydroxy group of galactose at the reducing end of the pentasaccharide. In contrast, through an alternative approach with two branched glycan units, a GM2-core trisaccharide, and a lacto-ganglio tetrasaccharide, the heptasaccharyl donor could be prepared and subsequently joined with a glucosyl ceramide cassette to afford the protected ganglioside, X2. Finally, global deprotection completed the synthesis, thus affording the pure ganglioside X2. 相似文献
78.
79.
《Angewandte Chemie (International ed. in English)》2017,56(7):1704-1718
Since the pioneering days of total synthesis and retrosynthetic analysis, the community has embraced guiding principles for planning synthetic approaches towards complex natural products. These guideposts have enabled the community to synthesize ever more complex compounds by applying prior knowledge gained in new settings. The recently isolated schinortriterpenoid family of natural products has attracted considerable synthetic attention and provided a rich opportunity to evaluate the lessons learned in the construction of complex, polycyclic scaffolds. In this Minireview, a detailed discussion of the synthetic work within this family is provided, including the six reported total syntheses, as well as a comparative analysis of the approaches utilized in their construction. 相似文献
80.