全文获取类型
收费全文 | 7819篇 |
免费 | 455篇 |
国内免费 | 686篇 |
专业分类
化学 | 4858篇 |
晶体学 | 27篇 |
力学 | 332篇 |
综合类 | 66篇 |
数学 | 982篇 |
物理学 | 2695篇 |
出版年
2024年 | 13篇 |
2023年 | 259篇 |
2022年 | 363篇 |
2021年 | 444篇 |
2020年 | 370篇 |
2019年 | 323篇 |
2018年 | 305篇 |
2017年 | 408篇 |
2016年 | 437篇 |
2015年 | 381篇 |
2014年 | 466篇 |
2013年 | 594篇 |
2012年 | 672篇 |
2011年 | 557篇 |
2010年 | 494篇 |
2009年 | 554篇 |
2008年 | 337篇 |
2007年 | 362篇 |
2006年 | 322篇 |
2005年 | 162篇 |
2004年 | 100篇 |
2003年 | 108篇 |
2002年 | 129篇 |
2001年 | 149篇 |
2000年 | 76篇 |
1999年 | 119篇 |
1998年 | 101篇 |
1997年 | 62篇 |
1996年 | 42篇 |
1995年 | 39篇 |
1994年 | 26篇 |
1993年 | 33篇 |
1992年 | 21篇 |
1991年 | 35篇 |
1990年 | 26篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 1篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1979年 | 2篇 |
1959年 | 2篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有8960条查询结果,搜索用时 31 毫秒
111.
112.
《Arabian Journal of Chemistry》2022,15(8):104019
Plant bacteria and viruses have a huge negative impact on food crops in the world. Therefore, it is important to create new and efficient green pesticides. In this paper, a series of myricetin derivatives containing quinazolinone sulfide were introduced. Good antibacterial and antiviral activities of the drug molecules 2-((3-((5,7-dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propyl)thio)-6-fluoro-3-phenylquinazolin-4(3H)-one (T5) and 2-((4-((5,7-dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butyl)thio)-6-methyl-3-phenylquinazolin-4(3H)-one (T15) respectively were found by biological activity screening. The value of dissociation constant (Kd) of compound T15 to TMV CP was 0.024 ± 0.006 μM, determined by Microscale thermophoresis (MST), which was far less than the value of 8.491 ± 2.027 μM of commercial drug ningnanmycin (NNM). The interaction between compound T15 and TMV CP was further verified by molecular docking. Compound T15 formed strong hydrogen bonds with residues SER:49 and SER:15 (1.92 Å, 2.20 Å, respectively), which were superior to the traditional hydrogen bonds formed by NNM with residue SER:215 (3.64 Å). In addition, the effects of compound T15 on the contents of chlorophyll and peroxidase (POD) in tobacco were studied, and the results indicated that compound T15 could enhance the disease resistance of tobacco plants to a certain extent. 相似文献
113.
《Arabian Journal of Chemistry》2022,15(4):103707
Alsophila spinulosa is a tree-like fern, and many evidences suggested that plant polyphenols had the potential therapeutic for Alzheimer s disease (AD). Herein, polyphenols (ASP) was isolated from A. spinulosa leaves and its major constituent were isoorientin and vitexin. ASP displayed excellent antioxidant activity and obvious anti-lipid peroxidation capacity in vitro. ASP improved the survival rate of C. elegans under high temperature by enhancing the antioxidant enzymes activities and decreasing the lipid peroxidation level. Moreover, ASP alleviated β-amyloid (Aβ) induced paralysis and reduced Aβ deposition, decreased reactive oxygen species (ROS) accumulation and improved the level of skn-1 mRNA. In addition, ASP decreased the levels of pdk-1 and akt-1 mRNA in P13K/AKT signaling pathway. In conclusion, ASP may be a potential ingredient for the alleviation of AD. 相似文献
114.
《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
115.
《Radiation Physics and Chemistry》2007,76(1):27-36
The efficiency of the electron-beam removal of harmful impurities from industrial flue gases was studied as applied to polycyclic and nitro-polycyclic aromatic hydrocarbons. The mathematical model of radiation-induced processes was proposed. The model includes aromatic molecules decomposition in gas-phase reactions, and their liquid-phase conversion in the aerosol droplets produced upon the binary volume condensation of water and sulfuric acid vapors. The presence of active species (atoms and radicals) in radiation zone and their reactions with aliphatic and aromatic hydrocarbons can result in an opposite effect: the formation of aromatic molecules and growth of their structure. Modelling study of such processes allows evaluating the efficiency of this purification technology at various initial conditions. Results of calculations are compared with available experimental data. 相似文献
116.
Recent advances on the deoximation reactions are reviewed in this review. It was shown that catalytic deoximation with molecular oxygen as the mild oxidant should be the developing trend of the reaction. 相似文献
117.
118.
H. E. Bjørnstad H. N. Lien Yu-Fu Yu B. Salbu 《Journal of Radioanalytical and Nuclear Chemistry》1992,156(1):165-173
Low level90Sr in environmental and biological samples is determined using a combined HDEHP solvent extraction-liquid scintillation procedure. Yttrium-90 is selectively extracted from nitric acid solution into 5% di(2-ethylhexyl) phosphoric acid (HDEHP) in toluene, and90Y in the organic phase is measured directly using an ultra low level liquid scintillation spectrometer.The working program of the Quantulus counter has been optimized. As the counting efficiency using liquid scintillation counting is high and the stripping and precipitation of Yttrium-90 oxalate is omitted, this procedure is simpler and more timesaving than traditional methods. The chemical recoveries of90Y were 85.1% for soil, 75.7% for milk and 65.3% for bone. The detection limit is 8 mBq. 相似文献
119.
《Journal of photochemistry and photobiology. A, Chemistry》2006,177(2-3):248-252
Steady-state and time resolved luminescence quenching measurements of (2T/2E)Cr(phen)33+ were used to investigate the association of phenols to sodium dodecyl sulfate (SDS) micelles. Steady-state results show the quenching process occurs in the micellar pseudo phase. Scatchard plots indicate that the process is a partition between aqueous and micelles. The k+ and k− rate constant have been evaluated from time resolved data and the binding constants were obtained. The trend found in the K's were 4-H-Ph < 2,6-diMe-Ph < 4-Br-Ph. We concluded that it is possible to use *Cr(phen)33+ as a luminescent probe to determine association parameters for quenchers to micelles of SDS. 相似文献
120.
Wine has become a commodity of significant commercial value, and the demand for high quality wine by consumers has been increasing. Suitable analytical techniques are needed for its quality control. Ultraviolet, Visible, Near-infrared and infrared spectroscopy is by far one of the most important techniques for determining the wine quality, including its components and characterization. This review will overview the available most recent applications of spectroscopic techniques in the past decade for wine quality prediction and discrimination both quantitatively and qualitatively. The fundamental principles of these techniques will be introduced briefly, and some innovative setups/instrumentations will also be illustrated. At last the limitations and prospects of spectroscopic techniques for wine industry will be discussed. 相似文献