全文获取类型
收费全文 | 1286篇 |
免费 | 48篇 |
国内免费 | 8篇 |
专业分类
化学 | 932篇 |
晶体学 | 33篇 |
力学 | 28篇 |
数学 | 69篇 |
物理学 | 280篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 17篇 |
2021年 | 19篇 |
2020年 | 39篇 |
2019年 | 43篇 |
2018年 | 31篇 |
2017年 | 40篇 |
2016年 | 58篇 |
2015年 | 41篇 |
2014年 | 92篇 |
2013年 | 103篇 |
2012年 | 95篇 |
2011年 | 127篇 |
2010年 | 60篇 |
2009年 | 75篇 |
2008年 | 90篇 |
2007年 | 86篇 |
2006年 | 62篇 |
2005年 | 44篇 |
2004年 | 49篇 |
2003年 | 47篇 |
2002年 | 37篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有1342条查询结果,搜索用时 15 毫秒
61.
62.
Susheel Kalia Sarita Kango Amit Kumar Yuvaraj Haldorai Bandna Kumari Rajesh Kumar 《Colloid and polymer science》2014,292(9):2025-2052
Hybrid nanomaterials have received voluminous interest due to the combination of unique properties of organic and inorganic component in one material. In this class, magnetic polymer nanocomposites are of particular interest because of the combination of excellent magnetic properties, stability, and good biocompatibility. Organic–inorganic magnetic nanocomposites can be prepared by in situ, ex situ, microwave reflux, co-precipitation, melt blending, and ceramic–glass processing and plasma polymerization techniques. These nanocomposites have been exploited for in vivo imaging, as superparamagnetic or negative contrast agents, drug carriers, heavy metal adsorbents, and magnetically recoverable photocatalysts for degradation of organic pollutants. This review article is mainly focused on fabrication of magnetic polymer nanocomposites and their applications. Different types of magnetic nanoparticles, methods of their synthesis, properties, and applications have also been reviewed briefly. The review also provides detailed insight into various types of magnetic nanocomposites and their synthesis. Diverse applications of magnetic nanocomposites including environmental and biomedical uses have been discussed. 相似文献
63.
Adil Anwar Hiba Anwar Takeshi Yamauchi Ryan Tseng Rajesh Agarwal Lawrence D Horwitz Zili Zhai Mayumi Fujita 《Photochemistry and photobiology》2020,96(4):870-876
Ultraviolet B (UVB) radiation is known as a culprit in skin carcinogenesis. We have previously reported that bucillamine (N-[2-mercapto-2-methylpropionyl]-L-cysteine), a cysteine derivative with antioxidant and anti-inflammatory capacity, protects against UVB-induced p53 activation and inflammatory responses in mouse skin. Since MAPK signaling pathways regulate p53 expression and activation, here we determined bucillamine effect on UVB-mediated MAPK activation in vitro using human skin keratinocyte cell line HaCaT and in vivo using SKH-1 hairless mouse skin. A single low dose of UVB (30 mJ cm−2) resulted in increased JNK/MAPK phosphorylation and caspase-3 cleavage in HaCaT cells. However, JNK activation and casaspe-3 cleavage were inhibited by pretreatment of HaCaT cells with physiological doses of bucillamine (25 and 100 µm ). Consistent with these results, bucillamine pretreatment in mice (20 mg kg−1) inhibited JNK/MAPK and ERK/MAPK activation in skin epidermal cells at 6–12 and 24 h, respectively, after UVB exposure. Moreover, bucillamine attenuated UVB-induced Ki-67-positive cells and cleaved caspase-3-positive cells in mouse skin. These findings demonstrate that bucillamine inhibits UVB-induced MAPK signaling, cell proliferation and apoptosis. Together with our previous report, we provide evidence that bucillamine has a photoprotective effect against UV exposure. 相似文献
64.
Gautam Rajesh Kumar Seth Debabrata 《Journal of Thermal Analysis and Calorimetry》2020,140(6):2633-2640
Journal of Thermal Analysis and Calorimetry - We have reported the thermal conductivities of three deep eutectic solvents (DESs). We have used choline chloride, N,N-diethyl ethanol ammonium... 相似文献
65.
Isaac O. Donkor Rajesh Devraj Sherry F. Queener Louis R. Barrows Aleem Gangjee 《Journal of heterocyclic chemistry》1996,33(6):1653-1661
A series of diaminobenzo[f]- and diaminobenzo[h]pyrimido[4,5-b]quinolines 1–11 were designed as 5-deaza tetracyclic nonclassical, lipophilic antifolates. The compounds were designed as conformationally semi-rigid and rigid analogs of 2,4-diamino-6-phenyl- 12 and 2,4-diamino-7-phenylpyrido[2,3-d]pyrimidines 13 and 14 . The target compounds were synthesized by cyclocondensation of chlorovinyl aldehydes obtained from appropriately substituted 1- or 2-tetralone, with 2,4,6-friaminopyrimidine. Compounds 1–11 were evaluated as inhibitors of P. carinii and T. gondii dihydrofolate reductases. These pathogens cause fatal opportunistic infections in AIDS patients. In addition, the selectivity of these agents was evaluated using rat liver dihydrofolate reductase as the mammalian source. In general the benzo[f]pyrimido[4,5-b]quinolines 1–5 were more potent than the corresponding benzo[h]pyrimido[4,5-b]quinoline analogues 6–11 against P. carinii and rat liver dihydrofolate reductase and were equipotent against T. gondii dihydrofolate reductase. Compounds 6–11 were moderately selective towards T. gondii dihydrofolate reductase with IC50S in the 10−7 M range. In contrast analogues 1–5 lacked selectivity against P. carinii or T. gondii dihydrofolate reductase and were, in general, potent inhibitors of rat liver dihydrofolate reductase with IC50S in the 10−8 M range. Analogues 1 and 4 were evaluated against a series of tumor cell lines in vitro and were found to have moderate antitumor activity (IC50 10−6 M). The structure activity/selectivity relationships suggest that benzo[f]pyrimido analogues 1–5 with the phenyl ring substitution in the “upper” portion of the tetracyclic ring are better accommodated within the rat liver (mammalian) dihydrofolate reductase and P. carinii dihydrofolate reductase active sites compared to the benzo[h]pyrimido analogues 6–11 which have the phenyl ring substitution in the “lower” portion of the tetracyclic ring. In contrast T. gondii dihydrofolate reductase does not discriminate between the isomers and binds to both series of compounds with similar affinities. 相似文献
66.
Venkataraman Vishwanathan Gajula Balakrishna Balraj Rajesh Venkatreddy Jayasri Lucky Sikhwivhilu Neil J. Coville 《Reaction Kinetics and Catalysis Letters》2007,92(2):311-317
A series of sulphate-promoted ZrO2 solid acid catalysts with different contents of SO4
2− were calcined at 450°C in air for 4 h and tested for the liquid-phase alkylation of catechol to guaiacol in a fixed-bed down-flow
reactor. The 5 wt.% SO4
2− on ZrO2 showed the best conversion (82%) and selectivity for guaiacol (84%) at 200°C and 1 bar pressure. A smooth correlation was
observed between the catalytical activity and surface acidity of sulphated zirconia. Based on our results, a surface mechanism
is proposed. 相似文献
67.
Dr. Joseph M. Slocik Dr. Zhifeng Kuang Prof. Marc R. Knecht Dr. Rajesh R. Naik 《Chemphyschem》2016,17(20):3252-3259
The ability to precisely and remotely modulate reversible binding interactions between biomolecules and abiotic surfaces is appealing for many applications. To achieve this level of control, an azobenzene‐based optical switch is added to nanoparticle‐binding peptides in order to switch peptide conformation and attenuate binding affinity to gold surfaces via binding and dissociation of peptides. 相似文献
68.
69.
70.
Ganesh P. Sanganwar Ram B. Gupta Alexandre Ermoline James V. Scicolone Rajesh N. Dave 《Journal of nanoparticle research》2009,11(2):405-419
Due to the increased use of nanocomposites, mixing at nanoscale has become important. Current mixing techniques can be classified
into: (a) dry mixing (mechanical mixing), (b) wet mixing, and (c) simultaneous production of mixed nanoparticles (when possible).
Dry mixing is in general not effective in achieving desired mixing at nanoscale, whereas wet mixing suffers from different
disadvantages like nanomaterial of interest should be insoluble, has to wet the liquid, and involves additional steps of filtration
and drying. This paper examines the use of pressurized carbon dioxide having high density and low viscosity to replace the
liquids (e.g., n-hexane, toluene). Ultrasound is applied to the suspension of nanopowders in gaseous and supercritical carbon dioxide where
high impact collisions during sonication help mixing and the final mixture is obtained by simple depressurization. The method
is tested for binary mixture of alumina/silica, silica/titania, MWNT (multiwalled carbon nanotubes)/silica, and MWNT/titania.
The effects of sonication intensity and pressure on the degree of mixing are studied. Comparative study is also done with
liquid n-hexane as a mixing media. Quantitative characterization (e.g., mean composition standard deviation, intensity of segregation)
of mixing of alumina/silica and silica/titania is done with energy-dispersive X-ray spectroscopy, and that of MWNT/silica
and MWNT/titania is done using field-emission scanning electron microscopy and day-light illumination spectrophotometry. Results
show that mixing in carbon dioxide at higher ultrasound amplitudes is as good as in liquid n-hexane, and the final mixed product does not contain any residual media as in the case of liquid n-hexane. 相似文献