全文获取类型
收费全文 | 2223篇 |
免费 | 321篇 |
国内免费 | 258篇 |
专业分类
化学 | 1694篇 |
晶体学 | 23篇 |
力学 | 124篇 |
综合类 | 17篇 |
数学 | 232篇 |
物理学 | 712篇 |
出版年
2024年 | 2篇 |
2023年 | 53篇 |
2022年 | 65篇 |
2021年 | 86篇 |
2020年 | 104篇 |
2019年 | 96篇 |
2018年 | 74篇 |
2017年 | 75篇 |
2016年 | 102篇 |
2015年 | 113篇 |
2014年 | 125篇 |
2013年 | 151篇 |
2012年 | 211篇 |
2011年 | 231篇 |
2010年 | 149篇 |
2009年 | 126篇 |
2008年 | 141篇 |
2007年 | 124篇 |
2006年 | 116篇 |
2005年 | 102篇 |
2004年 | 100篇 |
2003年 | 52篇 |
2002年 | 58篇 |
2001年 | 27篇 |
2000年 | 36篇 |
1999年 | 47篇 |
1998年 | 44篇 |
1997年 | 28篇 |
1996年 | 32篇 |
1995年 | 22篇 |
1994年 | 27篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 22篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有2802条查询结果,搜索用时 234 毫秒
91.
Meng Gui Bin Zhao Juyi Song Zhichao Zhang Zhaohui Peng Pinglan Li 《Applied biochemistry and biotechnology》2014,174(6):2295-2306
Paraplantaricin L-ZB1 was produced by Lactobacillus paraplantarum L-ZB1, which was isolated from the traditional China fermented sausage. In this work, paraplantaricin L-ZB1 was used to maintain quality of rainbow trout fillets at 4 °C. Rainbow trout fillets were left untreated (CK) or treated with 200 activity units (AU)/ml paraplantaricin L-ZB1 (P1), 400 AU/ml paraplantaricin L-ZB1 (P2) or 200 AU/ml Nisin (N). The treated samples were stored at 4 °C for up to 10 days, and the quality changes were determined by microbiological (total viable count [TVC], Enterobacteriaceae, Pseudomonas, spore-forming bacteria), sensory, chemical (pH, total volatile basic nitrogen [TVB-N]) and biochemical (biogenic amines, K value) methods. Results show that paraplantaricin L-ZB1 could inhibit the growth of microflora, especially Enterobacteriaceae, Pseudomonas and spore-forming bacteria during sample storage. Meanwhile, the increases of pH, TVB-N, K value and biogenic amine levels were significantly delayed in paraplantaricin L-ZB1-treated samples compared to the control group. Paraplantaricin L-ZB1 of 400 AU/ml extended the rainbow trout fillets’ shelf life to 4–6 days, and the sample showed good sensory characteristics. Therefore, paraplantaricin L-ZB1 could be used as a suitable biological preservative for chilled rainbow trout fillets. 相似文献
92.
93.
Jian-Ming Zhang Shang-Ru Zhai Bin Zhai Qing-Da An Ge Tian 《Journal of Sol-Gel Science and Technology》2012,64(2):347-357
Multifunctional nanomaterials with task-specific physicochemical properties, especially core?Cshell nanostructures with Fe3O4 core and NH2-functional shells (Fe3O4@SiO2?CNH2), have been extensively investigated as high-performance adsorbents, catalysts and catalyst supports; and in most cases the controllable sol?Cgel technique is the choice for fabrication of this kind of widely applied materials. Herein, we demonstrated that mono-dispersed and spherical Fe3O4@SiO2?CNH2 nanomaterials with magnetic response core, NH2-functional shell structure can be facilely prepared by co-condensation of TEOS with APTMS using a versatile sol?Cgel process. It was shown that the proper usage of APTMS and appropriate pre-hydrolysis time of TEOS were crucial and key steps for formation of highly uniform and desirable amino loading Fe3O4@SiO2?CNH2 materials. The TEOS pre-hydrolysis and the critical time (around 90?min) before the addition of APTMS prove to be vital for uniform structure evolution, while the appropriate concentration of APTMS (~2.28?mmol?L?1 in our system) leads to well-dispersed materials with relatively high loading of amino functionality. The as-prepared Fe3O4@SiO2?CNH2 magnetic nanoparticles prepared under optimum conditions possessing superparamagnetic behavior, uniform core?Cshell structure (~200?nm in diameter), relatively large BET surface area (~138?m2/g) and high incorporation of amino-functionality (~2.90?wt?%). 相似文献
94.
95.
96.
97.
A 2-dimensional gradual period photonic heterostructure was made with holography by use of non-uniform swelling effect of dichromated gelatin during processing. In this structure, the symmetric point group of triangle lattice was debased to C2V from C6V. Theoretical analysis and experimental results show that omnidirectional band gap in visible range can be achieved with this kind of heterostructure made by low refractive index materials. 相似文献
98.
99.
Qianqian Zhai Zhihua Lu Jing Wang Weina Wang Yudong Ma Caili Yue 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):803-811
AbstractA method of Fourier transform near-infrared (FT-NIR) spectroscopy combined with partial least squares (PLS) model was successfully applied to investigate the hydrolysis kinetics of four kinds of silane coupling agents (phenyltriethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltriethoxysilane, 3-chloropropyltriethoxysilane) in an acid-catalyzed EtOH system. The fast scanning speed and high sensitivity of the FT-NIR spectroscopy, and the powerful data processing ability of the PLS, enabled the method to quantitatively and accurately catch the fast changing H2O concentration during the hydrolysis processes without delay, realizing the study of the fast-paced hydrolysis reactions of the silane coupling agents. The results showed that electrophilic substitution occurred in the hydrolysis reactions, which followed second-order reactions and greatly depend on the catalyst concentration and reaction temperature. The hydrolysis rate constants, activation energy, and Arrhenius Frequency factors were gained. In conclusion, the FT-NIR PLS model is a powerful tool for hydrolysis kinetics researching of the silane coupling agents. 相似文献
100.
Three kinds of photoresponsive copolymers with azobenzene side chains were synthesized by radical polymerization of N‐4‐phenylazophenylacrylamide (PAPA) with N‐isopropylacrylamide (NIPAM), N,N‐diethylacrylamide (DEAM) or N,N‐dimethylacrylamide (DMAM) respectively. Their structures were characterized by FT‐IR, 1H‐NMR and UV/Vis spectroscopy. Their reversible photoresponses were studied with or without α‐cyclodextrin (α‐CD), which showed that both the copolymers and their inclusion complexes with α‐CD underwent rapid photoisomerization. The lower critical solution temperature (LCST) of the copolymers and their inclusion complexes with α‐CD were investigated by cloud point measurement, which showed that the LCST of three kinds of copolymers increased largely after adding α‐CD. After UV irradiation on the solutions of copolymers and their inclusion complexes, the LCST of the copolymers increased slightly with the absence of α‐CD, while decreased largely with the presence of α‐CD. Furthermore, the LCST reverted to its originality after visible light irradiation. This change of LCST could be reversibly controlled by UV and visible light irradiation alternately. In particular, in the copolymer of PAPA and DMAM, the reversible water solubility of the inclusion complexes could be triggered by alternating UV and visible light irradiation. 相似文献