全文获取类型
收费全文 | 395篇 |
免费 | 25篇 |
国内免费 | 21篇 |
专业分类
化学 | 310篇 |
晶体学 | 2篇 |
力学 | 1篇 |
综合类 | 67篇 |
数学 | 5篇 |
物理学 | 56篇 |
出版年
2023年 | 10篇 |
2022年 | 9篇 |
2021年 | 28篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 19篇 |
2014年 | 20篇 |
2013年 | 14篇 |
2012年 | 17篇 |
2011年 | 16篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 10篇 |
2007年 | 19篇 |
2006年 | 16篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 17篇 |
2002年 | 12篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1986年 | 1篇 |
排序方式: 共有441条查询结果,搜索用时 15 毫秒
411.
The properties of NR from rice varieties Yuanfengzao and Jingyin 127 are the same in molecular weight of native enzyme and subunit, optimum pH, K_m value for substrates NO_3~- and NADH, stability in vitro and immunological characteristics. The decay rate in vitro of the activity of the partially purified NR from Yuanfengzao is 20% lower than that from Jingyin 127. The results from antiserum titration and rocket immunoelectrophoresis indicated that the amount of NR in Yuanfengzao is about 1.5 times more than that in Jingyin 127. Further study on in vivo incorporation of ~3H-labeled amino acids into NR revealed that the rate of NR synthesis in Yuanfengzao is obviously higher than that in Jingyin 127. In vitro translation of mRNA showed that the products of NR-mRNA per unit of total mRNA of Yuanfengzao is much more than that of Jingyin 127. It is concluded that, therefore, NR activity in rice is regulated through NR synthesis and NR-inhibitory protein(s) system, the former is further controlled at the lev 相似文献
412.
Parboiling is gaining increasing attention as it can enhance the head rice yield (HRY) and nutritional quality of non-pigmented rice. The traditional parboiling process with high-temperature immersion requires a long immersion period and results in hard texture of cooked parboiled black rice (PBR), which may be addressed by ultrasound-assisted immersion. In this study, we evaluated the effect of power, time and temperature of ultrasonic immersion on the HRY, texture profile and nutritional quality of PBR. Proper ultrasound-assisted immersion could increase the HRY by about 20% and the GABA content by up to 133%, as well as reduce the arsenic and cadmium content by up to 61% and 79% relative to untreated black rice (UBR), respectively. Moreover, it could increase the content of essential minerals such as calcium, iron and zinc to some extent, and free and bound polyphenols, despite of a certain loss of anthocyanins. It could also improve the palatability of cooked rice. Furthermore, response surface experiments based on the Box-Behnken design were performed to obtain and validate the optimal conditions of ultrasound-assisted immersion (540 W, 45 min, 57 °C). On this basis, morphological changes might be one reason for the improved HRY, nutrition and texture of PBR compared with those of UBR, namely the disappearance of cracks near the aleurone layer and formation of new cracks in the interior of rice. 相似文献
413.
Due to the existence of many disulfide bonds in japonica rice bran protein (JRBP) molecules, their solubility is poor, which seriously affects other functional properties. To improve the functional characteristics of JRBP molecules, they were processed by ultrasound technology, and JRBP-catechin (CC) covalent complex was prepared. The structural and functional properties of indica and japonica rice bran proteins and their complexes were compared; furthermore, the changes in the structural and functional properties of JRBP-CC under different ultrasound conditions were investigated. The results showed that compared with indica rice bran protein (IRBP), the secondary structure of JRBP-CC was very different, the water holding capacity (WHC) was higher, and the emulsification performance was better. Different ultrasound conditions had different effects on the functional properties of JRBP-CC. When the ultrasound power was 200 W, the λmax redshift of the JRBP-CC complex was the most significant, the particle size was the smallest, the absolute value of the zeta potential was the largest, and the hydrophobicity and microstructure of the JRBP-CC complex were the best. Concurrently, the maximum WHC and oil holding capacity (OHC) of JRBP-CC under these conditions were 7.54 g/g and 6.87 g/g, respectively. Moreover, the emulsifying activity index (EAI) and emulsifying stability index (ESI) were 210 m2/g and 47.8 min, respectively, and the scavenging activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ABTS+ were 71.96 % and 80.07 %, respectively. 相似文献
414.
Cecilia Anchondo-Trejo Jaime Alonso Loya-Carrasco Toms Galicia-García Ivn Estrada-Moreno Mnica Mendoza-Duarte Lilisbet Castellanos-Gallo Rubn Mrquez-Melndez Beatriz Portillo-Arroyo Cesar Soto-Figueroa 《Molecules (Basel, Switzerland)》2021,26(1)
This study aimed to obtain a third-generation snack from native rice starch (NS), rice starch modified by extrusion (MS), nopal flour (NF) and xanthan gum (XG). These raw materials were characterized by proximal analysis, pH, particle size distribution, water absorption index (WAI) and water solubility index (WSI), degree of substitution (DS), differential scanning calorimetry (DSC), rheology, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The analysis of the response variables in the nine formulations of the snack: expansion index (EI), apparent density (AD), hardness (H), luminosity (L*) and tendency to green-red (a*), was performed through a composite central design (CCD), the selected formulations were characterized by SEM. Results showed an increase in WAI, 4.69 ± 0.04, and WSI, 12.61 ± 0.10, for MS, higher than NS values due to chemical modification. According to the color analysis the NF obtained a value of 60.73 ± 0.008 in L* and −6.51 ± 0.004 in a* with green tendency. The DS value obtained was 0.09 ± 0.005, being within the FDA’s permissible range for food use. By FTIR analysis, the acetyl group was corroborated. Finally, employing microwave cooking, snacks made from NS with concentrations of NF (5%) and XG (0%) obtained the highest EI value, 4.47, as well the low Dap and D value (0.37 g/cm3, 2.25 N, respectively), corroborated by SEM analysis. 相似文献
415.
为降低消解过程中硝酸使用量,满足重金属元素前处理“绿色”、“环保”的要求,本研究建立了测定大米中总砷含量的稀酸微波消解-原子荧光光谱法。通过单因素实验考察了硝酸浓度、过氧化氢体积、样品称取量和稀硝酸体积用量等对大米总砷测定的影响,得到最佳消解条件,最后应用建立的方法对市售20批大米进行测定。结果表明:最佳消解液组成为20%硝酸5 mL + 过氧化氢2.5 mL,总砷在0~20 μg/L浓度范围内线性关系良好,相关系数R2在0.998以上,检出限为0.0022 mg/kg,加标回收率变化范围为96.6%~102.8%,相对标准偏差(relative standard deviation, RSD)为3.6%。采用建立的方法对大米成分标准物质和实际样品测定,并与浓硝酸微波消解法及GB 5009.11-2014《食品中总砷及无机砷的测定》中干灰化法比较,结果一致(P > 0.05)。20批市售大米总砷含量范围为0.026~0.247 mg/kg,其中糙米平均含量高于精白米。该方法操作简便,重现性好,灵敏度、精密度、准确度高,适合在基层实验室推广应用。 相似文献
416.
Shishir Tandon 《International journal of environmental analytical chemistry》2017,97(14-15):1352-1361
Dissipation dynamics of fenoxaprop-p-ethyl (FPPE) and fenoxaprop acid (FPA) (metabolite) in rice field conditions was investigated for two consecutive seasons. FPPE dissipated rapidly in soil with average half life of 1.42–2.19 days. Dissipation followed first-order kinetics. The method was validated in terms of accuracy, linearity, specificity and precision. Linearity was in the range of 0.005–5 µg mL?1 with limit of detection as 0.002 and 0.001 µg mL?1 for fenoxaprop-p-ethyl and fenoxaprop acid, respectively. Quantitation limit in soil, grain, straw and husk were 0.005, 0.008, 0.01 and 0.01 µg g?1 for fenoxaprop-p-ethyl, and 0.005, 0.01, 0.01 and 0.01 µg g?1 for fenoxaprop acid, respectively. Recovery in soil, rice grains, straw and husk ranged from 81.60–93.40, 77.85–87.00, 75.20–84.40 and 76.00–87.20% for FPPE and 82.50–88.20, 76.25–83.00, 74.80–83.60 and 75.00–85.40% for FPA, respectively. Below detectable limit of residues of FPPE and metabolite were observed in soil, rice grain, husk and straw samples at harvest. FPPE and FPA were of short persistence under field conditions and residues were below European Union-Maximum Residue Limits in all matrices that would cause adverse effect on environment and human/animal health. 相似文献
417.
Rice straw is a common agricultural waste. In order to increase the added value of rice straw and improve the performance of rice straw biochar. MgO-modified biochar (MRBC) was prepared from rice straw at different temperatures, pyrolysis time and MgCl2 concentrations. The microstructure, chemical and crystal structure were studied using X-ray diffraction (XRD), a Scanning Electron Microscope (SEM), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption desorption isotherms and Elementary Analysis (EA). The results showed that the pyrolysis temperature had significant influence on the structure and physicochemical property of MRBCs. MRBC-2 h has the richest microporous structure while MRBC-2 m has the richest mesoporous structure. The specific surface area (from 9.663 to 250.66 m2/g) and pore volume (from 0.042 to 0.158 cm3/g) of MRBCs increased as temperature rose from 300 to 600 °C. However, it was observed MgCl2 concentrations and pyrolysis time had no significant influence on pore structure of MRBCs. As pyrolysis temperature increased, pH increased and more oxygen-containing functional groups and mineral salts were formed, while MgO-modified yield, volatile matter, total content of hydrogen, oxygen, nitrogen, porosity and average pore diameter decreased. In addition, MRBCs formed at high temperature showed high C content with a low O/C and H/C ratios. 相似文献
418.
419.
420.