全文获取类型
收费全文 | 28031篇 |
免费 | 3973篇 |
国内免费 | 2098篇 |
专业分类
化学 | 5391篇 |
晶体学 | 106篇 |
力学 | 5022篇 |
综合类 | 496篇 |
数学 | 10728篇 |
物理学 | 12359篇 |
出版年
2024年 | 62篇 |
2023年 | 304篇 |
2022年 | 816篇 |
2021年 | 800篇 |
2020年 | 957篇 |
2019年 | 836篇 |
2018年 | 768篇 |
2017年 | 1082篇 |
2016年 | 1235篇 |
2015年 | 904篇 |
2014年 | 1495篇 |
2013年 | 2175篇 |
2012年 | 1554篇 |
2011年 | 1834篇 |
2010年 | 1584篇 |
2009年 | 1848篇 |
2008年 | 1706篇 |
2007年 | 1727篇 |
2006年 | 1457篇 |
2005年 | 1318篇 |
2004年 | 1208篇 |
2003年 | 1022篇 |
2002年 | 991篇 |
2001年 | 790篇 |
2000年 | 746篇 |
1999年 | 657篇 |
1998年 | 605篇 |
1997年 | 448篇 |
1996年 | 379篇 |
1995年 | 362篇 |
1994年 | 330篇 |
1993年 | 278篇 |
1992年 | 251篇 |
1991年 | 188篇 |
1990年 | 172篇 |
1989年 | 126篇 |
1988年 | 124篇 |
1987年 | 137篇 |
1986年 | 114篇 |
1985年 | 129篇 |
1984年 | 133篇 |
1983年 | 74篇 |
1982年 | 96篇 |
1981年 | 62篇 |
1980年 | 29篇 |
1979年 | 39篇 |
1978年 | 31篇 |
1977年 | 29篇 |
1976年 | 16篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
991.
《Journal of Saudi Chemical Society》2021,25(12):101395
The kinetic model of the hydrolysis of lactose by β-galactosidase from Aspergillus niger immobilized on a commercial ceramic monoliths was estimated in the attendance of lactose and its hydrolysis reaction products galactose and glucose. The aim of this work was to developing kinetic model of lactase hydrolysis by Aspergillus niger. The variables in this study are temperature, pH, enzyme concentration, substrate concentration and final product. The optimum temperature used to achieve the best hydrolysis performance in the kinetic model selection was 55 and 60 °C. The optimum pH used for enzyme activity was about 3.5 to 4. Five kinetic models were proposed to confirm experimental data the enzymatic reaction of the lactose hydrolysis by the β-galactosidase. The kinetics of lactose hydrolysis by both Immobilized and soluble lactases were scrutinized in a batch reactor system in the lack of any mass conduction restriction. In both instance the galactose inhibition kinetic models predicted the experimental data. The model is capable to fit the experimental data correctly in the extensive experimental span studied. 相似文献
992.
An implicit account of the solvent effect can be carried out using traditional static quantum chemistry calculations by applying an external electric field to the studied molecular system. This approach allows one to distinguish between the effects of the macroscopic reaction field of the solvent and specific solute–solvent interactions. In this study, we report on the dependence of the simulation results on the use of the polarizable continuum approximation and on the importance of the solvent effect in nonpolar solvents. The latter was demonstrated using experimental data on tautomeric equilibria between the pyridone and hydroxypyridine forms of 2,6-di-tert-butyl-4-hydroxy-pyridine in cyclohexane and chloroform. 相似文献
993.
Xifeng Hou Yanhui Zheng Xiaolong Ma Yuheng Liu Zichuan Ma 《Molecules (Basel, Switzerland)》2021,26(4)
To expand the applications of graphene-based materials to biogas purification, a series of reduced graphene oxide aerogels (rGOAs) were prepared from industrial grade graphene oxide using a simple hydrothermal method. The influences of the hydrothermal preparation temperature on the textural properties, hydrophobicity and physisorption behavior of the rGOAs were investigated using a range of physical and spectroscopic techniques. The results showed that the rGOAs had a macro-porous three-dimensional network structure. Raising the hydrothermal treatment temperature reduced the number of oxygen-containing groups, whereas the specific surface area (SBET), micropore volume (Vmicro) and water contact angle values of the rGOAs all increased. The dynamic adsorption properties of the rGOAs towards hexamethyldisiloxane (L2) increased with increasing hydrothermal treatment temperature and the breakthrough adsorption capacity showed a significant linear association with SBET, Vmicro and contact angle. There was a significant negative association between the breakthrough time and inlet concentration of L2, and the relationship could be reliably predicted with a simple empirical formula. L2 adsorption also increased with decreasing bed temperature. Saturated rGOAs were readily regenerated by a brief heat-treatment at 100 °C. This study has demonstrated the potential of novel rGOA for applications using adsorbents to remove siloxanes from biogas. 相似文献
994.
Carmen van der Linde Monica Barone Silvia Turroni Patrizia Brigidi Enver Keleszade Jonathan R. Swann Adele Costabile 《Molecules (Basel, Switzerland)》2021,26(8)
The response of a coeliac and a healthy gut microbiota to the green algae Chlorella pyrenoidosa was evaluated using an in vitro continuous, pH controlled, gut model system, which simulated the human colon. The effect of C. pyrenoidosa on the microbial structure was determined by 16S rRNA gene sequencing and inferred metagenomics, whereas the metabolic activitywas determined by1H-nuclear magnetic resonancespectroscopic analysis. The addition of C. pyrenoidosa significantly increased the abundance of the genera Prevotella, Ruminococcus and Faecalibacterium in the healthy donor, while an increase in Faecalibacterium, Bifidobacterium and Megasphaera and a decrease in Enterobacteriaceae were observed in the coeliac donor. C. pyrenoidosa also altered several microbial pathways including those involved in short-chain fatty acid (SCFA) production. At the metabolic level, a significant increase from baseline was seen in butyrate and propionate (p < 0.0001) in the healthy donor, especially in vessels 2 and 3. While acetate was significantly higher in the healthy donor at baseline in vessel 3 (p < 0.001) compared to the coeliac donor, this was markedly decreased after in vitro fermentation with C. pyrenoidosa. This is the first in vitro fermentation study of C. pyrenoidosa and human gut microbiota, however, further in vivo studies are needed to prove its efficacy. 相似文献
995.
996.
997.
该文在免疫遗传算法(IGA)的基础上,提出一种改进免疫遗传算法(iIGA)用于近红外光谱波长变量的选择。该算法舍去了原算法中固定抗体相似度阈值的思想,取而代之的是抗体相似度阈值自适应,同时引入精英保留策略和贪心算法思想,使得算法朝着正确的方向进行局部性探优。将该算法在玉米的淀粉和蛋白质含量数据集上进行实验测试,建立偏最小二乘(PLS)分析模型,并与IGA、遗传算法(GA)以及全谱方法进行了对比。结果表明,在玉米淀粉含量的预测上,iIGA相较于原IGA算法,预测集均方根误差(RMSEP)从0.312 0降至0.298 0,预测集预测精度提升4.5%;在玉米蛋白质含量的预测上,RMSEP从0.124 4降至0.110 3,预测集预测精度提升11.3%。分别对预测淀粉和蛋白质模型的RMSEP值进行显著性检验,F值分别为165.22和182.05,P值分别为9.5 × 10-23和4.5 × 10-24,P值均小于0.05,因此,iIGA能显著提升模型预测精度。 相似文献
998.
Due to the rigid structure of 1,3,5-triaza-7-phosphaadamantane (PTA), its 31P chemical shift solely depends on non-covalent interactions in which the molecule is involved. The maximum range of change caused by the most common of these, hydrogen bonding, is only 6 ppm, because the active site is one of the PTA nitrogen atoms. In contrast, when the PTA phosphorus atom is coordinated to a metal, the range of change exceeds 100 ppm. This feature can be used to support or reject specific structural models of organometallic transition metal complexes in solution by comparing the experimental and Density Functional Theory (DFT) calculated values of this 31P chemical shift. This approach has been tested on a variety of the metals of groups 8–12 and molecular structures. General recommendations for appropriate basis sets are reported. 相似文献
999.
1000.