全文获取类型
收费全文 | 1209篇 |
免费 | 71篇 |
国内免费 | 97篇 |
专业分类
化学 | 336篇 |
晶体学 | 10篇 |
力学 | 608篇 |
综合类 | 17篇 |
数学 | 64篇 |
物理学 | 342篇 |
出版年
2024年 | 10篇 |
2023年 | 12篇 |
2022年 | 33篇 |
2021年 | 22篇 |
2020年 | 42篇 |
2019年 | 25篇 |
2018年 | 33篇 |
2017年 | 38篇 |
2016年 | 37篇 |
2015年 | 39篇 |
2014年 | 45篇 |
2013年 | 112篇 |
2012年 | 46篇 |
2011年 | 36篇 |
2010年 | 38篇 |
2009年 | 52篇 |
2008年 | 42篇 |
2007年 | 67篇 |
2006年 | 51篇 |
2005年 | 53篇 |
2004年 | 54篇 |
2003年 | 58篇 |
2002年 | 38篇 |
2001年 | 39篇 |
2000年 | 24篇 |
1999年 | 35篇 |
1998年 | 32篇 |
1997年 | 37篇 |
1996年 | 32篇 |
1995年 | 37篇 |
1994年 | 20篇 |
1993年 | 30篇 |
1992年 | 18篇 |
1991年 | 23篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1377条查询结果,搜索用时 9 毫秒
21.
Parichat Phalanisong Pensri Plangklang Alissara Reungsang 《Molecules (Basel, Switzerland)》2021,26(24)
Microalgae consortia were photoautotrophically cultivated in sequencing batch photobioreactors (SBPRs) with an alteration of the normal growth and starvation (nutrient limitation) phases to select consortia capable of polyhydroxyalkanoate (PHA) accumulation. At the steady state of SBPR operation, the obtained microalgae consortia, selected under nitrogen and phosphate limitation, accumulated up to 11.38% and 10.24% of PHA in their biomass, which was identified as poly(3-hydroxybutyrate) (P3HB). Photoautotrophic and mixotrophic batch cultivation of the selected microalgae consortia was conducted to investigate the potential of biomass and PHA production. Sugar source supplementation enhanced the biomass and PHA production, with the highest PHA contents of 10.94 and 6.2%, and cumulative PHA productions of 100 and 130 mg/L, with this being achieved with sugarcane juice under nitrogen and phosphate limitation, respectively. The analysis of other macromolecules during batch cultivation indicated a high content of carbohydrates and lipids under nitrogen limitation, while higher protein contents were detected under phosphate limitation. These results recommended the selected microalgae consortia as potential tools for PHA and bioresource production. The mixed-culture non-sterile cultivation system developed in this study provides valuable information for large-scale microalgal PHA production process development following the biorefinery concept. 相似文献
22.
Eutectic molecular liquids (EMLs) based on hydrogen‐bonding interaction and π–π stacking were prepared. We found that the thermodynamic properties like initial decomposition temperature and glass transition temperature of EMLs are mainly dominated by the hydrogen bond donor, which is beneficial for designing and preparing new EMLs. These new liquid systems could be applied in the field of environmental and material science. 相似文献
23.
建立了高效液相色谱-串联质谱(HPLC-MS/MS)结合加速溶剂萃取测定小型家用电器塑料部件中全氟辛酸(PFOA)的分析方法。样品冷冻粉碎后采用甲醇作溶剂进行快速溶剂萃取,萃取液经C18固相萃取柱富集净化后,以C18柱为分离柱,以甲醇-水为流动相,梯度洗脱,电喷雾负离子模式下多反应监测(MRM))模式检测。PFOA在0.5~100.0μg/L范围内线性关系良好(r2=0.998 9),回收率为93%~107%,相对标准偏差为2.9%~7.6%,检出限(S/N=3)为0.5μg/kg。该方法操作简便、灵敏度高,适用于小型家用电器塑料部件中全氟辛酸残留分析。 相似文献
24.
25.
针对化探样品中痕金的电感耦合等离子体质谱法快速测试方法,探讨了吸附酸度、解脱时间、吸附温度等对测试结果的影响。确立了电感耦合等离子体质谱法测定的最佳条件。方法检出限为:0.035 ng/g,准确度△lgC(n=12)为0.01~0.05,精密度RSD(n=12)为4.50~9.64。很好的解决金的快速测定问题,对地矿部门日益增多的化探任务,提高了测试速度,缩短了测试周期,值得推广。 相似文献
26.
固相萃取-高效液相色谱法同时测定食品塑料包装材料中9种光稳定剂 总被引:3,自引:0,他引:3
建立了同时测定食品塑料包装材料中9种紫外光稳定剂含量的高效液相色谱方法。样品用甲醇-乙酸乙酯混合溶剂超声提取,经固相萃取小柱净化后,以ZORBAX SB-C18柱(250 mm×4.6 mm, 5 μm)为分离色谱柱,甲醇和水为流动相,梯度洗脱,以310 nm为检测波长进行定性、定量分析。该方法前处理简单、易操作,9种紫外光稳定剂分离效果良好。9种紫外光稳定剂在0.2~10 mg/L范围内呈良好的线性关系,线性相关系数大于0.999;方法检出限为0.05~0.1 mg/L;实际样品中的加标回收率为70.2%~89.0%,相对标准偏差为0.4%~4.5%。该方法简单、准确,能够满足食品塑料包装材料中紫外光稳定剂的检测要求。 相似文献
27.
JD树脂刻蚀及涂层的XPS研究 总被引:2,自引:0,他引:2
JD光学树脂表面刻蚀过程的XPS研究表明,引进树脂遥COH,C=O,C-SO3H,COOH等基因随刻蚀温度的提高或时间的延长而增加,对其相对含量进行了计算,固化后的耐磨涂层具有SiO2结构,JD板材的最佳刻蚀条件为20℃,20min。 相似文献
28.
Masatoshi Hasegawa Daiki Hirano Mari Fujii Misako Haga Eiichiro Takezawa Shinya Yamaguchi Atsushi Ishikawa Takashi Kagayama 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):575-592
This work presents novel colorless polyimides (PIs) derived from 1R,2S,4S,5R‐cyclohexanetetracarboxylic dianhydride (H″‐PMDA). Isomer effects were also discussed by comparing with PI systems derived from conventional hydrogenated pyromellitic dianhydride, that is, 1S,2R,4S,5R‐cyclohexanetetracarboxylic dianhydride (H‐PMDA). H″‐PMDA was much more reactive with various diamines than H‐PMDA, and the former led to PI precursors with much higher molecular weights. The results can be explained from the quite different steric structures of these isomers. The thermally imidized H″‐PMDA‐based films were colorless regardless of diamines because of inhibited charge‐transfer interaction. In particular, the H″‐PMDA/4,4′‐oxydianiline system simultaneously achieved a very high Tg exceeding 300 °C, high toughness (elongation at break > 70%), and good solution processability. In contrast, the H‐PMDA‐based counterparts were essentially insoluble. The outstanding solubility of the former probably results from disturbed chain stacking by its nonplanar steric structure. An advantage of chemical imidization process is also proposed. In some cases, a copolymerization approach with an aromatic tetracarboxylic dianhydride was effective to improve the thermal expansion property. The results suggest that the H″‐PMDA‐based PI systems can be promising candidates for novel high‐temperature plastic substrate materials in electronic paper displays. A potential application as optical compensation film materials in liquid crystal displays (LCD) is also proposed in this work. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
29.
The paper deals with the study of the thermotropic liquid crystalline properties of a new azomethinic symmetric dimer and some of its structural heterogeneous mixtures with one of its reagents. Their thermotropic behaviour was monitored by polarised light microscopy, differential scanning microscopy and variable temperature X-ray diffraction measurements. The influence of the structural heterogeneity on the mesomorphic behaviour was established and some similarities with the mesomorphic behaviour of the polydisperse polymers were underlined. 相似文献
30.
结合新课标要求,揭示塑料薄膜撕扯实验在聚合物教学中的重要性、必要性。通过教学片段设计,发展学生“宏观辨识与微观探析、证据推理与模型认知”化学学科核心素养,并让学生认识物质的性能不仅取决于结构,也取决于生产工艺。并对人教版初、高中化学教材和教参中相关问题展开讨论和解释,以期更好地服务教学。 相似文献