全文获取类型
收费全文 | 1189篇 |
免费 | 193篇 |
国内免费 | 108篇 |
专业分类
化学 | 628篇 |
晶体学 | 17篇 |
力学 | 46篇 |
综合类 | 21篇 |
数学 | 179篇 |
物理学 | 599篇 |
出版年
2023年 | 26篇 |
2022年 | 32篇 |
2021年 | 37篇 |
2020年 | 41篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 46篇 |
2015年 | 38篇 |
2014年 | 56篇 |
2013年 | 62篇 |
2012年 | 83篇 |
2011年 | 98篇 |
2010年 | 76篇 |
2009年 | 75篇 |
2008年 | 75篇 |
2007年 | 54篇 |
2006年 | 49篇 |
2005年 | 51篇 |
2004年 | 44篇 |
2003年 | 50篇 |
2002年 | 38篇 |
2001年 | 35篇 |
2000年 | 24篇 |
1999年 | 43篇 |
1998年 | 47篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 29篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1490条查询结果,搜索用时 318 毫秒
991.
Li Chen Jinmei Zhou Jing Hu Yihui Chen Min Lin Yonghong Ruan Jinli Zheng Ailin Wei 《大学化学》2020,35(5):191-196
In the online organic chemistry and laboratory courses, the open or semi open quizzes before class and after class are adopted to explore the "dual quizzes teaching" mode on the network teaching platform. As the progress of "dual quizzes teaching", students' learning weakness, confidence and enthusiasm are improved continuously. Through the analysis of online students' learning data, questionnaire and interactive feedback, the teachers can evaluate the learning situation of the students and regulate instructional content in time. As a result of teaching online, the "dual quizzes teaching" mode has achieved highly positive effect. 相似文献
992.
Jie Wei Si‐Na Qin Jing‐Li Liu Xiang‐Yu Ruan Zhiqiang Guan Hao Yan Di‐Ye Wei Hua Zhang Jun Cheng Hongxing Xu Zhong‐Qun Tian Jian‐Feng Li 《Angewandte Chemie (International ed. in English)》2020,59(26):10343-10347
The spillover of hydrogen species and its role in tuning the activity and selectivity in catalytic hydrogenation have been investigated in situ using surface‐enhanced Raman spectroscopy (SERS) with 10 nm spatial resolution through the precise fabrication of Au/TiO2/Pt sandwich nanostructures. In situ SERS study reveals that hydrogen species can efficiently spillover at Pt‐TiO2‐Au interfaces, and the ultimate spillover distance on TiO2 is about 50 nm. Combining kinetic isotope experiments and density functional theory calculations, it is found that the hydrogen spillover proceeds via the water‐assisted cleavage and formation of surface hydrogen–oxygen bond. More importantly, the selectivity in the hydrogenation of the nitro or isocyanide group is manipulated by controlling the hydrogen spillover. This work provides molecular insights to deepen the understanding of hydrogen activation and boosts the design of active and selective catalysts for hydrogenation. 相似文献
993.
Zhangyong Si Hui Wen Lim Moon Y. F. Tay Yu Du Lin Ruan Haofeng Qiu Rubí Zamudio‐Vazquez Sheethal Reghu Yahua Chen Wen Shuo Tiong Kalisvar Marimuthu Partha Pratim De Oon Tek Ng Yabin Zhu Yunn‐Hwen Gan Yonggui Robin Chi Hongwei Duan Guillermo C. Bazan E. Peter Greenberg Mary B. Chan‐Park Kevin Pethe 《Angewandte Chemie (International ed. in English)》2020,59(17):6819-6826
Carbapenem‐resistant Gram‐negative bacteria (GNB) are heading the list of pathogens for which antibiotics are the most critically needed. Many antibiotics are either unable to penetrate the outer‐membrane or are excluded by efflux mechanisms. Here, we report a cationic block β‐peptide (PAS8‐b‐PDM12) that reverses intrinsic antibiotic resistance in GNB by two distinct mechanisms of action. PAS8‐b‐PDM12 does not only compromise the integrity of the bacterial outer‐membrane, it also deactivates efflux pump systems by dissipating the transmembrane electrochemical potential. As a result, PAS8‐b‐PDM12 sensitizes carbapenem‐ and colistin‐resistant GNB to multiple antibiotics in vitro and in vivo. The β‐peptide allows the perfect alternation of cationic versus hydrophobic side chains, representing a significant improvement over previous antimicrobial α‐peptides sensitizing agents. Together, our results indicate that it is technically possible for a single adjuvant to reverse innate antibiotic resistance in all pathogenic GNB of the ESKAPE group, including those resistant to last resort antibiotics. 相似文献
994.
Qian‐Qian Jin Chen‐Yang Zhang Wan‐Ni Wang Ben‐Jin Chen Juan Ruan Hai‐Sheng Qian 《Chemical record (New York, N.Y.)》2020,20(8):882-892
In this mini‐review, we highlighted the recent progresses in the controlled synthesis of metal sulfides hollow nanostructures via hard template technique. After a brief introduction about the formation mechanism of the inorganic hollow nanostructures via hard template technique, the discussions primarily focused on the emerging development of metal sulfides hollow nanostructures. Various synthetic strategies were summarized concerning the use of the hard template engaged strategies to fabricate various metal sulfides hollow nanostructures, such as hydrothermal method, solvothermal method, ion‐exchange, sulfidation or calcination etc. Finally, the perspectives and summaries have been presented to demonstrate that a facile synthetic technique would be widely used to fabricate metal sulfides hollow nanostructures with multi‐shells and components. 相似文献
995.
Dr. Qing Zhang Dr. Alvaro Mayoral Junyan Li Dr. Juanfang Ruan Prof. Viveka Alfredsson Dr. Yanhang Ma Prof. Jihong Yu Prof. Osamu Terasaki 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19571-19581
Zeolites are widely used in catalysis, gas separation, ion exchange, etc. due to their superior physicochemical properties, which are closely related to specific features of their framework structures. Although more than two hundred different framework types have been recognized, it is of great interest to explore from a crystallographic perspective, the atomic positions, surface terminations, pore connectivity and structural defects that deviate from the ideal framework structures, namely local structural modulation. In this article, we review different types of local modulations in zeolite frameworks using various techniques, especially electron microscopy (EM). The most recent advances in resolving structural information at the atomic level with aberration corrected EM are also presented, commencing a new era of gaining atomic structural information, not only for all tetrahedral atoms including point vacancies in framework but also for extra-framework cations and surface terminations. 相似文献
996.
Swine Manure-Based Pilot-Scale Algal Biomass Production System for Fuel Production and Wastewater Treatment—a Case Study 总被引:1,自引:0,他引:1
Min Min Bing Hu Michael J. Mohr Aimin Shi Jinfeng Ding Yong Sun Yongcheng Jiang Zongqiang Fu Richard Griffith Fida Hussain Dongyan Mu Yong Nie Paul Chen Wenguang Zhou Roger Ruan 《Applied biochemistry and biotechnology》2014,172(3):1390-1406
Integration of wastewater treatment with algae cultivation is one of the promising ways to achieve an economically viable and environmentally sustainable algal biofuel production on a commercial scale. This study focused on pilot-scale algal biomass production system development, cultivation process optimization, and integration with swine manure wastewater treatment. The areal algal biomass productivity for the cultivation system that we developed ranged from 8.08 to 14.59 and 19.15–23.19 g/m2?×?day, based on ash-free dry weight and total suspended solid (TSS), respectively, which were higher than or comparable with those in literature. The harvested algal biomass had lipid content about 1.77–3.55 %, which was relatively low, but could be converted to bio-oil via fast microwave-assisted pyrolysis system developed in our lab. The lipids in the harvested algal biomass had a significantly higher percentage of total unsaturated fatty acids than those grown in lab conditions, which may be attributed to the observed temperature and light fluctuations. The nutrient removal rate was highly correlated to the biomass productivity. The NH3-N, TN, COD, and PO4-P reduction rates for the north-located photo-bioreactor (PBR-N) in July were 2.65, 3.19, 7.21, and 0.067 g/m2?×?day, respectively, which were higher than those in other studies. The cultivation system had advantages of high mixotrophic growth rate, low operating cost, as well as reduced land footprint due to the stacked-tray bioreactor design used in the study. 相似文献
997.
Liang Zhang Xiaoqing Wang Zhenhua Ruan Ying Liu Xiaorui Niu Zhengbo Yue Zhimin Li Wei Liao Yan Liu 《Applied biochemistry and biotechnology》2014,172(2):1045-1054
Three pretreated corn stover (ammonia fiber expansion, dilute acid, and dilute alkali) were used as carbon source to culture Trichoderma reesei Rut C-30 for cellulase and xylanase production. The results indicated that the cultures on ammonia fiber expansion and alkali pretreated corn stover had better enzyme production than the acid pretreated ones. The consequent enzymatic hydrolysis was performed applying fungal enzymes on pretreated corn stover samples. Tukey’s statistical comparisons exhibited that there were significant differences on enzymatic hydrolysis among different combination of fungal enzymes and pretreated corn stover. The higher sugar yields were achieved by the enzymatic hydrolysis of dilute alkali pretreated corn stover. 相似文献
998.
N-Mono and N,N-disubstituted selenoamides are synthesized in a one-pot procedure from nitriles, selenium metal and NaBH4 followed by the amine group exchange of the intermediate primary selenoamide with an amine. 相似文献
999.
Hai-Bao Zhu Yun-Chang Fan Ya-Ling Qian Hong-Fang Tang Zheng Ruan Dan-Hua Liu Han Wang 《中国化学快报》2014,25(3):465-468
In the present work, a novel method to extract three kinds of spices, namely vanillin, ethyl vanillin and ethyl maltol from food products such as biscuit, chocolate and milk powder was developed. 1-Octyl-3-methylimidazolium chloride([Omim]Cl) aqueous solution was selected as the extracting medium. A 0.5 g powder of food product was extracted by 5.0 mL of [Omim]Cl aqueous solution(0.3 mol/L, pH 6.0) under ultrasonication at 50 8C, and then the extract was centrifuged for 10 min at 4000 rpm. The extract was filtered through a syringe filter and injected into ion chromatography system for analysis. The separation of the three spices was carried out on an anion exchange column. The detection wavelength was set at 280 nm. Compared with traditional extraction solvents, [Omim]Cl aqueous solution displayed particular advantages. The applicability of the proposed method to real sample was confirmed. Under the optimal conditions, good reproducibility of extraction performance was obtained, with the relative standard deviation(RSD) values ranging from 1.9% to 6.3%. The recoveries of spiked samples were between 79.8% and 95.8%. The detection limits(LOD, S/N = 3) of vanillin, ethyl vanillin and ethyl maltol were in the range of 20–45 mg/kg. The use of ionic liquid aqueous solution as extraction solvent was operationally easy and environmental-friendly. 相似文献
1000.
Two new ent-kaurane diterpenoids, ent-7a,14b-dihydroxykaur-16-en-15-one-20-oic acid(1) and 1,7a,12b,14b-tetrahydroxy-1,10-seco-ent-kaur-10,16-dien-15-one(2), together with six known ones(3–8), were isolated from the EtOAc extract of the aerial parts of Isodon excisoides. Their structures were elucidated on the basis of 1D NMR and 2D NMR analyses as well as HR-ESI-MS experiments. 相似文献