全文获取类型
收费全文 | 8207篇 |
免费 | 1163篇 |
国内免费 | 453篇 |
专业分类
化学 | 4164篇 |
晶体学 | 30篇 |
力学 | 899篇 |
综合类 | 193篇 |
数学 | 2005篇 |
物理学 | 2532篇 |
出版年
2024年 | 12篇 |
2023年 | 113篇 |
2022年 | 355篇 |
2021年 | 335篇 |
2020年 | 398篇 |
2019年 | 275篇 |
2018年 | 252篇 |
2017年 | 355篇 |
2016年 | 413篇 |
2015年 | 372篇 |
2014年 | 484篇 |
2013年 | 500篇 |
2012年 | 508篇 |
2011年 | 474篇 |
2010年 | 398篇 |
2009年 | 483篇 |
2008年 | 448篇 |
2007年 | 468篇 |
2006年 | 442篇 |
2005年 | 371篇 |
2004年 | 344篇 |
2003年 | 289篇 |
2002年 | 244篇 |
2001年 | 200篇 |
2000年 | 195篇 |
1999年 | 159篇 |
1998年 | 162篇 |
1997年 | 116篇 |
1996年 | 97篇 |
1995年 | 107篇 |
1994年 | 83篇 |
1993年 | 70篇 |
1992年 | 61篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 25篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1971年 | 2篇 |
排序方式: 共有9823条查询结果,搜索用时 15 毫秒
141.
A new synthetic method for the preparation of allyl amines has been developed. The key steps of this method are enantioselective addition of diethylzinc and [1,3]-chirality transfer through the [3.3] sigmatropic rearrangement of allyl cyanates. Stereocontrolled syntheses of lentiginosine (1) and polyoxamic acid derivative 2 from a common intermediate 7 derived from D-tartaric acid (8), have been accomplished. 相似文献
142.
143.
144.
145.
146.
147.
148.
低压涡轮内部流动及其气动设计研究进展 总被引:3,自引:0,他引:3
随着高空无人飞行器研究的不断升温, 高空低雷诺数条件下动力装置的研究越来越受到人们的重视.结合近年来国内外相关领域的研究工作, 对低雷诺数低压涡轮内部复杂流动机理的研究进展进行了介绍, 包括低雷诺数情况下低压涡轮内部非定常流动的特点, 叶片边界层分离及转捩现象机理, 上游周期性尾迹与下游叶片边界层相互作用机理等. 在此基础上给出了适合低雷诺数条件的低压涡轮气动设计方法:尾迹通过与边界层的相互作用, 能够抑制分离, 进而减小叶型损失, 在气动设计中有效引入非定常效应可以大幅度提高低压涡轮的气动负荷或降低气动损失, 最终达到提高性能的目的;数值及实验结果验证了这种设计方法的有效性. 相似文献
149.
Mahesh Attimarad Katharigatta Narayanaswamy Venugopala Muhammad S. Chohan Marysheela David Efren II Plaza Molina Nagaraja Sreeharsha Anroop Balachandran Nair Christophe Tratrat Abdulrahman Ibrahim Altaysan Abdulmalek Ahmed Balgoname 《Molecules (Basel, Switzerland)》2022,27(10)
A rapid and reproducible hydrophilic liquid chromatography (HILIC) process was established for concomitant determination of remogliflozin etabonate (RE), vildagliptin (VD), and metformin (MF) in a formulation. A face-centered central composite experimental design was employed to optimize and predict the chromatographic condition by statistically studying the surface response model and design space with desirability close to one. A HILIC column with a simple mobile phase of acetonitrile (65% v/v) and 20 mM phosphate buffer (35% v/v, pH 6, controlled with orthophosphoric acid) was used to separate RE, VD, and MF. RE, VD, and MF were separated in 3.6 min using an isocratic mode mobile phase flow at a flow rate of 1.4 mL at room temperature, and the analytes were examined by recording the absorption at 210 nm. The developed HILIC method was thoroughly validated for all parameters recommended by ICH, and linearity was observed in the ranges 20–150 µg/mL, 10–75 µg/mL, and 50–750 µg/mL for RE, VD, and MF, respectively, along with excellent regression coefficients (r2 > 0.999). The calculated percentage relative deviation and relative error ascertained the precision and accuracy of the method. The selectivity and accuracy were further confirmed by the high percentage recovery of added standard drugs to the formulation using the standard addition technique. The robustness of the HILIC processes was confirmed by developing a half-normal probability plot and Pareto chart, as the slight variation of a single factor had no significant influence on the assay outcomes. Utilization of the optimized HILIC procedure for concurrent quantification of RE, VD, and MF in solid dosage forms showed accurate and reproducible results. Hence, the fast HILIC method can be regularly employed for the quality assurance of pharmaceutical preparations comprising RE, VD, and MF. 相似文献
150.
Wantanwa Krongrawa Sontaya Limmatvapirat Supachai Saibua Chutima Limmatvapirat 《Molecules (Basel, Switzerland)》2022,27(13)
The major bioactive components of Kaempferia parviflora (KP) rhizomes, 3,5,7,3′,4′-pentamethoxyflavone (PMF), 5,7-dimethoxyflavone (DMF), and 5,7,4′-trimethoxyflavone (TMF), were chosen as the quantitative and qualitative markers for this plant material. In order to extract bioactive components (total methoxyflavones) from KP rhizomes, ultrasound-assisted extraction (UAE) was proposed as part of this study. Plackett–Burman design (PBD) and Box–Behnken design (BBD) were utilized to optimize the effects of UAE on extraction yields and total methoxyflavone contents in KP rhizomes. First, PBD was utilized to determine the effect of five independent variables on total yields and total methoxyflavone contents. The results indicated that the concentration of the extracting solvent (ethanol), the extraction time, and the ratio of solvent to solid were significant independent terms. Subsequently, BBD with three-level factorial experiments was used to optimize the crucial variables. It was discovered that the concentration of ethanol was the most influential variable on yields and total methoxyflavone contents. Optimum conditions for extraction yield were ethanol concentration (54.24% v/v), extraction time (25.25 min), and solvent-to-solid ratio (49.63 mL/g), while optimum conditions for total methoxyflavone content were ethanol concentration (95.00% v/v), extraction time (15.99 min), and solvent-to-solid ratio (50.00 mL/g). The relationship between the experimental and theoretical values was perfect, which proved that the regression models used were correct and that PBD and BBD were used to optimize the conditions in the UAE to obtain the highest yield and total methoxyflavone content in the KP rhizomes. 相似文献