全文获取类型
收费全文 | 20523篇 |
免费 | 3535篇 |
国内免费 | 2286篇 |
专业分类
化学 | 14677篇 |
晶体学 | 260篇 |
力学 | 1251篇 |
综合类 | 186篇 |
数学 | 2060篇 |
物理学 | 7910篇 |
出版年
2024年 | 75篇 |
2023年 | 467篇 |
2022年 | 669篇 |
2021年 | 730篇 |
2020年 | 816篇 |
2019年 | 788篇 |
2018年 | 661篇 |
2017年 | 623篇 |
2016年 | 972篇 |
2015年 | 978篇 |
2014年 | 1105篇 |
2013年 | 1442篇 |
2012年 | 1859篇 |
2011年 | 1889篇 |
2010年 | 1247篇 |
2009年 | 1106篇 |
2008年 | 1293篇 |
2007年 | 1279篇 |
2006年 | 1130篇 |
2005年 | 1006篇 |
2004年 | 720篇 |
2003年 | 628篇 |
2002年 | 573篇 |
2001年 | 432篇 |
2000年 | 413篇 |
1999年 | 470篇 |
1998年 | 355篇 |
1997年 | 369篇 |
1996年 | 310篇 |
1995年 | 296篇 |
1994年 | 302篇 |
1993年 | 246篇 |
1992年 | 196篇 |
1991年 | 198篇 |
1990年 | 177篇 |
1989年 | 112篇 |
1988年 | 86篇 |
1987年 | 89篇 |
1986年 | 60篇 |
1985年 | 44篇 |
1984年 | 43篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1975年 | 2篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
931.
932.
Jian‐Nan Xiang Li‐Hui Jiang Chao‐Yue Chen Zhi‐ying Fu Jun‐Fei Duan Xiao‐Xiao He 《Journal of carbohydrate chemistry》2013,32(7):595-614
New retinoyl sugar derivatives of 13‐cis‐retinoic acid were synthesized in three ways in this paper in order to enhance pharmacal effects, especially antiproliferative activities of 13‐cis‐retinoic acid. Their structures were confirmed by IR, 1H‐NMR, 13C‐NMR, and MS spectra and their antiproliferative activities were determined in vitro using human cancer lines. Results showed that some compounds possessed potential antitumor activities. 相似文献
933.
Wei-Bin Huang Cai-Yan Du Jian-An Jiang Ya-Fei Ji 《Research on Chemical Intermediates》2013,39(6):2849-2856
A method for concurrent synthesis of vanillin and isovanillin has been developed by a nonregioselective Vilsmeier–Haack reaction of O-alkyl guaiacols. O-Alkylation of guaiacol provided the corresponding O-alkyl guaiacol (1), which was then formylated with N-methylformanilide/phosphorus oxychloride to give a mixture of 4-alkoxy-3-methoxy-benzaldehyde (2) and 3-alkoxy-4-methoxybenzaldehyde (3). Finally, the obtained mixture underwent a selective dealkylation by anhydrous aluminium trichloride, while leaving methyl groups intact to simultaneously achieve the significant fine chemicals vanillin and isovanillin. 相似文献
934.
Yuan Zhu F. Y. Jiang Kexin Chen Feiyu Kang Z. K. Tang 《Journal of Sol-Gel Science and Technology》2013,66(1):180-186
Iron oxide/silica core–shell colloidal particles were prepared by basic reverse microemulsion (RM) method and two modified RM methods. By basic RM method, maximum particle size obtained was mere 40 nm. For building photonic crystals working in the visible range, the colloidal particles must be larger than 100 nm. Thus two modified RM methods were used. By alcohol modified RM method, short chain alcohols were used as co-surfactant. The particle size rose to near 100 nm, but the core–shell structure was comparatively poor. By emulsifier pair modified RM method, the particle size leapt to over 200 nm and a narrow growth window was found favorable to enhance the stability and rigidity of the surfactants layers. The core–shell mechanism was also discussed and a new four-step mechanism was proposed. 相似文献
935.
Li Zhang Li Tong Zhang Jing He Zhi Jun Lin Yan Jiang Li Fu Chen 《Journal of Sol-Gel Science and Technology》2013,68(1):150-154
Aluminum nitride (AlN) fibers were prepared from alumina gel fibers and by heat-treatment in ammonia. The influence of silica on the formation of AlN was investigated. It was shown that phase transformation of alumina (γ-Al2O3 to α-Al2O3) and nitridation reaction took place above 1,100 °C for pure alumina fiber. The addition of a small amount of silica (3 wt%) suppressed the formation of α-Al2O3 and preserved the highly reactive metastable alumina, and nitridation rate was enhanced. Fine grain (~20 nm) AlN fibers were obtained for pyrolysis at 1,150–1,250 °C for 3 h in ammonia, and AlN was identified as the sole crystalline phase. 相似文献
936.
Qumei Jin Fengyu Qu Jingjie Jiang Yan Dong Wei Guo Huiming Lin 《Journal of Sol-Gel Science and Technology》2013,66(3):466-471
A novel dual-drug delivery system based on mesoporous-macroporous silica/polyelectrolytes-SBA-15 has been synthesized. The structure and composition of these materials were characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and N2 adsorption–desorption measurements. In this system, water-soluble metformin hydrochloride and fat-soluble ibuprofen were used as model drugs to study the controlled release behavior. The pH-controlled release of individual drugs was obtained by the primary release of metformin hydrochloride from polyelectrolytes-SBA-15 in acid condition and the predominant release of ibuprofen from MMC in alkaline environment. The results show that the polyelectrolytes-SBA-15/mesoporous-macroporous silica can be used as dual-drug release system and the individual drug can be controlled release with the change of pH value of the environment. 相似文献
937.
Jipan Yu Dr. Haijun Yang Prof. Dr. Yuyang Jiang Prof. Dr. Hua Fu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4271-4277
Efficient copper‐catalyzed aerobic oxidative C? H and C? C functionalization of 1‐[2‐(arylamino)aryl]ethanones leading to acridones has been developed. The procedure involves cleavage of aromatic C? H and acetyl C? C bonds with intramolecular formation of a diarylketone bond. The protocol uses inexpensive Cu(O2CCF3)2 as catalyst, pyridine as additive, and economical and environmentally friendly oxygen as the oxidant, and the corresponding acridones with various functional groups were obtained in moderate to good yields. 相似文献
938.
939.
Dr. Yaqi Jiang Yanyan Jia Jiawei Zhang Lei Zhang Huang Huang Prof. Dr. Zhaoxiong Xie Prof. Dr. Lansun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(9):3119-3124
Pt? Cu alloy octahedral nanocrystals (NCs) have been synthesized successfully by using N,N‐dimethylformamide as both the solvent and the reducing agent in the presence of cetyltrimethylammonium chloride. Cu underpotential deposition (UPD) is found to play a key role in the formation of the Pt? Cu alloy NCs. The composition in the Pt? Cu alloy can be tuned by adjusting the ratio of metal precursors in solution. However, the Cu content in the Pt? Cu alloy NCs cannot exceed 50 %. Due to the fact that Cu precursor cannot be reduced to metallic copper and the Cu content cannot exceed 50 %, we achieved the formation of the Pt? Cu alloy by using Cu UPD on the Pt surface. In addition, the catalytic activities of Pt? Cu alloy NCs with different composition were investigated in electrocatalytic oxidation of formic acid. The results reveal that the catalytic performance is strongly dependent on Pt? Cu alloy composition. The sample of Pt50Cu50 exhibits excellent activity in electrocatalytic oxidation of formic acid. 相似文献
940.
A Rapid and Efficient Way to Dynamic Creation of Cross‐Reactive Sensor Arrays Based on Ionic Liquids
Wei Zhu Weina Li Haowei Yang Yin Jiang Chen Wang Prof. Dr. Yu Chen Prof. Dr. Guangtao Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11603-11612
Based on the simple counterion exchange of ionic liquids, a rapid, facile, and efficient strategy to create a cross‐reactive sensor array with a dynamic tunable feature was developed, and exemplified by the construction of a sensor array for the identification and classification of nitroaromatics and explosives mimics. To achieve a good sensing system with fast response, good sensitivity, and low detection limit, the synthesized ionic liquid receptors were tethered onto a silica matrix with a macro‐mesoporous hierarchical structure. Through the facile anion exchange approach, abundant ionic‐liquid‐based individual receptors with diversiform properties, such as different micro‐environments, diverse molecular interactions, and distinctive physico‐chemical properties, were easily and quickly synthesized to generate a distinct fingerprint of explosives for pattern recognition. The reversible anion exchange ability further endowed the sensor array with a dynamic tunable feature as well as good controllability and practicality for real‐world application. With the assistance of statistical analysis, such as principal component analysis (PCA) and linear discrimination analysis (LDA), an optimized‐size array with a good resolution was rationally established from a large number of IL‐based receptors. The performed experiments suggested that the ionic‐liquid‐based sensing protocol is a general and powerful strategy for creating a cross‐reactive sensor array that could find a wide range of applications for sensing various analytes or complex mixtures. 相似文献