全文获取类型
收费全文 | 244067篇 |
免费 | 6379篇 |
国内免费 | 3933篇 |
专业分类
化学 | 139175篇 |
晶体学 | 3483篇 |
力学 | 10288篇 |
综合类 | 300篇 |
数学 | 26952篇 |
物理学 | 74181篇 |
出版年
2021年 | 2339篇 |
2020年 | 2718篇 |
2019年 | 2793篇 |
2018年 | 3218篇 |
2017年 | 3249篇 |
2016年 | 4714篇 |
2015年 | 3445篇 |
2014年 | 4806篇 |
2013年 | 10510篇 |
2012年 | 9675篇 |
2011年 | 11369篇 |
2010年 | 7999篇 |
2009年 | 7767篇 |
2008年 | 10239篇 |
2007年 | 10219篇 |
2006年 | 9638篇 |
2005年 | 8716篇 |
2004年 | 7670篇 |
2003年 | 6717篇 |
2002年 | 6558篇 |
2001年 | 7170篇 |
2000年 | 5555篇 |
1999年 | 4231篇 |
1998年 | 3507篇 |
1997年 | 3419篇 |
1996年 | 3434篇 |
1995年 | 3001篇 |
1994年 | 3061篇 |
1993年 | 2897篇 |
1992年 | 3089篇 |
1991年 | 3117篇 |
1990年 | 2929篇 |
1989年 | 2768篇 |
1988年 | 2672篇 |
1987年 | 2577篇 |
1986年 | 2611篇 |
1985年 | 3361篇 |
1984年 | 3396篇 |
1983年 | 2842篇 |
1982年 | 3081篇 |
1981年 | 2831篇 |
1980年 | 2614篇 |
1979年 | 2796篇 |
1978年 | 2996篇 |
1977年 | 3032篇 |
1976年 | 3060篇 |
1975年 | 2793篇 |
1974年 | 2906篇 |
1973年 | 2956篇 |
1972年 | 2318篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Kondakov N. N. Mel´nikova T. M. Chekryzhova T. V. Mel´nikova M. V. Zinin A. I. Torgov V. I. Chizhov A. O. Kononov L. O. 《Russian Chemical Bulletin》2015,64(5):1142-1148
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained... 相似文献
22.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
23.
Metabolic profiles of dioscin in rats revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry 下载免费PDF全文
He Zhu Jin‐Di Xu Qian Mao Hong Shen Ming Kong Jian‐Ping Chen Song‐Lin Li 《Biomedical chromatography : BMC》2015,29(9):1415-1421
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
24.
25.
26.
27.
Natalia L. Calvo Sebastian O. SimonettiRubén M. Maggio Teodoro S. Kaufman 《Analytica chimica acta》2015
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. 相似文献
28.
29.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
30.
Sh. M. Khaliullin V. D. Zhuravlev V. G. Bamburov L. V. Ermakova 《Physics of Atomic Nuclei》2015,78(12):1382-1388
Submicron CaZrO3 powder is obtained in combustion reactions (solution combustion synthesis—SCS) with glycine. It is found that SCS reduces the sintering temperature of CaZrO3 powders. The dielectric properties of calcium zirconate ceramics are studied by the electrochemical impedance method. It is shown that a ceramics of powders obtained by the SCS method has high dielectric characteristics. 相似文献