全文获取类型
收费全文 | 233256篇 |
免费 | 3411篇 |
国内免费 | 1641篇 |
专业分类
化学 | 130840篇 |
晶体学 | 3304篇 |
力学 | 9250篇 |
综合类 | 90篇 |
数学 | 26152篇 |
物理学 | 68672篇 |
出版年
2020年 | 1921篇 |
2019年 | 2061篇 |
2018年 | 2642篇 |
2017年 | 2659篇 |
2016年 | 3945篇 |
2015年 | 2702篇 |
2014年 | 3880篇 |
2013年 | 9573篇 |
2012年 | 8242篇 |
2011年 | 10026篇 |
2010年 | 7110篇 |
2009年 | 6888篇 |
2008年 | 9383篇 |
2007年 | 9532篇 |
2006年 | 8882篇 |
2005年 | 8219篇 |
2004年 | 7368篇 |
2003年 | 6573篇 |
2002年 | 6529篇 |
2001年 | 7070篇 |
2000年 | 5416篇 |
1999年 | 3927篇 |
1998年 | 3232篇 |
1997年 | 3179篇 |
1996年 | 3197篇 |
1995年 | 2816篇 |
1994年 | 2907篇 |
1993年 | 2731篇 |
1992年 | 2968篇 |
1991年 | 3033篇 |
1990年 | 2850篇 |
1989年 | 2743篇 |
1988年 | 2661篇 |
1987年 | 2606篇 |
1986年 | 2612篇 |
1985年 | 3472篇 |
1984年 | 3550篇 |
1983年 | 2941篇 |
1982年 | 3180篇 |
1981年 | 2931篇 |
1980年 | 2728篇 |
1979年 | 2903篇 |
1978年 | 3087篇 |
1977年 | 3163篇 |
1976年 | 3180篇 |
1975年 | 2888篇 |
1974年 | 2993篇 |
1973年 | 3051篇 |
1972年 | 2377篇 |
1971年 | 1878篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
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
63.
64.
ABSTRACT A new density functional for the study of associating inhomogeneous fluids based on Wertheim's first-order thermodynamic perturbation theory is presented and compared to the most currently used associating density functionals. This functional is developed using the weighted density approximation in the range of association of hard spheres. We implement this functional within the framework of classical density functional theory together with modified fundamental measure theory to account for volume exclusion of hard spheres. This approach is tested against molecular simulations from literature of pure associating hard spheres and mixtures of non-associationg and associating hard spheres with different number of bonding sites close to a hard uniform wall. Furthermore, we compare and review our results with the performance of associating functionals from literature, one based on fundamental measure theory and the inhomogeneous version of Wertheim's perturbation theory. Results obtained with classical DFT and the three functionals show excellent agreement with molecular simulations in systems with one hard wall. For the cases of small pores where only one or two layers of fluid are allowed discrepancies between results with classical DFT and molecular simulations were found. 相似文献
65.
66.
67.
68.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
69.
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
70.
Dr. Zhoulong Fan Katherine L. Bay Dr. Xiangyang Chen Zhe Zhuang Han Seul Park Dr. Kap-Sun Yeung Prof. Dr. K. N. Houk Prof. Dr. Jin-Quan Yu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4800-4807
A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process. 相似文献