全文获取类型
收费全文 | 2945篇 |
免费 | 98篇 |
国内免费 | 21篇 |
专业分类
化学 | 2114篇 |
晶体学 | 21篇 |
力学 | 61篇 |
数学 | 487篇 |
物理学 | 381篇 |
出版年
2023年 | 26篇 |
2022年 | 62篇 |
2021年 | 101篇 |
2020年 | 65篇 |
2019年 | 60篇 |
2018年 | 61篇 |
2017年 | 49篇 |
2016年 | 107篇 |
2015年 | 95篇 |
2014年 | 110篇 |
2013年 | 180篇 |
2012年 | 185篇 |
2011年 | 254篇 |
2010年 | 156篇 |
2009年 | 127篇 |
2008年 | 184篇 |
2007年 | 204篇 |
2006年 | 150篇 |
2005年 | 146篇 |
2004年 | 130篇 |
2003年 | 94篇 |
2002年 | 89篇 |
2001年 | 34篇 |
2000年 | 29篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1912年 | 2篇 |
排序方式: 共有3064条查询结果,搜索用时 15 毫秒
71.
Frontispiece: Docking Strategy To Construct Thermostable,Single‐Crystalline,Hydrogen‐Bonded Organic Framework with High Surface Area 下载免费PDF全文
72.
73.
A triazolyl-di-ylidene ligand has been used for the preparation of a homodimetallic complex of gold, and a heterodimetallic compound of gold and iridium. Both complexes have been fully characterized and their molecular structures have been determined by means of X-ray diffraction. The catalytic properties of these two complexes have been evaluated in the reduction of nitroarenes by transfer hydrogenation using primary alcohols. The two complexes afford different reaction products; whereas the Au(I)-Au(I) catalyst yields a hydroxylamine, the Ir(III)-Au(I) complex facilitates the formation of an imine. 相似文献
74.
75.
Laurent A. Baumes Dr. Mireia Buaki Sogo Pedro Montes‐Navajas Dr. Avelino Corma Prof. Dr. Hermenegildo Garcia Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4489-4495
γ‐Hydroxybutyric acid (GHB), a colourless, odourless and tasteless chemical, has become one of the most dangerous illicit drugs of abuse today. At low doses, this drug is a central nervous system depressant that reduces anxiety and produces euphoria and relaxation, sedating the recipient. There is an urgent need for simple, easy‐to‐use sensors for GHB in solution. Here, we present a colorimetric sensor array based on supramolecular host–guest complexes of fluorescent dyes with organic capsules (cucurbiturils) for the detection of GHB. 相似文献
76.
77.
78.
Humeres E Debacher NA Franco JD Lee BS Martendal A 《The Journal of organic chemistry》2002,67(11):3662-3667
The acid decomposition of some p-substituted aryldithiocarbamates (arylDTCs) was observed in 20% aqueous ethanol at 25 degrees C, mu = 1.0 (KCl, for pH > 0). The pH-rate profiles showed a dumbell shape with a plateau where the observed first-order rate constant k(obs) was equal to k(o), the rate constant of the decomposition of the dithiocarbamic acid species. The acid dissociation constants of the dithiocarbamic acids (pK(a)) and their conjugate acids (pK(+)) were calculated from the pH-rate profiles. Comparatively, k(o) was more than 10(4)-fold faster than alkyldithiocarbamates (alkDTCs) with similar pK(N) (the acid dissociation constant of the parent amine). It was observed that the values of pK(a) and pK(+)were 5 and 8 units of pK, respectively, higher than the expected values from the pK(N) of alkylDTCs. The higher values were attributed to the inhibition of the delocalization of the nitrogen electron pair into the benzene ring because of the strong electron withdrawal effect of the thiocarbonyl group. Comparison of the activation parameters showed that the rate acceleration was due to a decrease in the enthalpy of activation. Proton inventory indicated the existence of a multiproton transition state, and it was consistent with an S to N proton transfer through a water molecule. There are two hydrogens contributing to a secondary SIE, and there are also two protons that are being transferred at the transition state to form a zwitterion followed by fast C-N bond cleavage. The mechanism could also be a concerted asynchronic process where the N-protonation is more advanced than the C-N bond breakdown. The kinetic barrier is similar to the torsional barrier of thioamides, suggesting that the driving force to reach the transition state is the needed torsion of the C-N bond that inhibits the resonance with the thiocarbonyl group and the aromatic moiety, increasing the basicity of the nitrogen and making the proton transfer thermodynamically favorable. 相似文献
79.
Nonlinear Dynamics - 相似文献
80.
Jadriane A. Xavier Thaissa L. Silva Eduardo Caio Torres-Santos Camila Calado de Vasconcelos Anastacio Boane Ricardo Alexandre dos Santos Andre Felippe A. Xavier Marília O.F. Goulart 《Current Opinion in Electrochemistry》2021
This review discusses the state of the art, challenges, and perspectives in recent applications of nitroaromatics and nitroheteroaromatics, which are redox-bio-activated drugs or leads, in Medicinal Chemistry. It deals mainly with the electrochemical approach toward the electron transfer-based molecular mechanisms of drug action, drug design, estimation and measurement of redox potentials, correlation of physicochemical and pharmacological data, and electrochemical studies of the main representatives of nitro-containing prodrugs, along with approaches to combat their toxicity issues, aiming at a better therapeutic profile. Electrochemical investigation plays essential roles, being strategic in the design and discovery of potential medicines. 相似文献