全文获取类型
收费全文 | 449604篇 |
免费 | 3027篇 |
国内免费 | 1058篇 |
专业分类
化学 | 210427篇 |
晶体学 | 5687篇 |
力学 | 24687篇 |
综合类 | 7篇 |
数学 | 65559篇 |
物理学 | 147322篇 |
出版年
2020年 | 3312篇 |
2019年 | 3893篇 |
2018年 | 11861篇 |
2017年 | 12461篇 |
2016年 | 10345篇 |
2015年 | 4508篇 |
2014年 | 7000篇 |
2013年 | 16022篇 |
2012年 | 15357篇 |
2011年 | 24187篇 |
2010年 | 16453篇 |
2009年 | 16745篇 |
2008年 | 21745篇 |
2007年 | 24504篇 |
2006年 | 12876篇 |
2005年 | 16034篇 |
2004年 | 13043篇 |
2003年 | 12260篇 |
2002年 | 10843篇 |
2001年 | 11185篇 |
2000年 | 8669篇 |
1999年 | 6568篇 |
1998年 | 5734篇 |
1997年 | 5473篇 |
1996年 | 5313篇 |
1995年 | 4769篇 |
1994年 | 4621篇 |
1993年 | 4666篇 |
1992年 | 4811篇 |
1991年 | 5215篇 |
1990年 | 4895篇 |
1989年 | 4947篇 |
1988年 | 4849篇 |
1987年 | 4801篇 |
1986年 | 4499篇 |
1985年 | 6005篇 |
1984年 | 6177篇 |
1983年 | 5032篇 |
1982年 | 5380篇 |
1981年 | 5203篇 |
1980年 | 4938篇 |
1979年 | 5303篇 |
1978年 | 5582篇 |
1977年 | 5493篇 |
1976年 | 5679篇 |
1975年 | 5220篇 |
1974年 | 5175篇 |
1973年 | 5397篇 |
1972年 | 4016篇 |
1971年 | 3483篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Dr. Jordan Donat Mr. Patrick Dubourdeaux Dr. Martin Clémancey Dr. Julia Rendon Clara Gervasoni Mr. Morgan Barbier Jessica Barilone Dr. Jacques Pécaut Prof. Dr. Serge Gambarelli Prof. Dr. Pascale Maldivi Prof. Dr. Jean-Marc Latour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202201875
Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two-electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor. 相似文献
12.
Saqib Kamal Arif I. Inamdar Kuan-Ru Chiou Batjargal Sainbileg Muhammad Usman Jenq-Wei Chen Tzuoo-Tsair Luo Michitoshi Hayashi Chen-Hsiung Hung Wen-Feng Liaw Kuang-Lieh Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202103905
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties. 相似文献
13.
Russian Chemical Bulletin - New representatives of (O-Si)-chelate compounds, N-(fluorosilyl)methyl derivatives of N-methylacetamide, N-methylbenzamide, N-phenylacetamide, and N-phenylbenzamide,... 相似文献
14.
Russian Journal of Applied Chemistry - Recent achievements in the field of the development of preparation methods and study of structure and properties of epoxy nanocomposites with metal-containing... 相似文献
15.
Journal of Experimental and Theoretical Physics - The surface current density of charge carriers in two-dimensional doubly periodic n-type semiconductor superlattices in an external magnetic field... 相似文献
16.
Tsyganova S. I. Fetisova O. Yu. Mazurova E. N. Taran O. P. Kuznetsov B. N. 《Russian Journal of Applied Chemistry》2022,95(3):408-416
Russian Journal of Applied Chemistry - A method for the disposal of hydrolysis lignin waste based on its modification with ZnCl2 and FeCl3 and subsequent carbonization at 800°C was proposed.... 相似文献
17.
Roopa K. P. Keshavamurthy K. Mahesh B. Veena K. P. Shankara B. S. Basavaiah K. 《Journal of Applied Spectroscopy》2022,89(4):809-818
Journal of Applied Spectroscopy - Three simple, sensitive, precise, and rapid spectrophotometric methods are developed and optimized for the assay of vardenafil in pharmaceutical formulations. The... 相似文献
18.
Theoretical and Mathematical Physics - We study a phenomenological model in which dark matter in the cosmological constant form is identified with the mean energy–momentum tensor of a... 相似文献
19.
Knyazev Yu. V. Kazak N. V. Gavrichkov V. A. Polukeev S. I. Ovchinnikov S. G. 《JETP Letters》2022,116(8):567-573
JETP Letters - Changes in the magnetic properties of FeBO3 single crystals in the course of spin crossover occurring with increasing pressure up to 63 GPa are studied both experimentally and... 相似文献
20.
Varfolomeev S. D. Panin A. A. Semenova N. A. Ublinskiy M. V. Akhadov T. A. Bykov V. I. Tsybenova S. B. 《Russian Chemical Bulletin》2022,71(3):591-594
A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.
相似文献