全文获取类型
收费全文 | 54254篇 |
免费 | 17861篇 |
国内免费 | 1748篇 |
学科分类
数理化 | 73863篇 |
出版年
2024年 | 461篇 |
2023年 | 4399篇 |
2022年 | 1933篇 |
2021年 | 2928篇 |
2020年 | 5172篇 |
2019年 | 2815篇 |
2018年 | 2874篇 |
2017年 | 1087篇 |
2016年 | 6141篇 |
2015年 | 6142篇 |
2014年 | 5784篇 |
2013年 | 6115篇 |
2012年 | 4358篇 |
2011年 | 2388篇 |
2010年 | 4307篇 |
2009年 | 4096篇 |
2008年 | 1994篇 |
2007年 | 1593篇 |
2006年 | 918篇 |
2005年 | 769篇 |
2004年 | 575篇 |
2003年 | 492篇 |
2002年 | 438篇 |
2001年 | 328篇 |
2000年 | 319篇 |
1999年 | 265篇 |
1998年 | 235篇 |
1997年 | 240篇 |
1996年 | 229篇 |
1995年 | 252篇 |
1994年 | 251篇 |
1993年 | 313篇 |
1992年 | 190篇 |
1991年 | 152篇 |
1990年 | 125篇 |
1989年 | 129篇 |
1988年 | 120篇 |
1980年 | 120篇 |
1979年 | 101篇 |
1978年 | 99篇 |
1977年 | 164篇 |
1976年 | 191篇 |
1975年 | 192篇 |
1974年 | 202篇 |
1973年 | 117篇 |
1972年 | 155篇 |
1971年 | 124篇 |
1970年 | 208篇 |
1969年 | 129篇 |
1968年 | 138篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Giang Truong Nguyen Prof. Dr. Liviu Ungur 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202200227
Employing radical bridges between anisotropic metal ions has been a viable route to achieve high-performance single-molecule magnets (SMMs). While the bridges have been mainly considered for their ability to promote exchange interactions, the crystal-field effect arising from them has not been taken into account explicitly. This lack of consideration may distort the understanding and limit the development of the entire family. To shed light on this aspect, herein we report a theoretical investigation of a series of N -radical-bridged diterbium complexes. It is found that while promoting strong exchange coupling between the terbium ions, the N -radical induces a crystal field that interferes destructively with that of the outer ligands, and thus reduces the overall SMM behavior. Based on the theoretical results, we conclude that the SMM behavior in this series could be further maximized if the crystal field of the outer ligands is designed to be collinear with that of the radical bridge. This conclusion can be generalized to all exchange-coupled SMMs. 相似文献
2.
3.
Dr. H. Schmieg Prof. Dr. P. Vielsack 《Archive of Applied Mechanics (Ingenieur Archiv)》1987,57(6):446-458
Übersicht Betrachtet wird ein zwangserregtes Zweikörpersystem mit wechselnden Bindungen infolge trockener Reibung. Stationäre Bewegungen werden als Grenzfall instationärer Einschwingvorgänge berechnet. Abhängig von den Systemparametern ergeben sich drei typische Bewegungsformen. Ihnen entsprechen dauernde Haftzustände, wechselnde Haft-Gleitzustände oder dauernde Gleitzustände an der Berührfläche beider Körper.
Intermittant constraints in a two-body-system with dry friction
Summary An externally excited two-body-system with intermittant constraints due to dry friction is considered. Stationary motions are calculated as limit cases of instationary transients. Depending on the parameters of the system, three typical modes are of interest. These correspond to permanent sticking, slipstick behaviour, or to permanent slipping in the contact surface of the bodies, respectively.相似文献
4.
5.
6.
Fei Chang Dongheng Zhang Haijian Yang Haibin Song 《Journal of organometallic chemistry》2004,689(5):936-946
The synthesized 1-aryliminomethylenylnaphthalen-2-ol derivatives reacted with nickel chloride to form bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes. All resultant compounds were structurally characterized by elemental analyses, IR and H NMR, and the structures of the formed complexes were elucidated by X-ray crystal structure analysis. The complexes show high catalytic activities for the vinyl polymerization of norbornene in the presence of methylaluminoxane. The catalytic activity variations have been followed by gas chromatography through monitoring the conversion of norbornene. 相似文献
7.
8.
Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis.
The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed moderate
activities for ethylene oligomerization.
Published in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
This article was submitted by the authors in English. 相似文献
9.
Akira Yanagisawa Prof. Dr. Takahiro Suzuki Takanori Koide Shogo Okitsu Takayoshi Arai Prof. Dr. 《化学:亚洲杂志》2008,3(10):1793-1800
A Barbier‐type regioselective propargylation of aldehydes and ketones with (3‐bromobut‐1‐ynyl)trimethylsilane has been achieved using reactive barium as a low‐valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of α,β‐unsaturated carbonyl compounds, only 1,2‐adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13. 相似文献
10.