全文获取类型
收费全文 | 734885篇 |
免费 | 24393篇 |
国内免费 | 11541篇 |
专业分类
化学 | 393669篇 |
晶体学 | 10278篇 |
力学 | 35937篇 |
综合类 | 584篇 |
数学 | 98915篇 |
物理学 | 231436篇 |
出版年
2022年 | 6762篇 |
2021年 | 8046篇 |
2020年 | 9133篇 |
2019年 | 9187篇 |
2018年 | 16240篇 |
2017年 | 16393篇 |
2016年 | 18269篇 |
2015年 | 11935篇 |
2014年 | 16115篇 |
2013年 | 33023篇 |
2012年 | 31348篇 |
2011年 | 41321篇 |
2010年 | 27860篇 |
2009年 | 27557篇 |
2008年 | 35942篇 |
2007年 | 37372篇 |
2006年 | 26435篇 |
2005年 | 27534篇 |
2004年 | 23024篇 |
2003年 | 20329篇 |
2002年 | 18592篇 |
2001年 | 19255篇 |
2000年 | 14991篇 |
1999年 | 11987篇 |
1998年 | 10165篇 |
1997年 | 9883篇 |
1996年 | 9792篇 |
1995年 | 8621篇 |
1994年 | 8420篇 |
1993年 | 8044篇 |
1992年 | 8625篇 |
1991年 | 8663篇 |
1990年 | 8169篇 |
1989年 | 7799篇 |
1988年 | 7604篇 |
1987年 | 7419篇 |
1986年 | 7139篇 |
1985年 | 9208篇 |
1984年 | 9262篇 |
1983年 | 7518篇 |
1982年 | 7733篇 |
1981年 | 7485篇 |
1980年 | 6931篇 |
1979年 | 7437篇 |
1978年 | 7758篇 |
1977年 | 7618篇 |
1976年 | 7581篇 |
1975年 | 7028篇 |
1974年 | 7110篇 |
1973年 | 7117篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation. 相似文献
172.
173.
Polypyrrole Shell@3D‐Ni Metal Core Structured Electrodes for High‐Performance Supercapacitors 下载免费PDF全文
Gao‐Feng Chen Yu‐Zhi Su Pan‐Yong Kuang Zhao‐Qing Liu Dao‐Yi Chen Xu Wu Nan Li Prof. Shi‐Zhang Qiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4614-4621
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively). 相似文献
174.
175.
176.
177.
178.
179.
180.
Rachida M’chaar Abdelaziz Sabbar Mouloud El Moudane Noureddine Ouerfelli 《哲学杂志》2020,100(11):1415-1438
ABSTRACT By applying the geometric models and the theoretical equation, the surface tension, the molar volume and the density were studied. The empirical calculations were carried out in temperature range 623?K?≤?T?≤?1123?K. Only few thermophysical properties were estimated for eight quinary alloys: Sn3.55Ag0.5Cu3Bi3Sb, Sn3.48Ag0.5Cu3Bi5Sb, Sn3.48 Ag0.5Cu5Bi3Sb, Sn3.40 Ag0.5Cu5Bi5Sb, Sn3.53Ag1Cu3Bi3Sb, Sn3.46Ag1Cu3Bi5Sb, Sn3.46Ag1Cu5Bi3Sb, Sn3.38Ag1Cu5Bi5Sb. The results show that surface tension and density have a linear appearance for all temperatures. We have also studied the influence of the composition and temperature in the studied alloys. The obtained theoretical results are compared with the experimental ones and with the conventional Pb–Sn welds. 相似文献