全文获取类型
收费全文 | 25129篇 |
免费 | 4004篇 |
国内免费 | 2379篇 |
专业分类
化学 | 17650篇 |
晶体学 | 309篇 |
力学 | 1529篇 |
综合类 | 110篇 |
数学 | 2922篇 |
物理学 | 8992篇 |
出版年
2024年 | 40篇 |
2023年 | 494篇 |
2022年 | 774篇 |
2021年 | 839篇 |
2020年 | 1002篇 |
2019年 | 976篇 |
2018年 | 794篇 |
2017年 | 706篇 |
2016年 | 1163篇 |
2015年 | 1104篇 |
2014年 | 1301篇 |
2013年 | 1752篇 |
2012年 | 2351篇 |
2011年 | 2408篇 |
2010年 | 1578篇 |
2009年 | 1503篇 |
2008年 | 1642篇 |
2007年 | 1504篇 |
2006年 | 1357篇 |
2005年 | 1152篇 |
2004年 | 839篇 |
2003年 | 643篇 |
2002年 | 609篇 |
2001年 | 445篇 |
2000年 | 436篇 |
1999年 | 522篇 |
1998年 | 430篇 |
1997年 | 438篇 |
1996年 | 452篇 |
1995年 | 361篇 |
1994年 | 309篇 |
1993年 | 238篇 |
1992年 | 235篇 |
1991年 | 203篇 |
1990年 | 169篇 |
1989年 | 144篇 |
1988年 | 98篇 |
1987年 | 112篇 |
1986年 | 90篇 |
1985年 | 83篇 |
1984年 | 48篇 |
1983年 | 43篇 |
1982年 | 37篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
991.
Generation of an N→B Ladder‐type Structure by Regioselective Hydroboration of an Alkenyl‐Functionalized Quaterpyridine 下载免费PDF全文
Markus Grandl Dr. Yu Sun Dr. Frank Pammer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):3976-3980
An unusual reactivity of 2‐(1‐alkenyl)‐pyridines towards hydroboration with 9H‐borabicyclo[3.3.1]nonane (9H‐BBN) has been employed to selectively introduce two borane groups into a conjugated quaterpyridine. Quantitative conversion of the substrate was observed with exclusive regioselectivity. A molecular structure that allows intramolecular N→B coordination was generated. The effect of the ladder formation on the molecular structure and the electronic properties of the conjugated system have been investigated. The synthetic strategy demonstrated herein offers a facile access to N→B ladder‐type structures from readily available substrates, and allows to simultaneously introduce several boron centers under mild conditions. 相似文献
992.
993.
Xiyuan Sun Jiguang Du 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2014,68(8):1-7
The effect of water conductivity on electrospraying of water was studied in combination with positive DC corona discharge generated in air. We used a point-to-plane geometry of electrodes with a hollow syringe needle anode opposite to the metal mesh cathode. We employed total average current measurements and high-speed camera fast time-resolved imaging. We visualized the formation of a water jet (filament) and investigated corona discharge behavior for various water conductivities. Depending on the conductivity, various jet properties were observed: pointy, prolonged, and fast spreading water filaments for lower conductivity; in contrast to rounder, broader, and shorter quickly disintegrating filaments for higher conductivity. The large acceleration values (4060 m/s2 and 520 m/s2 for 2 μS/cm and 400 μS/cm, respectively) indicate that the process is mainly governed by the electrostatic force. In addition, with increasing conductivity, the breakdown voltage for corona-to-spark transition was decreasing. 相似文献
994.
995.
996.
997.
Ozeki and Prodinger showed that the odd power sum of the first several consecutive Fibonacci numbers of even order is equal to a polynomial evaluated at a certain Fibonacci number of odd order. We prove that this polynomial and its derivative both vanish at 1, and will be an integer polynomial after multiplying it by a product of the first consecutive Lucas numbers of odd order. This presents an a?rmative answer to a conjecture of Melham. 相似文献
998.
H.G. Sun W. Chen H. Wei Y.Q. Chen 《The European physical journal. Special topics》2011,193(1):185-192
How to characterize the memory property of systems is a challenging issue in the modeling and analysis of complex systems.
This study makes a comparative investigation of integer-order derivative, constant-order fractional derivative and two types
of variable-order fractional derivatives in characterizing the memory property of systems. The advantages and potential applications
of two variable-order derivative definitions are highlighted through a comparative analysis of anomalous relaxation process. 相似文献
999.