全文获取类型
收费全文 | 501576篇 |
免费 | 6404篇 |
国内免费 | 1844篇 |
专业分类
化学 | 269661篇 |
晶体学 | 7302篇 |
力学 | 21285篇 |
综合类 | 9篇 |
数学 | 61659篇 |
物理学 | 149908篇 |
出版年
2020年 | 3450篇 |
2019年 | 3673篇 |
2018年 | 4981篇 |
2017年 | 4903篇 |
2016年 | 7450篇 |
2015年 | 5551篇 |
2014年 | 7724篇 |
2013年 | 22853篇 |
2012年 | 17337篇 |
2011年 | 21217篇 |
2010年 | 13490篇 |
2009年 | 13485篇 |
2008年 | 18916篇 |
2007年 | 19191篇 |
2006年 | 18227篇 |
2005年 | 18851篇 |
2004年 | 16967篇 |
2003年 | 14364篇 |
2002年 | 13063篇 |
2001年 | 14638篇 |
2000年 | 11243篇 |
1999年 | 8992篇 |
1998年 | 7384篇 |
1997年 | 7218篇 |
1996年 | 7067篇 |
1995年 | 6515篇 |
1994年 | 6186篇 |
1993年 | 6060篇 |
1992年 | 6708篇 |
1991年 | 6647篇 |
1990年 | 6240篇 |
1989年 | 6074篇 |
1988年 | 6298篇 |
1987年 | 5971篇 |
1986年 | 5762篇 |
1985年 | 8171篇 |
1984年 | 8370篇 |
1983年 | 6850篇 |
1982年 | 7468篇 |
1981年 | 7364篇 |
1980年 | 7116篇 |
1979年 | 7198篇 |
1978年 | 7440篇 |
1977年 | 7285篇 |
1976年 | 7354篇 |
1975年 | 6944篇 |
1974年 | 6909篇 |
1973年 | 7253篇 |
1972年 | 4375篇 |
1971年 | 3297篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
161.
162.
163.
164.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and... 相似文献
165.
Shaobo Cheng Vidushi Sharma Altug S. Poyraz Lijun Wu Xing Li Amy C. Marschilok Esther S. Takeuchi Kenneth J. Takeuchi Marivi Fernndez-Serra Yimei Zhu 《Chemical science》2020,11(19):4991
Tunneled metal oxides such as α-Mn8O16 (hollandite) have proven to be compelling candidates for charge-storage materials in high-density batteries. In particular, the tunnels can support one-dimensional chains of K+ ions (which act as structure-stabilizing dopants) and H2O molecules, as these chains are favored by strong H-bonds and electrostatic interactions. In this work, we examine the role of water molecules in enhancing the stability of K+-doped α-Mn8O16 (cryptomelane). The combined experimental and theoretical analyses show that for high enough concentrations of water and tunnel-ions, H2O displaces K+ ions from their natural binding sites. This displacement becomes energetically favorable due to the formation of K2+ dimers, thereby modifying the stoichiometric charge of the system. These findings have potentially significant technological implications for the consideration of cryptomelane as a Li+/Na+ battery electrode. Our work establishes the functional role of water in altering the energetics and structural properties of cryptomelane, an observation that has frequently been overlooked in previous studies.Water displaces potassium ions and initiates the formation of a homonuclear dimer ion (K2+) in the tunnels of hollandite. 相似文献
166.
167.
168.
169.
Vanessa R. Machado Louis P. Sandjo Giovanni L. Pinheiro Milene H. Moraes Mario Steindel Moacir G. Pizzolatti 《Natural product research》2018,32(3):275-281
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase. 相似文献
170.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献