全文获取类型
收费全文 | 25727篇 |
免费 | 4682篇 |
国内免费 | 3256篇 |
专业分类
化学 | 18106篇 |
晶体学 | 289篇 |
力学 | 1965篇 |
综合类 | 220篇 |
数学 | 2942篇 |
物理学 | 10143篇 |
出版年
2024年 | 50篇 |
2023年 | 524篇 |
2022年 | 703篇 |
2021年 | 843篇 |
2020年 | 1054篇 |
2019年 | 937篇 |
2018年 | 832篇 |
2017年 | 763篇 |
2016年 | 1204篇 |
2015年 | 1171篇 |
2014年 | 1399篇 |
2013年 | 1781篇 |
2012年 | 2296篇 |
2011年 | 2445篇 |
2010年 | 1620篇 |
2009年 | 1533篇 |
2008年 | 1773篇 |
2007年 | 1486篇 |
2006年 | 1553篇 |
2005年 | 1222篇 |
2004年 | 985篇 |
2003年 | 813篇 |
2002年 | 791篇 |
2001年 | 665篇 |
2000年 | 574篇 |
1999年 | 636篇 |
1998年 | 489篇 |
1997年 | 462篇 |
1996年 | 496篇 |
1995年 | 417篇 |
1994年 | 387篇 |
1993年 | 312篇 |
1992年 | 278篇 |
1991年 | 224篇 |
1990年 | 203篇 |
1989年 | 169篇 |
1988年 | 151篇 |
1987年 | 99篇 |
1986年 | 94篇 |
1985年 | 65篇 |
1984年 | 49篇 |
1983年 | 40篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1979年 | 4篇 |
1975年 | 1篇 |
1966年 | 1篇 |
1957年 | 7篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
A four-dimensional hyperchaotic system with five parameters is proposed. Its dynamical properties such as dissipativity, equilibrium points, Lyapunov exponent, Lyapunov dimension, bifurcation diagrams and Poincare maps are analyzed theoretically and numerically. Theoretical analyses and simulation tests indicate that the new system's dynamics behavior can be periodic attractor, chaotic attractor and hyperchaotic attractor as the parameter varies. Finally, the circuit of this new hyperchaotic system is designed and realized by Multisim software. The simulation results confirm that the chaotic system is different from the existing chaotic systems and is a novel hyperchaotic system. The system is recommendable for many engineering applications such as information processing, cryptology, secure communications, etc. 相似文献
973.
974.
975.
Microchimica Acta - A simple and sensitive electrochemical method was developed for the determination of trypsin by employing a specific heptapeptide (CRRRRRR) as a substrate. The positively... 相似文献
976.
Alexander M. Schneider Luyao Lu Eric F. Manley Tianyue Zheng Valerii Sharapov Tao Xu Tobin J. Marks Lin X. Chen Luping Yu 《Chemical science》2015,6(8):4860-4866
We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit. These polymers are effective bulk heterojunction solar cell materials when blended with phenyl-C71-butyric acid methyl ester (PC71BM). They achieve power conversion efficiencies (up to 5.33%) high for polymers having such large bandgaps, ca. 2.0 eV (optical) and 2.5 eV (electrochemical). Grazing incidence wide-angle X-ray scattering (GIWAXS) reveals strong correlations between π–π stacking distance and regularity, polymer backbone planarity, optical absorption maximum energy, and photovoltaic efficiency. 相似文献
977.
978.
Selective O-benzoylation of hydroxamic acids is achieved by the treatment of BPO and DABCO. Aliphatic alcohols are not reactive under these conditions. Various radical or oxidation sensitive functional groups are compatible with this protocol, and no anhydrous reagents or solvents are required for the high yields of the benzoylations. 相似文献
979.
Jian Zheng Philip A. Barrett Steven J. Pontonio Neil A. Stephenson Preeti Chandra Persefoni Kechagia 《Adsorption》2014,20(1):147-156
High-rate and high-density gas separation adsorbents used in vacuum pressure swing adsorption (VPSA) processes are described. Agglomerated zeolite Li–LSX compositions made using colloidal silica binding agents and having improved nitrogen pore diffusivity compared to like compositions prepared with traditional clay binders, are also described. Preparation methods for the colloidal silica-bound adsorbents are described together with their characterization by mercury (Hg) porosimetry, scanning electron microscopy (SEM) and low dead-volume breakthrough testing, from which the pore diffusivity is obtained. In this article, we show how the location and dispersion of the colloidal silica binding agent within the agglomerated zeolite particle yields pore-architectures that resemble “state-of-the-art” binderless adsorbents. In addition, we use VPSA process simulations to show that the best process performance is achieved by the combination of high-rate and high-density adsorbent properties. 相似文献
980.