全文获取类型
收费全文 | 11315篇 |
免费 | 1532篇 |
国内免费 | 1029篇 |
专业分类
化学 | 5924篇 |
晶体学 | 135篇 |
力学 | 522篇 |
综合类 | 83篇 |
数学 | 815篇 |
物理学 | 3121篇 |
无线电 | 3276篇 |
出版年
2024年 | 54篇 |
2023年 | 321篇 |
2022年 | 388篇 |
2021年 | 482篇 |
2020年 | 485篇 |
2019年 | 444篇 |
2018年 | 367篇 |
2017年 | 346篇 |
2016年 | 525篇 |
2015年 | 543篇 |
2014年 | 677篇 |
2013年 | 804篇 |
2012年 | 879篇 |
2011年 | 907篇 |
2010年 | 632篇 |
2009年 | 547篇 |
2008年 | 708篇 |
2007年 | 580篇 |
2006年 | 551篇 |
2005年 | 470篇 |
2004年 | 309篇 |
2003年 | 299篇 |
2002年 | 249篇 |
2001年 | 180篇 |
2000年 | 214篇 |
1999年 | 232篇 |
1998年 | 189篇 |
1997年 | 169篇 |
1996年 | 205篇 |
1995年 | 158篇 |
1994年 | 151篇 |
1993年 | 116篇 |
1992年 | 112篇 |
1991年 | 93篇 |
1990年 | 84篇 |
1989年 | 58篇 |
1988年 | 65篇 |
1987年 | 46篇 |
1986年 | 46篇 |
1985年 | 39篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1970年 | 12篇 |
1937年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Wang Ruo-Bin Wang Wei-Feng Xu Lin Pan Jeng-Shyang Chu Shu-Chuan 《Wireless Networks》2022,28(8):3411-3428
Wireless Networks - Improving localization performance is one of the critical issues in Wireless Sensor Networks (WSN). As a range-free localization algorithm, Distance Vector-Hop(DV-Hop) is... 相似文献
52.
Yibiao Pan 《Proceedings of the American Mathematical Society》1996,124(9):2821-2825
We consider boundedness properties of oscillatory singular integrals on and Hardy spaces. By constructing a phase function, we prove that boundedness may fail while boundedness holds for all . This shows that the theory and theory for such operators are fundamentally different.
53.
54.
The generalized Landweber iteration with a variable shaping matrix is used to solve the large linear system of equations arising in the image reconstruction problem of emission tomography. The method is based on the property that once a spatial frequency image component is almost recovered within in in the generalized Landweber iteration, this component will still stay within in during subsequent iterations with a different shaping matrix, as long as this shaping matrix satisfies the convergence criterion for the component. Two different shaping matrices are used: the first recovers low-frequency image components; and the second may be used either to accelerate the reconstruction of high-frequency image components, or to attenuate these components to filter the image. The variable shaping matrix gives results similar to truncated inverse filtering, but requires much less computation and memory, since it does not rely on the singular value decomposition. 相似文献
55.
根据在自由基引发剂存在下,8,9-苯并-2-亚甲基-1,4,6-三氧螺(4,4)壬烷(Ⅰ)可能存在的竞争反应,推导了动力学方程式。用红外光谱法测定了单体的消失速率和苯酞的生成速率。实验结果与推导动力学方程式相符。进一步证明了单体(Ⅰ)的增长反应由加成聚合和开环—异构化—加成这两个反应组成。这两个反应对总速率的相对贡献与单体浓度有关。得到了共聚物的结构。 相似文献
56.
E. M. F. of the Cell, Cd-Hg (2-phase)/CdAc2(m), Hg2Ac2(s)/Hg was measured at 20°, 25°, 30° and 40°C. The standard e. m. f. of the cell, Cd/CdAc3(m), Hg2Ac2(c)/Hg was evaluated as E°=1.1500?11.09×10?4T+1.06×10?8T2 The thermodynamic data of the reaction, Cd(c) + Hg2Ac2(c)=2Hg(l)+Cd++(aq)+2Ac?(aq) at 25°C were estimated as ΔF°=?42,139, ΔH°=?48,698 cal mole?1 and ΔS°=?22.0 cal deg?1 mole?1 at 25°C. The thermodynamic data for the formation of Hg2Ac2(s) were evaluated as ΔFf°=?202.3, ΔHf°=?154.5 Kcal mole?1 and S°=72.9 cal deg?1 mole?1. From measurements of the heats of solution of CdAc2·2H2O in aqueous solution, the relative partial molal enthalpies of cadmium acetate in aqueous solution were estimated. 相似文献
57.
The reaction of 1-alkynylcyclobutanols with aryl iodides in the presence of Pd(OAc)2 and Et3N in acetonitrile at 80°C for 24 h gives 2-disubstituted methylenecyclopentan-1-ones in modest to good yields. The tandem insertion-ring expansion process proceeds via the formation of an alkynyl π-complex, followed by migration of a carbon-carbon bond of the tert-alkanol to form the cyclopentanones stereoselectively. 相似文献
58.
59.
60.