全文获取类型
收费全文 | 3295篇 |
免费 | 746篇 |
国内免费 | 234篇 |
专业分类
化学 | 1332篇 |
晶体学 | 15篇 |
力学 | 794篇 |
综合类 | 34篇 |
数学 | 370篇 |
物理学 | 1730篇 |
出版年
2024年 | 6篇 |
2023年 | 33篇 |
2022年 | 129篇 |
2021年 | 118篇 |
2020年 | 121篇 |
2019年 | 95篇 |
2018年 | 97篇 |
2017年 | 87篇 |
2016年 | 133篇 |
2015年 | 135篇 |
2014年 | 164篇 |
2013年 | 242篇 |
2012年 | 167篇 |
2011年 | 207篇 |
2010年 | 161篇 |
2009年 | 206篇 |
2008年 | 221篇 |
2007年 | 226篇 |
2006年 | 230篇 |
2005年 | 206篇 |
2004年 | 175篇 |
2003年 | 171篇 |
2002年 | 144篇 |
2001年 | 100篇 |
2000年 | 114篇 |
1999年 | 76篇 |
1998年 | 77篇 |
1997年 | 69篇 |
1996年 | 56篇 |
1995年 | 50篇 |
1994年 | 44篇 |
1993年 | 37篇 |
1992年 | 26篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1970年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4275条查询结果,搜索用时 15 毫秒
41.
Mark D. Roberts 《General Relativity and Gravitation》2004,36(11):2423-2431
The paths of stars in galaxies have circular velocity independent of their distance from the centre of the galaxy. Newtonian mechanics with a logarithmic potential has such paths. In relativity these paths can be taken to be geodesics and this requirement places a restricting equation on the spacetime metric. This equation has a non-unique spherically symmetric solution that in the Newtonian limit has a logarithmic potential. It also can be solved in terms of a conformal factor. In particular it has solutions which are conformal to the vacuum-Einstein solutions and such spacetimes are solutions to the vacuum-Bach equations. Therefore it is suggested that the Bach equations describe dynamics on galactic length scales. 相似文献
42.
高斯光束照射下的圆盘夫琅禾费衍射 总被引:9,自引:3,他引:6
推导了高斯光束照射圆孔或圆盘的衍射场普遍表达式,计算了半波带数接近于零的情况下上述衍射场的数据,进而分析了圆盘衍射场在艾里斑中增加一个暗环的原因。 相似文献
43.
Manicka Dhanasekar Jianjun Han Qinghua Qin 《Finite Elements in Analysis and Design》2006,42(14-15):1314-1323
Much work on special elements that simplify geometrical modelling of structures containing holes, cracks and/ or inclusions has been reported extensively in the literature. This paper presents a hybrid-Trefftz element containing elliptic hole formulated using Hellinger–Reissner principle by employing trial functions based on the mapping technique and the Cauchy integral method. The element presented in this paper could be regarded as an improved formulation over Piltner [Special finite elements with holes and internal cracks, Int. J. Numer. Methods Eng. 21 (1985) 1471–1485] element because the chosen trail functions in this paper have provided relatively more stable solutions. The use of the element with other ordinary displacement-based finite elements has also yielded very accurate solutions even when very coarse meshes relative to the size of the elliptic hole have been used. 相似文献
44.
45.
Vasilis P. Barberis John A. Mikroyannidis 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3556-3566
A poly(p‐phenylenevinylene) derivative (PPV–TPA)] and a series of statistical copolyfluorenes (PF–TPA)] containing oxadiazole and triphenylamine segments along the main chain were synthesized by the Heck reaction and nickel‐mediated coupling, respectively. The PF–TPA copolyfluorenes with relatively low contents of oxadiazole and triphenylamine units were readily soluble in common organic solvents, whereas the other copolyfluorenes displayed lower solubility. PPV–TPA showed excellent solubility in solvents such as tetrahydrofuran (THF), dichloromethane, chloroform, and toluene. Thin films of the polymers absorbed light in the range of 375–396 nm and had optical band gaps of 2.76–2.98 eV. They emitted blue‐green light with a maximum at 414–522 nm. The fluorescence quantum yields in THF solutions were 0.08–0.53. The copolyfluorene PF–TPA thin films with high contents of oxadiazole and triphenylamine moieties emitted pure blue light that remained stable even after annealing at 150 °C for 4 h in air. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3556–3566, 2006 相似文献
46.
47.
圆柱型正交各向异性圆形薄板的非线性非对称弯曲问题(Ⅱ) 总被引:3,自引:3,他引:0
本文利用“正则摄动法”[2]研究文献[1]中由“两变量法”[3]所得到的关于Wnm,和的递推方程和递推边界条件的求解问题。求得了本问题的一致有效渐近解,最后作为实例,我们利用“混合摄动法”[4]研究了轴对称线性弯曲问题,并将所得结果与文献[5]中给出的精确解相比较,两者基本上是一致的。 相似文献
48.
49.
50.