全文获取类型
收费全文 | 60399篇 |
免费 | 14267篇 |
国内免费 | 5901篇 |
专业分类
化学 | 58272篇 |
晶体学 | 864篇 |
力学 | 2295篇 |
综合类 | 402篇 |
数学 | 4947篇 |
物理学 | 13787篇 |
出版年
2024年 | 80篇 |
2023年 | 516篇 |
2022年 | 1048篇 |
2021年 | 1233篇 |
2020年 | 2318篇 |
2019年 | 3568篇 |
2018年 | 2004篇 |
2017年 | 1737篇 |
2016年 | 4602篇 |
2015年 | 4859篇 |
2014年 | 5020篇 |
2013年 | 6080篇 |
2012年 | 5253篇 |
2011年 | 4544篇 |
2010年 | 4614篇 |
2009年 | 4574篇 |
2008年 | 4178篇 |
2007年 | 3464篇 |
2006年 | 3042篇 |
2005年 | 2887篇 |
2004年 | 2500篇 |
2003年 | 2201篇 |
2002年 | 2955篇 |
2001年 | 2232篇 |
2000年 | 1863篇 |
1999年 | 907篇 |
1998年 | 417篇 |
1997年 | 323篇 |
1996年 | 293篇 |
1995年 | 235篇 |
1994年 | 184篇 |
1993年 | 169篇 |
1992年 | 105篇 |
1991年 | 114篇 |
1990年 | 101篇 |
1989年 | 78篇 |
1988年 | 56篇 |
1987年 | 52篇 |
1986年 | 41篇 |
1985年 | 42篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1971年 | 2篇 |
1957年 | 5篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
强流脉冲电子束在材料中的能量沉积剖面、能量沉积系数和束流传输系数受其入射角的影响很大,理论计算了0.5~2.0MeV的电子束以不同的入射角在Al材料中的能量沉积剖面和能量沉积系数,并且还计算了0.4~1.4MeV电子束以不同入射角穿透不同厚度C靶的束流传输系数。计算结果表明,随着入射角的增大,靶材表面层单位质量中沉积的能量增大,电子在靶材料中穿透深度减小,能量沉积系数减小,相应的束流传输系数也减小;能量为0.5~2.0MeV的电子束当入射角在60°~70°时在材料表面层单位质量中沉积的能量较大。 相似文献
92.
采用溶解-反应量热法在具有恒温环境的溶解-反应热量计内,测定了[Gd(Gly)4(Im)(H2O)](ClO4)3和[Y(Gly)4(Im)(H2O)](ClO4)3两种稀土甘氨酸咪唑配合物的标准生成焓分别为(-3 461.46 ±0.22) kJ·mol-1 和(-3 926.6±0.90) kJ·mol-1. 相似文献
93.
Yang Mujie Zhao Jian Li Aibing Shen Zhiquan Zhang Mingjian Lin Senhao 《Journal of polymer science. Part A, Polymer chemistry》1989,27(11):3829-3835
This paper reports that 60Co γ-ray irradiation can convert cis-polyphenylacetylene (cis-PPA) films prepared with rare-earth coordination catalysts to highly photosensitive materials. The dependence of the photosensitivity on irradiation dose, preparation methods, and microstructure of the PPA films has been investigated by means of a potential discharge technique. The photosensitivity was enhanced with increasing irradiation dose. The critical dose to produce a light response was 5 × 103 Gy. The maximum surface potential discharge rate was 618 V/s, and the dark decay was approximately 2 V/s for cis-PPA films irradiated with 60Co γ-ray (dose: 2 × 105 Gy). The cis-transoidal-PPA and an electrophotographic photoreceptor device incorporating cis-PPA showed a higher irradiation effect. The structure and properties of 60Co γ-ray irradiated rare-earth PPA films are similar to the unirradiated films. 相似文献
94.
95.
96.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
97.
98.
Comparing with the exact solutions of the model system of one and two particles coupled to an axial rotor, the quality of the semi classical tilted axis cranking approximation is investigated. Extensive comparisons of the energies and M1 and E2 transition probabilities are carried out for the lowest bands. Very good agreement is found, except near band crossings. Various recipes to take into account finite K within the frame of the usual principal axis cranking are included into the comparison. A set of rules is suggested that permits to construct the excited bands from the cranking configurations, avoiding spurious states. 相似文献
99.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献
100.
The inhomogeneous Dirichlet problems concerning divergence form elliptic equations are studied. Optimal regularity requirements on the coefficients and domains for the W1,p theory, 1 < p < ∞, are obtained. The principal coefficients are supposed to be in the John‐Nirenberg space with small BMO seminorms. The domain is a Reifenberg domain. These conditions for the W1,p theory not only weaken the requirements on the coefficients but also lead to a more general geometric condition on the domains. In fact, these domains might have fractal dimensions. © 2004 Wiley Periodicals, Inc. 相似文献