全文获取类型
收费全文 | 23354篇 |
免费 | 2937篇 |
国内免费 | 1976篇 |
专业分类
化学 | 11801篇 |
晶体学 | 220篇 |
力学 | 952篇 |
综合类 | 120篇 |
数学 | 1809篇 |
物理学 | 6025篇 |
综合类 | 7340篇 |
出版年
2024年 | 84篇 |
2023年 | 406篇 |
2022年 | 618篇 |
2021年 | 730篇 |
2020年 | 782篇 |
2019年 | 688篇 |
2018年 | 628篇 |
2017年 | 583篇 |
2016年 | 855篇 |
2015年 | 948篇 |
2014年 | 1247篇 |
2013年 | 1488篇 |
2012年 | 1702篇 |
2011年 | 1715篇 |
2010年 | 1216篇 |
2009年 | 1160篇 |
2008年 | 1403篇 |
2007年 | 1213篇 |
2006年 | 1140篇 |
2005年 | 964篇 |
2004年 | 775篇 |
2003年 | 677篇 |
2002年 | 658篇 |
2001年 | 546篇 |
2000年 | 494篇 |
1999年 | 666篇 |
1998年 | 562篇 |
1997年 | 570篇 |
1996年 | 578篇 |
1995年 | 471篇 |
1994年 | 421篇 |
1993年 | 351篇 |
1992年 | 291篇 |
1991年 | 276篇 |
1990年 | 263篇 |
1989年 | 222篇 |
1988年 | 204篇 |
1987年 | 124篇 |
1986年 | 107篇 |
1985年 | 72篇 |
1984年 | 49篇 |
1983年 | 35篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 24篇 |
1976年 | 15篇 |
1974年 | 17篇 |
1970年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
In this paper we discuss thermodynamics parameters of black hole horizon and cosmological horizon in general high-dimensional space-time. We obtain that the entropy of a cosmological horizon can be described by the Cardy-Verlinde formula. However, the entropy of black hole horizon will be expressed in a form of the Cardy-Verlinde formula, if one adopts the methods given by Abbott and Deser to compute the mass of a black hole in general high-dimensional space-time. Through discussion, relation among various thermodynamics parameters of the black hole in general high-dimensional space-time is given. That is, differential formula of the first law of thermodynamics is obtained. Because we discuss the general high-dimensional space-time, our result has universality.
PACS: 04.20.Dw, 97.60.Lf 相似文献
72.
建立一个描述低能电子在多元多层介质中散射的物理模型,运用MonteCarlo方法模拟低能电子在靶体胶衬底中的复杂散射过程,在此基础上通过大量计算研究入射束能、胶层厚度、衬底材料等不同曝光条件对抗蚀剂沉积能密度分布的影响,获得沉积能分布规律:适量的低束能、薄胶层、低原子序数衬底可以使前散射电子对胶中沉积能密度分布的贡献增大、背散射电子的贡献减小,从而提高曝光分辨率.
关键词:
电子束曝光
MonteCarlo方法
低能电子散射
能量沉积 相似文献
73.
Methods to synthesize magnetic Fe3O4 nanoparticles and to modify the surface of particles are presented in the present investigation. Fe3O4 magnetic nanoparticles were prepared by the co-precipitation of Fe3+ and Fe2+, NH3·H2O was used as the precipitating agent to adjust the pH value, and the aging of Fe3O4 magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe3O4 magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe3O4 crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe3O4 magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe3O4 nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe3O4 nanoparticles. The dispersion of Fe3O4 in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe3O4/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe3O4 magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe3O4 nanoparticles. The Fe3O4 magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10−8 and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe3O4 nanoparticles in the fluid was 36.19 nm. 相似文献
74.
75.
By optimizing pump power ratio between 1st order backward pump and 2nd order forward pump on discrete Raman amplifier, we demonstrated over 2dB noise figure improvement without excessive non-linearity degradation. 相似文献
76.
HaiHuiXIE XiaoYiWEI JiDongWANG MeiFangLIU RenZhouYANG 《中国化学快报》2003,14(6):588-590
A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines. 相似文献
77.
Tunable microlens arrays using polymer network liquid crystal 总被引:1,自引:0,他引:1
A tunable-focus microlens array based on polymer network liquid crystal (PNLC) is demonstrated. The PNLC was prepared using an ultraviolet (UV) light exposure through a patterned photomask. The photocurable monomer in each of the UV exposed spot forms an inhomogeneous centro-symmetrical polymer network which acts as a lens when a homogeneous electric field is applied to the cell. The focal length of the microlens arrays is tunable with the applied voltage. 相似文献
78.
Simple Entanglement Measure for Multipartite Pure States 总被引:3,自引:0,他引:3
Feng Pan Feng Pan Feng Pan Dan Liu Guoying Lu J. P. Draayer 《International Journal of Theoretical Physics》2004,43(5):1241-1247
A simple entanglement measure for multipartite pure states is formulated based on the partial entropy of a series of reduced density matrices. Use of the proposed new measure to distinguish disentangled, partially entangled, and maximally entangled multipartite pure states is illustrated. 相似文献
79.
本文使用变分方法证明了三维标准切触球的标准勒让德扭结,至少存在一个弦连结适应于标准切触结构的任何选定切触形式,这部分证明了著名的阿诺德弦猜想。 相似文献
80.
The SmF_(2.01)was synthesized by reducing SmF_3 in H_2 stream.As it was doped inKM_gF_3 and KCaF_3.there was emission of Sm~(2+) in KMgF_3 but no emission of Sm~(2+) inKCaF_3 was observed. 相似文献