全文获取类型
收费全文 | 21508篇 |
免费 | 3911篇 |
国内免费 | 2573篇 |
专业分类
化学 | 15497篇 |
晶体学 | 221篇 |
力学 | 1504篇 |
综合类 | 179篇 |
数学 | 2447篇 |
物理学 | 8144篇 |
出版年
2024年 | 50篇 |
2023年 | 430篇 |
2022年 | 613篇 |
2021年 | 795篇 |
2020年 | 925篇 |
2019年 | 935篇 |
2018年 | 777篇 |
2017年 | 753篇 |
2016年 | 1066篇 |
2015年 | 1041篇 |
2014年 | 1203篇 |
2013年 | 1621篇 |
2012年 | 1937篇 |
2011年 | 2022篇 |
2010年 | 1411篇 |
2009年 | 1257篇 |
2008年 | 1474篇 |
2007年 | 1244篇 |
2006年 | 1174篇 |
2005年 | 918篇 |
2004年 | 723篇 |
2003年 | 640篇 |
2002年 | 651篇 |
2001年 | 579篇 |
2000年 | 443篇 |
1999年 | 491篇 |
1998年 | 383篇 |
1997年 | 332篇 |
1996年 | 323篇 |
1995年 | 258篇 |
1994年 | 227篇 |
1993年 | 228篇 |
1992年 | 180篇 |
1991年 | 162篇 |
1990年 | 153篇 |
1989年 | 128篇 |
1988年 | 84篇 |
1987年 | 65篇 |
1986年 | 62篇 |
1985年 | 47篇 |
1984年 | 36篇 |
1983年 | 35篇 |
1982年 | 30篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1979年 | 6篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1973年 | 7篇 |
1972年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Yi Jiang Chuan-Lei Jia Xue-Lin Wang Ke-Ming Wang Hong-Ji Ma 《Applied Surface Science》2006,253(5):2674-2677
A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 × 1015 ions/cm2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change. 相似文献
62.
Hong-Nian Li Xiao-Xiong WangWang-Feng Ding 《Journal of Electron Spectroscopy and Related Phenomena》2006
Using X-ray photoemission measurements, we have determined the attenuation length of C 1s photoelectrons in C60 film to be 21.5 Å with the incident photon energy of Mg Kα radiation. The inelastic mean free path calculated with the TPP-2M algorithm coincides fairly well with the experimentally determined attenuation length, indicating the validity of the algorithm to fullerene and fullerides. The inelastic mean free paths for some fullerides, i.e. K3C60, K6C60, Ba4C60, Sm2.75C60 and Sm6C60 are calculated to help the quantitative analyses of the photoemission spectra for these compounds. 相似文献
63.
新型X射线靶设计为:由SiO2和TiO2组成具有12个周期的一维光子晶体,在它的中间嵌入光靶材料层作为缺陷层,SiO2,TiO2和光靶层的光学厚度分别为λ4、λ4和λ2,λ为抽运激光波长.与普通平板光靶相比,当抽运光垂直照射到这种光靶时,靶层内部的光强将提高2个数量级,所以抽运激光的阈值强度将降低2个数量级,这有利于X射线激光的小型化.在同样的抽运激光照射下,X射线激光的强度将提高4个数量级,转换效率也将提高约4个数量级.由于平均电离度随抽运激光强度的提高而提高,所以采用这种光靶有利于使X射线激光向短波长推进.
关键词:
X射线激光
光子晶体
光波局域 相似文献
64.
Jie Xue Liang Chen Li Zhou Zhifeng Jia Yanping Wang Xinyuan Zhu Deyue Yan 《Journal of Polymer Science.Polymer Physics》2006,44(15):2050-2057
α‐Cyclodextrin (α‐CD) has been complexed with various poly(ethylene glycol) (PEG) derivatives in aqueous solution. It has been found that the end groups of PEG derivatives affect the complexation kinetics greatly, but have only a little influence on the thermodynamic behavior. By increasing the hydrophobicity of end groups, the complexation speeds up rapidly. On the other hand, the bulky end groups slow down the threading of polymeric guests into the cavity of CD. By changing the hydrophobicity and the size of end groups, the complexation rate can be adjusted in the range of several orders of magnitudes, which should be quite useful in the design of new supramolecular systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2050–2057, 2006 相似文献
65.
The nanocrystal samples of titanium dioxide doped with europium ion (Eu3+/TiO2 nanocrystal) are synthesized by the sol-gel method with hydrothermal treatment. The Eu3+ contents (molar ratio) in the samples are 0, 0.5%, 1%, 2%, 3% and 4%. The X-ray diffraction, UV-Vis spectroscopy data and scanning electron microscope image show that crystallite size is reduced by the doping of Eu3+ into TiO2. Comparing the Raman spectra of TiO2 with Eu3+/TiO2 (molar ratio Eu3+/TiO2=1%, 2% and 4%) nanocrystals at different annealing temperatures indicates that the anatase-to-rutile phase transformation temperatures of Eu3+/TiO2 nanocrystals are higher than that of TiO2. This is due to the formation of Eu-O-Ti bonds on the surface of the TiO2 crystallite, as characterized by the X-ray photoelectron spectroscopy. The photoluminescence spectra of TiO2 in Eu3+/TiO2 nanocrystals are interpreted by the surface self-trapped and defect-trapped exciton relaxation. The photoluminescence of Eu3+ in Eu3+/TiO2 nanocrystals has the strongest emission intensity at 2% of Eu3+ concentration. 相似文献
66.
External difference families (EDFs) are a type of new combinatorial designs originated from cryptography. In this paper, some
earlier ideas of recursive and cyclotomic constructions of combinatorial designs are extended, and a number of classes of
EDFs and disjoint difference families are presented. A link between a subclass of EDFs and a special type of (almost) difference
sets is set up. 相似文献
67.
Improving Construction for Connected Dominating Set with Steiner Tree in Wireless Sensor Networks 总被引:2,自引:0,他引:2
Manki Min Hongwei Du Xiaohua Jia Christina Xiao Huang Scott C.-H. Huang Weili Wu 《Journal of Global Optimization》2006,35(1):111-119
The connected dominating set plays an important role in ad hoc wireless networking. Many constructions for approximating the minimum connected dominating set have been proposed in the
literature. In this paper, we propose a new one with Steiner tree, which produces approximation solution within a factor of
6.8 from optimal. This approximation algorithm can also be implemented distributedly. 相似文献
68.
Yiming Huai Mahendra PakalaZhitao Diao Dmytro ApalkovYunfei Ding Alex Panchula 《Journal of magnetism and magnetic materials》2006
Spin-transfer driven switching was observed in MgO based magnetic tunnelling junctions (MTJ) with tunnelling magnetoresistance ratio of up to 160% and the average intrinsic switching current density (Jc0) down to 2 MA/cm2, which are the best known results reported in spin-transfer switched MTJ nanostructures. Based on a comparison of results both from MgO and AlOx MTJs, further switching current decrease via MgO dual structures with two pinned layers is discussed. 相似文献
69.
Baoqiang Li Dechang Jia Yu Zhou Qiaoling Hu Wei Cai 《Journal of magnetism and magnetic materials》2006
Chitosan/magnetite nanocomposite was synthesized induced by magnetic field via in situ hybridization in ambient condition. Results of XRD patterns and TEM micrographs indicated that magnetite particles with 10–20 nm were dispersed in chitosan homogeneously. An interesting result is that magnetite nanoparticles were assembled to form chain-like structures under the influence of the external magnetic field, which mimics the magnetite chains inside of magnetotatic bacteria. The saturated magnetization (Ms) of nano-magnetite in chitosan was 50.54 emu/g, which is as high as 54% of bulk magnetite. The remanence (Mr) and coercivity (Hc) were 4 emu/g and14.8 Oe, respectively, which indicated that magnetite nanoparticles were superparamagnetic. The key of route is that a pre-precipitated chitosan hydrogel membrane, used as chemical reactor, which controlled the precipitation of chitosan precipitation and in situ transformation of magnetite from the precursor simultaneously in the magnetic field environment. 相似文献
70.
We measure and calculate the aerial image modulation (AIM) of human retina for visible wavelengths based on the individual eye model. By employing the optical design software ZEMAX, we obtain the modulation transfer function (MTF) of human eye in visible wavelengths. Using CSV-1000 and VAF-1000, the contrast sensitivity function (CSF) and the visual acuity (VA) for the same eye are measured. Then the AIM of human retina could be acquired by the relations between MTF and CSF and between MTF and VA. The AIM of human retina is independent of MTF, and the values of AIM for normal eyes (without retina disease) are similar, so the assembly average for large numbers of normal eyes can be a standard AIM curve, which is helpful for the diagnosis of diseases in the retina system. 相似文献