全文获取类型
收费全文 | 6455篇 |
免费 | 1090篇 |
国内免费 | 1730篇 |
专业分类
化学 | 5053篇 |
晶体学 | 197篇 |
力学 | 346篇 |
综合类 | 155篇 |
数学 | 782篇 |
物理学 | 2742篇 |
出版年
2024年 | 13篇 |
2023年 | 83篇 |
2022年 | 208篇 |
2021年 | 195篇 |
2020年 | 224篇 |
2019年 | 260篇 |
2018年 | 218篇 |
2017年 | 239篇 |
2016年 | 226篇 |
2015年 | 283篇 |
2014年 | 367篇 |
2013年 | 490篇 |
2012年 | 507篇 |
2011年 | 547篇 |
2010年 | 517篇 |
2009年 | 520篇 |
2008年 | 570篇 |
2007年 | 512篇 |
2006年 | 447篇 |
2005年 | 463篇 |
2004年 | 317篇 |
2003年 | 259篇 |
2002年 | 253篇 |
2001年 | 254篇 |
2000年 | 266篇 |
1999年 | 147篇 |
1998年 | 88篇 |
1997年 | 69篇 |
1996年 | 73篇 |
1995年 | 61篇 |
1994年 | 63篇 |
1993年 | 55篇 |
1992年 | 61篇 |
1991年 | 40篇 |
1990年 | 50篇 |
1989年 | 51篇 |
1988年 | 41篇 |
1987年 | 43篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1966年 | 5篇 |
1965年 | 4篇 |
1959年 | 3篇 |
排序方式: 共有9275条查询结果,搜索用时 328 毫秒
21.
Zhihui Zhao Hui Dai Xiangmei Wu Haitao Chang Xiaoming Gao Mengjun Liu Pengfei Tu 《Chemistry of Natural Compounds》2007,43(4):374-376
A pectic polysaccharide was isolated from the fruits of Ziziphus jujuba Mill. cv. jinsixiaozao Hort. and its structure was characterized by acid hydrolysis, methylation, and NMR spectroscopies.
The purified fraction Ju-B-7 had a molecular mass of over 2000 kDa. Chemical and spectroscopic analyses indicated that Ju-B-7
is composed mainly of α-1,4-linked D-galactopyranosyluronic acid and 1,2-linked L-rhamnose with a molar ratio of 8.1:1. It can significantly stimulate
spleen cell proliferation in vitro (P<0.01, 10 μmg/mL).
Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 311–312, July–August, 2007. 相似文献
22.
抓好数学建模竞赛 推动数学教学改革 总被引:5,自引:0,他引:5
本文通过近几年组织数学建模教学和指导学生参加竞赛的实践 ,探索抓好数学建模竞赛 ,促进数学教学改革 ,推动数学素质教育 ,提高人才培养质量的途径、措施和方法 相似文献
23.
Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in the computer code CFX4.4 is further developed to accommodate the wall nucleation at the heated wall and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Additional comparison using empirical relationships for the active nucelation site density and local bubble diameter is also investigated. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress to circumvent the deficiency through the consideration of additional momentum equations or developing an algebraic slip model to account for bubble separation. 相似文献
24.
This article proves the existence of singular directions of value distribution theory for some transcendental holomorphic curves in the n-dimensional complex projective space Pn(C). An example is given to complement these results. 相似文献
25.
26.
相位差与q变形广义相干叠加态的压缩特性 总被引:1,自引:0,他引:1
对于q变形的非简谐振子广义相干态的叠加态β〉+eiφβeiδ〉,其量子涨落的可能高阶压缩阶数可以表示为k≠2πn/δ,这里n是整数.当δ=π时,压缩阶数不能是偶数即只能是奇数,这正是q变形非简谐振子广义奇偶相干态的结果.由此表明参数相位差δ对决定q变形的非简谐振子广义相干态叠加态的高阶压缩阶数起决定性作用. 相似文献
27.
The implementation of a nonzero-order joint transform correlator using the double port Mach-Zehnder interferometric technique is proposed and demonstrated. This approach provides on-line processing for directly removing the zero-order components of a joint power spectrum in one step and performs the nonzero-order optical correlation. Experimental results are presented and discussed. 相似文献
28.
Influence of Yb-Doped Nanoporous TiO2 Films on Photovoltaic Performance of Dye-Sensitized Solar Cells 下载免费PDF全文
Yb-doped TiO2 pastes with different Yb/TiO2 weight ratios are prepared in the sol-gel process to obtain dyesensitized solar cells (DSCs). The nanocrystalline size of Yb-TiO2 becomes smaller and the lattice parameters change. Lattice distortion is observed and dark current is detected. It is found that a part of Yb existing as insulating oxide Yb2O3 state acts as barrier layers at the electrode-electrolyte interface to suppress charge recombination. A Yb-doped TiO2 electrode applied in DSCs leads to a higher open-circuit voltage and a higher fill factor. How the Yb-doped TiO2 films affect the photovoltaic response of DSCs is discussed. 相似文献
29.
This work proposes and demonstrates the feasibility of gray image encryption using multiple polarization encoding, in which
the cascaded twisted nematic liquid crystal devices sandwiched between a crossed polarizer pair are used to implement exclusive
OR (XOR) logical encryption and decryption. The polarization encoding scheme provides a multichannel XOR logic operation to
secure bit-plane images derived from a gray image, according to the adiabatic following properties of twisted nematic liquid
crystal devices. Experimental data reveal that the multiple polarization encoding schemes for gray image encryption and decryption
are performed with acceptable image quality by selecting appropriate polarization orientation and modulation conditions. Both
analytic and experimental results are presented and discussed. 相似文献
30.
中西医治疗子宫内膜异位症性不孕的现状 总被引:3,自引:0,他引:3
本文综述了近年来现代医学及祖国传统医学对子宫内膜异位症(EMT)导致不孕的发病机理及治疗方面进展的概况。 相似文献