全文获取类型
收费全文 | 701篇 |
免费 | 34篇 |
国内免费 | 341篇 |
学科分类
数理化 | 1076篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 16篇 |
2012年 | 19篇 |
2011年 | 114篇 |
2010年 | 26篇 |
2009年 | 66篇 |
2008年 | 27篇 |
2007年 | 25篇 |
2006年 | 27篇 |
2005年 | 31篇 |
2004年 | 87篇 |
2003年 | 43篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 24篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 18篇 |
1994年 | 20篇 |
1993年 | 35篇 |
1992年 | 62篇 |
1991年 | 74篇 |
1990年 | 63篇 |
1989年 | 62篇 |
1988年 | 5篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1076条查询结果,搜索用时 15 毫秒
81.
An asymmetric metamaterial exhibiting an analog of double electromagnetically induced transparency(EIT) in the middle-infrared region is reported.The metamaterial consists of two-layered arrays of Ushaped rings embedded in a medium,with the lower layer rotated by 90°.Our simulations demonstrate that both maximum group indexes are extremely high at the two EIT-like positions.The group index reaches about thrice the currently reported maximum value at the high-frequency EIT-like position.The transmittance at the two transparency positions also possesses extremely high Q factors,which is conducive to controlling the propagation of electromagnetic waves. 相似文献
82.
LI Jing SHANG Yan-mei XIAO Chuan SONG Zhi-guang LI Ye-zhi HUANG Hua-min .College of Chemistry Jilin University .School of Public Health Changchun P.R.China .Key Laboratory for Supramolecular Structure Materials of Ministry of Education Changchun 《高等学校化学研究》2009,25(1)
(R)-4-Hydroxymethyl-2-thioxo thiazolidine as a new chiral catalyst in the asymmetric addition of diethyl-zinc to benzaldehyde was synthesized from (R)-4-hydroxymethyl-2-thioxo thiazolidine carboxylic acid and its crystal structure was determined by X-ray diffraction method. The compound was crystallized in the orthorhombic system, space group P212121 with unit cell dimensions a=0.67253(12) nm; b=0.89164(17) rim; c=1.06146(19) nm, volume 0.6365(2) nm3; Z=4, calculated denisity 1.557 Mg/m3; absorption coefficient 0.733 mm-1; F(000)=312. The X-ray crystal structure analysis reveals that the compound has a thione group. 相似文献
83.
The enlargement of the emitting aperture is usually one of the important methods of increasing vertical- cavity surface-emitting laser (VCSEL) optical output power. However, in a VCSEL with a larger aperture, the inhomogeneity in the injected current often causes inhomogeneous or even no emission. To solve this problem and to increase VCSEL output power, as well as to improve its thermal characteristics, we develop a new type of injected VCSEL with a larger aperture and a reticular electrode, where the conventional circular injection electrode of the P side is turned into a reticular one, and the heat sink is on the N side. The tests of the new VCSEL show an improvement in homogeneity in not only the injected current but also the emission intensity. The optical output power is also considerably increased, and the device optoelectronic performance is improved. 相似文献
84.
85.
86.
SHEN Zhen-wei JIN Hong-tao LI Chang CONG Yan-zhao NAN Wen-long BAI Liang JIN Ning-yi . College of Animal Science Veterinary Medicine Jilin University Changchun P. R. China . Genetic Engineering Laboratory Academy of Military Medical Sciences 《高等学校化学研究》2009,25(3)
Designing adjuvants that can induce strong cytotoxic T cell responses is largely required for preparing DNA vaccines. In this study we explored dual costimulatory molecules 4-1BBL and OX40L as adjuvants to improve the efficiency of the HIV multiple-epitope DNA vaccine. When explored in the human dendritic cell-T cell based coculture system,dual costimulatory molecules significantly enhanced the anti-HIV T cell response of the HIV mul-tiple-epitope DNA vaccine,as detected by intracellular cytokine staining t... 相似文献
87.
CHEN ShengBo & SONG JinHong College of Geoexploration Science Technology Jilin University Changchun China College of Resources Environment Jilin Agricultural University Changchun 《中国科学:物理学 力学 天文学(英文版)》2011,(8)
Atmospheric temperature-humidity profiles and land or sea surface temperature are coupled actions in the earth system process. Based on the numerical perturbation form of the atmospheric radiative transfer equation, a physics-based algorithm is pre- sented to integrate four pairs of MODIS measurements from the Terra and Aqua satellites to retrieve simultaneously atmospheric temperature-humidity profile, land-surface temperature and emissivity. Three pairs of MODIS data at two field sites in China, Luancheng... 相似文献
88.
Zhi-zhuang Joe 《高等学校化学研究》2011,(3):474-477
PTPRU is an MAM domain-containing receptor-like protein tyrosine phosphatase. Previous studies have demonstrated an important role of the enzyme in the maintenance of epithelial integrity and in the regulation of the Wnt/β-catenin signaling pathway. To better understand the function of PTPRU, we cloned and expressed the intracellular portion of PTPRU as a GST fusion protein in E. coli cells. We purified the protein to homogeneity and used it to immunize mice for antibody production. The resultant antibody s... 相似文献
89.
ZHAO Hai-feng WU Lei LU Ming HU Yu-lin HAN Xiao LI Zheng-qiang . Key Laboratory for Molecular Enzymology & Engineering Ministry of Education Jilin University Changchun P. R. China . Medical 《高等学校化学研究》2011,(3):450-454
Lipid-bound [VHb(406)] and lipid-free [VHb(402)] wide type Vitreoscilla hemoglobin were separated from E. coli BL21(DE3). The RZ is 3.30 for [VHb(406)] and 3.15 for [VHb(402)], respectively. VHb(406) shows a characteristic absorption band at 626 nm, while VHb(402) shows one at 644 nm, and it has more α-helix than VHb(402). Data of Raman spectra experiment shows under the excitation wavelength 488 nm, υ4 vibration of both VHb(402) and VHb(406) had a pure and strong signal at 1375 cm-1, which proves that iron... 相似文献
90.
HU Fang ZHANG Chun-hua ZHANG Song MING Xing CHEN Gang WEI Ying-jin WANG Chun-zhong . School of Materials Science Engineering Shenyang University of Technology Shenyang P. R. China . College of Physics State Key Laboratory of Superhard Materials Jilin University Changchun . College of Physical Science Technology Huanggang Normal University Huanggang 《高等学校化学研究》2011,(3):528-530
1 Introduction Low-dimensional nanostructures, such as nanorods, nanowires, and nanotubes, have received much attention for their superior optical, electrical, catalytic and magnetic properties. 相似文献