全文获取类型
收费全文 | 5770篇 |
免费 | 218篇 |
国内免费 | 58篇 |
专业分类
化学 | 3869篇 |
晶体学 | 41篇 |
力学 | 214篇 |
综合类 | 1篇 |
数学 | 547篇 |
物理学 | 1374篇 |
出版年
2022年 | 45篇 |
2021年 | 75篇 |
2020年 | 85篇 |
2019年 | 74篇 |
2018年 | 55篇 |
2017年 | 65篇 |
2016年 | 133篇 |
2015年 | 106篇 |
2014年 | 165篇 |
2013年 | 315篇 |
2012年 | 326篇 |
2011年 | 389篇 |
2010年 | 224篇 |
2009年 | 254篇 |
2008年 | 326篇 |
2007年 | 292篇 |
2006年 | 277篇 |
2005年 | 255篇 |
2004年 | 249篇 |
2003年 | 216篇 |
2002年 | 213篇 |
2001年 | 142篇 |
2000年 | 151篇 |
1999年 | 102篇 |
1998年 | 76篇 |
1997年 | 68篇 |
1996年 | 86篇 |
1995年 | 90篇 |
1994年 | 80篇 |
1993年 | 79篇 |
1992年 | 73篇 |
1991年 | 48篇 |
1990年 | 42篇 |
1989年 | 49篇 |
1988年 | 35篇 |
1987年 | 43篇 |
1986年 | 41篇 |
1985年 | 66篇 |
1984年 | 42篇 |
1983年 | 48篇 |
1982年 | 45篇 |
1981年 | 44篇 |
1980年 | 28篇 |
1979年 | 39篇 |
1978年 | 37篇 |
1977年 | 41篇 |
1976年 | 40篇 |
1975年 | 38篇 |
1974年 | 39篇 |
1973年 | 32篇 |
排序方式: 共有6046条查询结果,搜索用时 15 毫秒
31.
The chemometric calibration performance was systematically investigated by two parameters (changing the chemical matrix as well as the signal-to-noise ratio) of the NIR (near-infrared) spectrum. Three different analytes (hexane, cyclohexane, toluene) were selected and heptane was used as a solvent. The degree of spectral difference significantly affected the calibration performance. The largest structural difference between the analyte and the solvent provided the best calibration result for a given signal-to-noise ratio. Additionally, the signal-to-noise ratio of the spectra also directly influenced the calibration performance. Overall, the spectral difference and signal-to-noise ratio were the major factors for governing the chemometric calibration performance, especially in the low-concentration range. 相似文献
32.
Mitsunori Oda Yosuke Fukuchi Satoshi Ito Nguyen Chung Thanh Shigeyasu Kuroda 《Tetrahedron letters》2007,48(52):9159-9162
Reactions of pyrrolidine with 2 equiv of aldehydes without any catalyst in a pressurized vessel at 140–200 °C yielded 1,3-disubstituted pyrroles. -Branched aldehydes gave fairly good yields of the corresponding products by this method, which provides a facile non-oxidative procedure for synthesizing 1,3-dialkylpyrroles from inexpensive pyrrolidine and aldehydes. 相似文献
33.
34.
Hyun-Joo Kim Seog-Tae Han Jeong-Geun Kim Tai-Seong Kim Kwang-Dong Kim Chang-Hoon Lee Moon-Hee Chung Yong-Gi Kim 《International Journal of Infrared and Millimeter Waves》2002,23(1):135-147
The frequency tuning range of waveguide oscillator and its stability depend sensitively on the dimension of the resonance cap. Therefore the driving-point impedances with the various dimensions of the resonance cap are calculated by using HFSS(High Frequency Simulation System). In this paper the comparisons between theoretical results of the driving-point impedances as a function of frequency and that of experimental results are described. The oscillation frequency range could be predicted by using the theoretical evaluation methods which are proposed. It shows that resonance cap size and disc height have an effect on the frequency tuning characteristics of Gunn oscillator. 相似文献
35.
Tumor cells transduced with herpes simplex virus thymidine kinase gene have been intensively applied to the field of positron emission tomography via imaging of its substrate. As a pilot synthesis approach, a facile preparation of 5‐[125I] iodoarabinosyl uridine starting from commercially available uridine is reported herein. 相似文献
36.
The intensity dynamics of the double-clad Yb fibre laser have been characterised. Stabilisation of the fibre laser intensity by using uniform bi-directional pumping is demonstrated. For the single-end-pumped Yb fibre laser, the output becomes more stable for the shorter fibre length due to the higher threshold of stimulated Brillouin scattering, SBS, and Kerr effects and the reduction of saturated absorber effects caused by any unpumped fibre section. By additional pumping in a double-end-pumped configuration, the output power can be scaled higher before detecting high intensity pulses initiated by SBS in the Yb fibre laser due to the reduction of saturable absorption effect. It is confirmed that uniform pumping enhances the stability of the laser output. 相似文献
37.
38.
E.Y. Kang Yoon B. Kim K.Y. Kim Y.H. Chung H.K. Baik 《Journal of magnetism and magnetic materials》2006
FeSiBNb amorphous powder cores were prepared with the amorphous powder by gas atomization and subsequent hot pressing of resulting powder after creating oxide layers on the amorphous powder. Fully amorphous FeSiBNb powders with good soft magnetic properties were successfully obtained in the particle size range below 100 μm. FeSiBNb amorphous powder cores exhibit stable permeability up to 10 MHz, showing excellent high-frequency characteristics. 相似文献
39.
Hyeong Taek Ham Yeong Suk Choi Mu Guen Chee In Jae Chung 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):573-584
This work is to make carbon nanotubes dispersible in both water and organic solvents without oxidation and cutting nanotube threads. Polystyrene‐singlewall carbon nanotube (PS‐SWNT) composites were prepared with three different methods: miniemulsion polymerization, conventional emulsion polymerization, and mixing SWNT with PS latex. The two factors, crosslinking and surface coverage of PS are important factors for the mechanical and electrical properties, including dispersion states of SWNT in various solvents. The PS‐SWNT composite prepared via a conventional emulsion polymerization showed SWNT bundles entirely covered with PS, whereas the PS‐SWNT composite prepared via a miniemulsion polymerization showed SWNT partially covered with crosslinked PS nanoparticles. The method of mixing SWNTs with PS latex did not show the well dispersed state of carbon nanotubes because PS was not crosslinked and was dissolved in a solvent, and nanotubes separated from PS precipitated. So the PS nanoparticle‐SWNT composite had lower electrical resistance, and higher mechanical strength than the other composites made by the latter two methods. As the amount of SWNT increases, the bare surface area of SWNT increases and the electrical conductivity increases in the composite made by the miniemulsion polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 573–584, 2006 相似文献
40.
Anisha Gokarna Yong Hwan Kim Yong-Hoon Cho Min Su Lee In Cheol Kang Hyun Kyu Park Min Gon Kim Bong Hyun Chung 《Optical Review》2006,13(4):288-291
We demonstrate the fluorescence mapping of protein microarrays by the technique of scanning near-field optical microscopy
(SNOM) and confocal microscopy. Micron sized spots (300 μm) of human Immunoglobulin G (hIgG) protein with and without a Cy3
dye labeling have been fabricated on glass substrates by an immobilization method which makes use of calixcrown derivatives
termed Prolinker. We have also tried to probe into the well-known “doughnut effect” observed in fluorescence images of proteins
using the SNOM technique. The topographic and fluorescence SNOM images revealed that the number of proteins at the boundary
of the spot were more than at the center in the case of the microarray spot which showed brighter luminescence at the edge
than at the center in the confocal image. 相似文献