全文获取类型
收费全文 | 7967篇 |
免费 | 1341篇 |
国内免费 | 330篇 |
专业分类
化学 | 1092篇 |
晶体学 | 54篇 |
力学 | 177篇 |
综合类 | 38篇 |
数学 | 406篇 |
物理学 | 2588篇 |
无线电 | 5283篇 |
出版年
2024年 | 28篇 |
2023年 | 97篇 |
2022年 | 170篇 |
2021年 | 210篇 |
2020年 | 273篇 |
2019年 | 188篇 |
2018年 | 189篇 |
2017年 | 289篇 |
2016年 | 329篇 |
2015年 | 380篇 |
2014年 | 640篇 |
2013年 | 648篇 |
2012年 | 620篇 |
2011年 | 588篇 |
2010年 | 479篇 |
2009年 | 465篇 |
2008年 | 468篇 |
2007年 | 496篇 |
2006年 | 421篇 |
2005年 | 386篇 |
2004年 | 359篇 |
2003年 | 296篇 |
2002年 | 239篇 |
2001年 | 215篇 |
2000年 | 190篇 |
1999年 | 166篇 |
1998年 | 147篇 |
1997年 | 111篇 |
1996年 | 123篇 |
1995年 | 92篇 |
1994年 | 67篇 |
1993年 | 65篇 |
1992年 | 42篇 |
1991年 | 39篇 |
1990年 | 24篇 |
1989年 | 37篇 |
1988年 | 14篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有9638条查询结果,搜索用时 15 毫秒
81.
采用MOCVD技术在Al2O3(0001)衬底上生长了GaN薄膜,使用透射光谱、光致发光光谱和X射线双晶衍射三种技术测试了五类GaN薄膜样品,实验结果表明:GaN薄膜透射谱反映出的GaN质量与X射线双晶衍射测量的结果一致,即透射率越大,半高宽越小,结晶质量越好;而X射线双晶衍射峰半高宽最小的样品,其PL谱的带边峰却很弱,这说明PL谱反映样品的光学性能与X射线双晶衍射获得的结晶质量不存在简单的对应关系,同时还报导了一种特殊工艺生长的高阻GaN样品的RBS/沟道结果。 相似文献
82.
Tzong‐Ming Wu Shih‐Hsiang Lin 《Journal of polymer science. Part A, Polymer chemistry》2006,44(21):6449-6457
Size‐controllable polypyrrole (PPy)/multiwalled carbon nanotube (MWCNT) composites have been synthesized by in situ chemical oxidation polymerization directed by various concentrations of cationic surfactant cetyltrimethylammonium bromide (CTAB). Raman spectra, FTIR, SEM, and TEM were used to characterize their structure and morphology. These results showed that the composites are core (MWCNT)–shell (PPy) tubular structures with the thickness of the PPy layer in the range of 20–40 nm, depending on the concentration of CTAB. Raman and FTIR spectra of the composites are almost identical to those of PPy alone. The electrical conductivities of these composites are 1–2 orders of magnitude higher than those of PPy without MWCNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6449–6457, 2006 相似文献
83.
《Surface and interface analysis : SIA》2006,38(1):19-24
We have been developing a new analytical transmission electron microscope (TEM), called a coincidence TEM, which in principle enables elemental mapping images to be observed at a high signal‐to‐noise (S/N) ratio under very low dose radiation conditions. In this paper, we report the development of a coincidence TEM with a digital waveform measuring system for obtaining a coincidence elemental mapping image. In this system, analog signals detected by a Si(Li) detector and a multianode, position‐sensitive photomultiplier (PSPM) are continuously converted into 12‐bit digital waveform data at a rate of 100 MHz, and transferred to a PC. From the transferred digital waveform data, information on X‐ray photon energy, electron incident position, and detection times of both X rays and electrons are calculated by digital waveform measurement, which lead to the observation of a successful coincidence elemental mapping image. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
84.
Yang Jing Wen Xiang Lin Yang 《International Journal of Infrared and Millimeter Waves》1998,19(7):963-975
The modified quantum nonlinear Schrodinger equation of ultra-short pulse propagating in fiber is derived using dispersion relation and the Hamiltonian of the transmission system. The derived equation is solved with linearization approximation, and modulation instability is analyzed. The equation is also solved with Hartree approximation. The results indicate that pulse power, loss and self-steeping effect change the critical frequency, the maximum gain and the gain spectrum range, but the third order dispersion has no effect on modulation instability. The expectation value of optical field is average of a set of modified classical solitons, and higher order terms change the amplitude, pulse position and phase of soliton. 相似文献
85.
The microstructure of InxGa1−xAs/GaAs (5 nm/5 nm, x < 0 to 1.0), as grown by a metalorganic chemical vapor deposition two-step growth technique on Si(100)
at 450‡C, and subsequently annealed at 750‡C, is investigated using plan-view and cross-sectional transmission electron microscopy.
The variations in resultant island morphology and strain as a function of the In content were examined through the comparison
of the misfit dislocation arrays and moirés observed. The results are discussed in relation to the ways in which the island
relaxation process changes for high In content. 相似文献
86.
87.
88.
89.
我国法定可使用的合成食用色素主要有5种。即苋菜红、胭脂红、柠檬黄、日落黄和亮蓝。根据调色需要,它们常被混合配置应用.目前一般采用高效液相色谱和层析分离法分析,但尚缺少可靠的同时测定此5组分的化学计量学方法,Loosbroek曾用卡尔曼滤波光度法鉴 相似文献
90.