全文获取类型
收费全文 | 4826篇 |
免费 | 546篇 |
国内免费 | 466篇 |
专业分类
化学 | 2481篇 |
晶体学 | 48篇 |
力学 | 114篇 |
综合类 | 22篇 |
数学 | 284篇 |
物理学 | 1614篇 |
综合类 | 1275篇 |
出版年
2024年 | 11篇 |
2023年 | 42篇 |
2022年 | 104篇 |
2021年 | 88篇 |
2020年 | 136篇 |
2019年 | 115篇 |
2018年 | 130篇 |
2017年 | 163篇 |
2016年 | 214篇 |
2015年 | 191篇 |
2014年 | 307篇 |
2013年 | 329篇 |
2012年 | 248篇 |
2011年 | 306篇 |
2010年 | 251篇 |
2009年 | 282篇 |
2008年 | 288篇 |
2007年 | 288篇 |
2006年 | 330篇 |
2005年 | 246篇 |
2004年 | 237篇 |
2003年 | 228篇 |
2002年 | 185篇 |
2001年 | 137篇 |
2000年 | 106篇 |
1999年 | 137篇 |
1998年 | 88篇 |
1997年 | 104篇 |
1996年 | 75篇 |
1995年 | 69篇 |
1994年 | 64篇 |
1993年 | 47篇 |
1992年 | 47篇 |
1991年 | 44篇 |
1990年 | 40篇 |
1989年 | 23篇 |
1988年 | 33篇 |
1987年 | 25篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 24篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有5838条查询结果,搜索用时 7 毫秒
21.
以贵州省黔南州ASTER和TM影像为数据源,运用IMAGINE ERDAS V9.1软件为主要支撑,介绍不同影像的几何校正和拼接的基本原理和方法,使数据处理和应用达到优化,为影像收集困难地区开展遥感调查及应用提供新途径。 相似文献
22.
O. Maksimov P. Fisher M. Skowronski P.A. Salvador M. Snyder J. Xu X. Weng 《Journal of Crystal Growth》2008,310(11):2760-2766
MgO films were grown on (0 0 1) yttria-stabilized zirconia (YSZ) substrates by molecular beam epitaxy (MBE). The crystalline structures of these films were investigated using X-ray diffraction and transmission electron microscopy. Growth temperature was varied from 350 to 550 °C, with crystalline quality being improved at higher temperatures. The MgO films had a domain structure: (1 1 1)[1 1 2¯]MgO(0 0 1)[1 0 0]YSZ with four twin variants related by a 90° in-plane rotation about the [1 1 1]MgO axis. The observed epitaxial orientation was compared to previous reports of films grown by pulsed laser deposition and sputtering and explained as resulting in the lowest interface energy. 相似文献
23.
Formulas for calculating the spectral characteristics of waveguide arrays, which are incorporated into waveguide spectrum analyzers based on planar waveguides, channel waveguides, and fiber optical waveguides, are derived taking into account the contribution of both the waveguide dispersion and the material dispersion to the dispersion factor. These formulas are used to study the dependence of the dispersion factor on the waveguide-system parameters for specific models of waveguide arrays. It is shown that consideration of contributions of the waveguide dispersion and material dispersion can affect profoundly the spectral characteristics of waveguide arrays. 相似文献
24.
《Tetrahedron letters》2003,44(40):7411-7415
The first total synthesis of two E type I phytoprostanes from furan, azelaic acid monomethyl ester and rac-1,2-epoxybutane is described. The key features of our synthetic strategy encompass an enzymatic kinetic resolution of a hydroxycyclopentenone, a Co-salen hydrolytic kinetic resolution of a terminal epoxide and a tandem conjugate addition/diastereoselective protonation sequence to construct the protected phytoprostanes. Mild cleavage of the silyl protective groups followed by enzymatic ester hydrolysis afforded the free E-type phytoprostanes. 相似文献
25.
《Magnetic resonance in chemistry : MRC》2003,41(2):139-142
Bioassay‐guided fractionation of the methanol extract of Odontadenia macrantha afforded a new limonoid, odontadenin A (1) and two known triterpenoids, lupeol (2) and α‐amyrin (3). The structure of 1 was established on the basis of 1D and 2D NMR and high‐resolution fast atom bombardment mass spectrometric data. The new compound was found to possess moderate cytotoxicity against A2780, the ovarian cancer cell line. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
26.
结合案例,从分辨率的角度对监控系统中人面像的可分辨程度进行了论述,并说明了数字监控系统中提取的人面像在公安工作中的利用价值。 相似文献
27.
It is experimentally demonstrated that the image resolution from an in-line Fraunhofer hologram degrades appreciably when the centre of the diffraction pattern from a 5-bar resolution target is located asymmetrically in the hologram aperture. This effect is confirmed and analysed using calculated and experimentally measured images from holograms of a one-dimensional wire. Increasing asymmetry results in an increasing error in the measured linewidth, and a reduction of image resolution. A simple model based on average fringe contrast is used to predict this decrease in resolution with transverse object position. 相似文献
28.
29.
用导数的方法,给出了多元多项式具有重因式、能因式分解的必要条件和操作步骤,以及判断方程是否为重根的充分条件。并且,提供了中学教学中常见的二次六项式能否进行因式分解的条件。 相似文献
30.