全文获取类型
收费全文 | 1841篇 |
免费 | 314篇 |
国内免费 | 200篇 |
专业分类
化学 | 1351篇 |
晶体学 | 20篇 |
力学 | 99篇 |
综合类 | 14篇 |
数学 | 157篇 |
物理学 | 714篇 |
出版年
2024年 | 2篇 |
2023年 | 48篇 |
2022年 | 45篇 |
2021年 | 63篇 |
2020年 | 98篇 |
2019年 | 89篇 |
2018年 | 61篇 |
2017年 | 54篇 |
2016年 | 88篇 |
2015年 | 94篇 |
2014年 | 85篇 |
2013年 | 115篇 |
2012年 | 132篇 |
2011年 | 172篇 |
2010年 | 117篇 |
2009年 | 118篇 |
2008年 | 129篇 |
2007年 | 110篇 |
2006年 | 122篇 |
2005年 | 102篇 |
2004年 | 63篇 |
2003年 | 53篇 |
2002年 | 48篇 |
2001年 | 52篇 |
2000年 | 39篇 |
1999年 | 42篇 |
1998年 | 31篇 |
1997年 | 26篇 |
1996年 | 34篇 |
1995年 | 22篇 |
1994年 | 30篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1982年 | 1篇 |
排序方式: 共有2355条查询结果,搜索用时 15 毫秒
201.
202.
203.
The leakage current behaviours of polycrystalline BiFeO3 thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeO3 films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO3 films. 相似文献
204.
The resolution of electron energy loss spectroscopy (EELS) is limited by delocalization of inelastic electron scattering rather than probe size in an aberration corrected scanning transmission electron microscope (STEM). In this study, we present an experimental quantification of EELS spatial resolution using chemically modulated 2×(LaMnO(3))/2×(SrTiO(3)) and 2×(SrVO(3))/2×(SrTiO(3)) superlattices by measuring the full width at half maxima (FWHM) of integrated Ti M(2,3), Ti L(2,3), V L(2,3), Mn L(2,3), La N(4,5), La N(2,3) La M(4,5) and Sr L(3) edges over the superlattices. The EELS signals recorded using large collection angles are peaked at atomic columns. The FWHM of the EELS profile, obtained by curve-fitting, reveals a systematic trend with the energy loss for the Ti, V, and Mn edges. However, the experimental FWHM of the Sr and La edges deviates significantly from the observed experimental tendency. 相似文献
205.
反式乙烯基联吡啶表面增强拉曼光谱的密度泛函理论研究 总被引:1,自引:0,他引:1
反式乙烯基联吡啶具有极好的拉曼散射信号,经常用做探针分子.利用密度泛函理论(DFT)理论,采用BP86,BPw91和B3LYP等方法,Ag原子使用赝式基组,H,C,N等原子使用6-31+ +G(d,p)基组,计算了反式乙烯基联吡啶与银配合物(t-BPE-Ag)的Raman光谱,并且利用势能分布(PED)计算结果对t-BPE分子Raman光谱和SERS谱进行了详细的归属,DFT理论得到结果说明根据DFT理论计算t-BPE-Ag配合物得到的Raman光谱与实验SERS谱基本一致,并且键连Ag原子越多,与实验值会更接近,t-BPE-Ag配合物HOMO与LUMO的能级差估计在449~912 nm范围内. 相似文献
206.
使用低、高温两步法生长的高质量Ge薄膜作为缓冲层,在Si(001)衬底上采用分子束外延法生长出Ge0.975Sn0.025合金薄膜.X射线双晶衍射和卢瑟福背散射谱等测试结果表明,Ge0.975Sn0.025合金薄膜具有很好的晶体质量,并且没有发生Sn表面分凝.另外,Ge0.975Sn0.025合金薄膜在500 ℃下具有很好的热稳定性,有望在Si基光电器件中得到应用.
关键词:
GeSn
Ge
分子束外延
外延生长 相似文献
207.
The silk fibroin (SF) nanofiber mats with good water resistance and mechanical property were directly prepared by adding crosslinker
1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) into the electrospin solution. The effect of EDC on the morphology, structure
and physical properties of SF nanofiber mats was analyzed. With the addition of EDC, the average fiber diameter increased
from 262 to 635 nm. The results from FTIR, TG-DTA and X-ray diffraction showed that EDC induced the structural transition
from random coil to β-sheet conformation. Furthermore, the solubility and mechanical properties of SF nanofiber mats were
obviously improved when the crosslinker EDC was used. 相似文献
208.
考察了有向圈或圈并的r级合成图,分别确定了它们的所有圈长和圈数;用图论方法完全刻画了置换矩阵的组合合成。 相似文献
209.
Yue Hu Xiao‐Dong Li Guo‐Yu Li Ning Li Wen‐Jian Zuo Yi‐Mei Zeng He Meng Xian Li Jin‐Hui Wang 《Helvetica chimica acta》2010,93(5):1019-1024
Two new sesquiterpenoids, ferulactones A and B ( 1 and 2 , resp.), have been isolated from the roots of Ferula ferulaeoides (Steud.) Korov . Their structures and relative configurations were established by analysis of spectroscopic data. Their absolute configuration was assigned by application of the CD technique. 相似文献
210.
Yimin Mao Feng Zuo Jong Kahk Keum Benjamin S. Hsiao Derek W. Thurman Andy H. Tsou 《Journal of Polymer Science.Polymer Physics》2010,48(1):26-32
The crystallization behavior of isotactic propylene‐1‐hexene (PH) random copolymer having 5.7% mole fraction of hexene content was investigated using simultaneous time‐resolved small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques. For this copolymer, the hexene component cannot be incorporated into the unit cell structure of isotactic polypropylene (iPP). Only α‐phase crystal form of iPP was observed when samples were melt crystallized at temperatures of 40 °C, 60 °C, 80 °C, and 100 °C. Comprehensive analysis of SAXS and WAXD profiles indicated that the crystalline morphology is correlated with crystallization temperature. At high temperatures (e.g., 100 °C) the dominant morphology is the lamellar structure; while at low temperatures (e.g., 40 °C) only highly disordered small crystal blocks can be formed. These morphologies are kinetically controlled. Under a small degree of supercooling (the corresponding iPP crystallization rate is slow), a segmental segregation between iPP and hexene components probably takes place, leading to the formation of iPP lamellar crystals with a higher degree of order. In contrast, under a large degree of supercooling (the corresponding iPP crystallization rate is fast), defective small crystal blocks are favored due to the large thermodynamic driving force and low chain mobility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 26–32, 2010 相似文献