全文获取类型
收费全文 | 118260篇 |
免费 | 21570篇 |
国内免费 | 30575篇 |
专业分类
化学 | 85614篇 |
晶体学 | 3564篇 |
力学 | 8181篇 |
综合类 | 3138篇 |
数学 | 16945篇 |
物理学 | 52963篇 |
出版年
2024年 | 343篇 |
2023年 | 1669篇 |
2022年 | 4215篇 |
2021年 | 4200篇 |
2020年 | 4303篇 |
2019年 | 4120篇 |
2018年 | 3784篇 |
2017年 | 4835篇 |
2016年 | 4663篇 |
2015年 | 5835篇 |
2014年 | 7005篇 |
2013年 | 9189篇 |
2012年 | 10042篇 |
2011年 | 10616篇 |
2010年 | 9185篇 |
2009年 | 9226篇 |
2008年 | 10294篇 |
2007年 | 9253篇 |
2006年 | 8962篇 |
2005年 | 7618篇 |
2004年 | 5912篇 |
2003年 | 4435篇 |
2002年 | 4405篇 |
2001年 | 4239篇 |
2000年 | 4126篇 |
1999年 | 2799篇 |
1998年 | 1672篇 |
1997年 | 1467篇 |
1996年 | 1462篇 |
1995年 | 1267篇 |
1994年 | 1290篇 |
1993年 | 1152篇 |
1992年 | 1019篇 |
1991年 | 746篇 |
1990年 | 692篇 |
1989年 | 695篇 |
1988年 | 581篇 |
1987年 | 453篇 |
1986年 | 397篇 |
1985年 | 344篇 |
1984年 | 299篇 |
1983年 | 273篇 |
1982年 | 226篇 |
1981年 | 207篇 |
1980年 | 153篇 |
1979年 | 136篇 |
1978年 | 74篇 |
1977年 | 58篇 |
1976年 | 66篇 |
1974年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Yanlin Huang Kiwan Jang Wanxue Zhao Eunjin Cho Ho Sueb Lee Xigang Wang Dake Qin Ying Zhang Chanfang Jiang Hyo Jin Seo 《Journal of solid state chemistry》2007,180(12):3325-3332
Usually, Sm2+ ions could be reduced by heating the materials in reducing atmospheres. Exposure to ionizing radiations is also known to cause Sm3+→Sm2+ conversion. In this work, BaBPO5 doped with the samarium ion was prepared by high temperature solid-state reaction. Sm2+ ions were obtained by two different reduction methods, i.e., heating in H2 reduced atmosphere and X-ray irradiation. The measurements of X-ray diffraction (XRD), and scanning electron microscope (SEM) were investigated. It is found that the conversion of Sm3+→Sm2+ is very efficient in BaBPO5 hosts after X-ray irradiation. Sm2+ ions under these two reduction methods exhibit different characteristics that were studied by measurements of luminescence and decay. The results showed that the luminescence properties of Sm2+ ions in BaBPO5 were highly dependent on the sample preparation conditions. 相似文献
992.
重金属Pb2+对玉米苗生长的影响 总被引:11,自引:1,他引:10
以水栽培的玉米幼苗为材料,用不同浓度的醋酸铅溶液处理后,分别在第10天、第20天、第30天对玉米苗的根、茎、叶分别进行Pb^2+含量测定。分析结果:Pb^2+在玉米体内的分布表现为根〉叶〉茎;玉米中的叶绿素含量均降低;随着Pb^2+浓度的增大,玉米细胞的膜透性表现根〉叶〉茎依次升高;Pb^2+对玉米的伤害率的大小表现为根〉叶〉茎。该实验为进一步研究农作物对重金属Pb^2+的耐性和重金属Pb^2+在农作物体内的分布提供了可参考的数据。 相似文献
993.
如果一个图G存在一个k-列表安排使得G具有一个唯一列表染色,则称 G是唯一列表可染色图,简称UkLC图.我们称图G具有M(k)性质当且仅当G不 是UkLC图.本文在借鉴θr,s,t-图概念的基础上引入θr,s,t-图的定义,并证明:除了 r=s=t=2以外,θr,s,t-图都是U2LC图.利用如上结果我们给出M.Mahdian and E.S.Mahmoodian对U2LC图所作特征化的一个简单证明. 相似文献
994.
Kan‐Yi Pu Yi Chen Xiao‐Ying Qi Chun‐Yang Qin Qing‐Quan Chen Hong‐Yu Wang Yun Deng Qu‐Li Fan Yan‐Qin Huang Shu‐Juan Liu Wei Wei Bo Peng Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3776-3787
In this contribution, we demonstrate a new effective methodology for constructing highly efficient and durable poly(p‐phenyleneethynylene) (PPE) containing emissive material with nonaggregating and hole‐facilitating properties through the introduction of hole‐transporting blocks into the PPE system as the grafting coils as well as building the energy donor–acceptor architecture between the grafting coils and the PPE backbone. Poly(2‐(carbazol‐9‐yl)ethyl methacrylate) (PCzEMA), herein, is chosen as the hole‐transporting blocks, and incorporated into the PPE system as the grafting coils via atom transfer radical polymerization. The chemical structure of the resultant copolymer, PPE‐g‐PCzEMA, was characterized by NMR and gel permeation chromatography, showing that the desirable copolymer was obtained with the narrow polydispersity. The increased thermal stability of PPE‐g‐PCzEMA was confirmed by thermogravimetric analysis and differential scanning calorimetry along with its macroinitiator. The optoelectronic properties of this copolymer were studied in detail by ultraviolet‐visible absorption, photoluminescence emission and excitation spectra, and cyclic voltammogram (CV). The results indicate that PPE‐g‐PCzEMA exhibits the solid‐state luminescent property dominated by individual lumophores, and also the energy transfer process from the PCzEMA blocks to the PPE backbone with a relatively higher energy transfer efficiency in the solid‐state compared to that of the solution state. Additionally, the hole‐injection property is greatly facilitated due to the presence of PCzEMA, as confirmed by CV profiles. All these data indicate that PPE‐g‐PCzEMA is a good candidate for use in optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3776–3787, 2007 相似文献
995.
996.
一种新型有机电致微腔结构的双模发射 总被引:4,自引:4,他引:0
采用结构Glass/DBR/ITO/NPB/NPB:Alq/Alq/Al制作了有机微腔电致发光器件。将空穴传输材料与发光材料以一定比例混合作为发光层,为了便于对比,在不改变有机层的膜厚的情况下同时制作了传统的异质结微腔器件,发现两种器件的发光光谱有很大不同,器件的复合效率与传统的异质结器件相比也得到了很大提高,这是因为将两种有机材料混合能消除界面势垒,提高器件的复合效率,从而提高了器件的发光性能,实现了微腔双模发射,且两个模式的半峰全宽分别为8nm和12nm。通过进一步优化器件结构可以实现微腔白光发射。 相似文献
997.
严格解出了一种既荷电又荷磁,且电荷密度与磁荷密度之比为常量的静止球对称天体的共形平直内解. 相似文献
998.
Da-Zhi Li Li Gan Zi-Qiang Yang Zheng Liang Jia-Yin Li 《International Journal of Infrared and Millimeter Waves》1997,18(10):1885-1896
The dispersion characteristic of the plasma-loaded relativistic backward wave oscillator has been analyzed. The theoretical
model has been established and the numerical calculations accord with the experimental results, which provides some useful
suggestions on the designing of slow-wave structure of BWO. 相似文献
999.
1000.