全文获取类型
收费全文 | 19372篇 |
免费 | 2894篇 |
国内免费 | 3552篇 |
专业分类
化学 | 13921篇 |
晶体学 | 472篇 |
力学 | 2220篇 |
综合类 | 106篇 |
数学 | 563篇 |
物理学 | 8536篇 |
出版年
2024年 | 54篇 |
2023年 | 608篇 |
2022年 | 583篇 |
2021年 | 756篇 |
2020年 | 855篇 |
2019年 | 689篇 |
2018年 | 549篇 |
2017年 | 777篇 |
2016年 | 1066篇 |
2015年 | 861篇 |
2014年 | 1233篇 |
2013年 | 1525篇 |
2012年 | 1283篇 |
2011年 | 1291篇 |
2010年 | 1147篇 |
2009年 | 1243篇 |
2008年 | 1294篇 |
2007年 | 1379篇 |
2006年 | 1141篇 |
2005年 | 1014篇 |
2004年 | 1021篇 |
2003年 | 822篇 |
2002年 | 739篇 |
2001年 | 582篇 |
2000年 | 487篇 |
1999年 | 409篇 |
1998年 | 368篇 |
1997年 | 361篇 |
1996年 | 290篇 |
1995年 | 254篇 |
1994年 | 245篇 |
1993年 | 146篇 |
1992年 | 147篇 |
1991年 | 101篇 |
1990年 | 86篇 |
1989年 | 75篇 |
1988年 | 85篇 |
1987年 | 53篇 |
1986年 | 43篇 |
1985年 | 26篇 |
1984年 | 28篇 |
1983年 | 7篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 5篇 |
1979年 | 18篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 880 毫秒
991.
锂离子电池的有机正极材料由于具有比容量高、环境友好和廉价等优点,近年来成为研究的热点.但是,有机电极材料在液态电解液中的溶解流失易导致其容量迅速衰减,严重限制了它们的实际应用.本工作基于聚(甲基丙烯酸酯)/聚乙二醇的准固态电解质,考察了以柱[5]醌为正极的准固态锂二次电池的电化学性能.结果显示,柱[5]醌正极不仅保持了高容量的特性(首次放电容量410 mA h/g),并且循环寿命得到了有效提高.0.2 C下循环100周后,电极的容量保持率为88.5%,显示了柱[5]醌在高比能量准固态锂离子电池中的应用潜力. 相似文献
992.
993.
Metal-organic frameworks(MOFs)constructed from conjugated organic ligands are candidates for hybrid photoactive materials with potential applications.Compared to that from the ligands only,the intensity and wavelength of the luminescence could be tuned after they were incorporated in extended framework.In this report,by using an organic ligand with azolate moiety,benzo-bis(imidazole)(H2BBI),we synthesized two new MOF structures.Framework 1([Co(H2BBI)(DMSO)2Cl2]n,DMSO=dimethyl sulfoxide),constructed from tetrahedral Co(II)and H2BBI,exhibits zigzag 1D structure.Meanwhile,framework 2([Cu2(H2BBI)3(DMSO)6(NO3)4]n),a layered structure with hcb topology,was assembled from tetragonal pyramidal Cu(II)and H2BBI.Furthermore,2 exhibits strong luminescence emission(ex=280 nm).A blue shift of 40 nm(from 359 nm to 319 nm)was observed in framework 2 compared to the free ligand,which could be explained by the ligand-to-metal charge transfer in the network. 相似文献
994.
In this paper,the nanometer-sized(200 nm)quaternary rare-earth complex Eu(BA)(TTA)2phen was successfully prepared by using the method of optimizing chemical precipitation.The characterizations of these nanoparticles were performed by using elemental analysis,thermogravimetric analysis,infrared spectroscopy,fluorescence spectroscopy,transmission electron microscopy and luminescence quantum-yield.The results indicate that they are better than common ternary complexes at light-emitting performance,luminescence properties,thermal stability,uniformity and particle size;they can also be further mixed with a suitable polymer to form functional rare earth polymers.Compared to the common solid materials,the quaternary complex has better and unique characteristics such as nanoparticle size effect and surface effect.A foundation had been laid for the further expansion of its application in the field of light-emitting and magnetic materials. 相似文献
995.
Synthesis,Persistent Luminescence,and Thermoluminescence Properties of Yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce,Nd, Dy,Ho, Er,Tm, Yb) and Orange‐Red Sr3−xBaxSiO5:Eu2+, Dy3+ Phosphor 下载免费PDF全文
Dr. Ye Li Baohong Li Chenchen Ni Shuxia Yuan Jing Wang Prof. Qiang Tang Prof. Qiang Su 《化学:亚洲杂志》2014,9(2):494-499
Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr3?xBaxSiO5:Eu2+,Dy3+ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu2+ in Sr3SiO5 was significantly modified. The yellow persistent emission intensity of Eu2+ was greatly enhanced by a factor of 4.5 in Sr3SiO5:Eu2+,Nd3+ compared with the previously reported Sr3SiO5:Eu2+, Dy3+. Furthermore, Sr ions were replaced with equivalent Ba to give Sr3?xBaxSiO5:Eu2+,Dy3+ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu2+ is significantly improved by a factor of 2.7 in Sr3?xBaxSiO5:Eu2+,Dy3+ (x=0.2) compared with Sr3SiO5:Eu2+,Dy3+. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu2+ in Sr3?xBaxSiO5:Eu2+,RE3+ (RE=rare earth) is also proposed and discussed. 相似文献
996.
Glucose is directly related to brain activity and to diabetes.Therefore,developing a rapid and sensitive method for glucose detection is essential.Here,label-free glucose detection at attomole levels was realized by detecting the average diameter change of gold nanoparticles(AuNPs)utilizing dynamic light scattering(DLS).Single-strand DNA(ssDNA)adsorbed into the AuNPs’surfaces and prevented them from aggregating in solution that contained NaCl.However,ssDNA cleaved onto ssDNA fragments upon addition of glucose,and these fragments could not adsorb onto the AuNPs’surfaces.Therefore,in high-salt solution,AuNPs would aggregate and their average diameter would increase.Based on monitoring the average diameter of AuNPs with DLS,glucose could be detected in the range from 15 pmol/L to 2.0 nmol/L,with a detection limit of 8.3 pmol/L.Satisfactory results were also obtained when the proposed method was applied in human serum glucose detection. 相似文献
997.
Highly Efficient Orange and Warm White Phosphorescent OLEDs Based on a Host Material with a Carbazole–Fluorenyl Hybrid 下载免费PDF全文
Xiaoyang Du Yun Huang Dr. Silu Tao Xiaoxia Yang Chuan Wu Huaixin Wei Dr. Mei‐Yee Chan Dr. Vivian Wing‐Wah Yam Prof. Chun‐Sing Lee 《化学:亚洲杂志》2014,9(6):1500-1505
A new carbazole–fluorenyl hybrid compound, 3,3′(2,7‐di(naphthaline‐2‐yl)‐9H‐fluorene‐9,9‐diyl)bis(9‐phenyl‐9H‐carbazole) (NFBC) was synthesized and characterized. The compound exhibits blue‐violet emission both in solution and in film, with peaks centered at 404 and 420 nm. In addition to the application as a blue emitter, NFBC is demonstrated to be a good host for phosphorescent dopants. By doping Ir(2‐phq)3 in NFBC, a highly efficient orange organic light‐emitting diode (OLED) with a maximum efficiency of 32 cd A?1 (26.5 Lm W?1) was obtained. Unlike most phosphorescent OLEDs, the device prepared in our study shows little efficiency roll‐off at high brightness and maintains current efficiencies of 31.9 and 26.8 cd A?1 at a luminance of 1000 and 10 000 cd m?2, respectively. By using NFBC simultaneously as a blue fluorescence emitter and as a host for a phosphorescent dopant, a warm white OLED with a maximum efficiency of 22.9 Lm W?1 (21.9 cd A?1) was also obtained. 相似文献
998.
Phosphorescent Cyclometalated Iridium(III) Complexes That Contain Substituted 2‐Acetylbenzo[b]thiophen‐3‐olate Ligand for Red Organic Light‐Emitting Devices 下载免费PDF全文
Chen Yang Dr. Shiu‐Lun Lai Dr. Sharon Lai‐Fung Chan Dr. Kam‐Hung Low Dr. Gang Cheng Kwan‐Ting Yeung Dr. Chi‐Chung Kwok Prof. Dr. Chi‐Ming Che 《化学:亚洲杂志》2014,9(12):3572-3585
We report the synthesis of a new class of thermally stable and strongly luminescent cyclometalated iridium(III) complexes 1 – 6 , which contain the 2‐acetylbenzo[b]thiophene‐3‐olate (bt) ligand, and their application in organic light‐emitting diodes (OLEDs). These heteroleptic iridium(III) complexes with bt as the ancillary ligand have a decomposition temperature that is 10–20 % higher and lower emission self‐quenching constants than those of their corresponding complexes with acetylacetonate (acac). The luminescent color of these iridium(III) complexes could be fine‐tuned from orange (e.g., 2‐phenyl‐6‐(trifluoromethyl)benzo[d]thiazole (cf3bta) for 4 ) to pure red (e.g., lpt (Hlpt=4‐methyl‐2‐(thiophen‐2‐yl)quinolone) for 6 ) by varying the cyclometalating ligands (C‐deprotonated C^N). In particular, highly efficient OLEDs based on 6 as dopant (emitter) and 1,3‐bis(carbazol‐9‐yl)benzene (mCP) as host that exhibit stable red emission over a wide range of brightness with CIE chromaticity coordinates of (0.67, 0.33) well matched to the National Television System Committee (NTSC) standard have been fabricated along with an external quantum efficiency (EQE) and current efficiency of 9 % and 10 cd A?1, respectively. A further 50 % increase in EQE (>13 %) by replacing mCP with bis[4‐(6H‐indolo[2,3‐b]quinoxalin‐6‐yl)phenyl]diphenylsilane (BIQS) as host for 6 in the red OLED is demonstrated. The performance of OLEDs fabricated with 6 (i.e., [(lpt)2Ir(bt)]) was comparable to that of the analogous iridium(III) complex that bore acac (i.e., [(lpt)2Ir(acac)]; 6 a in this work) [Adv. Mater. 2011 , 23, 2981] fabricated under similar conditions. By using ntt (Hnnt=3‐hydroxynaphtho[2,3‐b]thiophen‐2‐yl)(thiophen‐2‐yl)methanone) ligand, a substituted derivative of bt, the [(cf3bta)2Ir(ntt)] was prepared and found to display deep red emission at around 700 nm with a quantum yield of 12 % in mCP thin film. 相似文献
999.
Direct Photocatalysis for Organic Synthesis by Using Plasmonic‐Metal Nanoparticles Irradiated with Visible Light 下载免费PDF全文
Recent advances in direct‐use plasmonic‐metal nanoparticles (NPs) as photocatalysts to drive organic synthesis reactions under visible‐light irradiation have attracted great interest. Plasmonic‐metal NPs are characterized by their strong interaction with visible light through excitation of the localized surface plasmon resonance (LSPR). Herein, we review recent developments in direct photocatalysis using plasmonic‐metal NPs and their applications. We focus on the role played by the LSPR of the metal NPs in catalyzing organic transformations and, more broadly, the role that light irradiation plays in catalyzing the reactions. Through this, the reaction mechanisms that these light‐excited energetic electrons promote will be highlighted. This review will be of particular interest to researchers who are designing and fabricating new plasmonic‐metal NP photocatalysts by identifying important reaction mechanisms that occur through light irradiation. 相似文献
1000.
Determination of the total tannin of white and red rind pomegranate (Punica granatum L.) has been carried out by colorimetry method using reagent 1,10 phenantroline. This method is based on reduction of iron (III) into iron (II) by tannin at temperature 800C for 20 min. Then the formed of iron (II) was reacted with 1,10 phenantroline to form orange red colour complex that could be measured by spectrophotometer visible at maximum absorption wavelength of 508 nm. The limit of detection (LOD) and the limit of quantitation (LOQ) obtained were 0.34 μg/mL and 1.14 μg/mL, respectively. This result was found to be linier with R value of 0.9984; accuracy as percent recovery was 84.69 ± 0.85% and coefficient of variant (KV) was 1.003% for white rind pomegranate while red rind pomegranate percent recovery was 84.38 ± 0,45% and coefficient of variant (KV) was 0.53%. The total tannin of white rind pomegranate was 18.28 ± 0.072%b/b and red rind pomegranate was 17.33 ± 0.081%b/b 相似文献