全文获取类型
收费全文 | 16655篇 |
免费 | 2978篇 |
国内免费 | 2219篇 |
专业分类
化学 | 12303篇 |
晶体学 | 209篇 |
力学 | 1017篇 |
综合类 | 135篇 |
数学 | 1960篇 |
物理学 | 6228篇 |
出版年
2024年 | 33篇 |
2023年 | 291篇 |
2022年 | 368篇 |
2021年 | 483篇 |
2020年 | 616篇 |
2019年 | 644篇 |
2018年 | 550篇 |
2017年 | 492篇 |
2016年 | 796篇 |
2015年 | 863篇 |
2014年 | 942篇 |
2013年 | 1237篇 |
2012年 | 1406篇 |
2011年 | 1465篇 |
2010年 | 1099篇 |
2009年 | 1061篇 |
2008年 | 1120篇 |
2007年 | 935篇 |
2006年 | 869篇 |
2005年 | 813篇 |
2004年 | 701篇 |
2003年 | 595篇 |
2002年 | 725篇 |
2001年 | 594篇 |
2000年 | 432篇 |
1999年 | 395篇 |
1998年 | 316篇 |
1997年 | 256篇 |
1996年 | 266篇 |
1995年 | 212篇 |
1994年 | 196篇 |
1993年 | 174篇 |
1992年 | 155篇 |
1991年 | 139篇 |
1990年 | 99篇 |
1989年 | 101篇 |
1988年 | 72篇 |
1987年 | 62篇 |
1986年 | 48篇 |
1985年 | 42篇 |
1984年 | 33篇 |
1983年 | 29篇 |
1982年 | 18篇 |
1981年 | 25篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1974年 | 8篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Jiazhong Zhang Haiping Xia Yongzhang Jiang Shuo Yang Xuemei Gu Jianli Zhang Haochuan Jiang Baojiu Chen 《Crystal Research and Technology》2015,50(7):574-579
Downconversion (DC) luminescence with emission at about 1000 nm under excitation of 448‐nm light in Ho3+/Yb3+ codoped α‐NaYF4 single crystal is realized. The crystal was grown by the Bridgman method using KF as an assisting flux in a NaF‐YF3 system. The energy‐transfer process and quantum cutting (QC) mechanisms are presented through the analysis of the spectra. The energy‐transfer processes of first‐ and second‐order cooperative DC are responsible for the increase of the emission intensity at 1000 nm, and it is the first‐order cooperative DC that is dominant for the DC process. When the Ho3+ concentration is fixed at about 0.8 mol%, the optimal concentration for ∼1000 nm emission is 3.02 mol% Yb3+ in the current research. The energy‐transfer efficiency and the total quantum efficiency are analyzed through the luminescence decay curves. The maximum quantum cutting efficiency approaches to 184.4% in α‐NaYF4 single crystals of 0.799 mol% Ho3+ and 15.15 mol% Yb3+. However, the emission intensity at 1000 nm decreases while the energy‐transfer efficiency from Ho3+ to Yb3+ increases, which may result from the fluorescence quenching between Ho3+ and Yb3+ ions, Yb3+ and Yb3+ ions. 相似文献
992.
Yongni Li Xuehang Wu Wenwei Wu Kaituo Wang Liqin Qin Sen Liao Yanxuan Wen 《Journal of Thermal Analysis and Calorimetry》2014,117(1):499-506
CeO2 was synthesized by calcining Ce2(C2O4)3·8H2O above 673 K in air. The precursor and its calcined products were characterized using thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectra, X-ray powder diffraction, scanning electron microscopy, and UV–Vis absorption spectroscopy. The result showed that cubic CeO2 was obtained when the precursor was calcined above 673 K in air for 2 h. The UV–Vis absorption spectroscopy studies showed that superfine CeO2 behaved as an excellent UV-shielding material. The thermal decomposition of the precursor in air experienced two steps, which are: first, the dehydration of eight crystal water molecules, then the decomposition of Ce2(C2O4)3 into cubic CeO2. The values of the activation energies associated with the thermal decomposition of Ce2(C2O4)3·8H2O were determined based on the Starink equation. 相似文献
993.
Electrochemical Synthesis of Tetrahexahedral Rhodium Nanocrystals with Extraordinarily High Surface Energy and High Electrocatalytic Activity
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Neng‐Fei Yu Dr. Na Tian Dr. Zhi‐You Zhou Long Huang Jing Xiao Yu‐Hua Wen Prof. Shi‐Gang Sun 《Angewandte Chemie (International ed. in English)》2014,53(20):5097-5101
Noble metal nanocrystals (NCs) enclosed with high‐index facets hold a high catalytic activity thanks to the high density of low‐coordinated step atoms that they exposed on their surface. Shape‐control synthesis of the metal NCs with high‐index facets presents a big challenge owing to the high surface energy of the NCs, and the shape control for metal Rh is even more difficult because of its extraordinarily high surface energy in comparison with Pt, Pd, and Au. The successful synthesis is presented of tetrahexahedral Rh NCs (THH Rh NCs) enclosed by {830} high‐index facets through the dynamic oxygen adsorption/desorption mediated by square‐wave potential. The results demonstrate that the THH Rh NCs exhibit greatly enhanced catalytic activity over commercial Rh black catalyst for the electrooxidation of ethanol and CO. 相似文献
994.
Visible‐Light‐Induced CS Bond Activation: Facile Access to 1,4‐Diketones from β‐Ketosulfones
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jun Xuan Zhu‐Jia Feng Prof. Dr. Jia‐Rong Chen Dr. Liang‐Qiu Lu Prof. Dr. Wen‐Jing Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(11):3045-3049
A novel method for the synthesis of 1,4‐diketones from β‐ketosulfones was developed by means of a visible light‐induced C?S bond activation process. Symmetrical and unsymmetrical 1,4‐diketones can be easily prepared in moderate to good yields. 相似文献
995.
Dr. Juliette Guérin Dr. Anne Léaustic Prof. Stéphanie Delbaere Dr. Jérôme Berthet Dr. Régis Guillot Dr. Cyril Ruckebusch Dr. Rémi Métivier Prof. Keitaro Nakatani Dr. Maylis Orio Dr. Michel Sliwa Dr. Pei Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12279-12288
A terthiazole‐based molecular switch associating 6π electrocyclization, excited state intramolecular proton transfer (ESIPT), and strong metal binding capability was prepared. The photochemical and photophysical properties of this molecule and of the corresponding nickel and copper complexes were thoroughly investigated by steady‐state and ultrafast absorption spectroscopy and rationalized by DFT/TDDFT calculations. The switch behaves as a biphotochrome with time‐dependent photochemical outcome and displays efficient ESIPT‐based fluorescence photoswitching. Both photochemical reactions are suppressed by nickel or copper metalation, and the main factors contributing to the quenching of the electrocyclization are discussed. 相似文献
996.
Inside Cover: Uniaxial Movements of a Metal–Cyanide Framework Switched by Weak Interactions through Dehydration and Rehydration (Chem. Eur. J. 27/2014)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
997.
Dr. Chi‐Shian Chen Yu‐Fang Lin Dr. Wen‐Yann Yeh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):936-940
Reactions of the open‐cage fullerene C63NO2(Py)(Ph)2 ( 1 ) with [Ru3(CO)12] produce [Ru3(CO)8(μ,η5‐C63NO2(Py)(Ph)2)] ( 2 ), [Ru2H(CO)3(μ,η7‐C63N(Py)(Ph)(C6H4))] ( 3 ), and [Ru(CO)(Py)2(η3‐C63NO2(Py)(Ph)2)] ( 4 ), in which the orifice sizes are modified from 12 to 8, 11, and 15‐membered ring, through ruthenium‐mediated C?O and C?C bond activation and formation. 相似文献
998.
Rational Design,Synthesis, and Evaluation of Tetrahydroxamic Acid Chelators for Stable Complexation of Zirconium(IV)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. François Guérard Dr. Yong‐Sok Lee Dr. Martin W. Brechbiel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5584-5591
Metals of interest for biomedical applications often need to be complexed and associated in a stable manner with a targeting agent before use. Whereas the fundamentals of most transition‐metal complexation processes have been thoroughly studied, the complexation of ZrIV has been somewhat neglected. This metal has received growing attention in recent years, especially in nuclear medicine, with the use of 89Zr, which a β+‐emitter with near ideal characteristics for cancer imaging. However, the best chelating agent known for this radionuclide is the trishydroxamate desferrioxamine B (DFB), the ZrIV complex of which exhibits suboptimal stability, resulting in the progressive release of 89Zr in vivo. Based on a recent report demonstrating the higher thermodynamic stability of the tetrahydroxamate complexes of ZrIV compared with the trishydroxamate complexes analogues to DFB, we designed a series of tetrahydroxamic acids of varying geometries for improved complexation of this metal. Three macrocycles differing in their cavity size (28 to 36‐membered rings) were synthesized by using a ring‐closing metathesis strategy, as well as their acyclic analogues. A solution study with 89Zr showed the complexation to be more effective with increasing cavity size. Evaluation of the kinetic inertness of these new complexes in ethylenediaminetetraacetic acid (EDTA) solution showed significantly improved stabilities of the larger chelates compared with 89Zr‐DFB, whereas the smaller complexes suffered from insufficient stabilities. These results were rationalized by a quantum chemical study. The lower stability of the smaller chelates was attributed to ring strain, whereas the better stability of the larger cyclic complexes was explained by the macrocyclic effect and by the structural rigidity. Overall, these new chelating agents open new perspectives for the safe and efficient use of 89Zr in nuclear imaging, with the best chelators providing dramatically improved stabilities compared with the reference DFB. 相似文献
999.
Palladium‐Catalyzed One‐Pot Three‐ or Four‐Component Coupling of Aryl Iodides,Alkynes, and Amines through CN Bond Cleavage: Efficient Synthesis of Indole Derivatives
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wei Hao Weizhi Geng Prof. Dr. Wen‐Xiong Zhang Prof. Dr. Zhenfeng Xi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(9):2605-2612
An efficient synthesis of N‐substituted indole derivatives was realized by combining the Pd‐catalyzed one‐pot multicomponent coupling approach with cleavage of the C(sp3)?N bonds. Three or four components of aryl iodides, alkynes, and amines were involved in this coupling process. The cyclopentadiene–phosphine ligand showed high efficiency. A variety of aryl iodides, including cyclic and acyclic tertiary amino aryl iodides, and substituted 1‐bromo‐2‐iodobenzene derivatives could be used. Both symmetric and unsymmetric alkynes substituted with alkyl, aryl, or trimethylsilyl groups could be applied. Cyclic secondary amines such as piperidine, morpholine, 4‐methylpiperidine, 1‐methylpiperazine, 2‐methylpiperidine, and acyclic amines including secondary and primary amines all showed good reactivity. Further application of the resulting indole derivatives was demonstrated by the synthesis of benzosilolo[2,3‐b]indole. 相似文献
1000.
Bin Zhou Yedi Xing Prof. Shu Miao Prof. Mingrun Li Prof. Wen‐Hua Zhang Prof. Can Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12426-12431
A facile colloidal approach to synthesize Ag8(Ge1?x,Snx)(S6?y,Sey) nanocrystals (NCs) in a highly controlled way across the entire compositional ranges (0≤x≤1, 0≤y≤6) has been developed. The NCs exhibit a uniform size distribution, highly crystalline structure, over 1 g scalable synthesis, and tunable band gaps in the range of 0.88–1.45 eV by varying their chemical compositions. The Ag8GeS6 NCs with a band gap of approximately 1.45 eV were employed as a model light harvester to assess their applicability in solar cells by a full solution‐processing device, yielding an efficiency of 0.28 % under AM1.5 illumination, demonstrating their application potential in solar energy utilization. 相似文献