全文获取类型
收费全文 | 546篇 |
免费 | 13篇 |
国内免费 | 12篇 |
专业分类
化学 | 265篇 |
晶体学 | 14篇 |
力学 | 27篇 |
数学 | 120篇 |
物理学 | 145篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 17篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 21篇 |
2014年 | 20篇 |
2013年 | 100篇 |
2012年 | 15篇 |
2011年 | 16篇 |
2010年 | 18篇 |
2009年 | 12篇 |
2008年 | 13篇 |
2007年 | 10篇 |
2006年 | 16篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 14篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1987年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1973年 | 4篇 |
1969年 | 3篇 |
1967年 | 6篇 |
1966年 | 5篇 |
1965年 | 7篇 |
1964年 | 4篇 |
1962年 | 9篇 |
1960年 | 4篇 |
1959年 | 3篇 |
1956年 | 3篇 |
1955年 | 4篇 |
1938年 | 2篇 |
1934年 | 2篇 |
1933年 | 4篇 |
1927年 | 2篇 |
1923年 | 2篇 |
排序方式: 共有571条查询结果,搜索用时 15 毫秒
31.
Avcıbaşı Uğur Türkyarar Taner Karadağ Ayşegül Bakan Buket Yavaşoğlu Nefise Ülkü Karabay Kuşat Kevser Akgöl Sinan Gülcemal Derya Tekin Volkan Müftüler Fazilet Zümrüt Biber Topal Gökcen Parlak Yasemin Gümüşer Fikriye Gül 《Journal of Radioanalytical and Nuclear Chemistry》2021,329(2):511-525
Journal of Radioanalytical and Nuclear Chemistry - The aim of this study is the synthesis of a novel 99mTc-labeld graft polymer and the biological evaluation of its in vitro and in vivo properties.... 相似文献
32.
MODELING HARVEST SCHEDULING IN MULTIFUNCTIONAL PLANNING OF FORESTS FOR LONGTERM WATER YIELD OPTIMIZATION 下载免费PDF全文
HAYATI ZENGIN ÜNAL ASAN SINAN DESTAN MURAT ENGIN ÜNAL AHMET YEŞIL PETE BETTINGER AHMET SALIH DEĞERMENCI 《Natural Resource Modeling》2015,28(1):59-85
In this study, wood production and hydrologic functions of forests were accommodated within a planning procedure for separate working circles (areas dedicated to certain forest functions) that were delineated according to an Ecosystem‐Based Functional Planning approach. Mixed integer goal programming was used as the optimization technique. The timing and scheduling of a maintenance cutting (partial harvest) was the decision variable in the modeling effort, and an original formulation was developed as a multiobjective planning procedure. Four sample planning strategies were developed and model outputs were evaluated according to these strategies. Spatial characteristics of stands were considered, and used to prohibit the regeneration of adjacent stands during the same time period. Because of the positive relationship between qualified water production and standing timber volume in the forest, the model attempts to maximize qualified water production levels by increasing standing volume stocks in the forest through the delay of regeneration activities. 相似文献
33.
Phosphonic acid functional polymers are currently of interest because of their high proton conductivity in humidified and anhydrous systems. In addition, heterocyclic compounds are used in anhydrous proton conducting polymer membranes. In that study, a new copolymer based on 1‐vinyl‐1,2,4‐triazole (VTri) and diisopropyl‐p‐vinylbenzyl phosphonate (VBP) was synthesized, and their thermal, chemical, and proton conducting properties were investigated. The copolymers were synthesized by free radical copolymerization of the corresponding monomers at several monomer feed ratios to obtain P(VTri‐co‐VBP) copolymers. The copolymer samples were then hydrolyzed to produce poly(vinyl triazole‐co‐vinyl phosphonic acid) copolymers. The composition of the copolymers was determined by elemental analysis. The copolymerization and hydrolysis reactions were verified by Fourier transform infrared spectroscopy and ion exchange capacity measurements. Thermogravimetry analysis indicates that the copolymers are thermally stable up to 300°C. In order to increase the proton conductivity, the copolymers were doped with H3PO4 at several stoichometric ratios. The proton conductivity increases with triazole and phosphoric acid content. In the absence of humidity, the copolymer electrolyte, P(VTri‐co‐VBPA)1:0.5 X = 2, showed a proton conductivity of 0.005 S/cm at 150°C. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
34.
Nonmetal cation (NMC) pentaborate structures were synthesized using the amino acid molecules as cations precursors. Chemical composition analysis, infrared spectroscopy, mass analysis, boron nuclear magnetic resonance, and thermal gravimetric analysis (TGA/DTA) methods were used for structural characterization. The hydrogen storage efficiency of molecules was also determined experimentally. The recorded infrared spectra support the structural similarities of the molecules. Stretchings of pentaborate rings and characteristic peaks of amino acids were detected in infrared spectra. When the thermal analysis curves were recorded, it was found that the structures showed similar decomposition steps. Due to the result of thermal decay, glassy boron oxide (B2O3) formation was observed as the final decomposition products of all molecules. Peaks associated with boric acid, triborate, and pentaborate were observed in the 11B spectra of these salts. Powder X-ray diffraction spectroscopy supports the presence of BO3 and BO4− groups regarding the presence of pentaborate rings. It also indicates the high crystallinity of the structures. The molecular cavities detected by brunauer–emmett–teller analysis were found to be 3.586, 1.922, 1.673, and 1.923 g/cm3. Low-molecular cavities can be attributed to the high hydrogen-bonding capacity of the structures. The hydrogen capture efficiency of the pentaborate salts was found to be in the range of 0.039-0. 相似文献
35.
36.
37.
Remziye Güzel Haslet Ekşi Zafer Üstündağ Ali Osman Solak 《Surface and interface analysis : SIA》2013,45(13):1821-1829
In this study, 4‐thiophenol modified glassy carbon electrode was prepared by the reduction of 4‐diazothiophenol tetrafluoroborate salt. Silver nanoparticles were attached to the thiophenol modified surface to prepare a thiophenol‐silver nanoparticle composite film. 4‐Aminothiopenol molecules were deposited by self‐assembling technique to form multi‐layered nanofilms of TP/SNP/PhNH2 on glassy carbon substrate. These surfaces were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, X‐ray photoelectron spectroscopy, reflectance‐absorption infrared spectroscopy, and ellipsometry at each multilayer film growth process. Atomic force microscopic images of GC/TP/SNP/PhNH2 surfaces were also acquired. The characterization methods show that the amine group containing surface permits the subsequent modification by a variety of coupling reactions for the immobilization of more complex systems. An application of the electrode modification for the determination of uric acid with a significantly lower detection limit is described. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
38.
以聚二甲基硅氧烷(PDMS)改性环氧树脂(HYSZ)为粘合剂,Sm2O3为功能颜料,纳米SiO2为微纳结构改性剂,制备得到了一种同时具有良好疏水性能和附着力的近红外吸收涂层。系统分析了PDMS和HYSZ质量比、邻苯二甲酸二辛酯(DOP)添加量、总填料添加量、 Sm2O3和纳米SiO2质量比对涂层性能的影响。结果表明:PDMS改性可明显降低涂层的表面能,从而使涂层的疏水性得到明显增强。利用DOP强化涂层韧性和微观搭桥作用可增强涂层整体性,从而可明显提高涂层的附着力和近红外吸收性能。涂层的表面粗糙度可随总填料添加量的增加而明显升高,进而可使涂层表现出更优的疏水性能。当涂层中PDMS和HYSZ质量比、 DOP添加量、总填料添加量、 Sm2O3和纳米SiO2质量比分别为1∶9, 20%, 50%和5.5∶4.5时,涂层同时具有良好的近红外低反射率(59.1%)、疏水性能(水接触角为137°)及附着力... 相似文献
39.
A comprehensive set of spectra for the benzene cation and the perdeuterated benzene cation has been recorded with full rotational resolution using zero kinetic energy photoelectron spectroscopy (ZEKE) at high resolution (up to 0.2 cm?1), using a slow-rising extraction pulse. With different rovibronic levels in the S1 6l state as intermediate resonance, the rotational transitions to the vibronic ground state of the cation have been recorded using two-colour, two-photon resonance enhanced multiphoton ionization. A simple spectator model has been employed to simulate the intensities of the ZEKE transitions. By fitting the simulations to the recorded spectra, improved values for the rotational constants and the Coriolis coupling parameters of benzene and perdeuterated benzene have been obtained. The CC and CH bond lengths of the cation have been deduced. The spectator model is shown to be reliable despite the fact that no specific allowance is made for the effect of final state interactions on the signal intensity. 相似文献
40.
Dr. Joachim RosenmÜller 《Probability Theory and Related Fields》1971,17(4):259-308
Ohne ZusammenfassungBesonders bedanken möchte ich mich bei Herrn Prof. K.Jacobs fÜr sein dauerndes Interesse an meinen BemÜhungen. 相似文献