全文获取类型
收费全文 | 937篇 |
免费 | 53篇 |
国内免费 | 6篇 |
专业分类
化学 | 609篇 |
晶体学 | 7篇 |
力学 | 38篇 |
综合类 | 1篇 |
数学 | 91篇 |
物理学 | 250篇 |
出版年
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 13篇 |
2019年 | 22篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 25篇 |
2015年 | 33篇 |
2014年 | 31篇 |
2013年 | 46篇 |
2012年 | 75篇 |
2011年 | 70篇 |
2010年 | 43篇 |
2009年 | 56篇 |
2008年 | 41篇 |
2007年 | 44篇 |
2006年 | 45篇 |
2005年 | 38篇 |
2004年 | 31篇 |
2003年 | 18篇 |
2002年 | 26篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 23篇 |
1998年 | 8篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1970年 | 4篇 |
1969年 | 3篇 |
排序方式: 共有996条查询结果,搜索用时 0 毫秒
61.
Selective Transfer Hydrogenation and Hydrogenation of Ketones Using a Defined Monofunctional (P^N(Bn)^N(Bn)^P)–RuII Complex 下载免费PDF全文
Shih‐Fan Hsu Prof. Dr. Bernd Plietker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4242-4245
A defined (P^N^N^P)–Ru complex possessing tertiary amines within the ligand backbone proved to be highly active both in transfer hydrogenations and hydrogenations of a variety of ketones. As compared to the existing catalytic systems, no bifunctional activation of H2 or of the substrate by the metal center and a secondary amine within the ligand backbone is required to obtain high activities at catalyst loadings of down to 10 ppm. 相似文献
62.
Jayachandran Jayakumar Guganchandar Vedarethinam Huan‐Chang Hsiao Shang‐You Sun Shih‐Ching Chuang 《Angewandte Chemie (International ed. in English)》2020,59(2):689-694
Quaternary ammonium salts were synthesized in moderate to good yields through double oxidative C?H bond activation on azobenzenes. The mechanism of the highly regioselective reaction of 2‐azobiaryls with alkenes to give orange‐red‐fluorescent cinnolino[2,3‐f]phenanthridin‐9‐ium salts and 15H‐cinnolino[2,3‐f]phenanthridin‐9‐ium‐10‐ide is proposed to involve ortho C?H olefination of the 2‐azobiaryl compound with the alkene, intramolecular aza‐Michael addition, concerted metalation–deprotonation (CMD), reductive elimination, and oxidation. 相似文献
63.
Chung‐An Chen Shih‐Chia Chen Muhammad J. A. Shiddiky Chien‐Fu Chen Kevin C.‐W. Wu 《Chemical record (New York, N.Y.)》2020,20(3):174-186
Metal nanoprobes have recently attracted board research interestinr their application in establishing sensing systems due to their unique optical, electrical, physical, and chemical properties. In comparison to gold and silver nanoprobes, analytical platform based on copper nanoprobes (Cu‐NPs) is still in the early stages of development. In this review, we focus on single‐stranded, and double‐stranded DNA capped Cu‐NPs sensing systems which have been designed for various analytes, including metal ions, anions, small molecules, biomolecules (DNA, RNA, and protein, etc.). In addition, the application of Cu‐NPs in biological labeling or bio‐imaging platforms has also been introduced and summarized. 相似文献
64.
Jen-Yi Hsu Jing-Fang Hsu Yet-Ran Chen Chia-Lang Shih Yi-Sheng Hsu Yi-Jen Chen Shu-Han Tsai Pao-Chi Liao 《Analytica chimica acta》2016
Human biomonitoring is the assessment of actual internal contamination of chemicals by measuring exposure markers, chemicals or their metabolites, in human urine, blood, serum, and other body fluids. However, the metabolism of chemicals within an organism is extremely complex. Therefore, the identification of metabolites is often difficult and laborious. Several untargeted metabolomics methods have been developed to perform objective searching/filtering of accurate-mass-based LC-MS data to facilitate metabolite identification. In this study, three metabolomics data processing approaches were used for chemical exposure marker discovery in urine with an LTQ-Orbitrap high-resolution mass spectrometry (HRMS) dataset; di-isononyl phthalate (DINP) was used as an example. The data processing techniques included the SMAIT, mass defect filtering (MDF), and XCMS Online. Sixteen, 83, and 139 probable DINP metabolite signals were obtained using the SMAIT, MDF, and XCMS procedures, respectively. Fourteen probable metabolite signals mined simultaneously by the three metabolomics approaches were confirmed as DINP metabolites by structural information provided by LC-MS/MS. Among them, 13 probable metabolite signals were validated as exposure-related markers in a rat model. Six (m/z 319.155, 361.127, 373.126, 389.157, 437.112 and 443.130) of the 13 exposure-related DINP metabolite signals have not previously been reported in the literature. Our data indicate that SMAIT provided an efficient method to discover effectively and systematically urinary exposure markers of toxicant. The DINP metabolism information can provide valuable information for further investigations of DINP toxicity, toxicokinetics, exposure assessment, and human health effects. 相似文献
65.
This report examines reactions of a series of Ir complexes supported by the diarylboryl/bis(phosphine) PBP pincer ligand with ethylene: (PBP)IrH4 (1), (PBP)IrH2(CO) (2), and (PBP)Ir(CO)2 (3). The outcomes of these reactions differ from those typical for Ir complexes supported by other pincer ligands and do not give rise to simple ethylene adducts or products of insertion of Ir into the C–H bond of ethylene. Instead, the elements of ethylene are incorporated into the molecules to result in B–C bonds. In the case of 2 and 3, ethylene addition results in the formation of B/Ir bridging ethylidene complexes 5 and 6. For 6, the addition of ethylene (and the analogous addition of 1-hexene) is shown to be partially reversible. Addition of ethylene to 2 and 3 is remarkable because they are saturated at Ir and yet the net outcome is such that ethylene binds without replacing any ligands already present. A mechanistic inquiry suggests that dissociation of CO from 3 or 6 is necessary in order for the addition or loss of ethylene to proceed.(PBP)Ir pincer complexes containing a boryl-iridium linkage reversibly bind ethylene as an ethylidene bridging B and Ir. 相似文献
66.
Titanium dioxide (TiO2), co-deposited with Fe and N, is first implanted with Fe by a metal plasma ion implantation (MPII) process and then annealed in N2 atmosphere at a temperature regime of 400-600 °C. First-principle calculations show that the (Fe, N) co-deposited TiO2 films produced additional band gap levels at the bottom of the conduction band (CB) and on the top of the valence band (VB). The (Fe, N) co-deposited TiO2 films were effective in both prohibiting electron-hole recombination and generating additional Fe-O and N-Ti-O impurity levels for the TiO2 band gap. The (Fe, N) co-deposited TiO2 has a narrower band gap of 1.97 eV than Fe-implanted TiO2 (3.14 eV) and N-doped TiO2 (2.16 eV). A significant reduction of TiO2 band gap energy from 3.22 to 1.97 eV was achieved, which resulted in the extension of photocatalytic activity of TiO2 from UV to Vis regime. The photocatalytic activity and removal rate were approximately two-fold higher than that of the Fe-implanted TiO2 under visible light irradiation. 相似文献
67.
Shin‐Yuh Chern Jeng‐Haur Horng Shih‐Han Chen 《Surface and interface analysis : SIA》2011,43(12):1509-1513
In this study, a numerical thermal model is developed for sliding block contact under various loads, sliding velocities and surface roughness. The temperature distributions are shown for perfectly insulated thermal conditions along noncontact surfaces. For a particular five‐peaks contact model, the maximum temperature at the central peak is slightly lhigher than the others. The temperature profile decreases as the distance to the symmetry axis increases, and then decreases dramatically at the noncontact area. It is clear to see that the maximum temperature locates at the symmetry central peak of the asperity contact area instead of the leading head of the smooth surface. The maximum temperature rise parameter increases as the pressure, sliding velocity and asperity roughness increased or conductivity decreased. This phenomenon becomes obvious for cases at high pressure, velocity and roughness and low conductivity. Particularly, the influence of roughness is not significant for low velocity. Similar results are found for the maximum temperature rise parameter difference between peaks or peaks/valleys. The simulation results of this asperity surface sliding block contact model are able to provide essential information for the components of microelectro—mechanical systems (MEMS) and biochemical reaction mechanism. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
68.
Difference in Conversions Between Dimethyl Sulfide and Methanethiol in a Cold Plasma Environment 总被引:1,自引:0,他引:1
Cheng-Hsien Tsai Wen-Jhy Lee Chuh-Yung Chen Perng-Jy Tsai Guor-Cheng Fang Minliang Shih 《Plasma Chemistry and Plasma Processing》2003,23(1):141-157
This study compared the conversion of two malodorous substances, dimethyl sulfide (CH3SCH3, DMS) and methanethiol (CH3SH) in a cold plasma reactor. The DMS and CH3SH were successfully destroyed at room temperature. DMS decomposed less than CH3SH at the same conditions. In oxygen-free condition, CS2 and hydrocarbons were the major products, while SO2 and COx were main compounds in oxygen-rich environments. The DMS/Ar plasma yielded more hydrocarbons and less CS2 than that of CH3SH/Ar plasma. In the CH3SH/O2/Ar plasma, rapid formation of SO and CO resulted in the yields much more amounts of SO2 and CO2 than those in the DMS/O2/Ar plasma; and remained only a trace of total hydrocarbons, CH2O, CH3OH, CS2, and OCS. The major differences between the reaction mechanisms of DMS and CH3SH were also proposed and discussed. 相似文献
69.
The mass-transter characteristics of a two-phase system formed by mixing a fixed quantity (20 v/v%) of organic solvent with an aqueous ferricyanide electrolyte solution in an RDE system were studied. The Levich eqution, I1 = 0.62 nFACbD2/3v?1/6ω1/2, was found to be applicable to the two-phase system with only a minor modification in the angular velocity (ω) at Reynolds numbers between 3–5 × 104. The experimental results indicate that the interfacial tension is the most important variable for the two-phase system. One group of organic solvents with smaller interfacial tension, such as benzene or toluene, needs a modification of the Levich equation by replacing the observed angular velocity (ωo) with the true angular velocity (ωt) which was observed to be 1.1 times the observed angular velocity. For the other group with larger interfacial tension, such as n-hexane or cyclohexane, there is no need to modify the observed angular velocity. In other words, the Levich equation may be expressed as I1 = 0.65 nFACbD2/3v?1/6ω1/2 for two-phase solution if the interfacial tension is smaller than 37.0 dyne/cm. 相似文献
70.
Dr. Sung‐Yu Ku Prof. Wen‐Yi Hung Chung‐Wen Chen Shih‐Wei Yang Ejabul Mondal Prof. Yun Chi Prof. Ken‐Tsung Wong 《化学:亚洲杂志》2012,7(1):133-142
In this study, we synthesized and characterized a series of spirobifluorene‐based bipolar compounds (D2 ACN, DNPACN, DNTACN, and DCzACN) in which a dicyano‐substituted biphenyl branch, linked orthogonally to a donor biphenyl branch bearing various diarylamines, acted as an acceptor unit allowing fine‐tuning of the morphological stability, triplet energy, bipolar transport behavior, and the HOMO and LUMO energy levels. The promising physical properties of these new compounds, together with their ability to transport electrons and holes with balanced mobilities, made them suitable for use as host materials in highly efficient phosphorescent organic light‐emitting diodes (PhOLEDs) with green iridium‐based‐ or red osmium‐based phosphors as the emitting layer (EML). We adopted a multilayer structure to efficiently confine holes and electrons within the EML, thus preventing exciton diffusion and improving device efficiency. The device incorporating D2 ACN doped with the red emitter [Os(bpftz)2(PPhMe2)2] (bpftz=3‐(trifluoromethyl)‐5‐(4‐tert‐butylpyridyl)‐1,2,4‐triazolate) gave a saturated red electrophosphorescence with CIE coordinates of (0.65, 0.35) and remarkably high efficiencies of 20.3 % (21 cd A?1) and 13.5 Lm W?1 at a practical brightness of 1000 cd m?2. 相似文献