全文获取类型
收费全文 | 205篇 |
免费 | 21篇 |
专业分类
化学 | 162篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 23篇 |
物理学 | 33篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 13篇 |
2011年 | 13篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 13篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有226条查询结果,搜索用时 31 毫秒
131.
We propose a new method for the performance evaluation of Open Queueing Networks with a Population Constraint (represented by a set of tokens). The method is based on the application of Approximate Mean Value Analysis (AMVA) algorithms. We present procedures for single class networks and for multiple class networks, subject to either a common constraint (shared tokens) or to classbased constraints (dedicated tokens). In fact, the new method is a unified framework into which all procedures for the different types of networks fit. We show how the new method relates to wellknown methods and present some numerical results to indicate its accuracy. 相似文献
132.
Dr. Frédéric Friscourt Prof. Dr. Christoph J. Fahrni Prof. Dr. Geert‐Jan Boons 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13996-14001
Fluorogenic reactions, in which non‐ or weakly fluorescent reagents produce highly fluorescent products, are attractive for detecting a broad range of compounds in the fields of bioconjugation and material sciences. Herein, we report that a dibenzocyclooctyne derivative modified with a cyclopropenone moiety (Fl‐DIBO) can undergo fast strain‐promoted cycloaddition reactions under catalyst‐free conditions with azides, nitrones, nitrile oxides, as well as mono‐ and disubstituted diazo‐derivatives. Although the reaction with nitrile oxides, nitrones, and disubstituted diazo compounds gave cycloadducts with low quantum yield, monosubstituted diazo reagents produced 1H‐pyrazole derivatives that exhibited an approximately 160‐fold fluorescence enhancement over Fl‐DIBO combined with a greater than 10 000‐fold increase in brightness. Concluding from quantum chemical calculations, fluorescence quenching of 3H‐pyrazoles, which are formed by reaction with disubstituted diazo‐derivatives, is likely due to the presence of energetically low‐lying (n,π*) states. The fluorogenic probe Fl‐DIBO was successfully employed for the labeling of diazo‐tagged proteins without detectable background signal. Diazo‐derivatives are emerging as attractive reporters for the labeling of biomolecules, and the studies presented herein demonstrate that Fl‐DIBO can be employed for visualizing such biomolecules without the need for probe washout. 相似文献
133.
Evidence for Degradation of the Chrome Yellows in Van Gogh’s Sunflowers: A Study Using Noninvasive In Situ Methods and Synchrotron‐Radiation‐Based X‐ray Techniques 下载免费PDF全文
Dr. Letizia Monico Prof. Koen Janssens Dr. Ella Hendriks Frederik Vanmeert Dr. Geert Van der Snickt Dr. Marine Cotte Dr. Gerald Falkenberg Prof. Brunetto Giovanni Brunetti Dr. Costanza Miliani 《Angewandte Chemie (International ed. in English)》2015,54(47):13923-13927
This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Gogh’s Sunflowers (Van Gogh Museum, Amsterdam). Noninvasive in situ spectroscopic analysis at several spots on the painting, combined with synchrotron‐radiation‐based X‐ray investigations of two microsamples, revealed the presence of different types of chrome yellow used by Van Gogh, including the lightfast PbCrO4 and the sulfur‐rich PbCr1?xSxO4 (x≈0.5) variety that is known for its high propensity to undergo photoinduced reduction. The products of this degradation process, i.e., CrIII compounds, were found at the interface between the paint and the varnish. Selected locations of the painting with the highest risk of color modification by chemical deterioration of chrome yellow are identified, thus calling for careful monitoring in the future. 相似文献
134.
135.
Bello D Aslam T Bultynck G Slawin AM Roderick HL Bootman MD Conway SJ 《The Journal of organic chemistry》2007,72(15):5647-5659
The design of a range of 4-position-modified D-myo-inositol 1,4,5-trisphosphate derivatives is described. The enantioselective synthesis of these compounds is reported, along with initial biological analysis, which indicates that these compounds do not act as D-myo-inositol 1,4,5-trisphosphate receptor agonists or antagonists. 相似文献
136.
Hexafluoro acetone CF3COCF3 has been shown to react rapidly with the CH2OO, CH3CHOO, and (CH3)2COO intermediates that are formed in the ozonolysis of C2H4, trans‐2‐C4H8, and 2,3‐dimethyl‐2‐butene, respectively, and to form products tentatively assigned to the corresponding secondary ozonides. Relative rate method applied to the C2H4 ozonolysis has indicated that CF3COCF3 reacts ∼13 times faster than CH3CHO. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 261–269, 1999 相似文献
137.
CF3O2CF3 was photolyzed at 254 nm in the presence of CO in 760 torr N2 or air at 296 K in a static reactor. In N2, the products CF3OC(O)C(O)OCF3 and CF3OC(O)O2C(O)OCF3 were detected by FTIR spectroscopy. In air, the only observed products were CF2O and CO2 and a chain process, initiated by CF3O, was invoked for the conversion of CO to CO2. From both product studies, a mechanism for the CF3O initiated oxidation of CO was derived, involving the addition reaction CF3O2 + CO → CF3OC(O). The rate constant for the reaction CF3O + CO at 296 K at a total pressure of 760 torr air was determined to be k(CF3O + CO) = (5.0 ± 0.9) × 10−14 cm3 molecule−1 s−1. © 1997 John Wiley & Sons, Inc. 相似文献
138.
Mousa Al‐Tarazi A. Bert M. Heesink Mohammed O. J. Azzam Salah Abu Yahya Geert F. Versteeg 《Crystal Research and Technology》2004,39(8):675-685
The precipitation kinetics of zinc sulfide were studied using a lab scale mixed‐suspension‐mixed‐product‐removal (MSMPR) precipitation reactor. The vessel was operated at different feed concentrations, molar ratios, stirrer speeds, pH‐values, feed injection positions and residence times. Primary nucleation and volume average crystal growth rates as well as agglomeration kernel were determined. Relationships were found between the rates of the different crystallization steps on the one hand and supersaturation, stirrer speeds, pH‐values, Zn2+ to S2‐ ratio, feed positions on the other. These show that larger crystals are obtained at high supersaturation, moderate stirrer speeds, small residence times, a pH‐value of around 5 and high Zn2+ to S2‐ ratios. One should realize though that the applied MSMPR method is not the most optimal technique for examining fast precipitation reactions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
139.
Geert Watson Parviz Gohari Derakhshandeh Sara Abednatanzi Johannes Schmidt Karen Leus Pascal Van Der Voort 《Molecules (Basel, Switzerland)》2021,26(4)
Herein, a highly N-rich covalent triazine framework (CTF) is applied as support for a RuIII complex. The bipyridine sites within the CTF provide excellent anchoring points for the [Ru(acac)2(CH3CN)2]PF6 complex. The obtained robust RuIII@bipy-CTF material was applied for the selective tandem aerobic oxidation-Knoevenagel condensation reaction. The presented system shows a high catalytic performance (>80% conversion of alcohols to α, β-unsaturated nitriles) without the use of expensive noble metals. The bipy-CTF not only acts as the catalyst support but also provides the active sites for both aerobic oxidation and Knoevenagel condensation reactions. This work highlights a new perspective for the development of highly efficient and robust heterogeneous catalysts applying CTFs for cascade catalysis. 相似文献
140.
Dr. Jun Guo Dr. Guojun Chen Dr. Xinghai Ning Dr. Xiuru Li Dr. Jianfeng Zhou Dr. Anna Jagielska Prof. Bingqian Xu Prof. Geert‐Jan Boons 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(15):4568-4574
A new atomic force microscopy (AFM)‐based chemo‐mechanical tweezer has been developed that can measure mechanical properties of individual macromolecules in supramolecular assembly and reveal positions of azide‐containing polymers. A key feature of the new technology is the use of an AFM tip densely modified with 4‐dibenzocyclooctynols (chemo‐mechanical tweezer) that can react with multiple azide containing macromolecules of micelles to give triazole “clicked” compounds, which during retracting phases of AFM imaging are removed from the macromolecular assembly thereby providing a surface topographical image and positions of azide‐containing polymers. The force–distance curves gave mechanical properties of removal of individual molecules from a supramolecular assembly. The new chemo‐mechanical tweezer will make it possible to characterize molecular details of macromolecular assemblies thereby offering new avenues to tailor properties of such assemblies. 相似文献