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排序方式: 共有270条查询结果,搜索用时 156 毫秒
171.
Cyclic seleninate esters serve as catalysts for the rapid oxidation of sulfides to sulfoxides, alkenes to epoxides, and enamines to α-hydroxyketones. Optimal conditions were found that minimize the overoxidation of the product sulfoxides to sulfones and the hydrolysis of epoxides to diols. In some examples such as styrene derivatives, oxidative cleavage was observed instead of epoxidation. The enamine oxidations proceed via the initial formation of dimeric 2,5-diamino-1,4-dioxane species, which were hydrolyzed in situ to the final products. The structure of one such dimer was confirmed by X-ray crystallography. 相似文献
172.
Davey RJ Sadiq G Back K Wilkinson L Seaton CC 《Chemical communications (Cambridge, England)》2012,48(14):1976-1978
While the use of additives to control the crystallization of polymorphs is well known, similar methodology to promote the crystallization of a metastable conglomerate over a stable racemic compound in enantiomeric systems has not been reported. Here we demonstrate this phenomenon in the case of 2-chloromandelic acid. 相似文献
173.
Yeasmin S Kim CH Park HJ Sheikh MI Lee JY Kim JW Back KK Kim SH 《Applied biochemistry and biotechnology》2011,164(3):294-304
Cellulase-free xylanase has potential for its application in the selective removal of hemicellulose from kraft pulp to give
good strength to paper. In this study, a gene (xyn) encoding cellulase activity–free xylanase enzyme (Xyn) was isolated from Paenibacillus polymyxa PPL-3. The xyn gene encoded a protein of 221 amino acids, and the purified Xyn was about 22.5 kDa measured by sodium dodecyl sulfate–polyacrylamide
gel electrophoresis. Moreover, the cellulase activity–free xylanase enzyme (Xyn) was displayed on the cell surface of Saccharomyces cerevisiae EBY100 using Aga2p as an anchor protein. Cell surface display of xylanase enzyme (Xyn) on S. cerevisiae EBY100 was confirmed by immunofluorescence microscopy. Optimum cell surface display of xylanase enzyme (Xyn) was observed
at pH 7 and 40 °C. Therefore, cell surface–displayed xylanase enzyme (Xyn) can be used in the paper industry. 相似文献
174.
We present here a practical synthesis of functional 3-amino-benzofurans through base-promoted intramolecular cyclization of (2-propargyl ether) arylimines. A systematic study of the cyclization system revealed that the presence and the amount of base played an essential role in this reaction. The results showed that the cyclization proceeded cleanly and smoothly under mild reaction conditions, employing potassium tert-butoxide as base, THF as solvent, at room temperature in a short reaction time (1 h). The generality of this reaction has been established with (2-propargyl ether) arylimines having both electron-withdrawing and electron-donating groups. 相似文献
175.
Seul‐Ong Kim Gi Back Lee Hyojung Cha Chan Eon Park Soon‐Ki Kwon Yun‐Hi Kim 《Journal of polymer science. Part A, Polymer chemistry》2014,52(9):1306-1314
Novel alkoxy anthracene (ODA)‐based polymeric semiconductors were designed for polymer solar cell applications. Alkoxyanthracene, which contains many π electrons and electron donating group, was easily synthesized. The copolymers, poly(alkoxy anthracene‐alt‐thiophene benzothiadiazole thiophene) poly(ODA‐TBT) and poly(alkoxy anthracene‐alt‐benzothiadiazole) poly(ODA‐BT), have been obtained by Suzuki coupling polymerization. Both polymers have ODA unit as a donor and benzothiadiazole as an acceptor. ODA‐TBT has thiophene linkages between ODA and benzothiadiazole. The optical, thermal, and electrochemical properties have been investigated by UV–visible absorption, thermal gravimetric analysis, differential scanning calorimetry, and CV. Organic thin‐film transistor using polymers showed that the hole mobility of poly(ODA‐alt‐TBT) was around 3.6 × 10?3 cm2/Vs with on/off ratio of 9.91 × 105 while that of poly(ODA‐alt‐BT) was around 1.21 × 10?2 cm2/Vs with on/off ratio of 2.64 × 106. Organic photovoltaic performance based on polymers were evaluated with a configuration of ITO/PEDOT:PSS/active layer/LiF/Al. Poly(ODA‐TBT) exhibits a short circuit current (Jsc) of 3.9 mA/cm2 and power conversion efficiency (PCE) of 1.4%, and poly(ODA‐BT) exhibits the Jsc of 6.4 mA/cm2 and PCE of 2.2%. The better device performance of poly(ODA‐BT) is attributed to its charge transfer ability and enhanced mobility and crystallinity although poly(ODA‐BT) does not have extended π‐conjugation due to twisted structure compared with poly(ODA‐TBT). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1306–1314 相似文献
176.
P. G. Varmette D. T. Shidot W. C. Ma A. V. Ramayya R. V. F. Janssens C. N. Davids J. H. Hamilton I. Ahmad H. Amro B. R. S. Babu B. Back K. S. Bindra D. J. Blumenthal L. T. Brown M. P. Carpenter W. L. Croft B. Crowell S. M. Fischer U. Garg R. G. Henry T. Ishii T. L. Khoo J. Kormicki T. Lauritsen C. J. Lister D. Nisius H. Penttila R. B. Piercey J. A. Winger S. J. Zhu andP. B. Semmes 《Physics letters. [Part B]》1997,410(2-4):103-109
In-beam γ-ray transitions in 181Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1/2−[521] ground state was observed up to 29/2−. A 5/2−[512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i13/2 orbitals and are proposed to decay to an i13/2 isomeric state associated with an oblate state. 相似文献
177.
Naphtho[2,1‐b:3,4‐b′]dithiophene‐based Bulk Heterojunction Solar Cells: How Molecular Structure Influences Nanoscale Morphology and Photovoltaic Properties
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Yu Jin Kim Ye Rim Cheon Jang Yeol Back Prof. Yun‐Hi Kim Dae Sung Chung Prof. Chan Eon Park 《Chemphyschem》2014,15(16):3626-3633
Organic bulk heterojunction photovoltaic devices based on a series of three naphtho[2,1‐b:3,4‐b′]dithiophene (NDT) derivatives blended with phenyl‐C71‐butyric acid methyl ester were studied. These three derivatives, which have NDT units with various thiophene‐chain lengths, were employed as the donor polymers. The influence of their molecular structures on the correlation between their solar‐cell performances and their degree of crystallization was assessed. The grazing‐incidence angle X‐ray diffraction and atomic force microscopy results showed that the three derivatives exhibit three distinct nanoscale morphologies. We correlated these morphologies with the device physics by determining the J–V characteristics and the hole and electron mobilities of the devices. On the basis of our results, we propose new rules for the design of future generations of NDT‐based polymers for use in bulk heterojunction solar cells. 相似文献
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