全文获取类型
收费全文 | 370篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
化学 | 265篇 |
晶体学 | 3篇 |
力学 | 4篇 |
数学 | 1篇 |
物理学 | 70篇 |
无线电 | 36篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 6篇 |
2012年 | 18篇 |
2011年 | 17篇 |
2010年 | 7篇 |
2009年 | 10篇 |
2008年 | 16篇 |
2007年 | 18篇 |
2006年 | 16篇 |
2005年 | 20篇 |
2004年 | 26篇 |
2003年 | 21篇 |
2002年 | 15篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1972年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有379条查询结果,搜索用时 11 毫秒
261.
We have studied the validity of the double‐probe method in recombining plasmas. Electron temperature (Te) measured with a double probe was quantitatively evaluated by taking into account the influences of plasma potential fluctuation, plasma resistivity, and electron density fluctuation on the current–voltage characteristics. Differential potential fluctuation and plasma resistivity between two electrodes have a minor effect on Te especially when the inter‐distance is small (typically 1 mm). Scattering of measured Te due to the density fluctuation was sufficiently suppressed by making the data acquisition time long (typically 4 s) and taking the average. There is a good agreement between Te measured with the optimized double‐probe method and that with laser Thomson scattering diagnostics. 相似文献
262.
The structure activity relationship (SAR) in the anti-cancer activities of pyrazolo[1,5-a]indole derivatives was investigated, and the following conclusions were obtained: 1) N(1)-quaternarization is essential for anti-cancer activity, 2) the size and polarity of the 2-substituent is crucial for in vitro activity which allows further investigation in an in vivo test, 3) the effect of the 4-substituent on the activity is minor compared with the other two factors. 相似文献
263.
Koichi Takaki Katsuyuki Takahashi Alexis Guionet Takayuki Ohshima 《Molecules (Basel, Switzerland)》2021,26(20)
Pulsed electric fields (PEFs), which are generated by pulsed power technologies, are being tested for their applicability in food processing through protein conformational change and the poration of cell membranes. In this article, enzyme activity change and the permeabilization of agricultural products using pulsed power technologies are reviewed as novel, nonthermal food processes. Compact pulsed power systems have been developed with repetitive operation and moderate output power for application in food processing. Firstly, the compact pulsed power systems for the enzyme activity change and permeabilization are outlined. Exposure to electric fields affects hydrogen bonds in the secondary and tertiary structures of proteins; as a result, the protein conformation is induced to be changed. The conformational change induces an activity change in enzymes such as α-amylase and peroxidase. Secondly, the conformational change in proteins and the induced protein functional change are reviewed. The permeabilization of agricultural products is caused through the poration of cell membranes by applying PEFs produced by pulsed discharges. The permeabilization of cell membranes can be used for the extraction of nutrients and health-promoting agents such as polyphenols and vitamins. The electrical poration can also be used as a pre-treatment for food drying and blanching processes. Finally, the permeabilization of cell membranes and its applications in food processing are reviewed. 相似文献
264.
H. Ohshima 《Colloid and polymer science》1997,275(5):480-485
A general theory for the electrophoresis of a cylindrical soft particle (i.e., a cylindrical hard colloidal particle coated
with a layer of ion-penetrable polyelectrolytes) in an electrolyte solution in an applied transverse or tangential electric
field is proposed. This theory unites two different electrophoresis theories for cylindrical hard particles and for cylindrical
polyelectrolytes. That is, the general mobility expression obtained in this paper tends to the mobility expression for a cylindrical
hard particle for the case where the polyelectrolyte layer is absent or the frictional coefficient in the poly-electrolyte
layer becomes infinity, whereas it tends to that for a cylin-drical polyelectrolyte in the absence of the particle core. Simple
approximate analytic mobility expressions are also presented.
Received: 29 August 1996 Accepted: 7 November 1996 相似文献
265.
To elucidate precise mechanisms of appositional mineralization of bone, structural features of mineralizing collagen fibrils of the osteoid in normal and hypocalcaemic rats were examined in detail by transmission electron microscopy. Ultrathin sections of the osteoid of various types of bones of the rats fed with regular or normal calcium diet often displayed electrondense segments in the specific regions of the collagen fibrils located immediately adjacent to the mineralization front or to the mineralization nodules. Such dense segments appeared only after Ur-Pb staining and were more distinct in undecalcified specimens. Dense segments were undetectable in ultrathin sections picked up on ethylene glycol instead of water in the trough, even after Ur-Pb staining. Collagen fibrils in the widened osteoid of hypocalcaemic rats fed with calcium-free diet failed to show electron-dense segments. A careful comparison between the hydrously or anhydrously processed adjacent sections of a normal rat bone indicated a drastic dissolution of electron-dense material from the bone matrix near the mineralization front in hydrously processed sections and, thus, implicated the presence of labile mineral-matrix complexes in the recently mineralized bone matrix. Such labile sediments were readily dissociated within the ultrathin sections while the sections were floating on water and immediately adsorbed onto the pre-mineralizing collagen fibrils, where some conformational changes might have occurred. These data indicate that highly electron-dense segments appearing in the osteoidal collagen fibrils are a type of process-induced product, which indirectly represent possible structural alterations in the segmental portions of pre-mineralizing collagen fibrils in the osteoid of rat bones. 相似文献
266.
Tosaki SY Horiuchi Y Nemoto T Ohshima T Shibasaki M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(6):1527-1544
We describe a new strategy for enantio- and diastereoselective syntheses of all possible stereoisomers of 1,3-polyol arrays. This strategy relies on a highly catalyst-controlled epoxidation of alpha,beta-unsaturated morpholinyl amides promoted by the Sm-BINOL-Ph(3)As[double bond]O (1:1:1) complex, followed by a conversion of morpholinyl amides into ketones and diastereoselective ketone reduction. Highly enantio- (up to >99 % ee) or diastereoselective (up to >99.5:0.5) epoxidation was achieved using 5-10 mol % of the Sm complex to afford synthetically very useful, nearly optically pure alpha,beta-epoxy morpholinyl amides. Stereoselectivity of the epoxidation was controlled by the chirality of BINOL with overwhelming inherent diastereofacial preference for the substrate. Combination with the syn- and anti-selective ketone reduction with the highly catalyst-controlled epoxidation allowed for an iterative strategy for the syntheses of all possible stereoisomers of 1,3-polyol arrays. Eight possible stereoisomers of 1,3,5,7-tetraol arrays were synthesized with high to excellent stereoselectivity. Moreover, the efficiency of the present strategy was successfully demonstrated by enantioselective syntheses of several 1,3-polyol/alpha-pyrone natural products, for example, cryptocaryolone diacetate. 相似文献
267.
Horiuchi Y Gnanadesikan V Ohshima T Masu H Katagiri K Sei Y Yamaguchi K Shibasaki M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(18):5195-5204
The development of a direct catalytic asymmetric aldol-Tishchenko reaction and the nature of its catalyst are described. An aldol-Tishchenko reaction of various propiophenone derivatives with aromatic aldehydes was promoted by [LaLi3(binol)3] (LLB), and reactivity and enantioselectivity were dramatically enhanced by the addition of lithium trifluoromethanesulfonate (LiOTf). First, we observed a dynamic structural change of LLB by the addition of LiOTf using 13C NMR spectroscopy, electronspray ionization mass spectrometry (ESI-MS), and cold-spray ionization mass spectrometry (CSI-MS). X-ray crystallography revealed that the structure of the newly generated self-assembled complex was a binuclear [La2Li4(binaphthoxide)5] complex 6. A reverse structural change of complex 6 to LLB by the addition of one equivalent of Li2(binol) was also confirmed by ESI-MS and experimental results. The drastic concentration effects on the direct catalytic asymmetric aldol-Tishchenko reaction suggested that the addition of LiOTf to LLB generated an active oligomeric catalyst species. 相似文献
268.
Takita R Yakura K Ohshima T Shibasaki M 《Journal of the American Chemical Society》2005,127(40):13760-13761
Asymmetric alkynylation of both aromatic and aliphatic aldehydes using catalytic amounts of In(III)/BINOL is described. Dual activation of both substrates due to the "bifunctional character" of the indium(III) catalyst enables a broad range of substrate generality with high enantioselectivity (83 to >99% ee). 相似文献
269.
Tosaki SY Tsuji R Ohshima T Shibasaki M 《Journal of the American Chemical Society》2005,127(7):2147-2155
The characteristic property of the lanthanide complex, which easily undergoes a dynamic ligand exchange and alters its structure and function in situ, is described. After the completion of the catalytic asymmetric epoxidation of various alpha,beta-unsaturated amides 2 in the presence of the Sm-(S)-BINOL-Ph3As=O (1:1:1) complex 1 (2-10 mol %), the addition of Me3SiN3 directly to the reaction mixture led to smooth epoxide-opening at room temperature, affording the corresponding anti-beta-azido-alpha-hydroxyamide 4 in excellent overall yield (up to 99%) with complete regioselectivity and excellent enantiomeric excess (up to >99%). The key to the success of the sequential process was the in situ generation of the highly reactive samarium azide complex through dynamic ligand exchange. In situ IR spectroscopy and other experiments provided strong evidence that the samarium azide complex was generated. In addition, the relatively high Lewis basicity of the amide moiety had a key role in the high reactivity of both the epoxidation and the epoxide-opening reactions. Examinations of other nucleophiles such as sulfur or carbon nucleophiles as well as transformations of epoxide-opened products are also described. 相似文献
270.
Ohshima H 《Journal of colloid and interface science》2002,248(2):499-503
A general expression as well as approximate expressions are derived for the electrophoretic mobility of dilute spherical colloidal particles in a salt-free medium containing only counter ions. It is shown that there is a certain critical value of the particle surface charge. When the particle surface charge is lower than the critical value, the electrophoretic mobility is proportional to the particle surface charge or the particle zeta potential, following Hückel's formula. When the particle surface charge is higher than the critical value, the electrophoretic mobility becomes independent of the particle surface charge. This is due to the effect of counter ion condensation in the vicinity of the particle surface. 相似文献