全文获取类型
收费全文 | 571篇 |
免费 | 11篇 |
专业分类
化学 | 539篇 |
晶体学 | 3篇 |
力学 | 2篇 |
数学 | 7篇 |
物理学 | 31篇 |
出版年
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 28篇 |
2011年 | 25篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 32篇 |
2007年 | 33篇 |
2006年 | 28篇 |
2005年 | 40篇 |
2004年 | 44篇 |
2003年 | 32篇 |
2002年 | 29篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1973年 | 5篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有582条查询结果,搜索用时 15 毫秒
41.
Unidirectional crystallization of charged colloidal silica due to the diffusion of a base 总被引:1,自引:0,他引:1
Murai M Yamada H Yamanaka J Onda S Yonese M Ito K Sawada T Uchida F Ohki Y 《Langmuir : the ACS journal of surfaces and colloids》2007,23(14):7510-7517
Dilute aqueous dispersions of charged colloidal silica (particle volume fraction = approximately 0.03-0.04, particle diameter = 110 nm) exhibit unidirectional crystal growth due to the diffusion of a weak base, pyridine (Py). Similar diffusion-crystallization is enabled by a salt of a weak acid and a strong base, sodium hydrogen carbonate (NaHCO3). The resulting crystals consist of columnar (or cubic) crystal grains with a maximum height of a few centimeters and a maximum width of 1 cm. The crystal growth process is attributed to a combination of (i) the diffusion of Py or NaHCO3 accompanied by a charging reaction of the silica particles and (ii) the charge-induced crystallization of the silica colloids. Theoretical growth curves based on the reaction-diffusion model for the case of Py were in good agreement with the observed curves. We also report the immobilization of the resulting large crystals by using a polymer hydrogel matrix. 相似文献
42.
An efficient synthesis of carbacyclin and its analogs (2-7) is described in which the stereospecific 1,4-hydrogenation of a 1,3-diene to an internal monoene plays a key role. That is, arene.Cr(CO)3 complex-catalyzed 1,4-hydrogenation of the dienes 13 and 58, obtainable from the Corey lactone in good yields, under high H2 pressure afforded the exocyclic olefins 14 and 61 stereospecifically in excellent yields, and these intermediates were converted to therapeutically useful carbacyclin (2) and its analogs 3-7 in a usual way. 相似文献
43.
M Shibasaki A Takahashi T Aoki H Sato S Yamada M Kudo K Kogi S Narita 《Chemical & pharmaceutical bulletin》1992,40(1):279-281
A synthesis of a novel and chemically stable homoisocarbacyclin analog, TY-11223 (3), has been accomplished. The analog (3), given intravenously or orally, showed potent and long-lasting activities in inhibiting platelet aggregation and, in addition, a good selectivity in biological activities. 相似文献
44.
Dr. Xinxin Tang Dr. Hidetoshi Noda Prof. Dr. Masakatsu Shibasaki 《Angewandte Chemie (International ed. in English)》2023,62(51):e202311027
The exponential proliferation of conformers makes it impossible to examine the entire population in most systems. Controlling conformational ensembles is thus pivotal in many areas of chemistry. Rh2(esp)2, a dicarboxylate-derived paddlewheel rhodium complex, is one of the most effective catalysts for nitrene chemistry. Its enormous success has led to preparing many analogous complexes. However, there has been little consideration for the conformational dynamics of the parent catalyst. Herein, we report a new ligand modification principle that prevents conformer interconversion. The resulting complex comprises two isolable conformers, whose structures have been determined by X-ray diffraction. Combined experimental and computational data has revealed similarities and dissimilarities between the conformationally confined and parent complexes. Three model cases have demonstrated the utility of conformational fixation in the development of stereoselective catalysts for nitrene transfer reactions. The design principle described in this study can be combined with other established modification strategies, serving as a springboard for further advancement of the chemistry of paddlewheel metal complexes. 相似文献
45.
DESIGN AND PERFORMANCE OF THE OKAZAKI LARGE SPECTROGRAPH FOR PHOTOBIOLOGICAL RESEARCH 总被引:7,自引:1,他引:7
Masakatsu WatanabeMasaki Furuya†Yasuhiro Miyoshi†Yasunori Inoue†Isao Iwahashi‡Koichi Matsumoto‡ 《Photochemistry and photobiology》1982,36(4):491-498
A computer-operated spectrograph was recently built at Okazaki, Japan. Different specimens can be placed on a horseshoe-shaped focal curve (10 m long) covering a wavelength range of 250 to 1000 nm so they can be irradiated simultaneously. The linear dispersion is about 0.8 nm/cm. The photon fluence rate on the focal curve is 5 x 1015 . photons x cm-2 x s-1 at 300nm and 1 x 1016 photons x cm-2 x s-1 at 600 and at 900 nm. The spectral half width is 5.5 nm or less on the focal curve. The stray light content is about 10-5 of the main peak at the peak wavelength ± 100 nm. Specimens are set in microcomputer-controlled threshold boxes so that wavelengths, photon fluence rates, photon fluences and timing of irradiations are controlled automatically according to a pre-programmed schedule. An optical fiber system is also provided for remote irradiations. 相似文献
46.
Dimethylaluminiun chloride has been found to cleave THP ethers selectively without any removal of t-butyldimethylsilyl ethers 相似文献
47.
Ultrafast charge resonant (CR) dynamics between two molecules in a dimer system has been studied theoretically and experimentally using 6-fs laser pulses and a thin film of amorphous-phase phthalocyanine tin(IV) dichloride (SnPc). The modulation of the absorbance change in the bleaching spectral range of the CR absorption band was analyzed to obtain the amount of charge resonantly transferred back and forth by a dimeric vibration induced by photoexcitation. The modulation can be explained in terms of a periodic change in the cross section and a periodic energy shift, where both are induced by the change in the overlap integral caused by the accordion-type intermolecular vibration. The associated change in distance between two molecules with the intermolecular vibration was estimated to be 0.09 A, which corresponds to 2.5% of the mean distance between the two SnPc molecules in the dimeric system. 相似文献
48.
Sugita M Yamaguchi A Yamagiwa N Handa S Matsunaga S Shibasaki M 《Organic letters》2005,7(23):5339-5342
[reaction, structure: see text] Chiral Y{N(SiMe3)2}3/linked-BINOL catalyst generated Y-enolate in situ from various hydroxyketones (R2 = aryl, heteroaryl). Beta-amino-alpha-hydroxy ketones (R1 = aryl, heteroaryl, alkenyl) were obtained syn-selectively (up to 96/4) in high ee (up to 98%) and good yield (up to 98% yield). 相似文献
49.
50.
Kato T Kawabata Y Fujii M Kato T Hato M Minamikawa H 《Journal of colloid and interface science》2007,312(1):122-129
Surfactant self-diffusion coefficients have been measured on a binary system of 1-O-beta-3,7-dimethyloctyl-D-maltopyranoside (beta-Mal(2)(Ger))/water and a mixed surfactant system of beta-Mal(2)(Ger)/1-O-beta-3,7-dimethyloctyl-D-glucopyranoside (beta-Glc(Ger))/water at 25 degrees C. For comparison, measurements have also been made on 1-O-beta-decyl-D-maltopyranoside (beta-Mal(2)C(10))/water and beta-Mal(2)C(10)/1-O-beta-decyl-D-glucopyranoside (beta-GlcC(10))/water. The hydrodynamic radius of beta-Mal(2)(Ger) micelles obtained from the micellar diffusion coefficient is around 3 nm and nearly equal to that of beta-GlcC(10) micelles within experimental error. In the mixed surfactant systems, the hydrodynamic radii for both systems increase with increasing X(G) (the mole fraction of beta-Glc(Ger) or beta-GlcC(10) in the total mixed solute) above X(G) congruent with 0.4 when the total surfactant concentration is kept constant at 2 wt%. The R(H) of beta-Glc(Ger)/Mal(2)(Ger) micelles increases more rapidly than beta-GlcC(10)/beta-Mal(2)C(10) micelles, and then phase separation occurs at X(G) congruent with 0.65. On the other hand, the R(H) of beta-GlcC(10)/beta-Mal(2)C(10) micelles continues to increase until the phase separation occurs at X(G) congruent with 0.92. Measurements have also been performed as a function of total surfactant concentration at constant X(G) (=0.6). The CMC of the beta-Glc(Ger)/Mal(2)(Ger) system is larger than that of the beta-GlcC(10)/beta-Mal(2)C(10) system as expected from the results of the pure surfactant systems published previously. The R(H) increases with increasing total surfactant concentration for both systems. At higher concentrations, the R(H) of beta-Glc(Ger)/Mal(2)(Ger) micelles increases more rapidly than beta-GlcC(10)/beta-Mal(2)C(10) micelles. These results can be explained by the fact that the geranyl and decyl chains have the same volume but different chain lengths. 相似文献