全文获取类型
收费全文 | 685篇 |
免费 | 27篇 |
专业分类
化学 | 523篇 |
晶体学 | 12篇 |
力学 | 6篇 |
数学 | 13篇 |
物理学 | 158篇 |
出版年
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 4篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 24篇 |
2012年 | 33篇 |
2011年 | 33篇 |
2010年 | 29篇 |
2009年 | 23篇 |
2008年 | 41篇 |
2007年 | 41篇 |
2006年 | 50篇 |
2005年 | 34篇 |
2004年 | 27篇 |
2003年 | 31篇 |
2002年 | 19篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 17篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有712条查询结果,搜索用时 265 毫秒
111.
Semiquinone radical anion of 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ(*-)) forms a strong hydrogen bond with protonated histidine (TolSQ(*-)/His x 2 H(+)), which was successfully detected by electron spin resonance. Strong hydrogen bonding between TolSQ(*-) and His x 2 H(+) results in acceleration of electron transfer (ET) from ferrocenes [R2Fc, R = C5H5, C5H4(n-Bu), C5H4Me] to TolSQ, when the one-electron reduction potential of TolSQ is largely shifted to the positive direction in the presence of His x 2 H(+). The rates of His x 2 H(+)-promoted ET from R2Fc to TolSQ exhibit deuterium kinetic isotope effects due to partial dissociation of the N-H bond in His x 2 H(+) at the transition state, when His x 2 H(+) is replaced by the deuterated compound (His x 2 D(+)-d6). The observed deuterium kinetic isotope effect (kH/kD) decreases continuously with increasing the driving force of ET to approach kH/kD = 1.0. On the other hand, His x 2 H(+) also promotes a hydride reduction of TolSQ by an NADH analogue, 9,10-dihydro-10-methylacridine (AcrH2). The hydride reduction proceeds via the one-step hydride-transfer pathway. In such a case, a large deuterium kinetic isotope effect is observed in the rate of the hydride transfer, when AcrH2 is replaced by the dideuterated compound (AcrD2). In sharp contrast to this, no deuterium kinetic isotope effect is observed, when His x 2 H(+) is replaced by His x 2 D(+)-d6. On the other hand, direct protonation of TolSQ and 9,10-phenanthrenequinone (PQ) also results in efficient reductions of TolSQH(+) and PQH(+) by AcrH2, respectively. In this case, however, the hydride-transfer reactions occur via the ET pathway, that is, ET from AcrH2 to TolSQH(+) and PQH(+) occurs in preference to direct hydride transfer from AcrH2 to TolSQH(+) and PQH(+), respectively. The AcrH2(*+) produced by the ET oxidation of AcrH2 by TolSQH(+) and PQH(+) was directly detected by using a stopped-flow technique. 相似文献
112.
Matsuoka D Iwata T Zikihara K Kandori H Tokutomi S 《Photochemistry and photobiology》2007,83(1):122-130
Phototropin is a blue-light photoreceptor in plants that mediates phototropism, chloroplast relocation, stomata opening and leaf expansion. Phototropin molecule has two photoreceptive domains named LOV1 (light-oxygen-voltage) and LOV2 in the N-terminus and a serine/threonine kinase domain in the C-terminus, and acts as a blue light-regulated kinase. Each LOV domain binds a flavin mononucleotide as a chromophore and undergoes unique cyclic reactions upon blue-light absorption that comprises a cysteinyl-flavin adduct formation through a triplet-excited state and a successive adduct break to revert to the initial ground state. The molecular reactions underlying the photocycle are reviewed and one of the probable molecular schemes is presented. Adduct formation alters the secondary protein structure of the LOV domains. This structural change could be transferred to the linker between the kinase domain and involved in the photoregulation of the kinase activity. The structural changes as well as the oligomeric structures seem to differ between LOV1 and LOV2, which may explain the proposed roles of each domain in the photoregulation of the kinase activity. The photoregulation mechanism of phototropin kinase is reviewed and discussed in reference to the regulation mechanism of protein kinase A, which it resembles. 相似文献
113.
114.
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
115.
Molecular aggregates of partially fluorinated quaternary ammonium salt gemini surfactants 总被引:1,自引:0,他引:1
Matsuoka K Yoshimura T Shikimoto T Hamada J Yamawaki M Honda C Endo K 《Langmuir : the ACS journal of surfaces and colloids》2007,23(22):10990-10994
The size and shape of novel partially fluorinated gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2-hydroxypropyl)ammonium]ethane bromide (CnFC3-2-C3CnF, where n=4, 6, and 8) were investigated in aqueous solution by means of light scattering and transmission electron microscopy (TEM). The sizes of these molecular aggregates changed with increasing carbon number of the alkyl chain and concentration. For example, the apparent hydrodynamic radius by dynamic light scattering was 18 nm at a concentration of cmcx5 for n=4, 115 nm at the cmcx15 for n=6, and 62 nm at the cmcx30 for n=8, at 298.2 K. The shapes of CnFC3-2-C3CnF aggregates drastically changed with the alkyl chain length; the aggregates were mainly in the form of large or irregular small aggregates (n=4), string-like aggregates (n=6), and vesicles (n=8). The bromide-ion activity was measured using a bromide-ion-selective electrode to determine the degree of counterion binding to the aggregates. The degree of counterion binding to aggregate was very small compared with that in the typical hydrogenated gemini surfactants. These results indicated that the small curvature of large aggregates was not influenced by an electrostatic repulsion between the cationic head groups in the case of the bulky molecular volume of fluorinated gemini surfactants. 相似文献
116.
Kanai T Sawada T Toyotama A Yamanaka J Kitamura K 《Langmuir : the ACS journal of surfaces and colloids》2007,23(7):3503-3505
The optical stop band in colloidal crystals is characterized by the central frequency and bandwidth. Although the former is known to be highly tunable by changing the lattice constant, the latter is basically determined by the refractive index contrast between the particles and the background medium that is intrinsic to the materials. In this study, we show that the effective bandwidth in gelled colloidal crystals can also be tuned by controlling the fabrication conditions. Single-domain gelled colloidal crystals were prepared by photopolymerization under various photoirradiation conditions. It was observed that the width of the stop band in the transmission or reflectance spectrum could be expanded by simply adjusting the irradiation time. 相似文献
117.
The homonuclear dipolar coupling of a directly bonded (13)C-(13)C pair has been used to create a dipolar double-quantum filter (D-DQF) to remove the natural-abundance (13)C background in (13)C[(2)H] rotational-echo double-resonance (REDOR) experiments. The most efficient version of this experiment has the D-DQF excitation and reconversion preceding the REDOR evolution period. Calculated and observed (13)C[(2)H]D-DQF-REDOR dephasings were in agreement for a test sample of mixed recrystallized labeled alanines. 相似文献
118.
N. S. Ishioka H. Matsuoka S. Watanabe A. Osa M. Koizumi T. Kume S. Matsuhashi T. Fujimura A. Tsuji H. Uchida T. Sekine 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(2):417-421
The positron emitters11C,13N and18F and their labeled compounds have been produced for studies on plants using a newly developed positron emitting tracer imaging
system. Although this system covers, at present, a limited area in a plant, the distribution of the positron emitter fed into
the plant can be visualized dynamically. Further development of positron-emitter-labeled compounds is expected to elucidate
the physiological function of plants in vivo. 相似文献
119.
Recurrence formulas for overlap, nuclear attraction, and electron-repulsion integrals over Laguerre Gaussian-type functions are presented. They have been derived using compact recurrence relations for homogeneous solid spherical harmonic operators but are rather lengthy as compared to those over Cartesian Gaussian-type functions. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 273–279, 1998 相似文献
120.
Shinobu Koda Masaki Miyamoto Maricela Toma Tatsuro Matsuoka Masahiro Maebayashi 《Ultrasonics sonochemistry》2009,16(5):655-659
This paper shows a systematic study of the 500 kHz frequency ultrasound efficiency on the microbial inactivation as a function of ultrasonic power delivered into the bacterial suspension. The inactivation of Escherichia coli IAM 12058, a Gram-negative bacterium and Streptococcus mutans JCM 5175, a Gram-positive bacterium is enhanced by increasing the ultrasonic power in the range of 1.7–12.4 W and the logarithm of survival ratio decreases linearly with irradiation time, except for E. coli sonicated with the highest power level. The rate constants were estimated in the linear region of the plots representing survival ratio logarithm vs. sonication time. A better understanding of the inactivation process at 500 kHz could be gained by suppressing the chemical effects with a radical scavenger. We find out that the rate constants increase with the ultrasonic power delivered into the solution and dramatically decrease by the addition of t-butanol as a radical scavenger to the bacterial suspension. For comparison, experiments were carried out at a low frequency level of 20 kHz. It was found out that for the same ultrasonic power delivered into the bacterial suspension, the inactivation was slightly enhanced at 500 kHz frequency. The examinations of bacterium performed with a TEM revealed lethal damages arising from the interaction of bacterial cells with the cavitational bubbles. A significant amount of empty cell envelopes as well as their cytoplasmatic content was detected. Thus, based on these new data, the mechanism of bacterial inactivation by ultrasounds at high frequency is discussed here. 相似文献