全文获取类型
收费全文 | 753篇 |
免费 | 25篇 |
国内免费 | 4篇 |
专业分类
化学 | 550篇 |
晶体学 | 13篇 |
力学 | 13篇 |
数学 | 31篇 |
物理学 | 175篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 14篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 21篇 |
2013年 | 34篇 |
2012年 | 36篇 |
2011年 | 35篇 |
2010年 | 27篇 |
2009年 | 32篇 |
2008年 | 41篇 |
2007年 | 34篇 |
2006年 | 37篇 |
2005年 | 23篇 |
2004年 | 29篇 |
2003年 | 24篇 |
2002年 | 23篇 |
2001年 | 23篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 16篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有782条查询结果,搜索用时 46 毫秒
771.
Akai Y Yamamoto T Nagata Y Ohmura T Suginome M 《Journal of the American Chemical Society》2012,134(27):11092-11095
The poly(quinoxaline-2,3-diyl)-based helically chiral phosphine ligands PQXphos exhibited high enantioselectivities up to 97% ee in palladium-catalyzed desymmetrization of meso-1,2-dialkylsubstituted-3-methylenecyclopropanes through silaborative cleavage of the C-C bond. The observed enantioselectivities were higher than those obtained with 2-diarylphosphino-1,1'-binaphthyl in our original report. Remarkable rate enhancement was also observed with a series of PQXphos in comparison with the corresponding low-molecular weight ligands. 相似文献
772.
Masahide Tona Kazuo Nagata Nobuyuki Nakamura Makoto Sakurai Shunsuke Ohtani 《Surface science》2006,600(1):124-132
We have observed secondary particles and photons emitted from hydrogen terminated Si(1 1 1) 1 × 1 surfaces in the interactions with highly charged ions (HCIs) of iodine having a wide range of charge state, q, from I17+ up to I53+, fully stripped iodine ion. A TOF-SIMS (time-of-flight secondary ion mass spectrometry) apparatus has been used to investigate secondary emissions where protons are dominant signals in the TOF spectra. Measured yields of H+ and show strong q-dependences, proportional to q3.4 and q5, respectively. For Si+, while the yield remains constant for q < ∼ 25, it begins increasing with q1.4 at higher q (∼25). The mechanism of secondary emissions is briefly discussed. 相似文献
773.
Ihara M Nishihara H Yoon KS Lenz O Friedrich B Nakamoto H Kojima K Honma D Kamachi T Okura I 《Photochemistry and photobiology》2006,82(3):676-682
In order to generate renewable and clean fuels, increasing efforts are focused on the exploitation of photosynthetic microorganisms for the production of molecular hydrogen from water and light. In this study we engineered a 'hard-wired' protein complex consisting of a hydrogenase and photosystem I (hydrogenase-PSI complex) as a direct light-to-hydrogen conversion system. The key component was an artificial fusion protein composed of the membrane-bound [NiFe] hydrogenase from the beta-proteobacterium Ralstonia eutropha H16 and the peripheral PSI subunit PsaE of the cyanobacterium Thermosynechococcus elongatus. The resulting hydrogenase-PsaE fusion protein associated with PsaE-free PSI spontaneously, thereby forming a hydrogenase-PSI complex as confirmed by sucrose-gradient ultracentrifuge and immunoblot analysis. The hydrogenase-PSI complex displayed light-driven hydrogen production at a rate of 0.58 mumol H(2).mg chlorophyll(-1).h(-1). The complex maintained its accessibility to the native electron acceptor ferredoxin. This study provides the first example of a light-driven enzymatic reaction by an artificial complex between a redox enzyme and photosystem I and represents an important step on the way to design a photosynthetic organism that efficiently converts solar energy and water into hydrogen. 相似文献
774.
Yamada K Tokumoto Y Nagata T Mafuné F 《The journal of physical chemistry. B》2006,110(24):11751-11756
Gold nanoparticles with an average diameter of approximately 8 nm (Au approximately 15,000) were irradiated with a tightly focused pulse laser at 355 nm in an aqueous solution of sodium dodecyl sulfate (SDS). Transient absorption spectra of the solution were measured at 25-100 ns after the laser irradiation. The observed transient absorption around 720 nm is assignable to the 2p <-- 1s transition of solvated electrons produced via multiple ionization of the gold nanoparticles. The nascent charge state of the gold nanoparticles was estimated from the transient absorbance. The dependence of the charge state on the SDS concentration shows a gradual increase from approximately +60 to approximately +70 in the 2 x 10(-4) to 3 x 10(-4) M range and an abrupt increase up to approximately +710 at the critical micelle concentration (CMC) of SDS, 8 x 10(-3) M. TEM measurements after laser irradiation reveal that the gold nanoparticles fragment into Au(approximately 1000) at a SDS concentration of 3 x 10(-4) M, whereas they are significantly dissociated into Au(approximately 100) above the CMC. The observed correlation between the nascent charge states and the extent of size reduction of the gold nanoparticles after the laser treatment indicates that the size reduction is caused by the Coulomb explosion of the highly charged gold nanoparticles. The mechanism of laser-induced size reduction is quantitatively discussed based on the liquid drop model. 相似文献
775.
[reaction: see text] Catalytic asymmetric allylation of 3,4-dihydro-6,7-dimethoxyisoquinoline was carried out using allyltrimethoxysilane in the presence of Cu(I) and tol-BINAP. The allyl adduct thus obtained was transformed to a chiral synthetic intermediate for (-)-emetine in good yield. The procedure was applied to the total synthesis of ent-emetine. 相似文献
776.
A practical method to evaluate the contributions of the nonlinear polarizability and anharmonicity of potentials from the experimental and simulation data by using double Fourier transformation is presented. In a Lennard-Jones potential system, an approximated expression of the fifth-order response function using the ratio between nonlinear polarizability and anharmonicity exhibits a good agreement with the results of the molecular dynamics simulation. In a soft-core case, the fifth-order Raman signal indicates that the system consists of the delocalized and localized modes, and only the delocalized mode affects the dramatic change of the fifth-order Raman response functions between solid and liquid phases through nonlinear polarizability. 相似文献
777.
Hiraishi T Masuda E Kanayama N Nagata M Doi Y Abe H Maeda M 《Macromolecular bioscience》2009,9(1):10-19
Pedobacter sp. KP-2 can degrade and metabolize thermally synthesized alpha,beta-poly(D,L-aspartic acid) (tPAA), which contains 70% of unnatural beta-amide units, with high-molecular-weight. In this study, gene cloning and molecular characterization of PAA hydrolase-1 from KP-2 was carried out. Gene analysis reveals that deduced amino acid sequence of the enzyme shows a similarity to only that of PAA hydrolase-1 from Sphingomonas sp. KT-1. GPC and NMR analyses of the hydrolyzed products of tPAA by PAA hydrolase-1 of KP-2 indicate that this enzyme cleaves the beta-beta amide linkage via endo-mode to yield oligo(aspartic acid) from tPAA. Taking the composition of tPAA and the substrate specificity of PAA hydrolase-1 into consideration, the enzyme possibly plays a crucial role in tPAA biodegradation by KP-2. 相似文献
778.
Ryo Masuda Takaya Mitsui Keiji Itoh Kouji Sakaki Hirotoshi Enoki Yumiko Nakamura Makoto Seto 《Hyperfine Interactions》2012,204(1-3):139-142
We have been developing a system for in situ M?ssbauer studies using synchrotron radiation (SR) to elucidate the mechanism of hydrogenation processes. In the system, samples reacts in a pressure-temperature chamber and SR-based M?ssbauer spectra using variable-frequency nuclear monochromator and energy spectra of inelastic nuclear resonant scattering (NRS) of SR are measured. As a feasibility study, the temperature dependence of the M?ssbauer and inelastic NRS spectra of 57Fe in c-GdFe2H3 under vacuum were measured. In both spectra, clear differences were observed between 373?K and 573?K. These differences can be interpreted by the change of microscopic environment around Fe at the dehydrogenation. Thus, it is confirmed that this system works well enough to perform the in-situ M?ssbauer study on the dehydrogenation of c-GdFe2H3. 相似文献
779.
Akiko Nagata Kazuto Iijima Ryota Sakamoto Yuka Mizumoto Miho Iwaki Masaki Takiwaki Yoshikuni Kikutani Seketsu Fukuzawa Minami Odagi Masayuki Tera Kazuo Nagasawa 《Molecules (Basel, Switzerland)》2022,27(8)
Blood levels of the vitamin D3 (D3) metabolites 25-hydroxyvitamin D3 (25(OH)D3), 24R,25-dihydroxyvitamin D3, and 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) are recognized indicators for the diagnosis of bone metabolism-related diseases, D3 deficiency-related diseases, and hypercalcemia, and are generally measured by liquid-chromatography tandem mass spectrometry (LC-MS/MS) using an isotope dilution method. However, other D3 metabolites, such as 20-hydroxyvitamin D3 and lactone D3, also show interesting biological activities and stable isotope-labeled derivatives are required for LC-MS/MS analysis of their concentrations in serum. Here, we describe a versatile synthesis of deuterium-labeled D3 metabolites using A-ring synthons containing three deuterium atoms. Deuterium-labeled 25(OH)D3 (2), 25(OH)D3-23,26-lactone (6), and 1,25(OH)2D3-23,26-lactone (7) were synthesized, and successfully applied as internal standards for the measurement of these compounds in pooled human serum. This is the first quantification of 1,25(OH)2D3-23,26-lactone (7) in human serum. 相似文献
780.