全文获取类型
收费全文 | 509篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
化学 | 409篇 |
晶体学 | 12篇 |
力学 | 3篇 |
数学 | 38篇 |
物理学 | 72篇 |
出版年
2024年 | 1篇 |
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 18篇 |
2013年 | 27篇 |
2012年 | 35篇 |
2011年 | 35篇 |
2010年 | 27篇 |
2009年 | 21篇 |
2008年 | 26篇 |
2007年 | 34篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 28篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1985年 | 3篇 |
1984年 | 11篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有534条查询结果,搜索用时 15 毫秒
121.
Choji Kashima Shigeki Hibi Tatsuya Maruyama Kazuo Harada Yoshimori Omote 《Journal of heterocyclic chemistry》1987,24(4):913-916
Carbazoles are the very important compounds in material science, nevertheless conventional syntheses required severe and complicated reaction conditions. In the process of preparation of pyrrole derivatives, we found that a primary amine hydrochloride 1 and 2,5-dimethoxytetrahydrofuran 2 were refluxed in a benzenewater (100:4 (v/v)) mixture to be obtained 9-substituted carbazole 5 in a high yield. This method is the one-pot synthesis of 9-substituted carbazoles 5 under mild and convenient conditions. 相似文献
122.
It was proved that 2-(1-phthalimido)alkyl-5-phenyloxazoles 3 were useful synthetic intermediates for peptide synthesis, where the oxazole ring acted as not only the carboxyl protecting group but also the carboxyl activating group upon ozonolysis. 相似文献
123.
A poly(amine ester) dendrimer with naphthyl units (G1N6) has been synthesized as a fluorescent chemosensor for metal ions. We investigated the metal-ion recognition of G1N6 by adding each of Ag(+), Al(3+), Ba(2+), Ca(2+), Cd(2+), Co(2+), Cu(2+), Fe(3+), Mg(2+), Ni(2+), and Zn(2+) in acetonitrile solution. Large changes were observed in the fluorescence spectra of G1N6 upon the addition of Al(3+), Cu(2+), and Zn(2+). 相似文献
124.
125.
Jun Fukuda Takafumi Iwura Shigehiro Yanagihara Kenji Kano 《Analytical and bioanalytical chemistry》2014,406(25):6257-6264
Hollow-fiber-flow field-flow fractionation (HF5) separates protein molecules on the basis of the difference in the diffusion coefficient, and can evaluate the aggregation ratio of proteins. However, HF5 is still a minor technique because information on the separation conditions is limited. We examined in detail the effect of different settings, including the main-flow rate, the cross-flow rate, the focus point, the injection amount, and the ionic strength of the mobile phase, on fractographic characteristics. On the basis of the results, we proposed optimized conditions of the HF5 method for quantification of monoclonal antibody in sample solutions. The HF5 method was qualified regarding the precision, accuracy, linearity of the main peak, and quantitation limit. In addition, the HF5 method was applied to non-heated Mab A and heat-induced-antibody-aggregate-containing samples to evaluate the aggregation ratio and the distribution extent. The separation performance was comparable with or better than that of conventional methods including analytical ultracentrifugation–sedimentation velocity and asymmetric-flow field-flow fractionation. 相似文献
126.
Yohei Kashima 《Journal of Functional Analysis》2012,262(6):2833-2860
Subdifferentials of a singular convex functional representing the surface free energy of a crystal under the roughening temperature are characterized. The energy functional is defined on Sobolev spaces of order ?1, so the subdifferential mathematically formulates the energy?s gradient which formally involves 4th order spacial derivatives of the surface?s height. The subdifferentials are analyzed in the negative Sobolev spaces of arbitrary spacial dimension on which both a periodic boundary condition and a Dirichlet boundary condition are separately imposed. Based on the characterization theorem of subdifferentials, the smallest element contained in the subdifferential of the energy for a spherically symmetric surface is calculated under the Dirichlet boundary condition. 相似文献
127.
Arief Budi Witarto Takafumi Ohtera Koji Sode 《Applied biochemistry and biotechnology》1999,77(1-3):159-168
We have previously reported that a chimeric pyrroloquinoline quinone (PQQ) glucose dehydrogenase (GDH), E97A3, which was made
up of 97% of Escherichia coli PQQGDH sequence and 3% of Acinetobacter calcoaceticus PQQGDH, showed increased thermal stability compared with both parental enzymes. Site-directed mutagenesis studies were carried
out in order to investigate the role of amino-acid substitution at the C-terminal region, Ser 771, of a chimeric PQQGDHs on
their thermal stability. A series of Ser 771 substitutions of a chimeric PQQGDH, E99A1, confirmed that hydrophobic interaction
governs the thermal stability of the chimeric enzymes. Comparison of the thermal denaturation of E. coli PQQGDH and E97A3 followed by far-ultraviolet (UV) circular dichroism (CD) spectroscopy revealed that E97 A3 acquired stability
at the first step of denaturation, which is reversible, and where no significant secondary structure change was observed.
These results suggested that the interaction between C-terminal and N-terminal regions may play a crucial role in maintaining
the overall structure of β-propeller proteins. 相似文献
128.
J. Alberto Rodríguez‐Velamazán Dr. Chiara Carbonera Dr. Miguel Castro Dr. Elías Palacios Dr. Takafumi Kitazawa Prof. Dr. Jean‐François Létard Prof. Dr. Ramón Burriel Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(29):8785-8796
In the series of polymeric spin‐crossover compounds Fe(X‐py)2[Ag(CN)2)]2 (py=pyridine, X=H, 3‐Cl, 3‐methyl, 4‐methyl, 3,4‐dimethyl), magnetic and calorimetric measurements have revealed that the conversion from the high‐spin (HS) to the low‐spin (LS) state occurs by two‐step transitions for three out of five members of the family (X=H, 4‐methyl, and X=3,4‐dimethyl). The two other compounds (X=3‐Cl and 3‐methyl) show respectively an incomplete spin transition and no transition at all, the latter remaining in the HS state in the whole temperature range. The spin‐crossover behaviour of the compound undergoing two‐step transitions is well described by a thermodynamic model that considers both steps. Calculations with this model show low cooperativity in this type of systems. Reflectivity and photomagnetic experiments reveal that all of the compounds except that with X=3‐methyl undergo light‐induced excited spin state trapping (LIESST) at low temperatures. Isothermal HS‐to‐LS relaxation curves at different temperatures support the low‐cooperativity character by following an exponential decay law, although in the thermally activated regime and for aX=H and X=3,4‐dimethyl the behaviour is well described by a double exponential function in accordance with the two‐step thermal spin transition. The thermodynamic parameters determined from this isothermal analysis were used for simulation of thermal relaxation curves, which nicely reproduce the experimental data. 相似文献
129.
A gas‐sensing system based on a dynamic nonlinear response shows enhanced selectivity of the sensor response toward sample vapors. A cyclic temperature composed of fundamental and 1.5‐th harmonics was applied to a SnO2 semiconductor gas sensor and the resulting conductance of the sensor was evaluated by a polynomial approximation. The dynamic nonlinear responses to the samples were further characterized by the addition of 1.5‐th harmonic perturbation as a frequency modulation. These characteristic sensor responses under frequency modulation were considered theoretically based on a reaction‐diffusion model for the semiconductor surface. 相似文献
130.
Munehiro Nishida Takafumi Kanayama Takaya Nakajo Toshiyuki Fujii Noriyuki Hatakenaka 《Physica C: Superconductivity and its Applications》2010,470(19):832-834
We propose a one-dimensional array of superconducting quantum interference devices (SQUIDs) composed of three asymmetrically positioned Josephson junctions to realize a discrete double sine-Gordon (DSG) model. Two fluxons in this SQUID array attract each other and form bound states with internal oscillation modes. We conduct numerical simulations of a discrete DSG equation, and show that the period of the internal oscillation of a moving fluxon pair exhibits relativistic time dilation except near the speed of light. We also show that driving with a pure alternating current causes progressive motion of the bound fluxon pair even in the presence of dissipation. 相似文献