全文获取类型
收费全文 | 364篇 |
免费 | 17篇 |
专业分类
化学 | 304篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 21篇 |
物理学 | 48篇 |
出版年
2023年 | 8篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 17篇 |
2012年 | 38篇 |
2011年 | 35篇 |
2010年 | 19篇 |
2009年 | 13篇 |
2008年 | 33篇 |
2007年 | 24篇 |
2006年 | 25篇 |
2005年 | 18篇 |
2004年 | 15篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有381条查询结果,搜索用时 31 毫秒
121.
Hattori R Yamada K Hasegawa K Ishikawa Y Ito Y Sakamoto Y Yoshida N 《Rapid communications in mass spectrometry : RCM》2008,22(21):3410-3414
The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages. 相似文献
122.
A simple and sensitive method for the determination of musty odorants, 2-methylisoborneol (MIB) and geosmin (GSM), in environmental water was developed by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry. MIB and GSM were separated within 10 min using a DB-1 capillary column and detected in the selective ion monitoring mode. HS-SPME using a polydimethylsiloxane/divinylbenzene fiber provided effective sample enrichment, and was carried out by fiber exposition at 70 degrees C for 30 min. Using this method, the calibration curves of MIB and GSM were linear in the range of 0-500 pg/mL, with a correlation coefficient above 0.9977 (n=24). The detection limits (S/N=3) of MIB and GSM were 0.9 and 0.6 pg/mL, respectively. This method was successfully applied to the analysis of environmental water samples without interference peaks. 相似文献
123.
Keita Sugiura Hideto Yoshida Koichiro Fukuda 《Journal of solid state chemistry》2008,181(10):2864-2868
Two types of new ternary carbides, Zr2Al4C5 and Zr3Al4C6, have been synthesized and characterized by X-ray powder diffraction. The crystal structures were refined from laboratory X-ray powder diffraction data (CuKα1) using the Rietveld method. These carbides form a homologous series with the general formula (ZrC)mAl4C3 (m=2 and 3). The crystal structures can be regarded as intergrowth structures where the Al4C3-type [Al4C4] layers are the same, while the NaCl-type [ZrmCm+1] layers increase in thickness with increasing m value. The new carbides are most probably the end members of continuous solid-solutions (ZrC)m[Al4−xSix]C3 with 0?x?0.44. 相似文献
124.
Nsouli NH Mal SS Dickman MH Kortz U Keita B Nadjo L Clemente-Juan JM 《Inorganic chemistry》2007,46(21):8763-8770
Interaction of the dilacunary polyanion precursor [gamma-GeW(10)O(36)](8-) with Fe(3+) ions in aqueous buffer medium (pH 4.8) results in the formation of two dimeric tungstogermanates depending on the reactant ratios. When using an Fe3+ to [gamma-GeW(10)O(36)](8-) ratio of 1:1, the asymmetric anion [K(H(2)O)(beta-Fe(2)GeW(10)O(37)(OH))(gamma-GeW(10)O(36))](12-) (1) is formed, whereas [{beta-Fe(2)GeW(10)O(37)(OH)2}2]12- (2) is formed when using a ratio of 2:1. Single-crystal X-ray analyses were carried out on Cs(3)K(9)[K(H(2)O)(beta-Fe(2)GeW(10)O(37)(OH))(gamma-GeW(10)O(36))].19H(2)O (CsK-1), which crystallizes in the triclinic system, space group P1, a = 11.4547(2), b = 19.9181(5), c = 21.0781(6) A, alpha = 66.7977(12), beta = 89.1061(12), gamma = 84.4457(11) degrees, and Z = 2 and on Cs(7)K(4)Na[{beta-Fe(2)GeW(10)O(37)(OH)(2)}(2)].39H(2)O (CsKNa-2), which crystallizes in the monoclinic system, space group C2/m, a = 32.7569(13), b = 12.2631(5), c = 14.2895(5) A, beta = 104.135(2) degrees , and Z = 2. Polyanion 1 consists of (beta-Fe(2)GeW(10)O(37)) and (gamma-GeW(10)O(36)) units linked via two Fe-O-W bridges and a central potassium ion. Two equivalent FeO(6) octahedra complete the belt of the beta-Keggin unit and link to the (gamma-GeW(10)O(36)) fragment. On the other hand, 2 consists of two {beta-Fe(2)GeW(10)O(37)(OH)(2)} units with four bridging hydroxo groups linking the four Fe(3+) ions, forming an eight-membered ring. The magnetic properties of CsK-1 and CsKNa-2 have been studied by magnetic susceptibility and magnetization measurements and fitted according to an isotropic exchange model. Both polyanions 1 and 2 exhibit diamagnetic ground states with a small amount of paramagnetic impurity. Electrochemistry studies on 1 and 2 were carried out in a pH 5 acetate medium. The two polyanions have in common the simultaneous reduction of all of their Fe(3+) centers. This observation suggests the existence of identical or almost-identical influences on these centers and their equivalence, especially in the reduced state. Controlled potential coulometry results indicate the presence of two Fe(3+) centers in 1 and four in 2. The splitting of the tungsten wave of 1 compared to the single tungsten wave of 2 is attributed to a difference in acid-base properties of the polyanions. Voltammetric peak-potential shifts as a function of pH were studied in the case of 2. 相似文献
125.
Pichon C Mialane P Dolbecq A Marrot J Rivière E Keita B Nadjo L Sécheresse F 《Inorganic chemistry》2007,46(13):5292-5301
Two new Cu(II) azido polyoxometalates compounds have been synthesized, and their structures were determined by X-ray crystallography. The compound Na(14)[SiW(9)O(34)Cu(3)(N(3))(2)(OH)(H(2)O)](2) x 24H(2)O (1) is built from two [SiW(9)O(34)Cu(3)(mu(1,1,3)-N(3))(2)(mu-OH)(H(2)O)](7-) subunits where the copper centers, connected by two azido ligands and one hydroxo group, form a nearly equilateral triangle. The two subunits are related by an inversion center and connected via the two mu(1,1,3)-N(3) ligands in an end-to-end fashion, affording a hexanuclear Cu(II) cluster. Linkage of these fragments via Cu-O=W bonds leads to a bidimensional arrangement of the polyoxometalate units. The complex LiK(14)Na(9)[P(8)W(48)O(184)Cu(20)(N(3))(6)(OH)(18)] x 60H(2)O (2) consists of two {Cu(5)(OH)(4)}(6+) and two {Cu(5)(OH)(2)(mu(1,1,3,3)-N(3))}(7+) subunits connected via four mu-OH and four mu(1,1)-N(3) additional ligands, the 20 copper centers being encapsulated in the [P(8)W(48)O(184)](40-) crown polyoxotungstate ligand. 1 represents the first multidimensional compound based on azido polyoxometalate (POM) units, and 2 represents by far the largest azido POM complex isolated to date. Magnetic measurements revealed an overall antiferromagnetic behavior for both compounds. Nevertheless, the study of the variation of the magnetization with the applied field indicates that 1 possesses a triplet ground state, which can be attributed to weak ferromagnetic interaction between the S = 1/2 triangular subunits. The stability of 1 and 2 evidenced by UV-vis spectroscopy and gel filtration chromatography, in particular at pH 5, has allowed a detailed study of their redox and electrocatalytic properties. For both compounds, the stability of the Cu(II)/Cu(I) couple is remarkable compared with the observations made in other Cu(II)-substituted POMs. Electrochemical quartz crystal microbalance measurements clearly demonstrate that the formation of the Cu(I) species occurs neatly without the formation of Cu(0). The accumulation of such Cu(II) centers within the complexes is a favorable condition to envision applications involving several electrons. The electrocatalytic reduction of dioxygen and hydrogen peroxide was achieved efficiently and has shown that the reactivity increases with the nuclearity and/or the Cu/W ratio of the POM complex. The dioxygen reduction is an overall four-electron process with water as the final product. Finally, the reduction of the W centers triggers a strong electrocatalysis of solvent reduction. 相似文献
126.
Ohtani Yuta Kumano Keita Saneshige Mami Takami Kei Hoshi Hajime 《Journal of Solid State Electrochemistry》2021,25(7):2107-2113
Journal of Solid State Electrochemistry - Despite their potential for use as a low-cost energy-conversion device, dye-sensitized solar cells (DSSCs) have not been widely utilized because they apply... 相似文献
127.
In previous studies, xylem parenchyma cells (XPCs) in the boreal softwood species larch, which has thick and rigid walls similar to those of XPCs in boreal hardwood species, were shown to respond to subfreezing temperature by deep supercooling during summer but change their freezing behavior to extracellular freezing during winter. In this study, we re-examined freezing behavior of XPCs in larch by observation of deep etching of frozen samples as well as observation of re-warmed samples after freezing using a cryo-scanning electron microscope. The results showed that XPCs in larch adapts to subfreezing temperature by deep supercooling throughout all seasons. Such freezing behavior is the same as that of XPCs in boreal hardwood species. 相似文献
128.
129.
Taku Aiga Dr. Yoshiyuki Manabe Keita Ito Tsung-Che Chang Dr. Kazuya Kabayama Shino Ohshima Prof. Yoshie Kametani Ayane Miura Hiroto Furukawa Dr. Hiroshi Inaba Prof. Kazunori Matsuura Prof. Koichi Fukase 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(40):17858-17864
Co-assembling vaccines composed of a lipidated HER2-derived antigenic CH401 peptide and either a lipophilic adjuvant, Pam3CSK4, α-GalCer, or lipid A 506, were evaluated as breast cancer vaccine candidates. This vaccine design was aimed to inherit both antigen multivalency and antigen-specific immunostimulation properties, observed in reported self-adjuvanting vaccine candidates, by using self-assembly and adjuvant-conjugated antigens. Under vaccination concentrations, respective lipophilic adjuvants underwent co-assembly with lipidated CH401, which boosted the anti-CH401 IgG and IgM production. In particular, α-GalCer was responsible for the most significant immune activation. Therefore, the newly developed vaccine design enabled the optimization of adjuvants against the antigenic CH401 peptide in a simple preparatory manner. Overall, the co-assembling vaccine design opens the door for efficient and practical self-adjuvanting vaccine development. 相似文献
130.
Takashi Ishizone Keita Kitazawa Takashi Suzuki Susumu Kawauchi 《Macromolecular Symposia》2013,323(1):86-91
Anionic polymerization of α-methylene-N-methylpyrrolidone ( MMP ) was carried out in THF at −78∼0 °C with diphenylmethylpotassium (Ph2CHK) and with diphenylmethyllithium (Ph2CHLi) in the presence of Lewis acidic diethylzinc (Et2Zn). Poly( MMP )s possessing predicted molecular weights based on the molar ratios between monomer and initiators and narrow molecular weight distributions (Mw/Mn < 1.1) were obtained in quantitative yields. It was demonstrated that the propagating chain end of poly( MMP ) was stable at −30 °C to form the polymers with well-defined chain structures. From the polymerizations at the various temperatures ranging from −50 to −30 °C, the apparent rate constant and the activation energy of the polymerization were estimated as follows: ln k = −6.93 × 103/T + 25.7 and 57 ± 5 kJ mol−1, respectively. 相似文献