全文获取类型
收费全文 | 662篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
化学 | 569篇 |
晶体学 | 4篇 |
力学 | 3篇 |
数学 | 17篇 |
物理学 | 94篇 |
出版年
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2016年 | 10篇 |
2015年 | 17篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 28篇 |
2011年 | 39篇 |
2010年 | 16篇 |
2009年 | 22篇 |
2008年 | 28篇 |
2007年 | 26篇 |
2006年 | 42篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 22篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 7篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 5篇 |
排序方式: 共有687条查询结果,搜索用时 328 毫秒
61.
Hirota K Hasegawa T Nakajima T Makino K Terada H 《Colloids and surfaces. B, Biointerfaces》2011,87(2):293-298
In this work we obtain the thermodynamic properties of mixed (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) PC and (1-stearoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (sodium salt)) PS monolayers. Measurements of compressibility (isotherms, bulk modulus, and excess area per molecule) and surface potential show that the properties of monolayers at the air–water interface depend on the concentration of ions (Na+ and K+) and the proportion of PS in the mixture. The dependence on PS arises because the molecule is originally bound to a Na+ counterion; by increasing the concentration of ions the entropy changes, creating a favorable system for the bound counterions of PS to join the bulk, leaving a negatively charged molecule. This change leads to an increase in electrostatic repulsions which is reflected by the increase in area per molecule versus surface pressure and a higher surface potential. The results lead to the conclusion that this mixture of phospholipids follows a non ideal behavior and can help to understand the thermodynamic behavior of membranes made of binary mixtures of a zwitterionic and an anionic phospholipid with a bound counterion. 相似文献
62.
The chiral Br?nsted acid (1b or 1c) has been shown to initiate the Hosomi-Sakurai reaction of imines with excellent enantioselectivities. The combined Br?nsted acid system has been developed to offer a new class of chiral Br?nsted acid catalysis. The present system proceeds through regeneration of the chiral Br?nsted acid by proton transfer from additional Br?nsted acid to silylated chiral Br?nsted acid, a newly elucidated mechanism for the role of the additional Br?nsted acid. 相似文献
63.
Momiyama N Konno T Furiya Y Iwamoto T Terada M 《Journal of the American Chemical Society》2011,133(48):19294-19297
Chiral bis-phosphoric acid 1 was designed to identify a new class of structural features in chiral Br?nsted acid catalysts. X-ray diffraction analysis revealed the single atropisomer 1, bearing S axial chirality at 3,3'-biaryl substituents on (R)-binaphthyl and intramolecular hydrogen bonding between the two phosphoric acid moieties. The newly designed bis-phosphoric acid 1 was evaluated in the Diels-Alder reaction of α,β-unsaturated aldehydes 4 with 1-N-acylamino-1,3-butadienes 3. After systematic variation of the catalyst substituents, as well as the N-acyl substituents of 1,3-butadiene, the use of an N-Cbz amidodiene 3a in the presence of bis-phosphoric acid 1e with a 2,4,6-tri-isopropylphenyl group was found to be optimal to yield the 1S,6R enantiomeric product 5aa in a Diels-Alder reaction of acrolein (4a). Application of this method to substituted substrates was found to be an efficient approach to the enantioselective synthesis of 3- and 3,6-substituted cyclic formylcarbamates 5. The specific character as well as the utility of 1e was further established by comparing its enantioselectivity, absolute stereochemistry, and catalytic efficiency with those of mono-phosphoric acid 2. 相似文献
64.
Miura H Kanebako M Shirai H Nakao H Inagi T Terada K 《Chemical & pharmaceutical bulletin》2011,59(6):686-691
The physicochemical characteristics and oral absorption of a poorly water-soluble drug, K-832, adsorbed onto porous silica (Sylysia 350), were compared with those of K-832 adsorbed onto non-porous silica (Aerosil 200). K-832 and silica were treated with supercritical CO(2) (scCO(2)) to produce K-832-Sylysia 350 and K-832-Aerosil 200 formulations. Scanning electron microscopy, polarizing microscopy, powder X-ray diffraction, and differential scanning calorimetry results suggested that K-832 mainly existed in an amorphous state in both formulations. The specific surface area of both formulations was much larger than that of pure K-832 crystals. The dissolution rate of K-832 from both formulations was considerably greater than that from corresponding physical mixtures due to rapid wetting of the hydrophilic carrier surfaces and amorphous state, the dissolution from the K-832-Sylysia 350 formulation being the fastest. In vivo absorption tests on the two formulations indicated no significant differences in their peak concentration (C(max)) and the area under their plasma concentration-time curve (AUC), while the concentrations of K-832 in the K-832-Sylysia 350 formulation were significantly higher than those in the K-832-Aerosil 200 formulation 1 h and 1.5 h after administration of these formulations (p<0.05). This could be attributed to the different dispersion states of K-832 in the formulations due to their different three-dimensional structures (porous and non-porous). In physical stability tests, the amorphous drugs in both formulations were stable at room temperature for at least 14 months. Thus, the absorption of poorly water-soluble drugs could be greatly improved by adsorption onto porous silica using scCO(2). 相似文献
65.
66.
Ikuo Yoneda 《Archive for Mathematical Logic》2003,42(5):423-433
We show that any relational generic structure whose theory has finite closure and amalgamation over closed sets is stable
CM-trivial with weak elimination of imaginaries.
Received: 21 December 2001 /
Published online: 5 November 2002
Mathematics Subject Classification (2000): 03C45
Key words or phrases: CM-triviality – Generic structures – Stability 相似文献
67.
Summary 8-Hydroxyquinoline (8-HOQ) was used for the preconcentration of Cd, Cu, Mn, Pb and Zn from seawater prior to their determination by graphite furnace atomic absorption spectrometry using an inner miniature cup for solid sampling technique. The metal ions in seawater were precipitated quantitatively in the pH range 7–8.5 with 8-HOQ alone. The precipitate thus formed was directly analysed by an atomic absorption spectrometer equipped with a specially deviced graphite furnace and miniature cup. The present method was confirmed to be highly reliable for analysis of seawater. Detection limits (3b) for Cd(II), Cu(II), Mn(II), Pb(II) and Zn(II) are 1.4, 10, 5, 10, and 6 ng l–1, respectively, for the analysis of a 400-ml portion of seawater samples. Corresponding precision of 6–14% is typical for determination 5-fold above the detection limits.
Direkte Analyse von Feststoffproben durch AAS nach Anreicherung von Spurenelementen aus Meerwasser mit 8-Hydroxychinolin相似文献
68.
69.
70.
Shigeru Nishiyama Yoshikazu Shizuri Daizo Imai Shosuke Yamamura Yukimasa Terada Masatake Niwa Kazuaki Kawai Hideyuki Furukawa 《Tetrahedron letters》1985,26(27):3243-3246
Isocitreoviridinol has been newly isolated from the mycelium of B. (IFO 6050) together with citreoviridinol, and their stereostructures have also been elucidated by means of chemical method: the 2,6-dioxabicyclo[3.2.1]octanes have been made, one of which is regarded as a promising synthetic intermediate of citreoviridinol. In addition, isocitreoviridinol diacetate has been derived from citreoviridin in 3 steps. 相似文献