全文获取类型
收费全文 | 455篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 349篇 |
晶体学 | 8篇 |
力学 | 3篇 |
数学 | 4篇 |
物理学 | 109篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 22篇 |
2011年 | 43篇 |
2010年 | 15篇 |
2009年 | 19篇 |
2008年 | 31篇 |
2007年 | 26篇 |
2006年 | 27篇 |
2005年 | 18篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1990年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有473条查询结果,搜索用时 15 毫秒
11.
Masato ItoAkihide Osaku Sachiko KitaharaMakoto Hirakawa Takao Ikariya 《Tetrahedron letters》2003,44(40):7521-7523
A ternary catalyst system of Cp*RuCl(cod)-2-diphenylphosphinoethylamine-KOt-Bu (Cp*=η5-C5(CH3)5, cod=1,5-cyclooctadiene) causes rapid racemization of chiral non-racemic sec-alcohols, which results from the reversible hydrogen transfer between sec-alcohols and ketones. Both tertiary phosphine and primary amine functionalities in the ligand are responsible for the high rate. 相似文献
12.
Pattara Tiew Hiromitsu TakayamaMariko Kitajima Norio AimiUdom Kokpol Warinthorn Chavasiri 《Tetrahedron letters》2003,44(35):6759-6761
Three new compounds, mansoxetane; 4′-(3-hydroxy-1,2-oxetanyl)-2′,2-dihydroxy-4-(2-formyl-1-ethyl)-6′,6-dimethoxy biphenyl, and mansonones R and S, together with two previously reported coumarins, mansorins A and C, and four known mansonones, mansonones C, E, G and H, were obtained from the methanolic extract of the heartwood from Mansonia gagei Drumm. Their structures were established by spectroscopic methods. 相似文献
13.
14.
Yasuo Kimura Takashi Hamasaki Hiromitsu Nakajima Akira Isogai 《Tetrahedron letters》1982,23(2):225-228
Aszonalenin () has been isolated from together with LL-S490β () and the structure of has been established by spectroscopic evidences and chemical transformation. 相似文献
15.
Sol-Gel Processing of Transparent PLZT((Pb,La)(Zr,Ti)O3) Fibers 总被引:1,自引:0,他引:1
Kitaoka Kenji Takahara Koji Kozuka Hiromitsu Yoko Toshinobu 《Journal of Sol-Gel Science and Technology》1999,16(1-2):183-193
PLZT((Pb,La)(Zr,Ti)O3) ceramic fibers were prepared by the sol-gel method from a solution of lead acetate trihydrate, lanthanum isopropoxide, zirconium n-propoxide and titanium isopropoxide containing 2-methoxyethanol as the solvent. The as-drawn gel fibers were pretreated in an autoclave and preheated in flowing H2O vapor prior to the heat-treatment for crystallization. The effects of autoclaving and preheating in flowing H2O vapor on the structure and composition of the resultant fibers were investigated. Optically transparent single phase perovskite PLZT fibers of 5–15 m in thickness and 5 cm in length were successfully prepared when the autoclave-treatment and the preheating in flowing H2O vapor were conducted prior to crystallization. These treatments are thought to promote hydrolysis of the organic groups and polycondensation reaction in the gel fibers, leading to the successful formation of dense, crack-free transparent PLZT fibers. 相似文献
16.
Kawahara K Sekiguchi A Kiyoki E Ueda T Shimamura K Kurosaki Y Miyaoka S Okabe H Miyajima M Kimura J 《Chemical & pharmaceutical bulletin》2003,51(3):336-338
Newly formulated cationic liposomes (TRX-liposomes) with four different mean diameters were injected into twelve male rats via the lateral tail vein in order to evaluate the effect of liposomal size on pharmacokinetic parameters. TRX-liposomes disappeared from the blood according to the one-compartment model and demonstrated maximum and minimum half-lives of ca. 14 h (mean diameter of 114.3 nm) and ca. 5 h (mean diameter of 285.9 nm), respectively. This prolonged half-life tended to decrease at the boundary of 114.3 nm mean diameter. The optimal size (114.3 nm) for prolonged circulation of TRX-liposomes was consistent with that of pegylated liposomes such as Doxil((R)), however, the half-life was different among these liposomes. The electric charge of the TRX-liposomal surface is assumed to be responsible for this difference. The results of the present study will be very useful in the design of long-circulating cationic liposomes. 相似文献
17.
1,3-Dipyrrolyl-1,3-propanediones, synthesized from pyrroles and malonyl chloride, form BF2 complexes, which represent a new class of naked-eye sensors for halide and oxoanions. The association mode for the interactions of both the pyrrolyl NH and bridging CH protons with anions was confirmed by 1H NMR chemical shifts in CD2Cl2 and supported by theoretical studies. The binding constants (Ka) were estimated as 8.1x10(4), 2.0x10(3), 3.3x10(2), 1.3x10(4), and 80 M(-1) for F-, Cl-, Br-, H2PO4(-), and HSO4(-) by UV/Vis absorption spectral changes in CH2Cl2. Augmentation of Ka compared with dipyrrolylquinoxaline for H2PO4(-) is much larger than those for other anions. Contrary to other anions, F- quenches the emission almost completely, which was detected by the fluorescence spectrum as well as the naked-eye. In the case of the chloride anion complex, the formation of Cl(-)-bridged 1D networks, in which anion is associated with two BF2 complexes, is observed in the solid state. 相似文献
18.
The rates of growth of single ozone cracks have been measured for vulcanizates of two butyl rubbers over the temperature range of 20–160°C. Over most of this range the rates are quantitatively related to the segmental mobility of the polymer and depend upon temperature in accord with the appropriate from of the WLF relation. The rates are also proportional to the concentration of ozone. It is therefore concluded that diffusion of ozone into the polymer before reaction is the rate-controlling step. This is contrasted with the behavior of butadiene–styrene copolymers, for which the rates of crack growth are also quantitatively related to the segmental mobility, but the rates are somewhat larger at equivalent mobilities and the dependence upon ozone concentration is smaller. The difference is attributed to different penetration distances before reaction in polymers containing low and high densities of reactive sites. 相似文献
19.
Design and preparation of pulsatile release tablet as a new oral drug delivery system. 总被引:6,自引:0,他引:6
To achieve time-controlled or site specific delivery of a drug in the gastrointestinal tract, an orally applicable pulsatile drug release system with the dry-coated tablet form was developed. The system consisted of a less water permeable outer shell and a swellable core tablet; from such a system, the drug was expected to be rapidly released after a certain period of time on the basis of time-controlled disintegration mechanism. Various model disks of outer shell, consisting of hydrogenated castor oil and polyethyleneglycol 6000, were tested for their water penetration rate. The experimental results showed that water penetration proceeded obeying the boundary retreating mechanism, so that the lag time of the system could be controlled by changing either the thickness or the composition of the outer shell. The swelling force of various commercially available disintegrants was quantitatively compared, and it was found that carboxymethylcellulose calcium was the preferable disintegrant to be used for the core tablet. On the basis of the results of a series of fundamental studies, various pulsatile release tablets of isoniazide with different lag times were designed. In the in vitro dissolution test, typical pulsatile release was achieved for all the tablets prepared, and a good correlation was found between the observed lag time and the estimated lag time calculated from an empirical equation deduced from the thickness and polyethyleneglycol 6000 content of the outer shell. 相似文献
20.
Jionghao He Shinjiro Machida Hiromitsu Kishi Kazuyuki Horie Hidemitsu Furukawa Rikio Yokota 《Journal of polymer science. Part A, Polymer chemistry》2002,40(14):2501-2512
A novel preparation approach for high‐performance polyimide gels that are swollen or have a jungle‐gym‐type structure is proposed. A new rigid and symmetric trifunctional amine, 1,3,5‐tris(4‐aminophenyl)benzene (TAPB), was synthesized as a crosslinker. Three different kinds of amic acid oligomers derived from pyromellitic dianhydride (PMDA), 4,4′‐oxydiphthalic anhydride (ODPA), p‐phenylenediamine (PDA), and 4,4′‐oxydianiline (ODA) were end‐crosslinked with TAPB at a high temperature to make polyimide networks with different structures. Transparent polyimide gels were obtained from the ODPA–ODA/TAPB series with high compression moduli of about 1 MPa at their equilibrium swollen states in N‐methylpyrrolidone. Microscopic phase separation occurred during the gelation–imidization process when polyimide networks were generated from PMDA–PDA/TAPB and PMDA–ODA/TAPB. After these opaque polyimide networks were dried, a jungle‐gym‐like structure was obtained for the PMDA–PDA/TAPB and PMDA–ODA/TAPB series; that is, there was a high void content inside the networks (up to 70%) and little volume shrinkage. These polyimide networks did not expand but absorbed the solvent and showed moduli as high as those of solids. Therefore, using the highly rigid crosslinker TAPB combined with the flexible monomers ODPA and ODA and the rigid monomers PMDA and PDA, we prepared swollen, high‐performance polyimide gels and jungle‐gym‐type polyimide networks, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2501–2512, 2002 相似文献