全文获取类型
收费全文 | 468篇 |
免费 | 22篇 |
专业分类
化学 | 365篇 |
晶体学 | 5篇 |
力学 | 8篇 |
数学 | 21篇 |
物理学 | 91篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 8篇 |
2017年 | 3篇 |
2016年 | 22篇 |
2015年 | 12篇 |
2014年 | 22篇 |
2013年 | 36篇 |
2012年 | 32篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 25篇 |
2008年 | 25篇 |
2007年 | 23篇 |
2006年 | 32篇 |
2005年 | 18篇 |
2004年 | 28篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1966年 | 3篇 |
排序方式: 共有490条查询结果,搜索用时 15 毫秒
121.
Takaaki Shimura 《Acta Appl Math》2000,63(1-3):411-432
A distribution is said to have regularly varying tail with index – (0) if lim
x(kx,)/(x,)=k
– for each k>0. Let X and Y be independent positive random variables with distributions and , respecitvely. The distribution of product XY is called Mellin–Stieltjes convolution (MS convolution) of and . It is known that D() (the class of distributions on (0,) that have regularly varying tails with index –) is closed under MS convolution. This paper deals with decomposition problem of distributions in D() related to MS convolution. A representation of a regularly varying function F of the following form is investigated: F(x)=
k=0
n–1
b
k
f(a
k
x), where f is a measurable function and a and b
k
(k=1,...,n–1) are real constants. A criterion is given for these constants in order that f be regularly varying. This criterion is applicable to show that there exist two distributions and such that neither nor belongs to D() (>0) and their MS convolution belongs to D(). 相似文献
122.
Takaaki Kajita 《Pramana》2009,72(1):109-117
Atmospheric, solar, reactor and accelerator neutrino oscillation experiments have measured Δm
122, sin2
θ
12, |Δm
232| and sin2 2θ
23. The next stage of the oscillation studies should be the observation of a finite sin2 2θ
13. If a non-zero sin2 2θ
13 is observed, the subsequent goals should be the observation of the CP violation and the determination sign of Δm
232. Possible future neutrino oscillation experiments that could assess these questions are discussed.
相似文献
123.
Atsushi Unemoto Yoshiki IwaiSatoshi Mitani Seung-Wook BaekSeitaro Ito Takaaki TomaiJunichi Kawamura Itaru Honma 《Solid State Ionics》2011,201(1):11-20
Lithium ion conducting solid-state composites consisting of lithium ion conducting ionic liquid, lithium bis(trifluoromethanesulfonyl)amide (Li-TFSA) dissolved 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide (EMI-TFSA), denoted by [yMLi+][EMI+][TFSA−] in this study, and various oxide particles such as SiO2, Al2O3, TiO2 (anatase and rutile) and 3YSZ are synthesized via a liquid route for the molar concentration of lithium, y, to be 1. The composite consists of SiO2 and the ionic liquid with y = 0.2 was also prepared. The ionic liquid are quasi-solidified at the above oxide particle surfaces when x is below 40 for y = 1 and x is below 30 for y = 0.2, corresponding to the confinable thickness of the ionic liquid at the oxides' surfaces to be approximately 5-10 nm regardless of the oxide compositions. The electrical conductivities of x vol.%[yMLi+][EMI+][TFSA-]-SiO2, Al2O3, TiO2s or 3YSZ composites are evaluated by ac impedance measurements. The quasi-solid-state composites exhibited liquid-like high apparent conductivity, e.g. 10− 3.3-10− 2.0 S cm− 1 in the temperature range of 323-538 K for SiO2-ionic liquid composites with y = 1. The self-diffusion coefficients of the constituent species of x vol.% [yMLi+][EMI+][TFSA−] (x is below 40, y = 0.2 and 1) − SiO2 are evaluated by the Pulse Gradient Spin Echo (PGSE)-NMR technique in the temperature range of 298-348 K. By the quasi-solidification of the ionic liquid at SiO2 particle surfaces, the absolute values of the diffusion coefficients of all constituent species decreased. The SiO2 surfaces work to promote ionization of ion pair, [EMI+][TFSA−], while significant influence on the solvation coordination, [Li(TFSA)n + 1]n−, was not observed. The apparent transport numbers of Li-containing species both in the bulk and the quasi-solidified ionic liquid showed similar values with each other, which was evaluated to be in the range of 0.010-0.017 for y = 0.2 and 0.051-0.093 for y = 1 in the abovementioned temperature range. 相似文献
124.
Yuji Minoura Takaaki Sugimura 《Journal of polymer science. Part A, Polymer chemistry》1966,4(11):2721-2734
The polymerization of methyl methacrylate (MMA) initiated by benzoyl peroxide (BPO) in the presence of diphenyl thiourea (DPTU) has been studied. It was found that the BPO–DPTU catalyst system was not an effective accelerating system but showed a relatively strong retarding effect. With DPTU derivatives, the polymerization rate was found to decrease with the increase in the electron-attracting forces of substituents attached to the phenyl groups of DPTU. In the polymerization of MMA initiated by AIBN, the addition of DPTU to the reaction systems affected neither the polymerization rate nor the degree of polymerization. From this fact, it might be concluded that DPTU itself serves as a radical scavenger. It seems most probable from the results of kinetic studies, iodometric titration, and from the effect of an oxidation product of DPTU (diphenyl formamidine disulfide) that the retardation effect observed is attributable to the action of the disulfide (DPFDS). By extending the Alfrey-Price scheme for the copolymerization reactions to the chain-transfer reactions, the Q and e values of DPFDS were determined. The apparent chain-transfer constants for DPTU and its derivatives were calculated by means of rate measurements and were correlated with substituent constants. The mechanism of the polymerization is discussed on the basis of these results. 相似文献
125.
Seiji Shinkai Katsuta Matsuo Michiko Sato Takaaki Sone Osamu Manabe 《Tetrahedron letters》1981,22(15):1409-1412
A photoresponsive surfactant with a cationic azobenzene head group (I) was synthesized. It was demonstrated that by mixing (I) with a conventional cationic micelle the rate of the micelle-catalyzed reaction (base-catalyzed proton abstraction from benzoin) can be controlled by light. The origin of the photocontrol was accounted for by the difference in the partitioning of trans-(I) and cis-(I) in the micelle phase. 相似文献
126.
Takaaki Horaguchi Takuji Kubo Kiyoshi Tanemura Tsuneo Suzuki 《Journal of heterocyclic chemistry》1998,35(3):649-653
Cyclohepta[cd]benzothiophene 3 , a new heterocyle, was synthesized starting from benzothiophene via eight steps in 14% total yield. Chemical reactions of 3 were examined on formylation, acetylation, bromination, catalytic hydrogenation and Diels-Alder reactions. The results show that the benzothiophene moiety of 3 has aromatic character and the carbon?carbon double bonds in a seven-membered ring posseses alkene-1ike character. 相似文献
127.
Absolute stereochemistry of amphidinolide E 总被引:1,自引:0,他引:1
The absolute configurations at eight chiral centers in amphidinolide E (1), a cytotoxic 19-membered macrolide isolated from a marine dinoflagellate Amphidinium sp., were determined to be 2R, 7R, 8R, 13S, 16S, 17R, 18R, and 19R on the basis of detailed analysis of NMR data and by chemical means. 相似文献
128.
Takaaki Tsurumi Shuichi Ozawa Satoshi Wada 《Journal of Sol-Gel Science and Technology》2003,26(1-3):1037-1040
Pb(Zr0.53Ti0.47)O3 (PZT) films of 10 to 50 m in thickness were prepared by a new sol-gel process using an interfacial polymerization technique. The interfacial polymerization process is that an alkoxide precursor solution is poured on the surface of water in a container to form a gel film at the interface between the two immiscible liquids. The precursor solution was prepared by adding PZT alkoxide solution, PZT powders coated with Pb5Ge3O11 (PG), and a surfactant into hexane solvent. After the polymerization at the interface, the gel films were gently placed on a silicon substrate by draining the water in the container. The gel films containing PZT powders were sintered at 950°C for 10 min to obtain crystallized PZT films. The remanent polarization of a PZT thick film was 33.1 C/cm2. The piezoelectric d
33 constant measured with a Mach-Zehnder interferometer was 225 pm/V and was independent of frequency from 0.2 to 3 kHz. 相似文献
129.
Kakiyama G Iida T Goto T Mano N Goto J Nambara T 《Chemical & pharmaceutical bulletin》2004,52(3):371-374
A method for the synthesis of 3alpha,7alpha,14alpha-trihydroxy-5beta-cholan-24-oic acid which is a possible candidate of bile acid metabolite in vertebrates was developed. The principal reactions involved were 1). stereoselective remote-hydroxylation of methyl ursodeoxycholate diacetate with dimethyldioxirane, 2). site-selective protection at C-3 by tert-butyldimethylsilylation of the resulting 3alpha,7alpha,14alpha-trihydroxy ester, 3). oxidation of the diol with pyridinium dichromate adsorbed on activated alumina, 4). stereoselective reduction of the 7-ketone with zinc borohydride, and 5). cleavage of the protecting group at C-3 with p-toluenesulfonic acid. A facile elimination of the 14alpha-hydroxy group under an acidic or neutral condition is also described. The synthetic reference compound is now available for comparison with unidentified biliary bile acids detected in vertebrate bile. 相似文献
130.
Qualitative and quantitative analysis of amino acids by capillary electrophoresis-electrospray ionization-tandem mass spectrometry 总被引:2,自引:0,他引:2
We describe a method to identify and quantify amino acids using capillary electrophoresis-electrospray ionization-triple-quadrupole tandem mass spectrometry (CE-ESI-MS/MS). Amino acids, including physiological amino acids, were first separated by CE under acidic pH conditions and then detected by MS/MS. To efficiently introduce the whole sample into the capillary, no electrical potential was applied to the electrospray probe until running electrophoresis. The position of the electrosprayer with respect to the MS capillary entrance drastically affected sensitivity and generation of cluster ions. MS/MS with multiple reaction monitoring (MRM) detection was performed to obtain sufficient selectivity and sensitivity. Under optimized CE-MS/MS conditions, the minimum detectable levels for 32 free amino acids normally found in proteins and other physiological amino acids were between 0.1 and 14 micromol/L with pressure injection of 50 mbar for 3 s (3 nL) at a signal-to-noise ratio of 3. For most amino acids, this constitutes a severalfold increase in sensitivity compared to CE-MS. The relative standard deviations (% RSD) for all amino acids were better than 0.4% for migration times and between 1.4% and 8.6% for peak areas (n = 10). Since amino acids exhibited characteristic MS/MS spectra, this approach is useful for the simultaneous, selective, quantitative, and reproducible analysis of amino acids in physiological and biological samples that contain various kinds of matrices. The power of the method was demonstrated by analyzing amino acids in human urine. 相似文献