全文获取类型
收费全文 | 1349篇 |
免费 | 30篇 |
国内免费 | 4篇 |
专业分类
化学 | 955篇 |
晶体学 | 19篇 |
力学 | 21篇 |
数学 | 90篇 |
物理学 | 298篇 |
出版年
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 34篇 |
2013年 | 49篇 |
2012年 | 79篇 |
2011年 | 75篇 |
2010年 | 32篇 |
2009年 | 38篇 |
2008年 | 87篇 |
2007年 | 72篇 |
2006年 | 69篇 |
2005年 | 58篇 |
2004年 | 64篇 |
2003年 | 51篇 |
2002年 | 70篇 |
2001年 | 41篇 |
2000年 | 18篇 |
1999年 | 15篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 20篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1973年 | 15篇 |
排序方式: 共有1383条查询结果,搜索用时 46 毫秒
101.
Yoshikazu Takada 《Annals of the Institute of Statistical Mathematics》1979,31(1):177-183
Summary Stein's positive part estimator forp normal means is known to dominate the M.L.E. ifp≧3. In this article by introducing some proirs we show that Stein's positive part estimator is posterior mode. We also consider
the Bayes estimators (posterior mean) with respect to the same priors and show that some of them dominate M.L.E. and are admissible. 相似文献
102.
103.
Makoto Kimura Kasumi Kashikura Satomi Yokoi Yumiko Koiwa Yoshikazu Tokuoka Norimichi Kawashima 《Optical Review》2005,12(3):207-210
We determined photodynamic therapy (PDT) efficacy using a flash wave (FW) and a continuous wave (CW) light, of which the fluence rate was 70 W/cm2, for murine thymic lymphoma cells (EL-4) cultivated in vitro. The irradiation frequency and the pulse width of the FW light were in the range of 1–32 Hz and less than one millisecond, respectively. 5-Aminolevulinic acid-induced protoporphyrin IX (ALA-PpIX) was used as a photosensitizer. When EL-4 with ALA administration was irradiated by the light for 4 h (irradiation fluence: 1.0J/cm2), the survival rate of EL-4 by the FW light was lower than that by the CW light, except for the FW light with irradiation frequency of 32 Hz, and decreased gradually with decreasing irradiation frequency. Moreover, the FW light, especially at lower irradiation frequency, was superior to the CW light for the generation of singlet oxygen in an aqueous PpIX solution. Therefore, thehigher PDT efficacy for EL-4 of the FW light would be caused by the greater generation of singlet oxygen in the cells. 相似文献
104.
A Reformatsky-type aldol reaction of alpha-chloroketones with aldehydes has been achieved using reactive barium as a low-valent metal in THF; this one-pot process is more effective for obtaining the desired beta-hydroxy ketones in high yields than the stepwise process in which barium enolates are prepared prior to the reaction with aldehydes. 相似文献
105.
Taniguchi T Yamanaka K Sumioka H Yamazaki T Tabata Y Kawarazaki S 《Physical review letters》2004,93(24):246605
The extraordinary Hall resistivity rho(xy) and the magnetization M of a canonical spin glass AuFe (8 at.% Fe) were measured simultaneously as functions of temperature with the best care to the thermal and the magnetic field hysteresis. The data of rho(xy) show an anomaly at the spin glass transition temperature T(g) and have different zero field cooling (ZFC) and field cooling (FC) measurements below T(g). Moreover, the value of rho(xy)/M, which represents the chiral susceptibility of the system in the present case, also shows the difference between ZFC and FC measurements. The results are consistent with the predictions of the chirality scenario of canonical spin glasses by Kawamura. 相似文献
106.
Yusuke Arai Tetsuji Yano Shuichi Shibata 《Journal of Sol-Gel Science and Technology》2004,32(1-3):189-194
Microspheres of refractive index of nD > 2.0 have been investigated. The organic-inorganic hybrid microspheres of nD = 1.72 were prepared by the vibrating orifice technique using titanium-tetra-n-butoxide (TTBu) and diphenyldimethoxysilane (DPhDMS). For lasing demonstration, Eu3+-doped microspheres were prepared using europium (III) thenoyltrifluoroacetonate [Eu(TTFA)3] as the dopant. The particles have good spherical shape, smooth surface and high optical transparency. The diameters of the particles could be controlled to within 0.1 m. Subsequent heating of the microspheres at 550°C under oxygen atmosphere resulted in an increase in the refractive index up to nD = 2.6 with retention of the spherical shape. Resonant emission was confirmed from Eu3 +-doped microspheres after heating at 400–550°C, by pumping with the 514.5 nm line of a CW- Ar+laser. 相似文献
107.
Sekiguchi A Inoue S Ichinohe M Arai Y 《Journal of the American Chemical Society》2004,126(31):9626-9629
The highly twisted tetrakis(di-tert-butylmethylsilyl)disilene 4 was prepared and reacted with (t)BuLi in THF, producing disilene anion radical 5 upon one-electron reduction. The anion radical 5 was isolated in the form of its lithium salt as extremely air- and moisture-sensitive red crystals. The molecular structure of 5 was established by X-ray crystallography, which showed a nearly orthogonal structure (twisting angle of 88 degrees ) along the central Si-Si bond, with a length of 2.341(5) A, which is 3.6% elongated relative to that of 4. The interesting feature of 5 is that one of the central Si atoms has radical character, whereas the other Si atom has silyl anion character. An electron spin resonance (ESR) study of the hyperfine coupling constants of the (29)Si nuclei indicates that rapid spin exchange occurs between these central Si atoms on the ESR time scale. 相似文献
108.
Control of the efficiency of photoisomerization by oxygen was demonstrated for 1,3,5-tristyrylbenzene dendrimers 1-3; the large dendrons do not significantly affect the photochemistry itself due to volume-conserving isomerization mechanisms but may affect the mobility of the molecules. 相似文献
109.
The composition of sterols was determined in a cultured marine dinoflagellate Heterocapsa circularisquama. Ten kinds of the sterol in H. circularisquama were identified by capillary gas chromatography-mass spectrometry. The major sterol was a 4-methyl sterol, 4alpha,23,24-trimethyl-5alpha-cholest-22E-en-3beta-ol (dinosterol) which is the common sterol in many dinoflagellates. 相似文献
110.
[reaction: see text] Polymer-supported bisBINOL ligands were successfully utilized for the immobilization of multicomponent asymmetric catalysts. The polymer-supported Al-Li-bis(binaphthoxide) (ALB) catalyst was more effective than the dendrimer-supported ALB in the Michael reaction of 2-cyclohexen-1-one with dibenzyl malonate affording the adduct in 91% yield with 96% ee. The polymer was also effective for the immobilization of a mu-oxodititanium complex that promoted carbonyl-ene reaction of ethyl glyoxalate with alpha-methyl styrene to provide the adduct with up to 98% ee. 相似文献