全文获取类型
收费全文 | 1880篇 |
免费 | 32篇 |
国内免费 | 8篇 |
专业分类
化学 | 1570篇 |
晶体学 | 12篇 |
力学 | 24篇 |
数学 | 79篇 |
物理学 | 235篇 |
出版年
2021年 | 9篇 |
2020年 | 16篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 9篇 |
2014年 | 22篇 |
2013年 | 75篇 |
2012年 | 53篇 |
2011年 | 92篇 |
2010年 | 49篇 |
2009年 | 49篇 |
2008年 | 80篇 |
2007年 | 92篇 |
2006年 | 99篇 |
2005年 | 99篇 |
2004年 | 104篇 |
2003年 | 82篇 |
2002年 | 96篇 |
2001年 | 27篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1995年 | 19篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 20篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 30篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 44篇 |
1984年 | 41篇 |
1983年 | 16篇 |
1982年 | 43篇 |
1981年 | 54篇 |
1980年 | 38篇 |
1979年 | 31篇 |
1978年 | 28篇 |
1977年 | 25篇 |
1976年 | 31篇 |
1975年 | 21篇 |
1974年 | 29篇 |
1973年 | 20篇 |
1967年 | 8篇 |
排序方式: 共有1920条查询结果,搜索用时 15 毫秒
991.
Kittaka S Ueda Y Fujisaki F Iiyama T Yamaguchi T 《Physical chemistry chemical physics : PCCP》2011,13(38):17222-17233
The freezing mechanism of water contacted with mesoporous silicas with uniform pore shapes, both cylindrical and cagelike, was studied by thermodynamic and structural analyses with differential scanning calorimetry (DSC) and X-ray diffraction (XRD) together with adsorption measurements. In the DSC data extra exothermic peaks were found at around 230 K for water confined in SBA-15, in addition to that due to the freezing of pore water. These peaks are most likely to be ascribed to the freezing of water present over the micropore and/or mesopore outlets of coronas in SBA-15. Freezing of water confined in SBA-16 was systematically analysed by DSC with changing the pore size. The freezing temperature was found to be around 232 K, close to the homogeneous nucleation temperature of bulk water, independent of the pore size when the pore diameter (d) < 7.0 nm. Water confined in the cagelike pores of SBA-16 is probably surrounded by a water layer (boundary water) at the outlets of channels to interconnect the pores and of fine corona-like pores, which is similar to that present at the outlet of cylindrical pores in MCM-41 and of cylindrical channels in SBA-15. The presence of the boundary water would be a key for water in SBA-16 to freeze at the homogeneous nucleation temperature. This phenomenon is similar to those well known for water droplets in oil and water droplets of clouds in the sky. The XRD data showed that the cubic ice I(c) was formed in SBA-16 as previously found in SBA-15 when d < 8.0 nm. 相似文献
992.
Takahashi Y Obara R Lin ZZ Takahashi Y Naito T Inabe T Ishibashi S Terakura K 《Dalton transactions (Cambridge, England : 2003)》2011,40(20):5563-5568
The structural and electrical properties of a metal-halide cubic perovskite, CH(3)NH(3)SnI(3), have been examined. The band structure, obtained using first-principles calculation, reveals a well-defined band gap at the Fermi level. However, the temperature dependence of the single-crystal electrical conductivity shows metallic behavior down to low temperatures. The temperature dependence of the thermoelectric power is also metallic over the whole temperature range, and the large positive value indicates that charge transport occurs with a low concentration of hole carriers. The metallic properties of this as-grown crystal are thus suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure. The present study shows that artificial hole doping indeed enhances the conductivity. 相似文献
993.
Yu DE Matsuda M Tajima H Naito T Inabe T 《Dalton transactions (Cambridge, England : 2003)》2011,40(10):2283-2288
The partially-oxidized TPP[M(Pc)L(2)](2) molecular conductors exhibit variable electronic and magnetic transport bulk materials properties due to central metal and axial ligand molecular modifications. The controllable electrical conductivity and giant negative magnetoresistance can be mainly attributable to the varying ligand field energy and physical bulkiness of the axial ligands which cause modulation in the intra-molecular π-d (Pc-M) and inter-molecular π-π (Pc-Pc) interactions in the TPP[M(Pc)L(2)](2) system, respectively. Characterization of the electronic conduction band utilizing one-dimensional (1-D) tight-binding approximation from infrared reflectance and thermoelectric power profile reveal consistent band widths of 0.43 eV-0.62 eV for the Co series (L = Br < Cl < CN) and 0.44-0.56 eV for the Fe series (L = Br < Cl < CN). The fixed band width suggests that stable electron conduction bands (transport pathway) can be constructed which can withstand the molecular π-d interaction modifications that severely alter the bulk electronic and magnetic materials properties of the TPP[M(Pc)L(2)](2) molecular conductors. 相似文献
994.
Deguchi J Hirahara T Oshimi S Hirasawa Y Ekasari W Shirota O Honda T Morita H 《Organic letters》2011,13(16):4344-4347
A novel alkaloid, cassiarin F (1), which showed potent antiplasmodial activity against Plasmodium falciparum in vitro, was isolated from the flowers of Cassia siamea, and its structure was elucidated on the basis of 2D NMR analyses. A total synthesis of 1 was also achieved by employing the Suzuki coupling constructing biaryl unit, nucleophilic aromatic substitution, and Houben-Hoesch type ring construction as key steps. 相似文献
995.
Hagiwara H Fukushima M Kinugawa K Matsui T Hoshi T Suzuki T 《Natural product communications》2011,6(3):311-313
The total synthesis of the recently isolated bicyclic sesquiterpenoid drechslerine B (2), isolated from the algicolous fungus Drechslera dematioidearare in the marine red alga Liagora viscida, has been achieved, starting from (S)-carvone (8), via an intramolecular aldol reaction and palladium-catalyzed carbon monoxide insertion as key reactions. 相似文献
996.
Ishiguro Y Inagi S Fuchigami T 《Langmuir : the ACS journal of surfaces and colloids》2011,27(11):7158-7162
In this paper, we report a novel electrochemical doping method for conducting polymer films based on bipolar electrochemistry. The electrochemical doping of conducting polymers such as poly(3-methylthiophene) (PMT), poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(aniline) (PANI) on a bipolar electrode having a potential gradient on its surface successfully created gradually doped materials. In the case of PEDOT film, the color change at the anodic side was also observed to be gradually transparent. PANI film treated by the bipolar doping gave a multicolored gradation across the film. The results of UV-vis and energy dispersive X-ray analyses for the doped films supported the distribution of dopants in the polymer films reflecting the potential gradient on the bipolar electrode. Furthermore, the reversibility of the bipolar doping of the PMT film was demonstrated by a spectroelectrochemical investigation. 相似文献
997.
998.
Yasutaka Mori Toshio Tagawa Masanori Fujita Toyohiko Kuno Satoshi Suzuki Takemi Matsui Masayuki Ishihara 《Journal of nanoparticle research》2011,13(7):2799-2806
A simple, environmentally friendly method for preparing highly size-controlled spherical silver nanoparticles was developed
that involved heating a mixture of silver-containing glass powder and an aqueous solution of glucose. The stabilizing agent
for silver nanoparticles was found to be caramel, which was generated from glucose when preparing the nanoparticles. The particle
size was independent of the reaction time, but it increased proportionally with the square root of the glucose concentration
in the range 0.25–8.0 wt% (corresponding to particle sizes of 3.48 ± 1.83 to 20.0 ± 2.76 nm). Difference of the generation
mechanism of silver nanoparticles between this inhomogeneous system and a system in which Ag+ was homogeneously dispersed was discussed. 相似文献
999.
1000.
Toshio Nishino Yasuyuki Yamada Ayumi Yamamoto Kentaro Tanaka 《Molecules (Basel, Switzerland)》2021,26(4)
A novel double-decker porphyrin complex, bis{meso-tetrakis(4-N-alkylpyridiniumyl)porphyrinato}cerium, was prepared. Electrochemical measurements revealed that this complex exhibited reversible redox waves corresponding to a 1e– redox reaction of the cerium center. Treating the complex alternately with an oxidant and a reductant resulted in the reversible redox switching between the oxidized and reduced states in an organic solvent. 相似文献