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排序方式: 共有217条查询结果,搜索用时 15 毫秒
91.
纳米ZnO的制备及发光特性研究 总被引:32,自引:0,他引:32
The samples of nano-size ZnO were prepared by precipitation, hydrolysis, sol-gel method and characterized by X-ray diffraction, Uv-Vis diffuse reflection spectrum, and time resolved luminescent spectrum. The results showed that the crystallite dimensions of all ZnO samples were coarsening with increasing annealing temperature and the grain sizes prepared by sol-gel method were obviously smaller than the others prepared by precipitation and hy-drolysis method. Under excitation of monochromatic light of wavelength 300nm, a strong and broad photolumines-cence (PL) emissions were observed in the wavelength range of 420~780nm. As the grain size decreased, the PL peak positions moved to shorter wavelengths. And as the annealing temperature increased, the peak intensity de-creased. The photoluminescence decay profile of ZnO was well described by three decay components of 46ns, 330ns and 1630ns. 相似文献
92.
Coordination of a bulky pyridinyl‐phosphine ( P?N ) ligand toward CuBr was investigated. However, this P?N donor behaves as a monodentate via the coordination of phosphine to form a bromide bridged dimeric [( P?N )Cu(μ‐Br)2Cu( P?N )], which was characterized by spectral and crystal structural analysis. It appeared that the “PCu(μ‐Br)2CuP” unit is planar with a short distance between Cu…Cu' [2.7585(9) Å]. The catalytic activity on Sonogashira coupling of phenylacetylene with aryl halides was studied. 相似文献
93.
94.
95.
Chen HS Chang WC Su C Li TY Hsu NM Tingare YS Li CY Shie JH Li WR 《Dalton transactions (Cambridge, England : 2003)》2011,40(25):6765-6770
A new series of N-heterocyclic carbene (NHC)-pyridine ruthenium complexes incorporating a carbene unit as an ancillary ligand were designed and successfully synthesized by using simple synthetic methods. The photophysical, electrochemical and photovoltaic properties of these NHC-pyridine based ruthenium complexes were investigated. These complexes showed photoelectric conversion efficiencies in the range of 6.43 ~ 7.24% under the illumination of AM 1.5 (100 mW cm(-2)). Interestingly, the modifications on the ancillary ligand of these sensitizers by removal of an alkoxyl group and replacement of the octyl chain with a 3,5-difluorobenzyl group showed a 13% increase in the conversion efficiency for the CifPR dye. These results demonstrated that structural modifications on the NHC-pyridine ancillary ligand of ruthenium complexes results in dye-sensitized solar cells exhibiting a comparable cell performance to that obtained using the standard N719 dye. 相似文献
96.
乙烯在Pt/Pt4+-TiO2上的可见光降解 总被引:5,自引:0,他引:5
以TiO2为主的光催化氧化技术存在太阳能利用率低(~5%)和光量子转化效率低(~4%)等缺点,使其工业应用受到制约,人们尝试用过渡金属离子掺杂和贵金属表面修饰等技术来提高催化剂对太阳能的利用率和光量子的转化效率,但目前将铂离子掺杂和铂金属表面修饰技术结合用于光催化 相似文献
97.
Ho CC Chen WS Shie TY Lin JN Kuo C 《Langmuir : the ACS journal of surfaces and colloids》2008,24(11):5663-5666
A novel synthetic approach for the efficient fabrication of Janus silica particles was demonstrated by embedment of zero-dimensional colloids on one-dimensional polymer fiber surfaces, followed by the surface modification on the exposed silica hemispheres. Electrospinning of poly(methyl methacrylate) and poly(4-vinyl pyridine) blends produced polymer fibers with high specific surface area and desired surface hydrophilicities. Fiber compositions determined the colloid adsorption density and uniformity. The colloid embedding resulted from the polymer softening was manipulated by the isothermal heat treatment. Subsequent silianization completed the amino functionalities on hemispherical surfaces of embedded silica colloids. Janus particles with uniform asymmetric chemical features were further labeled with gold nanoparticles before their recovery from fiber substrates. Fabrication of Janus particles, including colloid adsorption, temperature-driven embedding, and hemispherical surface modification, were investigated and are discussed. 相似文献
98.
We made ab initio electronic calculations of the structure and energetics of mixed hypermetalated hydrogen oxides, Li2NaOH and LiNa2OH. There exist five equilibrium geometries for each complex. In all levels of calculation the global minimum structure for Li2NaOH has C2v symmetry and a large distance between sodium and oxygen, 4.24 Å (MP2/6-31G*). The dissociation energies to all possible products were also calculated. Li2NaOH → Na + Li2OH δH = +25.33 kcal/mol (at MP4/6-311++G**//6-31G* + ZPE scaled by 0.9). All other dissociation processes are highly endothermic. Similar procedures were applied to LiNa2OH. The global minimum structure for LiNa2OH belongs to point group Cs. It is also endothermic to all possible dissociation paths. LiNa2OH →Na + LiNaOH δH = +12.72 kcal/mol (at MP4/6-311++G*//6-31G* + ZPE scaled by 0.9). The nuclear repulsion energy is crucial in energetics of the structures. The distribution of electron density and bonding properties for these equilibrium structures were analyzed. 相似文献
99.
The drag coefficient of an isolated, rigid cylindrical particle in a Carreau fluid is evaluated. The result of numerical simulation reveals that, in general, the shear-thinning nature of a Carreau fluid yields a drag coefficient smaller than that for the corresponding Newtonian fluid. Also, the smaller the Reynolds number, the more appreciable the decrease of the drag coefficient as the relaxation time constant of the Carreau fluid increases. The influence of the index parameter of a Carreau fluid on the drag coefficient depends largely on the magnitude of the relaxation time constant and is insensitive to the Reynolds number. Only if the relaxation time constant is sufficiently large is the influence of the index parameter on the drag coefficient significant. If the Reynolds number and/or the relaxation time constant is sufficiently large, the flow field upstream of a particle becomes asymmetric to that downstream. In general, the influence of the index parameter, the relaxation time constant, and the Reynolds number on the flow field follows the order index parameter相似文献
100.
Chuan-Pin Lee Shih-Chin Tsai Yi-Lin Jan Yuan-Yaw Wei Shi-Ping Teng Chun-Nan Hsu 《Journal of Radioanalytical and Nuclear Chemistry》2008,275(2):371-378
In this study, batch and through-diffusion experiments have been performed in order to determine the distribution coefficients
(K
d
), apparent diffusion coefficients (D
a
) and retardation factor (Rf), respectively. Both apparent and effective diffusion coefficient (D
a
and D
e
) of Cs were obtained by accumulative concentration method developed by Crank (1975). In addition, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing
the ability of radionuclide retardation. The distribution coefficients (K
d
) obtained by batch tests in 14 days under aerobic and anaerobic systems were 2.06 and 3.52 ml/g. Moreover, it is found in
through-diffusion test that Rf = 4.12 and 4.40 and K
d
= 0.97 and 1.06 of Cs did not have an obvious discrepancy in a length/diameter/ (L/D) ratio of 0.44 and 1.78. However, Rf and K
d
revealed a larger difference in an L/D ratio closing to 1 due to the geometric change of one-dimension diffusive hypothesis. Therefore, it demonstrates that Rf and K
d
obtained by through-diffusion experiments only could be achieved at a lower or larger L/D ratio and would be reliable for long-term performance assessment. 相似文献