全文获取类型
收费全文 | 4539篇 |
免费 | 108篇 |
国内免费 | 30篇 |
专业分类
化学 | 2326篇 |
晶体学 | 61篇 |
力学 | 200篇 |
综合类 | 5篇 |
数学 | 1042篇 |
物理学 | 1043篇 |
出版年
2023年 | 21篇 |
2022年 | 58篇 |
2021年 | 78篇 |
2020年 | 72篇 |
2019年 | 118篇 |
2018年 | 178篇 |
2017年 | 173篇 |
2016年 | 205篇 |
2015年 | 139篇 |
2014年 | 206篇 |
2013年 | 495篇 |
2012年 | 269篇 |
2011年 | 285篇 |
2010年 | 259篇 |
2009年 | 209篇 |
2008年 | 249篇 |
2007年 | 251篇 |
2006年 | 162篇 |
2005年 | 235篇 |
2004年 | 224篇 |
2003年 | 111篇 |
2002年 | 63篇 |
2001年 | 46篇 |
2000年 | 55篇 |
1999年 | 42篇 |
1998年 | 36篇 |
1997年 | 33篇 |
1996年 | 33篇 |
1995年 | 26篇 |
1994年 | 15篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1977年 | 10篇 |
1976年 | 17篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1968年 | 11篇 |
排序方式: 共有4677条查询结果,搜索用时 15 毫秒
31.
A. I. Kryukov A. V. Korzhak G. M. Tel’biz V. G. Il’in S. Ya. Kuchmii 《Theoretical and Experimental Chemistry》1998,34(2):93-98
An attempt has been made to create organized, highly efficient photocatalytic systems in the example of composite materials
consisting of blocks of a metallocomplex photocatalyst and a dark-stage catalyst, assembled on a zeolite matrix. The spectral
and photochemical properties of these systems have been investigated, and also their use in catalysis of hydrogen evolution
from alcohol-water media.
L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, Kiev
252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 103–108, March–April, 1998. 相似文献
32.
Inverse gas chromatography (IGC) was applied to characterize the surface of sepiolite. The adsorption thermodynamic parameters (the standard enthalpy (ΔH 0), entropy (ΔS 0) and free energy of adsorption (ΔG 0)), the dispersive component of the surface energy (γ S d ), and the acid/base character of sepiolite surface were estimated by using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (ΔG sp ), the specific enthalpy of adsorption (ΔH sp ), and the specific entropy of adsorption (ΔS sp ) of polar probes on sepiolite were determined. ΔH sp were correlated with the donor and modified acceptor numbers of the probes to quantify the acidic K A and the basic K D parameters of the sepiolite surface. The values obtained for the parameters K A and K D indicated an acidic character for sepiolite surface. 相似文献
33.
Radoslav D. Mii Radmila P. Marinkovi-Neduin Zoltán Schay István Nagy Jelena S. Kiurski Ern E. Kiss 《Reaction Kinetics and Catalysis Letters》2007,91(1):85-92
Investigations of a commercial NiMo/Al2O3 hydrodesulfurization (HDS) catalyst are directed towards optimization of the activation procedure of HDS catalyst concerning
active phase formation and thermal stability. Structural and textural data obtained with XRD, IR-FTIR, XPS and LTNA reveal
that the optimal temperature for the formation of active species on the catalyst surface and an appropriate pore structure
is 300°C. 相似文献
34.
High-resolution 17O NMR spectra have been collected for crystalline samples of lanthanum new phase, La3Si8N11O4. In conjunction with previously published 29Si and 15N spectra obtained for this phase, and in the light of the high-quality crystal structure data reported recently, a more detailed interpretation of the NMR spectra is presented than was possible in previous studies. The non-bridging oxygens in the structure are responsible for the single sharp peak seen in the 17O spectrum at 188 ppm; the remaining oxygens, occupying bridging sites shared with nitrogen, show up only weakly on the 17O spectrum as a broad diffuse band centered around zero ppm. The peak at −57.3 ppm on the 29Si spectrum is believed to correspond to an overlap of [SiN4] and [SiON3] environments, with the −68.2 ppm peak corresponding to an [SiO2N2] environment. 相似文献
35.
Alkali Blue 6B-attached poly(2-hydroxyethyl methacrylate) (poly(HEMA)) microporous films were investigated as chelate forming sorbents for heavy metal removal. Poly(HEMA) microporous films were prepared by UV-initiated photo-polymerization of HEMA in the presence of an initiator (azobisisobutyronitrile (AIBN)). Alkali Blue 6B was attached covalently. These films with a swelling ratio of 58%, and carrying 14.8 mmol Alkali Blue 6B m(-2) which were then used in the removal of Cd(II), Zn(II) and Pb(II) from aqueous media. Adsorption rates were very high, equilibrium was achieved in about 30 min. The maximum adsorption of heavy metal ions onto the Alkali Blue 6B-attached films were 41.4 mmol m(-2) for Cd(II), 52.4 mmol m(-2) for Zn(II), and 64.5 mmol m(-2) for Pb(II). When the heavy metal ions competed during the adsorption from a mixture the adsorption values for Cd(II), Zn(II) and Pb(II) were quite close. Heavy metal ions were desorbed by using 0.1 M HNO(3). A significant amount of the adsorbed heavy metal ions (up to 95%) could be desorbed in 30 min. Repeated adsorption/desorption cycles showed the feasibility of these novel dye-attached microporous films for heavy metal removal. 相似文献
36.
Several research groups have reported the presence of nanometer-sized particles (nanoslabs) in clear solutions, which precipitate the crystalline MFI (ZSM-5) structure. Debate about the growth mechanism for Al-free ZSM-5 (silicalite-1) has revolved around growth by small silicate units (monomers, dimers, etc.) from solution vs growth by nanoslab addition. A model developed for precipitation of uniform sized colloids by addition of sub-colloidal precursor units has been adapted for this zeolite synthesis system. Parameter values were adjusted for the simulation results to match experimental observations from work reported previously, at least to the extent possible. The model involved the simultaneous solution of up to 6000 ordinary differential equations, and required computation times of up to 24 h. The results shed light on the crystal growth mechanism, but pose questions for further investigations of the nucleation mechanism. 相似文献
37.
V. I. Lozinsky I. A. Simenel M. G. Semenova L. E. Belyakova M. M. Il’in V. Ya. Grinberg A. S. Dubovik A. R. Khokhlov 《Polymer Science Series A》2006,48(4):435-443
The free-radical copolymerization of N-vinylcaprolactam and N-vinylimidazole (at an initial comonomer ratio of 85: 15, mol/mol) initiated by a persulfate-tertiary amine redox system in 10% aqueous DMSO at 25 and 65°C (at temperatures below and above the temperature of phase separation in the reaction system, respectively) yielded macromolecular products that were subsequently separated into thermally precipitating and nonprecipitating fractions. Investigations of these fractions by capillary viscometry, static and dynamic laser light scattering, and high-sensitivity DSC showed that macromolecules of both types of copolymers are strongly associated in aqueous solutions. Upon heating of solutions of thermally nonprecipitating fractions, additional aggregation takes place and this phenomenon is accompanied by a decrease in the size of particles without loss in their solubility until at least 70°C is reached. As for the set of properties exhibited in aqueous solutions, the thermally nonprecipitating fraction of the copolymer synthesized at 65°C may be assigned to protein-like macromolecules. 相似文献
38.
A new triterpenoid saponin with novel sugar moiety (1), a new trisaccharide derivative (2), as well as a known monosaccharide derivative (3), were isolated from the dried stem of Epigyhum aurilum. The structures of compounds 1 and 2 were determined by MS and NMR spectram analyses. 相似文献
39.
Kubo T Hosoya K Nomachi M Tanaka N Kaya K 《Analytical and bioanalytical chemistry》2005,382(7):1698-1701
A molecularly imprinted polymer was prepared using a water-soluble crosslinking agent. An ionic complex was utilized as the assembly for the template molecule and the functional monomer, and water as porogenic solvent during preparation of the imprinted polymer. The results of chromatographic evaluations for the prepared polymer suggested that the polymer had much lower hydrophobicity compared with usual octadecyl group bonded silica or the usual molecular imprinted polymer prepared from ethyleneglycol dimethacrylate, and the selective recognition ability for template molecule in the completely aqueous condition. 相似文献
40.
Double gradient ion chromatography on a short carboxybetaine coated monolithic anion exchanger 总被引:1,自引:0,他引:1
An ultra-short 1.0 x 0.46 cm carboxybetaine coated monolithic anion exchanger has been used with a new double gradient ion chromatography (DG-IC) technique. The novel monolithic column can be used with flow rate gradients giving excellent peak efficiencies, and retention times can be simultaneously reduced through combining flow gradients with an eluent pH gradient. 相似文献