全文获取类型
收费全文 | 3363篇 |
免费 | 560篇 |
国内免费 | 351篇 |
专业分类
化学 | 2529篇 |
晶体学 | 41篇 |
力学 | 134篇 |
综合类 | 3篇 |
数学 | 339篇 |
物理学 | 1228篇 |
出版年
2024年 | 6篇 |
2023年 | 67篇 |
2022年 | 110篇 |
2021年 | 145篇 |
2020年 | 141篇 |
2019年 | 127篇 |
2018年 | 114篇 |
2017年 | 105篇 |
2016年 | 159篇 |
2015年 | 175篇 |
2014年 | 190篇 |
2013年 | 274篇 |
2012年 | 346篇 |
2011年 | 334篇 |
2010年 | 195篇 |
2009年 | 234篇 |
2008年 | 191篇 |
2007年 | 203篇 |
2006年 | 184篇 |
2005年 | 127篇 |
2004年 | 122篇 |
2003年 | 84篇 |
2002年 | 75篇 |
2001年 | 47篇 |
2000年 | 57篇 |
1999年 | 68篇 |
1998年 | 48篇 |
1997年 | 37篇 |
1996年 | 58篇 |
1995年 | 24篇 |
1994年 | 29篇 |
1993年 | 29篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4274条查询结果,搜索用时 15 毫秒
61.
Silicon nitride powders were synthesized in an atmospheric-pressure convection-stabilized arc using silicon and ammonia as reactants. The morphology and particle size distributions of the silicon nitride particles were characterized by SEM, TEM, and electron diffraction analyses. The silicon nitride particles collected in the plasma reactor were formed by either gas-condensed phase reactions or chemical vapor reactions. The morphologies of the particles formed by gas-condensed phase reactions consisted of -Si3N4 prisms, -Si3N4 matte, -Si3N4 needles, and spaghetti-like whiskers. For the homogeneously nucleated particles, the morphologies included dendrites, needles, platelets, and amorphous particles. Most of the particles formed were aggregates with particle size distributions ranging from 500 to 1500 Å depending on the location of injection of the reactants. 相似文献
62.
When trypsin reacts with Herring sperm DNA (hsDNA), Salmon sperm DNA (sDNA), and Calf thymus DNA (ctDNA) to form a complex,
the resonance Rayleigh scattering (RRS) was remarkably enhanced and new RRS spectra appear. These new spectra have similar
characteristics of RRS spectra. The maximum RRS peaks are at 307 nm (hsDNA, sDNA) and 290 nm (ctDNA), and other peaks are
at 350 nm. The scattering intensity is proportional to the concentration of DNA or trypsin; so this intereaction can be used
to determine trypsin using DNA or DNA using trypsin. In the determination of DNA using trypsin, the linear ranges for hsDNA,
sDNA, and ctDNA are 0–2.3, 0–2.5, and 0–1.9 μg·mL−1, and the detection limits are 0.4, 0.7, and 1.1 ng·mL−1, respectively. In the determination of trypsin using hsDNA, the linear range is 0–30.0 μg·mL−1, and the detection limit is 39.0 ng·mL−1. In this paper, the intereaction conditions were optimized. The affecting factors, chemical properties of the complex, and
the composition ratio of trypsin with DNA were investigated. Using trypsin as RRS probe, a sensitive method for the determination
of trace amounts of DNA was developed.
Translated from Chemical Journal of Chinese Universities, 2006, 27(3) (in Chinese) 相似文献
63.
Yan-Ping Yuan De-Yuan Kong Abraham Clearfield 《Journal of solid state chemistry》2005,178(6):2030-2035
The first organically templated 3d-4f mixed metal sulfates, [H2en]2{La2M(SO4)6(H2O)2} (M=Co 1, Ni 2) have been synthesized and structurally determined from non-merohedrally twinned crystals. The two compounds are isostructural and their structures feature a three-dimensional anionic network formed by the lanthanum(III) and nickel(II) ions bridged by sulfate anions. The La(III) ions in both compounds are 10-coordinated by four sulfate anions in bidentate chelating fashion, and two sulfate anions in a unidentate fashion. The transition metal(II) ion is octahedrally coordinated by six oxygens from four sulfate anions and two aqua ligands. The doubly protonated enthylenediamine cations are located at the tunnels formed by 8-membered rings (four La and four sulfate anions). 相似文献
64.
The syntheses of macrocyclic species composed of carborane derivatives joined via their carbon vertices by electrophilic mercury atoms are described. The reaction of closo-1,2-Li(2)[C(2)B(10)H(10)(-)(x)()R(x)()] with HgI(2) gives Li(2)[(1,2-C(2)B(10)H(10)(-)(x)()R(x)()Hg)(4)I(2)] [R = Et, x = 2 (5.I(2)Li(2)); R = Me, x = 2 (6.I(2)Li(2)); R = Me, x = 4 (7.I(2)Li(2))]. 6.I(2)(K.[18]dibenzocrown-6)(2) crystallizes in the monoclinic space group C2/m [a = 28.99(2) ?, b = 18.19(1) ?, c = 13.61(1) ?, beta = 113.74(2) degrees, V = 6568 ?(3), Z = 4, R = 0.060, R(w) = 0.070]; 7.I(2)(NBu(4))(2) crystallizes in the monoclinic space group P2(1)/c [a = 12.77(1) ?, b = 21.12(2) ?, c = 20.96(2) ?, beta = 97.87(2) degrees, V = 5600 ?(3), Z = 2, R = 0.072, R(w) = 0.082]. The precursor to 7, closo-8,9,10,12-Me(4)-1,2-C(2)B(10)H(8) (4), is made in a single step by reaction of closo-1,2-C(2)B(10)H(12) with MeI in trifluoromethanesulfonic acid. The free hosts 5, 6, and 7 are obtained by reaction of the iodide complexes with stoichiometric quantities of AgOAc. A (199)Hg NMR study indicates that sequential removal of iodide from 5.I(2)Li(2) and 6.I(2)Li(2) with aliquots of AgOAc solution leads to formation of two intermediate host-guest complexes in solution, presumed to be 5(6)ILi and 5(2)(6)(2).ILi. Crystals grown from a solution of 6.I(2)Li(2) to which 1 equiv of AgOAc solution had been added proved to be an unusual stack structure with the formula 6(3).I(4)Li(4) [tetragonal, I4/m, a = 21.589(2) ?, c = 21.666(2) ?, V = 10098 ?(3), Z = 2, R = 0.058, R(w) = 0.084]. Addition of 2 equiv of NBu(4)Br ion to 5 or 6 gives 5.Br(2)(NBu(4))(2) and 6.Br(2)(NBu(4))(2), respectively, while addition of 1 equiv of KBr to 6 forms 6.BrK. 5.Br(2)(NBu(4))(2) crystallizes in the triclinic space group P&onemacr;, [a = 10.433(1) ?, b = 13.013(1) ?, c = 15.867(2) ?, alpha = 91.638(2) degrees, beta = 97.186(3) degrees, gamma = 114.202(2) degrees, V = 1492 ?(3), Z = 1, R = 0.078, R(w) = 0.104]. The hosts 5 and 6 form 1:1 supramolecular adducts with the polyhedral anions B(10)I(10)(2)(-) and B(12)I(12)(2)(-) in solution. 相似文献
65.
S. M. Fields R. C. Kong J. C. Fieldsted M. L. Lee P. A. Peaden 《Journal of separation science》1984,7(6):312-318
Fused silica capillary columns with internal diameters from 100 to 25 μm were coated with SE-54 and evaluated under supercritical fluid chromatographic conditions using carbon dioxide as mobile phase. Experimental results compared well with theoretical predictions. At ten times the optimum mobile phase velocity and for a capacity factor, k of 3, efficiencies of 2300 to 5600 plates m?1 were obtained for column diameters of 100 to 25 μm, respectively. 相似文献
66.
Electrochemistry and in situ electrochemical scanning tunneling microscopy (STM) were used to study the blocking and structural properties of Shiff base V-ape-V self-assembled monolayers (SAMs) on the surface of Au(111) in perchloric acid solution. The complex-plane impedance plots for the SAM covered Au(111) electrodes, with the redox couple of Fe(CN)64–/3– present in solution, exhibit arc shapes, revealing that the electrochemical kinetics were controlled by the electron-transfer step. For bare Au(111), the electrode process was mass transport limited. The molecules adsorb on Au(111) with a flat-lying orientation and form a long-range well-defined adlayer. A new structure of
was observed in the double-layer potential region. A structural model is proposed to interpret the molecular registry with Au(111) substrate. 相似文献
67.
Biofingerprinting chromatogram analysis, which is defined as the comparison of fingerprinting chromatograms of the extract of traditional Chinese medicines (TCMs) before and after the interaction with biological systems (DNA, protein, cell, etc.), was proposed for screening and analysis of the multiple bioactive compounds in TCMs. A method of microdialysis sampling combined with high performance liquid chromatography (HPLC) was applied to the study of DNA-binding property for the extracts of TCMs. Seven compounds were found to bind to calf thymus DNA (ct-DNA) from the TCMs of Coptis chinensis Franch (Coptis), but only three ones from Phellodendron amurense Rupr. (Phellodendron) and none from Sophoraflavescens Ait. (Sophora) to bind to ct-DNA, respectively. Three of them were identified as berberine, palmatine and jatrorrhizine and their association constants (K) to ct-DNA were determined by microdialysis/HPLC. Competitive binding behaviors of them to ct-DNA were also investigated. 相似文献
68.
Zhang P Zhou X Tang Y Sham TK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(18):8502-8508
A hybrid preparative method was developed to prepare organosulfur-functionalized Au nanoparticles (NPs) on silicon nanowires (SiNWs) by reacting HAuCl(4) with SiNW in the presence of thiol. A number of organosulfur molecules-dodecanethiol, hexanethiol, 1,6-hexanedithiol, and tiopronin-were used to functionalize the Au surface. Size-selected NPs ranging from 1.6 to 7.5 nm were obtained by varying the S/Au ratio and the concentration of HAuCl(4). This method was further extended to the preparation Pd and Pd-Au bimetallic NPs on SiNWs. The morphology of the metal nanostructures was examined by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The local structure and bonding of the SiNW-supported metal nanostructures were studied using X-ray absorption fine structures (XAFS) [including both X-ray near-edge structures (XANES) and extended X-ray absorption fine structures (EXAFS)] at the Au L(3)-, Pd K-, S K-, and Si K-edges. It was also found that the annealing of the thiol-capped Au NPs up to 500 degrees C transforms the surface of the thiol-capped NPs to gold sulfide, as identified using Au L(3)- and S K-edge XANES. We also illustrate that this preparative approach can be used to form size-controllable Au NPs on carbon nanotubes. 相似文献
69.
Modeling of a counterflow plasma reactor 总被引:2,自引:0,他引:2
Modeling of a counterflow plasma reactor is presented, using liquid injection for the synthesis of fine particles. An experimental reactor has been developed in this laboratory, and feasibility has been demonstrated for synthesizing advanced ceramic powders. The flow field calculations show two major recirculating regions which are of importance for increasing the particles' residence time inside of the reactor. In addition, the temperature within these recirculation zones remains relatively uniform. For simulation, water droplet trajectories have been calculated for droplets produced by an injection probe. It is shown that the droplets in a size range below 50 m in diameter will follow the streamlines and evaporate completely within a short traveling distance. This finding suggests that this reactor configuration provides a favorable environment for the synthesis of fine particles using liquid precursors. 相似文献
70.