全文获取类型
收费全文 | 935篇 |
免费 | 58篇 |
国内免费 | 1篇 |
专业分类
化学 | 624篇 |
晶体学 | 20篇 |
力学 | 47篇 |
数学 | 99篇 |
物理学 | 204篇 |
出版年
2023年 | 10篇 |
2022年 | 27篇 |
2021年 | 35篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 33篇 |
2017年 | 29篇 |
2016年 | 55篇 |
2015年 | 49篇 |
2014年 | 40篇 |
2013年 | 75篇 |
2012年 | 59篇 |
2011年 | 73篇 |
2010年 | 45篇 |
2009年 | 34篇 |
2008年 | 57篇 |
2007年 | 42篇 |
2006年 | 35篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 14篇 |
2002年 | 20篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1964年 | 2篇 |
1963年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有994条查询结果,搜索用时 4 毫秒
21.
22.
23.
24.
Transgenic plants offer a promising system for large-scale production of therapeutic proteins such as monoclonal antibodies (mAbs). This paper describes a membrane-based process suitable for purification of a humanized mAb expressed in tobacco. Most monoclonal antibody purification schemes rely on the use of Protein A as the affinity ligand for antibody capture. The main objective of our work was to develop non-Protein A-based purification methods to avoid some of the problems and limitations associated with this ligand, e.g. cost, immunotoxicity, and antibody aggregation during elution. Ion exchange membrane chromatography (IEMC) was used for primary capture and preliminary purification of the mAb from tobacco juice. Hydrophobic interaction membrane chromatography (HIMC) was then used for high-resolution purification, followed by ultrafiltration for polishing, desalting and buffer exchange. Using this scheme, both high mAb purity (single peak in size exclusion chromatogram, i.e., ca. 100% purity) and high recovery (77% of mAb spiked into the tobacco extract) were achieved. Membrane chromatography is generally considered unsuitable for resolving bound proteins by gradient elution and is therefore commonly used in the bind and elute mode with a single-step change of mobile phase. We show that the gradient elution process in the HIMC step can be optimized to increase the resolution and thereby obtain product of high purity. 相似文献
25.
Venkatachalam G Raja N Pandiarajan D Ramesh R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,71(3):884-891
An interesting series of binuclear ruthenium(III) Schiff base complexes bearing bis-salophen/bis-naphophen units of the general composition [(EPh(3))(X)Ru-L-Ru(X)(EPh(3))] (where E=P or As; X=Cl or Br; L=binucleating dianionic tetradentate ligands) have been synthesized and characterized by analytical (elemental analysis, magnetic susceptibility measurements), spectral (FT-IR, UV-vis and EPR) and electrochemical methods. These ruthenium(III) complexes have two N(2)O(2) metal binding sites, which are linked to each other with a biphenyl bridge and acts as potential catalyst for oxidation of wide range of primary and secondary alcohols to corresponding aldehydes or ketones with moderate to high conversion in the presence of N-methylmorpholine-N-oxide (NMO). The formation of high-valent Ru(V)=O species as a catalytic active intermediate is proposed for the catalytic processes. 相似文献
26.
[reaction: see text] Chiral N-acylhydrazones derived from commercially available 4-benzyl-2-oxazolidinone provide a rigid, conformationally restricted template to impart facial selectivity in additions to C=N bonds. In the presence of indium(III) trifluoromethanesulfonate [In(OTf)3], N-acylhydrazones undergo highly diastereoselective fluoride-initiated additions of allylsilanes (aza-Sakurai reaction). Mechanistic studies including control experiments and comparisons with allyltributylstannane, allylmagnesium bromide, and allylindium species implicate a dual activation mechanism involving addition of an allylfluorosilicate species to a chelate formed from In(OTf)3 and the chiral N-acylhydrazone. The N-N bonds of the adducts are readily cleaved in a two-step protocol to provide synthetically useful homoallylic N-trifluoroacetamides. Further elaboration of the latter compounds through Wacker oxidation and olefin metathesis provides diversely functionalized building blocks and expands the potential applications of this C-C bond construction approach to asymmetric amine synthesis. 相似文献
27.
N. Raman J. Dhaveethu Raja A. Sakthivel 《Russian Journal of Coordination Chemistry》2008,34(6):400-406
A new series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Hg(II), and VO(IV) have been
designed and synthesized from the Schiff base derived from cinnamidene-4-aminoantipyrine and 2-aminophenol by involving the
carbonyl group of 4-aminoantipyrine. The structural features have been arrived from their elemental analyses, magnetic susceptibility,
molar conduction, FAB mass, IR, UV-Vis, 1H NMR and ESR spectral studies. The data show that the complexes have composition of the ML2 type. The UV-Vis, magnetic susceptibility, and ESR spectral data of the complexes suggest an octahedral geometry around the
central metal ion except the VO(IV) complex, which has a square-pyramidal geometry. The redox behavior of the copper and vanadyl
complexes has been studied by cyclic voltammetry. The antimicrobial activity of the ligand and its complexes has been extensively
studied on microorganisms such as Salmonella typhi, Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Aspergillus niger, and Rhizoctonia bataicola. It has been found that most of the complexes have higher activities than that of the free ligand. The nuclease activity
of the above metal complexes shows that the complexes cleave DNA through redox chemistry. In the presence of H2O2, the complexes are capable of cleaving calf thymus DNA.
The text was submitted by the authors in English. 相似文献
28.
Duraiswamy SukanyaDuraisamy Senthil Raja Nattamai S.P. BhuvaneshKaruppannan Natarajan 《Polyhedron》2011,30(6):1108-1113
New hexa-coordinated Ru(III) complexes of the type [Ru(H2Pzdc)(EPh3)3X2] have been synthesized by reacting 3,5-pyrazole dicarboxylic acid (H3Pzdc) with the appropriate starting complexes [RuX3(EPh3)3] (where X = Cl or Br; E = P or As). The ligand behaves as a bidentate monobasic chelate. All the complexes have been characterized by analytical and spectroscopic (IR, electronic and EPR) data. Single-crystal X-ray analysis of the complex [Ru(H2Pzdc)(PPh3)2Cl2]·C6H6·C2H5OH revealed that the coordination environment around the ruthenium center consists of an NOP2Cl2 octahedron. The planar ligand occupies the equatorial position along with two chlorine atoms, while the triphenylphosphine groups occupy the axial positions. The electrochemical behavior of the new complexes was studied using cyclic voltammetry. The new mononuclear ruthenium complexes are capable of acting as catalysts for the oxidation of alcohols. 相似文献
29.
Gunasekaran Raja Chinnasamy Jayabalakrishnan 《Central European Journal of Chemistry》2013,11(6):1010-1018
A series of new ruthenium(II) complexes were synthesized with Schiff bases derived from salicylaldehyde / o-hydroxyacetophenone/ o-vanillin / 2-hydroxy-1-naphthaldehyde with thiosemicarbazide and acetyl furan. They are characterized by elemental analysis, IR, electronic, 1H NMR, 13C NMR and mass spectral studies. The elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). Four of these complexes were tested for its binding with CT-DNA using absorption spectroscopic studies and two of these complexes exhibit efficient DNA cleavage activity. 相似文献
30.
Nielsen CB Ashraf RS Schroeder BC D'Angelo P Watkins SE Song K Anthopoulos TD McCulloch I 《Chemical communications (Cambridge, England)》2012,48(47):5832-5834
A series of benzotrithiophene-containing random terpolymers for polymer solar cells is reported. Through variations of the two other components in the terpolymers, the absorption profile and the frontier energy levels are optimized and maximum power conversion efficiencies are nearly doubled (5.14%) relative to the parent alternating copolymer. 相似文献