全文获取类型
收费全文 | 1024篇 |
免费 | 34篇 |
专业分类
化学 | 554篇 |
晶体学 | 13篇 |
力学 | 26篇 |
数学 | 219篇 |
物理学 | 246篇 |
出版年
2022年 | 22篇 |
2021年 | 27篇 |
2020年 | 18篇 |
2019年 | 26篇 |
2018年 | 23篇 |
2017年 | 24篇 |
2016年 | 37篇 |
2015年 | 19篇 |
2014年 | 44篇 |
2013年 | 68篇 |
2012年 | 62篇 |
2011年 | 62篇 |
2010年 | 48篇 |
2009年 | 39篇 |
2008年 | 60篇 |
2007年 | 44篇 |
2006年 | 32篇 |
2005年 | 30篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 9篇 |
1966年 | 8篇 |
1965年 | 6篇 |
1962年 | 5篇 |
1959年 | 5篇 |
1958年 | 9篇 |
1957年 | 8篇 |
1956年 | 8篇 |
1955年 | 10篇 |
1954年 | 10篇 |
1941年 | 6篇 |
1940年 | 5篇 |
1936年 | 10篇 |
1935年 | 6篇 |
排序方式: 共有1058条查询结果,搜索用时 671 毫秒
21.
John B. Hynes Alenka Tomai
Arvind Kumar Veena Kumar James H. Freisheim 《Journal of heterocyclic chemistry》1991,28(8):1981-1986
A series of thirty eight 2,4-diaminoquinazolines having diverse substitution patterns on the aromatic ring was evaluated for inhibitory activity against dihydrofolate reductase (DHFR) obtained from a human lymphoblast cell line. Many of these compounds were also evaluated as inhibitors of rat liver DHFR under the same experimental conditions. In most instances the results obtained with each enzyme were comparable indicating that the rodent enzyme is a suitable model for the human DHFR as far as the determination of I50 values is concerned. The results demonstrate that relatively simple 5-substituted- or 5,6-disubstituted-2,4-diaminoquinazolines can be potent DHFR inhibitors. The presence of a nonpolar substituent at position 7 or 8 was highly detrimental to inhibitory potency. 相似文献
22.
Kotha A Raman RC Ponrathnam S Kumar KK Shewale JG 《Applied biochemistry and biotechnology》1998,74(3):191-203
Various glycidyl methacrylate (GMA) copolymers were synthesized by suspension polymerization, using pentaerythritol triacrylate (PETA), trimethylolpropane triacrylate (TMPTA), and trimethylolpropane trimethacrylate (TRIM) as crosslinking comonomers. These copolymers were evaluated for the immobilization of penicillin G acylase. Broad pore-size distribution that was observed was in the range 5-300 nm. Both surface area and pore volume increased with increase in the mole fraction of crosslinking comonomer (increasing crosslink density). The pore volume of the copolymers was more than doubled by including lauryl alcohol as porogen. Binding of penicillin G acylase (PGA) was quantitative on highly crosslinked copolymers. The expression of bound PGA was better on the relatively more hydrophilic GMA-TMPTA and GMA-PETA copolymer supports compared to the GMA-TRIM copolymers. Among the different copolymers studied, GMA-TMPTA copolymer 7411 exhibited highest activity of immobilized penicillin G acylase (167.4 IU/g) with 35.1% expression. 相似文献
23.
Raman Natarajan Kulandaisamy Antonysamy Thangaraja Chinnathangavel Jeyasubramanian Kadarkaraithangam 《Transition Metal Chemistry》2003,28(1):29-36
Neutral tetradentate chelate complexes of CuII, NiII, CoII, MnII, ZnII and VOII have been prepared in EtOH using Schiff bases derived from acetoacetanilido-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol. Microanalytical data, magnetic susceptibility, i.r., u.v.–vis., 1H-n.m.r. and e.s.r. spectral techniques were used to confirm the structures of the chelates. Electronic absorption and i.r. spectra of the complexes suggest a square-planar geometry around the central metal ion, except for VOII and MnII complexes which have square-pyramidal and octahedral geometry respectively. The cyclic voltammetric data for the CuII complexes in MeCN show two waves for copper(II) copper(III) and copper(II) copper(I) couples, whereas the VOII complexes in MeCN show two waves for vanadium(IV) vanadium(V) and vanadium(IV) vanadium(III) couples. The e.s.r. spectra of the CuII, VOII and MnII complexes were recorded in DMSO solution and their salient features reported. The in vitro antimicrobial activity of the investigated compounds was tested against the microorganisms such as Salmonella typhi, Staphylococcus aureus, Klebsiella pneumoniae, Bacillus subtilis, Shigella flexneri, Pseudomonas aeruginosa, Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates have higher antimicrobial activity than the free ligands. 相似文献
24.
Some tetracoordinated complexes having the formulae, [AgL4]X (L = Triphenyl-arsine; X = NO, ClO and BrO) and [AgL3X] (L = Triphenyl-arsine/phosphine; X = SCN? and NCO?) have been prepared and characterised by analyses, conductance, magnetic susceptibility and infra-red spectroscopy. 相似文献
25.
26.
Synthesis,characterization and biological screening studies of mixed ligand complexes using flavonoids as precursors
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Flavonoids are a group of plant phenolics that provide various health benefits through cell signalling pathways and antioxidant effects. In the present study, a new series of mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) were synthesized by incorporating curcumin and quercetin flavonoid precursors. The structural features of the synthesized complexes were explored using elemental analysis, thermogravimetric analysis, UV–visible, infrared, NMR, mass and electron paramagnetic resonance spectral analyses and conductivity measurements. These data support an octahedral geometry of the synthesized complexes. In silico biological activity score for the ligand was predicted using PASS online software. ADMET properties were studied using VLS3D online software. Anti‐inflammatory and antioxidant activities were experimentally validated which prove that theoretical predictions are in agreement with the experimental results. Interestingly the synthesized complexes interact with calf thymus DNA through groove binding mode. Moreover, they have good potential to cleave pUC19 DNA. Minimum inhibitory concentration values of the synthesized complexes reveal that they have better antimicrobial efficacy than the ligands. 相似文献
27.
28.
29.
Biological contour,molecular docking and antiproliferative studies of DNA targeted histidine based transition metal(II) complexes: Invention and its depiction
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A novel series of histidine derived transition metal complexes were synthesized and characterized by multispectral techniques such as UV‐Vis., FT IR, EPR, NMR, ESI‐mass analysis and other physico‐chemical methods like elemental analysis, molar conductivity, magnetic susceptibility. The synthesized compounds were attempted for their biological prospective. The biological studies involved are DNA interaction (binding and damage), antimicrobial, antioxidant, antiproliferative and molecular docking. DNA interaction studies were carried out with the help of UV‐Vis absorption titration, viscosity measurement and cyclic voltammetric techniques which revealed that the synthesized compounds could interact with CT‐DNA through intercalative binding mode. A gel electrophoresis assay demonstrated the ability of complexes to cleave the supercoiled pUC18 DNA. The antioxidant property shows that the metal complexes have preferable ability to scavenge hydroxyl radical than the ligand. Moreover, the antimicrobial assay indicates that these complexes are good antimicrobial agents against various pathogens. Furthermore, the in vitro antiproliferative activities of the complexes were examined on HeLa, Hep G2 and NIH 3 T3 cell lines using an MTT assay. The morphological changes were investigated using Hoechst 33258 staining apoptosis assay. In addition, molecular docking studies were executed to considerate the nature of binding of the synthesized complexes with protein and DNA. 相似文献
30.