全文获取类型
收费全文 | 3460篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
综合类 | 3篇 |
化学工业 | 23篇 |
金属工艺 | 3篇 |
机械仪表 | 2篇 |
建筑科学 | 9篇 |
矿业工程 | 1篇 |
能源动力 | 3篇 |
轻工业 | 10篇 |
石油天然气 | 1篇 |
武器工业 | 2篇 |
无线电 | 10篇 |
一般工业技术 | 8篇 |
冶金工业 | 3374篇 |
自动化技术 | 16篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 1篇 |
2011年 | 26篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2006年 | 1篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2000年 | 3篇 |
1999年 | 118篇 |
1998年 | 1125篇 |
1997年 | 653篇 |
1996年 | 389篇 |
1995年 | 194篇 |
1994年 | 178篇 |
1993年 | 228篇 |
1992年 | 13篇 |
1991年 | 28篇 |
1990年 | 27篇 |
1989年 | 41篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 1篇 |
1983年 | 7篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 26篇 |
1979年 | 1篇 |
1978年 | 10篇 |
1977年 | 75篇 |
1976年 | 136篇 |
1971年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有3467条查询结果,搜索用时 0 毫秒
941.
942.
943.
Cobalt oxide nanoparticles (NPs) are highly consistent dispersed into the blend polymers rather than other NPs. Also, the ability of polyvinyl alcohol-polyethylene glycol (PVA-PEG) to form homogenous blend attained it essential characteristics that allow it to be suitable candidate for numerous industrial applications. Thus in the present work, Co3O4 nano-oxide, was synthesized by the sol-gel procedure and PVA-PEG/Co3O4 nanocomposite NCP films were synthesized by the casting technique. Samples from the synthesized NCP were exposed to γ doses between 20 and 230 kGy. The induced alterations in the synthesized NCP due to gamma irradiation have been illustrated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared (FTIR), and UV spectroscopes. Further, Color divergence between the blank and the irradiated films has been estimated. Gamma doses between 60 and 230 kGy lead to the prevalence of intermolecular crosslinking, which enhances the disordered phase. This is reflected in a rise in the degradation temperature values from 225°C to 236°C indicating an improvement in the thermostability of the NCP samples. Moreover, the γ-radiation induces defects that split the ordered portion, reducing Tm from 238°C to 229°C. In addition, the band gap decreases from 5.24 to 4.61 eV with increasing the γ doses to 230 kGy, signifying disorder character. Finally, the NCP samples showed a color change by γ radiation, as ΔE raised with increasing dose. The resultant improvements in the optical properties of the NCP samples allow it to be used in optoelectronic and dosimetric applications. 相似文献
944.
Some viruses induce changes in membrane permeability during infection. We have shown previously that the porcine strain of rotavirus, OSU, induced an increase in the permeability to Na+, K+, and Ca2+ during replication in MA104 cells. In this work, we have characterized the divalent cation entry pathway by measuring intracellular Ca2+ in fura-2-loaded MA104 and HT29 cells in suspension. The permeability to Ca2+ and other cations was evaluated by the change of the intracellular concentration following an extracellular cation pulse. Rotavirus infection induced an increase in permeability to Ca2+, Ba2+, Sr2+, Mn2+, and Co2+. The rate of cation entry decreased over time as the intracellular concentration increased during the first 20 s. This indicates that regulatory mechanisms, including channel inactivation, are triggered. La3+ did not enter the cell and blocked the entry of the divalent cations in a dose-dependent manner. Metoxyverapamil (D600), a blocker of L-type voltage-gated channels, partially inhibited the entry of Ca2+ in virus-infected MA104 and HT29 cells. The results suggest that rotavirus infection of cultured cells activates a cation channel rather than nonspecific permeation through the plasma membrane. This activation involves the synthesis of viral proteins through mechanisms yet unknown. The increase in intracellular Ca2+ induced by the activation of this channel may be related to the increase in cytoplasmic and endoplasmic reticulum Ca2+ pools required for virus maturation and cell death. 相似文献
945.
ME Jones MR Visser M Klootwijk P Heisig J Verhoef FJ Schmitz 《Canadian Metallurgical Quarterly》1999,43(2):421-423
The activities of eight fluoroquinolones and linezolid, quinupristin-dalfopristin (Synercid), gentamicin, and vancomycin were tested against 96 ciprofloxacin-susceptible and 205 ciprofloxacin-resistant Staphylococcus aureus strains. Overall, clinafloxacin, followed by moxifloxacin and trovafloxacin, was the most active quinolone tested. For all isolates, linezolid and quinupristin-dalfopristin showed activities that were at least comparable to vancomycin, with no cross-resistance to any other test compound. 相似文献
946.
DM Woodcock ME Linsenmeyer JP Doherty WD Warren 《Canadian Metallurgical Quarterly》1999,79(2):251-256
The p16 (CDKN2/MTS-1/INK4A) gene is one of several tumour-suppressor genes that have been shown to be inactivated by DNA methylation in various human cancers including breast tumours. We have used bisulphite genomic sequencing to examine the detailed sequence specificity of DNA methylation in the CpG island promoter/exon 1 region in the p16 gene in DNA from a series of human breast cancer specimens and normal human breast tissue (from reductive mammaplasty). The p16 region examined was unmethylated in the four normal human breast specimens and in four out of nine breast tumours. In the other five independent breast tumour specimens, a uniform pattern of DNA methylation was observed. Of the nine major sites of DNA methylation in the amplified region from these tumour DNAs, four were in non-CG sequences. This unusual concentration of non-CG methylation sites was not a general phenomenon present throughout the genome of these tumour cells because the methylated CpG island regions of interspersed L1 repeats had a pattern of (almost exclusively) CG methylation similar to that found in normal breast tissue DNA and in DNA from tumours with unmethylated p16 genes. These data suggest that DNA methylation of the p16 gene in some breast tumours could be the result of an active process that generates a discrete methylation pattern and, hence, could ultimately be amenable to therapeutic manipulation. 相似文献
947.
Invasive glioma cells migrate preferentially along central nervous system (CNS) white matter fiber tracts irrespective of the fact that CNS myelin contains proteins that inhibit cell migration and neurite outgrowth. Previous work has demonstrated that to migrate on a myelin substrate and to overcome its inhibitory effect, rat C6 and human glioblastoma cells require a membrane-bound metalloproteolytic activity (C6-MP) which shares several biochemical and pharmacological characteristics with MT1-MMP. We show now that MT1-MMP is expressed on the surface of rat C6 glioblastoma cells and is coenriched with C6-MP activity. Immunodepletion of C6-MP activity is achieved with an anti-MT1-MMP antibody. These data suggest that MT1-MMP and the C6-MP are closely related or identical. When mouse 3T3 fibroblasts were transfected with MT1-MMP they acquired the ability to spread and migrate on the nonpermissive myelin substrate and to infiltrate into adult rat optic nerve explants. MT1-MMP-transfected fibroblasts and C6 glioma cells were able to digest bNI-220, one of the most potent CNS myelin inhibitory proteins. Plasma membranes of both MT1-MMP-transfected fibroblasts and C6 glioma cells inactivated inhibitory myelin extracts, and this activity was sensitive to the same protease inhibitors. Interestingly, pretreatment of CNS myelin with gelatinase A/MMP-2 could not inactivate its inhibitory property. These data imply an important role of MT1-MMP in spreading and migration of glioma cells on white matter constituents in vitro and point to a function of MT1-MMP in the invasive behavior of malignant gliomas in the CNS in vivo. 相似文献
948.
949.
EP Leeflang S Tavaré P Marjoram CO Neal J Srinidhi H MacFarlane ME MacDonald JF Gusella M de Young NS Wexler N Arnheim 《Canadian Metallurgical Quarterly》1999,8(2):173-183
Trinucleotide repeat disease alleles can undergo 'dynamic' mutations in which repeat number may change when a gene is transmitted from parent to offspring. By typing >3500 sperm, we determined the size distribution of Huntington's disease (HD) germline mutations produced by 26 individuals from the Venezuelan cohort with CAG/CTG repeat numbers ranging from 37 to 62. Both the mutation frequency and mean change in allele size increased with increasing somatic repeat number. The mutation frequencies averaged 82% and, for individuals with at least 50 repeats, 98%. The extraordinarily high mutation frequency levels are most consistent with a mutation process that occurs throughout germline mitotic divisions, rather than resulting from a single meiotic event. In several cases, the mean change in repeat number differed significantly among individuals with similar somatic allele sizes. This individual variation could not be attributed to age in a simple way or to ' cis ' sequences, suggesting the influence of genetic background or other factors. A familial effect is suggested in one family where both the father and son gave highly unusual spectra compared with other individuals matched for age and repeat number. A statistical model based on incomplete processing of Okazaki fragments during DNA replication was found to provide an excellent fit to the data but variation in parameter values among individuals suggests that the molecular mechanism might be more complex. 相似文献
950.
Succinyl-CoA synthetase (SCS) carries out the substrate-level phosphorylation of GDP or ADP in the citric acid cycle. A molecular model of the enzyme from Escherichia coli, crystallized in the presence of CoA, has been refined against data collected to 2.3 A resolution. The crystals are of space group P4322, having unit cell dimensions a=b=98.68 A, c=403.76 A and the data set includes the data measured from 23 crystals. E. coli SCS is an (alphabeta)2-tetramer; there are two copies of each subunit in the asymmetric unit of the crystals. The crystal packing leaves two choices for which pair of alphabeta-dimers form the physiologically relevant tetramer. The copies of the alphabeta-dimer are similar, each having one active site where the phosphorylated histidine residue and the thiol group of CoA are found. CoA is bound in an extended conformation to the nucleotide-binding motif in the N-terminal domain of the alpha-subunit. The phosphoryl group of the phosphorylated histidine residue is positioned at the amino termini of two alpha-helices, one from the C-terminal domain of the alpha-subunit and the other from the C-terminal domain of the beta-subunit. These two domains have similar topologies, despite only 14 % sequence identity. By analogy to other nucleotide-binding proteins, the binding site for the nucleotide may reside in the N-terminal domain of the beta-subunit. If this is so, the catalytic histidine residue would have to move about 35 A to react with the nucleotide. 相似文献