全文获取类型
收费全文 | 4903篇 |
免费 | 9篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 23篇 |
综合类 | 10篇 |
化学工业 | 88篇 |
金属工艺 | 34篇 |
机械仪表 | 24篇 |
建筑科学 | 54篇 |
矿业工程 | 6篇 |
能源动力 | 13篇 |
轻工业 | 78篇 |
水利工程 | 15篇 |
石油天然气 | 9篇 |
武器工业 | 1篇 |
无线电 | 88篇 |
一般工业技术 | 171篇 |
冶金工业 | 4130篇 |
原子能技术 | 24篇 |
自动化技术 | 148篇 |
出版年
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 33篇 |
2012年 | 23篇 |
2011年 | 35篇 |
2010年 | 24篇 |
2009年 | 45篇 |
2008年 | 44篇 |
2007年 | 66篇 |
2006年 | 32篇 |
2005年 | 39篇 |
2004年 | 32篇 |
2003年 | 29篇 |
2002年 | 23篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 165篇 |
1998年 | 1308篇 |
1997年 | 722篇 |
1996年 | 500篇 |
1995年 | 291篇 |
1994年 | 241篇 |
1993年 | 265篇 |
1992年 | 46篇 |
1991年 | 63篇 |
1990年 | 64篇 |
1989年 | 67篇 |
1988年 | 48篇 |
1987年 | 51篇 |
1986年 | 45篇 |
1985年 | 45篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 36篇 |
1981年 | 31篇 |
1980年 | 40篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 73篇 |
1976年 | 165篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1971年 | 7篇 |
1944年 | 5篇 |
排序方式: 共有4916条查询结果,搜索用时 15 毫秒
991.
Colleen Varaidzo Manyumwa
zlem Tastan Bishop 《International journal of molecular sciences》2021,22(6)
Carbonic anhydrases (CAs) have been identified as ideal catalysts for CO2 sequestration. Here, we report the sequence and structural analyses as well as the molecular dynamics (MD) simulations of four γ-CAs from thermophilic bacteria. Three of these, Persephonella marina, Persephonella hydrogeniphila, and Thermosulfidibacter takaii originate from hydrothermal vents and one, Thermus thermophilus HB8, from hot springs. Protein sequences were retrieved and aligned with previously characterized γ-CAs, revealing differences in the catalytic pocket residues. Further analysis of the structures following homology modeling revealed a hydrophobic patch in the catalytic pocket, presumed important for CO2 binding. Monitoring of proton shuttling residue His69 (P. marina γ-CA numbering) during MD simulations of P. hydrogeniphila and P. marina’s γ-CAs (γ-PhCA and γ-PmCA), showed a different behavior to that observed in the γ-CA of Escherichia coli, which periodically coordinates Zn2+. This work also involved the search for hotspot residues that contribute to interface stability. Some of these residues were further identified as key in protein communication via betweenness centrality metric of dynamic residue network analysis. T. takaii’s γ-CA showed marginally lower thermostability compared to the other three γ-CA proteins with an increase in conformations visited at high temperatures being observed. Hydrogen bond analysis revealed important interactions, some unique and others common in all γ-CAs, which contribute to interface formation and thermostability. The seemingly thermostable γ-CA from T. thermophilus strangely showed increased unsynchronized residue motions at 423 K. γ-PhCA and γ-PmCA were, however, preliminarily considered suitable as prospective thermostable CO2 sequestration agents. 相似文献
992.
993.
WG Rice JA Turpin CA Schaeffer L Graham D Clanton RW Buckheit D Zaharevitz MF Summers A Wallqvist DG Covell 《Canadian Metallurgical Quarterly》1996,39(19):3606-3616
Conservation of the Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys retroviral zinc finger sequences and their absolute requirement in both the early and late phases of retroviral replication make these chemically reactive structures prime antiviral targets. We recently reported that select 2,2'-dithiobisbenzamides (DIBAs) chemically modify the zinc finger Cys residues, resulting in release of zinc from the fingers and inhibition of HIV replication. In the current study we surveyed 21 categories of disulfide-based compounds from the chemical repository of the National Cancer Institute for their capacity to act as retroviral zinc finger inhibitors. Aromatic disulfides that exerted anti-HIV activity tended to cluster in the substituted aminobenzene, benzoate, and benzenesulfonamide disulfide subclasses. Only one thiuram derivative exerted moderate anti-HIV activity, while a number of nonaromatic thiosulfones and miscellaneous disulfide congeners were moderately antiviral. Two compounds (NSC 20625 and NSC 4493) demonstrated anti-cultures. The two compounds chemically modified the p7NC zinc fingers in two separate in vitro assays, and interatomic surface molecular modeling docked the compounds efficiently but differentially into the zinc finger domains. The combined efforts of rational drug selection, cell-based screening, and molecular target-based screening led to the identification of zinc finger inhibitors that can now be optimized by medicinal chemistry for the development of biopharmaceutically useful anti-HIV agents. 相似文献
994.
JL Larson MK Covey CA Vitalo CG Alex M Patel MJ Kim 《Canadian Metallurgical Quarterly》1996,45(4):203-210
Validity and test-retest liability of the 12-minute distance (12MD) walk, a measure of functional status, were examined in patients with chronic obstructive pulmonary disease. Four tests were administered at weekly intervals. Performance increased (p < .01) over the first three tests. Test-retest reliability was r34 = .98 (df = 46) for tests 3 and 4. The 12MD walk correlated with the Sickness Impact Profile, Physical Dimension (r = -.45); forced expiratory volume in 1 second % predicted ( r = .40); maximal inspiratory pressure (PImax) (r = .52); and exercise-related breathlessness (r = -.49). Exercise-related breathlessness and PImax accounted for 42% of the variance. The validity and reliability of the 12MD walk were supported. 相似文献
995.
996.
997.
The shuttle vector pS189 was treated with each of the four configurational isomers of benzo[c]phenanthrene 3,4-dihydrodiol 1,2-epoxide, and the modified DNA was used as a template in a polymerase arrest assay examining the supF gene. Sites at which polymerase (Sequenase, version 2.0) progress along the template was blocked were presumed to be at or near sites of adduct formation. The polymerase arrest sites were compared with recently reported mutation hotspots induced by these agents in this gene (Bigger et al., Proc. Natl. Acad. Sci. USA, 89: 368-372, 1992). For 31 of 32 mutation hotspots, a polymerase arrest band was present at or 1 or 2 nucleotides 3'- to that site, indicating that adduct formation tended to be associated with mutation hotspots. However, the arrest bands near mutation hotspots were not particularly prominent in all cases, and there were many sites of substantial polymerase arrest that were not in the vicinity of mutation hotspots. Thus, factors in addition to chemical selectivity must play key roles in determining sites of mutation. 相似文献
998.
999.
N Tanahashi K Yokota JY Ahn CH Chung T Fujiwara E Takahashi GN DeMartino CA Slaughter T Toyonaga K Yamamura N Shimbara K Tanaka 《Canadian Metallurgical Quarterly》1997,2(3):195-211
The information processing capabilities of biomolecular excitable media based on nonlinear dynamic mechanisms are discussed. Given even the simplest medium geometry, dynamics and information processing features inherent in biomolecular excitable media proves to be diverse and sophisticated. For the case of pseudo two-dimensional versions these media can be described in terms of neural networks having lateral connections. The main responses of shunting on-center off-surround feedback neural networks and pseudo two-dimensional excitable systems to the external excitations are surprisingly similar. The excitable media are capable of short-time memory, of contour enhancement and quenching or amplifying small features depending on medium state. The analogies discussed reaffirm specific neural net characteristics of excitable media and give the opportunity to estimate more accurate excitable medium characteristics. 相似文献
1000.