全文获取类型
收费全文 | 2366篇 |
免费 | 30篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 26篇 |
综合类 | 5篇 |
化学工业 | 159篇 |
金属工艺 | 42篇 |
机械仪表 | 40篇 |
建筑科学 | 66篇 |
矿业工程 | 21篇 |
能源动力 | 22篇 |
轻工业 | 123篇 |
水利工程 | 8篇 |
石油天然气 | 6篇 |
无线电 | 120篇 |
一般工业技术 | 208篇 |
冶金工业 | 1416篇 |
原子能技术 | 10篇 |
自动化技术 | 128篇 |
出版年
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 22篇 |
2015年 | 13篇 |
2014年 | 32篇 |
2013年 | 67篇 |
2012年 | 28篇 |
2011年 | 46篇 |
2010年 | 35篇 |
2009年 | 47篇 |
2008年 | 50篇 |
2007年 | 45篇 |
2006年 | 37篇 |
2005年 | 35篇 |
2004年 | 36篇 |
2003年 | 33篇 |
2002年 | 21篇 |
2001年 | 25篇 |
2000年 | 28篇 |
1999年 | 65篇 |
1998年 | 414篇 |
1997年 | 245篇 |
1996年 | 168篇 |
1995年 | 103篇 |
1994年 | 80篇 |
1993年 | 98篇 |
1992年 | 29篇 |
1991年 | 39篇 |
1990年 | 35篇 |
1989年 | 43篇 |
1988年 | 32篇 |
1987年 | 34篇 |
1986年 | 22篇 |
1985年 | 36篇 |
1984年 | 9篇 |
1983年 | 23篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 42篇 |
1976年 | 49篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2400条查询结果,搜索用时 9 毫秒
1.
2.
JM Rumsey BC Donohue DR Brady K Nace JN Giedd P Andreason 《Canadian Metallurgical Quarterly》1997,54(12):1481-1489
The influence of ionic strength and composition on the binding and inhibition of human leukocyte elastase by glycosaminoglycans with variable degree and position of sulfation was investigated. The kinetic mechanism of inhibition had a hyperbolic, mixed-type character with a competitive component that was promoted by low ionic strength, reduced by phosphate ions, and which also depended on the substrate and glycosaminoglycan structure. Enzyme binding was a cooperative phenomenon that varied with ionic strength and composition. The inhibition patterns correlated with the cationic character of elastase and with the distribution of arginines on its molecular surface, most notably with residues located in the vicinity of the substrate binding region. The order of affinity for elastase binding was chondroitin 4-sulfate < chondroitin 6-sulfate < dermatan sulfate, iduronate-containing derivatives being superior with respect to the glucuronate-containing counterparts. Additional sulfation at both the 4- and 6- positions or at the N- and 4-positions of the N-acetylgalactosamine moiety decidedly improved the inhibitory efficiency. The results highlight a fundamental physiological role of enzyme-glycosaminoglycan interactions. In the azurophil granule of the human polymorphonuclear neutrophil, elastase and other enzymes are bound to a matrix of chondroitin 4-sulfate because this is the only glycosaminoglycan that simultaneously offers good binding for enzyme compartmentalization together with prompt release from the bound state at the onset of phagocytosis. 相似文献
3.
4.
Widely tunable bottom-emitting vertical-cavity SOAs 总被引:1,自引:0,他引:1
Cole G.D. Bjorlin E.S. Wang C.S. MacDonald N.C. Bowers J.E. 《Photonics Technology Letters, IEEE》2005,17(12):2526-2528
We present bottom-emitting tunable vertical-cavity semiconductor optical amplifiers (VCSOAs) with an effective wavelength tuning range of >20 nm. These devices utilize a high reflectivity micromechanically tunable Bragg mirror as the back reflector. Compared with our first generation tunable VCSOAs, the bottom-emitting devices exhibit a two-fold increase in the effective tuning range as well as a five-fold reduction in the required tuning voltage. 相似文献
5.
6.
7.
YC Lo L Brett CJ Kenyon SD Morley JI Mason BC Williams 《Canadian Metallurgical Quarterly》1998,24(3-4):559-563
We have employed polyclonal antibodies to a peptide sequence of bovine steroidogenic acute regulatory (StAR) protein and human placental 3beta-hydroxysteroid dehydrogenase (3beta-HSD) to determine the localisation and distribution of these proteins in rat and bovine adrenal glands. Immunohistochemical staining demonstrated the presence of StAR protein in the zona glomerulosa (ZG), zona fasciculata (ZF), zona reticularis (ZR) and in the medulla of both species. For 3beta-HSD, immunostaining was observed in the ZG, ZF and ZR of the rat adrenal and was absent in the medulla. Immunoblotting experiments showed intense bands for StAR protein (30 kDa, 37 kDa) in the mitochondria of bovine ZG, ZF and medulla and a less intense band (30 kDa) in the microsomes. In rat ZG and ZF/R mitochondria only the 30 kDa protein was present. For 3beta-HSD, an intense band (42 kDa) was found in microsomes and mitochondria of rat and bovine ZG and ZFR. A very faint signal for 3beta-HSD was seen in adrenal medulla. In conclusion, StAR (or a closely related) protein is present throughout the adrenal gland in rat and bovine species in contrast to 3beta-HSD which is confined to the steroidogenic zones. The possible function of StAR protein in the adrenal medulla merits investigation. 相似文献
8.
With increasing life span of patients with CF, more women with CF are becoming pregnant and others are seeking information about the risks involved during pregnancy and delivery. A striking limitation of the available information is the lack of large prospective studies of pregnant patients with CF matched for age and disease severity compared with their non-pregnant cohorts. A study investigating the effect of pregnancy on morbidity and mortality is being completed by the Cystic Fibrosis Foundation. We recommend that all women with CF be offered contraceptive measures and counseling on the maternal and fetal risks of pregnancy, including the genetic risks for the child. The issue of who will raise the child in the event of subsequent morbidity or maternal mortality should ideally be prospectively discussed. 相似文献
9.
Surface-induced dissociation (SID) has been used to produce daughter ion spectra of small protonated peptides generated by fast atom bombardment (FAB). The relative abundances of daughter ions depends critically upon the energy of the ion/surface collision. A wide array of decomposition processes may be observed using ELAB collision energies in the range 10-20 eV. At approximately 13-eV collision energy, the variety of decomposition processes is maximized for the small peptides studied; hence, maximum structural information may be deduced. Collisionally-activated dissociations (CAD) using argon gas and the identical protonated peptides could not produce as large an array of daughter ions in a constant condition experiment. An apparent contradiction is thereby posed because SID is known to produce a narrow distribution of ion internal energies relative to CAD. This apparent contradiction is resolved by considering the rather large kinetic energy spread of ions leaving the FAB source. For the SID process, this large initial kinetic energy distribution is converted into a significantly wider spread in center-of-mass collision energy, leading to a broader variety of decomposition processes (high and low energy) compared to CAD. 相似文献
10.
PB Imrey LA Jackson PH Ludwinski AC England GA Fella BC Fox LB Isdale MW Reeves JD Wenger 《Canadian Metallurgical Quarterly》1996,143(6):624-630
Between February 1991 and April 1992, eight undergraduates at a US residential university and one at a nearby 2-year college contracted serogroup C meningococcal disease. A case-control investigation with 20 controls per case, oropharyngeal carriage surveys, and multilocus enzyme electrophoresis (MEE) of serogroup C isolates were used to identify factors contributing to the outbreak. All eight sterile-site isolates from cases were closely related by MEE and were similar (though not identical) to the strain associated with the 1991-1992 epidemic of meningococcal disease in eastern Canada. Disease was associated with cigarette smoking (p = 0.012), recent patronage of campus-area bars (p = 0.034), estimated amount of time spent in campus-area bars (p = 0.0003), and, especially, recent patronage of one specific bar, bar A (p = 0.0006; odds ratio = 23.1, 95% confidence interval 3.0-571.5). In carriage surveys, 1,528 throat cultures taken from (primarily student) noncases yielded only five (0.3%) strains that were identical by MEE to those from cases. Two of these were found among 22 cultures obtained from bar A employees in spring 1992. Some cases in this outbreak may have followed transmission of the epidemic strain in bar A. Campus bar environments may facilitate the spread of meningococcal disease among teenagers and young adults. 相似文献