全文获取类型
收费全文 | 461篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 26篇 |
金属工艺 | 3篇 |
机械仪表 | 1篇 |
建筑科学 | 4篇 |
能源动力 | 3篇 |
轻工业 | 11篇 |
无线电 | 11篇 |
一般工业技术 | 8篇 |
冶金工业 | 388篇 |
自动化技术 | 10篇 |
出版年
2024年 | 1篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 8篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 1篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 2篇 |
1999年 | 14篇 |
1998年 | 89篇 |
1997年 | 71篇 |
1996年 | 39篇 |
1995年 | 31篇 |
1994年 | 24篇 |
1993年 | 26篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1977年 | 15篇 |
1976年 | 25篇 |
1975年 | 1篇 |
排序方式: 共有467条查询结果,搜索用时 15 毫秒
91.
Capillary electrophoresis has been presented as a resourceful technique for monitoring the purity of synthetic metallophthalocyanines and evaluating comparatively purification procedures. In this study, the tetrasulfonated cobalt(II) phthalocyanine was synthesized by the condensation method and submitted to several purification procedures such as continuous Soxhlet extraction with ethanol and dioxane, percolation through a gel-filled chromatographic column, and salting-out precipitation in acid medium followed by washing with alkaline solution. The efficiency of each procedure, or combined procedures, was then evaluated by capillary electrophoresis in citrate buffer solution under constant voltage conditions and direct UV-VIS detection at 630 nm and 260 nm. The inorganic anion and cation composition of the purified fractions was also investigated by indirect UV analysis in chromate/cetyltrimethylammonium bromide (CTAB) and imidazole/hydroxyisobutyric acid (HIBA) electrolyte systems, at 254 nm and 214 nm, respectively. The electropherograms obtained at 630 nm showed a high-intensity peak surrounded by satellite peaks of small intensity with migration time of approximately 5-6 min. This profile is indicative of the formation of positional isomers under the synthesis conditions. The electropherograms obtained at 260 nm were useful to monitor contaminants, such as reaction by-products or unreacted starting materials. The salting-out precipitation of the crude product led to a good-quality product with 80% purity (elemental analysis based on nitrogen content), which is comparable to the purity of commercially available tetrasulfonated derivatives. Both UV and infrared (IR) spectra of the purified product resemble that of standards. The capillary electrophoresis ion analysis of the treated product revealed the presence of sodium carbonate as the major contaminant. The combined treatment of salting-out precipitation followed by percolation in a Sephadex column (Pharmacia, S?o Paulo, Brazil) was successful for the removal of carbonate ion. However, the percolation procedure seemed to cause minor demetallation of the macrocycle ring, as confirmed by the presence of free cobalt(II) in the electropherogram of the column eluted fraction. 相似文献
92.
93.
94.
95.
The members of the family Schistosomatidae, dioecious Digenea, are discussed with regard to their distribution, intermediate and definitive host-parasite relationships. The biological species concept is considered together with the difficulties of its application to Schistosoma spp. and the Digenea. The correlation between pairing of adult schistosomes, physical and sexual development and the maintenance of reproductive potential is emphasised. Development of the female reproductive system does not depend upon species-specific pairing. In some combinations, e.g., Schistosoma haematobium/Schistosoma intercalatum and Schistosoma bovis/Schistosoma curassoni, a specific mate choice system apparently does not exist, whereas it does in other combinations, e.g., Schistosoma mansoni/Schistosoma intercalatum. In mixed infections change of mate may occur and when the opportunity arises heterospecific pairs of worms will change partners to conspecific pairs. Interspecific pairing in adult schistosomes will lead to either hybridisation or parthenogenesis. Yet the majority of schistosomes that inhabit the same definitive host maintain their genetic identity: specific mate recognition, site selection within the host and heterologous immunity have been suggested as isolating mechanisms. Experimental intraspecific crosses have enabled evaluation of the degree to which some populations separated and became reproductively isolated through pre-mating isolating mechanisms, indicative of incipient speciation, e.g., the Lower Guinea and Zaire strains of S. intercalatum. The occurrence and significance of parthenogenesis in schistosomes and other species of Digenea are discussed. The consequences of interspecific mating interactions in schistosomes with regard to parasite epidemiology, interspecific competition and genetic heterogeneity are debated. Geographical isolation and host specificity represent important pre-zygotic isolating mechanisms. It is suggested that site selection within the host and heterologous immunity may both reduce interspecific genetic interchange when digenean parasites utilise the same definitive host. 相似文献
96.
97.
VR Müller 《Canadian Metallurgical Quarterly》1976,98(5):261-268
Report on 34 patients with gonodal dysgenesis and chromosomal aberrations ranging in age from 4 to 28 years. The observation time amount to five years on the average. 23 urological examinations revealed 12 kidney malformations (=52,2 percent). Special pathological x-ray findings on hands and writs were significantly more frequent in Turner's disease than in normal population. In T.S. the average value of conspicicous dactyloscopic findings was about 3,0 patient, (in family members it was 0,9 test person). In the most of all cases the psychological examination resulted in dependence and less of contact. Sexuell inclinations are denied. The hormonal substitution was carried out with "Mestranol" or with "Sequenz-Ovosiston". 相似文献
98.
VR Kshettry TJ Kroshus MI Hertz DW Hunter SJ Shumway RM Bolman 《Canadian Metallurgical Quarterly》1997,63(6):1576-1583
BACKGROUND: Airway anastomosis complications continue to be a source of morbidity for lung transplant recipients. METHODS: This study analyzes incidence, treatment, and follow-up of airway anastomotic complications occurring in 127 consecutive lung transplant airway anastomoses (77 single lung and 25 bilateral sequential lung). Complications were categorized as stenosis (11), granulation tissue (8), infection (7), bronchomalacia (5), or dehiscence (3). Follow-up after treatment ranged from 6 months to 4 years. RESULTS: Nineteen airway anastomosis complications (15.0%) occurred in 18 patients. Telescoping the airway anastomosis reduced the complication rate to 12 of 97 (12.4%), compared with 7 of 30 (23.3%) for omental wrapping, (p = 0.15). Complications developed in 13 of 77 single-lung airway anastomoses (16.9%) versus 6 of 50 bilateral sequential lung recipients (12.0%). Treatment consisted of stenting (9 airway anastomoses), bronchodilation (8), laser debridement (4), rigid bronchoscopic debridement (2), operative revision (2), and growth factor application (2). There was no difference in actuarial survival between patients with or without airway anastomosis complications (p = 1.0). CONCLUSIONS: Airway anastomosis complications can be successfully managed in the immediate or late postoperative period with good outcome up to 4 years after intervention. 相似文献
99.
Five aromatic constituents of essential oils (cineole, citral, geraniol, linalool and menthol) were tested for antimicrobial activity against eighteen bacteria (including Gram-positive cocci and rods, and Gram-negative rods) and twelve fungi (three yeast-like and nine filamentous). In terms of antibacterial activity linalool was the most effective and inhibited seventeen bacteria, followed by cineole, geraniol (each of which inhibited sixteen bacteria), menthol and citral aromatic compounds, which inhibited fifteen and fourteen bacteria, respectively. Against fungi the citral and geraniol oils were the most effective (inhibiting all twelve fungi), followed by linalool (inhibiting ten fungi), cineole and menthol (each of which inhibited seven fungi) compounds. 相似文献
100.
S Komatsu J Panés JM Russell DC Anderson VR Muzykantov M Miyasaka DN Granger 《Canadian Metallurgical Quarterly》1997,29(2):683-689
Recent reports indicate that bacterial endotoxin (lipopolysaccharide) and cytokines elicit a more profound increase in the surface expression of intercellular adhesion molecule-1 (ICAM-1) in cultured endothelial cells derived from spontaneously hypertensive (SHR) versus normotensive Wistar-Kyoto rats (WKY). Our objective in this study was to characterize and compare in vivo ICAM-1 expression in SHR and WKY under basal conditions and after 5 hours of endothelial cell activation with either lipopolysaccharide (5 mg/kg i.p.) or tumor necrosis factor-alpha (TNF-alpha; 1, 5, and 10 micrograms/kg i.p.). ICAM-1 expression was quantified in different tissues by the double-radiolabeled monoclonal antibody technique. When constitutive (baseline) ICAM-1 expression was corrected for endothelial cell surface area, significantly higher values were noted in SHR than WKY but only in splanchnic organs. Lipopolysaccharide and TNF-alpha elicited significant increases in ICAM-1 expression in all tissues of both WKY and SHR. However, the magnitude of the lipopolysaccharide-induced ICAM-1 upregulation in heart, stomach, skeletal muscle, and brain was significantly lower in SHR than WKY. A similar blunted ICAM-1 upregulation was noted in the stomach of SHR after administration of 5 micrograms/kg TNF-alpha. The differences in induced ICAM-1 expression between SHR and WKY do not appear to be due to differences in endothelial cell surface area or plasma glucocorticoid levels. These results suggest that chronic arterial hypertension results in altered ICAM-1 expression on the endothelium, which may contribute to the abnormal inflammatory responses associated with this disease. 相似文献