全文获取类型
收费全文 | 959篇 |
免费 | 1篇 |
专业分类
化学工业 | 1篇 |
机械仪表 | 1篇 |
冶金工业 | 957篇 |
自动化技术 | 1篇 |
出版年
2022年 | 1篇 |
2016年 | 1篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 1篇 |
1999年 | 21篇 |
1998年 | 284篇 |
1997年 | 168篇 |
1996年 | 104篇 |
1995年 | 51篇 |
1994年 | 62篇 |
1993年 | 57篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1978年 | 5篇 |
1977年 | 35篇 |
1976年 | 80篇 |
1975年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有960条查询结果,搜索用时 15 毫秒
41.
OBJECTIVES: Little information is available about the intake of very-long-chain n-3 fatty acids in random samples of populations. We examined if the intake of these fatty acids was associated with gender, social status and lifestyle in a similar way as other indicators for a healthy diet in a nationwide survey. DESIGN AND SUBJECTS: Data were obtained from self-administered quantitative food frequency questionnaires filled in by a representative sample of Norwegian men and women, aged 16-79 y. 3144 (63%) of the invited subjects responded with acceptable questionnaires. RESULTS: Daily intake of very-long-chain n-3 fatty acids was on average 0.9 g/d and 0.4% of total energy was derived from these fatty acids. Energy derived from very-long-chain n-3 fatty acids was slightly higher among men than women, and two-fold higher among subjects aged 60-79 vs 16-29 y. White collar workers had higher intake of very-long-chain n-3 fatty acids than blue collar workers. Men and women in the highest quartile of intake of very-long-chain n-3 fatty acids had 2-3 E% higher fat intake (mostly mono- and polyunsaturated fatty acids), as compared to individuals in the lowest quartile. They also had 3-4 fold higher daily intake of retinol and vitamin D, as well as 20-50% higher intake of fruits and vegetables, dietary fibre and vitamin C. CONCLUSIONS: Intake of very-long-chain n-3 fatty acids was correlated to indicators for healthy dietary habits. However, contrary to many other indicators of a healthy diet, energy derived from very-long-chain n-3 fatty acids was not significantly associated with female gender or non-smoking. 相似文献
42.
43.
44.
Although thoracoscopic sympathectomy or sympathicotomy is the best treatment for hyperhidrosis palmaris, a new approach of clipping only without transection of T2-sympathetic trunk is just as effective. Aside from the guaranteed cure of hyperhidrosis, this new method has fewer complications and has the advantage of recovery of the sympathetic tone in the hands if the procedure is reversed by the removal of the clips. Between March 18 and September 30 of 1996, 326 patients (190 female and 136 male with a mean age of 20.5 years) underwent thoracoscopic T2-sympathetic block by clipping to treat hyperhidrosis. Good results and few complications were noted during follow up six months to one year postoperatively. Five of the 326 patients, all female, had the operation reversed because of intolerable compensatory sweating. Three recovered from the compensatory sweating within two months and had less palmar sweating than before their sympathetic block; the fourth achieved relief of compensatory sweating after nine months, and the fifth reported no improvement. 相似文献
45.
A neostriatal habit learning system in humans 总被引:1,自引:0,他引:1
Amnesic patients and nondemented patients with Parkinson's disease were given a probabilistic classification task in which they learned which of two outcomes would occur on each trial, given the particular combination of cues that appeared. Amnesic patients exhibited normal learning of the task but had severely impaired declarative memory for the training episode. In contrast, patients with Parkinson's disease failed to learn the probabilistic classification task, despite having intact memory for the training episode. This double dissociation shows that the limbic-diencephalic regions damaged in amnesia and the neostriatum damaged in Parkinson's disease support separate and parallel learning systems. In humans, the neostriatum (caudate nucleus and putamen) is essential for the gradual, incremental learning of associations that is characteristic of habit learning. The neostriatum is important not just for motor behavior and motor learning but also for acquiring nonmotor dispositions and tendencies that depend on new associations. 相似文献
46.
AC Lidral PA Romitti AM Basart T Doetschman NJ Leysens S Daack-Hirsch EV Semina LR Johnson J Machida A Burds TJ Parnell JL Rubenstein JC Murray 《Canadian Metallurgical Quarterly》1998,63(2):557-568
Nonsyndromic cleft lip with or without cleft palate (CL/P) and nonsyndromic cleft palate only (CPO) are common congenital anomalies with significant medical, psychological, social, and economic ramifications. Both CL/P and CPO are examples of complex genetic traits. There exists sufficient evidence to hypothesize that disease loci for CL/P and CPO can be identified by a candidate-gene linkage-disequilibrium (LD) strategy. Candidate genes for clefting, including TGFA, BCL3, DLX2, MSX1, and TGFB3, were screened for LD with either CL/P or CPO in a predominantly Caucasian population, with both case-control- and nuclear-family-based approaches. Previously reported LD for TGFA with both CL/P and CPO could not be confirmed, except in CL/P patients with a positive family history. Also, in contrast to previous studies, no LD was found between BCL3 and either CL/P or CPO. Significant LD was found between CL/P and both MSX1 and TGFB3 and between CPO and MSX1, suggesting that these genes are involved in the pathogenesis of clefting. In addition, a mutation search in the genes DLX2, MSX1, and TGFB3 was performed in 69 CPO patients and in a subset of the CL/P patients. No common mutations were found in the coding regions of these genes; however, several rare variants of MSX1 and TGFB3 were found that may alter the latters' normal function. These results form the basis for future research, including (a) mutation searches in the MSX1 and TGFB3 genes in Caucasian CL/P patients and (b) extension of the search for MSX1 mutations in CPO patients to the noncoding regions. 相似文献
47.
LR Dekker H Rademaker JT Vermeulen T Opthof R Coronel JA Spaan MJ Janse 《Canadian Metallurgical Quarterly》1998,97(17):1724-1730
BACKGROUND: Patients with heart failure show a very high incidence of arrhythmias and sudden death that is often preceded by ischemia; however, data on electrophysiological changes during ischemia in failing myocardium are sparse. We studied electrical uncoupling during ischemia in normal and failing myocardium. METHODS AND RESULTS: Tissue resistance, intracellular Ca2+ concentration (Indo-1 fluorescence ratio), and mechanical activity were simultaneously determined in arterially perfused right ventricular papillary muscles from 11 normal and 15 failing rabbits. Heart failure was induced by combined volume and pressure overload. Before sustained ischemia, muscles were subjected to control perfusion (non-PC) or ischemic preconditioning (PC). The onset of uncoupling during ischemia was equal in non-PC normal (13.6+/-0.9 minutes of ischemia) and non-PC failing hearts (13.3+/-0.7 minutes of ischemia). PC postponed uncoupling in normal hearts by 10 minutes. In failing hearts, however, PC caused a large variability in the onset of uncoupling during ischemia (mean, 12.2+/-2.1; range, 5 to 22 minutes of ischemia). The duration of uncoupling process was prolonged in failing hearts (12.9+/-0.9 minutes) compared with normal hearts (7.8+/-0.4 minutes). The degree of heart failure and relative heart weight of the failing hearts significantly correlated with the earlier uncoupling after PC and the duration of uncoupling. In every experiment, the start of Ca2+ rise and contracture preceded uncoupling during ischemia. CONCLUSIONS: The duration of the process of ischemia-induced electrical uncoupling in failing hearts is prolonged compared with that in normal hearts. Ischemic PC has detrimental effects in severely failing papillary muscles because it advances the moment of irreversible ischemic damage. 相似文献
48.
49.
It is proposed that both polar and radical reactions should be considered when discussing radical ion reactivity. The fact that only the polar reactivity has dominated previous discussions is pointed out. It is argued that if the configuration mixing model is applicable for the estimation of radical cation-nucleophile (or cation-nucleophile) combination reaction barriers, the theory should also explain the reactivity of the proton toward anionic nucleophiles. The model severely overestimates reaction barriers for the latter reactions. The discussion is centered around the following hypothesis: In the absence of severe steric effects, the reactivity of radical ions, especially evident in the reactions with radicals (for example very few radical cations react with dioxygen at measurable rates), is dominated by the degree of coupling between charge and radical centers. Evidence from the literature supporting the hypothesis is presented for a number of different classes of radical ion reactions. Further work to test the validity of the hypothesis is proposed for many of the reaction types. Triarylmethyl radicals and carbenium ions are suggested as models to which the radical and polar reactivities of 9,10-diarylanthracene radical cations may be compared. It is concluded that the radical cation/carbenium ion comparison (for the reaction with acetate ion) would show similar reactivities while the radical cation/free radical comparison (for the reaction with dioxygen) would fail, since no reaction at all would be observed with the radical cation while the free radical reacts rapidly. 相似文献
50.