全文获取类型
收费全文 | 2577篇 |
免费 | 6篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 19篇 |
金属工艺 | 5篇 |
机械仪表 | 1篇 |
建筑科学 | 2篇 |
轻工业 | 16篇 |
石油天然气 | 3篇 |
无线电 | 23篇 |
一般工业技术 | 19篇 |
冶金工业 | 2471篇 |
原子能技术 | 5篇 |
自动化技术 | 18篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 8篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 10篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 78篇 |
1998年 | 814篇 |
1997年 | 409篇 |
1996年 | 289篇 |
1995年 | 162篇 |
1994年 | 122篇 |
1993年 | 177篇 |
1992年 | 30篇 |
1991年 | 24篇 |
1990年 | 31篇 |
1989年 | 20篇 |
1988年 | 30篇 |
1987年 | 33篇 |
1986年 | 23篇 |
1985年 | 26篇 |
1983年 | 2篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 26篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 54篇 |
1976年 | 111篇 |
1974年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有2583条查询结果,搜索用时 11 毫秒
71.
72.
73.
L S?vendahl LE Underwood KM Haldeman MH Ulshen PK Lund 《Canadian Metallurgical Quarterly》1997,138(2):734-740
Cytokines and insulin-like growth factors (IGFs) are involved in the induction and/or perpetuation of inflammatory bowel disease. The effect of fasting on inflammatory bowel disease was studied in a mouse experimental model of acute colitis caused by adding dextran sulfate sodium (DSS) to drinking water. Animals were either fed ad libitum or fasted (water only) for 2 days before death. Inflammation and tissue damage, measured as a colitis activity score, were markedly reduced in fasted (2.4 +/- 0.1) compared to fed (5.3 +/- 0.1) DSS animals (P < 0.0001). Colon interleukin-1 beta (IL-1 beta), IGF-I, and tumor necrosis factor-alpha messenger RNAs (mRNAs) were quantified by Northern blot hybridization and expressed as a percentage of mRNA abundance in fed controls. In DSS mice, IL-1 beta mRNA was elevated in the fed group (954 +/- 155%; P < 0.001), but was suppressed in fasted animals (71.1 +/- 11%). IGF-I mRNA also was elevated in fed DSS mice (421 +/- 71%; P < 0.01). This increase was attenuated in fasted DSS mice (202 +/- 17%; P < 0.01 compared to fed DSS mice). Tumor necrosis factor-alpha mRNA was increased in fed DSS mice (162 +/- 15%; P < 0.01), but was not significantly lower in fasted animals. By in situ hybridization, IL-1 beta mRNA was localized to the lamina propria of colonic mucosa in fed DSS animals, but was not detectable in other groups. We conclude that fasting has a protective effect on the progression of acute DSS, induced colitis. This is associated with decreased expression of IL-1 beta and IGF-I mRNAs in the colon. 相似文献
74.
LR Alexander AM Spungen MH Liu M Losada WA Bauman 《Canadian Metallurgical Quarterly》1995,76(9):819-822
OBJECTIVE: To determine the overall effect of paraplegia and pressure sores on resting metabolic rate. DESIGN: Unblinded, case-control study using a convenience sample. SETTING: Hospital primary care setting. PATIENTS: Fourteen individuals with paraplegia and pressure sores (PS-Para), 24 with paraplegia in good health (NPS-Para), and 23 non-spinal cord injury (SCI) controls. MAIN OUTCOME MEASURES: The planned outcome measures consisted of resting metabolic rate, percent of predicted resting metabolic rate, resting metabolic rate per kilogram body weight, and resting metabolic rate per meter squared body surface area. Post hoc analyses were used to identify the effect of completeness of lesion, smoking, and pressure sores on percent of predicted resting metabolic rate and resting metabolic rate per kilogram body weight. RESULTS: Percent of predicted resting metabolic rate and resting metabolic rate per kilogram body weight were significantly higher in the PS-Para group than in the NPS-Para or control groups (115% +/- 4% vs 100% +/- 2% or 107% +/- 2%, p < .05) and (25.9 +/- 1.2 vs 21.4 +/- 0.6 or 22.5 +/- 0.4 kcal/kg, p < .05, respectively). The resting metabolic rate per meter squared body surface area was significantly higher in the PS-Para group than in NPS-Para group (973 +/- 39 vs 874 +/- 20kcal/m2, p < .05). In the PS-Para group, current smokers had significantly higher resting metabolic rate per kilogram body weight than nonsmokers (27.3 +/- 1.7 vs 24.0 +/- 1.4kcal/kg, p < .01). Controlling for the effects of smoking in a multiple regression model, those in the PS-Para group had significantly (p < .001) greater percent of predicted resting metabolic rate and resting metabolic rate per kilogram body weight than those in the NPS-Para group. CONCLUSIONS: These findings indicate that individuals with SCI may have a decreased percent of predicted resting metabolic rate and those with pressure sores may have a hypermetabolic state. This hypermetabolic state is significantly higher than that resulting from smoking. Because ordinary prediction equations for energy expenditure may not be accurate when applied to subjects with paraplegia and pressure sores, quantification of energy needs by indirect calorimetry is recommended. 相似文献
75.
Growth hormone prepared by recombinant DNA technology (somatropin) has been commercially available for over 11 years. More than 38,000 children have been treated with different growth hormone products. While the best response to treatment occurs in children with severe growth hormone deficiency, therapy with growth hormone will increase the rate of statural growth in children with short stature of many different aetiologies. There are few studies of the effect of growth hormone treatment of final adult height, and the magnitude of this effect is harder to gauge, particularly in children with idiopathic short stature. Other benefits of growth hormone treatment in children include improvement in psychosocial functioning and physiological parameters, such as bone mineral density. Adverse effects associated with growth hormone treatment have been relatively uncommon. Most of the safety data on growth hormone have come from large postmarketing databases maintained by 2 pharmaceutical companies. The adverse event profile reported in children treated with growth hormone is different from that found in adults. Peripheral oedema and carpal tunnel syndrome, which are common in adults treated with growth hormone and frequently result in treatment discontinuation, are rare in children. Intracranial hypertension is rare, but can occur in children with growth hormone deficiency, Ullrich-Turner syndrome or renal insufficiency during the first 8 to 12 weeks after the start of growth hormone treatment; it has seldom been reported in adults with growth hormone deficiency. Children with growth hormone deficiency, Ullrich-Turner syndrome or renal insufficiency are prone to develop slipped capital femoral epiphyses both before and during growth hormone treatment. Therefore, limping and complaints of hip or knee pain should be carefully investigated. 相似文献
76.
MH Buc-Caron 《Canadian Metallurgical Quarterly》1995,2(1):37-47
Analyses tested the following contrasting hypotheses: a) The occurrence of a new symptom in the presence of ongoing life stress increases the attribution of symptoms to illness and increases the use of health care; b) new symptoms occurring in the presence of ongoing life stress are attributed to stressors if they are ambiguous indicators of illness, and they are unlikely to motivate care-seeking if the stressor, i.e., the perceived cause, is of recent onset. The 43-to-92-year old subjects in this longitudinal study were less likely to seek care for the ambiguous symptoms they experienced during the previous week if there was a concurrent life stressor that began during the previous 3 weeks; these symptoms were attributed to stress rather than to illness, and subjects tolerated the emotional distress caused by the combination of a stressor and an ambiguous symptom. Subjects were less willing to tolerate the combined distress of an ambiguous symptom and a concurrent life stressor if the stressor onset was not recent; under such conditions, subjects were more likely to seek health care. Current life stressors did not affect care-seeking for symptoms that were clear signs of disease; these symptoms were readily identified as health threats in need of medical attention. The findings contribute to a better theoretical understanding of how individuals perceive their physical states and how they cope with stress. Practical implications of these findings for increasing efficient use of health care services are also discussed. 相似文献
77.
The significance of prenatal and perinatal complications (biological risk) and of family adversity (psychosocial risk) on early child development was examined in a prospective study. Developmental outcome of 350 infants was assessed by measures of motor, cognitive, and social-emotional functioning at 3, 24, and 54 months. Results indicated a differential impact of risk factors on specific outcomes. Whereas psychosocial risks became more prominent with growing age and were related to poorer child outcome in all areas of functioning, biological risks decreased in influence and predominantly resulted in poorer motor development. The contributions of biological and psychosocial risks on outcomes were additive. A number of individual risk factors emerged as significant predictors of later maladaptation. 相似文献
78.
MH Koolhaas G van der Zwan F van Mourik R van Grondelle 《Canadian Metallurgical Quarterly》1997,72(4):1828-1841
The origin of the nonconservative nature of the circular dichroism (CD) spectrum of bacteriochlorophyll dimers is investigated. It is shown that coupling between the Qy and Qx transitions can, under rather restricting circumstances, lead to an asymmetrical CD spectrum: only for a limited set of relative orientations of the monomers within the dimer is the spectrum found to be asymmetrical. The relation between intensity and asymmetry of the CD spectrum is elucidated. The results are applied to the B820 subunit of the LH1 antenna system and subsequently to the antenna system LH1 itself. Differences in the geometry of the BChls in LH1 versus the LH2 structure are discussed. 相似文献
79.
BJ Cardinal 《Canadian Metallurgical Quarterly》1995,80(1):255-258
The readability levels of 10 articles each from the Journal of Health Education, Journal of Physical Education, Recreation and Dance, Research Quarterly for Exercise and Sport, and Strategies: A Journal for Physical and Sport Educators were estimated. On average, the 40 articles were written at the college junior level (M = 14.9, SD = 1.6); however, significant between-journal differences were found, with between-journal effect sizes ranging from 0.36 to 3.64. 相似文献
80.
MH Selikson J Jaggi PD Mozley L Lodhi J McCue H Vu R Forrest 《Canadian Metallurgical Quarterly》1997,42(8):1605-1617
The accuracy of radiation dose estimates from radiopharmaceutical administrations has recently become more important for three main reasons: (i) clinical providers are demanding more information on diagnostic procedures; (ii) regulatory groups are scrutinizing dosimetry for research subjects; and (iii) accurate organ doses are crucial in therapeutic administrations. These dose estimates are a sensitive function of the residence times. Because most clinical data acquisition protocols are limited to the first 24 h after dose administration, the area under the remainder of the time-activity curve (TAC) must be estimated. Estimation methods range from assuming physical decay only (overly conservative) to extrapolating end point physiological kinetics (overly liberal). This study demonstrates how much the results from these two methods vary and develops an alternative method which more accurately estimates this remainder term. A method, called the minimum detectable compartment (MDC), is constructed so that an accurate dose estimate can be made with a realistic measure of the remainder term. The method for determining MDC uses standard hypothesis testing. Using an analogue of the traditional minimal detectable activity calculation, a model with and without constant compartments is fitted to the TAC. The size of the constant compartment is varied until the relative likelihood of the two models meets the desired measure of power and sensitivity. Computer simulations of a simple mono-exponential are used to demonstrate the MDC as a function of the model, the number of data points, the range of the data and the noise in the data. The MDC is a very sensitive function of the data range. It falls by more than 50% when the data range is increased from two to three half-lives. In addition, the MDC is moderately sensitive to the noise in the data and relatively insensitive to the number of data points. These findings suggest that the MDC method can also be uses a priori to indicate what type of data collection regimen is necessary to achieve a certain accuracy. 相似文献