全文获取类型
收费全文 | 1772篇 |
免费 | 62篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 10篇 |
综合类 | 2篇 |
化学工业 | 123篇 |
金属工艺 | 6篇 |
机械仪表 | 25篇 |
建筑科学 | 25篇 |
能源动力 | 39篇 |
轻工业 | 42篇 |
水利工程 | 6篇 |
石油天然气 | 4篇 |
无线电 | 227篇 |
一般工业技术 | 184篇 |
冶金工业 | 1053篇 |
原子能技术 | 1篇 |
自动化技术 | 90篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 20篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 24篇 |
2016年 | 37篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 52篇 |
2012年 | 43篇 |
2011年 | 45篇 |
2010年 | 43篇 |
2009年 | 30篇 |
2008年 | 39篇 |
2007年 | 34篇 |
2006年 | 49篇 |
2005年 | 26篇 |
2004年 | 30篇 |
2003年 | 34篇 |
2002年 | 41篇 |
2001年 | 22篇 |
2000年 | 10篇 |
1999年 | 54篇 |
1998年 | 333篇 |
1997年 | 198篇 |
1996年 | 107篇 |
1995年 | 75篇 |
1994年 | 78篇 |
1993年 | 67篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 32篇 |
1976年 | 72篇 |
1975年 | 2篇 |
排序方式: 共有1837条查询结果,搜索用时 15 毫秒
11.
AS Leong 《Canadian Metallurgical Quarterly》1993,15(2):88-98
Microwaves (MWs) were first introduced as a method of fixation just over 20 years ago. In recent years their use has extended far beyond that of a safe, clean and rapid method of fixation of tissue blocks and large specimens, including brains. MWs accelerate the action of cross-linking fixatives and can greatly accelerate the various stages of tissue processing to produce a paraffin block in 30 min. An extensive range of ultrafast MW-stimulated special stains has been developed, and immunohistochemical procedures can be completed in 20 min by employing MWs. Cellular antigens are distinctly better preserved in tissues fixed by MWs than by conventional cross-linking fixatives. Also, the cytomorphology of cryostat sections irradiated in Wolman's solution is clearly improved. MWs can similarly be applied for fixation and staining of preparations for transmission and scanning electron microscopy, and they also greatly accelerate polymerisation of resins. In the current climate of cost containment, this wide range of applications makes the MW oven an invaluable addition to the diagnostic laboratory. 相似文献
12.
Li L.W. Yeo T.S. Kooi P.S. Leong M.S. 《Antennas and Propagation, IEEE Transactions on》1994,42(9):1360
The parameter set for the exponential raindrop size distribution model presented by Yeo, Kooi and Leong (see ibid. vol.41, P.709, 1993) was derived using a data set measured in Singapore. A limitation to the model is that it is accurate only for small rain rate or when the rain medium consists predominantly of small droplets with diameter D is < λ/π . A new parameter set that enables accurate computation of rain attenuation for droplets with diameter D = λ/π has since been derived using the same data set. This new parameter set has been proven to be more accurate in the computation of rain attenuation 相似文献
13.
In farm animals as in human, reproduction is affected by changes in the level of energetic balance. The main factors that link metabolism and reproduction, like insulin, IGFs, glucose, FFA, leptin and NPY, act on hypothalamo-pituitary axis as well as on gonads by directly altering gametogenesis. 相似文献
14.
This study evaluates characteristics associated with alcohol consumption or alcohol-related problems in an elderly population, as detected by CAGE questionnaire and self-reported alcohol intake respectively. Data were obtained from a multidimensional study carried out in a community-dwelling population aged 70-75 (n = 1205, 389 males and 816 females) living in the city center of Brescia, in northern Italy. All information was gathered by self-report. Male gender, better mood, daily function, somatic health, not living alone, and being married were significantly associated with self-reported alcohol consumption. Male gender, poorer cognitive function, and income dissatisfaction were significantly associated with alcohol problems as detected by CAGE. Data suggest that self-report of alcohol intake, though intrinsically loaded with imperfect internal consistency, does not necessarily indicate risk of alcoholism; on the contrary, it can reveal the positive psychological attitude of the drinking habit. CAGE questionnaire, which is sensitive to alcohol related problems, is associated with poor psychosocial conditions. 相似文献
15.
OBJECTIVES: A randomized trial was conducted to evaluate the effectiveness of a work-site health promotion program in reducing obesity and the prevalence of cigarette smoking. METHODS: Thirty-two work sites were randomized to treatment or no treatment for 2 years. Treatment consisted of health education classes combined with a payroll-based incentive system. Evaluation was based on cohort and cross-sectional surveys. RESULTS: Of 10,000 total employees in treatment work sites, 2041 and 270 participated in weight control and smoking cessation programs, respectively. Weight losses averaged 4.8 lbs, and 43% of smoking participants quit. Net 2-year reductions in smoking prevalence in treatment vs control work sites were 4.0% and 2.1% in cross-sectional and cohort surveys, respectively. No treatment effect was found for weight. Treatment effects for smoking prevalence and weight were both positively correlated with participation rates in the intervention programs (r = .45 for smoking and r = .55 for weight). CONCLUSIONS: This work-site health promotion program was effective in reducing smoking prevalence at a cost that is believed to make the investment worthwhile. 相似文献
16.
17.
To provide insight into the stream of Medicare payments over time, a sixteen-year longitudinal study examines three age cohorts of beneficiaries, looking separately at beneficiaries who died during the study period and those who survived. The common wisdom that a small minority of the population accounts for a large majority of health care expenditures is tempered when health care use is examined over an extended period of time. By putting high average costs in the final years of life in the context of a cohort's total lifetime experience, the study shows a leveling of spending over time, resulting in a lower concentration of health care resources on a small fraction of the population. 相似文献
18.
A number of receptor subtypes mediate hormonal responses to serotonin (5-HT). To test the hypothesis that the hypothalamic paraventricular nucleus (PVN) mediates 5-HT1A and 5-HT2 receptor-mediated oxytocin, PRL, and corticosterone responses, we studied the effects of the 5-HT1A agonist ipsapirone and the 5-HT2A/2C agonist 1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane (DOI) after surgical PVN lesions or sham operations. Chronically cannulated, conscious, freely moving, male Wistar rats were injected iv (1 mg/kg) shortly after (3-4 days) and 5 weeks after (35-37 days) the operations. In sham-operated rats, ipsapirone caused marked elevations in plasma PRL and corticosterone, but not oxytocin concentrations, whereas DOI increased plasma concentrations of all three hormones. Short term PVN lesions prevented ipsapirone-induced corticosterone and DOI-induced oxytocin responses. DOI-induced PRL and corticosterone responses were also markedly inhibited 3-4 days after lesioning, although small rises over the baseline values were still observed. The ipsapirone-induced PRL response was unaffected by the lesioning. Five weeks after PVN lesioning, partial recoveries were observed in ipsapirone- and DOI-induced corticosterone and DOI-induced oxytocin responses, whereas DOI-induced PRL responses remained suppressed. The present findings suggest that the PVN or neural pathways close to it mediate oxytocin, PRL, and corticosterone responses to the 5-HT2 receptor agonist DOI as well as corticosterone, but not PRL, responses to the 5-HT1A receptor agonist ipsapirone. The results after long term PVN lesioning show that the oxytocin and corticosterone responses may be partially restored with time after lesioning. 相似文献
19.
PURPOSE: The neurologic effect of induced hyperglycemia in the postischemic period was investigated with a rat aortic occlusion model. METHODS: Sprague-Dawley rats weighing 200 to 350 gm were anesthetized, intubated, and ventilated with 1% to 1.5% halothane. Temperature was continuously monitored and maintained at 37 degrees +/- 0.5 degrees C. The chest was opened, the thymus excised, and the aortic arch exposed. Snares were placed around the aorta distal to the left subclavian artery and the right and left subclavian arteries. The three vessels thus isolated were occluded for 8 minutes. With snare release and withdrawal, the rats received an intraperitoneal injection of 5% dextrose in water (2 gm/kg) or an equivalent volume of 0.9% saline solution. In a second group of rats the administration of glucose or saline solution was delayed until 30 minutes after snare release. Blood samples for blood glucose determination were obtained before operation, before occlusion, immediately after occlusion, and 15, 30, 45, 60, and 240 minutes after occlusion. A neurologic deficit score was assigned at 1, 4, 18, and 24 hours after occlusion to quantify hindlimb neurologic deficit based on 15-point scale (0 = normal, 15 = severe deficit). Sham-operated rats received the same operation and injection, but the snares were only manipulated and not made occlusive. RESULTS: The rats that were administered glucose immediately after snare release showed a statistically significant exacerbation of lower extremity neurologic deficit at 24 hours after occlusion (p < or = 0.05, Mann-Whitney U test). The sham-operated rats were normal (0 score) at 24 hours. Significant elevation of blood glucose (321 +/- 33 mg/dl) was seen in the glucose-injected rats at 15 minutes and continued for up to 4 hours after occlusion (p = 0.040 and 0.014, respectively; Student's t test). CONCLUSION: Postischemic hyperglycemia immediately after a standard spinal cord ischemic stress worsens neurologic outcome. 相似文献
20.
G Testa RM Goldstein A Toughanipour O Abbasoglu R Jeyarajah MF Levy BS Husberg TA Gonwa GB Klintmalm 《Canadian Metallurgical Quarterly》1998,227(4):590-599
The ability to acquire a motor and cognitive skill was investigated in 26 patients with schizophrenia and 26 normal participants using repeated testing on the Tower of Toronto puzzle. Seven patients with defective performance were retested using additional trials and immediate feedback designed to facilitate problem solving. A component analysis of performance was used based on J. R. Anderson's (1987) model of cognitive skill learning. Patients exhibited a performance deficit on both motor and cognitive skills. However, their acquisition rate was similar to that of normal participants on most parameters, indicating that skill learning suffered little or no impairment. Performance deficit was accounted for by poor problem-solving ability, explicit memory, and general intellectual capacities. It was remediable in some, but not all, patients. Remediation failure was also related to severe defects of cognitive functions. 相似文献