全文获取类型
收费全文 | 1101篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 3篇 |
化学工业 | 14篇 |
金属工艺 | 3篇 |
机械仪表 | 1篇 |
建筑科学 | 16篇 |
矿业工程 | 1篇 |
轻工业 | 19篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 1篇 |
一般工业技术 | 8篇 |
冶金工业 | 1020篇 |
自动化技术 | 11篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 4篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 32篇 |
1998年 | 265篇 |
1997年 | 168篇 |
1996年 | 121篇 |
1995年 | 65篇 |
1994年 | 57篇 |
1993年 | 65篇 |
1992年 | 7篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 28篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 28篇 |
1976年 | 62篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有1102条查询结果,搜索用时 15 毫秒
71.
72.
73.
G Wu PK Davis NE Flynn DA Knabe JT Davidson 《Canadian Metallurgical Quarterly》1997,127(12):2342-2349
This study was conducted to determine whether endogenous synthesis of arginine plays a role in regulating arginine homeostasis in postweaning pigs. Pigs were fed a sorghum-based diet containing 0. 98% arginine and were used for studies at 75 d of age (28.4 kg body weight). Mitochondria were prepared from the jejunum and other major tissues for measuring the activities of Delta1-pyrroline-5-carboxylate (P5C) synthase and proline oxidase (enzymes catalyzing P5C synthesis from glutamate and proline, respectively) and of ornithine aminotransferase (OAT) (the enzyme catalyzing the interconversion of P5C into ornithine). For metabolic studies, jejunal enterocytes were incubated at 37 degrees C for 30 min in Krebs-Henseleit bicarbonate buffer containing 2 mmol/L L-glutamine, 2 mmol/L L-[U-14C]proline, and 0-200 micromol/L gabaculine (an inhibitor of OAT). The activities of P5C synthase, proline oxidase and OAT were greatest in enterocytes among all of the tissues studied. Incubation of enterocytes with gabaculine resulted in decreases (P < 0.05) in the synthesis of ornithine and citrulline from glutamine and proline. When gabaculine was orally administered to pigs (0.83 mg/kg body weight) to inhibit intestinal synthesis of citrulline from glutamine and proline, plasma concentrations of citrulline (-26%) and arginine (-22%) decreased (P < 0.05), whereas those of alanine (+21%), ornithine (+17%), proline (+107%), taurine (+56%) and branched-chain amino acids (+21-40%) increased (P < 0.05). On the basis of dietary arginine intake and estimated arginine utilization, the endogenous synthesis of arginine in the 28-kg pig provided >/=50.2% of total daily arginine requirement. Taken together, our results suggest an important role for endogenous synthesis of arginine in regulating arginine homeostasis in postweaning growing pigs, as previously shown in neonatal pigs. 相似文献
74.
75.
PK Ramachandran Nair 《Journal of the science of food and agriculture》2007,87(9):1613-1619
The success of modern agricultural and forestry production can be largely attributed to monoculture systems using a few select species. In the drive for maximizing yield and profit, the age‐old tradition of using combined farming systems was essentially avoided and in some cases this has resulted in environmental problems such as land and water degradation and increased land clearing. During the last 30 years, however, the positive benefits of agroforestry to the producer and the environment have been increasingly recognized. Combining trees and crops in spatial or temporal arrangements has been shown to improve food and nutritional security and mitigate environmental degradation, offering a sustainable alternative to monoculture production. By providing supportive and complimentary roles with a flexible approach, agroforestry can offer specific social and environmental benefits across a range of landscapes and economies. More research and effort is needed to explore the full potential of agroforestry applications and to fuel awareness. As the plethora of benefits of agroforestry are realized, modern land‐use systems are evolving towards a more sustainable and holistic approach to land management. Copyright © 2007 Society of Chemical Industry 相似文献
76.
PK Woodard D Li EM Haacke PJ Dhawale S Kaushikkar B Barzilai AC Braverman PA Ludbrook AN Weiss JJ Brown SA Mirowitz TK Pilgram FR Gutierrez 《Canadian Metallurgical Quarterly》1998,170(4):883-888
OBJECTIVE: Our objective was to study the ability of three-dimensional MR angiography with retrospective respiratory gating to reveal stenoses in proximal coronary arteries on source and projection images. CONCLUSION: Proximal coronary artery stenoses can be identified using three-dimensional MR angiography with retrospective respiratory gating, both with projection images and on source images alone. Reasons for missed lesions included collateral vessels and retrograde flow distal to complete occlusion and volume averaging of vessels with adjacent structures. Causes of false-positive interpretations included small foci of decreased signal intensity distal to complete occlusion, partial volume effects on individual partitions, and regions of distal vessels leaving the imaging plane. 相似文献
77.
根据铝合金挤压模具的服役条件及其对材料的要求,分析现场模具的失效形式和验证所采取的提高寿命的措施。对3Cr2W8V钢和炉外真空精炼(VHWD)4Cr5MoV1Si钢进行了全面性能与生产对比试验证明:4Cr5MoV1Si钢用于制作铝合金挤压模是较理想的材料,能够显著提高模具的寿命。通过热磨损、热疲劳试验,比较两种材料的热磨损抗力和热疲劳的抗力;并观察其微观表面形貌。 相似文献
78.
PK Downes 《Canadian Metallurgical Quarterly》1998,185(6):270-274
79.
European Inland Fisheries Advisory Commission Working Party on Water Quality Criteria for European Freshwater Fish 《Water research》1973,7(7):1011-1022
In establishing water quality criteria for European inland fisheries, the effect of ammonia is an important factor to be considered. Sewage effluent, effluents from certain industries and from agriculture are common sources of ammonia in water.The harmful effects of ammonia on fish are related to the pH value and the temperature of the water due to the fact that only the un-ionized fraction of ammonia is poisonous. The un-ionized fraction increases with rising pH value, and with rising temperature.Fish differ slightly in their tolerance to ammonia depending on species. The difference in tolerance being more significant for short periods of exposure. The difference in tolerance is, however, not great enough to justify different criteria for different species.The lowest toxic concentration found for salmonids is 0·2 mg NH3 1−1 (un-ionized), but other adverse effects caused by prolonged exposure are only absent at concentrations lower than 0·025 mg NH3 1−1 (un-ionized). Concentrations of total ammonia which contain this amount of un-ionized ammonia vary from 19·6 mg 1−1 (pH 7·0, 5°C) to 0·12 mg 1−1 (pH 8·5, 30°C).The criterion should not be applied to temperatures below 5°C or to pH values above 8·5 when other factors have to be taken into consideration. 相似文献
80.
In 2012, the government of Bihar revived 34 non-functioning public tubewells using solar panels. The performance of 16 of these wells over 12 months was tracked and analyzed using data from tubewell operators and 240 farmers. Access to affordable irrigation from solar pumps led to a 9–10% increase in productivity of rice and wheat. Furthermore, in a severe drought, farmers could grow paddy in the entire area irrigated by solar pumps, when nearly 40% of other land was left fallow. Solar pumps can help increase crop productivity, reduce the cost of irrigation, and make agriculture more resilient to climate change. 相似文献