全文获取类型
收费全文 | 2229篇 |
免费 | 2篇 |
专业分类
综合类 | 1篇 |
化学工业 | 18篇 |
金属工艺 | 1篇 |
机械仪表 | 4篇 |
轻工业 | 10篇 |
石油天然气 | 1篇 |
无线电 | 7篇 |
一般工业技术 | 11篇 |
冶金工业 | 2177篇 |
自动化技术 | 1篇 |
出版年
2015年 | 1篇 |
2014年 | 1篇 |
2011年 | 1篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 5篇 |
2004年 | 2篇 |
2003年 | 8篇 |
2002年 | 2篇 |
1999年 | 78篇 |
1998年 | 644篇 |
1997年 | 400篇 |
1996年 | 228篇 |
1995年 | 139篇 |
1994年 | 115篇 |
1993年 | 122篇 |
1992年 | 33篇 |
1991年 | 44篇 |
1990年 | 29篇 |
1989年 | 37篇 |
1988年 | 29篇 |
1987年 | 31篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 2篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 22篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 62篇 |
1976年 | 110篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有2231条查询结果,搜索用时 31 毫秒
101.
102.
103.
Effects of waterlogging at different stages of development on the growth and yield of winter wheat 总被引:1,自引:0,他引:1
Robert Q. Cannell Robert K. Belford Kenneth Gales Colin W. Dennis Robert D. Prew 《Journal of the science of food and agriculture》1980,31(2):117-132
The response of winter wheat to waterlogging at different stages of growth outdoors was studied for 3 years using lysimeters containing undisturbed monoliths of sandy loam and clay soils. The treatments were selected as the most extreme likely to occur in field conditions in Britain, i.e. waterlogging to the soil surface for up to 16 days in October, 42 days in January and February and 6 days in May. Waterlogging in midwinter was common to all experiments. Yield losses from mid-winter waterlogging ranged from 15% when yields were heavy (10 t ha?1), to nil when yields were light (3-4 t ha?1) after the plants had been affected by frost damage in late winter and by take-all. Winter wheat was most sensitive to waterlogging after germination but before emergence. At this stage, 16 days waterlogging killed all seedlings and 6 days waterlogging depressed plant populations to 12% (clay) and 38% (sandy loam) of the control. However, there was vigorous compensatory growth in the remainder of the growing season and yield was only depressed to about 82% of the control. When the crop was waterlogged at any stage after emergence plant populations were not affected; however, winter waterlogging treatments usually depressed shoot numbers and, to a lesser extent, ear numbers at harvest. Shoot survival under waterlogged conditions seemed related to nitrogen availability in the soil. The amount of ‘take-all’ (Gaeumannomyces graminis var. tritici) was increased by waterlogging. 相似文献
104.
105.
Robert J. Thomson Robert K. Belford Robert Q. Cannell 《Journal of the science of food and agriculture》1983,34(11):1159-1162
Post-germination but pre-emergence waterlogging of winter wheat for 3 days or more, delayed emergence and decreased the final number of plants in two experiments on sandy loam and clay soils in outdoor conditions. Coating seeds with calcium peroxide improved emergence to a small extent, but would appear to offer only a small benefit to establishment of wheat already treated with insecticide/fungicide dressings and sown under normal conditions in the field. 相似文献
106.
Phasic changes in cardiac reactivity to innocuous stimuli, presented in a sensory disparity paradigm, were used to evaluate habituation and learning processes in five decerebrate subjects. Three subjects showed systematic changes over trials in the pattern of cardiac response to simple auditory or visual stimuli, indicative of habituation. In addition, tests for associative learning were given after repeated presentations of two paired stimuli. The appearance of a marked cardiac orienting response, to the unpredictable omission of the second stimulus, documented the development of a conditioned association in these same three subjects. One additional subject failed to show a consistent pattern of response to the stimuli, and another demonstrated a consistent response which was not subject to habituation. Overall, these findings support the view that learning processes are not solely the product of the cerebral hemispheres, but reflect general integrative features of the human neuraxis. 相似文献
107.
108.
109.
110.
VN Ngo H Korner MD Gunn KN Schmidt DS Riminton MD Cooper JL Browning JD Sedgwick JG Cyster 《Canadian Metallurgical Quarterly》1999,189(2):403-412
Mice deficient in the cytokines tumor necrosis factor (TNF) or lymphotoxin (LT) alpha/beta lack polarized B cell follicles in the spleen. Deficiency in CXC chemokine receptor 5 (CXCR5), a receptor for B lymphocyte chemoattractant (BLC), also causes loss of splenic follicles. Here we report that BLC expression by follicular stromal cells is defective in TNF-, TNF receptor 1 (TNFR1)-, LTalpha- and LTbeta-deficient mice. Treatment of adult mice with antagonists of LTalpha1beta2 also leads to decreased BLC expression. These findings indicate that LTalpha1beta2 and TNF have a role upstream of BLC/CXCR5 in the process of follicle formation. In addition to disrupted follicles, LT-deficient animals have disorganized T zones. Expression of the T cell attractant, secondary lymphoid tissue chemokine (SLC), by T zone stromal cells is found to be markedly depressed in LTalpha-, and LTbeta-deficient mice. Expression of the SLC-related chemokine, Epstein Barr virus-induced molecule 1 ligand chemokine (ELC), is also reduced. Exploring the basis for the reduced SLC expression led to identification of further disruptions in T zone stromal cells. Together these findings indicate that LTalpha1beta2 and TNF are required for the development and function of B and T zone stromal cells that make chemokines necessary for lymphocyte compartmentalization in the spleen. 相似文献