全文获取类型
收费全文 | 3222篇 |
免费 | 1篇 |
专业分类
化学工业 | 16篇 |
金属工艺 | 4篇 |
建筑科学 | 3篇 |
矿业工程 | 2篇 |
能源动力 | 2篇 |
轻工业 | 6篇 |
无线电 | 3篇 |
一般工业技术 | 6篇 |
冶金工业 | 3172篇 |
原子能技术 | 1篇 |
自动化技术 | 8篇 |
出版年
2020年 | 2篇 |
2018年 | 1篇 |
2015年 | 1篇 |
2013年 | 3篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2008年 | 3篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 4篇 |
1999年 | 70篇 |
1998年 | 923篇 |
1997年 | 539篇 |
1996年 | 392篇 |
1995年 | 237篇 |
1994年 | 162篇 |
1993年 | 184篇 |
1992年 | 20篇 |
1991年 | 33篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1983年 | 5篇 |
1982年 | 19篇 |
1981年 | 25篇 |
1980年 | 33篇 |
1979年 | 3篇 |
1978年 | 10篇 |
1977年 | 131篇 |
1976年 | 258篇 |
1975年 | 9篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3223条查询结果,搜索用时 0 毫秒
991.
992.
Jejunal absorption of glucose, electrolytes, and vitamin A was investigated in rats. A Tyrode solution containing glucose, sodium, and potassium in concentrations two and four times higher than usual was infused through the jejunal loops of jaundiced and control rats during 40 min. The glucose values in the influx and effluent were not different during the experiment time. However, the concentrations of sodium and potassium of the effluent decreased with concentrations twice normal. The osmotic pressure of the effluent was directly related to the electrolytic concentration. When the perfusate fluid was four times higher, the differences between sham and jaundiced groups remained unchanged. The osmotic pressure means of the jaundiced group decreased during the experimental time. The absorption of vitamin A increased during the 40-min experiment time in the control rats. On the other hand, vitamin A concentration in the perfused lumen of the jaundiced group did not change over the time. These data indicate that obstructive jaundice has little influence on glucose and electrolytes absorption, while vitamin A is impaired by this condition. 相似文献
993.
The study of the central regulation of the circulation in the past has been directed primarily at observing reflex responses to stimulation of peripheral receptors and at producing changes in cardiovascular parameters during electrical stimulation of central sites. These studies have demonstrated that the nervous system can regulate the circulation to different vascular beds with a high degree of specificity and that it has the ability to provide a range of coordinated responses which are appropriate to the metabolic needs of a particular behavioural pattern. In addition, it has become firmly established that the nervous system is capable of coupling cardiovascular changes with other autonomic and somatic activities to produce an integrated response. In the last decade it has become apparent that although the mode of operation of central cardiovascular regulation has been described in general terms, very little is known about the accurate anatomical localization of neuronal circuits and pathways and of impulse traffic corresponding to the changes in cardiovascular parameters that have been observed. This essay reviews recent information on discrete neuronal circuits and pathways and their mode of operation in electrophysiological terms. One of the most serious difficulties in this endeavour is the problem of demonstrating specificity of pathways and circuits because patterns of firing of afferent and efferent peripheral nerves can be usually identified, but the demonstration of specificity of central structures is a conceptual and technical challenge to the most skilled investigator. Several studies have been made in the last decade in an attempt to trace anatomically and functionally pathways involved in central cardiovascular regulation. Progress has been made especially with regard to the precise sites of termination of cardiovascular afferent fibres and the pattern of discharge of efferent cardiovascular neurons; some work has also been done to trace discrete pathways between the hypothalamus and the medulla and the medulla and the spinal cord. However, in view of the difficulties of establishing the specificity of cardiovascular pathways, progress will depend on the acquisition of a wiring diagram of simple cardiovascular reflex arcs before attempts are made to study the functional interactions of regions in the brain that have been traditionally associated with central regulation of the circulation. Future experiments should concentrate less on the demonstration of cardiovascular responses to stimulation or lesions in the central nervous system and more on the connections of discrete regions.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
994.
SV Slonitski? AA Maevski? VB Mantulenko EV Frisman 《Canadian Metallurgical Quarterly》1980,14(4):754-758
The influence of acetamide (AA) on the native DNA molecule conformation has been studied by methods of flow birefringence and viscometry. On one hand, it was shown that hydrodynamical and optical behaviour of the macromolecule at extremely low additions of AA is qualitatively the same as in the presence of nonelectrolytes which stabilize the water structure. On the other hand, the influence of intermediate and large AA concentrations on the native DNA molecule conformation is qualitatively the same as of corresponding urea concentrations, which is known to be a structure-breaker. The influence of AA on the thermostability of the native DNA molecule as well as on the stacking-association constant of adenosine has been studied by a spectrophotometric method. The obtained data confirm the hypothesis of the importance of ion-dipole interactions between nonelectrolytes and the phosphate groups of the DNA molecule. 相似文献
995.
996.
EK Balashova DL Pevzner VI Rozengart OE Sherstobitov AA Abduvarkhabov 《Canadian Metallurgical Quarterly》1976,48(4):460-464
Hydrophobity (coefficient in distribution in the hexane water system) and the content of cholinesterase organophosphorous inhibitors (OPI) of the structure Ro (CH3) P (O) SC2H4 SC2H5 were studied in the rat brain. When the O-alkyl radical is increased hydrophobity rises and the relative content of free OPI in the brain extracted by chloroform decreases. With an increase in R from the ethyl to butyl one the ability to the additional inhibition of the brain own cholinesterase lowers due to incubation of homogenate at 37 degrees C, that evidences for an essential drop in the studied series of the free OPI fraction relative to the free OPI extracted by chloroform. 相似文献
997.
998.
999.
1000.