全文获取类型
收费全文 | 2246篇 |
免费 | 0篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 9篇 |
金属工艺 | 1篇 |
轻工业 | 7篇 |
水利工程 | 1篇 |
无线电 | 3篇 |
一般工业技术 | 8篇 |
冶金工业 | 2211篇 |
原子能技术 | 1篇 |
自动化技术 | 3篇 |
出版年
2021年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2016年 | 1篇 |
2013年 | 3篇 |
2012年 | 4篇 |
2010年 | 2篇 |
2007年 | 1篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 74篇 |
1998年 | 709篇 |
1997年 | 434篇 |
1996年 | 249篇 |
1995年 | 131篇 |
1994年 | 98篇 |
1993年 | 125篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 23篇 |
1988年 | 33篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 16篇 |
1978年 | 3篇 |
1977年 | 61篇 |
1976年 | 144篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1968年 | 1篇 |
1964年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有2246条查询结果,搜索用时 0 毫秒
71.
JR Lave CR Keane CJ Lin EM Ricci G Amersbach CP LaVallee 《Canadian Metallurgical Quarterly》1998,279(22):1820-1825
CONTEXT: Although there is considerable interest in decreasing the number of US children who do not have health insurance, there is little information on the effect that health insurance has on children and their families. OBJECTIVE: To determine the impact of children's health insurance programs on access to health care and on other aspects of the lives of the children and their families. DESIGN: A before-after design with a control group. The families of newly enrolled children were interviewed by telephone using an identical survey instrument at baseline, at 6 months, and at 12 months after enrollment into the program. A second group of families of newly enrolled children were interviewed 12 months after the initial interviews to form a comparison sample. SETTING: The 29 counties of western Pennsylvania, an area with a population of 4.1 million people. SUBJECTS: A total of 887 families of newly enrolled children were randomly selected to be interviewed; 88.3% agreed to participate. Of these, 659 (84%) responded to all 3 interviews. The study population consists of 1031 newly enrolled children. The children were further classified into those who were continuously enrolled in the programs. The 330 comparison families had 460 newly enrolled children. MAIN OUTCOME MEASURES: The following access measures were examined: whether the child had a usual source of medical or dental care; the number of physician visits, emergency department visits, and dentist visits; and whether the child had experienced unmet need, delayed care, or both for 6 types of care. Other indicators were restrictions on the child's usual activities and the impact of being insured or uninsured on the families. RESULTS: Access to health care services after enrollment in the program improved: at 12 months after enrollment, 99% of the children had a regular source of medical care, and 85% had a regular dentist, up from 89% and 60%, respectively, at baseline. The proportion of children reporting any unmet need or delayed care in the past 6 months decreased from 57% at baseline to 16% at 12 months. The proportion of children seeing a physician increased from 59% to 64%, while the proportion visiting an emergency department decreased from 22% to 17%. Since the comparison children were similar to the newly enrolled children at enrollment into the insurance programs, these findings can be attributed to the program. Restrictions on childhood activities because of lack of health insurance were eliminated. Parents reported that having health insurance reduced the amount of family stress, enabled children to get the care they needed, and eased family burdens. CONCLUSIONS: Extending health insurance to uninsured children had a major positive impact on children and their families. In western Pennsylvania, health insurance did not lead to excessive utilization but to more appropriate utilization. 相似文献
72.
73.
The application of alumino silicate alkali ion sources to the study of ion desorption of surface gas
Investigations are described which illustrate the compatibility of alumino silicate alkali ion sources with an UHV (~10?11 torr) vacuum environment. The application of the sources to the determination of ion desorption efficiency of surface gas is demonstrated, as well as their use as a basis for a technique of ion stimulated surface gas analysis. 相似文献
74.
75.
Results of follow-up examinations of 132 ears with serous or mucous middle ear effusions indicate that this disease is common in childhood and is also found in adults. In childhood adenoid growth as well as repeated catarrhal infection of the paranasal sinuses and the weakness of the levator palati play an important role in the development of middle ear effusions and deafness. With the aid of the operation microscope we were able to recognize this characteristic disease through the tympanic membrane. We perform regularly adenoidectomy together with paracentesis in this condition. In cases which had undergon several adenoidectomies we limit our treatment in the first instance to paracentesis. If cure is not so achieved we insert an inert tube into the tympanic membrane after the paracentesis. In persistent and difficult cases of glue ear radiation of the eustachion tube and antrotomy may be necessary. 相似文献
76.
EM Burns 《Canadian Metallurgical Quarterly》1976,57(12):48-54, 80
77.
Several viral isolates from ticks (Ornithodoros coriaceus) and from the blood of cattle which aborted after exposure to these ticks were found to be identical by reciprocal cross serum-neutralization tests. Characterization studies indicate that the virus is a member of the Togaviridae family, although specific identification is still incomplete. Whether its natural host is the tick or bovine animals is also unknown. Pregnant cows inoculated with the agent by all conventional parenteral routes, including intrafetal, delivered healthy calves at term. It was concluded, therefore, that it was not a bovine pathogen and that the abortions which occurred after tick-exposure were due to a 2nd agent in O coriaceus ticks which also harbor the virus. While several ciruses believed to be tick-borne have been isolated from cattle in various parts of the world, it is believed that the present report describes the first isolation in the Western Hemisphere for a viral agent from Argasid ticks which has been demonstrated to replicate in cattle. 相似文献
78.
Very low birth weight children at school age: comparison of neonatal management methods 总被引:1,自引:0,他引:1
ES Steiner EM Sanders EC Phillips CR Maddock 《Canadian Metallurgical Quarterly》1980,281(6250):1237-1240
The outcome of 293 infants born to a geographically defined community and weighing 501-1500 g was investigated. Medical intervention in the newborn period had been avoided. Morbidity was assessed at school age. Of the infants, 236 had been live born in the labour ward of this hospital; of these, 117 (49.6%) died in the neonatal period, one (0.4%) died in the first year, four (1.7%) were untraced, 13 (5.5%) had major handicap, 29 (12.3%) had minor handicap, and 72 (30.5%) were considered to be normal. In terms of survival, handicap, and intellectual with that of infants born over the same period (1963-71) in areas where intensive methods of perinatal care were used. These results imply that postnatal survival and potential of infants of very low birth weight are by no means prejudiced when only experienced nursing care is available. 相似文献
79.
P Puigdoménech P Martínez J Palau EM Bradbury C Crane-Robinson 《Canadian Metallurgical Quarterly》1976,65(2):357-363
Proton magnetic resonance and other measurements have been carried out in order to study the behaviour of the lysine-rich histones phi 1 in the sperm chromatin of certain marine invertebrates. Well defined particles (12 S) have been obtained from this chromatin by nuclease treatment. Chromatin solubility as a function of ionic strength shows a relaxation at salt concentrations higher than in the case of calf thymus nucleoprotein. Nuclear magnetic resonance (NMR) studies show that the release of histone from DNA occurs both in chromatin and in the reconstituted complexes at practically the same ionic strength as solubility relaxation. The higher the arginine content of a given phi 1, the higher the ionic strength at which both effects take place. The NMR results demonstrate that arginine residues are bound more strongly than lysine residues. The data overall show that phi 1 histones play a role in the contraction mechanism of sperm chromatin similar to that of H 1 histone in calf thymus chromatin. The highly contracted state of sperm chromatin is directly related to the increased arginine content of the phi 1 histone. 相似文献
80.