全文获取类型
收费全文 | 7924篇 |
免费 | 102篇 |
国内免费 | 1篇 |
学科分类
工业技术 | 8027篇 |
出版年
2021年 | 47篇 |
2019年 | 45篇 |
2018年 | 50篇 |
2017年 | 57篇 |
2016年 | 73篇 |
2015年 | 51篇 |
2014年 | 82篇 |
2013年 | 183篇 |
2012年 | 164篇 |
2011年 | 226篇 |
2010年 | 194篇 |
2009年 | 206篇 |
2008年 | 227篇 |
2007年 | 232篇 |
2006年 | 199篇 |
2005年 | 202篇 |
2004年 | 185篇 |
2003年 | 162篇 |
2002年 | 142篇 |
2001年 | 148篇 |
2000年 | 163篇 |
1999年 | 206篇 |
1998年 | 741篇 |
1997年 | 458篇 |
1996年 | 374篇 |
1995年 | 232篇 |
1994年 | 215篇 |
1993年 | 265篇 |
1992年 | 148篇 |
1991年 | 145篇 |
1990年 | 140篇 |
1989年 | 158篇 |
1988年 | 143篇 |
1987年 | 116篇 |
1986年 | 136篇 |
1985年 | 121篇 |
1984年 | 87篇 |
1983年 | 89篇 |
1982年 | 79篇 |
1981年 | 65篇 |
1980年 | 67篇 |
1979年 | 78篇 |
1978年 | 79篇 |
1977年 | 110篇 |
1976年 | 177篇 |
1975年 | 58篇 |
1974年 | 56篇 |
1973年 | 53篇 |
1972年 | 37篇 |
1971年 | 36篇 |
排序方式: 共有8027条查询结果,搜索用时 15 毫秒
61.
In pre-industrial times, honey was the main source of concentrated sweetness in the diets of many peoples. There are no precise figures for per capita consumption during most periods in history because honey was part of either a hunter-gatherer or subsistence economy. Until now, historians and food writers have proposed that it was a scarce commodity available only to a wealthy few. We do know, however, that in a cash economy honey was sold in large units (gallons and even barrels) and it was present in such abundance that mead, made from honey, was a common alcoholic drink. A reappraisal of the evidence from the Stone Age, Antiquity, the Middle Ages and early Modern times suggests that ordinary people ate much larger quantities of honey than has previously been acknowledged. Intakes at various times during history may well have rivalled our current consumption of refined sugar. There are implications therefore for the role of sugar in modern diets. Refined sugar may not have displaced more nutrient-rich items from our present-day diets but only the nutritionally comparable food, honey. 相似文献
62.
The present study was designed to investigate the type and extent of degeneration occurring in the human central auditory system subsequent to profound hearing loss. The authors have examined the size of one population of neurons in the ventral cochlear nucleus in seven subjects with profound hearing loss (audiometric responses poorer than 90-100 dB HL). Six normal subjects, ages 35-78, were used as controls. Cell size in the hearing-impaired subjects ranged from normal to reduced by more than 50 percent. Two factors appear to contribute to the variability in cell size reduction. The correlation coefficient (Spearman rs) of cell size with duration of profound deafness was -0.48, indicating a moderate tendency for neurons to become smaller with longer periods of deafness. The correlation coefficient of cell size with number of surviving cochlear ganglion cells was 0.73, indicating a stronger tendency for neurons to be larger with greater eighth nerve innervation of the cochlear nucleus. Two cases of Scheibe degeneration showed the most severe degenerative change in the central auditory system. 相似文献
63.
There is a general impression in the literature that women are more accurate reporters of familial psychiatric history. In this regard, this study presents data from a large cohort of young men (n = 427) and women (n = 607) who in answering a questionnaire self-reported alcohol abuse symptoms for various biological relatives. No significant gender differences emerged for any of the family history comparisons including reports for father, mother, either parent, any first- or second-degree relatives, or men or women relatives. The findings are discussed in the context of the existing literature. 相似文献
64.
65.
66.
67.
This article estimates workplace injury costs in the U.S. These costs have been studied in less detail than most injury costs. Our methods, which mostly use regularly published data, produce order-of-magnitude estimates. Overall, workplace injuries cost the U.S. an estimated $140 billion annually. This estimate includes $17 billion in medical and emergency services, $60 billion in lost productivity, $5 billion in insurance costs, and $62 billion in lost quality of life. One sixth of the societal costs result from the 3% of workplace injuries in motor vehicle crashes. Motor vehicle costs per injury are almost 6 times the workplace injury average. 相似文献
68.
69.
70.
Consideration is given to the control problem in a linear stochastic differential system where constant noise intensities in equations of state and observation are prescribed only accurate within the membership of some known sets. For control optimization, an integral root-mean-square performance criterion is used. The problem is solved by the transition to a dual one, which makes it possible to prove the existence of a saddle point of the criterion and obtain an explicit expression for the minimax control operator as functions of the solution to the dual problem. To solve the latter, an iteration algorithm is proposed; the convergence of the algorithm is proved and investigated by a model example. 相似文献