全文获取类型
收费全文 | 7319篇 |
免费 | 124篇 |
国内免费 | 14篇 |
学科分类
工业技术 | 7457篇 |
出版年
2022年 | 37篇 |
2021年 | 43篇 |
2019年 | 40篇 |
2018年 | 77篇 |
2017年 | 55篇 |
2016年 | 67篇 |
2015年 | 72篇 |
2014年 | 97篇 |
2013年 | 258篇 |
2012年 | 159篇 |
2011年 | 195篇 |
2010年 | 142篇 |
2009年 | 157篇 |
2008年 | 199篇 |
2007年 | 201篇 |
2006年 | 199篇 |
2005年 | 193篇 |
2004年 | 175篇 |
2003年 | 155篇 |
2002年 | 146篇 |
2001年 | 145篇 |
2000年 | 150篇 |
1999年 | 167篇 |
1998年 | 753篇 |
1997年 | 416篇 |
1996年 | 325篇 |
1995年 | 208篇 |
1994年 | 210篇 |
1993年 | 194篇 |
1992年 | 129篇 |
1991年 | 111篇 |
1990年 | 104篇 |
1989年 | 108篇 |
1988年 | 111篇 |
1987年 | 108篇 |
1986年 | 109篇 |
1985年 | 122篇 |
1984年 | 105篇 |
1983年 | 79篇 |
1982年 | 87篇 |
1981年 | 85篇 |
1980年 | 75篇 |
1979年 | 71篇 |
1978年 | 70篇 |
1977年 | 98篇 |
1976年 | 153篇 |
1975年 | 40篇 |
1974年 | 42篇 |
1973年 | 51篇 |
1972年 | 43篇 |
排序方式: 共有7457条查询结果,搜索用时 10 毫秒
41.
42.
43.
44.
45.
46.
Two trials were conducted in which a total of twenty-eight Friesian bulls (12 months old) were slaughtered 0, 1, 2, 4, 7, 9 or 10 days after they had been mixed with unfamiliar animals overnight. The resulting behavioural interactions and associated physical activity led to large rises in plasma creatine phosphokinase (CPK) activity and free fatty acid (FFA) concentration and a decrease in plasma lactate. In the second trial the relative number of interactions engaged in by each animal was estimated. Bulls which exhibited the most interactions had the highest levels of plasma CPK and FFA after mixing. Liver and muscle glycogen were depleted by mixing. Animals killed on days 0 and 1 after mixing had low concentrations of liver glycogen compared with animals allowed longer to recover. Concentrations of glycogen in the M. longissimus dorsi (LD) had recovered by day 4 and in the M. psoas by day 2. Muscle glycogen concentrations were reflected in the ultimate pH (pHu) of the meat. All animals killed immediately after mixing produced carcasses with pHu>6. in the LD. By the second day of recovery muscle glycogen stores had been repleted sufficiently so that all animals had muscles with pHu<6. However, the LD from these animals was still very slightly darker than those killed after 7 or more days of recovery although this was probably not commercially significant. It was concluded that, if young bulls from separate rearing groups are mixed before slaughter, either on the farm or during lairage, then they require resting with food for at least 48 h before being killed to ensure that no carcasses are produced with high pHu in the musculature. 相似文献
47.
48.
Information Systems Security (ISS) has constantly been ranked as a key concern for Information Systems (IS) managers. Research in the field has largely assumed rational choice (functional) approaches to managing ISS. Such approaches do not give due recognition to the role of improvisation in ISS work. Empirical evidence in organisations suggests that in the context of dynamic, volatile and uncertain environments practitioners are both rational and adaptive (a manifestation of improvisation). In this paper, we conceptualise and demonstrate the manifestation of improvisation in ISS. In order to develop a better understanding of improvisation in ISS activities, hermeneutical and exegetical techniques were employed. Empirical data were collected through in-depth interviews in a single case study. The data obtained were analysed and interpreted hermeneutically. Generally it was found that improvisation is manifested in ISS activities. Implications of these and other findings for the scholarly community and for practical use are discussed. 相似文献
49.
50.
H. R. Brown 《Journal of Materials Science》1982,17(2):469-476
A model is proposed for mixed-mode crack propagation in materials which show shear lips on the fracture surface. The model is shown to predict the existance of a brittle-ductile transition as the specimen thickness is decreased. The predictions of the model are compared with published experimental data on a number of polymers including polycarbonate, and good agreement is found. 相似文献