全文获取类型
收费全文 | 1930篇 |
免费 | 267篇 |
出版年
2021年 | 28篇 |
2020年 | 30篇 |
2019年 | 30篇 |
2018年 | 27篇 |
2017年 | 27篇 |
2016年 | 30篇 |
2015年 | 61篇 |
2014年 | 64篇 |
2013年 | 85篇 |
2012年 | 91篇 |
2011年 | 90篇 |
2010年 | 63篇 |
2009年 | 46篇 |
2008年 | 79篇 |
2007年 | 87篇 |
2006年 | 57篇 |
2005年 | 61篇 |
2004年 | 57篇 |
2003年 | 53篇 |
2002年 | 59篇 |
2001年 | 60篇 |
2000年 | 58篇 |
1999年 | 59篇 |
1998年 | 25篇 |
1997年 | 25篇 |
1996年 | 19篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 39篇 |
1991年 | 48篇 |
1990年 | 36篇 |
1989年 | 46篇 |
1988年 | 32篇 |
1987年 | 41篇 |
1986年 | 35篇 |
1985年 | 40篇 |
1984年 | 41篇 |
1983年 | 26篇 |
1982年 | 30篇 |
1981年 | 16篇 |
1980年 | 26篇 |
1979年 | 26篇 |
1978年 | 14篇 |
1977年 | 22篇 |
1976年 | 12篇 |
1975年 | 16篇 |
1974年 | 28篇 |
1973年 | 26篇 |
1972年 | 13篇 |
排序方式: 共有2197条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Pines responded to inoculation with Bursaphelenchus xylophilus by changes in reducing and nonreducing carbohydrate concentrations dependent on the pine species and the pathotype of B. xylophilus with which the trees were inoculated. Carbohydrate concentrations, in compatible pine-nematode pathotype combinations, decreased initially after inoculation and then increased slightly before decreasing to approximately 10% of the control levels as the seedlings wilted. In compatible nematode pathotype-pine species combinations, carbohydrate concentrations decreased and then increased as the nematode population densities declined. 相似文献
5.
Sucrose phosphorylase is an interesting biocatalyst that can glycosylate a variety of small molecules using sucrose as a cheap but efficient donor substrate. The low thermostability of the enzyme, however, limits its industrial applications, as these are preferably performed at 60°C to avoid microbial contamination. Cross-linked enzyme aggregates (CLEAs) of the sucrose phosphorylase from Bifidobacterium adolescentis were found to have a temperature optimum that is 17°C higher than that of the soluble enzyme. Furthermore, the immobilized enzyme displays an exceptional thermostability, retaining all of its activity after 1 week incubation at 60°C. Recycling of the biocatalyst allows its use in at least ten consecutive reactions, which should dramatically increase the commercial potential of its glycosylating activity. 相似文献
6.
Three different pennation angle assumptions are compared to experimental data from Huijing and Woittiez (Neth. J. Zool. 34, 21-32, 1984) that relate fibre length to angle of pennation changes. The assumptions tested are: (1) neglecting pennation; (2) assuming a fixed pennation; and (3) assuming a constant muscle volume and thickness resulting in pennation angle being dependent on fibre length. Each assumption is compared by transforming fibre force/length and force/velocity characteristics to muscle properties. In general, the fixed pennation assumption provides the worst estimate of muscle force output with a peak error of 0.31 Fo during isometric contractions at small muscle lengths. A better estimate of muscle force output was provided by neglecting pennation entirely. The assumption that the pennation angle changed with fibre length maintained an error of less than 0.05 Fo for most lengths and velocities tested and provided the best estimate of muscle force output. 相似文献
7.
Jan G. de Winter 《BMJ (Clinical research ed.)》1953,2(4836):604-605
8.
9.
10.
Alfred Buschinger Werner Ehrhardt Ursula Winter 《Ethology : formerly Zeitschrift fur Tierpsychologie》1980,53(3):245-264
Slavemaking occurs in 8 genera or ants belonging to 2 subfamilies. Their raiding behaviour is described and compared. The basic organisation of a raid comprises scouting, recruitment, fight, and brood transportation. These elements can ordinarily be derived from the behaviour of the independent host species. Certain trends in the evolution of recruitment and fighting behaviour are discussed. “Intraspecific slavery”, which has been described by various authors, probably belongs to territorial behaviour. We doubt whether it represents an evolutionary precursor of true, interspecific slavery. 相似文献