全文获取类型
收费全文 | 2533篇 |
免费 | 403篇 |
国内免费 | 552篇 |
专业分类
3488篇 |
出版年
2024年 | 19篇 |
2023年 | 118篇 |
2022年 | 94篇 |
2021年 | 136篇 |
2020年 | 182篇 |
2019年 | 186篇 |
2018年 | 163篇 |
2017年 | 150篇 |
2016年 | 176篇 |
2015年 | 155篇 |
2014年 | 138篇 |
2013年 | 164篇 |
2012年 | 127篇 |
2011年 | 139篇 |
2010年 | 95篇 |
2009年 | 125篇 |
2008年 | 137篇 |
2007年 | 134篇 |
2006年 | 122篇 |
2005年 | 82篇 |
2004年 | 88篇 |
2003年 | 93篇 |
2002年 | 84篇 |
2001年 | 55篇 |
2000年 | 61篇 |
1999年 | 54篇 |
1998年 | 59篇 |
1997年 | 53篇 |
1996年 | 52篇 |
1995年 | 40篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 30篇 |
1991年 | 19篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1958年 | 3篇 |
排序方式: 共有3488条查询结果,搜索用时 15 毫秒
1.
ABSTRACT The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship. 相似文献
2.
3.
4.
Distinct effects of climate warming on populations of silver fir (Abies alba) across Europe 下载免费PDF全文
5.
David J. Campbell 《Human ecology: an interdisciplinary journal》1984,12(1):35-64
From 1972 to 1976 rainfall in Kajiado District of Kenya was below normal. The capacity of the farming and herding systems to cope with the consequent reduction in production is discussed within a context of changing land-use patterns and altered resource availability. It is concluded that land-use planning to allocate the available land and water resources and to promote off-farm employment is required to reduce the vulnerability of the population to future drought conditions. 相似文献
6.
7.
The growth and the reproductive tactics of gudgeon, Gobio gobio (L.) were assessed in three contrasting streams of the Iberian Peninsula: the Rivers Moros and Ucero, tributaries of the R. Duero, and the R. MatarrańGa, a tributary of the R. Ebro. The R. Duero gudgeon have spread in the last 50 years while their presence in the lower tributaries of the R. Ebro followed the construction of reservoirs in the mid 1960s. The life histories of the Moros and MatarrańnGa gudgeon are very similar; rapid growth in spring, early reproduction (1 -year-old), high reproductive cost, short life-span and trend to semelparity. Both populations are strongly influenced by the severe summer droughts that result in (I) reduction in the condition coefficient, (2) reduction in the growth rate (particularly in the River MatarrańGa), (3) single spawning and (4) no gonad development in the summer. The gudgeon in the Ucero delay maturity, grow slower, are multi-spawners and have a longer life span. All the Duero populations come from the same genetic pool and they are actually connected through the populations living along this river basin, whereas the MatarrańGa population is not genetically linked, we hypothesize that the differences between these populations are environmentally induced. 相似文献
8.
9.
L. L. WALLACE 《The New phytologist》1987,105(4):619-632
10.
This paper examines the effects of the 1984 drought upon household wealth differences in a community of Ariaal pastoralists of northern Kenya. The database consists of 1985 post-drought livestock counts and informants' statements of species-specific drought loss, compared to 1976 livestock counts on the same 38 households. The analysis confirms the hypothesis that the drought resulted in increased household wealth inequalities. It is suggested that the combination of differential herd growth, differential participation in the cash market, and differential loss to the drought has contributed to a polarization within Ariaal of rich and poor, resulting in rural proletarianization and urban migration. 相似文献