全文获取类型
收费全文 | 8478篇 |
免费 | 62篇 |
国内免费 | 36篇 |
专业分类
安全科学 | 176篇 |
废物处理 | 411篇 |
环保管理 | 621篇 |
综合类 | 1648篇 |
基础理论 | 1926篇 |
环境理论 | 14篇 |
污染及防治 | 2686篇 |
评价与监测 | 613篇 |
社会与环境 | 457篇 |
灾害及防治 | 24篇 |
出版年
2023年 | 75篇 |
2022年 | 180篇 |
2021年 | 190篇 |
2020年 | 100篇 |
2019年 | 117篇 |
2018年 | 253篇 |
2017年 | 276篇 |
2016年 | 362篇 |
2015年 | 249篇 |
2014年 | 398篇 |
2013年 | 637篇 |
2012年 | 412篇 |
2011年 | 531篇 |
2010年 | 368篇 |
2009年 | 328篇 |
2008年 | 477篇 |
2007年 | 453篇 |
2006年 | 371篇 |
2005年 | 307篇 |
2004年 | 242篇 |
2003年 | 235篇 |
2002年 | 205篇 |
2001年 | 174篇 |
2000年 | 107篇 |
1999年 | 85篇 |
1998年 | 50篇 |
1997年 | 48篇 |
1996年 | 41篇 |
1995年 | 62篇 |
1994年 | 72篇 |
1993年 | 28篇 |
1992年 | 43篇 |
1991年 | 41篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1986年 | 38篇 |
1984年 | 26篇 |
1983年 | 26篇 |
1982年 | 31篇 |
1966年 | 40篇 |
1965年 | 42篇 |
1964年 | 26篇 |
1963年 | 32篇 |
1962年 | 26篇 |
1961年 | 36篇 |
1960年 | 29篇 |
1959年 | 26篇 |
1958年 | 26篇 |
1957年 | 35篇 |
1956年 | 29篇 |
排序方式: 共有8576条查询结果,搜索用时 187 毫秒
101.
102.
103.
104.
105.
In insect societies, the presence and condition of egg-layers can be assessed with pheromones. Exocrine secretions are expected to vary in time in order to give up-to-date information on an individuals reproductive physiology. In the queenless monogynous ant Streblognathus peetersi, we allowed a previously infertile high-ranking worker to accede to the alpha rank, thus triggering the onset of her oogenesis (15 replicates). We then studied her interactions with an established egg-layer from the same colony after different durations, ranging from 20 h to several days. Even though her eggs are only ready to be laid after 30 days, the new alpha was recognised within 1–2 days. Detection occurred at a distance of a few millimetres, suggesting the involvement of a pheromone with low volatility, such as cuticular hydrocarbons. When the new alpha had differentiated for >48 h, she was attacked by the established egg-layer. In all cases, low-ranking workers eventually immobilised one of the two alphas: the new alpha was the target if she had differentiated only recently, suggesting that police workers select the dominant worker with the less fertile odour. Using the behaviour of ants as our measure, we demonstrate that a dominants olfactory signal changes rapidly with a modification in her social status, and it occurs well before the onset of egg-laying. 相似文献
106.
107.
108.
109.
110.
Fetal aspartylglucosaminuria (AGU) was studied during the first trimester of pregnancy in six at-risk pregnancies using chorionic villus samples. The activity of aspartylglucosaminidase (AGA) was high in five cases, indicating an unaffected fetus. This was confirmed through delivery of healthy newborns with a normal pattern of urinary oligosaccharides. Low enzyme activity in an uncultured biopsy specimen and in cultured amniotic fluid cells in one case demonstrated that the fetus was affected. The pregnancy was terminated and the prenatal diagnosis was confirmed by showing reduced AGA activity in cultured fibroblasts of the fetus. 相似文献