全文获取类型
收费全文 | 17118篇 |
免费 | 166篇 |
国内免费 | 121篇 |
专业分类
安全科学 | 466篇 |
废物处理 | 710篇 |
环保管理 | 2115篇 |
综合类 | 2916篇 |
基础理论 | 4356篇 |
环境理论 | 11篇 |
污染及防治 | 4658篇 |
评价与监测 | 1155篇 |
社会与环境 | 911篇 |
灾害及防治 | 107篇 |
出版年
2023年 | 111篇 |
2022年 | 234篇 |
2021年 | 247篇 |
2020年 | 152篇 |
2019年 | 175篇 |
2018年 | 349篇 |
2017年 | 346篇 |
2016年 | 488篇 |
2015年 | 367篇 |
2014年 | 533篇 |
2013年 | 1291篇 |
2012年 | 658篇 |
2011年 | 858篇 |
2010年 | 633篇 |
2009年 | 679篇 |
2008年 | 856篇 |
2007年 | 816篇 |
2006年 | 701篇 |
2005年 | 630篇 |
2004年 | 533篇 |
2003年 | 522篇 |
2002年 | 476篇 |
2001年 | 547篇 |
2000年 | 386篇 |
1999年 | 254篇 |
1998年 | 162篇 |
1997年 | 180篇 |
1996年 | 184篇 |
1995年 | 219篇 |
1994年 | 224篇 |
1993年 | 168篇 |
1992年 | 154篇 |
1991年 | 189篇 |
1990年 | 183篇 |
1989年 | 171篇 |
1988年 | 128篇 |
1987年 | 123篇 |
1986年 | 141篇 |
1985年 | 104篇 |
1984年 | 121篇 |
1983年 | 121篇 |
1982年 | 133篇 |
1981年 | 117篇 |
1980年 | 109篇 |
1979年 | 121篇 |
1978年 | 79篇 |
1977年 | 80篇 |
1975年 | 83篇 |
1973年 | 76篇 |
1972年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
231.
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
232.
R. G. Tiessen A. M. W. van Elsacker-Niele Chr. Vermeij-Keers D. Oepkes J. van Roosmalen M. C. B. Gorsira 《黑龙江环境通报》1994,14(3):173-176
A fetus with multiple structural defects was seen at prenatal ultrasound examination. After termination of the pregnancy a bilateral cleft lip, alveolus, and palate; micrognathia; and webbed joints were seen. Fetal tissues showed indications of infection, intranuclear inclusion bodies, chronic stress, haemolysis, arterial wall damage, and profuse haemorrhage. Parvovirus B19 DNA was detected in fetal tissues by dot hybridization after polymerase chain reaction. The possibility of parvovirus B19 infection leading to congenital malformations is discussed. 相似文献
233.
We present a remarkable chain of events in which percutaneous umbilical cord sampling was performed in an attempt to clarify a situation of possible fetal sex chromosome mosaicism in an amniotic fluid culture and led to the discovery that the mother herself had a 45,X/46,XX/ 47.XXX chromosome constitution. This may have simply represented the chance concurrence of pseudo-mosaicism in the amniotic fluid culture of a woman with an abnormal sex chromosome constitution, but it is also possible that the 45,X colony was maternal in origin. Although clearly a most unusual circumstance, the possibility should be kept in mind when termination of a pregnancy is being considered because of apparent mosaicism in a prenatal diagnostic study. 相似文献
234.
235.
236.
Alan B. Bolten Peter Feinsinger Herbert G. Baker Irene Baker 《Die Naturwissenschaften》1990,77(9):452-452
237.
Val A. Catanzarite MD Ph.D. David B. Schrimmer Cynthia Maida Art Mendoza 《黑龙江环境通报》1995,15(3):229-235
The sinusoidal fetal heart rate pattern has been described in association with severe fetal anaemia, with fetal hypoxaemia, and with the administration of parenteral narcotics. Here, we report a case of decreased fetal movement in which a sinusoidal tracing was recorded. The sonographic diagnosis of a massive fetal intracranial haemorrhage was made. A non-interventive approach was taken and the fetus died soon after in utero. We review 28 previous cases in which the prenatal sonographic diagnosis of fetal intracranial haemorrhage was made, including the underlying maternal and fetal factors and neonatal outcomes. We propose that the sinusoidal tracing in this case was due to the intracranial bleed and suggest that fetal intracranial haemorrhage be considered in the sonographic evaluation of the fetus with a sinusoidal pattern. 相似文献
238.
B. Sikkema-Raddatz R. H. Sijmons M. B. Tan-Sindhunata A. Y. Van Der Veen R. Brunsting B. De Vries J. R. Beekhuis D. J. Bekedam B. Van Aken B. De Jong 《黑龙江环境通报》1995,15(5):467-473
We report two cases of apparently balanced complex de novo chromosomal rearrangements (BCCR) detected prenatally at 17 weeks and 10 weeks of gestation, respectively. Chromosomes were studied using GTG-banding and fluorescent in situ hybridization (FISH). In one case four chromosomes and in the other case three chromosomes were involved in the rearrangements. One of the pregnancies was terminated and no external or internal abnormalities were detected at autopsy. The other pregnancy continued to term. Level III ultrasound examination showed no abnormalities. The child is now 3 years old and has neither congenital anomalies nor evidence of delayed psychomotor development. 相似文献
239.
240.