全文获取类型
收费全文 | 7896篇 |
免费 | 65篇 |
国内免费 | 57篇 |
专业分类
安全科学 | 192篇 |
废物处理 | 382篇 |
环保管理 | 630篇 |
综合类 | 1310篇 |
基础理论 | 1855篇 |
环境理论 | 6篇 |
污染及防治 | 2479篇 |
评价与监测 | 659篇 |
社会与环境 | 465篇 |
灾害及防治 | 40篇 |
出版年
2023年 | 77篇 |
2022年 | 207篇 |
2021年 | 240篇 |
2020年 | 115篇 |
2019年 | 119篇 |
2018年 | 265篇 |
2017年 | 292篇 |
2016年 | 382篇 |
2015年 | 261篇 |
2014年 | 389篇 |
2013年 | 580篇 |
2012年 | 428篇 |
2011年 | 508篇 |
2010年 | 339篇 |
2009年 | 303篇 |
2008年 | 440篇 |
2007年 | 390篇 |
2006年 | 311篇 |
2005年 | 307篇 |
2004年 | 333篇 |
2003年 | 297篇 |
2002年 | 226篇 |
2001年 | 153篇 |
2000年 | 79篇 |
1999年 | 80篇 |
1998年 | 43篇 |
1997年 | 47篇 |
1996年 | 41篇 |
1995年 | 57篇 |
1994年 | 50篇 |
1993年 | 21篇 |
1992年 | 32篇 |
1991年 | 38篇 |
1990年 | 30篇 |
1989年 | 28篇 |
1988年 | 20篇 |
1987年 | 21篇 |
1986年 | 34篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1975年 | 12篇 |
1966年 | 19篇 |
1965年 | 12篇 |
1964年 | 15篇 |
1956年 | 12篇 |
排序方式: 共有8018条查询结果,搜索用时 15 毫秒
81.
The aim of this study was to determine whether there is increased leakage of neuron-specific enolase (NSE) and S-100 protein into amniotic fluid in pregnancies with neural tube defects, since both these proteins are produced by neural tissue, and to compare the value of these substances for detecting such defects with that of the more conventional techniques of alpha-fetoprotein (AFP) and acetylcholinesterase (AChE) gel electrophoresis. Amniotic samples from 25 mid-pregnancies (15–17 weeks' gestation) with neural tube defects (14 with open spina bifida and 11 with anencephaly) and from seven mid-pregnancies with abdominal wall defects were compared with a control material consisting of 80 amniotic fluid samples from 80 consecutive mid-pregnancy amniocenteses, with normal karyotypes and AFP concentrations. All of the above cases of abnormalities were primarily detected through increased AFP levels in the amniotic fluid. Amniotic fluid samples from 13 pregnancies with fetuses with autosomal chromosomal abnormalities and seven amniotic fluid samples contaminated with blood were also included in the investigation. It is concluded from the results that the conventional AFP assay combined with AChE gel electrophoresis is the best method for screening amniotic fluid for neural tube defects and defects of the abdominal wall. Neither NSE nor S-100 assay alone proved to be superior for the detection of these cases in mid-trimester amniotic fluid. The S-100 assay, however, could give additional information in cases where AChE gel electrophoresis is not decisive; for example, in samples contaminated with blood. 相似文献
82.
83.
84.
85.
86.
87.
88.
We report relatively high citrulline concentration in amniotic fluid of a citrullinemic fetus suggesting that prenatal detection of this condition could be done on this basis in conjunction with a direct or an indirect determination of argininosuccinate synthetase activity in amniotic fluid cells. 相似文献
89.
The larvae and pupae of the ladybird Thalassa saginata develop inside colonies of the dolichoderine ant Dolichoderus bidens. This association is the first specific and obligatory relationship recorded between ants and ladybirds. The ants provide shelter and protection to the larvae but the diet of the latter remains unclear. The integration of T. saginata larvae into the ant colonies is achieved by mimicking the cuticular patterns of the ants brood. Moreover, the larvae secrete substances from their hairs and anal gland that are likely to enhance their attractiveness. 相似文献
90.
Caching or storing surplus prey may reduce the risk of starvation during periods of food deprivation. While this behaviour occurs in a variety of birds and mammals, it is infrequent among invertebrates. However, golden orb-web spiders, Nephila edulis, incorporate a prey cache in their relatively permanent web, which they feed on during periods of food shortage. Heavier spiders significantly reduced weight loss if they were able to access a cache, but lost weight if the cache was removed. The presence or absence of stored prey had no effect on the weight loss of lighter spiders. Furthermore, N. edulis always attacked new prey, irrespective of the number of unprocessed prey in the web. In contrast, females of Argiope keyserlingi, who build a new web every day and do not cache prey, attacked fewer new prey items if some had already been caught. Thus, a necessary preadaptation to the evolution of prey caching in orb-web spiders may be a durable or permanent web, such as that constructed by Nephila. 相似文献