全文获取类型
收费全文 | 16397篇 |
免费 | 172篇 |
国内免费 | 137篇 |
专业分类
安全科学 | 448篇 |
废物处理 | 629篇 |
环保管理 | 2295篇 |
综合类 | 2571篇 |
基础理论 | 4468篇 |
环境理论 | 4篇 |
污染及防治 | 4320篇 |
评价与监测 | 1014篇 |
社会与环境 | 854篇 |
灾害及防治 | 103篇 |
出版年
2022年 | 115篇 |
2021年 | 129篇 |
2020年 | 106篇 |
2019年 | 150篇 |
2018年 | 224篇 |
2017年 | 220篇 |
2016年 | 354篇 |
2015年 | 240篇 |
2014年 | 360篇 |
2013年 | 1276篇 |
2012年 | 442篇 |
2011年 | 637篇 |
2010年 | 538篇 |
2009年 | 521篇 |
2008年 | 695篇 |
2007年 | 694篇 |
2006年 | 660篇 |
2005年 | 510篇 |
2004年 | 592篇 |
2003年 | 522篇 |
2002年 | 483篇 |
2001年 | 702篇 |
2000年 | 471篇 |
1999年 | 282篇 |
1998年 | 241篇 |
1997年 | 218篇 |
1996年 | 228篇 |
1995年 | 248篇 |
1994年 | 271篇 |
1993年 | 219篇 |
1992年 | 247篇 |
1991年 | 222篇 |
1990年 | 254篇 |
1989年 | 238篇 |
1988年 | 193篇 |
1987年 | 173篇 |
1986年 | 158篇 |
1985年 | 167篇 |
1984年 | 192篇 |
1983年 | 180篇 |
1982年 | 185篇 |
1981年 | 179篇 |
1980年 | 137篇 |
1979年 | 153篇 |
1978年 | 131篇 |
1977年 | 117篇 |
1975年 | 118篇 |
1974年 | 115篇 |
1973年 | 110篇 |
1972年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Rosalind Aughwane Emma Ingram Edward D. Johnstone Laurent J. Salomon Anna L. David Andrew Melbourne 《黑龙江环境通报》2020,40(1):38-48
Objective
Magnetic resonance imaging (MRI) of placental invasion has been part of clinical practice for many years. The possibility of being better able to assess placental vascularization and function using MRI has multiple potential applications. This review summarises up-to-date research on placental function using different MRI modalities.Method
We discuss how combinations of these MRI techniques have much to contribute to fetal conditions amenable for therapy such as singletons at high risk for fetal growth restriction (FGR) and monochorionic twin pregnancies for planning surgery and counselling for selective growth restriction and transfusion conditions.Results
The whole placenta can easily be visualized on MRI, with a clear boundary against the amniotic fluid, and a less clear placental-uterine boundary. Contrasts such as diffusion weighted imaging, relaxometry, blood oxygenation level dependent MRI and flow and metabolite measurement by dynamic contrast enhanced MRI, arterial spin labeling, or spectroscopic techniques are contributing to our wider understanding of placental function.Conclusion
The future of placental MRI is exciting, with the increasing availability of multiple contrasts and new models that will boost the capability of MRI to measure oxygen saturation and placental exchange, enabling examination of placental function in complicated pregnancies. 相似文献993.
994.
Testes mass in megachiropteran bats varies in accordance with sperm competition theory 总被引:4,自引:0,他引:4
D. J. Hosken 《Behavioral ecology and sociobiology》1998,44(3):169-177
Sperm competition is a widespread phenomenon influencing a range of characters, including investment in gonadal tissue. Conspecific
proximity is one factor which can influence the risk of sperm competition and hence testicular investment, and decreased confidence
of paternity may be one cost of group living. Aspects of female biology may also influence spermatogenic investment and sperm
morphology. This study examines the associations between relative testes mass and roost-group size across 17 species of Megachiroptera.
Associations between breeding season duration and investment in spermatogenesis are also examined, as are associations between
female reproductive tract dimensions and testes mass and dimensions of spermatozoa across all bats. Relative testes mass was
significantly positively associated with roost-group size at a species level and after appropriate phylogenetic control (pairwise
comparisons and comparison of independent contrasts). There were no significant relationships between breeding season duration
and relative testes mass. Across all bats, neither testes mass nor sperm length were significantly related to dimensions of
the female tract. The results are discussed in the context of sperm competition.
Received: 7 January 1998 / Accepted after revision: 8 August 1998 相似文献
995.
Summary. Workers of the amblyoponine species Mystrium rogeri employ trail communication during recruitment to food sources and new nest sites. The trail pheromone originates from a hitherto
unknown sternal gland located in the 7th abdominal sternite. The recruiting ant deposits the gland secretions by a special
gaster-dragging behavior. The recruitment behavior can be complemented by a rapid vertical body shaking performed by some
recruiting ants inside the nest. M. rogeri workers possess a large pygidial gland, the secretion of which elicits a repellent response in other ant species.
Received 25 May 1998; accepted 15 June 1998. 相似文献
996.
The bioaccumulation potential of endosulfan was determined by constantly exposing male and female adult crayfish, Procambarus clarkii to 100 ppb Thiodan insecticide for 8 wks. The crayfish were removed at 2 wk intervals and the uptake by tissues (whole-body) was determined by electron capture gas-chromatography. The same number of pre-exposed crayfish (100 ppb Thiodan) were transferred to endosulfan-free water after 8 wks, and insecticide loss (depuration) was similarly quantitated. The maximum amount of insecticide and its metabolites detected after 8 wks were 197 ppb endosulfan II, 18 ppb endosulfan I and 3 ppb endosulfan sulfate. During the first 4 wks of depuration, endosulfan loss from cryfish tissues occurred rapidly, and only 3 ppb endosulfan I remained. No endosulfan II and sulfate were detected beyond 4 wks. The residues in male vs female were not significant statistically. Bioaccumulation factor (BF) for endosulfan II for crayfish tissues was 1.97, which is considerably lower than for other aquatic invertebrates (26 for scallop, Chlamys opercularis and 600 for mussel, Mytilus edulis. The presence of endosulfan sulfate in the tissues cannot be considered as 'detoxification' which is as toxic as the parent compound. 相似文献
997.
998.
A QSAR study has been carried out on several organotin compounds using physical and topological parameters (log P, pKa, 1x and 1xv) and acute toxicity data on Daphnia magna. Equations with significant correlation and high predictive capacity have been found. 相似文献
999.
1000.