全文获取类型
收费全文 | 43038篇 |
免费 | 437篇 |
国内免费 | 535篇 |
专业分类
安全科学 | 1287篇 |
废物处理 | 1874篇 |
环保管理 | 5173篇 |
综合类 | 8135篇 |
基础理论 | 11083篇 |
环境理论 | 36篇 |
污染及防治 | 11096篇 |
评价与监测 | 2746篇 |
社会与环境 | 2321篇 |
灾害及防治 | 259篇 |
出版年
2022年 | 412篇 |
2021年 | 421篇 |
2020年 | 317篇 |
2019年 | 390篇 |
2018年 | 679篇 |
2017年 | 655篇 |
2016年 | 1005篇 |
2015年 | 794篇 |
2014年 | 1162篇 |
2013年 | 3256篇 |
2012年 | 1412篇 |
2011年 | 1965篇 |
2010年 | 1555篇 |
2009年 | 1648篇 |
2008年 | 1971篇 |
2007年 | 1978篇 |
2006年 | 1715篇 |
2005年 | 1506篇 |
2004年 | 1340篇 |
2003年 | 1415篇 |
2002年 | 1307篇 |
2001年 | 1621篇 |
2000年 | 1153篇 |
1999年 | 708篇 |
1998年 | 492篇 |
1997年 | 509篇 |
1996年 | 521篇 |
1995年 | 605篇 |
1994年 | 644篇 |
1993年 | 497篇 |
1992年 | 511篇 |
1991年 | 509篇 |
1990年 | 535篇 |
1989年 | 475篇 |
1988年 | 407篇 |
1987年 | 384篇 |
1986年 | 344篇 |
1985年 | 341篇 |
1984年 | 363篇 |
1983年 | 367篇 |
1982年 | 349篇 |
1981年 | 337篇 |
1980年 | 270篇 |
1979年 | 295篇 |
1978年 | 257篇 |
1977年 | 202篇 |
1976年 | 198篇 |
1975年 | 220篇 |
1972年 | 207篇 |
1971年 | 194篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Klaus Peter Sauer Thomas Lubjuhn Jörn Sindern Harald Kullmann Joachim Kurtz Conny Epplen Jörg Thomas Epplen 《Die Naturwissenschaften》1998,85(5):219-228
Panorpa vulgaris has become a model insect for testing theories of sexual selection. This contribution summarizes that which has been learned
in recent years and presents new data that clearly show that the mating system of P. vulgaris is not simply a resource-defense polygyny, as has previously been thought. In P. vulgaris neither the pattern in food exploitation nor the ratio of variance in the lifetime reproductive success of the two sexes
is in accordance with that expected in resource defense polygynous mating systems. Lifetime mating duration is the most important
proximate determinant of male fitness. Males employing alternative mating tactics obtain copulations of varying duration in
relation to the following sequence: saliva secretion 1 food offering 1 no gift. The number of salivary masses which males
provide to females during their lifetime is significantly correlated with the lifetime condition index. The condition index
depends on the fighting prowess of males and their ability to find food items. Thus saliva secretion of Panorpa is considered a Zahavian handicap, which can serve as an honest quality indicator used by mating females. Our results confirm
four main predictions of the indicator model of the theory of sexual selection: (a) the indicator signals high ecological
quality of its bearer, (b) the indicator value increases with phenotypic quality, (c) the indicator value is positively correlated
with the genetic quality affecting offspring fitness in a natural selection context, and (d) the quality indicator is more
costly for low- than for high-quality individuals. The evolutionary consequences of the mating pattern and the sperm competition
mechanism in P. vulgaris are discussed in the context the way in which sexual selection creates and maintains sperm mixing and the evolution of a
promiscuous mating system. 相似文献
992.
993.
994.
P. A. Hurley Mr R. H. T. Ward B. Teisner R. K. Iles M. Lucas J. G. Grudzinskas 《黑龙江环境通报》1993,13(10):903-908
Serum PAPP-A measurements taken from 254 women in the first trimester are reported. Eleven chromosomal abnormalities were detected. The mean serum PAPP-A levels in cases of Down syndrome were 0.44 MOM at 9 weeks gestation, 0.15 MOM at 10 weeks, and 0.29 MOM at 11 weeks. The PAPP-A level at 10 weeks was below those of pregnancies which aborted spontaneously. At 11 weeks, the pregnancies with Down syndrome recorded the lowest PAPP-A levels at that gestation. On this small sample, offering chorionic villus sampling to women with singleton pregnancies and a PAPP-A level below 0.3 MOM (approximately 6.5 per cent of this at-risk group) would have detected all the Down syndrome fetuses at 10 weeks and 50 per cent at 11 weeks without selecting those cases destined to abort. This suggests that serum PAPP-A should continue to be investigated as a potential first-trimester screening test for Down syndrome. 相似文献
995.
A laboratory scale study was conducted to assess the feasibility of the new coupling of rotating biological contactor (RBC) plus porous biomass support system (PBSS) using polyurethane foam as porous support media to biodegrade petroleum refinery wastewater. Polyurethane foam was attached on disks of two four-stage laboratory scale cascade connected RBC units.The two RBC units were operated simultaneously at different but constant, flowrates giving hydraulic loading rates of 0.01, 0.02, 0.03, 0.04 m3/m2/d in two runs keeping the same rotational speed 10 r/min throughout. Organic loading was a less controllable factor in this study.For all of the hydraulic loadings, it was found that the removal efficiency of total chemical oxygen demand (TCOD) and oil were above 80 percent. Ammonia nitrogen and phenol removal were above 90 and 80 percent respectively. The maximum biomass concentration within polyurethane foam was about 30 g/m2 in the first stage for 0.03 m3/m2/d hydraulic loading.The results show that t 相似文献
996.
从燃烧的煤和油中排放出来的极性污染物,包含有多种含氮、氧和硫的极性多环芳烃(PAH),这些极性组分比非极性组分常具有更强的致癌和致突变性。目前,正相高效液相色谱(NP-HPLC)常被用来分离分析这类极性组分。 但是,要提高这些极性组分分离的选择性,现大多采用梯度洗脱的方法。也就是改变流动相极性的方法。本文介绍了一种高压电场耦合色谱柱的新方法。这种技术除了具 相似文献
997.
998.
Chondroectodermal dysplasia (Ellis-van Creveld syndrome) has previously been diagnosed prenatally only once, using fetoscopy. We report on two consecutive pregnancies in a woman at risk of having a child with the syndrome during which fetoscopic visualization was performed. Ellis-van Creveld syndrome was diagnosed prenatally in one instance, while it could be excluded in the other one. Non-invasive prenatal diagnosis of the syndrome is discussed. 相似文献
999.
The effects of reduced oxygen concentrations in the gas phase over the culture medium on colony formation and cell proliferation were investigated in high and low cell density primary and secondary cultures of amniotic fluid cells. Using two standard culture methods (25 cm2 plastic flasks and Leighton type tubes) a significantly reduced culture time was observed at high cell density for mass cultures by incubation within a low oxygen tension gas phase (2.5 per cent to 7.5 per cent O2) instead of conventional air (18 per cent O2). At low cell density colony formation was significantly enhanced in cultures grown at reduced oxygen tension. Using gas permeable membranes as support, lowering the oxygen tension from 7.5 per cent to 2.5 per cent yielded an increase in plating efficiency of cells from approximately 5 per cent to 25 per cent, whereas plating efficiency was less than 2 per cent for cells grown at ambient 18 per cent O2. It is suggested that low oxygen tension in the gas phase is an effective means of enhancing clonal growth in amniotic fluid cell cultures, thereby reducing both culture time and risk of culture failure. 相似文献
1000.