全文获取类型
收费全文 | 18881篇 |
免费 | 198篇 |
国内免费 | 147篇 |
专业分类
安全科学 | 446篇 |
废物处理 | 731篇 |
环保管理 | 2408篇 |
综合类 | 4103篇 |
基础理论 | 4419篇 |
环境理论 | 14篇 |
污染及防治 | 4673篇 |
评价与监测 | 1189篇 |
社会与环境 | 1151篇 |
灾害及防治 | 92篇 |
出版年
2022年 | 125篇 |
2021年 | 154篇 |
2019年 | 130篇 |
2018年 | 271篇 |
2017年 | 260篇 |
2016年 | 383篇 |
2015年 | 314篇 |
2014年 | 445篇 |
2013年 | 1306篇 |
2012年 | 542篇 |
2011年 | 786篇 |
2010年 | 604篇 |
2009年 | 701篇 |
2008年 | 786篇 |
2007年 | 860篇 |
2006年 | 777篇 |
2005年 | 634篇 |
2004年 | 624篇 |
2003年 | 610篇 |
2002年 | 591篇 |
2001年 | 682篇 |
2000年 | 446篇 |
1999年 | 341篇 |
1998年 | 230篇 |
1997年 | 260篇 |
1996年 | 264篇 |
1995年 | 282篇 |
1994年 | 278篇 |
1993年 | 243篇 |
1992年 | 223篇 |
1991年 | 227篇 |
1990年 | 216篇 |
1989年 | 178篇 |
1988年 | 183篇 |
1987年 | 168篇 |
1986年 | 170篇 |
1985年 | 165篇 |
1984年 | 186篇 |
1983年 | 185篇 |
1982年 | 187篇 |
1981年 | 160篇 |
1980年 | 148篇 |
1979年 | 143篇 |
1978年 | 146篇 |
1977年 | 125篇 |
1976年 | 105篇 |
1975年 | 110篇 |
1974年 | 125篇 |
1971年 | 100篇 |
1967年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
481.
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
482.
483.
484.
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
485.
486.
An efficient, reproducible and rapid fused silica capillary column gas chromatographic method, in splitless mode, for analysing of the three chloroanthracene isomers is described. The method affords efficient separation and good linearity for each isomer in the range of 0.2 -200 μg/ml. The method can also be used in separation and determination of another thirty three aromatic and their halosubstituted compounds. This paper also presents the applications of the method in analysing of complex products mixture from reaction of the selected aromatic compounds with hydrogen chloride on fly ash surface from municipal incinerator. 相似文献
487.
Prenatal diagnosis of Sandhoff disease (infantile onset) at 16 weeks gestation has been made by detection and analysis of N-acetylglucosaminyl-oligosaccharides in amniotic fluid using high performance liquid chromatography. The elution profile for the branched chain oli-gosaccharides was identical with that obtained with neonatal and infantile Sandhoff urine. The concentration of the oligosaccharides in the fluid was 1/100th that of urine but when calculated relative to creatinine the levels were similar. No oligosaccharides were detected in normal control amniotic fluids (10 patients) at a similar gestational age. Based on the levels of the amniotic fluid oligosaccharides and the sensitivity limits of the assay, prenatal diagnosis of patients with the juvenile onset form of the disease may also be possible with this technique. 相似文献
488.
At 10 weeks' gestation, chorionic villus biopsy was obtained from a woman at risk for Sanfilippo type C disease. Acetyl-CoA: α-glucosaminide N-acetyltransferase activity was markedly deficient. The pregnancy was terminated at 12 weeks' gestation and follow-up study on fetal fibroblasts confirmed the diagnosis. 相似文献
489.
Bilateral cleft lip and cleft palate can be diagnosed by ultrasonography prior to 20 weeks of pregnancy. The anomaly produces an abnormal facial profile and, on cross-section, the clefts in the maxilla are demonstrable. The method is illustrated by sonograms from a fetus in which the defect was diagnosed before trisomy 13 became known by karyotyping. 相似文献
490.