全文获取类型
收费全文 | 34538篇 |
免费 | 466篇 |
国内免费 | 422篇 |
专业分类
安全科学 | 1080篇 |
废物处理 | 1485篇 |
环保管理 | 4889篇 |
综合类 | 5766篇 |
基础理论 | 9366篇 |
环境理论 | 16篇 |
污染及防治 | 8834篇 |
评价与监测 | 2041篇 |
社会与环境 | 1710篇 |
灾害及防治 | 239篇 |
出版年
2022年 | 265篇 |
2021年 | 279篇 |
2020年 | 267篇 |
2019年 | 243篇 |
2018年 | 465篇 |
2017年 | 456篇 |
2016年 | 721篇 |
2015年 | 568篇 |
2014年 | 829篇 |
2013年 | 2733篇 |
2012年 | 1078篇 |
2011年 | 1540篇 |
2010年 | 1219篇 |
2009年 | 1295篇 |
2008年 | 1517篇 |
2007年 | 1575篇 |
2006年 | 1352篇 |
2005年 | 1143篇 |
2004年 | 1146篇 |
2003年 | 1070篇 |
2002年 | 1036篇 |
2001年 | 1249篇 |
2000年 | 974篇 |
1999年 | 587篇 |
1998年 | 428篇 |
1997年 | 456篇 |
1996年 | 446篇 |
1995年 | 536篇 |
1994年 | 467篇 |
1993年 | 444篇 |
1992年 | 412篇 |
1991年 | 422篇 |
1990年 | 441篇 |
1989年 | 402篇 |
1988年 | 360篇 |
1987年 | 350篇 |
1986年 | 338篇 |
1985年 | 315篇 |
1984年 | 394篇 |
1983年 | 329篇 |
1982年 | 397篇 |
1981年 | 343篇 |
1980年 | 291篇 |
1979年 | 313篇 |
1978年 | 251篇 |
1977年 | 230篇 |
1975年 | 205篇 |
1974年 | 232篇 |
1973年 | 225篇 |
1972年 | 215篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
391.
Foraging desert ants, Cataglyphis fortis, encounter different sequences of visual landmarks while navigating by path integration. This paper explores the question whether the storage of landmark information depends on the context in which the landmarks are learned during an ant's foraging journey. Two experimental set-ups were designed in which the ants experienced an artificial landmark panorama that was placed either around the nest entrance (nest marks) or along the vector route leading straight towards the feeder (route marks). The two training paradigms resulted in pronounced differences in the storage characteristics of the acquired landmark information: memory traces of nest marks were much more robust against extinction and/or suppression than those of route marks. In functional terms, this result is in accord with the observation that desert ants encounter new route marks during every foraging run but always pass the same landmarks when approaching the nest entrance. 相似文献
392.
Population differences in anti-predator behaviour have been demonstrated in several species, although less is known about the genetic basis of these traits. To determine the extent of genetic differences in boldness (defined as exploration of a novel object) and shoaling within and between zebrafish (Danio rerio) populations, and to examine the genetic basis of shoaling behaviour in general, we carried out a study that involved laboratory-raised fish derived from four wild-caught populations. Controlling for differences in rearing environment, significant inter-population differences were found in boldness but not shoaling. A larger shoaling experiment was also performed using one of the populations as the basis of a North Carolina type II breeding design (174 fish in total) to estimate heritability of shoaling tendency. A narrow-sense heritability estimate of 0.40 was obtained, with no apparent dominance effects. 相似文献
393.
394.
395.
396.
397.
R. Riffaldi 《Agriculture, ecosystems & environment》1983,10(4):353-359
The distribution and composition of humic and fulvic acids have been investigated in the following organic wastes: straw, farmyard manure, sewage sludge, poultry manure, municipal refuse compost and pig slurry. Of the total organic carbon, the proportion present as humic carbon varied from about 13% in the compost to 50% in the pig slurry; the humic compounds extracted are characterized by a variable chemical composition. As compared to the natural humic substances from soil organic matter, these compounds show a lower content of acidic functional groups, lower E4/E6 and C/H ratios and can be classified as young forms of humic substances. 相似文献
398.
Egyptian Blue, a multicomponent synthetic blue pigment has been recorded in ancient Egypt since the Fourth Dynasty of the Old Kingdom (2600–2480 B.C.). The pigment consisting of cuprorivaite (CaCuSi4O10) with variable amounts of wollastonite (CaSiO3), Cu-rich glass and cuprite (Cu3O) or tenorite (CuO) was prepared by melting the copper-rich ingredient with lime and desert sand. Low melting temperatures (below 742 °C) were achieved by addition of flux-like plant ashes. The high quality of the pigments collected from monuments of the Fifth Dynasty (2480–2320 B.C.) may indicate that the first manufacture was in early dynastic or perhaps predynastic eras. During the reign of Thutmosis III (18th Dynasty, 1490–1436 B.C.) probably bronze filings were first applied as starting material, thus indicating a technological innovation. This new method was employed till the Roman times. 相似文献
399.
Hurler's disease was excluded in a fetus at 23 weeks' gestation by demonstrating normal iduronidase activity in fetal leucocytes following failure of amniotic cell culture after amnic-centesis at 16 and 19 weeks' gestation. The diagnosis was confirmed in the neonate. 相似文献
400.