全文获取类型
收费全文 | 44859篇 |
免费 | 511篇 |
国内免费 | 544篇 |
专业分类
安全科学 | 1355篇 |
废物处理 | 2022篇 |
环保管理 | 5761篇 |
综合类 | 7591篇 |
基础理论 | 12052篇 |
环境理论 | 28篇 |
污染及防治 | 11613篇 |
评价与监测 | 2905篇 |
社会与环境 | 2300篇 |
灾害及防治 | 287篇 |
出版年
2022年 | 405篇 |
2021年 | 406篇 |
2020年 | 303篇 |
2019年 | 376篇 |
2018年 | 627篇 |
2017年 | 658篇 |
2016年 | 1016篇 |
2015年 | 765篇 |
2014年 | 1172篇 |
2013年 | 3543篇 |
2012年 | 1441篇 |
2011年 | 1976篇 |
2010年 | 1613篇 |
2009年 | 1635篇 |
2008年 | 1973篇 |
2007年 | 2050篇 |
2006年 | 1795篇 |
2005年 | 1522篇 |
2004年 | 1425篇 |
2003年 | 1499篇 |
2002年 | 1347篇 |
2001年 | 1727篇 |
2000年 | 1212篇 |
1999年 | 742篇 |
1998年 | 537篇 |
1997年 | 557篇 |
1996年 | 560篇 |
1995年 | 658篇 |
1994年 | 646篇 |
1993年 | 551篇 |
1992年 | 571篇 |
1991年 | 545篇 |
1990年 | 593篇 |
1989年 | 549篇 |
1988年 | 473篇 |
1987年 | 450篇 |
1986年 | 398篇 |
1985年 | 406篇 |
1984年 | 470篇 |
1983年 | 412篇 |
1982年 | 446篇 |
1981年 | 387篇 |
1980年 | 321篇 |
1979年 | 343篇 |
1978年 | 318篇 |
1977年 | 250篇 |
1975年 | 259篇 |
1974年 | 250篇 |
1972年 | 248篇 |
1971年 | 248篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
155.
156.
157.
Guest Editorial
A view from the countryside 相似文献158.
Interactions between the red algaPlocamium hamatum J. Agardh (Rhodophyta) and other benthic organisms including the alcyonacean soft coralSinularia cruciata (Tixier-Durivault) were investigated on an inshore fringing reef environment in whichP. hamatum was the dominant large fleshy alga. Field observations of sessile reef organisms including octocorals and sponges living in close proximity toP. hamatum revealed that varying degrees of tissue necrosis were suffered by the invertebrates when in physical contact with the alga. In order to establish whether the chemical constituents of the alga, especially chloromertensene, played a role in this necrosis, manipulative field experiments were carried out in the Pelorus Channel, Palm Island group (18°34S; 146°29E), North Queensland, Australia, in November and December 1988. The first experiment involved the relocation of healthy plants and soft corals into contact and non-contact situations on a mesh grid. In all cases of contact betweenP. hamatum andS. cruciata, the soft coral suffered tissue necrosis (n=6,p=0.0022). The second experiment had the same design, but involved the use of artificial plants both uncoated and coated with natural levels of chloromertensene, in contact withS. cruciata. In all cases of contact with coated treatments, necrosis was observed inS. cruciata (n=4,p=0.025). In cases where uncoated artificial fronds were placed in contact with soft corals,S. cruciata showed minor abrasion effects, but no appreciable necrosis. Coated treatments were not fouled by epiphytes during the experiment and were not consumed by predators. Uncoated treatments were rapidly reduced in size by predation and any remaining material was biofouled. These experiments thus demonstrated that the deleterious effects observed in soft corals in the field were caused by contact with the algaP. hamatum, that these effects were indeed chemically mediated by chloromertensene, and that physical contact without chemical intervention caused no such deleterious effects. This is the first experimental evidence which conclusively demonstrates allelopathy between an alga and other marine organisms and identifies the compound responsible for the observed allelopathic effects. 相似文献
159.
In vitro studies of the submerged angiospermRuppia maritima: Auxin and cytokinin effects on plant growth and development 总被引:1,自引:0,他引:1
Axenic tissue cultures ofRuppia maritima L. were established and propagated clonally in vitro from terminal rhizome segments collected from Tampa Bay, Florida, USA. Cultures were maintained in a base medium consisting of synthetic seawater supplemented with half-strength Murashige and Skoog salts and 1% sucrose at pH 5.6. The effects of five cytokins [6-furfurylaminopurine (kinetin), 6-benzylaminopurine (BAP), 2-isopentyladenine (2iP), 6-(4-hydroxy-3-methyl-but-2-enylamino) purine (zeatin), andn-phenyl-n-1,2,3-thidiazol-5yl urea (thidiazuron)] and one auxin [napthalene acetic acid (NAA)] on explant growth and development were investigated. Cytokinin additions resulted in a 3- to 4-fold increase in nodal production, branching, and biomass ofR. maritima after 12 wk in culture. Cultures responded in a dose-dependent manner to 2iP but exhibited broad dose-response curves to kinetin, BAP, zeatin, and thidiazuron. NAA addition resulted in increased leaf and internodal lengths, but reduced the number of leaves per node and the rhizome biomass. The addition of NAA almost completely suppressed root growth in media without cytokinins and had an antagonistic effect on nodal production and branching in cytokinin-supplemented media. 相似文献
160.
Protein, lipid, phosphorus, and organic carbon contents, as well as electron transport system (ETS) activity, lactatedehydrogenase activity, and gut evacuation rate, were measured in four interzonal species of Pacific copepods:Calanus australis, C. pacificus, Eucalanus inermis, andE. elongatus f.hyalinus, collected at the upwelling areas off Peru (8°S) and California (27°N), and in the middle of the North Pacific (30°N), from February to April 1987. The two Eucalanidae species —E. inermis andE. elongatus — have distinctive biochemical and elemental body composition and rates of main physiological processes. Relative protein, lipid, phosphorus, and organic carbon contents (µg mg–1 wet weight) in these species were, respectively, ca. 1/7 to 1/10, 1/5 to 1/20, 1/5 to 1/10, and 1/5 those inCalanus spp. Likewise, oxygen uptake rate per unit of wet weight (based on ETS activity) inE. inermis andE. elongatus was 5 to 10% of that in calanids; a similar difference was found in phosphorus excretion rate. In addition, gut evacuation rates inE. inermis andE. elongatus were ca. one-fifth of those inCalanus spp. Based on these data, we considered the eucalanids as belonging to a distinctive physiological group, figuratively named jelly-body copepods. In contrast with calanids, active lactatedehydrogenase has been found in the bodies ofE. inermis andE. elongatus, apparently allowing them to survive for a long time in layers of extremely low oxygen content (<0.2 ml l–1). The adaptive value of physiological features in these eucalanids and typical calanids is compared. 相似文献