全文获取类型
收费全文 | 3305篇 |
免费 | 30篇 |
国内免费 | 171篇 |
专业分类
安全科学 | 96篇 |
废物处理 | 195篇 |
环保管理 | 289篇 |
综合类 | 586篇 |
基础理论 | 775篇 |
环境理论 | 2篇 |
污染及防治 | 1128篇 |
评价与监测 | 239篇 |
社会与环境 | 183篇 |
灾害及防治 | 13篇 |
出版年
2023年 | 17篇 |
2022年 | 69篇 |
2021年 | 39篇 |
2020年 | 24篇 |
2019年 | 37篇 |
2018年 | 116篇 |
2017年 | 50篇 |
2016年 | 76篇 |
2015年 | 84篇 |
2014年 | 89篇 |
2013年 | 265篇 |
2012年 | 89篇 |
2011年 | 157篇 |
2010年 | 138篇 |
2009年 | 150篇 |
2008年 | 160篇 |
2007年 | 186篇 |
2006年 | 140篇 |
2005年 | 117篇 |
2004年 | 143篇 |
2003年 | 138篇 |
2002年 | 114篇 |
2001年 | 239篇 |
2000年 | 143篇 |
1999年 | 71篇 |
1998年 | 40篇 |
1997年 | 47篇 |
1996年 | 33篇 |
1995年 | 40篇 |
1994年 | 42篇 |
1993年 | 41篇 |
1992年 | 30篇 |
1991年 | 35篇 |
1990年 | 27篇 |
1989年 | 32篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1975年 | 12篇 |
1973年 | 9篇 |
1972年 | 10篇 |
排序方式: 共有3506条查询结果,搜索用时 15 毫秒
431.
Incidental mortality of harbour porpoises, Phocoena phocoena, from captures in fishing gear has been documented consistently as severe in some European waters. Since fishing effort varies
greatly among regions, management units must be defined for more effective conservation of this species. In this study, analysis
of mitochondrial DNA (mtDNA) restriction fragments was performed to investigate the population structure of harbour porpoises
in the Baltic Sea, the joint Kattegat–Skagerrak Seas and off the west coast of Norway. Mitochondrial DNA of 65 harbour porpoises
collected from three regions was analysed with nine restriction enzymes. Analysis of the heterogeneity in the frequency distribution
of haplotypes among provisional subpopulations revealed significant differences, which supports the recognition of three different
subpopulations and thus three separate management units. Furthermore, indices of haplotypic diversity (range: 0.211 to 0.628)
and nucleotide diversity (range: 0.070 to 0.168) of these provisional subpopulations were much lower than for western North
Atlantic subpopulations, which is consistent with the view that harbour porpoises in European waters, particularly in the
Baltic Sea, are depleted.
Received: 21 August 1996 / Accepted: 19 September 1996 相似文献
432.
Cysts of the planktonic oligotrich ciliate Strombidium conicum were isolated from sediment samples, collected monthly in Onagawa Bay on the northeastern Pacific coast of Japan, and incubated
under laboratory conditions of 20 °C in light. The excystment ability changed seasonally in a regular manner, which was demonstrated
by alternation of three characteristic seasonal patterns of the cumulative excystment curve, i.e., rapid, delayed and transitional
patterns. While the transitional excystment pattern was characteristic during the period from spring to midsummer, the rapid
pattern occurred during late summer to early winter. The pattern changed again to transitional in midwinter and finally returned
to the delayed pattern in late winter or early spring. We suggest that mud temperature was the most determinative factor of
this seasonality in excystment ability. Such synchronization of annual excystment helps this species to proliferate rapidly
and maintain the vegetative part of the population in the upper water column for a longer period of time where it is subjected
to the dispersion process due to water movement.
Received: 17 September 1996 / Accepted: 18 November 1996 相似文献
433.
Occurrence of a crinotoxin and hemagglutinin in the skin mucus of the moray eel Lycodontis nudivomer
The tropical Indo-Pacific moray eel Lycodontis nudivomer possesses a mucous skin secretion which shows hemolytic, toxic and hemagglutinating activities. The active components were extracted from the mucous secretion with 0.02 M phosphate buffer (pH 7.5) and purified by DEAE-cellulose and Sephadex G-200 column chromatography. The component(s) responsible for the hemolytic-toxic activities differ(s) from that (those) causing the hemagglutinating activity. The hemolysin was unstable in the presence of heat, acidic and alkaline media, and several organic solvents. It was undialyzable throught a cellophane membrane, and showed an absorption maxium at 280 nm in the phosphate buffer (pH 7.5). The hemolytic activity was completely lost when treated with trypsin, indicating that the hemolysin is a protein. Histochemical examination on the epidermis of L. nudivomer revealed the presence of clubbed peculiar cells, in addition to common mucous cells, which we speculate produced the hemolytic-toxic component(s). Eight other species of morays were found to possess clubbed peculiar cells similar to those of L. nudivomer in their epidermis. There are marked differences, however, in the abundance of these cells among these muraenids. 相似文献
434.
435.
A new in situ gradostat was devised to study the dynamics of natural communities having nutrient gradients within aquatic habitats. This semi-enclosed mesocosm consisted of three components: i.e. three transparent, concentric cylindrical culture chambers, with diameters of 70, 60 and 40 cm, and 20 cm deep, supported by four flotation buoys, a medium reservoir, and a pump to supply the medium to the mesocosm. Water exchange between compartments was achieved via holes in the cylindrical walls, the number and size of the holes being chosen to regulate the rate of exchange. Sterile culture medium was pumped into the central (first) chamber and diffused outwards into the second and third chambers through the perforated walls. Suitable perforations could achieve a concentration gradient of up to 9.5 times between the first and third chambers within 12 h. The system was designed with the following characteristics: (1) an experimental semi-enclosed system in the natural environment; (2) to maintain equivalence with the external water except for the experimental factors; and (3) to form a manipulable gradient of experimental factors across the mesocosm. Using the in situ gradostat, the response of a natural phytoplankton community to a nitrate gradient was determined. A gradient from oligotrophic to eutrophic was maintained for 10 days in an oligotrophic pond. The mean growth rate of phytoplankton was lower in the eutrophic zone than that in the mesotrophic zone, where the highest mean growth rate was observed. The growth rate of each dominant phytoplankter showed its own pattern, but all rates were highest in the mesotrophic environment of the second chamber. 相似文献
436.
A survey of the degree of imposex in populations of the commercial muricid Bolinus brandaris (L.) was carried out at six locations along the Catalan Coast (NW Mediterranean). Imposex was found to be a widespread phenomenon; the occurrence of a penis was observed in all females studied with the exception of those from St. Carles (South of Catalunya) where only 37% were affected. Other indices such as Relative Penis Length (RPL) and Vas Deferens Sequence (VDS) were applied; RPL varied from 4.5% in St. Carles--the least affected area--to 29.8% in the vicinity of Barcelona; similar results were obtained for VDS. Tissue organotin residues ranged from 6 to 140 ng g(-1) w.w. as Sn. Despite legislation restricting the use of tributyltin (TBT) in antifouling paints, this paper evidences the occurrence of organotin pollution far from the source, with levels of both TBT and triphenyltin (TPhT) high enough to cause environmental concern. 相似文献
437.
M. H. N. Tabrizi S. E. Said A. W. Badr Y Mashor S. A. Billings 《Journal of the American Water Resources Association》1998,34(6):1333-1339
ABSTRACT: Model estimation and prediction of a river flow system are investigated using nonlinear system identification techniques. We demonstrate how the dynamics of the system, rainfall, and river flow can be modeled using NARMAX (Nonlinear Autoregressive Moving Average with eXogenuous input) models. The parameters of the model are estimated using an orthogonal least squares algorithm with intelligent structure detection. The identification of the nonlinear model is described to represent the relationship between local rainfall and river flow at Enoree station (inputs) and river flow at Whitmire (output) for a river flow system in South Carolina. 相似文献
438.
Long-term temporal-spatial dynamics of marine coastal water quality in the Tolo Harbor, Hong Kong, China 总被引:5,自引:0,他引:5
IntroductionToloHarborislocatedinthenortheasternpartofHongKong .Itisanearlyland lockedwaterbodywithonlyonenarrowexittotheopenseaatMirsBay(Fig .1) .Itslengthandsurfaceareaareapproximately 15kmand 5 2km2 ,respectively .Theaveragedepthvariesfromlessthan10min… 相似文献
439.
IntroductionPolycyclicaromatichydrocarbons (PAHs)arewidespreadenvironmentalpollutantsintheatmosphere.Theyaregeneratedinthecombustion .Themajorsourcesidentifiedincludefossilfuels,vehiculartraffic,industrialprocesses,smokinganddomesticheating (Peltonen ,1995) .T… 相似文献
440.
IntroductionBeingatypicalpolycyclicaromatichydrocarbons(PAHs) ,benzo[a]pyrene(BaP)deservesseriousstudybecausePAHsarenowrecognizedasmajorenvironmentalpollutants .ExposuretoPaHsisvirtuallyunavoidableandisstronglysuspendedofbeingacausativefactorincertaintumo… 相似文献