全文获取类型
收费全文 | 31033篇 |
免费 | 336篇 |
国内免费 | 226篇 |
专业分类
安全科学 | 833篇 |
废物处理 | 1155篇 |
环保管理 | 4328篇 |
综合类 | 6102篇 |
基础理论 | 8269篇 |
环境理论 | 13篇 |
污染及防治 | 7817篇 |
评价与监测 | 1751篇 |
社会与环境 | 1141篇 |
灾害及防治 | 186篇 |
出版年
2018年 | 329篇 |
2017年 | 348篇 |
2016年 | 545篇 |
2015年 | 431篇 |
2014年 | 628篇 |
2013年 | 2367篇 |
2012年 | 826篇 |
2011年 | 1174篇 |
2010年 | 913篇 |
2009年 | 988篇 |
2008年 | 1183篇 |
2007年 | 1243篇 |
2006年 | 1121篇 |
2005年 | 921篇 |
2004年 | 911篇 |
2003年 | 929篇 |
2002年 | 865篇 |
2001年 | 1114篇 |
2000年 | 807篇 |
1999年 | 492篇 |
1998年 | 378篇 |
1997年 | 397篇 |
1996年 | 417篇 |
1995年 | 466篇 |
1994年 | 451篇 |
1993年 | 418篇 |
1992年 | 414篇 |
1991年 | 422篇 |
1990年 | 438篇 |
1989年 | 428篇 |
1988年 | 379篇 |
1987年 | 363篇 |
1986年 | 340篇 |
1985年 | 331篇 |
1984年 | 375篇 |
1983年 | 349篇 |
1982年 | 394篇 |
1981年 | 349篇 |
1980年 | 306篇 |
1979年 | 312篇 |
1978年 | 298篇 |
1977年 | 258篇 |
1976年 | 244篇 |
1975年 | 231篇 |
1974年 | 276篇 |
1973年 | 261篇 |
1972年 | 248篇 |
1971年 | 221篇 |
1970年 | 196篇 |
1967年 | 196篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
741.
Skelly JM Fredericksen TS Savage JE Snyder KR 《Environmental pollution (Barking, Essex : 1987)》1996,94(2):235-240
Ambient concentrations of ozone (O(3)) and carbon dioxide (CO(2)) were measured at locations from the forest floor to the top of the canopy in a deciduous forest at the Moshannon State Forest in northcentral Pennsylvania. O(3) concentrations were measured from May-September for three years (1993-1995) while CO(2) concentrations were measured only during July and August of 1994. O(3) concentrations increased steadily during the day at all locations, peaking during the middle to late afternoon hours. O(3) concentrations then steadily declined to their lowest point, just before dawn. Vertical O(3) concentration gradients varied seasonally and among years. However, O(3) concentrations were highest within the forest canopy and lowest at the forest floor, with an average difference of approximately 13%. Differences in O(3) concentrations between the canopy and forest floor were greatest at night. O(3) concentrations were slightly higher at locations within the canopy than above the canopy. CO(2) concentrations were consistenly higher near the forest floor and were higher above the canopy than within the canopy. CO(2) concentrations were higher at night than during the day at all locations, especially near the forest floor. 相似文献
742.
Johnstone RM Court GS Fesser AC Bradley DM Oliphant LW MacNeil JD 《Environmental pollution (Barking, Essex : 1987)》1996,93(2):109-120
Levels of eggshell thinning, and organochlorine residues in egg contents, blood plasma of adults and juveniles, tissue samples, and prey species were determined for a population of migratory Peregrine Falcons (Falco peregrinus tundrius) breeding in the Canadian Arctic. Temporal trends were assessed by comparing data collected during 1991-1994, with data from 1982-1986, for the same population. Shells (n=54) from 1991-1994 averaged 15% thinner than eggs produced prior to the introduction of DDT. No improvement in shell thickness was detected between decades. Mean DDE residue levels in eggs showed a decline from 7.6 mg kg (1982-1986) to 4.5 mg kg (1991-1994), but there was no significant change in SigmaPCB residues. Moreover, the proportion of clutches with eggs exceeding critical SigmaPCB, DDE, and dieldrin residue levels (10%) did not change between decades. Relative to Greenland and Alaskan populations, F. p. tundrius at Rankin Inlet show high levels of organochlorine contamination and little reduction in residues over the last decade. These Tundra Peregrines continue to be exposed to organochlorines in Latin America; however, results also link relatively high levels in the study population with waterfowl species that do not leave Canada in winter. 相似文献
743.
France RL 《Environmental pollution (Barking, Essex : 1987)》1996,94(2):189-193
Population biomass and production of the amphipod Hyalella azteca (Saussure) were found to be related to alkalinity (ranging from 0.2 to 58.1 mg liter(-1)) in 10 Canadian Shield lakes in south-central Ontario. Biomass and production of amphipods in the two lakes characterized by spring depressions of pH below 5.0 were found to be lower than those for populations inhabiting lakes that did not experience such acid pulses. The proportional biomass of amphipods in relation to the total littoral zoobenthos community was lower in lakes of low alkalinity than in circumneutral or hardwater lakes. Because production in these amphipod populations is known to depend closely on population abundance, the labour-intensive derivation of production rates yields relatively little information for biomonitoring that cannot be obtained from abundance data alone. 相似文献
744.
Economists have tried to estimate the demand for recreation under conditions of congestion, struggling especially with a model that uses observed rather than stated behaviour to obtain results. This paper reports statistical analyses of data on perceptions, mitigating behaviour and management preferences in order to highlight the difficulties related to empirical analysis of congestion. We offer evidence that may be of assistance to those wishing to construct measures of congestion for use in an observed behaviour model. The results may also be useful to recreation area managers who can implement a quota or permit system or change site entry or access fees to control access to the site they manage. 相似文献
745.
Zhang YJ Bryan ND Livens FR Jones MN 《Environmental pollution (Barking, Essex : 1987)》1997,96(3):361-367
The interactions of a range of actinide elements (Th, U, Np, Pu, Am) with humic substances from the Needle's Eye natural analogue site were studied by gel permeation chromatography. Bulk humic substances were isolated by ammonia extraction, followed by dialysis against distilled water and freeze-drying. The gel permeation results suggest that Needle's Eye humic substances can be fractionated into three incompletely resolved fractions with average molecular weights determined by analytical ultracentrifugation around 49 000 for Fraction 1, around 14 700 for Fraction 2 and around 8000 for Fraction 3. Although there are significant differences between the organic matter elution patterns in individual gel permeation experiments, presumably due to differences in column packing, these are much smaller than the differences between metal ions. The uranium that is naturally present in these humic substances is largely bound in the late-eluting fraction. Spikes of the early actinides, including Np and Pu in controlled valency states, have been added to the humic substances, and gel permeation of the spiked humic substances shows that the three humic fractions vary greatly in their effectiveness and selectivity as ligands for early actinides. 相似文献
746.
Lepp NW Hartley J Toti M Dickinson NM 《Environmental pollution (Barking, Essex : 1987)》1997,95(3):363-369
Patterns of soil copper contamination have been examined in the vicinity of a copper rod rolling plant in Prescot, Merseyside, UK. The site, established in 1975, was found to possess clear patterns of soil copper contamination, with the highest levels of HNO3 and water-extractable fractions encountered in the factory grounds adjacent to the location of the furnace chimney. The majority of the copper had accumulated in the upper soil horizons. The site is surrounded by planted lawns, established at different times after the commissioning of the plant. The species composition of the extant grassland communities, found at sites with differing soil copper levels, was compared to the composition of the original seed mixtures sown at each of ten sites. These surveys clearly showed that different levels of soil copper contamination had produced significant changes in grassland composition with time. At the most polluted site, copper tolerant Agrostis capillaris clones were the main grasses present only two years after the area was sown with a four-species mixture of non-tolerant grass seed. Lolium perenne possessed extreme sensitivity to copper. A number of dicotyledonous species, normally considered sensitive to elevated copper levels, were found to be unaffected where such conditions had arisen after plants had established from seed. 相似文献
747.
R. Boonyatumanond M.S. Tabucanon C. Siriwong P. Prinyatanakun 《Environmental monitoring and assessment》1997,44(1-3):315-325
Water samples from the Chao Phraya River, the main river in Thailand were collected and analyzed during 1988–1994. Organochlorine pesticides such as HCHs, DDTs, aldrin, dieldrin and chlordanes were determined. Aldrin and dieldrin had high frequencies of occurrence in water samples. The concentration median of the pesticides was approximately one order of magnitude higher than those of total HCHs and DDTs. Levels of aldrin were relatively high in the upstream while levels of DDTs were high in the urban area of Bangkok during 1989–1990. p,p-DDE levels were relatively higher in 1992. No clear trends in the levels of pesticides were observed. 相似文献
748.
J. J. Jesudason R. H. Marchessault T. Saito 《Journal of Polymers and the Environment》1993,1(2):89-98
The synthetic analogue of a bacterially produced polyester, poly(-hydroxybutyrate) (PHB) was synthesized from racemic -butyrolactone using anin situ trimethyl aluminum-water catalyst. The polymer was fractionated into samples differing in molecular weight and isotactic diad content. The latter was closely related to degree of crystallinity. The biodegradation of these fractions were examined by monitoring mass loss over time in the presence of anAlcaligenes faecalis T1 extracellular bacterial poly(-hydroxybutyrate) depolymerase. The fraction with high isotactic diad tacticity content showed little or no degradation over a 50 hour incubation period, whereas the fraction of intermediate isotactic diad content degraded in a continuous steady fashion at a rate that was less than that for bacterial PHB. The low isotactic diad fraction underwent a rapid initial degradation, followed by no further mass loss. The presence of stereoblocks in the polymer structure of the various fractions was an influence on the degree of susceptibility towards degradation and is related to sample crystallinity. 相似文献
749.
Nast W Mortensen L Fischer K Fitting I 《Environmental pollution (Barking, Essex : 1987)》1993,80(1):85-90
Grafted Norway spruce trees were subjected to exposure beginning in April 1988, to one of four different air treatments in open-top chambers: Charcoal filtered air (CF), non-filtered air (NF), non-filtered air with the addition of O(3) during summer (NFO), and SO(2) plus NO(2) during winter (NFOSN). CF trees were considered as the reference group. No effects on growth parameters were observed. Samples of the two youngest needle year classes were taken late in November 1989 for enzyme determinations. The activity of ascorbic acid peroxidase (A-POD) increased the same level in all treatments, and activities of catalase and dehydroascorbic acid reductase (DHA-R) increased only in NF and NFO treatments. A higher level of activity in the NFOSN treatment was observed only for glucose-6-phosphate-dehydrogenase (Glc-6-P-DH) and non-specific peroxidase (POD). Isoelectric focusing of POD showed a changed pattern in the NFOSN treatment. Neither activity nor isoelectric focusing of superoxidase dismutase (SOD) was changed in any of the treatments. 相似文献
750.
Slugs (Deroceras reticulatum and Arion subfuscus) were sampled from two distinct sites, an uncontaminated site at Dinas Powys and a Pb-contaminated, disusedmine site at Llantrisant. Batches of the slugs were exposed for ten days under laboratory conditions to an artificial diet consisting of a 5% (w/v) agar + 5% (w/v) sucrose matrix contaminated with different concentrations of Pb, as Pb (NO(3))(2). The food 'cubes' contained approximately 0, 10, 100, and 1000 microg Pb ml(-1). Tissue-Pb concentrations increased with increasing dietary-Pb concentration in both species. However, at the highest Pb exposure (1000 microg ml(-1)) the tissue-Pb concentrations in D. reticulatum and A. subfuscus sampled originally from the clean site were higher than those in their counterparts from the contaminated site, even though the Llantrisant slugs had significantly higher baseline Pb concentrations than the Dinas Powys slugs. It is suggested that these observations indicate metal tolerance phenotypically expressed as reduced accumulation in the populations with a history of Pb-exposure in their natural habitat. We discuss how biomonitoring may be affected by the way in which different slug populations deal with metals. 相似文献