全文获取类型
收费全文 | 4364篇 |
免费 | 36篇 |
国内免费 | 18篇 |
专业分类
安全科学 | 68篇 |
废物处理 | 275篇 |
环保管理 | 270篇 |
综合类 | 725篇 |
基础理论 | 894篇 |
环境理论 | 5篇 |
污染及防治 | 1515篇 |
评价与监测 | 401篇 |
社会与环境 | 257篇 |
灾害及防治 | 8篇 |
出版年
2023年 | 49篇 |
2022年 | 134篇 |
2021年 | 133篇 |
2020年 | 53篇 |
2019年 | 54篇 |
2018年 | 164篇 |
2017年 | 119篇 |
2016年 | 217篇 |
2015年 | 129篇 |
2014年 | 253篇 |
2013年 | 420篇 |
2012年 | 270篇 |
2011年 | 264篇 |
2010年 | 201篇 |
2009年 | 148篇 |
2008年 | 244篇 |
2007年 | 248篇 |
2006年 | 226篇 |
2005年 | 156篇 |
2004年 | 130篇 |
2003年 | 121篇 |
2002年 | 98篇 |
2001年 | 61篇 |
2000年 | 45篇 |
1999年 | 36篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 26篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1975年 | 7篇 |
1970年 | 7篇 |
1967年 | 8篇 |
1966年 | 11篇 |
1965年 | 17篇 |
1964年 | 29篇 |
1963年 | 13篇 |
1962年 | 17篇 |
1961年 | 16篇 |
1960年 | 10篇 |
1959年 | 27篇 |
1958年 | 30篇 |
1957年 | 19篇 |
1956年 | 13篇 |
1955年 | 18篇 |
1954年 | 7篇 |
排序方式: 共有4418条查询结果,搜索用时 15 毫秒
991.
Hydrochemical changes between 1991 and 2001 were assessed based on two synoptic stream surveys from the 820-km2 region of the Slavkov Forest and surrounding area, western Czech Republic. Marked declines of sulfate, nitrate, chloride, calcium and magnesium in surface waters were compared with other areas of Europe and North America recovering from acidification. Declines of sulfate concentration in the Slavkov Forest (-30 microeq L(-1) yr(-1)) were more dramatic than declines reported from other sites. However, these dramatic declines of strong acid anions did not generate a widespread increase of stream water pH in the Slavkov Forest. Only the most acidic streams experienced a slight increase of pH by 0.5 unit. An unexpected decline of stream water pH occurred in slightly alkaline streams. 相似文献
992.
Feasibility of two different extraction methods involving solid-liquid extraction and Soxhlet extraction, previously used for the determination of lipid contents and PCB levels on powdered full-fat milk, are now examined for simultaneous PCDD/F analysis. The results of this study are consistent with those found for PCBs. The solid-liquid procedure provides the most efficient extraction of both labelled spiked and endogenous PCDD/Fs with the lowest variability. The average recoveries were 101% (R.S.D. = 6.9%) for 13C12-2,3,7,8-TCDD and 95% (R.S.D. = 11%) for 13C12-1,2,3,4,7,8-HxCDD. The R.S.D.s for endogenous 2,3,7,8-PCDD/Fs were in the 9.3-25% range. In addition, this methodology simplified the subsequent clean-up step as it allowed a semi-selective extraction of the apolar lipids from the milk. The proposed method was applied to simultaneous PCB and PCDD/F analyses in different brands of powdered full-fat milks commercially available in Spain. In all cases, very similar PCB and PCDD/F levels were found. Differences among batches from the same manufacturer were even lower. The total i-TEQ average for PCDDs and PCDFs in the 22 powdered full-fat milk samples analysed was 1.87 pg/g fat basis. This value was similar to those found in cow's milk from other European countries. 相似文献
993.
Yorianta?Sasaerila Regine?Gries Gerhard?Gries Grigori?Khaskin Skip?King Stephen?Takács Hardi?) 《Chemoecology》2003,13(2):89-93
Summary. During peak calling activity by male oil palm bunch
moths, Tirathaba mundella Walker (Lepidoptera: Pyralidae), their
hairpencils, wings or entire body were extracted in hexane. Gas
chromatographic-electroantennographic detection (GC-EAD) analyses of
hair pencil extracts revealed four compounds that consistently elicited
responses from female antennae. The NMR spectrum of isolated compound 1,
and mass spectra and retention indices of compounds 1–4 suggested that
they were (3S,6S)-2,2,6-trimethyl-6-vinyl-tetrahydro-pyran-3-ol (1),
4-hydroxy-3-methoxy-benzaldehyde (2, vanillin),
6,10,14-trimethyl-2-pentadecanone (3), and
6,10,14-trimethyl-2-pentadecanol (4). Comparative GC and GC-MS analyses
of hair pencils extract and synthetic standards confirmed these
structural assignments. Moreover, comparative chromatography of
synthetic and hairpencil-isolated 1 on a Cyclodex-B column (which
separated the four stereoisomers with baseline resolution) revealed that
male T. mundella produce the SS-stereoisomer (SS-1). In field cage
bioassay experiments in Palembang, Indonesia, synthetic SS-1 and
vanillin in combination, but not singly, attracted female T. mundella.
SS-1 plus vanillin were as effective as male T. mundella in attracting
females. Compounds 3 and 4 did not enhance the blend's attractiveness.
Received October 11 2002; accepted March 14, 2003.
R1D="
Correspondence to: Gerhard Gries, email: gries@sfu.ca 相似文献
994.
M. Matucha M. Gryndler S. T. Forczek H. Uhlířová K. Fuksová P. Schröder 《Environmental Chemistry Letters》2003,1(2):127-130
The fate of chloroacetic acids (CAA) in forest soils was studied using radio-indicator methods. We showed that chloroacetic acids are both microbially degraded and simultaneously formed by chloroperoxidase-mediated chlorination of acetic and humic acids. The degree of biodegradation of chloroacetic acids in soil depends on their concentration. Dichloroacetic acid (DCA) is degraded faster than trichloroacetic acid (TCA). Chlorination of acetic acid led to a fast formation of dichloroacetic acid, whereas chlorination of humic acids gave rise to trichloroacetic acid. Both processes lead to a steady state in soil, participate in the chlorine cycle and possibly also in decomposition of organic matter in forest ecosystems. 相似文献
995.
Hugh?DrummondEmail author Cristina?Rodríguez Adriana?Vallarino Claudia?Valderrábano Gabriela?Rogel Emilio?Tobón 《Behavioral ecology and sociobiology》2003,53(5):287-296
According to the desperado sibling hypothesis, chicks of obligately siblicidal species kill their junior broodmates as early as possible because junior broodmates face dire ecological prospects and are consequently predisposed to aggressively overthrow elder broodmates by all-out aggression. The agonistic behavior of junior chicks is virtually unknown because they die so young. We investigated the agonistic behavior of hypothetical desperados by fostering junior brown boobies (Sula leucogaster, an obligately siblicidal species) into nests of the blue-footed booby (S. nebouxii, a facultatively siblicidal species) containing an older singleton blue-foot chick. Controls were junior blue-footed boobies fostered into the same situation. Junior brown boobies were 7 times more aggressive than controls and most of them dominated their elder and larger nestmates. Four of nine brown booby juniors showed relentless aggression, delivering up to 711 pecks, bites and pushes (including "expulsion pushes") per hour, thereby overwhelming nestmates 90% heavier and permanently expelling one of them from the nest. Similarly, in natural broods of two surviving brown booby chicks, the losing chick was 13 times as aggressive as blue-foot subordinates, up to at least age 7 weeks. Contrast of the two species of booby suggests the evolution of agonistic roles within broods may be partly driven by selection on potential victims to express a level and type of aggressiveness appropriate to their status-related ecological prospects. 相似文献
996.
In recent decades numerous diversity indices have been introduced. Among them the quadratic entropy index Q expresses the mean difference between two individuals chosen from the community at random. Differing from diversity indices habitually employed, Q does not satisfy a property postulated earlier for those measures. Namely, the uniform distribution of species does not necessarily yield the maximal index value. Q is based on the difference matrix of species. For a given matrix one can seek for the vector yielding the maximum quadratic entropy. This task leads to a quadratic programming problem. Using the appropriate program of a program package, we determined the maximum vector for a genetic difference matrix of crane species, as published in the literature. We discovered that some components (frequencies) in the maximum vector are equal to zero. That is, by maximizing the quadratic diversity some species can be eliminated. We discuss briefly the possible implications of this observation. Moreover, even if all elements in the maximum vector are positive, the elements can differ. 相似文献
997.
Copulatory plugs do not assure high first male fertilisation success: sperm displacement in a lizard
Pedro L. Moreira Vera L. Nunes José Martín Octávio S. Paulo 《Behavioral ecology and sociobiology》2007,62(2):281-288
Sperm competition selects for opposing male defensive and offensive reproductive traits, and its outcome may be determined
by the effectiveness to which one trait has evolved to out-compete the other. We tested the effectiveness of a first male
plug physical interference with a second male insemination (defence) vs the effectiveness of plug and associated sperm displacement
by a second male (offence) on the outcome of sperm competition in Iberian rock lizards. We conducted a double mating experiment
where we compared the proportion of eggs per clutch fertilised by the same second males (against the same first males) when
they copulated with females 30 min (first male plug adhered firmly inside the female cloaca) and 4 h (first male plug loosely
adhered or shed from the female cloaca) after first males. We found that second males fertilised the majority of the eggs
per clutch in the 30-min treatment, whereas fertilisations were equally shared between the two males in the 4-h treatment.
These results show that plugs have little defensive effectiveness, and thus, do not assure high first male fertilisation success.
Instead, sperm displacement appears to be associated with plug displacement. That is, because sperm embedded in first male
plugs, and displaced from competition for fertilisations by second males, is expected to increase in number with decreasing
time allowed for female sperm transport, second males thus enjoy higher fertilisation success. This study shows that offensive
plug displacement out-competes plug defensive role in Iberian rock lizards. Moreover, it reveals sperm displacement as a novel
sperm competition mechanism in reptiles. 相似文献
998.
Hugh Drummond Edda González José Luis Osorno 《Behavioral ecology and sociobiology》1986,19(5):365-372
Summary Reproduction in the blue-footed boody was examined for evidence of parent-offspring conflict over infanticidal reduction of the brood. Parental investment was analysed by measuring clutch characteristics, and chick growth and mortality in four seasons. Direct observations were made of behavioral development to determine the social roles of family members. The modal clutch was two similar-sized eggs, which hatched 4.0 days apart due to a 5.1-day laying interval and immediate incubation of the first egg. On average, senior chicks grew faster than their sibs in years of good or poor growth (Fig. 2), maintaining the initial size disparity for at least 65 days (Fig. 1). Differential mortality of junior chicks was associated not with poor personal growth, but with a 20–25% weight deficiency of the senior sib, implying siblicidal brood reduction triggered at a weight threshold. Senior chicks established behavioral dominance through low-frequency pecking, but ordinarily did not eliminate their sibs nor substantially suppress their begging (Fig. 3), even when their own growth was 16% below potential. Parents fed dominant chicks more frequently than subordinates, but did not intervene in inter-sib aggression, even when it reached a siblicidal level. The weight and possibly the dominance relation between sibs was inverted in 12% of pairs. The theoretical prediction of conflict over elimination of the junior chick was not supported; rather, parents and senior chick cooperate, as if their fitness interests were congruent. Further, provisional tolerance of the junior chick by its underweight senior sib is consistent with self-sacrifice to increase the latter's inclusive fitness. 相似文献
999.
László Zsolt Garamszegi Balázs Rosivall Gergely Hegyi Eszter Szöllösi János Török Marcel Eens 《Behavioral ecology and sociobiology》2006,60(5):663-671
In intrasexual conflicts, contestants can rely on relative or absolute size of status badges to mediate aggressive behavior. Most studies focus on the response of focal animals to variation in status badges of their competitors; few have simultaneously considered the traits of both participants under experimental conditions. By simulating territorial intrusions, we tested the importance of two sexual traits [forehead patch size (FPS) and wing patch size (WPS)] in territorial behavior of males in a Hungarian population of the collared flycatcher, Ficedula albicollis. We presented a stimulus male to an unpaired resident male to examine whether the characteristics of the territory owner or those of the challenger were associated with the latency of the first attack of the owner, which is a good predictor of the territorial behavior in general. WPS of the stimulus male was a significant determinant of the latency of the first attack, as males with a larger WPS elicited quicker attacks from the residents than males with a small WPS. From the residents’ perspective, age appeared to influence their territorial behavior, as yearlings had shorter attack latencies than older males. Additionally, latency could be considered an individual-specific attribute because it varied consistently among males, even when the WPS of the stimulus male was controlled, and it was associated with pairing success. Contrary to findings in a Swedish population, FPS seemed to be unimportant in male–male competition in our population, which suggests population differences in the role of the two plumage traits. Our results indicate that in a territorial conflict, the characteristics of both participants are important. 相似文献
1000.
Celia A Harvey Arnulfo Medina Dalia Merlo Sánchez Sergio Vílchez Blas Hernández Joel C Saenz Jean Michel Maes Fernando Casanoves Fergus L Sinclair 《Ecological applications》2006,16(5):1986-1999
As tropical regions are converted to agriculture, conservation of biodiversity will depend not only on the maintenance of protected forest areas, but also on the scope for conservation within the agricultural matrix in which they are embedded. Tree cover typically retained in agricultural landscapes in the neotropics may provide resources and habitats for animals, but little is known about the extent to which it contributes to conservation of animal species. Here, we explore the animal diversity associated with different forms of tree cover for birds, bats, butterflies, and dung beetles in a pastoral landscape in Nicaragua. We measured species richness and abundance of these four animal taxa in riparian and secondary forest, forest fallows, live fences, and pastures with high and low tree cover. We recorded over 20,000 individuals of 189 species including 14 endangered bird species. Mean abundance and species richness of birds and bats, but not dung beetles or butterflies, were significantly different among forms of tree cover. Species richness of bats and birds was positively correlated with tree species richness. While the greatest numbers of bird species were associated with riparian and secondary forest, forest fallows, and pastures with >15% tree cover, the greatest numbers of bat species were found in live fences and riparian forest. Species assemblages of all animal taxa were different among tree cover types, so that maintaining a diversity of forms of tree cover led to conservation of more animal species in the landscape as a whole. Overall, the findings indicate that retaining tree cover within agricultural landscapes can help conserve animal diversity, but that conservation efforts need to target forms of tree cover that conserve the taxa that are of interest locally. Preventing the degradation of remaining forest fragments is a priority, but encouraging farmers to maintain tree cover in pastures and along boundaries may also make an important contribution to animal conservation. 相似文献