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761.
762.
R. I. C. C. Francis 《Marine Biology》1995,124(2):169-176
A problem in the radiometric estimation of age using whole otoliths is the necessity to specify otolith-mass growth. Unless it can be assumed that otolith-mass growth is linear, parameters describing this growth will occur in the radiometric equation used to estimate age. Previous authors have assumed that the values of these parameters must be known before age can be estimated. This leads to circular reasoning: to estimate the age of a fish (and thus infer its growth) prior knowledge about the growth of the otolith is needed. A reanalysis of published radiometric data for Hoplostethus atlanticus is presented to illustrate two new approaches that avoid this assumption and thus the problem of circular reasoning. The first calculates the age that is most probable for each sample given the radiometric and otolith-mass data; the second estimates a lower bound for the maximum age. These analyses depend on correcting a misinterpretation of the otolith-mass term in a common radiometric equation. The effect of between-individual variability in otolith growth rates on the radiometric method is discussed. 相似文献
763.
Turbot (Scophthalmus maximus L.) were reared at 12 and 16°C until 26 d after hatching. At both temperatures, starting at the neural plate stage, somites were initially formed every 75 min. Expressed as a percentage of development time (DT, fertilisation to 90% larvae hatching) somite formation occurred relatively earlier during embryogenesis at 12°C (45% DT) than at 16°C (55% DT). At 12°C, after the 32-somite stage the rate of somite formation decreased to one every 300 min. The larvae hatched after 6 d at 12°C and 3 d at 16°C at a relatively primitive stage of development, prior to the opening of the mouth and anus, with unpigmented eyes, and a straight gut. Temperature altered the relative timing of organogenesis in the larval stages. At 12°C, the following characters appeared (in this order): swimbladder>loop in the gut (at the time of yolk exhaustion)>caudal fin. In contrast, at 16°C, the caudal fin appeared at the same time as the loop in the gut. At 16°C, spines formed on the head in the region of the otic capsule at the time the swimbladder formed and the yolk was exhausted, but were absent in 12°C larvae. At both temperatures, in 1 d-old larvae the myotomes just behind the yolk-sac contained 200 inner muscle fibres (presumptive white muscle). The initial growth of inner muscle was largely due to hypertrophy, but by 26 d at 12°C and 11 d at 16°C hyperplastic growth became important, as evidenced by a significant increase in the number of small fibres (<10 m2). By 26 d the average number of inner muscle fibres had increased to 341 at 12°C and 988 at 16°C. New muscle fibres were added in distinct germinal zones at the dorsal and ventral apices of the myotomes. Metamorphosis was associated with a thickening of the superficial (presumptive red) muscle layer and the appearance of tonic muscle fibres. 相似文献
764.
765.
A fine-mesh seine net was used at regular intervals to collect fishes from the entrance channel and basin of the Blackwood
River Estuary (south-western Australia), from Deadwater Lagoon, which is joined to the entrance channel by a narrow and shallow
water-course and thus constitutes part of this estuary, and from Flinders Bay into which the estuary discharges. Sampling
was at six-weekly intervals between February and December 1994. The juveniles of some marine species, such as Pelates sexlineatus, Rhabdosargus sarba and Aldrichetta forsteri, were either found only in the estuary or were in far higher densities in the estuary than in Flinders Bay. In contrast,
the juveniles of some other marine species, such as Sillago schomburgkii, were relatively abundant in both environments, while others such as S. bassensis, Pelsartia humeralis, Lesueurina platycephala and Spratelloides robustus were either far more abundant in Flinders Bay or entirely restricted to this marine embayment. The various marine species
found in inshore waters thus apparently vary considerably in their “preference” for estuaries as nursery areas. Although some
marine species were abundant in the shallows of the estuary, the fish fauna of these waters was dominated by the estuarine-spawning
species Leptatherina wallacei, Favonigobius lateralis, L. presbyteroides and Atherinosoma elongata. The above regional differences help account␣for the very marked difference that was found between the compositions of the
shallow-water␣ichthyofaunas of Flinders Bay and each of the three estuarine regions. The ichthyofaunal compositions of the
basin and channel underwent pronounced changes during winter, when freshwater discharge increased markedly and salinities
in the estuary thus declined precipitously. This faunal change was mainly attributable to the emigration of marine stragglers,
a reduction in the densities of marine estuarine-opportunist species such as Pelates sexlineatus and R. sarba, and the immigration of large numbers of both young 0+ Aldrichetti forsteri from the sea and of L. wallacei from the river. Although most of the above species were also abundant in Deadwater Lagoon, the ichthyofaunal composition
of this region did not undergo the same seasonal changes, presumably due to the lack of riverine input and thus the maintenance
of relatively high salinities throughout the year. The number of marine straggler species was much lower in Deadwater Lagoon
than in the estuary basin, reflecting a far more restricted tidal exchange with the entrance channel. However, the overall
density of fishes was far higher in Deadwater Lagoon than in the estuary basin or entrance channel, due mainly to the far
higher densities of the estuarine species Atherinosoma elongata and L. wallacei and of the 0+ age class of the marine species R. sarba. The high densities of certain species in Deadwater Lagoon are assumed to be related, at least in part, to the high level of
productivity and protection that is provided by the presence of patches of Ruppia megacarpa, an aquatic angiosperm that was not present in the estuary basin or entrance channel.
Received: 3 December 1996 / Accepted: 19 December 1996 相似文献
766.
The purpose of this investigation was to establish reproductive phenology of the dioecious marine floridean red alga Polysiphonia lanosa (L.) Tandy. Specifically, the distribution and frequencies of male and female plants, timing of their sexual maturity, fecundity
and success of fertilization were investigated. The presence of cystocarps was taken as an indication of syngamy. Populations
of P. lanosa in the Bay of Fundy reproduce in spring, summer and autumn. Both male and female filaments were present in equal abundance
at all sampling locations, grew in close proximity, and occurred with equal abundance at all elevations above chart datum.
During the growing season most of the mature plants contained reproductive organs with apparently functional gametangia containing
gametes the structure and behavior of which conformed to those reported in the literature for other species of the genus.
Male and female plants of P. lanosa matured synchronously during late May to early July at all collecting sites. The ratio of spermatia to carpogonia calculated
for the sampled population was high, 3000–4800 spermatia:1 carpogonium. At the end of the growing season (late October) the
fertilization success was at its maximum of 50 to 90% and at its minimum in July at 24%. The three free-living life-history
phases (females, males and tetrasporophytes) were abundant and occurred with equal frequency, indicating that a complete life
cycle was common at the studied location.
Received: 10 December 1996 / Accepted: 16 January 1997 相似文献
767.
B. I. Bergström 《Marine Biology》1997,128(3):397-407
Based on demographic analysis of four different temporally enclosed demes of Pandalus borealis in Gullmarsfjorden on the Swedish west coast and published information, I discuss the notion of environmental sex determination
in protandric pandalid shrimps as suggested by sex allocation theory. Demographic results showed that age structure and mortality
rates varied substantially between four studied periods without noticeable effects on the age of sex change in the fjord populations.
The majority of shrimps changed sex at an approximate age of 3 years and became females at an age of 3 to 4 years, however,
low proportions (4 to 7%) of 2nd year females (transitional at ca. 1 year) and 3rd year females (5 to 12%) (transitional at
ca. 2 years) were present each year. Low proportions of primary females were also found in two of the temporally enclosed
demes, in 1985 (9%) and in 1987 (5%). These results do not indicate that yearly variations in age structure, mortality, or
frequency of older breeders in the breeding population affect the age of sex change in temporally enclosed fjord demes of
this protandric species. An alternative to assuming that the protandric mode of reproduction in pandalid shrimp is combined
with environmental sex determination is suggested.
Received: 24 September 1996 / Accepted: 6 November 1996 相似文献
768.
Allison T. Moody Sabina I. Wilhelm Maureen L. Cameron-MacMillan Carolyn J. Walsh Anne E. Storey 《Behavioral ecology and sociobiology》2005,57(3):224-230
Behavioral precursors of 12 divorces were examined in 30 color-banded pairs of common murres (Uria aalge) over six breeding seasons. Common murres are long-lived seabirds that typically return each year to the same mate and nest site in dense colonies. At least one parent is present continuously from egg lay to chick fledging. Murres, therefore, have considerable opportunities to compare their mates parental behavior with that of several familiar neighbors. Previous reproductive success was lower for divorcing birds than for reuniting pairs. As predicted by the better option hypothesis, there were clear choosers (seven females and five males) that initiated divorce by moving to a new birds site or by courting a new partner at their current site. Choosers improved their reproductive success after the divorce, whereas their previous partners, the victims did not. Yearly divorce rates (average 8.2% per year) were significantly correlated with yearly mortality rates. Divorces appear to be opportunistic: pairs divorced after varying numbers of reproductive failures with the immediate precursor usually being the disappearance (death) of a murre from a successful neighboring site. In contrast to the delays experienced by victims, choosers formed new pairs quickly and laid their eggs no later than reuniting pairs. Prior to the divorce, victims fed their chicks less often than choosers, and some engaged in other behaviors that compromised egg or chick survival. These observations suggest that deficiencies in parental behavior were precursors to the divorce. This report is one of the first cases where reproductive failure of divorcing pairs has been linked to deficits in the parental behavior of the subsequent divorce victim.Communicated by C. Brown 相似文献
769.
Rosborg I Nihlgård B Gerhardsson L Gernersson ML Ohlin R Olsson T 《Environmental geochemistry and health》2005,27(3):217-227
This study presents the concentrations of about 50 metals and ions in 33 different brands of bottled waters on the Swedish market. Ten of the brands showed calcium (Ca) concentrations ≤10 mg L−1 and magnesium (Mg) levels <3 mg L−1, implying very soft waters. Three of these waters had in addition low concentrations of sodium (Na; <7 mg L−1), potassium (K; <3 mg L−1) and bicarbonate (HCO3 ≤31 mg L−1). These brands were collected from barren districts. Nine of the brands were collected from limestone regions. They showed increased Ca-levels exceeding 50 mg L−1 with a maximum of 289 mg L−1. Corresponding Mg-levels were also raised in two brands exceeding 90 mg L−1. Two soft and carbonated waters were supplemented with Na2CO3 and NaCl, resulting in high concentrations of Na (644 and 648 mg L−1) and chloride (Cl; 204 and 219 mg L−1). Such waters may make a substantial contribution to the daily intake of NaCl in high water consumers. The storage of carbonated drinking water in aluminum (Al) cans increased the Al-concentration to about 70 μg L−1. Conclusion As there was a large variation in the material as regards concentrations of macro-elements such as Ca, Mg, Na, K and Cl. Supplementation with salts, e.g., Na2CO3, K2 CO3 and NaCl, can lead to increased concentrations of Na, K and Cl, as well as decreased ratios of Ca/Na and larger ratios of Na/K. Water with high concentrations of e.g., Ca and Mg, may make a substantial contribution to the daily intake of these elements in high water consumers. Al cans are less suited for storage of carbonated waters, as the lowered pH-values may dissolve Al. The levels of potentially toxic metals in the studied brands were generally low. 相似文献
770.