全文获取类型
收费全文 | 40286篇 |
免费 | 399篇 |
国内免费 | 298篇 |
专业分类
安全科学 | 1053篇 |
废物处理 | 1604篇 |
环保管理 | 5467篇 |
综合类 | 5848篇 |
基础理论 | 11750篇 |
环境理论 | 22篇 |
污染及防治 | 9999篇 |
评价与监测 | 2543篇 |
社会与环境 | 2465篇 |
灾害及防治 | 232篇 |
出版年
2022年 | 261篇 |
2021年 | 235篇 |
2019年 | 262篇 |
2018年 | 945篇 |
2017年 | 886篇 |
2016年 | 1045篇 |
2015年 | 637篇 |
2014年 | 837篇 |
2013年 | 2675篇 |
2012年 | 1230篇 |
2011年 | 2110篇 |
2010年 | 1632篇 |
2009年 | 1662篇 |
2008年 | 2020篇 |
2007年 | 2282篇 |
2006年 | 1460篇 |
2005年 | 1334篇 |
2004年 | 1235篇 |
2003年 | 1267篇 |
2002年 | 1251篇 |
2001年 | 1561篇 |
2000年 | 1091篇 |
1999年 | 668篇 |
1998年 | 536篇 |
1997年 | 524篇 |
1996年 | 536篇 |
1995年 | 589篇 |
1994年 | 526篇 |
1993年 | 463篇 |
1992年 | 495篇 |
1991年 | 453篇 |
1990年 | 473篇 |
1989年 | 497篇 |
1988年 | 415篇 |
1987年 | 351篇 |
1986年 | 316篇 |
1985年 | 364篇 |
1984年 | 352篇 |
1983年 | 392篇 |
1982年 | 380篇 |
1981年 | 320篇 |
1980年 | 287篇 |
1979年 | 321篇 |
1978年 | 259篇 |
1977年 | 230篇 |
1976年 | 235篇 |
1975年 | 228篇 |
1974年 | 212篇 |
1973年 | 212篇 |
1972年 | 226篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Cements from two species of barnacles, Balanuseburneus Gould and Balanus crenatus Bruguiére, were analyzed to identify the number and nature of proteins present. B. crenatus cement was composed mainly of a small peptide cross-linked into aggregates ranging in size from ˜ 3 kD to 40–50 kD. These
aggregates could be reduced with 2-mercaptoethanol (2-ME) in the presence of sodium dodecyl sulfate (SDS) but only after incubation
at 40 °C for 12 to 24 h and only when the cement was recently formed. Reductive alkylation of cysteine residues with 4-vinylpyridine
produced a water-soluble peptide of less than 5 kD. By comparison, the cement of B. eburneus could be dissolved only partially in SDS and 2-ME when heated at 100 °C for 10 min. Five major proteins were identified by
SDS-PAGE: 7, 22, 36 and 58 kD bands for which N-terminal sequence and amino acid compositions are presented; and a 52 kD band
for which sequence data are given. A minor protein band of ˜ 80 kD has the same N-terminus as the 36 kD band. CNBr digests
of individual proteins produced peptides for which sequence and composition data are also presented. The study was conducted
during 1993 to 1995. In general, the proteins identified from B. crenatus cement are similar to those characterized from B. eburneus, and they are different in composition and sequence than those previously reported from Mytilus edulis.
Received: 7 August 1996 / Accepted: 8 October 1996 相似文献
992.
In French Guiana, parabiotic societies (natural mixed colonies) are frequently found in ant gardens. Crematogaster limata parabiotica (Myrmicinae), often associated with Camponotus femoratus (Formicinae), was found for the first time in parabiosis with ponerine ants: Pachycondyla goeldii and Odontomachus mayi. A detailed study of the relationships between Cr. l. parabiotica and O. mayi showed that each species is aggressive towards allospecific or conspecific individuals belonging to another colony, but tolerates
allospecific individuals from the multi-species society. Studies of cuticular substances of the four ant species were made
using gas chromatography. The results showed that each species, living alone or in parabiosis, possesses a specific chemical
profile. Thus, the ants are able to recognise nestmate and non-nestmate individuals of the associated species, even though
their cuticular profiles are different. The hypothesis that the nestmate allospecific profile is learned is suggested to explain
this pattern of recognition.
Received: 5 June 1996 / Accepted after revision: 17 October 1996 相似文献
993.
Osmoregulatory ability of mature chum salmon (Oncorhynchus keta) during spawning migration was examined by following the changes in gill Na+, K+-ATPase activity and in the distribution and morphology of chloride cells. Mature chum salmon caught in Otsuchi Bay, northern
Honshu Island, Japan, died within 5 d in seawater (SW) in association with a marked increase in plasma osmolality, whereas
the fish transferred to fresh water (FW) maintained plasma osmolality efficiently. Gill Na+, K+-ATPase activity decreased in both SW-maintained and FW-transferred fish. Well-developed chloride cells, identified by immunocytochemical
staining specific for Na+, K+-ATPase, were present mainly in the filament epithelium of immature fish caught in the ocean. In mature fish caught in the
bay, however, additional chloride cells were also found in the lamellar epithelium. The number of filament chloride cells
decreased markedly in the mature fish both in SW and in FW, whereas the number of lamellar chloride cells was maintained.
These results suggest that the loss of hypoosmoregulatory ability in mature chum salmon may be attributable to the decrease
in filament chloride cells and associated decrease in gill Na+, K+-ATPase activity, and also that appearance of lamellar chloride cells may be preparatory to the forthcoming upstream migration.
Received: 14 April 1997 / Accepted: 5 May 1997 相似文献
994.
L. E. C. Conceição T. van der Meeren J. A. J. Verreth M. S. Evjen D. F. Houlihan H. J. Fyhn 《Marine Biology》1997,129(2):255-265
The present paper studied the influence of different food regimes on the free amino acid (FAA) pool, the rate of protein
turnover, the flux of amino acids, and their relation to growth of larval turbot (Scophthalmus maximus L.) from first feeding until metamorphosis. The amino acid profile of protein was stable during the larval period although
some small, but significant, differences were found. Turbot larvae had proteins which were rich in leucine and aspartate,
and poor in glutamate, suggesting a high leucine requirement. The profile of the FAA pool was highly variable and quite different
from the amino acid profile in protein. The proportion of essential FAA decreased with development. High contents of free
tyrosine and phenylalanine were found on Day 3, while free taurine was present at high levels throughout the experimental
period. Larval growth rates were positively correlated with taurine levels, suggesting a dietary dependency for taurine and/or
sulphur amino acids. Reduced growth rates in Artemia-fed larvae were associated with lower levels of free methionine, indicating that this diet is deficient in methionine for
turbot larvae. Leucine might also be limiting turbot growth as the different diet organisms had lower levels of this amino
acid in the free pool than was found in the larval protein. A previously presented model was used to describe the flux of
amino acids in growing turbot larvae. The FAA pool was found to be small and variable. It was estimated that the daily dietary
amino acid intake might be up to ten times the larval FAA pool. In addition, protein synthesis and protein degradation might
daily remove and return, respectively, the equivalent of up to 20 and 10 times the size of the FAA pool. In an early phase
(Day 11) high growth rates were associated with a relatively low protein turnover, while at a later stage (Day 17), a much
higher turnover was observed.
Received: 19 March 1997 / Accepted: 14 April 1997 相似文献
995.
996.
Polychaetes belonging to the genus Capitella are often present in high numbers in organic-rich sediments polluted with, e.g., oil components, and Capitella spp. may have a great impact on the biogeochemistry of these sediments. We examined the influence of Capitella sp. I on microbial activity in an organic-rich marine sediment contaminated with the polycyclic aromatic hydrocarbon, fluoranthene.
Capitella sp. I were added to microcosms (10 000 ind m−2) and the impact of a pulse-sedimentation of fluoranthene-contaminated sediment (3 mm layer) was studied for a period of 12
d after sedimentation. The sediment oxygen uptake and total sediment metabolism (TCO2 production) increased in cores with worms (71 to 131%), whereas the anaerobic activity, measured as sulfate reduction rate
12 d after sedimentation, was lower compared to cores without worms. The effect of fluoranthene on sulfate reduction was most
pronounced in the presence of worms, with a 34% reduction versus 16% in cores without worms. The reduced sulfur pools in cores
with worms were smaller than in cores without worms, suggesting that the reduced anaerobic activity was caused by increased
oxidation of the sediment, which may favor O2 and other electron-acceptors (e.g. NO3
−, Fe3+, Mn4+) in organic matter decomposition. The sediment oxygen uptake and TCO2 production did not show significant changes due to fluoranthene treatment, indicating that these parameters were either less
sensitive to fluoranthene stress or recovered more rapidly (i.e. within 48 h) than sulfate reduction rates. Bioturbation by
Capitella sp. I altered the depth profile of fluoranthene such that fluoranthene was found in deeper sediment layers (down to 2 cm)
where diffusional loss and microbial breakdown probably are reduced relative to surface layers. In cores without worms, fluoranthene
was found down to 1 cm, with 75% remaining in the upper 5 mm.
Received: 5 December 1996 / Accepted: 11 February 1997 相似文献
997.
Cultures of asexually reproducing populations of the oligochaete Paranaislitoralis (Müller) collected from six different patches (3 to 50 m apart) on an intertidal mud flat in Flax Pond, New York, on two
occasions, June and October 1993, showed significant differences among lines in life span, number of offspring produced, and
in finite rate of increase (λ). Although growth rates were significantly lower in October than in June, they were always positive
(λ > 1) in the laboratory cultures reared in field-collected sediment, while field data show that the densities of P. litoralis decreased sharply in summer and autumn from a seasonal high in early June. Cultures of worms reared at high densities without
renewal of sediment crashed, and effects on individuals were irreversible: worms from late (declining) stages of population
growth had a significantly higher mortality and lower reproduction than worms from earlier stages, also when transferred to
high-quality food. Genetical analysis using RAPDs (random amplified polymorphic DNA) confirmed the existence of several clones
of P. litoralis in our cultures. Experiments where parent and offspring were cultured in sediments of different qualities showed clone–environment
interactions in the number of asexual offspring produced, but not in age at first reproduction. Clones also differed in that
some showed significant parental effects of sediment quality on life-history characteristics while other clones did not. Our
results indicate that P.litoralis populations in Flax Pond are not an example of a population subdivided into a set of permanent source and sink subpopulations,
but rather an example of a continuously shifting mosaic of local growth conditions.
Received: 21 April 1997 / Accepted: 3 September 1997 相似文献
998.
Frank J. Joyce 《Behavioral ecology and sociobiology》1993,32(2):71-77
Summary Rufous-naped wrens (Campylorhynchus rufinucha) in northwestern Costa Rica build breeding nests most frequently in ant-acacia trees (Acacia collinsii) and occasionally near wasp nests in ant-acacia trees. By moving occupied wasp nests (Polybia rejecta) to randomly chosen ant-acacia trees with wren nests, I tested the hypothesis that wrens nesting near wasp nests were more likely to fledge young than wrens not nesting near wasp nests. Wrens whose nests were near experimentally relocated wasp nests were significantly more likely to fledge young (37.5% of 16 attempts in 1987 and 75% of 12 attempts in 1988) than were wrens whose nests had no wasp nests placed near them (0% of 16 attempts in 1987 and 20% of 15 attempts in 1988). In 15 cases, repeated nesting attempts occurred in the same trees both with and without experimentally-placed wasp nests. Analysis of these data allowed a comparison of the effect of wasp nests on fledging success while differences among trees were controlled. Within the same tree, nesting attempts associated with wasp nests were significantly more likely to fledge young than nesting attempts without wasp nests. Predation was the primary cause of nest failure, and within forest, white-faced monkeys (Cebus capucinus) were the most important predators. The difference in success of wren nests with and without wasps and observations of predators indicate that enhancement of fledging success was due to deterrence of predatory vertebrates by wasps. 相似文献
999.
Use of signature whistles during separations and reunions by wild bottlenose dolphin mothers and infants 总被引:1,自引:0,他引:1
We examine the contexts and patterns of signature whistle production by wild bottlenose dolphin mother-infant pairs (Tursiops spp.) to gain insight into the functional significance of whistles. Results are based on focal observations and simultaneous recordings of underwater vocalizations. Whistles occur primarily when mother-infant pairs are separated, and the probability of whistles increases with distance of separation. The timing of whistles during separations varies, but whistles tend to be produced in repetitive series and are generally concentrated toward the later stages of the separation, i.e., during the process of reunion. Although we focused on infants, mothers do not appear to whistle during separations as frequently as infants. Infant whistles may function to facilitate reunions by conveying information to the mother concerning the infant's motivation to reunite and/or its location. Infant whistles could induce a cooperative response from the mother including approach, slowing to allow the infant to catch up or whistling. Highly individualized signature whistles may be particularly useful in a fission-fusion society in which individuals (mothers and infants as well as adults) join and leave temporary parties in a fluid manner, yet maintain consistent, long-term associations with particular individuals.
Correspondence to: R.A. Smolker 相似文献
1000.
Summary We hypothesise that foraging group size (FGS) and population group size (PGS) in primates and carnivores are related to quantifiable variables indexing the intensity of exploitative competition. Group size is predicted to increase with both food density and travel capabilities, as estimated by the constraint-free day-range (DRs), i.e. the day-range of a solitary individual uninfluenced by competition from conspecifics. We test this exploitation competition hypothesis among primates and carnivores, using data on populations, species and genera. Food density was indexed by population density. Where DRs could be estimated by regression it was found to be correlated with observed day-range (DRm). DRs was therefore indexed by DRm in all species. Population density and DRm were associated with each other, but in a multiple regression each variable contributed independently to explaining variation in group size. PGS was predicted better than FGS, but regressions involving either measure of group size were significant in all analyses. The multiple regression analyses were validated by the method of linear contrasts, which accounts for possible lack of independence among taxa. We conclude that species differences in group size are influenced by both food density and DRs. This suggests that variation in the intensity of exploitation competition is partly responsible for differences in group size.Correspondence to: R.W. Wrangham 相似文献