全文获取类型
收费全文 | 40596篇 |
免费 | 401篇 |
国内免费 | 292篇 |
专业分类
安全科学 | 1107篇 |
废物处理 | 1546篇 |
环保管理 | 5284篇 |
综合类 | 7592篇 |
基础理论 | 10891篇 |
环境理论 | 34篇 |
污染及防治 | 10484篇 |
评价与监测 | 2340篇 |
社会与环境 | 1764篇 |
灾害及防治 | 247篇 |
出版年
2022年 | 277篇 |
2021年 | 268篇 |
2019年 | 298篇 |
2018年 | 548篇 |
2017年 | 535篇 |
2016年 | 786篇 |
2015年 | 673篇 |
2014年 | 923篇 |
2013年 | 2902篇 |
2012年 | 1133篇 |
2011年 | 1683篇 |
2010年 | 1340篇 |
2009年 | 1407篇 |
2008年 | 1683篇 |
2007年 | 1795篇 |
2006年 | 1596篇 |
2005年 | 1322篇 |
2004年 | 1337篇 |
2003年 | 1271篇 |
2002年 | 1249篇 |
2001年 | 1542篇 |
2000年 | 1128篇 |
1999年 | 719篇 |
1998年 | 519篇 |
1997年 | 544篇 |
1996年 | 550篇 |
1995年 | 614篇 |
1994年 | 572篇 |
1993年 | 505篇 |
1992年 | 533篇 |
1991年 | 505篇 |
1990年 | 487篇 |
1989年 | 510篇 |
1988年 | 456篇 |
1987年 | 405篇 |
1986年 | 361篇 |
1985年 | 386篇 |
1984年 | 401篇 |
1983年 | 417篇 |
1982年 | 433篇 |
1981年 | 367篇 |
1980年 | 325篇 |
1979年 | 359篇 |
1978年 | 309篇 |
1977年 | 271篇 |
1976年 | 284篇 |
1975年 | 265篇 |
1974年 | 259篇 |
1973年 | 243篇 |
1972年 | 263篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
361.
Chromosomal and nuclear characteristics of deep-sea hydrothermal-vent organisms: correlates of increased growth rate 总被引:2,自引:0,他引:2
A range of tissue and cell types from adult and juvenile stages of vent- and non-vent-dwelling deep-sea and shallow-water organisms were compared for signs of cell division, in preparation for a cytogenetic study of the different groups. Virtually all the Mid-Atlantic Ridge (MAR) vent species (bresiliid shrimp, bathymodiolid mussel, branchipolynoid polychaete, and a range of small gastropods) showed an abundance of metaphase chromosome spreads, indicating a generally high intrinsic rate of cell division, irrespective of their phylogenetic group. In comparison, similar tissues and life-history stages (i.e. gonad, developing eggs and gill) from two deep-sea bathypelagic crustaceans, Hymenodora and Gnathophausia, failed to yield any convincing evidence of cell division. This indicated that rates of growth and reproduction in the rest of the deep sea are extremely low. While much has been written about the contrasting growth rates of vent versus non-vent organisms, this is the first direct evidence of differences in cell-division rate between vent and non-vent species, which undoubtedly reflects contrasting conditions relating to food availability and temporal stability in these two deep-sea environments. The cells of shallow-water marine invertebrates (Mytilus, Nucella, Littorina, Pomatoceros and Crangon), based on the results of previous cytogenetic investigations, occupy an intermediate position with respect to their cell-division kinetics. When chromosome numbers, DNA content and nuclear diameters were compared between vent and non-vent species, this showed that no change had occurred in these characters since the time of vent colonisation. Representative chromosome spreads from hydrothermal-vent organisms are shown here for the first time. 相似文献
362.
363.
M. Zimmer J. P. Danko S. C. Pennings A. R. Danford A. Ziegler R. F. Uglow T. H. Carefoot 《Marine Biology》2001,138(5):955-963
Three isopod species (Crustacea: Isopoda), commonly found in the intertidal and supratidal zones of the North American Pacific
coast, were studied with respect to symbiotic microbiota in their midgut glands (hepatopancreas). Ligia pallasii (Oniscidea: Ligiidae) contained high numbers of microbial symbionts in its hepatopancreatic caeca. Numbers of endosymbionts
were strongly reduced by ingestion of antibiotics. By contrast, the hepatopancreas of Idotea wosnesenskii (Valvifera: Idoteidae) and Gnorimosphaeroma oregonense (Sphaeromatidea: Sphaeromatidae) did not contain any microbiota. Results of feeding experiments suggest that microbial endosymbionts
contribute to digestive processes in L. pallasii, the most terrestrial of the three isopods that we studied. The acquisition of digestion-enhancing endosymbionts may have
been an important evolutionary step allowing isopods to colonize terrestrial habitats where relatively indigestible leaf litter
is the primary food source. By contrast, the ability to digest phenolic compounds was most developed in one of the more marine
species, suggesting that this trait may have evolved independently in isopod species that consume a phenolic-rich diet, whether
in marine habitats or on land.
Received: 28 August 2000 / Accepted: 8 December 2000 相似文献
364.
Spatial and temporal pattern in seagrass community composition and productivity in south Florida 总被引:4,自引:1,他引:3
We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance
of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites,
delimiting 12,800 km2 of seagrass beds in the 17,000-km2 survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km2. The range of T. testudinum was almost as extensive (6,400 km2), followed by Syringodium filiforme (4,400 km2), Halodule wrightii (3,000 km2) and Halophila engelmanni (50 km2 ). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m−2day−1, with a range of 0.05–3.29 g m−2 day−1. Specific productivity ranged between 3.2 and 34.2 mg g−1 day−1, with a mean of 18.3 mg g−1 day−1. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the
study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 1010 g S. filiforme, which translate to a yearly production of 9.4 × 1011 g T. testudinum leaves and 2.4 × 1011 g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing
these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as
a benchmark against which future change in the system can be quantified.
Received: 30 January 2000 / Accepted: 24 July 2000 相似文献
365.
M. Böhm U. Hentschel A. Friedrich L. Fieseler R. Steffen V. Gamulin I. Müller W. Müller 《Marine Biology》2001,139(6):1037-1045
The aim of this study was the documentation of the molecular immune response of Suberites domuncula upon bacterial infection. Additionally, the bacteria that are naturally present in the sponge after prolonged aquarium maintenance were characterized. After 6 months of maintenance of S. domuncula in seawater aquaria, only one bacterial 16S rDNA sequence could be recovered, which belongs to the genus Pseudomonas. Concomitantly, morphologically uniform bacteria were found encapsulated in bacteriocytes. These findings indicate that certain bacteria, possibly of the genus Pseudomonas, are able to persist for long periods in host bacteriocytes. Subsequent to performing a previously established infection assay with S. domuncula, a potentially pathogenic Vibrio sp. was isolated from the tissues. Furthermore, the host tissue disintegrated and asexual propagation bodies (gemmules) were formed. In order to gain insights into the molecular events occurring after bacterial infection, the stress-response kinases, p38 protein kinase and JNK protein kinase, were analyzed. It is demonstrated that these two kinases are activated (phosphorylated) upon incubation of the tissue with the bacterial endotoxin lipopolysaccharide (LPS). Moreover, LPS strongly inhibits protein synthesis. It is concluded that there are many functionally different interactions between S. domuncula and bacteria and that the animal possesses mechanisms to differentiate between bacteria and to respond accordingly. 相似文献
366.
We determined the nuclear 18S rRNA sequences for 41 species of octocorals and used these to address the validity of the historical
ordinal divisions and the current subordinal divisions within the subclass Octocorallia. We also explored the phylogenetic
affinities of the species Dendrobrachia paucispina, which was originally classified in the order Antipatharia (subclass Ceriantipatharia) although polyp structure indicates
it belongs in the subclass Octocorallia. Trees constructed using maximum likelihood techniques are incongruent with the current
and historical taxonomy of the Octocorallia. There appeared to be three major clades of octocorals. The first clade included
most, but not all, pennatulaceans as a monophyletic group. The second clade contained 21 species, representing all major octocoral
groups other than pennatulaceans. The third clade contained members from three suborders of the Alcyonacea and one member
of the Pennatulacea. These data could not be used to distinguish the branching order of the three major clades. The species
D. paucispina had a close affinity with the genera Corallium and Paragorgia (Alcyonacea: Scleraxonia), although its morphology suggests it is more similar to the genus Chrysogorgia (Alcyonacea: Calcaxonia). The morphological character of dimorphism (the presence of both autozooids and siphonozooids within
a single colony) corresponded loosely with the topology of the most likely trees, and a single origin of dimorphism could
not be rejected. Despite sampling from the majority of families within the Octocorallia, many of the relationships within
this group remain ambiguous.
Received: 16 June 2000 / Accepted: 14 September 2000 相似文献
367.
The caridean shrimp Lysmata wurdemanni (Gibbes) displays protandric simultaneous hermaphroditism with out-crossing, but not all males become simultaneous hermaphrodites (euhermaphrodites). In this laboratory study, we attempted to determine why some shrimp remain males. In our experiment, we grew L. wurdemanni from postlarvae to adults in several group sizes and observed their reproductive function. We found that all shrimp reared in isolation become euhermaphrodites. When cultured in a group, the proportion of shrimp remaining male decreased with increasing group size. Except for those that mated within a day, inter-molt euhermaphrodite-phase shrimp (with or without embryos) and inter-molt male-phase shrimp fertilized eggs successfully. On the other hand, euhermaphrodite shrimp can only mate as females and have their eggs fertilized during a narrow post-molt window (less than 12 h) in each molt cycle (10 days). The fertilization rate of male-euhermaphrodite pairs was similar to that of euhermaphrodite-euhermaphrodite pairs. There are at least two non-exclusive explanations for the persistence of male shrimp in a group. In certain group compositions, an individual may gain more reproductive fitness as a large male with multiple mating partners than as a small female with low clutch size. Alternatively, the presence of male-phase individuals, with variable molt-cycle duration (5-8 days), may be necessary to ensure mating. This study is the first direct experimental demonstration of social control of sex change in the decapod crustaceans. 相似文献
368.
A Systematic Test of an Enterprise Strategy for Community-Based Biodiversity Conservation 总被引:6,自引:0,他引:6
N. Salafsky H. Cauley G. Balachander B. Cordes J. Parks C. Margoluis S. Bhatt C. Encarnacion D. Russell R. Margoluis 《Conservation biology》2001,15(6):1585-1595
Abstract: A commonly held belief is that if people can benefit financially from enterprises that depend on nearby forests, reefs, and other natural habitats, then they will take action to conserve and sustainably use them. The Biodiversity Conservation Network brought together conservation and development organizations and local communities to systematically test this hypothesis across 39 conservation project sites in Asia and the Pacific. Each project implemented one or more community-based enterprises such as setting up an ecotourism lodge, distilling essential oils from wild plant roots, producing jams and jellies from forest fruits, harvesting timber, or collecting marine samples to test for pharmaceutical compounds. Each project team collected the biological, enterprise, and social data necessary to test the network's hypothesis. We present the results of this test. We found that a community-based enterprise strategy can lead to conservation, but only under limited conditions and never on its own. We summarize the specific conditions under which an enterprise strategy will and will not work in a decision chart that can be used by project managers to determine whether this strategy might make sense at their site. We also found that an enterprise strategy can be subsidized and still create a net gain that pays for conservation. Based on our experiences, we recommend developing "learning portfolios" that combine action and research to test other conservation strategies. 相似文献
369.
One-day-old anarchistic (selected for successful worker reproduction) and wild-type honey-bee workers were introduced into queenright colonies of honey-bees of two treatments. In treatment 1, all eggs and larvae were offspring of queens from an anarchistic line. In treatment 2, all eggs and larvae were offspring of wild-type queens. In both treatments, adult workers were wild type. This experimental arrangement was used to test the importance of larval genotype on ovary activation in young adult workers. After 12 days, the introduced bees were dissected to determine the frequency of ovary activation. In those colonies provided with wild-type brood, 0% of introduced wild-type bees and 16% of anarchistic bees had activated ovaries. In those colonies provided with anarchistic brood, 13% of introduced wild-type bees and 41% of anarchistic bees had activated ovaries. These results strongly support the hypothesis that selection for high levels of worker reproduction in anarchistic stocks has reduced the amount or composition of brood pheromones produced by larvae that normally signal workers to refrain from reproduction. They also suggest that anarchistic workers have a higher threshold for these signals than wild-type bees. 相似文献
370.