全文获取类型
收费全文 | 762篇 |
免费 | 39篇 |
国内免费 | 126篇 |
专业分类
安全科学 | 98篇 |
废物处理 | 18篇 |
环保管理 | 92篇 |
综合类 | 396篇 |
基础理论 | 171篇 |
污染及防治 | 57篇 |
评价与监测 | 32篇 |
社会与环境 | 40篇 |
灾害及防治 | 23篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 24篇 |
2014年 | 23篇 |
2013年 | 51篇 |
2012年 | 54篇 |
2011年 | 48篇 |
2010年 | 31篇 |
2009年 | 49篇 |
2008年 | 57篇 |
2007年 | 73篇 |
2006年 | 64篇 |
2005年 | 43篇 |
2004年 | 38篇 |
2003年 | 30篇 |
2002年 | 32篇 |
2001年 | 31篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 15篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有927条查询结果,搜索用时 453 毫秒
201.
水中有机成分及其对饮用水质的影响 总被引:3,自引:0,他引:3
微量有机污染物和氯化消毒副产物对饮用水构成直接威胁,是饮用水中要重点控制的;天然大分子有机物对水质构成间接影响,导致胶体稳定性提高、增加药耗;藻类和代谢产物影响常规处理工艺效果,对水质产生不良影响。 相似文献
202.
邻苯二酚2,3-双加氧酶基因克隆、定位和高效表达 总被引:8,自引:2,他引:8
采用特异性引物,以菲、芘降解菌株ZL5的代谢性质粒为模板,扩增出邻苯二酚2,3—双加氧酶(C23O)基因,将该基因和表达载体pET—30a( )连接,转化E.coli JM109(DE3),获得了高效表达的转化子,SDS—PAGE结果表明,转化子的C23O蛋白不仅在细胞内存在,而且能被分泌到胞外,薄层扫描显示,转化子细胞内和细胞外表达蛋白总量占细胞总蛋白的42%,酶活分析表明,分布在转化子细胞内、外的表达蛋白都具有较高的C23O比活力,Southern杂交将菌株ZL5的C23O基因定位在内生质粒的不同酶切片段上。图5表1参12。 相似文献
203.
Jacques M. Pasteels Claudine Theuring Donald M. Windsor Thomas Hartmann 《Chemoecology》2003,13(1):55-62
Summary. Sequestration and processing of pyrrolizidine alkaloids
(PAs) by leaf beetles of the genus Platyphora were investigated. Tracer
experiments with labeled alkaloids were performed with P. eucosma
feeding on Koanophyllon panamense (Asteraceae, tribe Eupatorieae). P.
eucosma catalyzes the same reactions previously demonstrated for P.
boucardi specialized to Prestonia portobellensis (Apocynaceae): (i)
epimerization of rinderine to intermedine; (ii) esterification of
retronecine yielding insect-specific PAs; (iii) efficient transport of
the PAs as free bases into the defensive secretions. P. bella feeding on
Tournefortia cuspidata (Boraginaceae) shows the same sequestration
behavior and ability to synthesize the specific retronecine esters. P.
ligata, a species phylogenetically closely related to the PA adapted
species and clustering in the same clade, but feeding on a host plant
devoid of PAs, feeds easily on PA treated host-plant leaves, but does
not sequester or metabolize PAs. P. kollari a species clustering outside
the PA clade refused to feed on its food-plant leaves painted with PAs.
The results are discussed in relation to host-plant selection of the PA
adapted species and the role of PAs in chemical defense.
Received 20 September 2002; accepted 18 November 2002. 相似文献
204.
Cédric Alaux Malvina Boutot Pierre Jaisson Abraham Hefetz 《Behavioral ecology and sociobiology》2007,62(2):213-222
Worker sterility in the bumblebee Bombus terrestris is conditional and is linked to the social development of the colony. Workers refrain from reproducing or overtly challenging
the queen until gyne production has initiated, at the so-called competition point (CP). It is not known whether this behavior
is hard-wired or workers show reproductive plasticity. It also remains unclear whether worker reproductive decision is under
queen and/or worker control. In this study, we tested worker reproductive plasticity in an attempt to assess whether and under
which conditions worker sterility/fertility are reversible. We introduced egg-laying workers into colonies with different
social structures for 1 week then monitored their reproductive status. We revealed a remarkable reproductive plasticity in
the introduced workers that was social-condition-dependent. In the presence of a pre-CP queen, the introduced workers reverted
to sterility, whereas in the presence of a post-CP queen, such workers remained egg-layer. Reversion to sterility does not
occur when direct contact with the queen is prevented, as the introduced workers remained egg-layer in the queenright colonies
with a confined queen. Egg-laying workers that were introduced into queenless colonies mostly maintained their fertility regardless
of colony social phase. This shows that worker transition from cooperative to selfish behavior is reversible depending on
the social context. 相似文献
205.
Summary. Larvae of the turnip sawfly, Athalia rosae L. (Hymenoptera: Tenthredinidae), sequester glucosinolates of their host plants, namely members of the Brassicaceae family,
in their haemolymph. Therefore, they need to circumvent myrosinase activities of the plant tissue which normally hydrolyse
the glucosinolates after plant damage. Effects of varying levels of glucosinolates and myrosinases on the performance of A. rosae were investigated using homozygous lines of Brassica juncea (L.) with either (1) low glucosinolate (lowGS) and low myrosinase (lowMR), (2) high glucosinolate (highGS) and high myrosinase (highMR), or (3) high glucosinolate (highGS) and low myrosinase (lowMR) levels. To insure that the given quantities remained as constant as possible, newly hatched larvae were enclosed on the
second-youngest leaf of a plant, and were offered a new plant of comparable physiological age (6-leaf-stage) every day. The
performance of A. rosae was little affected by leaf quality. Body masses of eonymphs and adults were on average lowest on the highGS/highMR-line, but these differences were rarely significant. The pupal developmental times of females and males were longest on
the highGS/lowMR-line in only one of two replicate experiments. All other performance traits (developmental times of larvae, egg numbers,
adult longevity) were not significantly different. Glucosinolates, sequestered by the larvae, are carried through the pupal
stage. The glucosinolate concentration measured in adult insects reflected the level of the host plant line, without showing
any obvious costs for sequestration. Obviously, A. rosae is highly tolerant to variation in the glucosinolate-myrosinase system of its host.
In addition, induced changes of glucosinolate concentrations and myrosinase activities caused by 24 h-feeding of groups of
three small larvae were analysed in the second-youngest leaves. In contrast to the patterns most herbivores evoke on Brassicaceae,
namely an increase of both glucosinolate concentration and myrosinase activity, we detected a significant decrease of both
traits in all three lines where the respective trait was originally high in the plants. Although glucosinolate levels dropped in the highGS lines about 50%, these still contained higher concentrations than the lowGS line. Whereas the activity of soluble myrosinases remained highest in the highMR line, even after a decrease to almost 30% due to feeding, the levels of insoluble myrosinases converged after feeding in
lowMR and highMR lines. Levels of the signalling molecule salicylic acid slightly decreased on average after feeding, whereas jasmonic acid
was below the detection threshold in almost all samples. The concentration of several molecules varies strongly in plant tissue
with age and can change due to induction by herbivore feeding. Therefore, if performance of an insect species is measured
on plants with specific traits, the variability in these traits needs to be carefully controlled in experiments. 相似文献
206.
Central-place foraging theory has been unable to explain the load selection behavior of leaf-cutting ants (Atta spp., Attini: Formicidae). We suggest that this is due to incomplete consideration of the sequence of behaviors involved in resource acquisition by these ants. Unlike most central-place foragers, leaf-cutting ants do not return to their nests with food. Instead, the leaf fragments they gather must be processed within the nest to convert them to substrate for fungal gardens. We have shown previously that leaf fragment size affects the rate of distribution and processing of leaf tissue inside laboratory nests of Atta colombica. Including these tasks in the calculation of foraging rate may help explain load selection and other features of central-place foraging by Atta colonies. Here we develop a mathematical model of the complete sequence of external and internal tasks that lead to addition of substrate to fungal gardens. Using realistic parameter values, the leaf fragment sizes predicted to maximize a colony's rate of foraging in this broad sense correspond well with the mean fragment sizes actually collected by Atta colonies in the field. The optimal fragment size for global performance in the model is below the size that would maximize the delivery rate by above-ground foragers. The globally optimal size also fails to maximize the rate of either fragment distribution or fragment processing within the nest. Our results show how maximum collective performance of an ensemble of linked tasks may require behavior that would appear suboptimal in a piecemeal analysis of tasks. 相似文献
207.
Anna K. Hundsdoerfer Jeannette Ndaya Tshibangu Bernhard Wetterauer Michael Wink 《Chemoecology》2005,15(4):261-267
Summary. The larvae of the hawkmoth species Hyles euphorbiae have a conspicuous aposematic colouration and show gregarious behaviour. It has thus been suggested that they sequester phorbol
esters from their food plants which include different species of the genus Euphorbia (Euphorbiaceae) for chemical protection against predators. To test this hypothesis in more detail, we fed larvae an artificial
diet with three doses of 12-tetradecanoyl-phorbol-13-acetate (TPA), then examined the faeces and the larval tissues, such
as integument, haemolymph and gut of the caterpillars for the presence of TPA. In order to determine the ability of the larvae
to detoxify phorbol esters, other larvae were directly injected with a TPA solution and analysed in the same manner. Our study
indicates that the larvae of Hyles euphorbiae do not sequester phorbol esters. Upon oral application TPA was not found in the larval integument or the haemolymph. Instead,
it was mostly metabolised (about 70–90%). Nevertheless, about 10-30% were retained and recovered in the faeces. The larvae
were also able to metabolise and thus detoxify the phorbol ester when TPA was injected directly into the body. These hawkmoth
caterpillars are relatively large and have a gut full of plant material, which they regurgitate into the direction of the
predator when attacked in nature. Since phorbol esters are very potent toxins and irritants, we postulate that the gut content
(and especially the plant slurry disgorged as regurgitant from the anterior gut) alone could be aversive for a potential predator,
even if some metabolism has taken place. Thus, although H. euphorbiae caterpillars do not actively sequester phorbol esters, their aposematic colouration appears to be based on chemical defence
through phorbol esters retained in the gut. 相似文献
208.
耕地土壤碳固存的措施与潜力 总被引:3,自引:0,他引:3
土壤CO2排放与土壤退化、土壤有机质(SOC)含量减少和土壤质量下降密切相关。耕地具有较大的碳固存潜力。通过采用最佳管理措施(BMPs)和进行土壤修复来提高土壤质量,能增加SOC含量和提高土壤生产力,并能部分起到减缓温室效应的作用。文章从土壤固碳的机制入手,系统总结了在耕作土壤碳固存方面的研究。从土壤侵蚀控制、退化土壤修复、保护性耕作、残落物管理,改善农作物制度等方面,论述了耕地的固碳潜力,并提出了一系列实现碳固存的措施。最后估算出耕地土壤总的固碳潜力为0.73~0.87Pg/a。研究表明,在替代性能源开发之前,耕地碳固存是一项切实可行的措施。 相似文献
209.
Robert E. Page Jr. Gene E. Robinson M. Kim Fondrk Medhat E. Nasr 《Behavioral ecology and sociobiology》1995,36(6):387-396
There have been numerous reports of genetic influences on division of labor in honey bee colonies, but the effects of worker genotypic diversity on colony behavior are unclear. We analyzed the effects of worker genotypic diversity on the phenotypes of honey bee colonies during a critical phase of colony development, the nest initiation phase. Five groups of colonies were studied (n = 5–11 per group); four groups had relatively low genotypic diversity compared to the fifth group. Colonies were derived from queens that were instrumentally inseminated with the semen of four different drones according to one of the following mating schemes: group A, 4 A-source drones; group B, 4 B-source drones; group C, 4 C-source drones; group D, 4 D-source drones; and group E, 1 drone of each of the A-D drone sources. There were significant differences between colonies in groups A-D for 8 out of 19 colony traits. Because the queens in all of these colonies were super sisters, the observed differences between groups were primarily a consequence of differences in worker genotypes. There were very few differences (2 out of 19 traits) between colonies with high worker genotypic diversity (group E) and those with low diversity (groups A-D combined). This is because colonies with greater diversity tended to have phenotypes that were average relative to colonies with low genotypic diversity. We hypothesize that the averaging effect of genotypic variability on colony phenotypes may have selective advantages, making colonies less likely to fail because of inappropriate colony responses to changing environmental conditions. 相似文献
210.
There is a genetic component to plasticity in age polyethism in honey bee colonies, such that workers of some genotypes become precocious foragers more readily than do workers of other genotypes, in colonies lacking older bees. Using colonies composed of workers from two identifiable genotype groups, we determined that intracolony differences in the likelihood of becoming a precocious forager are a consequence of differences in rates of behavioral development that are also evident under conditions leading to normal development. An alternative hypothesis, that differences in the likelihood of becoming a precocious forager are due to differences in general sensitivity to altered colony conditions, was not supported. In three out of three trials, workers from the genotype group that was more likely to exhibit precocious foraging in single cohort colonies also foraged at relatively younger ages in colonies in which workers exhibited normal behavioral development. In contrast, in three out of three trials, workers from the genotype group that was more likely to exhibit precocious foraging in single-cohort colonies did not show disproportionately more overaged nursing in colonies in which workers exhibited delayed development. These results indicate that genotypic differences in plasticity in age-related division of labor are based on genotypic differences in rates of behavioral development. 相似文献