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301.
302.
污染稻、麦籽实中Cd、Cu、Pb的分布及其存在形态初探 总被引:31,自引:0,他引:31
采用组织化学及溶剂提取法研究了污染水稻、小麦籽实中Cd、Cu、Pb的分布及存在形态.结果表明,3种金属元素在水稻、小麦籽实各形态结构中的浓度具有明显不均一性,胚中浓度显著高于胚乳,颖壳,皮层中浓度也较高;糙米、麦粒中的Cd、Cu、Pb在去离子水、0.1mol EDTA、1%醋酸、2.5% NaCl、0.2%NaOH、70%乙醇中的溶出比例有显著差异;综合2项试验结果可以看出Cd、Cu、Pb在籽实中主要与谷物成分结合形成配合物,其优势形态是蛋白质结合态. 相似文献
303.
通过用氧化铝柱层析和等梯度呷醇:水=85%:15%)反相高效液相色谱(C18硅烷柱)紫外检测器254nm,测定30多种油品和我国海洋环境油类样品中的多环芳烃(PAHs),建立了溢油PAHs模糊指数结果表明,油类PAHs响应因子和相对保留值的变异系数分别在8.4%-16.5%和0.00%-5.4%之间,回收率在74.6%-111.2%之间,精密度和准确度较好;海洋环境油类的多环芳烃模糊指数值(0.00383-0.01839)与润滑油类的值(0.00106-0.00942)接近,较石油及其它产品油的值(0.06983-1.00000)低;用润滑油类作为标准油,PAHs模糊指数作为溢油芳烃类监测的指示物(指标),可提高监测海洋环境油类的代表性和可靠性 相似文献
304.
常压非平衡态等离子体降解挥发性烃类污染物 总被引:30,自引:1,他引:29
采用无声放电产生的非平衡态等离子体,对含有易挥发性有机化合物正己烷、环己烷、苯和甲苯4种典型的烃类废气的空气进行了处理.结果表明,对于一个大气压下正己烷含量(体积分数)为0.26%、0.79%、13%的宁气,在12kV的电压下放电ls,正己烷的降解率分别为88%、81.8%、64.9%.含有环己洗、苯及甲苯浓度为0.26%的空气,在同样的条件下,放电ls后,环己烷、苯及甲苯降解率分别为87.4%、8l%和70.3%,其主要降解产物为CO2和H2O.还研究了污染物浓度与氧含量对非平衡态等离子体法降解挥发性烃类污染物的影响 相似文献
305.
306.
307.
Pharmacophagous acquisition of clerodendrins by the turnip sawfly (Athalia rosae ruficornis) and their role in the mating behavior 总被引:3,自引:0,他引:3
Summary. Adults of the turnip sawfly, Athalia rosae ruficornis (Tenthredinidae: Hymenoptera), frequently visit a plant, Clerodendron trichotomum (Verbenaceae), and feed pharmacophagously on the glandular trichomes on the leaf surface. A series of neo-clerodane diterpenoids (e.g. clerodendrins B and D) contained in glandular organs on the leaf surface stimulate feeding of the sawflies (both males and
females). The adults fed selectively on the trichomes were found to sequester a series of the bitter-tasting diterpenes (clerodendrin
D, ajugachin A, athaliadiol) in the body tissues, which suggested their primary role as defense substances against predators.
Females fed on Clerodendron leaves or on clerodendrin B or D were more successful in mating than unfed females. Thus, females seem to obtain an advantage
in mating success through the acquisition of the defensive principles from the Clerodendron plant.
Received 20 April 1999; accepted 29 June 1999 相似文献
308.
Chemical defense and evolutionary trends in biosynthetic capacity among dorid nudibranchs (Mollusca: Gastropoda: Opisthobranchia) 总被引:5,自引:0,他引:5
Summary. An evolutionary scenario incorporating recent advances in phylogenetic research begins with an opisthobranch-pulmonate common
ancestor that was herbivorous and had some diet-derived chemical defense. The Nudibranchia and their closest relatives, the
Notaspidea, form a lineage the ancestors of which had switched to feeding upon sponges and deriving protection from metabolites
contained in them. Subsequently there have been repeated shifts in food and defensive metabolites, and trends are evident
in the ability to detoxify, sequester and utilize metabolites from food, as well as to synthesize defensive compounds de novo. The Notaspidea display a minor adaptive radiation that foreshadows a more extensive one in the various lineages of nudibranchs.
This review emphasizes changes that have occurred within the Holohepatica, or dorid nudibranchs (order Doridacea). Their sister-group,
the Cladohepatica, consists of three other orders, Dendronotacea, Arminacea, and Aeolidiacea, in which there has been a shift
from sponges to Cnidaria as food. The Dendronotacea often feed upon Octocorallia, which combine spicules, chemical defense,
and stinging capsules and thereby suggest a transition from feeding on sponges. A previous diet of Octocorallia is suggested
by the defensive use of prostaglandins in the dendronotacean Tethys fimbria, which eats crustaceans. A shift to bryozoans in some Arminacea is accompanied by use of different metabolites. Dorid nudibranchs
evidently began as sponge-feeders, but some lineages have shifted to a variety of other food organisms, and others have specialized
in the kind of sponges they feed on and how they do it. There have been shifts to bryozoans (Ectoprocta) and ascidians (Chordata:
Urochordata) that track metabolites rather than the taxonomy of the food. There is a crude correlation between the genealogy
and the defensive metabolites of the sponge-feeding dorids. De novo synthesis is well documented in this order and the metabolites are appropriately positioned so as to have an adaptive effect.
The hypothesis that the capacity for de novo synthesis was acquired by gene transfer across lineages is rejected, partly on the basis of different chirality of metabolites
in the nudibranchs and their food organisms. Instead it is proposed that there has been a preadaptive phase followed by evolution
in a retrosynthetic mode, with selection favoring enzymes that enhance the yield of end products that are already present
in the food.
Received 5 February 1999; accepted 26 July 1999 相似文献
309.
Summary. Several species of the flea beetles genus Longitarsus are able to sequester pyrrolizidine alkaloids (PAs) from their host plants. In five Longitarsus species we compare the concentration of PAs present in their host plants belonging to the Asteraceae or Boraginaceae with
those found in the beetles. To get an estimate of the intrapopulation variability, three samples of five beetles each and
five individual plants were analyzed for each comparison. A strong intrapopulation variability could be detected both among
plant and beetle samples. The total concentration found in the beetles varied strongly between species. The local host plant
and its phenology influence the concentrations present in the beetles as evidenced in comparisons of a single beetle species
from two different hosts and of one beetle species collected at the same site at different times of the year. In addition,
different beetle species apparently vary in their capacity to sequester the alkaloids, at the lowest extreme the mean PA concentration
in the beetles (0.034 μg PA/mg dry weight) was 1/30 of the mean concentration found in the plant leaves (L. aeruginosus from Eupatorium cannabinum), at the highest extreme (2.098 μg PA/mg dw) the concentration in the beetles was a 1000 fold higher than in the plant leaves
(L. nasturtii from Symphytum officinale). The highest mean concentration found in the beetles was 3.446 μg/mg dw (L. exoletus from Cynoglossum officinale). The absolute concentrations found in the beetles are comparable to other insects which have been shown to be effectively
defended against their potential predators.
Received 22 June 1999; accepted 25 August 1999 相似文献
310.
Andrés González Frank C. Schroeder Athula B. Attygalle Aleš Svatoš Jerrold Meinwald Thomas Eisner 《Chemoecology》1999,9(3):105-112
Summary. Female Photuris fireflies sequester defensive steroidal pyrones (lucibufagins) from male fireflies of the genus Photinus. Lucibufagin analyses of Photuris females and Photinus ignitus males show that the lucibufagin mixtures of predator and prey differ in their composition. Analyses of whole body extracts
showed that P. ignitus males contain a mixture of eight non-glycosylated lucibufagins, composed mostly of compounds with two oxygenated positions
in the steroidal A-ring (C-3, C-5). After feeding on P. ignitus males, Photuris females contain six major lucibufagins. Three of these compounds are not present in the prey, including the novel lucibufagin
glycoside 5β,11α-dihydroxy-12-oxo-3β-O-β-D-xylopyranosylbufalin, and two other lucibufagins with a trioxygenated A-ring (C-2,
C-3, C-5). These results indicate that Photuris females transform the sequestered lucibufagins both by glycosylation and oxidation, which could affect the systemic transportability
of these compounds due to an increase in their polarity.
Received 18 February 1999; accepted 19 April 1999. 相似文献