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排序方式: 共有1143条查询结果,搜索用时 15 毫秒
471.
Frans J. Los MD Adriana M. Hagenaars Jan Marrink Titia E. Cohen-Overbeek Johannes L. J. Gaillard Helen Brandenburg 《黑龙江环境通报》1992,12(4):285-292
Early second-trimester oligohydramnios was associated with normal maternal serum alpha-fetoprotein (MSAFP) levels in nine out of 26 cases (35 per cent). Congenital malformations of the fetal urinary tract resulting in fetal anuria were present in nine cases; in seven of them, normal MSAFP levels were measured. In contrast, normal MSAFP levels were established in only 2 out of the 17 cases without fetal malformations. These data suggest that fetal urine is the major source of elevated AFP in the maternal compartment in early second-trimester oligohydramnios. This is further supported by the lack of any relationship between concentrations of MSAFP non-reactive with Concanavalin A, originating mainly from the yolk sacderived amniotic fluid AFP pool, and the presence of fetal diuresis. Three out of 26 women had experienced early second-trimester oligohydramnios in a previous pregnancy, suggesting the existence of a recurrence risk for this condition. 相似文献
472.
Jan Ahlers Andreas Gies und J?rn Wogram 《Umweltwissenschaften und Schadstoff-Forschung》2004,16(4):217-218
Ohne Zusammenfassung 相似文献
473.
Potentials and drawbacks of chelate-enhanced phytoremediation of soils. 总被引:28,自引:0,他引:28
Paul R?mkens Lucas Bouwman Jan Japenga Cathrina Draaisma 《Environmental pollution (Barking, Essex : 1987)》2002,116(1):109-121
Chelate-enhanced phytoremediation has been proposed as an effective tool for the extraction of heavy metals from soils by plants. However, side-effects related to the addition of chelates, e.g. metal leaching and effects on soil micro-organisms, were usually neglected. Therefore, greenhouse and lysimeter studies were conducted to study the phytoremedation potential of EDGA and citric acid and to evaluate its effects on microbial activity and leaching of Cd, Zn Cu and Pb. Grass, lupine and yellow mustard were grown on a moderately polluted acid (pH 4.5) sandy soil that contained 2 mg kg(-1) Cd and 200 mg kg(-1) Zn. Citric acid appeared to be degraded microbially within a few days after addition which limited its potential for long-lasting remediation studies. EDGA enhanced metal solubility but plant uptake did not increase accordingly. The metal shoot:root ratio increased upon addition of EDGA but it also reduced the net shoot and root biomass production of both lupine and yellow mustard. Bacterial biomass was higher in both the citric and EDGA treated pots but bacterial activity remained unaffected. The number of microbivorous nematodes was greatly reduced upon addition of EDGA which was most likely related to the reduced biomass production and, to a smaller extent, to the changes in the composition of the available food. Furthermore, EDGA enhanced metal leaching in the lysimeter study which could lead to groundwater pollution. To prevent these unwanted side-effects, careful management of phytoremediation methods, therefore, seems necessary. 相似文献
474.
Klaus Schneider Jan Oltmanns Thomas Radenberg Thomas Schneider Dagmar Pauly-Mundegar 《Environmental science and pollution research international》1996,3(3):135-138
The uptake of nitroaromatic compounds by plants from the soil was studied at an ammunition site. After the development of analytical methods for 2,4,6-trinitrotoluene, aminodinitrotoluenes and dinitrotoluenes in plant material, we could show that these substances accumulated in the roots of plants and are found to a lesser extent inleaves and stems. We observed only moderate differences between various plant species. It is likely that a metabolic transformation in plants leads to the formation of dinitrotoluenes which are considered to be potent carcinogens. Results from soils with a wide range of explosive concentrations show a good correlation between the plant and soil concentrations. The relative accumulation in plant material is higher at lower soil concentrations. At low soil concentrations of about 1 mg trinitrotoluene/kg soil, an accumulation factor of about 0.5 can be derived. These data are an important input for the risk assessment of ammunition sites. 相似文献
475.
476.
477.
The influence of copper(II)chloride on selected key enzymes and metabolites in intermediary metabolism and the energy charge potential of the hyperregulating shore crab, Carcinus maenas (L.) were investigated. Crabs, collected in Odense Fjord, Denmark between September 1989 and May 1990, were exposed to 10 ppm copper(II)chloride, in 10 ppt salinity seawater at 15°C for up to 1 wk. Hexokinase activity was 77% lower in the posterior gills and 60% lower in the midgut gland than in control crabs. Phosphofructokinase activity was reduced in the midgut gland by 82% but was unaffected in the gills. Pyruvate kinase activity was undetectable in the gills of exposed crabs and reduced by 47% in the midgut gland. Citrate synthase activity was depressed by 30% in the posterior gills and unaffected in other tissues. Copper exposure had no apparent effect on tissue cytochrome c oxidase activity. Chela muscle was the only tissue in which copper exposure did not bring about reductions in the enzyme activities tested. As a result of 1 wk of copper exposure the average lactate level increased by 3.5-fold in haemolymph, 9.3-fold in posterior gills and 6.5-fold in midgut gland. The average glucose level was raised by a factor of 6 in the haemolymph, 3.4 in the posterior gills and 1.2 in the midgut gland. Energy charge potential was at a very high level (ca. 0.9) and was unaffected by copper exposure. 相似文献
478.
479.
Dominance relationships in solitary species may be an important factor in the maintenance of long-term, stable relationships
among territorial neighbors. We examined the mediation of intraspecific interactions in a solitary, territorial kangaroo rat,
Dipodomys heermanni, and tested whether unfamiliar kangaroo rats establish a dominance hierarchy and then decrease aggression and increase communication
(via footdrumming and sandbathing) after initial interactions and the establishment of a social structure. Results revealed
that both dominance hierarchies and familiarization with particular individuals are likely to mediate social interactions.
After only one pairing per dyad, an almost linear dominance hierarchy emerged, which became perfectly linear after a 90-min
familiarization period. During the course of subsequent interactions between dyad partners, fighting decreased and non-agonistic
communication increased. Dominant kangaroo rats sandbathed at higher rates than subordinates, possibly to deposit scent to
advertise competitive ability, whereas subordinate kangaroo rats footdrummed from inside the burrow, which seemed to indicate
an unwillingness to interact. We suggest the kangaroo rats use a conditional strategy when deciding to fight (be dominant)
or withdraw (be subordinate) by employing different modes to communicate status and minimize the potential risk of injury
during unnecessarily prolonged fights. 相似文献
480.