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141.
Filippo Galimberti Simona Sanvito Chiara Braschi Luigi Boitani 《Behavioral ecology and sociobiology》2007,62(2):159-171
Reproductive effort is a key parameter of life history because it measures the resources allocated to reproduction at the
expense of growth and maintenance. Male reproductive effort always had a minor role with respect to female effort both in
the development of theories and in field research. Elephant seals are an ideal subject for reproductive effort studies because
they fast during the breeding season, splitting the phase of energy acquisition from the phase of energy use for breeding.
In this paper, we present results on male reproductive effort (weight loss estimated by photogrammetry) in southern elephant
seals (Mirounga leonina), the most dimorphic and polygynous of all mammal species. We show that total reproductive effort increases with age, with
no sign of late decrease or senescence. Male reproductive effort in this species depends mostly on behavioral factors, i.e.,
the success in competition with other males, and the intensity of interaction with females. A large effort results in large
gains in both mating success and fertilizations. The large reproductive success that a few males are able to achieve come
at a big cost in terms of energy expenditure, but this cost does not seem to affect the likelihood of survival to the following
breeding season. 相似文献
142.
This work aims at discussing some concepts pertaining to the theory and practice of environmental modelling in view of the results of several model validation exercises performed by the group “Model validation for radionuclide transport in the system watershed-river and in estuaries” of project EMRAS (Environmental Modelling for Radiation Safety) supported by the IAEA (International Atomic Energy Agency). The analyses here performed concern models applied to real scenarios of environmental contamination. In particular, the reasons for the uncertainty of the models and the EBUA (empirically based uncertainty analysis) methodology are discussed. The foundations of multi-model approach in environmental modelling are presented and motivated. An application of EBUA to the results of a multi-model exercise concerning three models aimed at predicting the wash-off of radionuclide deposits from the Pripyat floodplain (Ukraine) was described. Multi-model approach is, definitely, a tool for uncertainty analysis. EBUA offers the opportunity of an evaluation of the uncertainty levels of predictions in multi-model applications. 相似文献
143.
Forty-two samples of building materials commonly used in Italian dwellings were surveyed for natural radioactivity. External (gamma), as defined and used by the European Commission, and internal (alpha) hazard indexes were calculated and radon specific exhalation rate and emanation fraction were measured. The accumulation method, by using the E-PERM electret ion chambers, was employed to determine specific exhalation rates of 222Rn. Several of the materials had hazard indexes that exceeded the European Commission limit values. However, it was evident that limit values for internal hazard indexes set based on Rn emanation should take into account the properties and use of the materials. For example, Rn emanation from basalt and glazed tiles was substantially lower than the Rn emanation from other materials with similar hazard indexes. Clearly there is need for improved guidelines and regulations in this area. 相似文献
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146.
The paper presents the results of a study on radiological impacts resulting from a zircon sand processing plant located in the North-Eastern part of Italy. Activity concentrations of radionuclides found in materials associated with this industrial process are presented as well as the results of the assessment of the annual effective doses to the workers and the members of the public. Gamma-spectrometric analyses were performed on "raw" sands, end-products, and soils sampled near the plant. Thermoluminescent dosimeters, electric pumps and electret ion chambers were used to measure the external irradiation, the indoor dust concentrations and the radon concentrations, respectively. The ground-level air concentration of radioactive particulate near the plant and the deposition of particulate matter were estimated by a Gaussian model (ISCLT3). Finally, the annual effective doses, calculated as provided for by Directive 96/29/Euratom, were estimated to be 1.7 mSv y(-1) for workers and 4.4 microSv y(-1) for members of the public. 相似文献
147.
148.
Approaches to semi-synthetic minimal cells: a review 总被引:1,自引:0,他引:1
Following is a synthetic review on the minimal living cell, defined as an artificial or a semi-artificial cell having the
minimal and sufficient number of components to be considered alive. We describe concepts and experiments based on these constructions,
and we point out that an operational definition of minimal cell does not define a single species, but rather a broad family
of interrelated cell-like structures. The relevance of these researches, considering that the minimal cell should also correspond
to the early simple cell in the origin of life and early evolution, is also explained. In addition, we present detailed data
in relation to minimal genome, with observations cited by several authors who agree on setting the theoretical full-fledged
minimal genome to a figure between 200 and 300 genes. However, further theoretical assumptions may significantly reduce this
number (i.e. by eliminating ribosomal proteins and by limiting DNA and RNA polymerases to only a few, less specific molecular
species). Generally, the experimental approach to minimal cells consists in utilizing liposomes as cell models and in filling
them with genes/enzymes corresponding to minimal cellular functions. To date, a few research groups have successfully induced
the expression of single proteins, such as the green fluorescence protein, inside liposomes. Here, different approaches are
described and compared. Present constructs are still rather far from the minimal cell, and experimental as well as theoretical
difficulties opposing further reduction of complexity are discussed. While most of these minimal cell constructions may represent
relatively poor imitations of a modern full-fledged cell, further studies will begin precisely from these constructs. In conclusion,
we give a brief outline of the next possible steps on the road map to the minimal cell.
相似文献
Pier Luigi Luisi (Corresponding author)Email: |
Francesca FerriEmail: |
Pasquale StanoEmail: |
149.
False negative detections may bias the surveys for rare species and reduce the reliability of models based on the proportion
of occupied patches. We assessed the detectability of the Eurasian otter Lutra lutra through the standard survey method by analysing the detection history of 28 sampling stretches surveyed monthly between March
2001 and January 2003. Each survey negative for otter spraints was considered as a false negative if the otter had been recorded
in the previous and/or following month (respectively, cFN and FN). Otter marking intensity (MI) (MI=N° of spraints per kilometre)
was calculated and assumed to represent an index of its relative abundance. Spraints were found in 81.7% of all surveys. Yearly
MI ranged from 1.02 to 101.4 spraints per kilometre. In 2002, mean MI was significantly lower than in the previous year, while
no clear seasonal trend could be outlined. The minimum number of surveys required to establish the occurrence of the otter,
as estimated by a probability model, was 2.6 and was inversely related to MI. For a sub-sample of 18 sampling stretches, the
relation between the frequency of both cFN and FN and five variables of potential interest for otters was tested by means
of stepwise linear multiple regressions, yielding two highly significant models, which both included only MI as the explanatory
variable. The frequency of both FN and cFN was correlated to MI and the resulting equations used to assess the percentage
of surveys positive for otters in both years. After the correction for non-detections, otter site occupancy did not vary between
the 2 years, except for one river when applying the more conservative estimate of false negatives (cFN). Multiple visits and
the assessing of MI should become standard components of otter surveys. This approach has broad applicability and may be applied
to assess the large-scale distribution of other rare or elusive mammalian carnivores. 相似文献