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231.
232.
Richard Frye James W. McFarland 《Journal of the American Water Resources Association》1980,16(1):31-35
ABSTRACT: The traditional “requirements” approach to water system planning presumes perfectly inelastic demand and arbitrarily selects a fixed water requirement per capita per day as a planning target. Economists have often pointed out that such a policy leads to over-investment in water supply facilities; a superior approach would maximize some measure of net benefits incorporating price-sensitive demand. Using a dynamic programming model to depict an investment problem in Rhode Island, we find that ambiguities about how to incorporate price-sensitive demand into a decision framework may make such an approach as arbitrary as the requirements approach. Water conservation responses may be a function of other social parameters than water price; if so, variations in these social parameters should be regarded as economic alternatives to water supply investments. 相似文献
233.
David W. Layton 《Journal of the American Water Resources Association》1978,14(1):133-143
Abstract: There are four known geothermal resource areas in the Imperial Valley that have a combined potential of over 4,000 megawatts of electrical energy for 25 years. Water resources available to support geothermal enerfy development are imprted Colorado River water, agricultural waste waters, Salton Sea water, and groundwater. In addtion, geothermal power plants can produce their own cooling water from steam condensate. Nevertheless, the relatively high water requirements of geothermal facilities along with a series of real and potential constraints may cause water supply dilemmas involving both the acquistion and use of cooling water. Important constraints are institutional policies, water supply costs, technical problems, and impacts upon the Salton Sea. These constranits and related dilemmas are examined in light of relevanty information on the valley's water resources, geothermal resources and energy technologies, cooling water requrements, and water supply options. 相似文献
234.
高氟环境对奶牛生产和繁殖性能的影响 总被引:3,自引:0,他引:3
通过检测宁夏某地奶牛内外环境中的饮水、饲料和土壤氟、硒、铜及血氟、毛氟、尿氟和全血硒、铜,证实该场奶牛高氟低硒低硐。日粮添加0。26mg/kg硒和3.2mg/kg铜。连续饲喂3个月,低硒低铜现象消失,但高氟仍旧存在。高氟使奶牛子宫复旧时间、首次发情时间 科后配妊天数分别延长6.6d、6d和38.5d,产后孕酮含量始终低于健康奶牛,同时,奶牛胎衣不下发病率和乳房炎发病率分别高于健康奶牛16.7%和1 相似文献
235.
Walter R. Tschinkel 《Behavioral ecology and sociobiology》1998,43(4-5):247-257
Many benefits and risks of cooperative colony founding (pleometrosis) have been identified, but rarely have the proximate
factors that lead to association been considered. This study examined the choices queens make during the first few hours after
mating, and some of the correlates of those choices. Queens had a strong affinity for preformed holes in the soil and readily
used these as their initial founding chambers. This affinity was so strong that in a field experiment, the dispersion pattern
of preformed holes controlled the final dispersion of colony-founding queens. Attraction to partially formed holes is thus
an important cause of pleometrosis. The excavation of complete founding chambers incurred no measurable cost on the subsequent
reproductive output of queens, suggesting that the primary benefit of using preformed holes is to remove the queen quickly
from exposure to predation and desiccation. In the field, pairs of queens offered five equivalent preformed holes in soil
were more likely to share the same hole if the holes were shallow and close together. In these experiments, queens modified
preformed soil holes so that the test holes were no longer equivalent, causing the choice of queen and hole to become confounded.
Laboratory experiments in plaster arenas with unmodifiable holes confirmed the field experiments: queens were more likely
to share a hole when the holes were shallow than when they were deep. Because queens entering adequately deep holes seldom
reemerged, this suggested that the likelihood of sharing increased with increasing contact between queens, that is, when queens
were readily and frequently detected. Such contacts will also predict the future competitive environments to be experienced
by incipient colonies, and may temper the tendency of queens to associate. However, experiments in which queens were exposed
to high and low densities before pairing in the choice arenas failed to show an effect on the choice to join the resident
queen. Queens that joined a resident queen differed in their robustness from queens that did not join. Queens choosing their
own partners did no better reproductively than those assigned partners at random. Overall, this study suggests that (1) newly
mated queens are under strong selection to leave the soil surface and do so by using any available holes, whether dug by another
queen or of some other origin; (2) they are attracted to other queens, and are more likely to cofound as contact with the
potential cofoundress becomes more frequent and (3) they choose whether or not to cofound partly on the basis of their own
reproductive characteristics.
Received: 20 November 1997 / Accepted after revision: 14 March 1998 相似文献
236.
The EU vision of sustainable agriculture, land use, forestry and management of natural resources contributes to the balanced exploitation of the environment, taking into account rural development strategy. Whilst the EU directs activities through legislative tools, national systems of public administration are responsible for the implementation of the respective laws. Despite there not being acquis communautaire in public administration, non-formal cooperation has nevertheless emerged and systems of national public administration have to meet EU criteria and ensure the effective implementation of legislation. The paper presents an analysis of how Slovak state administration has converged with EU requirements in the field of sustainable agriculture, land use, forestry and natural resources. Administrative convergence is considered through the internal convergence represented by capacities without legal subjectivity, and through external convergence represented by legal and administrative subjectivity. Both approaches are observed at the central level within specialized public authorities. Local state administration is characterized by the creation of internal administrative capacities with the challenging delimitation of which competences are affected by the process of administrative convergence. 相似文献
237.
The DCA (Drug Control Authority), Ministry of Health, Malaysia implemented the phase three registration of traditional medicines on January 1st, 1992. As such, a total of 100 products in various pharmaceutical dosage forms of a herbal preparation obtained in Malaysia, containing tongkat Ali hitam, either single or combined preparations, were analyzed for the contamination of a heavy toxic metal, lead, using atomic absorption spectrophotometer, after performing a simple random sampling to enable each sample an equal chance of being selected in an unbiased manner. Results showed that 17% of these products contained 10.3–20.3?ppm of lead, and therefore, do not comply with the quality requirement for traditional medicines in Malaysia. The quality requirement for traditional medicines in Malaysia is not exceeding 10?ppm for lead. Out of these 17 products, 7 products have been registered with the DCA, Malaysia whilst the rest, however, have not registered with the DCA, Malaysia. Although this study showed that 83% of the products complied with the quality requirement for traditional medicines in Malaysia pertaining to lead, however, they cannot be assumed safe from lead contamination because of the risk of batch-to-batch variability. 相似文献
238.
Isabelle Amat Emmanuel Desouhant Carlos Bernstein 《Behavioral ecology and sociobiology》2009,63(4):563-572
When foraging partially depleted patches (i.e., a fraction of hosts are already parasitized), female parasitoids must decide:
1—whether to superparasitize, and 2—whether to stay in their current patch (thus missing the opportunity of finding a better
patch elsewhere). To make these decisions, parasitoids may rely on different cues, produced both by the environment and by
conspecifics. Animals thriving in different environments may differ in cues they use. In the solitary parasitoid Venturia canescens, thelytokous (asexual) and arrhenotokous (sexual) individuals are found in two contrasting environments. Thelytokous females,
from anthropogenic conditions, are known to cope with superparasitism in an adaptive way. On the other hand, little is known
about superparasitism by arrhenotokous females. We compared the host exploitation strategies of thelytokous and arrhenotokous
females in partially depleted patches. Hosts parasitized by thelytokous females were more frequently avoided than those parasitized
by arrhenotokous females, suggesting a stronger chemical marking of the former. Only thelytokous females used information
from conspecifics for patch-leaving decisions. The conformity of the differences in the behavior of thelytokous and arrhenotokous
females with the environmental conditions they experience in their habitat is discussed. 相似文献
239.
240.
Ståle Liljedal Geir Rudolfsen Ivar Folstad 《Behavioral ecology and sociobiology》2008,62(11):1805-1811
In postcopulatory sexual selection both sperm competition and cryptic female choice are considered to be important selective
agents, but their relative importance for male fertilization success has received little attention. We tested whether sperm
quality, male spawning coloration, male heterozygosity, and genetic overlap with the female explained a male’s fertilization
success in controlled in vitro fertilization competition trials between equal numbers of sperm from pairs of male Arctic charr
(Salvelinus alpinus), an external fertilizer. Offspring were genotyped to determine each males’ share of paternity. The velocity of a male’s
sperm relative to the velocity of the competing male’s sperm was the best predictor of male fertilization success. Yet, sperm
velocity was not related to spawning coloration or male heterozygosity. In fact, the most brightly colored male in a pair
had the lowest fertilization probability. This could result from cryptic female choice for pale males, but might rather be
a result of paler males producing more competitive sperm than more colored males. Furthermore, the more microsatellite alleles
a male shared with the female relative to the competing male, the higher fertilization success he had. We argue that this
latter may be an effect of assortative cryptic female choice, which might prevent hybridization with sympatric Arctic charr
morphs or one form of kin selection. 相似文献