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101.
E. Z. Cameron W. L. Linklater K. J. Stafford E. O. Minot 《Behavioral ecology and sociobiology》2000,47(4):243-249
In many mammalian species, female success in raising offspring improves as they age. The residual reproductive value hypothesis
predicts that each individual offspring will be more valuable to the mother as she ages because there is less conflict between
the current and potential future offspring. Therefore, as mothers age, their investment into individual offspring should increase.
Empirical evidence for an influence of declining residual reproductive value on maternal investment is unconvincing. Older
mothers may not invest more, but may be more successful due to greater experience, allowing them to target their investment
more appropriately (targeted reproductive effort hypothesis). Most studies do not preclude either hypothesis. Mare age significantly
influenced maternal investment in feral horses living on the North Island of New Zealand. Older mares, that were more successful
at raising foals, were more protective for the first 20 days of life, but less diligent thereafter. Total maternal input by
older mothers did not seem to be any greater, but was better targeted at the most critical period for foal survival and a
similar pattern was observed in mares that had lost a foal in the previous year. In addition, older mothers were more likely
to foal in consecutive years, supporting the hypothesis that they are investing less than younger mares in individual offspring.
Therefore, older mothers seem to become more successful by targeting their investment better due to experience, not by investing
more in their offspring.
Received: 22 September 1999 / Received in revised form: 30 October 1999 / Accepted: 6 November 1999 相似文献
102.
103.
Fujita EM Zielinska B Campbell DE Arnott WP Sagebiel JC Mazzoleni L Chow JC Gabele PA Crews W Snow R Clark NN Wayne WS Lawson DR 《Journal of the Air & Waste Management Association (1995)》2007,57(6):705-720
The U.S. Department of Energy Gasoline/Diesel PM Split Study examined the sources of uncertainties in using an organic compound-based chemical mass balance receptor model to quantify the contributions of spark-ignition (SI) and compression-ignition (CI) engine exhaust to ambient fine particulate matter (PM2.5). This paper presents the chemical composition profiles of SI and CI engine exhaust from the vehicle-testing portion of the study. Chemical analysis of source samples consisted of gravimetric mass, elements, ions, organic carbon (OC), and elemental carbon (EC) by the Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciation Trends Network (STN) thermal/optical methods, polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, alkanes, and polar organic compounds. More than half of the mass of carbonaceous particles emitted by heavy-duty diesel trucks was EC (IMPROVE) and emissions from SI vehicles contained predominantly OC. Although total carbon (TC) by the IMPROVE and STN protocols agreed well for all of the samples, the STN/IMPROVE ratios for EC from SI exhaust decreased with decreasing sample loading. SI vehicles, whether low or high emitters, emitted greater amounts of high-molecular-weight particulate PAHs (benzo[ghi]perylene, indeno[1,2,3-cd]pyrene, and coronene) than did CI vehicles. Diesel emissions contained higher abundances of two- to four-ring semivolatile PAHs. Diacids were emitted by CI vehicles but are also prevalent in secondary organic aerosols, so they cannot be considered unique tracers. Hopanes and steranes were present in lubricating oil with similar composition for both gasoline and diesel vehicles and were negligible in gasoline or diesel fuels. CI vehicles emitted greater total amounts of hopanes and steranes on a mass per mile basis, but abundances were comparable to SI exhaust normalized to TC emissions within measurement uncertainty. The combustion-produced high-molecular-weight PAHs were found in used gasoline motor oil but not in fresh oil and are negligible in used diesel engine oil. The contributions of lubrication oils to abundances of these PAHs in the exhaust were large in some cases and were variable with the age and consumption rate of the oil. These factors contributed to the observed variations in their abundances to total carbon or PM2.5 among the SI composition profiles. 相似文献
104.
Nicholas J. Wald Jonathan P. Bestwick Wayne J. Huttly Jonathan Aldis Antoni Borrell Sandy Goodburn Ian Mills 《黑龙江环境通报》2018,38(13):1079-1085
The aims of this study were to determine whether assumptions used in prenatal screening for Down syndrome in twin pregnancies are valid and derive estimates of risk and screening performance in twin pregnancies using observed data. Data were collected on nuchal translucency, chorionicity, pregnancy associated plasma protein-A (PAPP-A), and free ß human chorionic gonadotrophin (free ß-hCG) from 61 twin pregnancies with Down syndrome and 7302 unaffected twin pregnancies. Distribution parameters were determined and used to estimate screening performance. The assumption that proportional differences in serum marker levels in affected and unaffected singleton pregnancies apply to twin pregnancies was not confirmed. Median free β-hCG value in monochorionic affected twin pregnancies (2.63 multiples of the median [MoM]; 95% CI, 1.79-3.22 MoM) was lower than that assuming proportionality (3.76 MoM), and the median PAPP-A value in dichorionic affected twin pregnancies (1.88 MoM; 95% CI, 1.60-2.17 MoM) was higher than that based on proportionality (1.33 MoM). The detection rate was 87% for a 3% false-positive rate in monochorionic twin pregnancies and 74% in dichorionic twin pregnancies compared with 86% in singleton pregnancies. Estimates of screening performance in Down syndrome twin pregnancies do not need to rely on assumptions and can take account of chorionicity and gestational age. 相似文献
105.
Conserving genetic diversity requires an assessment of the distribution of genetic variants in relation to patterns of land
use and environmental variation at a regional scale. This assessment requires a novel approach to integrating and analyzing
the genetic and environmental data across spatial scales. To explore the integration of genetic data with other geospatial
data sets, we developed a GIS-based approach for examining patterns of genetic diversity for several species of salamanders
in southern Appalachians. The genetic data, from allozyme surveys in the genetics literature, were integrated into a GIS database
along with related attributes including population identifications and spatial locations. Using existing geospatial data,
we classified sample locations as being either protected from anthropogenic disturbance (e.g., National Parks, Wilderness
Areas) or as unprotected (e.g., private lands, multiple-use lands in National Forests). We used multidimensional scaling of
allelic frequencies and contributions of populations to interpopulation differences in allelic richness to determine which
populations had genetic characteristics most different from other populations in the sample. Measures of genetic differentiation
were integrated into the GIS database to facilitate spatial analysis and visualization of the indices in relation to land
use. This approach was useful for both identification of populations with components of genetic variation that were not well
represented at protected sites and for identifying areas of species distributions where more genetic sampling would be necessary
to make informed management decisions. Our approach could be readily adapted for use by managers and geneticists working with
other species and types of genetic markers. 相似文献
106.
Wayne M. Wendland 《Journal of the American Water Resources Association》2001,37(3):685-693
ABSTRACT: Illinois data from 168 months (1986–1999) were investigated to determine the responses of surface‐water and ground‐water resources to precipitation. Such responses were generally within the month of occurrence or one to two months later, with recovery being reached another one to three months into the future, depending on season of the year. Although the drought of 1988 immediately impacted surface‐water and ground‐water resources, the time of recovery was substantially longer compared to those of individual dry months, generally continuing for several months. The extremely wet summer of 1993 resulted in elevated responses in water resources almost immediately, but in this instance continued through the following fall and winter, into the spring of 1994. 相似文献
107.
Penguins may exhibit plasticity in their diving and foraging behaviors in response to changes in prey availability. Chinstrap
penguins are dependent predators of Antarctic krill in the Scotia Sea region, but krill populations have fluctuated in recent
years. We examined the diet of chinstrap penguins at Livingston Island, South Shetland Islands, in relation to their diving
and foraging behavior using time-depth recorders over six breeding seasons: 2002–2007. When krill were smaller, more chinstrap
penguins consumed fish. In these years, chinstrap penguins often exhibited a shift to deep dives after sundown, and then resumed
a shallower pattern at sunrise. These night dives were unexpectedly deep (up to 110 m) and mean night dive depths sometimes
exceeded those from the daytime. The average size of krill in each year was negatively correlated to mean night dive depths
and the proportion of foraging trips taken overnight. Based on these patterns, we suggest that when krill were small, penguins
increasingly targeted myctophid fish. The average krill size was negatively correlated to the time chinstrap penguins spent
foraging which suggests that foraging on smaller krill and fish incurred a cost: more time was spent at sea foraging. 相似文献
108.
We used radio telemetry and observations to study the activity patterns and behavior of gentoo penguin chicks at Admiralty
Bay, King George Island, South Shetland Islands in 2005 during their “fledging period”; defined as the time between a chick’s
first trip to sea and its final dispersal from the breeding colony. Gentoo penguins exhibited delayed dispersal of young and
extended parental provisioning, behaviors not observed in other Pygoscelis species. Chicks took their first trip to sea at a mean age of 70 days of age, before finally departing the colony at a mean
age of 82 days. During this fledging period, individual chicks made an average of five trips to sea. Trip duration increased
significantly as chicks aged, with trips to sea becoming similar to literature values of adult foraging trips in both timing
and duration. Behavioral observations and mass dynamics confirmed that many chicks were still being fed during this fledging
period, with parental feeding behaviors most often observed in the late afternoon to evening hours. We hypothesize that these
behaviors provide an opportunity for chicks to gain experience at sea prior to dispersal and might allow them to develop foraging
skills before they are completely independent. 相似文献
109.
110.
Thanigaivel S. Rajendran Saravanan Gnanasekaran Lalitha Chew Kit Wayne Tran Dang Thuan Tran Hoang-Dung Nghia Nguyen Khoi Show Pau Loke 《Environmental Chemistry Letters》2023,21(2):821-837
Environmental Chemistry Letters - Fossil fuel depletion and carbon dioxide emissions are calling for carbon neutral energies such as algal biofuels, yet actual production of agal biofuels is... 相似文献