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731.
732.
Measurement errors in spawner abundance create problems for fish stock assessment scientists. To deal with measurement error, we develop a Bayesian state-space model for stock-recruitment data that contain measurement error in spawner abundance, process error in recruitment, and time series bias. Through extensive simulations across numerous scenarios, we compare the statistical performance of the Bayesian state-space model with that of standard regression for a traditional stock-recruitment model that only considers process error. Performance varies depending on the information content in data, as determined by stock productivity, types of harvest situations, and amount of measurement error. Overall, in terms of estimating optimal spawner abundance SMSY, the Ricker density-dependence parameter β, and optimal harvest rate hMSY, the Bayesian state-space model works best for informative data from low and variable harvest rate situations for high-productivity salmon stocks. The traditional stock-recruitment model (TSR) may be used for estimating α and hMSY for low-productivity stocks from variable and high harvest rate situations. However, TSR can severely overestimate SMSY when spawner abundance is measured with large error in low and variable harvest rate situations. We also found that there is substantial merit in using hMSY (or benchmarks derived from it) instead of SMSY as a management target. 相似文献
733.
We develop regional-scale eutrophication models for lakes, ponds, and reservoirs to investigate the link between nutrients and chlorophyll-a. The Bayesian TREED (BTREED) model approach allows association of multiple environmental stressors with biological responses, and quantification of uncertainty sources in the empirical water quality model. Nutrient data for lakes, ponds, and reservoirs across the United States were obtained from the Environmental Protection Agency (EPA) National Nutrient Criteria Database. The nutrient data consist of measurements for both stressor variables (such as total nitrogen and total phosphorus), and response variables (such as chlorophyll-a), used in the BTREED model. Markov chain Monte Carlo (McMC) posterior exploration guides a stochastic search through a rich suite of candidate trees toward models that better fit the data. The Bayes factor provides a goodness of fit criterion for comparison of resultant models. We randomly split the data into training and test sets; the training data were used in model estimation, and the test data were used to evaluate out-of-sample predictive performance of the model. An average relative efficiency of 1.02 between the training and test data for the four highest log-likelihood models suggests good out-of-sample predictive performance. Reduced model uncertainty relative to over-parameterized alternative models makes the BTREED models useful for nutrient criteria development, providing the link between nutrient stressors and meaningful eutrophication response. 相似文献
734.
We study the spreading of contagious diseases in a population of constant size using susceptible-infective-recovered (SIR) models described in terms of ordinary differential equations (ODEs) and probabilistic cellular automata (PCA). In the PCA model, each individual (represented by a cell in the lattice) is mainly locally connected to others. We investigate how the topological properties of the random network representing contacts among individuals influence the transient behavior and the permanent regime of the epidemiological system described by ODE and PCA. Our main conclusions are: (1) the basic reproduction number (commonly called R0) related to a disease propagation in a population cannot be uniquely determined from some features of transient behavior of the infective group; (2) R0 cannot be associated to a unique combination of clustering coefficient and average shortest path length characterizing the contact network. We discuss how these results can embarrass the specification of control strategies for combating disease propagations. 相似文献
735.
Gabriel Ramos-Fernández Denis Boyer Filippo Aureli Laura G. Vick 《Behavioral ecology and sociobiology》2009,63(7):999-1013
We use two novel techniques to analyze association patterns in a group of wild spider monkeys (Ateles geoffroyi) studied continuously for 8 years. Permutation tests identified association rates higher or lower than chance expectation,
indicating active processes of companionship and avoidance as opposed to passive aggregation. Network graphs represented individual
adults as nodes and their association rates as weighted edges. Strength and eigenvector centrality (a measure of how strongly
linked an individual is to other strongly linked individuals) were used to quantify the particular role of individuals in
determining the network's structure. Female–female dyads showed higher association rates than any other type of dyad, but
permutation tests revealed that these associations cannot be distinguished from random aggregation. Females formed tightly
linked clusters that were stable over time, with the exception of immigrant females who showed little association with any
adult in the group. Eigenvector centrality was higher for females than for males. Adult males were associated mostly among
them, and although their strength of association with others was lower than that of females, their association rates revealed
a process of active companionship. Female–male bonds were weaker than those between same-sex pairs, with the exception of
those involving young male adults, who by virtue of their strong connections both with female and male adults, appear as temporary
brokers between the female and male clusters of the network. This analytical framework can serve to develop a more complete
explanation of social structure in species with high levels of fission–fusion dynamics.
This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and
R. James) 相似文献
736.
Potential banana skins in animal social network analysis 总被引:2,自引:2,他引:0
Social network analysis is an increasingly popular tool for the study of the fine-scale and global social structure of animals.
It has attracted particular attention by those attempting to unravel social structure in fission–fusion populations. It is
clear that the social network approach offers some exciting opportunities for gaining new insights into social systems. However,
some of the practices which are currently being used in the animal social networks literature are at worst questionable and
at best over-enthusiastic. We highlight some of the areas of method, analysis and interpretation in which greater care may
be needed in order to ensure that the biology we extract from our networks is robust. In particular, we suggest that more
attention should be given to whether relational data are representative, the potential effect of observational errors and
the choice and use of statistical tests. The importance of replication and manipulation must not be forgotten, and the interpretation
of results requires care.
This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and
R. James). 相似文献
737.
Quantifying Eradication Success: the Removal of Feral Pigs from Santa Cruz Island, California 总被引:2,自引:0,他引:2
Abstract: A major challenge facing pest-eradication efforts is determining when eradication has been achieved. When the pest can no longer be detected, managers have to decide whether the pest has actually been eliminated and hence to decide when to terminate the eradication program. For most eradication programs, this decision entails considerable risk and is the largest single issue facing managers of such programs. We addressed this issue for an eradication program of feral pigs ( Sus scrofa ) from Santa Cruz Island, California. Using a Bayesian approach, we estimated the degree of confidence in the success of the eradication program at the point when monitoring failed to detect any more pigs. Catch-effort modeling of the hunting effort required to dispatch pigs during the eradication program was used to determine the relationship between detection probability and searching effort for different hunting methods. We then used these relationships to estimate the amount of monitoring effort required to declare eradication successful with criteria that either set a threshold for the probability that pigs remained undetected (type I error) or minimized the net expected costs of the eradication program (cost of type I and II errors). For aerial and ground-based monitoring techniques, the amount of search effort required to declare eradication successful on the basis of either criterion was highly dependent on the prior belief in the success of the program unless monitoring intensities exceeded 30 km of searching effort per square kilometer of search area for aerial monitoring and, equivalently, 38 km for ground monitoring. Calculation of these criteria to gauge the success of eradication should form an essential component of any eradication program as it allows for a transparent assessment of the risks inherent in the decision to terminate the program. 相似文献
738.
Model averaging (MA) has been proposed as a method of accommodating model uncertainty when estimating risk. Although the use
of MA is inherently appealing, little is known about its performance using general modeling conditions. We investigate the
use of MA for estimating excess risk using a Monte Carlo simulation. Dichotomous response data are simulated under various
assumed underlying dose–response curves, and nine dose–response models (from the USEPA Benchmark dose model suite) are fit
to obtain both model specific and MA risk estimates. The benchmark dose estimates (BMDs) from the MA method, as well as estimates
from other commonly selected models, e.g., best fitting model or the model resulting in the smallest BMD, are compared to
the true benchmark dose value to better understand both bias and coverage behavior in the estimation procedure. The MA method
has a small bias when estimating the BMD that is similar to the bias of BMD estimates derived from the assumed model. Further,
when a broader range of models are included in the family of models considered in the MA process, the lower bound estimate
provided coverage close to the nominal level, which is superior to the other strategies considered. This approach provides
an alternative method for risk managers to estimate risk while incorporating model uncertainty.
相似文献
Matthew W. WheelerEmail: |
739.
INTRODUCTION: In this paper a sensitivity analysis is performed to investigate how big the impact would be on the current ranking of crash locations in Flanders (Belgium) when only taking into account the most serious injury per crash instead of all the injured occupants. RESULTS: Results show that this would lead to a different selection of 23.8% of the 800 sites that are currently considered as dangerous. CONCLUSIONS: Considering this impact quantity, the researchers want to sensitize government that giving weight to the severity of the crash can correct for the bias that occurs when the number of occupants of the vehicles are subject to coincidence. Additionally, probability plots are generated to provide policy makers with a scientific instrument with intuitive appeal to select dangerous road locations on a statistically sound basis. Impact on industry Considering the impact quantity of giving weight to the severity of the crash instead of to all the injured occupants of the vehicle on the ranking of crash sites, the authors want to sensitize government to carefully choose the criteria for ranking and selecting crash locations in order to achieve an enduring and successful traffic safety policy. Indeed, giving weight to the severity of the crash can correct for the bias that occurs when the number of occupants of the vehicles are subject to coincidence. However, it is up to the government to decide which priorities should be stressed in the traffic safety policy. Then, the appropriate weighting value combination can be chosen to rank and select the most dangerous crash locations. Additionally, the probability plots proposed in this paper can provide policy makers with a scientific instrument with intuitive appeal to select dangerous road locations on a statistically sound basis. Note that, in practice, one should not only rank the crash locations based on the benefits that can be achieved from tackling these locations. Future research is also needed to incorporate the costs of infrastructure measures and other actions that these crash sites require in order to enhance the safety on these locations. By balancing these costs and benefits against each other, the crash locations can then be ranked according to the order in which they should be prioritized. 相似文献
740.
井塌事故在钻井过程极其常见,由于钻井液、井身结构等设计不合理,以及钻井过程的误操作均会造成井塌的发生,其后果主要是造成卡钻、卡套管等事故,严重时造成井眼毁坏。为了对井塌事故进行危险性分析,采用贝叶斯网络与故障树相结合的方法,避免传统故障树方法的局限性。首先对井塌事故的所有危险因素进行辨识建立故障树,然后将故障树转化为贝叶斯网络,建立条件概率表,运用贝叶斯网络的推理能力对井塌事故进行危险性分析。对井塌事故各基本事件概率分布的计算分析结果表明,考虑事件的多态性,综合利用故障树分析法和贝叶斯网络法能有效提高井塌事故分析的有效性,推算出井塌事故概率分布更为准确。 相似文献