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11.
12.
Grard Letac 《Revue canadienne de statistique》1991,19(2):229-232
This note exhibits two independent random variables on integers, X1 and X2, such that neither X1 nor X2 has a generalized Poisson distribution, but X1 + X2 has. This contradicts statements made by Professor Consul in his recent book. 相似文献
14.
交互式多媒体呈现系统一般由呈现内容和呈现控制流程两部分组成。通过引入通用转换网络,对交互式多媒体应用系统的内部呈现流程进行了形式化描述;讨论了该形式化描述下呈现流程的重用性;提出了将呈现流程与呈现内容相分离的系统实现策略;给出了呈现内容描述和可呈现对象相结合的呈现内容表示方法。该策略和方法可用于设计实现交互式多媒体呈现系统创作平台,利用该平台创作的呈现系统能够并发地呈现多种媒体形式的信息,系统及其组成部件具有良好的可重用性。 相似文献
15.
Kaatje Bollaerts Marc Aerts Christel Faes Koen Grijspeerdt Jeroen Dewulf Koen Mintiens 《Risk analysis》2008,28(2):427-440
The quantification of the relationship between the amount of microbial organisms ingested and a specific outcome such as infection, illness, or mortality is a key aspect of quantitative risk assessment. A main problem in determining such dose-response models is the availability of appropriate data. Human feeding trials have been criticized because only young healthy volunteers are selected to participate and low doses, as often occurring in real life, are typically not considered. Epidemiological outbreak data are considered to be more valuable, but are more subject to data uncertainty. In this article, we model the dose-illness relationship based on data of 20 Salmonella outbreaks, as discussed by the World Health Organization. In particular, we model the dose-illness relationship using generalized linear mixed models and fractional polynomials of dose. The fractional polynomial models are modified to satisfy the properties of different types of dose-illness models as proposed by Teunis et al . Within these models, differences in host susceptibility (susceptible versus normal population) are modeled as fixed effects whereas differences in serovar type and food matrix are modeled as random effects. In addition, two bootstrap procedures are presented. A first procedure accounts for stochastic variability whereas a second procedure accounts for both stochastic variability and data uncertainty. The analyses indicate that the susceptible population has a higher probability of illness at low dose levels when the combination pathogen-food matrix is extremely virulent and at high dose levels when the combination is less virulent. Furthermore, the analyses suggest that immunity exists in the normal population but not in the susceptible population. 相似文献
16.
The benchmark dose (BMD) is an exposure level that would induce a small risk increase (BMR level) above the background. The BMD approach to deriving a reference dose for risk assessment of noncancer effects is advantageous in that the estimate of BMD is not restricted to experimental doses and utilizes most available dose-response information. To quantify statistical uncertainty of a BMD estimate, we often calculate and report its lower confidence limit (i.e., BMDL), and may even consider it as a more conservative alternative to BMD itself. Computation of BMDL may involve normal confidence limits to BMD in conjunction with the delta method. Therefore, factors, such as small sample size and nonlinearity in model parameters, can affect the performance of the delta method BMDL, and alternative methods are useful. In this article, we propose a bootstrap method to estimate BMDL utilizing a scheme that consists of a resampling of residuals after model fitting and a one-step formula for parameter estimation. We illustrate the method with clustered binary data from developmental toxicity experiments. Our analysis shows that with moderately elevated dose-response data, the distribution of BMD estimator tends to be left-skewed and bootstrap BMDL s are smaller than the delta method BMDL s on average, hence quantifying risk more conservatively. Statistically, the bootstrap BMDL quantifies the uncertainty of the true BMD more honestly than the delta method BMDL as its coverage probability is closer to the nominal level than that of delta method BMDL. We find that BMD and BMDL estimates are generally insensitive to model choices provided that the models fit the data comparably well near the region of BMD. Our analysis also suggests that, in the presence of a significant and moderately strong dose-response relationship, the developmental toxicity experiments under the standard protocol support dose-response assessment at 5% BMR for BMD and 95% confidence level for BMDL. 相似文献
17.
Michael Weba 《Statistical Papers》2002,43(3):445-452
n possibly different success probabilities p
1, p
2, ..., p
n
is frequently approximated by a Poisson distribution with parameter λ = p
1 + p
2 + ... + p
n
. LeCam's bound p
2
1 + p
2
2 + ... + p
n
2 for the total variation distance between both distributions is particularly useful provided the success probabilities are
small.
The paper presents an improved version of LeCam's bound if a generalized d-dimensional Poisson binomial distribution is to be approximated by a compound Poisson distribution.
Received: May 10, 2000; revised version: January 15, 2001 相似文献
18.
The mean density of bacteria in a water body is commonly monitored using quantal assay. This paper describes the use of local scoring in estimating the spatial distribution of mean density from quantal assay results at a set of point locations. An application to estimating the mean density of fecal conform bacteria in a coastal pond is presented. Model diagnostics based on a parametric bootstrap are also presented. 相似文献
19.
王志坚 《苏州科技学院学报(社会科学版)》1998,(1)
以 X_2(G)记一图 G 之全色数,全着色 Ramsey 数 X_2(m,n)为最小正整数 p,使得每一p 阶图 G 或有X_2(G)≥in加,或其补图■满足 X_2(■)≥n。本文给出 X_2(m,n)的上、下界。 相似文献
20.