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111.
112.
Several panel unit root tests that account for cross-section dependence using a common factor structure have been proposed in the literature recently. Pesaran's (2007) cross-sectionally augmented unit root tests are designed for cases where cross-sectional dependence is due to a single factor. The Moon and Perron (2004) tests which use defactored data are similar in spirit but can account for multiple common factors. The Bai and Ng (2004a) tests allow to determine the source of nonstationarity by testing for unit roots in the common factors and the idiosyncratic factors separately. Breitung and Das (2008) and Sul (2007) propose panel unit root tests when cross-section dependence is present possibly due to common factors, but the common factor structure is not fully exploited. This article makes four contributions: (1) it compares the testing procedures in terms of similarities and differences in the data generation process, tests, null, and alternative hypotheses considered, (2) using Monte Carlo results it compares the small sample properties of the tests in models with up to two common factors, (3) it provides an application which illustrates the use of the tests, and (4) finally, it discusses the use of the tests in modelling in general. 相似文献
113.
We compare the forecast accuracy of autoregressive integrated moving average (ARIMA) models based on data observed with high and low frequency, respectively. We discuss how, for instance, a quarterly model can be used to predict one quarter ahead even if only annual data are available, and we compare the variance of the prediction error in this case with the variance if quarterly observations were indeed available. Results on the expected information gain are presented for a number of ARIMA models including models that describe the seasonally adjusted gross national product (GNP) series in the Netherlands. Disaggregation from annual to quarterly GNP data has reduced the variance of short-run forecast errors considerably, but further disaggregation from quarterly to monthly data is found to hardly improve the accuracy of monthly forecasts. 相似文献
114.
In this paper we present a Wald or distance test for testing the stability of a linear dynamic model. Stability requires that all latent roots of the system simultaneously satisfy inequality restrictions. Unlike previous tests proposed in the literature our procedure is capable of testing the restrictions simultaneously. Therefore, the test asymptotically has the correct size. The procedure can be applied in practice if stability is not a requirement for identification of the dynamic model. 相似文献
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116.
The problem of missing observations in regression models is often solved by using imputed values to complete the sample. As an alternative for static models, it has been suggested to limit the analysis to the periods or units for which all relevant variables are observed. The choice of an imputation procedure affects the asymptotic efficiency of the method used to subsequently estimate the parameters of the model. In this note, we show that the relative asymptotic efficiency of three estimators designed to handle incomplete samples depends on parameters that have a straightforward statistical interpretation. In terms of a gain of asymptotic efficiency, the use of these estimators is equivalent to the observation of a percentage of the values which are actually missing. This percentage depends on three R2-measures only, which can be straightforwardly computed in applied work. Therefore it should be easy in practice to check whether it is worthwhile to use a more elaborate estimator. 相似文献
117.
Oswin Aichholzer Franz Aurenhammer Günter Rote Yin-Feng Xu 《Journal of Combinatorial Optimization》1998,2(4):361-369
The well-known greedy triangulation GT(S) of a finite point set S is obtained by inserting compatible edges in increasing length order, where an edge is compatible if it does not cross previously inserted ones. Exploiting the concept of so-called light edges, we introduce a definition of GT(S) that does not rely on the length ordering of the edges. Rather, it provides a decomposition of GT(S) into levels, and the number of levels allows us to bound the total edge length of GT(S). In particular, we show |GT(S)| 3 · 2k + 1|MWT(S)|, where k is the number of levels and MWT(S) is the minimum-weight triangulation of S. 相似文献
118.
Adaptive paediatric investigation plans,a small step to improve regulatory decision making in drug development for children? 下载免费PDF全文
Different arguments have been put forward why drug developers should commit themselves early for what they are planning to do for children. By EU regulation, paediatric investigation plans should be agreed on in early phases of drug development in adults. Here, extrapolation from adults to children is widely applied to reduce the burden and avoids unnecessary clinical trials in children, but early regulatory decisions on how far extrapolation can be used may be highly uncertain. Under special circumstances, the regulatory process should allow for adaptive paediatric investigation plans explicitly foreseeing a re‐evaluation of the early decision based on the information accumulated later from adults or elsewhere. A small step towards adaptivity and learning from experience may improve the quality of regulatory decisions in particular with regard to how much information can be borrowed from adults. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
119.
Michael TATZBER Franz MUTSCH Ernst LEITGEB Michael ENGLISCH Axel MENTLER Martin GERZABEK 《福建农林大学学报(哲学社会科学版)》2011,(5):26-29
碳酸盐检测是土壤科学中的常规检测。在本研究中,用中红外光谱方法对采自奥地利130多个不同的森林区域的大量土壤样品进行评价。评价了有机层中的20条谱带和矿物土壤中15条谱带区域,并且通过模型计算检测了被调查土壤样品中的碳酸盐。对于有机层的所有样品,相关系数都很低(R2=0.68),可以通过对F(中度分解的有机物)和H(高度腐烂的有机物质)的混合样品进行组分离来增加相关系数。FH层土壤、森林类型土壤、矿质土壤母质的相关系数达到R2=0.92。对于所有0到5和5至10cm的矿质土壤层,相关系数从一开始就很高(R2=0.97),当隔离一组石灰岩作为母质的10个样品时,相关系数可以增加到R2=0.99。最后,本研究着重介绍了土壤样品的化学多样性对于中红外光谱检测土壤中碳酸盐的影响潜力。 相似文献
120.
Arnold Zellner Franz C. Palm 《Econometrica : journal of the Econometric Society》2000,68(5):1293-1293