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71.
We consider a continuous-time model for the evolution of social networks. A social network is here conceived as a (di-) graph on a set of vertices, representing actors, and the changes of interest are creation and disappearance over time of (arcs) edges in the graph. Hence we model a collection of random edge indicators that are not, in general, independent. We explicitly model the interdependencies between edge indicators that arise from interaction between social entities. A Markov chain is defined in terms of an embedded chain with holding times and transition probabilities. Data are observed at fixed points in time and hence we are not able to observe the embedded chain directly. Introducing a prior distribution for the parameters we may implement an MCMC algorithm for exploring the posterior distribution of the parameters by simulating the evolution of the embedded process between observations. 相似文献
72.
In this paper, we consider simple random sampling without replacement from a dichotomous finite population. We investigate accuracy of the Normal approximation to the Hypergeometric probabilities for a wide range of parameter values, including the nonstandard cases where the sampling fraction tends to one and where the proportion of the objects of interest in the population tends to the boundary values, zero and one. We establish a non-uniform Berry–Esseen theorem for the Hypergeometric distribution which shows that in the nonstandard cases, the rate of Normal approximation to the Hypergeometric distribution can be considerably slower than the rate of Normal approximation to the Binomial distribution. We also report results from a moderately large numerical study and provide some guidelines for using the Normal approximation to the Hypergeometric distribution in finite samples. 相似文献
73.
One classical design criterion is to minimize the determinant of the covariance matrix of the regression estimates, and the designs are called D-optimal designs. To reflect the nature that the proposed models are only approximately true, we propose a robust design criterion to study response surface designs. Both the variance and bias are considered in the criterion. In particular, D-optimal minimax designs are investigated and constructed. Examples are given to compare D-optimal minimax designs with classical D-optimal designs. 相似文献
74.
75.
Various test statistics are discussed which can be used for detecting changes in the parameters of an autoregressive time series. In this first part of our study, the limiting behavior of the test statistics is derived under the null hypothesis of no change as well as under alternatives. In a forthcoming second part of our investigation, these asymptotic results will be compared to some corresponding bootstrap procedures, and a small simulation study will be conducted. 相似文献
76.
In this article a general result is derived that, along with a functional central limit theorem for a sequence of statistics, can be employed in developing a nonparametric repeated significance test with adaptive target sample size. This method is used in deriving a repeated significance test with adaptive target sample size for the shift model. The repeated significance test is based on a functional central limit theorem for a sequence of partial sums of truncated observations. Based on numerical results presented in this article one can conclude that this nonparametric sequential test performs quite well. 相似文献
77.
Two independent random samples are drawn from two multivariate normal populations with mean vectors μ1 and μ2 and a common
variance-covariance matrix Σ. Ahmed and Saleh (1990) considered preliminary test maximum likelihood estimator (PMLTE) for estimating μ1 based on the Hotelling's T
N
2, when it is suspected that μ1=μ2. In this paper, the PTMLE based on the Wald (W), Likelihood Ratio (LR) and Lagrangian Multiplier (LM) tests are considered. Using the quadratic risk function, the conditions of superiority of the proposed estimator for departure
parameter are derived. A max-min rule for the size of the preliminary test of significance is presented. It is demonstrated
that the PTMLE based on W test produces the highest minimum guaranteed efficiencies compared to UMLE among the three test procedures. 相似文献
78.
蒋平 《福建农林大学学报(哲学社会科学版)》2006,(4)
以在自然界中筛选到的一株产纤维素酶的丝状真菌尖镰孢菌F.oxysporumL19为材料,定时测定尖镰孢菌在10种碳源中的纤维素酶活力,发现酶的合成受培养基中碳源种类的调节控制。结构相对完整的纤维类物质(微晶纤维素、TYPE50、CMC、醋酸纤维素)诱导活性较高,二糖(乳糖、麦芽糖、蔗糖)和单糖(葡萄糖和D-木糖)几乎没有诱导作用,麸皮汁液体培养液表现出了较高的诱导活力。菌丝在麸皮汁培养液上的生长状况的研究表明,菌丝的生长情况与酶的产生存在不同步性。这为下一步酶的纯化和分子生物学的研究中选择不同生长期的培养也提供了依据。 相似文献
79.
Robust estimating equation based on statistical depth 总被引:2,自引:0,他引:2
In this paper the estimating equation is constructed via statistical depth. The obtained estimating equation and parameter
estimation have desirable robustness, which attain very high breakdown values close to 1/2. At the same time, the obtained
parameter estimation still has ordinary asymptotic behaviours such as asymptotic normality. In particular, the robust quasi
likelihood and depth-weighted LSE respectively for nonlinear and linear regression model are introduced. A suggestion for
choosing weight function and a method of constructing depth-weighed quasi likelihood equation are given.
This paper is supported by NNSF projects (10371059 and 10171051) of China. 相似文献
80.
Gemai Chen 《Revue canadienne de statistique》1996,24(3):363-372
Very often in regression analysis, a particular functional form connecting known covariates and unknown parameters is either suggested by previous work or demanded by theoretical considerations so that the deterministic part of the responses has a known form. However, the underlying error structure is often less well understood. In this case, the transform-both-sides (TBS) models are appropriate. In this paper we generalize the usual TBS models and develop tests to assess goodness of fit when fitting TBS or GTBS models. Parameter estimation is discussed, and tests based on the Cramér-von Mises statistic and the Anderson-Darling statistic are presented with a table suitable for finite-sample applications. 相似文献