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131.
Summary This paper solves some D-optimal design problems for certain Generalized Linear Models where the mean depends on two parameters
and two explanatory variables. In all of the cases considered the support point of the optimal designs are found to be independent
of the unknown parameters. While in some cases the optimal design measures are given by two points with equal weights, in
others the support is given by three point with weights depending on the unknown parameters, hence the designs are locally
optimal in general. Empirical results on the efficiency of the locally optimal designs are also given. Some of the designs
found can also be used for planning D-optimal experiments for the normal linear model, where the mean must be positive.
This research was carried out in part at University College, London as an M.Sc. project. Thanks are due to Prof. I. Ford (University
of Glasgow) and Prof. A. Giovagnoli (University of Perugia) for their valuable suggestions and critical observations. 相似文献
132.
袁嘉祖 《北京林业大学学报(社会科学版)》2002,(Z1)
该文从中国人口快速增长、经济建设加快、用水量逐年增大 ,加上气候变暖、少雨干旱将持续到 2 0 15年 ,我国北方水生态环境日趋恶化现状 ,说明在丰水区筑坝截流、调丰补歉势在必行 ,完全符合生态经济学发展原则和国际水法 相似文献
133.
Formulae are provided that define the ‘bend points’, the beginning and end of the essentially linear dose–response region, for the four‐parameter logistic model. The formulae are expressed in both response and dose units. The derivation of the formulae is shown in order to illustrate the general nature of the methodology. Examples are given that describe how the formulae may be used while planning and conducting bioassays. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
134.
Lesa L. Aylward Robert C. Brunet Thomas B. Starr Gaétan Carrier Elizabeth Delzell Hong Cheng Colleen Beall 《Risk analysis》2005,25(4):945-956
Recent studies demonstrating a concentration dependence of elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suggest that previous estimates of exposure for occupationally exposed cohorts may have underestimated actual exposure, resulting in a potential overestimate of the carcinogenic potency of TCDD in humans based on the mortality data for these cohorts. Using a database on U.S. chemical manufacturing workers potentially exposed to TCDD compiled by the National Institute for Occupational Safety and Health (NIOSH), we evaluated the impact of using a concentration- and age-dependent elimination model (CADM) (Aylward et al., 2005) on estimates of serum lipid area under the curve (AUC) for the NIOSH cohort. These data were used previously by Steenland et al. (2001) in combination with a first-order elimination model with an 8.7-year half-life to estimate cumulative serum lipid concentration (equivalent to AUC) for these workers for use in cancer dose-response assessment. Serum lipid TCDD measurements taken in 1988 for a subset of the cohort were combined with the NIOSH job exposure matrix and work histories to estimate dose rates per unit of exposure score. We evaluated the effect of choices in regression model (regression on untransformed vs. ln-transformed data and inclusion of a nonzero regression intercept) as well as the impact of choices of elimination models and parameters on estimated AUCs for the cohort. Central estimates for dose rate parameters derived from the serum-sampled subcohort were applied with the elimination models to time-specific exposure scores for the entire cohort to generate AUC estimates for all cohort members. Use of the CADM resulted in improved model fits to the serum sampling data compared to the first-order models. Dose rates varied by a factor of 50 among different combinations of elimination model, parameter sets, and regression models. Use of a CADM results in increases of up to five-fold in AUC estimates for the more highly exposed members of the cohort compared to estimates obtained using the first-order model with 8.7-year half-life. This degree of variation in the AUC estimates for this cohort would affect substantially the cancer potency estimates derived from the mortality data from this cohort. Such variability and uncertainty in the reconstructed serum lipid AUC estimates for this cohort, depending on elimination model, parameter set, and regression model, have not been described previously and are critical components in evaluating the dose-response data from the occupationally exposed populations. 相似文献
135.
In this article, we describe a straightforward method for solving the probability of at least one malignant cell by time t, and the associated hazard function, in the general (i.e., nonhomogeneous) two-stage Moolgavkar-Venzon-Knudson (MVK) model of cancer. The method consists of solving four coupled ordinary differential equations derived from the Kolmogorov backward equations for this process. The relationship of this method to previously proposed solutions is discussed. 相似文献
136.
巴·苏和 《中央民族大学学报(哲学社会科学版)》2005,(4)
蒙古文学研究的基础和前提是蒙古文学史料。随着国内外蒙古文学研究的不断拓展和深入,蒙古文学史料搜集整理已逐步发展成为蒙古文学史料学。蒙古文学史料学包括蒙古文学的田野调查、史料整理、考订、选录、笺释、校注、校勘、辑评等诸多研究内涵。中国蒙古文学研究取得巨大成就,得益于蒙古文学史料学的长足发展。我们应当总结以往蒙古文学史料学研究的经验,使蒙古文学史料学更加系统化、科学化和理论化。 相似文献
137.
P. Battipaglia 《Statistical Methods and Applications》1996,5(2):179-202
Summary The evaluation of the performance of seasonal adjustment procedures is an issue of practical importance in view of the unobservable
nature of the components. Looking at just one indicator when judging the overall quality of a procedure may be misleading,
even though this is common practice when many series are involved.
The main purpose of this paper is to compare the information content of different synthetic indicators with reference to the
X-11-ARIMA procedure.
Sixty-six different types of monthly seasonal series are generated and the seasonal component then extracted by carrying out
X-11-ARIMA with standard options. The correlation between the pseudo-true error for each series and various synthetic indicators
allows us to compare the latter's reliability, under both the hypotheses of minimum and maximum variance of the pseudo-true
seasonal component.
We show that the overall quality indexQ-the indicator most commonly adopted by users of the X-11-ARIMA-is always outperformed by the simpler diagnostics based on
the stability of the estimates.
In particular, the “sliding-spans” indicator, proposed by Findley et al. (1990) and included in the diagnostics of the new
X-12 procedure, shows a much stronger correlation with the pseudo-true error in the seasonal adjustment.
We also show that the total forecasting errors in the one-year-ahead extrapolation of the seasonal component have a good informative
power and perform almost as well as the “sliding-spans” indicator. 相似文献
138.
The authors examined nineteen nonprofit performing arts organizations, investigating the distribution of influence among organizational members, the grouping of volunteers and staff in organizational structures, and the effectiveness of the organizations. The organizations' effectiveness was assessed using multiple performance indicators. The analysis revealed five groupings or configurations of influence, which correlated to the organizations exhibiting the highest and lowest levels of organizational effectiveness. The authors conclude that a variety of structures are associated with good performance but structural dysfunctions are associated with organizational failure, and that members' commitment to an organization's structure is an important element of success. 相似文献
139.
Hansen PE 《Mathematical Population Studies》1989,2(1):37-67
A review of the Leslie matrix model theory and its literature 1941-1987 is presented. The point of view is that of a mathematician who focuses on the parts of the theory which are relevant to demography. Works of a decidedly applied nature are not dealt with. 相似文献
140.
Mullan BP 《International migration (Geneva, Switzerland)》1989,27(1):69-86
This paper postulates that there is a continuous exchange of information and knowledge between those who share the common bond of having migrated to the US. The individual components of this information exchange constitute social networks. The 2 hypotheses tested are 1) immediate social networks and people known in the US facilitate the flow of information both to new migrants and between established migrants, thus promoting upward social mobility; and 2) access to broader network ties, organization membership, extra-ethnic friendships, and familiarity with established institutions smooths the transition process, resulting in increased social position. The data used comes from a study conducted in 1982-1983 in 4 Mexican sending communities (2 rural, 2 urban), for a total of 440 migrants. Results show that migrants in every socioeconomic bracket reported access to some or all social network characteristics. There was contact with either a family member or acquaintances from the migrants' town of origin. Over 50% of migrants reported knowing many fellow townspeople. Twice as many migrants belong to a sports club as to a social or religious organization. Very few rural migrants report knowing no townspeople, while 32% of urban migrants claim no knowledge of fellow migrants from their town of origin. Urban origin migrants report more contacts with those of other ethnicity than rural migrants. Those employed in agriculture are least acquainted with social information and contacts, while those in skilled and service sectors are well acquainted with them. The results of fact and analysis show that 1) access to personal US networks results in an average 4.4 point advantage in occupational prestige scores over no access, and 2) utilizing institutional US networks combined with any cumulative US experience gives a migrant a 5 point advantage over a fellow migrant with identical experience level but no institutional network contacts. This is also true for institutional Mexican networks. Thus success or failure in migrating is partly due to migrants' societal infrastructure and the fact that available information and social networks are accessed and utilized differently by different migrants. 相似文献