全文获取类型
收费全文 | 96572篇 |
免费 | 1032篇 |
国内免费 | 1814篇 |
专业分类
系统科学 | 2213篇 |
丛书文集 | 1853篇 |
教育与普及 | 610篇 |
理论与方法论 | 649篇 |
现状及发展 | 38073篇 |
研究方法 | 1746篇 |
综合类 | 52080篇 |
自然研究 | 2194篇 |
出版年
2015年 | 975篇 |
2014年 | 1236篇 |
2013年 | 1614篇 |
2012年 | 1741篇 |
2011年 | 3978篇 |
2010年 | 1422篇 |
2009年 | 1605篇 |
2008年 | 2287篇 |
2007年 | 2356篇 |
2006年 | 2301篇 |
2005年 | 2424篇 |
2004年 | 3191篇 |
2003年 | 2905篇 |
2002年 | 2897篇 |
2001年 | 3114篇 |
2000年 | 2308篇 |
1999年 | 2180篇 |
1998年 | 1258篇 |
1997年 | 1302篇 |
1996年 | 1040篇 |
1994年 | 1088篇 |
1993年 | 1066篇 |
1992年 | 1579篇 |
1991年 | 1420篇 |
1990年 | 1476篇 |
1989年 | 1211篇 |
1988年 | 1156篇 |
1987年 | 1124篇 |
1986年 | 1088篇 |
1985年 | 1245篇 |
1984年 | 1034篇 |
1982年 | 920篇 |
1981年 | 952篇 |
1980年 | 1121篇 |
1979年 | 2036篇 |
1978年 | 1788篇 |
1977年 | 1763篇 |
1976年 | 1421篇 |
1975年 | 1508篇 |
1974年 | 1727篇 |
1973年 | 1766篇 |
1972年 | 1828篇 |
1971年 | 2051篇 |
1970年 | 2505篇 |
1969年 | 2038篇 |
1968年 | 1908篇 |
1967年 | 1906篇 |
1966年 | 1642篇 |
1965年 | 1246篇 |
1958年 | 1084篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
当被评价的决策单元的其输入向量增加后,其效率指数为原来的r倍时,极大化其输出向量,称这一问题是面向输出的r-逆DEA问题,它是通常的逆DEA问题的推广.通过构建两个特殊的线性规划模型,得到了r-逆DEA问题的一类特殊形式解的求法,并用数值实例加以说明. 相似文献
122.
Kang J.Y. Xu F.C. 《中国科学基金(英文版)》2004,(2):57-58,64
1 Introduction
Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].
…… 相似文献
123.
汤燕瑜 《玉林师范学院学报》2004,25(2):111-114
高师院校肩负着培养基础教育师资的重任。衡量师资素质的重要标准之一,是教师职业素质与技能掌握、运用的程度。因而职业技能教育是高师教育中一个重要组成部分。本文通过对高师院校英语职业技能教育的反思,以及对基础教育发展需求分析,提出从可持续发展、教育的内在价值与创新教育的三个层面探讨高师英语职业技能教育改革。 相似文献
124.
In econometrics, as a rule, the same data set is used to select the model and, conditional on the selected model, to forecast. However, one typically reports the properties of the (conditional) forecast, ignoring the fact that its properties are affected by the model selection (pretesting). This is wrong, and in this paper we show that the error can be substantial. We obtain explicit expressions for this error. To illustrate the theory we consider a regression approach to stock market forecasting, and show that the standard predictions ignoring pretesting are much less robust than naive econometrics might suggest. We also propose a forecast procedure based on the ‘neutral Laplace estimator’, which leads to an improvement over standard model selection procedures. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
125.
A fast and accurate method based on FTIR is developed for determining the lignin content and its characteristic bands in alkali solutions. The work consisted of two main parts: 1) establishing a predictive model and 2) determination of the accuracy of the model. The model was derived by applying the partial least squares algorithm for multivariate analyses to a set of spectrum data obtained from selected IR absorption regions in the range of 1600 - 900 cm-1. The model was tested with spent liquors obtained from commercial pulp mills.The accuracy of the predictive model is extremely high suitable for commercial applications,particularly for monitoring the dynamic response of modern kraft pulping processes. 相似文献
126.
127.
This paper assesses the information content of two survey indicators for consumption developments in the near future for eight European countries in the period 1985–1998. Empirical work on this topic typically focuses on consumer confidence, the perceptions of buyers of consumption goods. This paper examines whether perceptions of sellers of consumption goods, measured by retail trade surveys, may also improve short‐term monitoring of consumption. We find that both consumer confidence and retailer confidence embody valuable information, when analysed in isolation. For France, Italy and Spain we conclude that adding retail confidence does not improve the indicator model once consumer confidence has been included. For the UK the reverse case is obtained. For the remaining four countries we show that combining consumer sentiment and retail trade confidence into a composite indicator leads to optimal results. Our results suggest that incorporating information from retail trade surveys may offer significant benefits for the analysis of short‐term prospects of consumption. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
128.
129.
省级旅游市场供给环境及其评价方法研究--以山东省为例 总被引:1,自引:0,他引:1
余洁 《山东师范大学学报(自然科学版)》2002,17(4):51-54
旅游市场供给的内容十分丰富,其质量和效益的高低可通过对旅游市场的供给环境分析加以确定。本文在对旅游市场供给环境做简要分析的基础上,主要采用层次分析法对山东省旅游市场供给环境做出综合评价,为供给方充分利用和认识市场环境,发挥优势,寻找市场机会提供参考依据。 相似文献
130.