首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1253篇
  免费   299篇
  2021年   15篇
  2020年   10篇
  2019年   101篇
  2018年   68篇
  2017年   68篇
  2016年   121篇
  2015年   84篇
  2014年   83篇
  2013年   259篇
  2012年   85篇
  2011年   93篇
  2010年   70篇
  2009年   48篇
  2008年   66篇
  2007年   66篇
  2006年   44篇
  2005年   19篇
  2004年   35篇
  2003年   29篇
  2002年   20篇
  2001年   21篇
  2000年   29篇
  1999年   3篇
  1998年   14篇
  1997年   17篇
  1996年   12篇
  1995年   14篇
  1994年   11篇
  1993年   3篇
  1992年   4篇
  1991年   2篇
  1989年   1篇
  1988年   1篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1983年   1篇
  1982年   4篇
  1980年   3篇
  1979年   2篇
  1978年   1篇
  1977年   6篇
  1976年   2篇
  1975年   1篇
  1974年   2篇
  1971年   1篇
  1969年   1篇
  1968年   1篇
  1951年   1篇
排序方式: 共有1552条查询结果,搜索用时 300 毫秒
181.
The objective of this paper is to compare fractal‐based parameters calculated by different fractal methods for urban built‐up areas and to link the observed spatial variations to variables commonly used in urban geography, urban economics, or land‐use planning. Computations are performed on Brussels, Belgium. Two fractal methods (correlation and dilation) are systematically applied for evaluating the fractal dimension of built‐up surfaces; correlation is used to evaluate the fractal dimension of the borders (lines). Analyses show that while fractal dimension is ideal for distinguishing the morphology of Brussels, each estimation technique leads to slightly different results. Interesting associations are to be found between the fractal dimensions and rent, distance, income, and planning rules. Despite its limitations, fractal analysis seems to be a promising tool for describing the morphology of the city and for simulating its genesis and planning. The model is robust: it replicates the urban spatial regularities and patterns, and could hence fruitfully be integrated into intra‐urban simulation processes.  相似文献   
182.
183.
ABSTRACT This paper surveys recent evidence on the determinants of (national and/or foreign) industrial location. We find that the basic analytical framework has remained essentially unaltered since the early contributions of the early 1980s while, in contrast, there have been advances in the quality of the data (more firm and plant level information, geographical disaggregation, panel structure, etc.) and, to a lesser extent, the econometric modeling. We also identify certain determinants (neoclassical and institutional factors) that tend to provide largely consistent results across the reviewed studies. In light of this evidence, we finally suggest future lines of research.  相似文献   
184.
185.
ABSTRACT It has long been recognized that the forces that lead to the agglomeration of economic activity and to aggregate growth are similar. Unfortunately, few formal frameworks have been advanced to explore this link. We critically discuss the literature and present a simple framework that can circumvent some of the main obstacles we identify. We discuss the main characteristics of an equilibrium allocation in this dynamic spatial framework, present a numerical example to illustrate the forces at work, and provide some supporting empirical evidence.  相似文献   
186.
187.
The age of Neanderthal remains and associated sediments from El Sidrón cave has been obtained through different dating methods (14CAMS, U/TH, OSL, ESR and AAR) and samples (charcoal debris, bone, tooth dentine, stalagmitic flowstone, carbonate‐rich sediments, sedimentary quartz grains, tooth enamel and land snail shells). Detrital Th contamination rendered Th/U dating analyses of flowstone unreliable. Recent 14C contamination produced spurious age‐values from charcoal samples as well as from inadequately pretreated tooth samples. Most consistent 14C dates are grouped into two series: one between 35 and 40 ka and the other between 48 and 49 ka. Most ESR and AAR samples yielded concordant ages, ranging between 39 and 45 ka; OSL dating results permitted adequate bracketing of the sedimentary layer that contained the human remains. Our results emphasize the value of multi‐dating approaches for the establishment of reliable chronologies of human remains.  相似文献   
188.
The employment of synchrotron techniques complemented by conventional laboratory systems has allowed us to deepen and improve our knowledge of Roman wall painting procedures. The palette identified in wall paintings from Pompeii and Herculaneum from the second century bc includes goethite, hematite, cinnabar, glauconite, Egyptian blue, and other components such as calcite and aragonite. Proof of the use of organic binders is provided by FTIR and PY–GC/MS. Therefore, the possibility of the use of ‘a secco’ techniques cannot be ruled out. Pigments in wall paintings are usually found in small percentages and conventional X‐ray diffractometers do not detect them. Synchrotron radiation – high‐resolution X‐ray powder diffraction has allowed identification with only a few micrograms of sample.  相似文献   
189.
This paper explains, with the example of a Roman object (the ‘Mars from Oberweningen’, Switzerland), why neutrons can be used preferentially for the non‐destructive analysis of metallic objects of relatively large size. This method is superior to the conventional X‐ray tomography method due to the higher penetration ability in metals such as copper, tin and even lead. With this method, differing materials can also easily be differentiated. In this way, the inner and outer structures of objects can be observed with the help of tools based on mathematical algorithms. Slices at arbitrary positions and segmentation of different material clusters aid the understanding of manufacturing processes and can describe the present preservation status. This helps in selecting optimal and additional conservation measures in museums for further preservation. Beside the qualitative overview on structure and inner properties of the objects, quantitative information can be derived about material content and composition. This method and the subsequently needed facilities for this method are available at PSI for similar studies on demand.  相似文献   
190.
Social differentiation is characterized by differences in social status and wealth, which are established and maintained by controlling and constraining the labour and flow of resources. This would affect the development of various aspects of a settlement in establishing hierarchical relationships. This study focuses on identifying the variations in the distribution of certain resources, such as imported goods, that help interpret the social meaning, particularly with regard to social status and wealth, of house structures having different shapes in an ethnic settlement in Taiwan. A petrographic study and residue analysis of the pottery along with spatial examination of the material remains were conducted to achieve the goal.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号