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   5738篇
  免费   419篇
  6157篇
  2021年   28篇
  2020年   63篇
  2019年   196篇
  2018年   172篇
  2017年   180篇
  2016年   233篇
  2015年   175篇
  2014年   168篇
  2013年   1586篇
  2012年   221篇
  2011年   217篇
  2010年   220篇
  2009年   191篇
  2008年   155篇
  2007年   177篇
  2006年   143篇
  2005年   82篇
  2004年   86篇
  2003年   85篇
  2002年   83篇
  2001年   88篇
  2000年   82篇
  1999年   69篇
  1998年   76篇
  1997年   66篇
  1996年   69篇
  1995年   61篇
  1994年   60篇
  1993年   47篇
  1992年   46篇
  1991年   39篇
  1990年   26篇
  1989年   44篇
  1988年   38篇
  1987年   52篇
  1986年   40篇
  1985年   44篇
  1984年   53篇
  1983年   45篇
  1982年   37篇
  1981年   42篇
  1980年   56篇
  1979年   47篇
  1978年   29篇
  1977年   57篇
  1976年   37篇
  1975年   38篇
  1974年   25篇
  1972年   25篇
  1970年   26篇
排序方式: 共有6157条查询结果,搜索用时 15 毫秒
991.
This article analyzes the mechanisms through which metropolitan governance is established in Montreal's aeronautics sector, one of the most important and innovative industries in the region. The article also examines the role of lead firms, socio‐economic actors, and public agencies from a territorial point of view. It is established that on the one hand the existence of a small number of prime producers at the local level facilitates productive linkages among businesses through subcontracting, and on the other hand, the intensive participation of intermediate socio‐economic agencies and organizations ensures a metropolitan anchoring of the sector and creates a strong territorial identity among the players.  相似文献   
992.
Wetlands are common in Coastal Western Hemlock forests yet the hydrologic processes that generate runoff from small swamps are not completely understood. Direct field observations, hydrologic, and electrical conductivity data were collected from a gently sloping forested swamp complex from July to November 2009. Swamps occupied depressions between raised mounds (0.1 to 3 m high) and were connected by an ephemeral creek. Runoff was controlled by antecedent moisture conditions and influenced by basin microtopography. Two hydrologic regimes occurred during the study period and different runoff processes dominated each regime. Runoff was generated by subsurface flow during dry antecedent conditions as swamps remained hydrologically disconnected from each other. Runoff was generated by surface outflow from hydrologically connected swamps during wet antecedent conditions as ponded water spilled out of the depressions. The forested swamp complex produced a faster but limited hydrologic response during dry antecedent conditions compared to a slower but greater hydrologic response during wet antecedent conditions. Stormwater runoff and runoff ratios were up to two orders of magnitude higher in wet conditions than during similarly sized events in dry conditions. These factors should be considered when designing monitoring programs or runoff models in forested swamps with significant microtopography. Field surveys and estimates of hydrologic inputs and outputs may be useful in predicting the potential hydrologic connectivity of isolated forested swamps.  相似文献   
993.
994.
995.
Numerous Hellenic terms have been gradually adopted during the development of modern medical science. Moreover, there are a significant number of words that derive directly from the Hippocratic texts. Hippocrates (ca. 460-ca. 377 BC), revered as the father of medicine, and his followers left behind a valuable heritage of medical knowledge that, practically, laid the foundations of Western medicine. Their theories, collected in Corpus Hippocraticum, transformed medicine by adding, mainly, clinical observation and inductive reasoning as significant parts of medical diagnosis and treatment. Additionally, Hippocratic writings have provided an invaluable heritage of medical terms for all medical fields. The present article examines the Hellenic and Hippocratic terminology referring to the spine and how this vocabulary has influenced and dominated upon modern spinal onomatology.  相似文献   
996.
997.
青海藏族聚居区实现长治久安的思考及对策   总被引:1,自引:0,他引:1  
在现代社会,民族问题是影响国家和社会长期稳定的重要因素之一。本文对青海藏族聚居区的长治久安问题进行了客观分析并针对政府决策和执行提出了对策建议。  相似文献   
998.
In this paper, a detailed overview of the Holocene evolution of the North Dvina river (ND) delta (southern White Sea) is presented; it is based on radiocarbon dating, geomorphological and other field surveys, and plant macrofossil and palynological data. We have identified three main stages of the delta evolution: estuary erosional (Allerød — 5700 cal BC), lagoon or tidal-marsh (5700 cal BC — 3700 cal BC) and fan-delta accumulative (3700 cal BC — present). These stages are correlated with local climatic curves, sea level changes, glacioisostatic raise curve and Baltic Sea stages. A variety of landforms has been identified and dated within the delta. These results help to explain the spatial and temporal patterns in the prehistoric human occupation of this area.  相似文献   
999.
This object-specific case study focuses on cupreous artifacts excavated from the Great Temple complex of Petra, Jordan to demonstrate how the use of compositional X-ray analyses alongside two experimental applications (ImageJ software and nanoindentation) have the potential to generate different and otherwise unobtainable information about archaeological metals. The study highlights the value of using multiple techniques as a means of resolving the ambiguities that tend to arise from interpretations of single-sited measurements on objects and from single-instrumental analyses during studies of production processes and consequent material performance. Employing different techniques on multiple localities within a sample permits the gathering of precise information about the behavior of and interrelationships between variables that affect the objects’ fabrication and use, particularly composition, structure, and hardness properties. The resulting data are interpreted in association with contextual archaeological information from Petra to consider the use-life and potential significance of these objects.  相似文献   
1000.
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