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   2724篇
  免费   38篇
  2024年   3篇
  2023年   15篇
  2022年   25篇
  2021年   38篇
  2020年   83篇
  2019年   42篇
  2018年   43篇
  2017年   43篇
  2016年   42篇
  2015年   73篇
  2014年   45篇
  2013年   240篇
  2012年   158篇
  2011年   223篇
  2010年   187篇
  2009年   249篇
  2008年   206篇
  2007年   236篇
  2006年   217篇
  2005年   157篇
  2004年   44篇
  2003年   92篇
  2002年   57篇
  2001年   58篇
  2000年   48篇
  1999年   27篇
  1998年   20篇
  1997年   14篇
  1996年   23篇
  1995年   10篇
  1994年   14篇
  1993年   11篇
  1992年   1篇
  1991年   11篇
  1990年   2篇
  1985年   1篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
  1976年   1篇
排序方式: 共有2762条查询结果,搜索用时 15 毫秒
11.
Relatively little is known about the possibilities and limitations of voluntary public programs. The so-called 33/50 Program for reducing releases of certain toxic chemicals into the environment provides a useful instance for examination. In an investigation of toxics-reduction outcomes, with states as units of analysis, economic and policy variables help to explain the results. In particular, channels and approaches used In communicating policy intentions are related to outcomes. Voluntary programs can make a difference, but the details of execution, including the extent and nature of field efforts, influence outcomes.  相似文献   
12.
试论人类身高的地域差异规律及其成因   总被引:1,自引:0,他引:1  
人类身高高纬高于低纬,牧区高于农区、沿海高于内地、低海拔高于高海拔、城市高于农村、发达国家高于发展中国家。其主要原因是气温的高低、光照的多少和营养的差异。  相似文献   
13.
本文论述了图们江地区国际性城市体系建设的必要性,提出了城市体系等级结构、职能结构和空间结构的构建设想及管理原则,并初步估算了城市体系发展各项基础设施建设及投资规模。  相似文献   
14.
The bodies and glazes of 27 early Western Zhou proto‐porcelain samples from Yejiashan cemetery, Hubei Province, were analysed using LA‐ICP–AES, SEM, XRD, a thermal expansion instrument and other analytical methods. The results indicated that the bodies of all samples were characterized by high silicon and low aluminium, and were made with porcelain stone raw materials found in the south of China. The glazes are typical of high‐temperature calcium glazes of the CaO (MgO) – K2O (Na2O) – Al2O3 – SiO2 series, with relatively high Mn and P content, which was probably caused by the addition of plant ashes. The physical properties and phase compositions of Yejiashan proto‐porcelain show that firing processes were still in the early stages of development in ancient China. Multivariate statistical analyses indicated that Yejiashan proto‐porcelain might have come from the Deqing area, in Zhejiang Province. These results provide new archaeological evidence for research on issues related to material flow in the Western Zhou dynasty.  相似文献   
15.
Yelang (夜郎), a mysterious state located in the south‐western area of early China and dating from the Bronze Age to the Early Iron Age (1300 bc – ad 25), is a cultural interactive junction between the Yunnan–Guizhou Plateau and the Yangtze River Basin. The Zhongshui Basin in Weining County, Guizhou Province, was one of the important distribution areas of the Yelang civilization. This area, which includes sites at Jigongshan (鸡公山; 1300 – 800 bc ), Hongyingpan (红营盘; 700 – 400 bc ) and Yinzitan (银子坛; 400 bc – ad 25), has provided a very integrated chronology, spanning from the Bronze Age to the Early Iron Age in the eastern Yunnan – western Guizhou area. To investigate human migration and horse‐trading at these Yelang sites, we conducted a strontium isotopic analysis on the teeth enamel of humans and horses unearthed from these three sites. The results indicated the following: (1) people at the earlier sites (Jigongshan and Hongyingpan) were all indigenous, whereas in the Yinzitan cemetery, there was a more immigrant population, and all the people who were buried in an upper limb flexed supine position were non‐local; and (2) most of the horses found at the Jigongshan and Yinzitan sites show different provenances, probably related to the famous Dian (滇) and Zuo (筰) horses recorded in historical documents, providing more clues for further study on horse‐trading in South‐West China during the Bronze Age and the Early Iron Age.  相似文献   
16.
A human skull, buried about 2500 years ago in a Bronze Age cemetery at Jinggouzi, a site of an important ethnic group in ancient China, appeared to have characteristics of fibrous dysplasia. The CT images indicated a reduction in bone density and relatively homogeneous lesions. More features were revealed using CT reconstruction techniques. Lesions seen in low‐magnification images using a 3D deep‐field microscope had an irregular honeycomb‐like structure. At higher magnification, the trabeculae morphology and the gaps between the trabeculae were irregular and varied in size and shape. Paraffin‐embedded specimens stained with HE showed trabeculae with tortuous irregular arrangements varying in shape and width. The irregular trabeculae of woven bone has been described as having fibrous dysplasia. Molecular analysis of the GNAS gene indicated no mutation. This provides a non‐invasive approach for us to make more comprehensive diagnoses and to assist research into ancient human diseases.  相似文献   
17.
18.
复色釉陶是汉代低温铅釉陶中的一个特殊品种,其施釉烧制工艺系在普通单色釉陶的基础上,于一件器物上施加两种及以上釉料,以低温一次入窑烧制而成,呈现出绚丽的艺术效果,达到了汉代釉陶的高峰。此类釉陶主要分布于宝鸡、济源和延安及其周边地区;最早出现于西汉中晚期,流行于西汉晚期至东汉初期。就施釉工艺而言,其多色施釉技术与北魏时期的二色釉陶一脉相承,并在北齐时期与新出现的"瓷胎铅釉陶"二次烧制技术相结合,形成了北齐特有的多色瓷胎铅釉陶器,为后来唐三彩的出现奠定了技术基础。  相似文献   
19.
滕州前掌大墓地中随葬兵器的墓葬较多,特别是女性墓葬中随葬兵器的现象较之于其他地区更为多见亦罕见于海岱地区。产生这种现象的原因可能与商末周初时女性社会地位较高和前掌大地处战事频繁的东夷重地有关,也许正因如此,前掌大墓地的女性生前可能参与作战。  相似文献   
20.
Shear walls are important lateral force-resistant components of tall buildings. Hence, a reliable numerical model that can accurately represent the mechanical characteristics and large deformations of shear walls is critical for realistic collapse simulation of tall buildings. Based on the theory of generalized conforming element, a high-performance quadrilateral flat shell element, NLDKGQ, accounting for the large deformation using the updated Lagrangian formulation, is proposed herein and implemented in OpenSees. The reliability of NLDKGQ is validated using classical benchmark problems and reinforced concrete specimens. In addition, its capability in simulating the collapse of a tall building is also demonstrated.  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