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   2325篇
  免费   33篇
  2024年   1篇
  2023年   13篇
  2022年   18篇
  2021年   21篇
  2020年   83篇
  2019年   34篇
  2018年   34篇
  2017年   40篇
  2016年   39篇
  2015年   55篇
  2014年   31篇
  2013年   119篇
  2012年   138篇
  2011年   197篇
  2010年   150篇
  2009年   232篇
  2008年   204篇
  2007年   220篇
  2006年   181篇
  2005年   147篇
  2004年   36篇
  2003年   83篇
  2002年   47篇
  2001年   53篇
  2000年   47篇
  1999年   29篇
  1998年   20篇
  1997年   11篇
  1996年   22篇
  1995年   10篇
  1994年   14篇
  1993年   13篇
  1992年   2篇
  1991年   11篇
  1990年   2篇
  1985年   1篇
排序方式: 共有2358条查询结果,搜索用时 15 毫秒
971.
从西汉史可见都城长安"千余人"集会,"守阙上书"的情景。"阙下"曾经发生大规模的武装冲突。而宫阙前特殊事件的发生,"吏民聚观者"甚至可达"数万人",也说明这里有规模可观的空间。民众可以比较自由地进行公共活动的空间是"市"。刘据在"巫蛊之祸"时曾经策动"市"的群众"数万人"与丞相军激战。"里巷仟佰"也曾经成为民众"聚会"场所。而礼制建筑区也有相当宽阔的空地。不过这是不允许民间活动使用的空间。总体说来,西汉长安宫殿区的宏大规模,使得普通居民的生存条件受到严重压抑,而公共活动空间相对有限,使得都市功能的实现,不得不以诸陵邑作为补充。考察西汉长安和东汉洛阳的城市规划和城市建设,可以发现公共空间的区别。东汉洛阳已经有空间更为充裕的公众活动场所。城市史进程中都会职能和交往条件的这一重要变化,也体现了汉代都市社会构成形式和社会生活形态的若干历史特征。  相似文献   
972.
王宏斌 《历史研究》2013,(1):100-114,192
两次鸦片战争期间,清政府的禁烟政策遇到内外两种阻力:一方面,英国政府极力庇护中国沿海地区的鸦片走私贸易,企图劝诱中国官员承认鸦片贸易合法化;另一方面,贩卖鸦片利益集团、受贿的不法官吏、鸦片吸食者和各级行政司法官员构成来自中国内部四种禁烟运动的阻力。在此背景之下,《查禁鸦片烟章程》对鸦片吸食者判处死刑的条款在执行过程中难以得到有力贯彻,禁烟运动也因此逐渐形成 "明禁暗弛"的局面。从实施效果看,主张用死刑对付吸食者的建议并不完全可取,而反对 "将食烟之人拟以死罪",主张慎刑并以 "常例治之"的看法则有一定合理性。  相似文献   
973.
Wang, H., Li, S., Zhang, Q., Fang, Y., Wang, B. & Zhang, H., 13.02.2015. A new species of Aboilus (Insecta, Orthoptera) from the Jurassic Daohugou beds of China, and discussion of forewing coloration in Aboilus. Alcheringa 39, xxx–xxx. ISSN 0311-5518

He Wang* [], Sha Li* [], Qi Zhang* [], Yan Fang [], Bo Wang? [] and Haichun Zhang [], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China.*Also affiliated with University of Chinese Academy of Sciences, Beijing 100049, PR China. ?Also affiliated with Steinmann Institute, University of Bonn, Bonn 53115, Germany.

A new species of Aboilinae (Orthoptera: Prophalangopsidae), Aboilus perbellus, is described and illustrated based on three well-preserved forewings recovered from the Middle–Upper Jurassic Daohugou beds of Inner Mongolia, China. The new species differs from all congeneric forms in its special forewing coloration and features of its wing venation. To date, three types of forewing coloration have been found among different species of Aboilus at Daohugou, suggesting that these taxa inhabited different ecotopes.  相似文献   
974.
Liu, Q., Zhang, H.C., Wang, B., Fang, Y., Zheng, D.R., Zhang, Q. & Jarzembowski, E.A., 2014. A new saucrosmylid lacewing (Insecta, Neuroptera) from the Middle Jurassic of Daohugou, Inner Mongolia, China. Alcheringa 38. ISSN 0311-5518.

A new genus and new species of Saucrosmylidae (Insecta, Neuroptera) are described (Daohugosmylus castus) based on a well-preserved hindwing from the Middle Jurassic of Daohugou, Inner Mongolia, China. Daohugosmylus gen. nov. is distinguished by a large and nearly semi-circular hindwing, relatively wide R1 space possessing several rows of cells, anteriorly bent Rs, dense crossveins over the entire wing, and smooth outer margin.

Qing Liu (corresponding author) [], Haichun Zhang [], Bo Wang [], Yan Fang [], Daran Zheng [], Qi Zhang [] and Edmund A Jarzembowski [], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, 210008, PR China; secondary address of Daran Zheng & Qi Zhang, University of Chinese Academy of Sciences, Beijing, 100049, PR China; and Ed Jarzembowski, Department of Earth Sciences, The Natural History Museum, London SW7 5BD, UK. Received 13.11.2013; revised 20.1.2014; accepted 21.1.2014.  相似文献   
975.
A new genus with two new species, Scabolyda orientalis gen. et sp. nov. and Scabolyda incompleta sp. nov., assigned to the subfamily Juralydinae in the family Pamphiliidae are described and illustrated. They were collected from the Middle Jurassic Jiulongshan Formation and the Lower Cretaceous Yixian Formation in northeastern China. They represent the first fossil pamphiliids described from China.  相似文献   
976.
王黎  王梓元 《史学集刊》2013,(3):103-109
19世纪中期,英国面临美国追求平等的挑战。虽然帕麦斯顿首相在维护英帝国利益时,惯以海外用兵或以武力相威胁,但面对来自美国的挑战,他却常受掣肘以至有所妥协。这不仅为日后美国的崛起奠定了基础,而且挑战了大国间"难逃权力和平转移厄运"的观点。为此,探析帕麦斯顿时期的英美关系是必要的。毫无疑问,加拿大易受美国攻击的考虑、英美之间日趋互补的经贸关系、困扰英国的欧洲时局等均为重要原因。然而,英美在磨合过程中形成的对世界体系的认同,则是促使拥有全球利益的英国最后接受美国以平等地位加入其主导的世界体系的主要考虑。  相似文献   
977.
Perth is the largest city in Western Australia and home to three-quarters of the state's residents. In recent decades, there have been a lot of earthquake activities just east of Perth in an area known as the South-West Seismic Zone. Previous numerical results of site response analyses based on limited available geology information for PMA indicated that Perth Basin might amplify the bedrock motion by more than 10 times at some frequencies and at some sites. Hence, more detailed studies on site characterization and amplification are necessary. The microtremor method using spatial autocorrelation (SPAC) processing is a useful tool for gaining thickness and shear wave velocity (SWV) of sediments and has been adopted in many previous studies. In this study, the response spectrum of rock site corresponding to the 475-year return period for PMA is defined according to the probabilistic seismic hazard analysis (PSHA) based on the latest ground motion attenuation model of Southwest Western Australia. Site characterization in PMA is performed using two microtremor measurements, namely SPAC technique and H/V method. The clonal selection algorithm (CSA) is introduced to perform direct inversion of SPAC curves to determine the soil profiles of representative PMA sites investigated in this study. Using the simulated bedrock motion as input, the responses of the soil sites are estimated using numerical method based on the shear-wave velocity vs. depth profiles determined from the SPAC technique. The response spectrum of the earthquake ground motion on surface of each site is derived from the numerical results of the site response analysis, and compared with the respective design spectrum defined in the Australian Earthquake Loading Code. The comparison shows that the code spectra are conservative in the short period range, but may slightly underestimate the response spectrum at some long period range.  相似文献   
978.
A nested lumped-parameter model (LPM) consisting of frequency-independent springs and dashpots is proposed to represent the foundation-soil dynamic system with strongly frequency-dependent impedance in time domain. Due to the convergence and robustness of the complex Chebyshev polynomial, it is used to approximate the dynamic flexibility of the foundation by least-square curve-fitting technique. The comparisons with existing LPMs show that the present model can express the impedance by using a small number of elements and reduce oscillation of the solution appearing in simple polynomial approximations. Finally, several examples of foundations with irregular geometries are presented to show the application of nested LPMs.  相似文献   
979.
This article investigates the seismic behavior of masonry infilled RC frames with/without openings. Four full-scale, single-story, and single-bay specimens were tested under constant vertical loads and quasi-static cyclic lateral loads. The experimental results showed that the infill wall was more influential in stiffness than in load-resisting capacity. The opening increased the ductility ratio of the structure due to the uniform distribution and slow propagation of cracks. Finally, simplified micro finite element models are established to simulate the tested specimens, which effectively predict the load-displacement response of the structures and the crack damage of masonry infill wall with acceptable accuracy.  相似文献   
980.
Microseismic (MS) technology has been widely adopted for monitoring coal and rock dynamic disasters. Insights into MS wave characteristics contribute to the accurate prediction of these disasters. In this study, MS wave characteristics were analysed from three aspects: the signal spectra, wavelet packet energy and fractal features. It is shown that prior to the rock burst, the MS wave main frequency decreased following a power law, the amplitude linearly increased, the wavelet packet energy tended to become concentrated on the low frequency bands, and the correlation dimension decreased. When the rock burst occurred, the MS wave main frequency, wavelet packet energy and correlation dimension declined to their lowest levels. Meanwhile, the amplitude rose to a maximum. Therefore, the MS wave characteristics in this study were found to effectively identify and extract precursor information of value for predicting rock dynamic disasters.  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