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   1186篇
  免费   179篇
  国内免费   254篇
测绘学   100篇
大气科学   296篇
地球物理   292篇
地质学   505篇
海洋学   143篇
天文学   57篇
综合类   112篇
自然地理   114篇
  2024年   7篇
  2023年   34篇
  2022年   52篇
  2021年   70篇
  2020年   42篇
  2019年   54篇
  2018年   56篇
  2017年   58篇
  2016年   65篇
  2015年   49篇
  2014年   57篇
  2013年   72篇
  2012年   45篇
  2011年   67篇
  2010年   61篇
  2009年   65篇
  2008年   61篇
  2007年   60篇
  2006年   30篇
  2005年   36篇
  2004年   27篇
  2003年   29篇
  2002年   46篇
  2001年   41篇
  2000年   29篇
  1999年   64篇
  1998年   52篇
  1997年   44篇
  1996年   32篇
  1995年   32篇
  1994年   28篇
  1993年   26篇
  1992年   24篇
  1991年   15篇
  1990年   19篇
  1989年   17篇
  1988年   6篇
  1987年   5篇
  1986年   5篇
  1985年   8篇
  1984年   4篇
  1983年   7篇
  1982年   4篇
  1981年   3篇
  1980年   4篇
  1978年   2篇
  1977年   2篇
  1975年   1篇
  1970年   1篇
  1954年   1篇
排序方式: 共有1619条查询结果,搜索用时 15 毫秒
31.
An integrated view encompassing the networks for public and private transport modes as well as the activity programs of travelers is essential for accessibility analysis. In earlier research, the multi-state supernetwork has been put forward by the authors as a suitable technique to model the system in such an integrated fashion. An essential part of a supernetwork involving multi-modal and multi-activity is the personalized transportation network, which is an under-researched topic in the academic community. This article attempts to develop a heuristic approach to construct personalized transportation networks for an individual's activity program. In this approach, the personalized network consists of two types of network extractions from the original transportation system: public transport network and private vehicle network. Three examples are presented to illustrate that the public transport network and private vehicle network can represent an individual's attributes and be applied in large-scale applications for analyzing the synchronization of land-use and transportation systems.  相似文献   
32.
There are nearly 700 cities in China, each with their own particular characteristics of natural environment quality and rates of economic development. When people are able to choose a city to live in, they will take into account these characteristics in order to improve their lifestyles. Based on geographic information system technology and the analytic hierarchy process method, a model of the living environment suitability index (LESI) for the larger cities of China was designed. The LESI was constructed by using the factors of economic condition, convenience and livable degree, natural environment and natural resources. The LESI model was then applied to compare the living conditions in 35 major cities in China in 2007, including 30 provincial capitals and 5 sub-provincial cities. LESI values were higher for cities in southeast China than for cities in the northwest. The highest LESI values were mainly distributed along the Chinese southeast coast and the Yangtze River Delta. Cities with the lowest LESI values were found in the centre and north of China. Of the 35 cities, 4 had highly suitable living environments and 7 had unsuitable living environments.  相似文献   
33.
Ye  Chao  Chen  Mingxing  Chen  Ruishan  Liao  Chuan 《地理学报(英文版)》2022,32(7):1405-1408
Journal of Geographical Sciences -  相似文献   
34.
In this paper, 183 chemical analyses of clinopyroxenes are collected from mantle-derived inclusions inCenozoic basalts of eastern China. Through synthetic studies of the relevant data, their mineral chemistry andgeological significance are discussed. Based on the composition fo clinopyroxenes the authors conclude that theCenozoic upper mantle in eastern China is of the continental, primitive, metasomatic and high-temperaturetypes and is related to rift structural environment and variation in composition of basalts. The geobarometry ofclinopyroxenes indicates that Cenozoic basalts of eastern China are derived from the asthenosphere and thatthe average depth of faults progressively increases from south to north and from east to west.  相似文献   
35.
作者通过对我国东部新生代玄武岩中巨晶Cpx的109个样品的化学成分的统计、计算及投影,研究了Cpx巨晶的产状、物性及矿物化学的主要特征,并对其成因信息提出了自己的看法。Cpx巨晶的成分以A1_2O_3、A1~(v1)较高而Ti、Mg'中等为特征。但在“反应边”中,A1_2O_3、Na_2O、A1、A1~(v1)则明显降低。我国巨晶以普通辉石为主,而透辉石、次透辉石及顽透辉石少见。国内不同地区的Cpx巨晶成分也略有不同:华南区巨晶的Wo较高而A1_2O_3较低;华北区Fs、A1_2O_3较高;而东北区En较高而A1_2O_3中等。有关Cpx巨晶的成因信息,作者的观点是:(1)巨晶Cpx是寄主玄武岩浆在上地幔中结晶的产物,而不是地幔解体的捕虏晶。(2)我国巨晶Cpx的结晶温度是1021—1209℃,压力为1.4—3.2GPa,所以,Cpx巨晶的结晶深度为48—104Km。(3)我国东部新生代玄武岩均产于大陆板块内部,以碱性玄武岩成分为主,而拉斑玄武岩较少。  相似文献   
36.
Zheng  Mingguo  Liang  Cheng  Huang  Bin  Liao  Yishan  Yuan  Zaijian 《Hydrogeology Journal》2021,29(7):2429-2439
Hydrogeology Journal - Although there is a general consensus that spatial heterogeneity is ubiquitous in hydrological responses, it is common practice to assume a constant specific discharge among...  相似文献   
37.
We report the results of fully three-dimensional numerical simulations of nonlinear convection in a Boussinesq fluid in an annular channel rotating about a vertical axis with lateral no-slip or stress-free sidewalls, stress-free top and bottom, uniformly heated from below, a problem first studied by Davies-Jones and Gilman (1971 Davies-Jones, RP and Gilman, PA. 1971. Convection in a rotating annulus uniformly heated from below.. J. Fluid Mech., 46: 6581.  [Google Scholar]) and Gilman (1973 Gilman, PA. 1973. Convection in a rotating annulus uniformly heated from below. Part 2. Nonlinear results. J. Fluid Mech., 57: 381400.  [Google Scholar]). A substantial range of the Rayleigh number R (Rc≤R≤O(100 Rc)), where Rc denotes the critical value at the onset of convection) is considered. It is found that the wall-localized convection mode, unaffected by the velocity boundary condition imposed on the sidewalls, is nonlinearly robust. Both directions of travelling waves, one propagating against the sense of rotation near the outer sidewall and the other propagating in the same sense as the rotation in the vicinity of the inner sidewall, are always present in the nonlinear solutions. In contrast to nonlinear convection in a rotating Bénard layer, neither convection rolls nor the Küpper–Lortz instability can exist in a rotating annular channel because of the effect of the sidewalls. It is the nonlinear interaction between the wall-localized modes and the internal mode that plays an essential role in determining the nonlinear properties of convection in a rotating annular channel. Our studies reveal systematically the various nonlinear phenomena, from steady travelling waves trapped in the vicinities of the sidewalls to convective turbulence exhibiting columnar structure.  相似文献   
38.
39.
在漫长的旧社会 ,由于各种原因 ,使得我国沿海地区居民的法制意识比较淡薄。我国加入WTO后 ,经济生活乃至社会生活将要严格遵守规则 ,从而也将促使我国沿海地区的法制意识增强。  相似文献   
40.
根据“三个代表”的思想 ,社会主义宪法应该代表先进生产力的发展要求。中国的宪法发展说明 ,什么时候代表了中国先进社会生产力发展的要求 ,什么时候中国宪法就能健康发展  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