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   2412篇
  免费   305篇
  国内免费   402篇
测绘学   206篇
大气科学   404篇
地球物理   538篇
地质学   957篇
海洋学   279篇
天文学   212篇
综合类   131篇
自然地理   392篇
  2024年   10篇
  2023年   34篇
  2022年   93篇
  2021年   137篇
  2020年   103篇
  2019年   124篇
  2018年   141篇
  2017年   126篇
  2016年   164篇
  2015年   171篇
  2014年   165篇
  2013年   176篇
  2012年   173篇
  2011年   182篇
  2010年   156篇
  2009年   146篇
  2008年   154篇
  2007年   131篇
  2006年   103篇
  2005年   92篇
  2004年   54篇
  2003年   55篇
  2002年   48篇
  2001年   50篇
  2000年   38篇
  1999年   29篇
  1998年   18篇
  1997年   30篇
  1996年   35篇
  1995年   16篇
  1994年   12篇
  1993年   18篇
  1992年   12篇
  1991年   13篇
  1990年   8篇
  1989年   4篇
  1988年   11篇
  1986年   7篇
  1985年   5篇
  1984年   6篇
  1983年   10篇
  1982年   6篇
  1980年   4篇
  1978年   4篇
  1977年   4篇
  1976年   4篇
  1973年   3篇
  1972年   4篇
  1971年   4篇
  1969年   3篇
排序方式: 共有3119条查询结果,搜索用时 78 毫秒
21.
The goal of this study is to estimate the efficiency of dewatering operations in Alassio Beach, north Italy by following an integrated approach which included beach volume calculations, daily mapping of the shoreline position, examination of specific beach widening events and daily comparisons of morphodynamic characteristics of the drained beach versus a control section which included wave run-up, bar patterns, rip migration, evolution of the berm and cusp morphology.  相似文献   
22.
絮凝法强化大生活用海水一级处理研究   总被引:3,自引:0,他引:3  
研究了无机絮凝剂石灰、硫酸铝、聚合氯化铝、聚合硫酸铁和氯化铁单独使用及其与有机高分子絮凝剂聚丙烯酰胺(PAM)配合使用时强化大生活用海水一级处理的效果,结果表明,无机絮凝剂与有机絮凝剂配合使用时有很好的强化效果,COD去除率最高达61%,且对SS和BOD也有一定的去除效果。  相似文献   
23.
24.
In the bounds of the consistent dynamic interpretation of gravitation (gravidynamics) a gravitational field has been divided into two components: scalar and tensor, each one interacting with its source by the same coupling constant. Consequently, a spherically-symmetrical gravitational field in vacuum generated by a massive object influences test bodies as an algebraic sum of attraction and repulsion. Field energy in vacuum around the source is also a sum of energies of two components — purely tensor and scalar ones of gravitation. At distances from a gravitating object much greater than its gravitational radius, energies of each separate field component are equal to each other at the same point of space.In the bounds of gravidynamics based on the so-called Einstein's linearized equation and proceeding from general principles of theory of classical fields a statement (a theorem) has been formulated on the static gravitational field of a collapsar: a spherically-symmetric object generating a static field in vacuum may always only occupy a finite, nonzero volume.  相似文献   
25.
As a new method, the ultraviolet spectrum technique is applied to studying the connectivity of biode-gradable heavy oil reservoirs. The similarity of crude oils can be judged according to the extinction coefficient (E) because aromatic hydrocarbons and non-hydrocarbons have conjugated bonds and obvious absorption in the ultraviolet range, and different materials have different characteristics and additives. The relationship diagram is made in terms of the extinction coefficients (E) of the samples by taking E as the Y-axis and wavelength as the X-axis. The connectivity of oil reservoirs is estimated according to the curve positions and characteristic fingerprints of the sampies. The connectivity of part of the reservoirs in the western part of the QHD32-6 oilfield was studied with this method. The results showed that the connectivity of samples from wells F7 and F8 in the Nm-2 oil reservoir zone is good, that of samples from wells F17 and F20 in the Nm-1 oil reservoir zone also is good, and that of samples from wells F17, F19, and F20 is poor.  相似文献   
26.
基于GIS的北京城市形态研究   总被引:1,自引:0,他引:1  
经典的城市形态理论包括同心圆理论、扇形理论和多核心理论.利用2002年北京市土地利用图,采用GIS缓冲区分析的方法,分析了北京市各功能用地的方向特征和圈层特征.结果表明:北京市的土地利用体现了明显的圈层特征,同时各类功能用地在各方向的分布又明显受到了河流、交通干道和工业区等地理要素的影响.北京没有形成城市总体规划的多中心布局,第一道绿化隔离地区中绿地面积没有明显高出其他地区,基本上已经失去了中心城区和边缘集团隔离开的功能.总体上,北京城市空间形态主要是同心圆和扇形的结合,更接近同心圆理论和扇形理论的混合形式.  相似文献   
27.
地质和岩土工程光纤传感监测技术综述   总被引:3,自引:0,他引:3  
光纤传感器与常规传感器相比具有很大的优越性,已经成为地质和岩土工程监测领域中的研究热点。本文介绍了光纤传感监测系统的种类、基本测量原理和目前国内外的研究发展状况,并对各种传感技术的性能和特点进行了比较,指出了光纤传感监测技术应用于地质和岩土工程监测尚需研究的相关课题。  相似文献   
28.
Most Large igneous provinces (LIPs) are emplaced within <10 Ma, with a main pulse of the magmatism in<1 Ma[1]. For example, the Siberian Traps [2] and the Deccan Traps [3] were probably erupted within one million years. Many events, such as the Columbia River event, feature a single pulse of magmatism, followed by a protrac-ted period of magmatism at a much lower rate that is linked to a plume tail[4].  相似文献   
29.
The accurate radiative transfer model GOMETRAN, initially designed to yield radiances at TOA in the wavelength range 240–790 nm, has been extended to allow for the computation of actinic fluxes down to 175 nm and for the calculation of photolysis frequencies in the atmosphere. The capability of the extended model PHOTOGT (PHOTOGOMETRAN) is demonstrated in a number of successful comparison studies both with recent experiments (ground-based, balloonborne, airborne) and model calculations of radiances, actinic fluxes and photolysis frequencies in the stratosphere and troposphere. In an atmospheric case study, the impact of new quantum yield data for the O3 » O2+O(1 d) photodissociation channel on the photolytic production of O(1 d) atoms in the lower atmosphere has been quantified.  相似文献   
30.
Major-element and REE compositions of 14 diamondiferous eclogites from the Udachnaya kimberlite in Yakutia, Siberia have been determined by electron microprobe and secondary ion mass spectrometer (SIMS). Based on previous clinopyroxene classification schemes (e.g., Taylor and Neal 1989), all of these eclogite xenoliths belong to Group B/C, although some of the garnet compositions and mineral REE abundances are inconsistent with the indicated groups. This demonstrates the inadequacy of the classification scheme based on African eclogites for application to Siberian samples. Because of the coarse grain size of the Udachnaya nodules, meaningful modal abundances could not be obtained. However, reconstructed REE compositions using various garnet: clinopyroxene ratios demonstrate relative insensitivity to changes in mode for common eclogitic assemblages. Many of these reconstructed REE compositions show LREE depletions. Some depletions are consistent with an origin (either directly or through partial melting) as normal or Type-I ocean floor basalt. Others, however, require material of eclogitic or pyroxenitic affinities to undergo partial melting; this facilitates the depletion of LREE while leaving the HREE at nearly original levels. Many of the eclogites of South Africa are consistent with a protolith of anomalous or Type II ocean floor basalt. This fundamental difference between the two regions is the likely cause of the inconsistencies with the chemicallybased classification.  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