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   3838篇
  免费   742篇
  国内免费   1090篇
测绘学   392篇
大气科学   694篇
地球物理   903篇
地质学   2026篇
海洋学   653篇
天文学   215篇
综合类   359篇
自然地理   428篇
  2024年   46篇
  2023年   136篇
  2022年   238篇
  2021年   276篇
  2020年   266篇
  2019年   282篇
  2018年   264篇
  2017年   248篇
  2016年   249篇
  2015年   237篇
  2014年   243篇
  2013年   222篇
  2012年   271篇
  2011年   247篇
  2010年   232篇
  2009年   194篇
  2008年   201篇
  2007年   162篇
  2006年   146篇
  2005年   128篇
  2004年   104篇
  2003年   78篇
  2002年   101篇
  2001年   88篇
  2000年   94篇
  1999年   129篇
  1998年   123篇
  1997年   97篇
  1996年   113篇
  1995年   73篇
  1994年   63篇
  1993年   72篇
  1992年   59篇
  1991年   51篇
  1990年   34篇
  1989年   16篇
  1988年   24篇
  1987年   11篇
  1986年   12篇
  1985年   2篇
  1984年   6篇
  1983年   4篇
  1982年   6篇
  1981年   6篇
  1979年   3篇
  1958年   3篇
  1957年   2篇
  1954年   1篇
  1933年   2篇
  1931年   1篇
排序方式: 共有5670条查询结果,搜索用时 15 毫秒
71.
衡阳盆地红层的磁性地层学研究   总被引:2,自引:1,他引:2  
葛同明 Vinde.  H 《地质学报》1994,68(4):379-388
本文用磁性地层学方法研究衡阳盆地白垩纪-第三忆地层,建立了该地层的磁极性序列。以地磁极性年代表为时间标尺,并辅之岩石的^39Ar-^40Ar同位素年代测定值,研究了各地层单元的生成年代,为地层时代的确定提供了依据。研究认为,衡阳盆地东北组时代属早白垩世;神皇山时代为早白垩世-晚白垩世;载家坪组时代为晚白垩世;东塘组和霞流市组时代属古新世。  相似文献   
72.
Half-smooth tongue sole (Cynoglossus semilaevis) is a promising species for aquaculture in China.The wild population of C. semilaevis is under threat from environmental factors. Microsatellite markers are very suitable for assessing genetic diversity. Four microsatellite-enriched libraries of half smooth tongue sole (Cynoglossus semilaevis) were constructed,from which 57 polymorphic microsatellites were isolated and characterized.The polymorphism of these microsatellites was assessed by genotyping in 30 ind...  相似文献   
73.
Pang  Yue  Fan  Dejiang  Sun  Xiaoxia  Sun  Xueshi  Liu  Ming  Yang  Zuosheng 《中国海洋大学学报(英文版)》2020,19(4):801-810
For a long time, most studies about pyrite have focused on sediments while only a few have focused on pyrite in water. In this study, a method that combines the scanning electron microscopy(SEM) and the energy dispersive X-ray spectrometry(EDS) was used to compare pyrite particles suspended in water to those in associated bottom sediments, both obtained from the mixing zone of the Yangtze Estuary. It was found that the pyrite particles in the two media have similar morphologies and size distributions. The particle morphology mainly includes two types, single crystal and aggregate, and the particle size mainly ranges from 0.5 to 2 μm. The pyrite particles in water exhibit an increase in relative content towards the sea, and their transport and deposit processes are mainly affected by hydrodynamic conditions. It is concluded that the pyrite particles in the suspended matter mainly derived from the resuspension of sediments, which are products of the early diagenesis. Precursor minerals may appear during the formation of pyrite, but are generally restricted by the diagenetic environment and local microenvironment.  相似文献   
74.
小东沟组由王钰等(1954)命名。由于小东沟组内涵含混,自创建以来,已使许多地层工作者对小东沟组的涵义、时代的理解,特别是使用于区域地层划分和对比中造成了一定困难。作者从小东沟组岩石组合、生物群特征,以及在地层系统中的位置等方面对小东沟组涵义进行了重新厘定,认为小东沟组是独立于小岭组之外的晚侏罗世岩石地层单位。鉴于小东沟组存在的缺欠,作者建议在本溪东营坊、新宾东昌台、桓仁暖河子寻找模式剖面。  相似文献   
75.
Outburst risk of barrier lakes in Sichuan,China   总被引:1,自引:1,他引:1  
34 barrier lakes induced by earthquake have been formed by wedged debris on the river channels after a massive earthquake happening on May 12 in Sichuan, China. Among them, the Tangjiashan Barrier Lake is the largest one. It faces very urgent risk of dam breaking when water level reaches the top and begins overflow in case of storm rainfalls and continually aftershocks, threatening already devastated cities and villages with about 1.5 million people downstream. The outburst of a similar barrier lake occurred in the Minjiang River in 1933, causing a catastrophic flood. Risk analysis indicates that not all barrier lakes are highly dangerous. Only those lakes with very high dams and water to be filled up in short period need to be dealt with immediately.  相似文献   
76.
ENVISAT测高数据波形重跟踪分析研究   总被引:5,自引:4,他引:5  
对卫星测高技术中的波形重跟踪技术及其算法进行了详细分析讨论.同时分析了波形重跟踪中最小二乘解初值及权的确定,根据ENVISAT的SGDR波形数据,利用波形重跟踪技术研究了开阔海域上的距离改正情况(一般距离改正为20~30cm)。结果表明,重跟踪改正后的精度,18Hz距离优于1Hz距离。  相似文献   
77.
为研究卫星在不同高度对地面重力变化的检测能力,利用地面获得的重力场时间和空间变化,采用空间域向上解析延拓原理,将地面数据向上解析延拓到数百千米的不同高度。计算分析表明,如果地表存在93×10-8ms-2的重力变化量,在450km高度可观测到20×10-8ms-2的重力变化。所以利用卫星重力观测技术进行地震监测,其观测精度应优于20×10-8ms-2。  相似文献   
78.
Sky surveys represent one of the most important efforts to improve developments in astrophysics,especially when using new photometric bands. We are performing the Stellar Abundance and Galactic Evolution(SAGE) survey with a self-designed SAGE photometric system, which is composed of eight photometric bands. The project mainly aims to study the stellar atmospheric parameters of ~0.5 billion stars in ~12 000 deg2 of the northern sky, which mainly focuses on Galactic astronomy, as well as some aspects of extragalactic astronomy. This work introduces the detailed data reduction process of the test field NGC 6791, including the data reduction of single-exposure images and stacked multi-exposure images, and properties of the final catalog.  相似文献   
79.
The Plastic Scintillator Detector(PSD) onboard the DArk Matter Particle Explorer(DAMPE)is designed to measure cosmic ray charge(Z) and to act as a veto detector for gamma ray identification.To fully exploit the charge identification potential of PSD and to enhance its capability to identify gamma ray events, we develop an alignment method for the PSD. The path length of a given track in the volume of a PSD bar is derived taking into account the shift and rotation alignment corrections. By examining energy spectra of corner-passing events and fully contained events, position shifts and rotations of all PSD bars are obtained, and are found to be on average about 1 mm and 0.0015 radian respectively. To validate the alignment method, we introduce artificial shifts and rotations of PSD bars into the detector simulation.These shift and rotation parameters can be recovered successfully by the alignment procedure. As a result of the PSD alignment procedure, the charge resolution of the PSD is improved from 4% to 8%, depending on the nuclei.  相似文献   
80.
元素丰度与星系演化(Stellar Abundance and Galactic Evolution,SAGE)是自主设计的能够准确计算恒星大气参数以及消光的新测光系统。对北天除银盘外共计约12 000 deg2的天区开展了SAGE系统测光巡天,计划获取约5亿颗恒星的高精度测光数据。单次曝光条件下100σ完备星等uSC~17. 3,vSAGE~16. 8(AB星等),这些为研究银河系提供宝贵的测光资料。介绍了巡天专用的数据处理程序的研究和开发,主要研究了针对单幅图像的快速自动化处理过程,重点介绍数据改正、天体测量校正、测光和流量定标过程,以及数据结果和数据质量检测等。  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