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   17455篇
  免费   2979篇
  国内免费   4628篇
测绘学   2808篇
大气科学   3102篇
地球物理   4059篇
地质学   6809篇
海洋学   3066篇
天文学   1501篇
综合类   1564篇
自然地理   2153篇
  2024年   37篇
  2023年   182篇
  2022年   556篇
  2021年   629篇
  2020年   836篇
  2019年   825篇
  2018年   717篇
  2017年   886篇
  2016年   857篇
  2015年   1020篇
  2014年   1006篇
  2013年   1194篇
  2012年   1143篇
  2011年   1146篇
  2010年   929篇
  2009年   1096篇
  2008年   1212篇
  2007年   1422篇
  2006年   1343篇
  2005年   1178篇
  2004年   976篇
  2003年   836篇
  2002年   743篇
  2001年   550篇
  2000年   687篇
  1999年   641篇
  1998年   483篇
  1997年   361篇
  1996年   299篇
  1995年   231篇
  1994年   200篇
  1993年   195篇
  1992年   169篇
  1991年   107篇
  1990年   62篇
  1989年   92篇
  1988年   56篇
  1987年   46篇
  1986年   40篇
  1985年   21篇
  1984年   13篇
  1983年   6篇
  1982年   7篇
  1981年   3篇
  1980年   5篇
  1979年   2篇
  1978年   2篇
  1977年   2篇
  1971年   2篇
  1954年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Current plate motions   总被引:57,自引:0,他引:57  
  相似文献   
52.
53.
54.
Keck's Long Wavelength Spectrometer (LWS), is the facility instrument used for imaging and spectroscopy in the wavelength range of 3–28 μm at the Keck Observatory. LWS uses an 128 × 128 Si:As blocked impurity band (BIB) array manufactured by the Boeing Corporation. This paper discusses the method used for optimizing the detector's operating parameters at a temperature of 8.5 K and bias voltage of 1.2 V. A process for characterizing detective quantum efficiency of BIB detectors is also presented. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
55.
The paper deals with the methods of formation pressure evaluation for a single well by using the very common ac-cepted parameters, such as drilling exponent , and flowline temperature , etc. which is part of compiling the end well report.  相似文献   
56.
57.
1 IntroductionDiscontinuousDeformationAnalysis(DDA)developedbyShiin 1 980’s[1 ,2 ] maybeusedtocalculatethedeformationanddisplacementsinamulti blocksystemandtoanalyzetherelationbe tweenforcesanddisplacementsinthesystem .Ifthesurveydisplacementofeverypointordirectionisknown,alldisplacementsanddeformationsofblocks,eventheglide ,theclosureandthestretchoftheboundary planeofblocks ,canbecalculated .TheresultisoptimallyfittedaccordingtotheLeastSquarePrinciple.DDAismainlyusedinrockblockssystems…  相似文献   
58.
Linux 防火墙的研究与设计   总被引:4,自引:0,他引:4  
阐述了Linux2.4内核的防火墙Linux的原理,并分析了netfilter的设计与实现,叙述了Linux的动态地址转换,介绍了在Linux下基于netfilter架构如何开发自己的防火墙并给出具体实例。  相似文献   
59.
We propose a zero-point photometric calibration of the data from the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) on board the Hubble Space Telescope , based on a spectrum of Vega and the most up-to-date in-flight transmission curves of the camera. This calibration is accurate at the level of a few hundredths of a magnitude. The main purpose of this effort is to transform the entire set of evolutionary models into a simple observational photometric system for ACS/WFC data, and to make them available to the astronomical community. We provide the zero-points for the most used ACS/WFC bands, and give basic recipes for calibrating both the observed data and the models. We also present the colour–magnitude diagram from ACS data of five Galactic globular clusters, spanning the metallicity range  −2.2 <[Fe/H] < −0.04  , and we provide fiducial points representing their sequences from several magnitudes below the turn-off to the red giant branch tip. The observed sequences are compared with the models in the newly defined photometric system.  相似文献   
60.
Based on the Germany Koldwey Station's 1994-2003 conventional observation hourly data, this paper conducts a statistical analysis on the short-term climate characteristics for an arctic tundra region (Ny-(A)lesund island) where our first arctic expedition station (Huanghe Station) was located. Affected by the North Atlantic warming current, this area has a humid temperate climate, and the air temperature at Ny-(A)lesund rose above 0 ℃ even during deep winter season during our research period. The wind speed in this area was low and appeared most at southeast direction. We find that the temperature at Ny-(A)lesund rose in the faster rate (0.68 ℃/10 a) than those at the whole Arctic area. Compared with the floating ices where our expedition conducted in the Arctic, Ny-(A)lesund was warmer and more humid and had lower wind speed. Comparison of the near surface air temperature derived by NCEP/NCAR reanalysis to the conventional measurements conducted at the Koldwey site in Ny-(A)lesund area shows a good agreement for winter season and a significant difference for summer season.  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