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   68624篇
  免费   11608篇
  国内免费   14990篇
测绘学   6877篇
大气科学   8994篇
地球物理   14984篇
地质学   37466篇
海洋学   7881篇
天文学   3184篇
综合类   4837篇
自然地理   10999篇
  2024年   206篇
  2023年   718篇
  2022年   1862篇
  2021年   2209篇
  2020年   2421篇
  2019年   2703篇
  2018年   2215篇
  2017年   2722篇
  2016年   2878篇
  2015年   3077篇
  2014年   3885篇
  2013年   4157篇
  2012年   4171篇
  2011年   4503篇
  2010年   3736篇
  2009年   4555篇
  2008年   4506篇
  2007年   4935篇
  2006年   4775篇
  2005年   4007篇
  2004年   3780篇
  2003年   3497篇
  2002年   2969篇
  2001年   2641篇
  2000年   2460篇
  1999年   2300篇
  1998年   2063篇
  1997年   1834篇
  1996年   1597篇
  1995年   1381篇
  1994年   1367篇
  1993年   1178篇
  1992年   917篇
  1991年   646篇
  1990年   554篇
  1989年   462篇
  1988年   348篇
  1987年   218篇
  1986年   164篇
  1985年   127篇
  1984年   59篇
  1983年   41篇
  1982年   53篇
  1981年   39篇
  1980年   42篇
  1979年   41篇
  1978年   50篇
  1977年   43篇
  1976年   26篇
  1954年   22篇
排序方式: 共有10000条查询结果,搜索用时 999 毫秒
101.
Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens.  相似文献   
102.
103.
讨论了应用曲面拟合技术和利用离散的重力观测点的重力变化对特定研究区的重力场变化进行数值模拟以获取该区重力变化空间梯度场图像的具体方法;并应用该方法获得了2004年3月福建安溪3.6级地震前的重力变化空间梯度场图像,发现空间梯度场图像能清晰地反映出地震前重力场群体性变化的差异性;利用此方法对2005年6月~2006年3月间台湾海峡西岸重力场变化进行数值模拟,获得其空间梯度场图像。  相似文献   
104.
105.
We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particular.  相似文献   
106.
107.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra.  相似文献   
108.
109.
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented.  相似文献   
110.
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