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   345篇
  免费   58篇
  国内免费   362篇
测绘学   1篇
大气科学   124篇
地球物理   119篇
地质学   223篇
海洋学   117篇
天文学   63篇
综合类   38篇
自然地理   80篇
  2024年   15篇
  2023年   83篇
  2022年   29篇
  2021年   43篇
  2020年   18篇
  2019年   21篇
  2018年   19篇
  2017年   16篇
  2016年   9篇
  2015年   34篇
  2014年   67篇
  2013年   37篇
  2012年   15篇
  2011年   25篇
  2010年   14篇
  2009年   13篇
  2008年   18篇
  2007年   22篇
  2006年   19篇
  2005年   19篇
  2004年   13篇
  2003年   20篇
  2002年   15篇
  2001年   18篇
  2000年   21篇
  1999年   14篇
  1998年   17篇
  1997年   15篇
  1996年   17篇
  1995年   12篇
  1994年   13篇
  1993年   13篇
  1992年   5篇
  1991年   7篇
  1990年   8篇
  1989年   9篇
  1988年   6篇
  1987年   3篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
排序方式: 共有765条查询结果,搜索用时 31 毫秒
11.
On the basis of the observation data of Kuroshio since 1984 and relative historical data in the East China Sea, spatial and temporal variation of water mass mixing characteristic in the observation area is analysed. The main results are as follows.  相似文献   
12.
INTRODUCTIONTheDenglouCape ,inthesouthwestoftheLeizhouPeninsula ,isatthenorthmarginoftropicalzone .SeveralresearchesandcartographiesoftheregionalgeomorphologyandQuater narygeology ,whichwerecarriedoutinthepast,allincludethisarea (MGL ,SCSIO ,CAS ,1 978;GPCSGRCZT…  相似文献   
13.
INTRODUCTION Sea urchin is a marine animal of economic value. The gonad of Hemicentrotus pulcherrimus A. Agassiz and Anthocidaris crassispina A. Agassiz may be offered as food and medicine, the sea urchin shell may be used as fertilizer and artware and moreover, the sea urchin eggs are important materials for the studies in embryology and molecular biology. With the increasing exportation of sea urchins in China, the natural resources are gradually decreasing. In order to satisfy people's growing needs of sea  相似文献   
14.
In this paper the Morlet complex wavelet munction was applied to analyze the evolution features of multi-scale wave-intensity during a torrential rain process.Separating the suhsynoptic scale system on temperature of black body(TBB) fields during a torrential rain process over the Middle and Lower Reaches of Changjiang River in the last dekad of July 1998,the evolution of multi-scale wave-intensity can be expressed by wavelet modules,and its coherence was investigated with the cross spectrum between the multi-scale waves.The results show that the process of the accumulation and release on the energy of meso-β scale system was shown in the torrential rain process,and the meso-α scale system had an interference effect on the meso-β system in a shorter period.  相似文献   
15.
A 2-D global chemistry-transport model is set up in this paper.The model simulates the atmospheric ozone distributions well with specified dynamical conditions.The analysis of ozone variation mechanism shows that ozone is chemically in quasi-equilibrium except for the polar night region where the variation of ozone concentration is under the control of dynamical processes,that the oxygen atoms which produce ozone are mainly provided by the photolysis of O2 in the upper stratosphere and by the photolysis of NO2 in the lower stratosphere and the troposphere.and that the ozone is destroyed mainly by NOx:the reactions between NOx and O3 and the odd oxygen cycle contribute 80% to more than 90% of the ozone destruction.  相似文献   
16.
核能设施所在地地质环境热规律的初步探讨   总被引:1,自引:0,他引:1  
本文在前苏联核电站地下水温变化观测资料的基础上,初步探讨了工艺成因地下热场的形成、展布规律及由此而可能引起的不良地质现象。提出了水温增值的计算公式,并指出在温差大的地段可能形成热应力,从而产生热机械过程,造成环境生态影响。  相似文献   
17.
Yixunite and damiaoite Were found in a cobalt- and copper-bearing platinum ore vein of a contact metasomatic deposit. The chief ore minerals are bornite, chalcopyrite, magnetite and carrollite. The platinum minerals include moncheite, sperrylite, daomanite, cobalt malanite and cooperite. Yixunite and damiaoite occur as immiscible globules, 1.0 to 2.0 mm in diameter. Yixunite is always in the central part of a globule. It is opaque with metallic lustre, bright white colour and black streak. HM = 5.8; VHN50 = 634 kg/mm2 (573-681 kg/ mm2); insoluble in HCl, HNO3, HF or H3PO4; no cleavage; no magnetism. Density is hard to measure because of small grain size. Calculated density = 18.21 g/cm3. Reflective colour is bright white with a yellowish tint. Isotropic. The mean analytical results (ranges) (%) are: Pt 82.8 (81.8-83.6), In 16.4(15.6-17.1) and total 99.2. The empirical formula (based on 4 atoms) is Pt2.993 In1.007 . The five strongest lines of X-ray diffraction (hkl, d,I) are 111, 2.30 (100); 200, 1.99 (  相似文献   
18.
Changchengite occurs in chromite orebodies in dunite and in platinum placer deposits in chromite orebodies nearby. The mineral occurs as massive aggregates or veinlets on margins of iridisite (IrS2) and replaces it. Opaque. Lustre metallic. Colour steel-black. Streak black. Hm = 3.7. VHN20= 165 kg/ mm2. Isotropic. Cleavage none. Density 11.96 g/ cm3. Seven electron microprobe analyses give the following mean chemical results (wt. %): S 7.2, Cu 0.3, Te 0.4, Ir 41.2, Pt 2.8 and Bi 47.3 with total 99.1. The simplified formula is IrBiS. The strongest X-ray powder diffraction lines (hkl, d, I) are 210, 2.75 (70); 211, 2.51 (60); 311, 1.860 (100); 440. 1.090 (50) and 600, 1.027 (50). The X-ray powder diffraction pattern is similar to that of mayingite. After the diffraction data are indexed the mineral is determined to be cubic. The space group is P213 with a = 0.6164(4) nm, V = 0.2342 nm3 and Z = 4.  相似文献   
19.
INTRODUCTION Tunnel typeanchoragehasobviousadvantages inbearingcapacityversusinvestment(LiuandHu,1996).However,itisrarelyusedinapracticalpro jectbecauseofitsrequirementofgoodrockcondi tions.Siduhebridge(Fig.1),whichliesintheBa dongmountainsinthewestplatea…  相似文献   
20.
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