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   1018篇
  免费   193篇
  国内免费   292篇
测绘学   48篇
大气科学   341篇
地球物理   264篇
地质学   480篇
海洋学   90篇
天文学   30篇
综合类   124篇
自然地理   126篇
  2024年   7篇
  2023年   12篇
  2022年   55篇
  2021年   50篇
  2020年   52篇
  2019年   72篇
  2018年   68篇
  2017年   76篇
  2016年   81篇
  2015年   54篇
  2014年   78篇
  2013年   45篇
  2012年   60篇
  2011年   63篇
  2010年   55篇
  2009年   58篇
  2008年   37篇
  2007年   55篇
  2006年   44篇
  2005年   51篇
  2004年   33篇
  2003年   26篇
  2002年   27篇
  2001年   21篇
  2000年   31篇
  1999年   68篇
  1998年   43篇
  1997年   32篇
  1996年   32篇
  1995年   20篇
  1994年   20篇
  1993年   20篇
  1992年   18篇
  1991年   10篇
  1990年   8篇
  1989年   8篇
  1988年   4篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1980年   1篇
  1958年   1篇
排序方式: 共有1503条查询结果,搜索用时 437 毫秒
991.
Several papers have reported that part or whole leafy thallus seemingly consisting of zygotospores can give rise to both blades and conchocelis in the same culture ofPorphyra. Study on samples of wild and cultivatedPorphyra yezoensis andP. oligospermatangia were conducted to clarify the origination of the young blades in the culture. It is confirmed that single cells on the blade of both species, which normally intermixed with zygotospores, germinated into young blades. TEM and SEM observation has shown that the single cells ofPorphyra yezoensis had typical features of female gamete (carpogonia) but archeospore. Therefore, the female gametes are responsible in developing leafy thalli. This project was sponsored by the NSFC (No. C-0205-05-39770593)  相似文献   
992.
On the centimeter scale of lithologic change, we conduct poly-statistic analysis on the sedimentary behavior and dynamic features of the stratigraphic sequence from upper Dalong formation to lower Daye formation, which across the Permian-Triassic boundary in East Hubei. From the perspective of stochastically dynamic system, the depositional process of upper Dalong formation can be regarded as a stable Markovian process with weakly stratigraphie correlation and randomly lithologic alteration. Compared to it, the depositional process of lower Daye formation was unstable Markovian process with much closer stratigraphic correlation and ordered lithologic change. As for the replacement style of the sedimental cycle, the former was chaotic, while the latter was periodical. Otherwise, although the overall depositional process of the two formations was continuous, their dynamic characteristics were obviously different. So this P-T sedimental boundary can also be regarded as a dynamic limit. It was a kind of depositional reaction in response to a catastrophic alteration when the geological environment was in continuous change but came over a certain threshold state.  相似文献   
993.
1 Geologic setting and layout of the DSS observation network In the studied area there are three major tectonic units, which are referred to as Tianshan fold system, Tarim basin and West Kunlun fold system (Bureau of Geology and Mineral Resources of Xinjiang Uygur Autonomous Region, 1993). The Tianshan fold system is a polycyclic geosyncline on the north edge of Tarim basin, and an orogenic zone resulting from collision and convergence between Tarim block and the Junggar-North Tianshan…  相似文献   
994.
Temperature and methane records over the last 2 ka in Dasuopu ice core   总被引:4,自引:0,他引:4  
High resolution δ18O and methane records over the last 2ka have been reconstructed from Dasuopu ice core recovered from the Himalayas. Analysis shows that the δ18O record correlates well with the Northern Hemispheric temperature, Dunde ice core record, and with temperature record in eastern China. The warming trend detected in δ18O record from the last century is similar to that during the Medieval warm period. There is a dramatic increasing in methane concentration in the Dasuopu ice core, which reached 1031 nmol ⋅ mol-1 in 1997. Moreover, methane concentration in the Dasuopu ice core is about 15%-20% higher than that in Antarctica and Greenland. There is a positive correlation between methane concentration and δ18O in Dasuopu ice core.  相似文献   
995.
强对流(冰雹)云中水凝物的积累和云水的消耗   总被引:22,自引:5,他引:22  
许焕斌  段英 《气象学报》2002,60(5):575-584
在冰雹云中过冷水的累积对冰雹增长起重要作用。文中回顾了水凝物累积和过冷水消耗机制中的不确定性 ,利用三维Euler强对流云模式和三维Lagrange粒子群运行增长模式 ,重新研究了对流云中水凝物粒子的累积机制和过冷水的消耗图像 ,得出以下结果 :(1)强对流 (冰雹 )云具有翻滚式对流流场 ,流场的性质决定云中存在着一个动力吸引区 ,它处于主上升气流区旁侧水平气流近于零的区域 ,粒子在增长运行中向这里集中 ,造成水凝物的累积 ;(2 )这种粒子的集中和水凝物的累积 ,是流场动力特征和粒子增长行为相互作用的表现 ;(3)粒子的集中和水凝物的累积是动态循环式的 ,而不是静态平衡式的 ,粒子可以进入吸引区 ,也可以吹离吸引区 ,在进入和吹离的循环中动态地形成了集中和累积 ,累积可以发生在主上升气流上方 ,也可以延伸到其下方 ;(4)粒子的集中和水凝物的累积是受流场和粒子运动的动力过程控制的 ,而累积粒子是液相雨滴 ,或是固相霰粒、雪团和冰雹是受降水发展过程属液相或固相占优势来决定的 ;(5 )云水场中云水量 ,只在大粒子的集中区才被显著消耗 ;而在区外的云水量消耗不显著 ;(6 )对于云水含量高达 6 g/kg的云水场 ,播撒粒子浓度达到 10 0个 /m3 时 ,在考虑消耗时 ,已不能增长成直径大于 1cm的冰雹。  相似文献   
996.
C1相干算法及其在三维地震勘探解释中的应用   总被引:4,自引:0,他引:4  
作者在文中详细讨论了二维和三维C1相干算法,根据三维C1相干算法的特点,结合二维地震数据体的特点,考虑到三维地震勘探在各大矿区的全面普及,针对三维地震资料开发出了一套实用的应用程序进行相干处理和解释,通过对实际三维地震资料的处理,分析结果表明,C1相干技术对三维地震资料的构造,岩性解释有明显的效果。  相似文献   
997.
We define a distance between sedimentary successions to compare their dissimilarity formally. Distance definition is based on attributed syntactic representation. One-dimensional successions can be represented by a string of lithofacies symbols sequentially or vertically. Each symbol can also have a vector of attributes that can provide other information on lithofacies such as thickness. The distance of any two successions is then defined consisting of its syntactic and attribute subdistances. Syntactic distance measures difference of vertical lithofacies change between two successions and attribute distance measures difference of thickness of corresponding lithofacies. Clustering is used to test validity of distance definition and its potential application to analysis of cycle-dominated sedimentary successions. Example is from the Namurian-A succession in Kincardine basin, central Scotland. There are 56 cycles in intervals of about 300 m each in two boreholes. Recognition of intermediate cycles depends on correctly determining of types of these short cycles and their vertical stacking pattern. Intermediate cycles have better potential in high-resolution stratal correlation regionally. Syntactic clustering results show that 56 short cycles can be classified into four groups with distinctive geological interpretation, which further helps reveal hierarchical cyclic architecture of the whole succession.  相似文献   
998.
介绍了俄罗斯采用声谱分析方法研究岩破碎过程和钻探规程的情况和结果,讨论了岩石破碎与声波的关系,说明了钻进时如何测量声波,分析了孔底功率,碎岩声波和钻头胎体温度与钻探工况(抛光,正常钻进,烧钻)的关系。  相似文献   
999.
季内西太平洋副热带高压异常进退的数值模拟   总被引:1,自引:0,他引:1  
用中科院大气所的IAP-AGCM模式,对海温和季内北太平洋副热带高压异常活动进行控制性试验,得到;西太平洋高异常对热带西太平洋,南海,孟加拉湾的海温异常有两个月的滞后响应且西太平洋副高异常和东太平洋副高异常总是相伴出现的,后者出现要早些;当上述海区SST正异常时,500hPa上来自东西两个方向的位势波在西太平洋汇集的位置要偏北,相应副高的位置也持续偏北,两者吻合很好;在上述海温异常作用下,当东亚高  相似文献   
1000.
段丽 《气象》1997,23(6):44-48
该文采用天气动力学分析方法,重点探讨北部湾低压向北部湾热带风暴发展的时空手物理机制,文章着重讨论了这类过程的高低层形势特征和空间结构,并通过诊断场计算分析揭示了这类过程的空间动力场插手玫各层的水汽分布特征,归纳出了北部湾低压向热带风暴发展的短期预报着眼点。  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