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   3090篇
  免费   575篇
  国内免费   732篇
测绘学   45篇
大气科学   624篇
地球物理   558篇
地质学   2087篇
海洋学   326篇
天文学   502篇
综合类   80篇
自然地理   175篇
  2024年   14篇
  2023年   41篇
  2022年   68篇
  2021年   94篇
  2020年   92篇
  2019年   82篇
  2018年   105篇
  2017年   118篇
  2016年   131篇
  2015年   113篇
  2014年   133篇
  2013年   147篇
  2012年   120篇
  2011年   171篇
  2010年   129篇
  2009年   210篇
  2008年   232篇
  2007年   252篇
  2006年   259篇
  2005年   217篇
  2004年   196篇
  2003年   171篇
  2002年   166篇
  2001年   108篇
  2000年   157篇
  1999年   137篇
  1998年   106篇
  1997年   99篇
  1996年   95篇
  1995年   69篇
  1994年   65篇
  1993年   60篇
  1992年   41篇
  1991年   22篇
  1990年   41篇
  1989年   30篇
  1988年   25篇
  1987年   18篇
  1986年   13篇
  1985年   15篇
  1984年   12篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1980年   7篇
  1979年   1篇
  1978年   4篇
  1977年   1篇
  1954年   1篇
排序方式: 共有4397条查询结果,搜索用时 781 毫秒
41.
南极中山站大气气溶胶的化学组成及其来源的判别   总被引:1,自引:1,他引:1  
从1998年3月7日至1999年11月23日历时21个月,在南极中山站连续采集89个海洋气溶胶样品,本文提供全部样品的13种化学元素Cu、Pb、Zn、Cd、Fe、Al、Mn、Cr、V、K、Na、Ca、Mg含量的实测值.研究表明中山站气溶胶化学成份的含量具有季节性变化的特征.通过相关分析、因子分析、富集因子等方法判别不同时间段中山站气溶胶化学成份的来源。  相似文献   
42.
林峰  许清辉 《台湾海峡》1990,9(3):251-255
利用潮输沙量的计算方法,估算了闽江口入海口内3个断面所包围区域溶解态镉、铅和铜的收支平衡,从而研究了这些重金属的河口行为。  相似文献   
43.
下辽河平原—辽东湾的新构造运动   总被引:7,自引:0,他引:7  
通过地质、地貌及地球物理资料分析研究,发现下辽河平原—辽东湾的新构造运动的主要特征除了断裂发育、火山活动早期剧烈而晚期衰弱、现代地震活跃以及地壳差异和反差升降运动明显之外,还显示了:(1)深大断裂的控制性,(2)沉降中心的迁移性,(3)构造运动的阶段性和旋回性.  相似文献   
44.
川西南周公山及邻区下二叠统的中-低孔、中-低渗碳酸盐岩储层的储集空间以次生成因的溶孔、溶洞和构造裂缝为主.研究认为,多世代方解石胶结、化学充填作用以及埋藏期的压实(溶)作用是孔隙很难得到保存的主要原因;同生-准同生期的混合水云化作用和表生期、埋藏期的流体溶蚀作用则产生了大量的次生溶孔、洞,使储层的孔渗性得到明显的改善;构造破裂作用可以产生新的储集空间,还影响各储集体之间及单一储集体内部空隙的连通.成岩相分为混合水云化-溶蚀-破裂相、溶蚀-胶结相和胶结-压实-压溶相.各种成岩作用的叠加形成了现今下二叠统油气储层的分布格局.  相似文献   
45.
塔里木盆地塔河地区下石炭统巴楚组沉积演化   总被引:2,自引:0,他引:2       下载免费PDF全文
以塔里木盆地加里东期和海西两期构造运动为背景,结合现有的岩心、露头、测井、录井和地震资料,对巴楚组可识别出早期的辫状河三角洲沉积,中期的渴湖沉积和盐湖沉积,以及晚期的咸化溻湖沉积。本文分别从横向上和纵向上对塔河地区巴楚组沉积演化进行深入分析;总结了巴楚组构造运动与沉积响应之间的关系,以期为该地区的下石炭统巴楚组的进一步勘探提供科学依据。  相似文献   
46.
The Wakamiko submarine crater is a small depression located in Kagoshima Bay, southwest Japan. Marine shallow‐water hydrothermal activity associated with fumarolic gas emissions at the crater sea floor (water depth 200 m) is considered to be related with magmatic activity of the Aira Caldera. During the NT05‐13 dive expedition conducted in August 2005 using remotely operated vehicle Hyper‐Dolphine (Japan Agency for Marine‐Earth Science and Technology), an active shimmering site was discovered (tentatively named the North site) at approximately 1 km from the previously known site (tentatively named the South site). Surface sediment (up to 30 cm) was cored from six localities including these active sites, and the alteration minerals and pore fluid chemistry were studied. The pore fluids of these sites showed a drastic change in chemical profile from that of seawater, even at 30 cm below the surface, which is attributed to mixing of the ascending hydrothermal component and seawater. The hydrothermal component of the North site is estimated to be derived from a hydrothermal aquifer at 230°C based on the hydrothermal end‐member composition. Occurrence of illite/smectite interstratified minerals in the North site sediment is attributed to in situ fluid–sediment interaction at a temperature around 150°C, which is in accordance with the pore fluid chemistry. In contrast, montmorillonite was identified as the dominant alteration mineral in the South site sediment. Together with the significant low potassium concentration of the hydrothermal end‐member, the abundant occurrence of low‐temperature alteration mineral suggests that the hydrothermal aquifer in the South site is not as high as 200°C. Moreover, the montmorillonite is likely to be unstable with the present pore fluid chemistry at the measured temperature (117°C). This disagreement implies unstable hydrothermal activity at the South site, in contrast to the equilibrium between the pore fluid and alteration minerals in the North site sediment. This difference may reflect the thermal and/or hydrological structure of the Wakamiko Crater hydrothermal system.  相似文献   
47.
Studies of Mesozoic granites associated with rare earth element (REE)‐rich weathered crust deposits in southernmost Jiangxi Province indicate that they have high‐K to shoshonite compositions and belong to ilmenite‐series I‐type granites. Of the studied rocks at 59–292 ppm of bulk REE content, the highest are seen in the biotite granites of Dingnan (358, 429 ppm) and mafic biotite granite of the Wuliting Granite (344 ppm) near the Dajishan tungsten mine, both areas where weathered‐crust REE deposits occur. REE‐bearing accessory minerals in these granites are mainly zircon, apatite and allanite, and REE‐fluorocarbonates are common. REE enrichment occurs in the rims of apatite crystals, and in fluorocarbonates that occur along grain boundaries of and cracks in major silicate minerals, and in fluorocarbonates that replaced altered biotite. It is therefore thought that a major part of the REE content of these granites was concentrated during deuteric activity, rather than during magmatic crystallization. The crack‐filling REE‐fluorocarbonates could subsequently have been easily leached out and deposited in weathered crust developed during a long period of exposure.  相似文献   
48.
对塔中低凸起地层水化学特征与不整合之间关系的研究结果表明,地层水化学特征对不整合具有很好的响应。在遭受强烈抬升和剥蚀、之间形成不整合的奥陶系和志留系,以及紧靠不整合面附近的石炭系CⅢ油组,其地层水具有矿化度、Cl-含量、K Na 含量和r(Cl-Na)/rMg值相对较小,而HCO3-含量、rNa/rCl值和rSO42-×100/rCl值相对较大的特点,反映出地质历史时期大气降水的影响。在志留系与石炭系之间以及志留系与奥陶系之间的不整合面附近,地层水的矿化度、r(Cl-Na)/rMg值和B3 含量变小,而rNa/rCl值和rSO24-×100/rCl值变大,具有典型的遭受大气淋滤的地层水化学基本特征。  相似文献   
49.
The lithological-stratigraphic study of volcanogenic-siliceous rocks developed on the left side of the Machtovaya River, a right tributary of the Amur River, yielded the first radiolarian assemblages of the late Late Tithonian, the late Late Tithonian-early Valanginian, and the middle-late Albian age. It is established that the stratigraphic succession of volcanogenic-siliceous rocks in this area is composed of upper Tithonian-Valanginian dark red to red-brown cherts with basalts in the lower part of the section and Albian dark gray clayey cherts, olive-gray siliceous-tuffaceous argillites, and tufaceous siltstones in its upper part. The replacement of cherts by their clayey varieties likely occurred in the Aptian. The composition, structure, and age of these strata and the rocks constituting the Kiselevka-Manoma accretionary complex are different, which indicates their different tectonic origin.  相似文献   
50.
We estimate (/T) P of the lower mantle at seismic frequencies using two distinct approaches by combining ambient laboratory measurements on lower mantle minerals with seismic data. In the first approach, an upper bound is estimated for |(/T) P | by comparing the shear modulus () profile of PREM with laboratory room-temperature data of extrapolated to high pressures. The second approach employs a seismic tomography constraint ( lnV S / lnV P ) P =1.8–2, which directly relates (/T) P with (K S /T) P . An average (K S /T) P can be obtained by comparing the well-established room-temperature compression data for lower mantle minerals with theK S profile of PREM along several possible adiabats. Both (K S /T) and (/T) depend on silicon content [or (Mg+Fe)/Sil of the model. For various compositions, the two approaches predict rather distinct (/T) P vs. (K S /T) P curves, which intersect at a composition similar to pyrolite with (/T) P =–0.02 to –0.035 and (K S /T) P =–0.015 to –0.020 GPa/K. The pure perovskite model, on the other hand, yields grossly inconsistent results using the two approaches. We conclude that both vertical and lateral variations in seismic velocities are consistent with variation due to pressure, temperature, and phase transformations of a uniform composition. Additional physical properties of a pyrolite lower mantle are further predicted. Lateral temperature variations are predicted to be about 100–250 K, and the ratio of ( lnp/ lnV S ) P around 0.13 and 0.26. All of these parameters increase slightly with depth if the ratio of ( lnV S / lnV P ) P remains constant throughout the lower mantle. These predicted values are in excellent agreement with geodynamic analyses, in which the ratios ( ln / lnV S ) P and ( / lnV S ) P are free parameters arbitrarily adjusted to fit the tomography and geoid data.  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