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   1217篇
  免费   197篇
  国内免费   338篇
测绘学   29篇
大气科学   85篇
地球物理   611篇
地质学   731篇
海洋学   223篇
天文学   10篇
综合类   24篇
自然地理   39篇
  2024年   3篇
  2023年   8篇
  2022年   38篇
  2021年   46篇
  2020年   43篇
  2019年   55篇
  2018年   60篇
  2017年   70篇
  2016年   63篇
  2015年   73篇
  2014年   80篇
  2013年   97篇
  2012年   83篇
  2011年   79篇
  2010年   85篇
  2009年   104篇
  2008年   92篇
  2007年   90篇
  2006年   114篇
  2005年   65篇
  2004年   63篇
  2003年   37篇
  2002年   46篇
  2001年   36篇
  2000年   32篇
  1999年   37篇
  1998年   32篇
  1997年   16篇
  1996年   17篇
  1995年   17篇
  1994年   12篇
  1993年   10篇
  1992年   7篇
  1991年   5篇
  1990年   10篇
  1989年   5篇
  1988年   1篇
  1987年   3篇
  1986年   2篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   2篇
  1979年   1篇
  1978年   1篇
  1976年   1篇
  1973年   2篇
  1972年   2篇
排序方式: 共有1752条查询结果,搜索用时 562 毫秒
341.
通过模型试验研究,得到海岸岸坡、气室宽度与频率响应和吸能效率之间的关系和规律,验证了一种理论计算方法的可靠性,证明该计算方法对波能电站的设计和工程选址有一定的参考价值。  相似文献   
342.
The hydrodynamic performance of the oscillating water column type shoreline-mounted wave-power device is numerically studied within linear wave theory by using a boundary element method based on the Wehausen and Laitone 3D shallow water Green's function. In order to verify the numerical model, a 1:12 physical model with different bottom slopes was constructed and tested in a wave basin under regular wave conditions. The effects of the bottom slope on the hydrodynamic performance are investigated by both analytical and experimental methods.  相似文献   
343.
凝胶渗透色谱法测定壳聚糖分子量 ,以葡聚糖为标准品 ,用 2种不同的凝胶柱 (PLaquagel- OH柱和 TSK G4 0 0 0 PWXL柱 )测定 4种样品的分子量及其分布 ,并经过普适标定。比较结果发现 :PL aquagel- OH柱效果稍好于 TSK G4 0 0 0 PWXL柱。两柱所得重均分子量平均偏差为 0 .17%~ 3.38% ,数均分子量的平均偏差为 0 .90 %~ 3.5 7% ,分子量分布宽度指数 1.34~ 1.5 4。  相似文献   
344.
After the Aznalcóllar mining spill (April, 1998) different ecosystems along the Guadiamar river and the Guadalquivir estuary were impacted by high concentrations of metals. The concentration of metals Zn, Cd, Pb, Cu and As has been detected as a good tracer of the pathway of the toxic spill. Different individuals of the fish Solea senegalensis and the clam Scrobicularia plana were exposed to contaminated sediments after the accidental spill in the south-west Spain. The induction of metallothioneins in fish and the bioaccumulation of metals in clams were determined in different tissues to determine the biological adverse effect associated with the heavy metals from the spill. A relationship between the enrichment of metals in the tissues and the induction of metallothioneins was determined for those assays performed using contaminated sediments. The bioaccumulation of metals indicates that the risk associated with the spill should be continuously evaluated to establish the sublethal effects related to the accident.  相似文献   
345.
For load-controlled and displacement-controlled test data of piles cyclically axially loaded in clay, the displacement conditions are suggested for determining the shaft capacity. According to the suggested displacement conditions, not only the results of shaft capacity from laboratory model piles are close to those from in-situ piles, but also the results of load-controlled tests are in satisfactory agreement with those of displacement-controlled tests. Moreover, based on the test data of laboratory model piles in combination with the test data published, the paper suggests the values of the normalized shaft capacity of piles under a variety of static and cyclic loading combinations.  相似文献   
346.
In this paper, the control performance is investigated of Circular Tuned Liquid Column Dampers (CTLCD) over torsional response of offshore platform structures excited by ground motions. Based on the equation of motion for the CTLCD-structure system, the optimal control parameters of CTLCD are given through some derivations on the supposition that the ground motion is a stochastic process. The influence of systematic parameters on the equivalent damping ratio of the structures is analyzed with purely torsional vibration and translational-torsional coupled vibration, respectively, The results show that the Circular Tuned Liquid Column Damper (CTLCD) is an effective torsional response control device.  相似文献   
347.
Abstract. Vertical profiles of temperature, nutrients (silicate, phosphate, and nitrate), chlorophyll a and phytoplankton abundance are given for six stations located in the Gulf of California, June 1982, above 1 % of light intensity. The vertical distribution of phytoplankton was related to the water column structure: stratified stations had a defined nutricline and subsurface chlorophyll and phytoplankton abundance maxima were present, which were found to be related to the depth of the principal thermocline; vertical distribution of taxa was not uniform and low affinity values (< 0.5) were calculated among depths at these stations. Despite the irregular vertical distribution of chlorophyll and cell number, there was a great affinity in the species composition throughout the euphotic zone at well-mixed or weakly stratified stations. Nanoplankton organisms, mainly coc-colithophorids, were the most important numerical contributors at the chlorophyll maxima, except when this was superficial, in which case diatoms were the most numerous group. Some patterns of the vertical distribution of the main phytoplankton groups ( e.g. , diatoms, dinoflagellates, and microflagellates) are shown. The spectrum of diversity in the water column was useful only for mixed-waters. The relationship between stability, nutrients, and phytoplankton - regarding their vertical distribution - and the importance of physical and biological processes on phytoplankton ecology are discussed.  相似文献   
348.
In order to further document the relation between redox conditions and the sedimentary record of Mn, U and Mo in a transitory anoxic water basin, their distribution has been studied along two profiles in the Thau lagoon (France). Sediments and pore-water have been sampled at two contrasting sites located, respectively, in the shellfish-farming area and in the centre of the lagoon. In the shellfish-farming area, the particulate organic carbon (POC) data indicate a more rapid organic matter mineralisation compared to the centre of the lagoon. This results in a sharper redox gradient characterized by the appearance of H2S in pore-water a few millimetres below the sediment–water interface. In the centre of the lagoon, H2S appears at a depth of 35 cm.In both cores, sedimentary Mn is relatively depleted through out the whole sedimentary column and varies with the proportion of clay minerals. After an initial release into solution at the sediment–water interface in relation to Mn-oxide reductive dissolution, authigenic U is immobilized when sulphides appear. Despite the occurrence of anoxic conditions at the sediment–water interface at the site influenced by shellfish farming, the burial of U is reduced by bioturbation, which raises reducing sediments to the surface. In the centre of the lagoon, Mo profiles reflect continuous diffusion into pore water and immobilization at 15 cm probably in anoxic microenvironments. At shellfish farms, dissolved Mo undergoes removal with sulphides but contrary to U, sedimentary Mo does not appear to be strongly affected by bioturbation. The profile indicates an increase in the frequency of anoxia crises during the second half of the 20th century.  相似文献   
349.
于1982年12月-1984年5月,以青岛汇泉湾习见的马粪海胆为材料,运用0.5mol/L KCl或0.5mol/L LiCl诱导法得到其卵母细胞;差速离心技术提取其线粒体;SDS萃取到线体核酸;再以羟基磷灰石柱层析分离邮线粒体核酸各组分。结果表明,从所得各种分离产物测不出任何蛋白质,所以,应用上述各种方法和技术,能够有效地分离出海胆卵母细胞线粒体中的DNA,rRNA,tRNA和多核苷酸。  相似文献   
350.
采集中国北方某砂岩型铀矿床中的含铀矿石样品,共进行7组土柱模拟实验,分别探究氧化-还原条件、HCO-3浓度、有机质和微生物对铀迁移转化的影响。结果表明:氧化-还原条件改变对铀迁移转化会产生重要影响,含氧入渗水带来的氧化环境使含水介质中沉淀态铀大量氧化溶解;HCO-3的促解吸作用及铀酰络合物的强迁移能力对地下水中铀迁移转化影响较大;有机质会参与含水介质中矿物吸附点位竞争,从而造成铀的解吸;微生物作为氧化-还原反应的催化剂,在氧化剂氧化沉淀态铀的反应中起重要作用;氧化作用、解吸作用和溶解作用对地下水中铀迁移转化的贡献比例分别为65.28%、23.91%和10.81%。  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