首页 | 官方网站   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   2606篇
  免费   426篇
  国内免费   453篇
地球科学   3485篇
  2024年   4篇
  2023年   36篇
  2022年   72篇
  2021年   77篇
  2020年   95篇
  2019年   100篇
  2018年   70篇
  2017年   91篇
  2016年   94篇
  2015年   105篇
  2014年   125篇
  2013年   124篇
  2012年   132篇
  2011年   137篇
  2010年   145篇
  2009年   193篇
  2008年   173篇
  2007年   171篇
  2006年   167篇
  2005年   160篇
  2004年   160篇
  2003年   130篇
  2002年   142篇
  2001年   122篇
  2000年   127篇
  1999年   112篇
  1998年   87篇
  1997年   74篇
  1996年   39篇
  1995年   41篇
  1994年   43篇
  1993年   33篇
  1992年   35篇
  1991年   7篇
  1990年   15篇
  1989年   10篇
  1988年   8篇
  1987年   2篇
  1986年   7篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1980年   3篇
  1978年   1篇
  1927年   1篇
  1905年   1篇
  1900年   1篇
  1880年   2篇
  1877年   2篇
  1875年   1篇
排序方式: 共有3485条查询结果,搜索用时 468 毫秒
101.
单新建  柳稼航  马超 《地震学报》2004,26(5):474-480
利用差分干涉雷达测量技术获取的宏观震中区的同震形变场,结合对地震活动性、震源机制、野外考察等资料分析,对昆仑山口西8.1级地震同震形变场特征进行了研究. 结果表明:宏观震中位于库赛湖东北侧,宏观震中区发震断层可分为两个形变中心区域,其中西段长约42 km,东段长约48 km,整个发震断层主破裂段长90 km;由干涉形变条纹分布格局可清楚地判断出发震断层的左旋走滑特征;断层两盘变形特征不同,南盘变形程度明显大于北盘;宏观震中附近最大斜距向位移量为288.4 cm,最小斜距向位移量为224.0 cm,宏观震中发震断层最大左旋水平位错为738.1 cm,最小地面左旋水平位错为551.8 cm.   相似文献   
102.
近断层地震动对地表结构物造成严重的破坏,它具有明显的方向性和脉冲型特征. 在速度时程中含有大幅值、长周期的脉冲波,对结构响应影响很大. 为简化计算和分析的需要,在既有的等效速度脉冲模型的基础上,建议了较为合理等效速度脉冲模型. 在充分收集脉冲型近断层地震记录的基础上,对等效速度脉冲模型的脉冲周期、脉冲强度及卓越脉冲数等参数进行了研究,并与以往研究者的结果进行比较,以利于近断层区结构的抗震设计.   相似文献   
103.
云南地区4级地震频度异常特征与强震关系研究   总被引:2,自引:0,他引:2  
王兰兰  刘丽芳 《内陆地震》2004,18(4):359-364
对云南地区18次MS≥6强震事件前中、小地震活动过程进行了分析,发现在这些地震发生前1—3年近场区2°×2°范围内4级地震频度基本上出现了显著增强现象,可以用4级地震年累计频度进行定量描述。通过全时空的扫描,确定年累计频度N≥4为异常阈值,该指标通过了置信度97.5%的R值内符检验。并用调整单元对强震附近4级地震活动增强现象给予了物理解释。  相似文献   
104.
Rate constants for the gas-phase reactions of OH radicals, NO3 radicals and O3 with the C7-carbonyl compounds 4-methylenehex-5-enal [CH2=CHC(=CH2)CH2CH2CHO], (3Z)- and (3E)-4-methylhexa-3,5-dienal [CH2=CHC(CH3)=CHCH2CHO] and 4-methylcyclohex-3-en-1-one, which are products of the atmospheric degradations of myrcene, Z- and E-ocimene and terpinolene, respectively, have been measured at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained (in cm3 molecule–1 s–1 units) were: for 4-methylenehex-5-enal, (1.55 ± 0.15) × 10–10, (4.75 ± 0.35) × 10–13 and (1.46 ± 0.12) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; for (3Z)-4-methylhexa-3,5-dienal: (1.61 ± 0.35) × 10–10, (2.17 ± 0.30) × 10–12, and (4.13 ± 0.81) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; for (3E)-4-methylhexa-3,5-dienal: (2.52 ± 0.65) × 10–10, (1.75 ± 0.27) × 10–12, and (5.36 ± 0.28) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; and for 4-methylcyclohex-3-en-1-one: (1.10 ± 0.19) × 10–10, (1.81 ± 0.35) × 10–12, and (6.98 ± 0.40) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively. These carbonyl compounds are all reactive in the troposphere, with daytime reaction with the OH radical and nighttime reaction with the NO3 radical being predicted to dominate as loss processes and with estimated lifetimes of about an hour or less.  相似文献   
105.
Aerobic granular sludge was successfully cultivated in a sequencing batch reactor (SBR) treating wastewater from the malting process with a high content of particulate organic matter. At an organic loading rate of 3.2 kg/(m3 d) CODtotal and an influent particle concentration of 0.95 g/L MLSS an average removal of 50% in CODtotal and 80% in CODdissolved could be achieved. A comparison of granular and flocculent sludge grown under the same operating conditions showed no significant difference in removal efficiency although granules exhibited a higher metabolic activity in terms of specific oxygen uptake rate (rO2, X). Two distinct mechanisms of particle removal were observed for granular sludge: during initial granule formation, particles were incorporated into the biofilm matrix. For mature granules, a high level of protozoa growth on the granule surface accounted for the ability to remove particulate COD. Combined evaluation of the development in MLSS content and sludge bed settling rate (i.e., mean derivative of the normalized sludge volume) was found to be an adequate method for monitoring the characteristic settling properties of a granulizing sludge bed. By means of this method, a distinct substrate gradient out of several operating conditions was concluded to have the biggest impact on the formation of aerobic granular sludge.  相似文献   
106.
In a survey in Greece from 1987 to 2000 hepatotoxic cyanobacterial blooms were observed in 9 out of 33 freshwaters. Microcystins (MCYSTs) were detected by HPLC in 7 of these lakes, and the total MCYST concentration per scum dry weight ranged from 50.3 to 1638 ± 464 μg g—1. Cyanobacterial genera (Microcystis, Anabaena, Anabaenopsis, Aphanizomenon, Cylindrospermopsis) with known toxin producing taxa were present in 31 freshwaters. From our data and a review of the literature, it would appear that Mediterranean countries are more likely 1) to have toxic cyanobacterial blooms consisting of Microcystis spp. and 2) to have higher intracellular MCYST concentrations. A case study in Lake Kastoria is used to highlight seasonal patterns of cyanobacterial and MCYST‐LR occurrence and to assess cyanotoxin risk. Cyanobacterial biovolume was high (> 11 μL L—1) throughout the year and was in excess of Guidance Level 2 (10 μL L—1) proposed by WHO for recreational waters and Alert Level 2 for drinking water. Further, surface water samples from April to November exceeded Guidance Level 3, with the potential for acute cyanobacterial poisoning. Intracellular MCYST‐LR concentrations (max 3186 μg L—1) exceeded the WHO guideline for drinking water (1 μg L—1) from September to November with a high risk of adverse health effects. Preliminary evidence indicates that in 3 lakes microcystins are accumulated in some aquatic organisms. Generally, a high risk level can be deduced from the data for the Mediterranean region.  相似文献   
107.
Limnological characteristics of Lake Burdur in Lake District in south‐western Turkey are presented. It is a deep, tectonic (estimated max. depth 100 m), athalassic, highly alkaline, and saline lake. A set of physical and chemical variables was monitored, phyto‐ and zooplankton was sampled from surface layer of the lake during 1997. Physico‐chemical variables indicated that the lake is hyposaline and composed of some hydrochemically different water layers formed by groundwater sources located on the bottom of the lake. The phytoplankton composition of Lake Burdur consisted of Cyanophyta, Chlorophyta, Bacillariophyta, Dinophyta, and Chrysophyta. The abundance and number of species of Chlorophyta and Cyanophyta were higher than the other taxa. The zooplankton composition of the Lake consisted of Rhizopoda, Rotifera, and Crustacea. Number of species of Rotifera was higher than the other taxa. The diversities of the phyto‐ and zooplankton were calculated according to the Shannon‐Weaver diversity index. The diversity of each group was found to be low in the lake.  相似文献   
108.
109.
The investigation on damages to frozen soil sites during the West Kunlun Mountains Pass earthquake with Ms 8.1 in 2001 shows that the frozen soil in the seismic area is composed mainly of moraine, alluvial deposit, diluvial deposit and lacustrine deposit with the depth varying greatly along the earthquake rupture zone. The deformation and rupture of frozen soil sites are mainly in the form of coseismic fracture zones caused by tectonic motion and fissures,liquefaction, seismic subsidence and collapse resulting from ground motion. The earthquake fracture zones on the surface are main brittle deformations, which, under the effect of sinlstral strike-slip movement, are represented by shear fissures, tensional cracks and compressive bulges. The distribution and configuration patterns of deformation and rupture such as fissures, liquefaction, seismic subsidence and landslides are all related to the ambient rock and soil conditions of the earthquake area. The distribution of earthquake damage is characterized by large-scale rupture zones, rapid intensity attenuation along the Qinghai-Xizang (Tibet) Highway, where buildings distribute and predominant effect of rock and soil conditions.  相似文献   
110.
Rou Jie 《中国地震研究》2004,18(4):357-364
At 19:33 p. m on September 27, 2003, an earthquake with M7.9 occurred in the RussiaMongolia-China boundary Region. It was strongly felt in the Altay region of Xinjiang. The losses caused by the earthquake was 76 million yuan (RMB). Some information about the earthquake was outlined, including basic parameters, focal mechanism, evaluation of earthquake disaster losses and so on. The satellite remote sensing information worked initial analysis for deformation of ground and failure phenomenon.  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-23

京公网安备 11010802026262号