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   1015篇
  免费   258篇
  国内免费   230篇
测绘学   73篇
大气科学   206篇
地球物理   284篇
地质学   571篇
海洋学   99篇
天文学   14篇
综合类   119篇
自然地理   137篇
  2024年   5篇
  2023年   18篇
  2022年   89篇
  2021年   80篇
  2020年   61篇
  2019年   60篇
  2018年   82篇
  2017年   72篇
  2016年   75篇
  2015年   60篇
  2014年   74篇
  2013年   61篇
  2012年   50篇
  2011年   64篇
  2010年   61篇
  2009年   47篇
  2008年   52篇
  2007年   41篇
  2006年   45篇
  2005年   46篇
  2004年   32篇
  2003年   33篇
  2002年   14篇
  2001年   18篇
  2000年   24篇
  1999年   23篇
  1998年   32篇
  1997年   26篇
  1996年   28篇
  1995年   20篇
  1994年   21篇
  1993年   16篇
  1992年   23篇
  1991年   9篇
  1990年   8篇
  1989年   5篇
  1988年   12篇
  1987年   1篇
  1986年   7篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1981年   1篇
  1979年   1篇
  1958年   1篇
排序方式: 共有1503条查询结果,搜索用时 265 毫秒
961.
The LAMOST spectra and Kepler light curves are combined to investigate the detached eclipsing binary KIC 8098300,which shows the O'Connell effect caused by spot...  相似文献   
962.
牛纯  侯国本 《海岸工程》1998,17(3):72-73
试验首先通过自流引水沉沙,将淤临淤背区各抬高2m.再通过堆沙,将现黄河堤加宽50m,临背淤区各淤宽300m,把黄堤加固成梯形台阶状,达到加固黄河堤防及综合利用之目的。  相似文献   
963.
热带气旋路径资料库的建立和中国气象局9210工程紧密结合一起,在MICAPS上方便地实现热带气旋路径的显示,叠加,放大漫游等功能;在建立相似预报方法时引用谐波分析的方法来模拟热带气旋前期路径,使用较为先进的相似离度方法进行相似预报,在9711号热带风暴预报试验中取得了较好的效果。  相似文献   
964.

Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were −7.4 and 5.4 g·m−2·d−1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were −12.8 and 5.8 g·m−2·d−1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m−2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m−2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m−2·s−1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature.

  相似文献   
965.
Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were ?7.4 and 5.4 g·m?2·d?1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were ?12.8 and 5.8 g·m?2·d?1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m?2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m?2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m?2·s?1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature.  相似文献   
966.
Wentao Ma 《Natural Hazards》2012,62(1):141-148
Dongjing reservoir with storage capacity of 955 million m3 and 150 m dam height had been set up in Guizhou province, southeastern China on May in 2005. After filling with water in August 20, 2009, the reservoir-induced earthquake in 20 km took place first in September 2009 at the 440 m water level. When the water level changes, the number of earthquakes is increased rapidly. On January 17, 2010, the largest M 4.4 earthquake with depth of 7 km has happen and month frequency achieved 21 events at the highest water level. M 4.4 earthquake caused rock collapse with the disaster of killed six people and nine injure. After our investigation and study, the reason of higher epicentral intensity of earthquake was the surface effect of near-field elastic wave transmission. The disaster of rock falls certainly depended on the very very shallow earthquake, the height of valley and fault. Comparing as same magnitude of natural earthquake, very shallow earthquake increased 1–2° of epicentral intensity I0, more than twice amplitude of S-wave at 200 m height of valley and the largest displacement on fault. The superposition of three factors has increased the epicentral intensity of earthquake and directly caused rock collapse with the disaster of killed six people and nine injure.  相似文献   
967.
Heat flow was measured on the Lomonosov Ridge during the 5th Chinese National Arctic Expedition in 2012. To derive the time-temperature curve, resistivity data were transformed to temperature by the resistivity- temperature program. Direct reading and linear regression methods were used to calculate the equilibrium temperature, which were regressed against the depth of the probes in sediment to derive the geothermal gradient. Then, heat flow was calculated as the product of geothermal gradient and thermal conductivity of sediments. The heat flow values on the basis of the two methods were similar (i.e., 67.27 mW/m2 and 63.99 mW/m2, respectively). The results are consistent with the measurements carried out at adjacent sites. The age of the Lomonosov Ridge predicted by the heat flow-age model was 62 Ma, which is in accordance with the inference that the ridge was separated from Eurasia at about 60 Ma.  相似文献   
968.
Syn-collisional transform faulting of the Tan-Lu fault zone,East China   总被引:21,自引:0,他引:21  
Origin of the continental-scale Tan-Lu fault zone (TLFZ), East China, remains controversial. About 550 km sinistral offset of the Dabie orogenic belt (DOB) and Sulu orogenic belt (SOB) is shown along the NE-NNE-striking TLFZ. Syn-collisional, sinistral ductile shear belts in the TLFZ have been identified. Thirteen phengite bulk separates from the mylonites were dated by the 40Ar/39Ar method. They gave cooling ages of the 198–181 Ma for the shear belts along the eastern margin of the DOB and 221–210 Ma from the western margin of the SOB. Distribution of the foreland basin deposits suggests that sinistral offset of the DOB and SOB by the TLFZ took place prior to deposition of the Upper Triassic strata. The marginal structures around the DOB and SOB support syn-collisional faulting, and indicate anticlockwise rotation of the DOB during the displacement. The folding and thrust faulting related to crustal subduction, coeval with the Tan-Lu faulting, is older than the foreland basin deposition related to the orogenic exhumation. Several lines of evidence demonstrate that the TLFZ was developed as a syn-collisional transform fault during latest Middle to earliest Late Triassic time when the DOB and SOB experienced crustal subduction of the South China Block (SCB). Eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting.  相似文献   
969.
小麦腥黑穗病气象条件分析及防治措施   总被引:1,自引:0,他引:1  
本文主要通过对晋城市2005年、2006年及历年平均气象要素与农业气象观测资料对比,分析气象条件对小麦腥黑穗病农业病害的影响程度,从而提出治理对策。  相似文献   
970.
孟津县一次龙卷天气过程分析   总被引:1,自引:0,他引:1  
利用灾后调查资料、常规观测资料及三门峡市多普勒雷达资料,分析2007年7月发生在洛阳市孟津县的严重风灾,结果表明:这是孟津县首次在非观测区确认的龙卷灾害;该龙卷为非超级单体龙卷,在反射率因子图上几乎没有任何明显特征,而在风暴径向速度图上呈现为较明显的小尺度涡旋特征;具有显著的低层辐合高层辐散的特征;低的抬升凝结高度和低层明显的垂直风切变及合适的对流有效位能、对流抑制能量是产生龙卷适宜的环境条件;在高低空深厚的槽前西南急流引导下,来自洛阳市西部的弱回波快速东北偏北移到孟津境内强烈快速发展,形成的强回波遇到近地面层的辐合线在弱冷空气的触发下诱发龙卷暴发.  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