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   1635篇
  免费   344篇
  国内免费   426篇
测绘学   73篇
大气科学   463篇
地球物理   443篇
地质学   771篇
海洋学   214篇
天文学   121篇
综合类   182篇
自然地理   138篇
  2024年   3篇
  2023年   26篇
  2022年   55篇
  2021年   61篇
  2020年   52篇
  2019年   63篇
  2018年   59篇
  2017年   61篇
  2016年   75篇
  2015年   63篇
  2014年   57篇
  2013年   88篇
  2012年   80篇
  2011年   89篇
  2010年   87篇
  2009年   86篇
  2008年   87篇
  2007年   114篇
  2006年   85篇
  2005年   52篇
  2004年   47篇
  2003年   74篇
  2002年   49篇
  2001年   49篇
  2000年   77篇
  1999年   106篇
  1998年   96篇
  1997年   79篇
  1996年   86篇
  1995年   63篇
  1994年   55篇
  1993年   56篇
  1992年   35篇
  1991年   28篇
  1990年   26篇
  1989年   20篇
  1988年   31篇
  1987年   12篇
  1986年   12篇
  1985年   10篇
  1984年   12篇
  1983年   10篇
  1982年   8篇
  1981年   6篇
  1980年   5篇
  1978年   3篇
  1976年   3篇
  1975年   1篇
  1973年   1篇
  1972年   1篇
排序方式: 共有2405条查询结果,搜索用时 718 毫秒
991.
针对西峰油田长8油藏低渗、细孔喉、砂岩泥质含量高等储层特点,分析了储层堵塞的原因,通过理论及试验优化出了本区块酸化增产的酸液配方。使用土酸酸化角井成功率相对较高,边井成功率低,复合有机酸酸化增产技术从应用效果看好于土酸酸化,为该地区措施提高单井产量积累了一定宝贵经验。  相似文献   
992.
993.
????1992??12???2007??5?μ??????????о???????????仯??????????????????14?????????????30??N??????????????????????????57.7 mm??40.9 mm??????????????????????????????о?????????????????????ζ??????SOI????????????????????????????????????????????SOI???????30??N??????SLA??SOI???????????????γ??????????SLA??SOI???к???????????????????????????糡??????????????????SLA??γ???????????????????????????????30??N ???????????????????????????????????????????????????????????????????????????????????????SLA??????????·???????u??????????????????????????30??N ?????????????????????????????u??????????????70???????23????????????u????????SLA??SOI????????????????????????????????????????е?????????????30??N ???????????????????u????SOI???????ENSO????????????????????????糡???????????糡???γ????????????????????仯???????????á?????ENSO????????????????????????????  相似文献   
994.
?????α????????????????????????????BP???????????????α??????????????????????????????????????????????????????????????????????????????????BP??????????????????Ч????  相似文献   
995.
Vegetation dynamics and hydrological processes are major components of terrestrial ecosystems, and they interact strongly with each other. Studies of hydrological responses to vegetation dynamics are usually conducted on a long-term scale, whereas the hydrological responses within a single year have rarely been studied. In the present study, Poyang Lake runoff (PYL-R) model, a new hydrological model coupled with leaf area index (LAI) remote sensing products, was established and applied to simulate the runoff process in the Poyang Lake Watershed. The simulation results obtained in three sub-watersheds of the Poyang Lake Watershed (Ganjiang Watershed, Xinjiang Watershed, and Fuhe Watershed) agreed well with the observations (Nash efficiency coefficient values and R values exceeded 0.6 and 0.9, respectively). The PYL-R experiment (PYL-R-E) model was designed as a contrast model without considering the impact of LAI. The simulated monthly runoff results obtained using the PYL-R and PYL-R-E models were compared, and the within-year changes in the differences between the two results were analysed to evaluate and quantify the impact of vegetation dynamic on runoff. From January to July, when LAI values increased by around 2.6 m2 m−2, monthly runoff depth differences between PYL-R and PYL-R-E results increased by 35.25, 27.98, and 29.14 mm in the Ganjiang, Xinjiang, and Fuhe watersheds, respectively. Dense vegetation caused high interception and evapotranspiration during summer, which largely reduced runoff. By contrast, during winter, the effect of vegetation was weaker on runoff process whereas the impacts of other factors (e.g., precipitation) were higher. The sensitivity of monthly runoff to vegetation dynamics varied greatly throughout the whole year. In particular, during August and September, the LAI-caused runoff changes were very high, accounting for 28–42% of monthly runoff in the sub-watersheds. Our findings clarify the effects of changes in vegetation on hydrological processes over short time scales, thereby providing insights into the effects of scale on eco-hydrological processes.  相似文献   
996.
Four seasonal rainfall simulations in 2009 and 2010 were applied to a field containing 36 plots (0.75 × 2 m each), resulting in 144 runoff events. In all simulations, a constant rate of rainfall was applied then halted 60 min after initiation of runoff, with plot‐scale monitoring of runoff every 5 min during that period. Runoff was simulated with the Kinematic Runoff and Erosion/Simulator of Transport with Infiltration and Runoff (KINEROS2/STWIR) field‐scale model, whose hydrodynamics are based on the kinematic wave equation. Because of the non‐linear nature of the model and a highly parameterized model with respect to the available data, several approaches were investigated to upscale nine runoff‐related parameters from a series of small monitored plots to the field scale. Inverse modeling was performed using the model‐independent Parameter ESTimation (PEST) algorithm to individually calibrate the nine KINEROS2/STWIR parameters on 36 plots. The parameters were averaged, and bootstrapping was used to assess uncertainty of the parameters via estimation of confidence intervals (CI). A Monte Carlo simulation using the bootstrap results showed reasonable field‐scale representation of flow rates. Median values of calibrated parameters were within the 95% CI obtained with bootstrapping. The simulated results for the median values associated with the 90% CI flow rates produced similar trends as those exhibited with the observed data, suggesting that median values of the calibrated parameters from the PEST inverse modeling could be used to represent the field scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
997.
The performance of temperature‐index melt models is particularly affected by the choice of near‐surface lapse rate used to determine the sum of positive daily temperatures at different elevations, and by the choice of factor used to relate this sum to the rate of melting. Data from the Langjökull ice cap are used in this study to quantify the influence of lapse‐rate and degree‐day factor variation on temperature‐index melt simulations. The lapse rate was significantly lower during summer than in spring or autumn, as a result of diabatic cooling, reducing boundary‐layer sensitivity to free‐air temperature change. The summer lapse rate was also significantly lower than the saturated adiabatic lapse rate. A sensitivity of approximately 600 mm water equivalent (w.e.) cumulative June–August melt per 0.1 °C 100 m–1 change in lapse rate was found across a 500‐m altitude range. The sensitivity to a 1‐mm w.e. °C–1 day–1 change in degree‐day factors varied more: from approximately 500 mm w.e. cumulative summer melt at low elevation to approximately 200 mm w.e. at high elevation, reflecting the decline in melt rates associated with the greater persistence of snow with increasing altitude. The determination of a degree‐day factor for snow is complicated by the densification of the ageing snowpack, but the application of a parameterization for near‐surface density on the basis of albedo helped account for the development of snow water equivalence. Lapse rate was parameterized as a function of standardized anomalies in 750 hPa reanalysis temperature and significantly improved the simulation of cumulative summer melt compared with models applying the saturated adiabatic lapse rate. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
998.
The paper has developed and proposed a synthesis analysis method based on the robust satellite data analysis technique(RST) to detect seismic anomalies within the bi-angular advanced along-track scanning radiometer(AATSR) gridded brightness temperature(BT)data based on spatial/temporal continuity analysis. The proposed methods have been applied to analyze the Yushu(Qinghai, China) earthquake occurred on 14 th April 2010,and a full AATSR data-set of 8 years data from March2003 to May 2010 with longitude from 91°E to 101°E and latitude from 28°N to 38°N has been analyzed. Combining with the tectonic explanation of spatial and temporal continuity of the abnormal phenomena, the analyzed results indicate that the infrared radiation anomalies detected by the AATSR BT data with nadir view appear and enhance gradually along with the development and occurring of the earthquake, especially along the Ganzi-Yushu fault, Nu River fault and Jiali-Chayu fault; more infrared anomalies along the earthquake fault zone(Lancangjiang fault and Ning Karma Monastery-Deqin fault) are detected using the proposed synthesis analysis method, which can also characterize the activity of seismic faults more precisely.  相似文献   
999.
Colocation mining is one of the major spatial data mining tasks. When discovering colocation patterns, spatial statistics or data mining approaches are commonly used. Colocation mining results are typically presented in a textual form and do not provide any spatial information; thus, the results lack an intuitive approach to obtain cognition of colocation rules. Here, we propose a visualization approach to discover colocation patterns for two independent point distributions and generate visual results. This approach makes use of the ability of human color perception. For two geographic features, our approach first generates density surfaces of the input features and then visualizes the density surfaces using a red or green light with different intensities. Then, based on the law of additive color mixing, our approach mixes the colors of the two density surfaces to generate a colocation rule map. The visualization approach can also provide local details of colocation and be used for local colocation analysis. Users can detect colocation patterns and their distribution from the colocation rule maps. We use both synthetic data and real data to test the performance of our approach.  相似文献   
1000.
Yu  Xiaoxiao  Li  Tiegang  Gu  Dongqi  Feng  Aiping  Liu  Shihao  Li  Ping  Xu  Guoqiang  Yan  Wenwen  Zhang  Zhiwei  Zhu  Zhengtao 《中国海洋湖沼学报》2019,37(3):982-997
Sediment grain size in the deltaic environment of the Luanhe River(LR), Liaoning, China,contains sediment transport pathway information useful in elucidating the shoreline change and fluvialmarine interaction. In this study, we utilized numerical partitioning of the sedimentary components and geostatistical grain size trend analysis(GSTA) to define the sediment transport pattern in the Luanhe River delta(LRD) and interpolated the sediment transport pattern using content changes of end numbers(EM).EM1(the mean grain size 7.12 Φ, fine silt), EM2(2.37 Φ, fine sand), and EM3(1.27 Φ, medium sand)components were identified by the numerical partitioning by GSTA. Kriging interpolation method was used to interpolate the parameters of the grain size for the regular grid, and the interpolation radius was 0.015 decimal degree. We chose 0.09 decimal degree as the characteristic distance for GSTA in the semivariogram model using the geostatistical method. The FB(-) case(finer, better sorted and more negatively skewed) was adopted in GSTA for its satisfaction in the Global Moran's I test. The result of the GSTA shows that the sediments in the south barriers(SBs) were transported to the southwest of the study area. The sediments in the north, in the SE direction of sediment transport trend from the river mouth, indicated that the sediments in the north of the study area were transported from the LR to the northern beaches, and to the south and east of the study area. The sediment transport trend that simplified by GSTA as the FB(-) case was approved by the content changes of sedimentary components(i.e. EM1, EM2, and EM3). In addition, the turbulent jet diffusion pattern indicated that the coarse sediments(EM3) were delivered by LR during the flood season, and the EM2 and EM1 were from wave and tide, respectively.  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