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   357篇
  免费   12篇
  国内免费   9篇
测绘学   42篇
大气科学   16篇
地球物理   63篇
地质学   137篇
海洋学   15篇
天文学   68篇
综合类   15篇
自然地理   22篇
  2023年   2篇
  2022年   4篇
  2021年   10篇
  2020年   6篇
  2019年   4篇
  2018年   16篇
  2017年   17篇
  2016年   22篇
  2015年   12篇
  2014年   14篇
  2013年   25篇
  2012年   17篇
  2011年   16篇
  2010年   15篇
  2009年   16篇
  2008年   15篇
  2007年   14篇
  2006年   13篇
  2005年   9篇
  2004年   10篇
  2003年   8篇
  2002年   5篇
  2001年   4篇
  2000年   4篇
  1999年   6篇
  1998年   3篇
  1997年   6篇
  1996年   4篇
  1995年   6篇
  1994年   4篇
  1992年   2篇
  1991年   7篇
  1990年   5篇
  1989年   4篇
  1988年   6篇
  1987年   7篇
  1986年   4篇
  1985年   3篇
  1984年   4篇
  1983年   3篇
  1982年   3篇
  1981年   6篇
  1980年   2篇
  1979年   4篇
  1978年   4篇
  1977年   2篇
  1975年   1篇
  1972年   2篇
  1971年   1篇
  1969年   1篇
排序方式: 共有378条查询结果,搜索用时 15 毫秒
291.
Ahead of the Conference of Parties (COP) 24 where countries will first take stock of climate action post Paris, this paper assesses India’s progress on its nationally determined contribution (NDC) targets and future energy plans. We find that, although India is well on track to meet its NDC pledges, these targets were extremely modest given previous context. Furthermore, there is considerable uncertainty around India’s energy policy post 2030 and if current plans for energy futures materialise, the Paris Agreement’s 2 degrees goal will be almost certainly unachievable. India’s role in international climate politics has shifted from obstructionism to leadership particularly following the announcement of withdrawal by the United States from the Paris Agreement, but analysis reveals that India’s ‘hard’ actions on the domestic front are inconsistent with its ‘soft’ actions in the international climate policy arena. Going forward, India is likely to face increasing calls for stronger mitigation action and we suggest that this gap can be bridged by strengthening the links between India’s foreign policy ambitions, international climate commitments, and domestic energy realities.

Key policy insights

  • India’s NDC pledges on carbon intensity and share of non-fossil fuel capacity are relatively modest given domestic context and offer plenty of room to increase ambition of action.

  • India’s ‘soft’ leadership in global climate policy can be matched by ‘hard’ commitments by bringing NDC pledges in line with domestic policy realities.

  • There is significant uncertainty around future plans for coal power in India which have the potential to exceed the remaining global carbon budget for 2 degrees.

  相似文献   
292.
The Soil Conservation Service curve number (SCS-CN) method, also known as the Natural Resources Conservation Service curve number (NRCS-CN) method, is popular for computing the volume of direct surface runoff for a given rainfall event. The performance of the SCS-CN method, based on large rainfall (P) and runoff (Q) datasets of United States watersheds, is evaluated using a large dataset of natural storm events from 27 agricultural plots in India. On the whole, the CN estimates from the National Engineering Handbook (chapter 4) tables do not match those derived from the observed P and Q datasets. As a result, the runoff prediction using former CNs was poor for the data of 22 (out of 24) plots. However, the match was little better for higher CN values, consistent with the general notion that the existing SCS-CN method performs better for high rainfall–runoff (high CN) events. Infiltration capacity (fc) was the main explanatory variable for runoff (or CN) production in study plots as it exhibited the expected inverse relationship between CN and fc. The plot-data optimization yielded initial abstraction coefficient (λ) values from 0 to 0.659 for the ordered dataset and 0 to 0.208 for the natural dataset (with 0 as the most frequent value). Mean and median λ values were, respectively, 0.030 and 0 for the natural rainfall–runoff dataset and 0.108 and 0 for the ordered rainfall–runoff dataset. Runoff estimation was very sensitive to λ and it improved consistently as λ changed from 0.2 to 0.03.  相似文献   
293.
294.
Geochemical and rock-magnetic investigations were carried out on a sediment core collected from the SE Arabian Sea at 1420 m depth in oxygenated waters below the present-day oxygen minimum zone. The top 250 cm of the core sediments represent the last 35 kaBP. The · 18O values of Globigerinoides ruber are heaviest during the Last Glacial Maximum (LGM) and appear unaffected by low-saline waters transported from the Bay of Bengal by the strong northeast monsoon and West Indian coastal current. The signatures of Bølling-Allerød and Younger Dryas events are distinct in the records of magnetic susceptibility, organic carbon (OC) and · 18O. Glacial sediments show higher OC, CaCO3, Ba, Mo, U and Cd, while the early-to-late Holocene sediments show increasing concentrations of OC, CaCO3, Ba, Cu, Ni and Zn and decreasing concentrations of Mo, U and Cd. Productivity induced low-oxygenated bottom waters and reducing sedimentary conditions during glaciation, and productivity and oxygenated bottom waters in the Holocene are responsible for their variation. The core exhibits different stages of diagenesis at different sediment intervals. The occurrence of fine-grained, low-coercivity, ferrimagnetic mineral during glacial periods is indicative of its formation in organic-rich, anoxic sediments, which may be analogous to the diagenetic magnetic enhancement known in sapropels of the Mediterranean Sea and Japan Sea. The glacial sediments exhibiting reductive diagenesis with anoxic sedimentary environment in this core correspond to reductive diagenesis and intermittent bioturbation (oxygenation) reported in another core in the vicinity. This suggests that the poorly oxygenated bottom water conditions during glacial times should not be generalized, but are influenced locally by productivity, sedimentation rates and sediment reworking.  相似文献   
295.
296.
The variations of spring water radon concentration and meteorological parameters were analysed in relation to the seismic activities in Garhwal Himalaya, India. The radon anomalies were classified on the basis of statistical treatment of the daily observations. The precise measurements of water discharge rate from the spring have been made along with radon measurements for earthquake precursory study. The earthquakes with epicentral distances less than 150 km were considered by an empirical relationship. Pre-, co-, and post-seismic changes in the radon concentration were taken carefully into account in the empirical relationship to establish this behaviour as a potential earthquake precursor. The empirical relationship has been validated by the radon data recorded from the spring waters. The magnitudes of the earthquakes were estimated by using the empirical relationship by introducing computed correlation coefficient of radon and meteorological parameters. The calculated magnitude of some local earthquakes matches exactly with the magnitude recorded by the laboratory seismograph. The possible mechanisms that may cause a radon anomaly are also discussed.  相似文献   
297.
The present study was aimed at removing cadmium ions from aqueous solution through batch studies using adsorbents, such as, granular activated carbon (GAC) and activated clay (A‐clay). GAC was of commercial grade where as the A‐clay was prepared by acid treatment of clay with 1 mol/L of H2SO4. Bulk densities of A‐clay and GAC were 1132 and 599 kg/m3, respectively. The surface areas were 358 m2/g for GAC and 90 m2/g for A‐clay. The adsorption studies were carried out to optimize the process parameters, such as, pH, adsorbent dosage, and contact time. The results obtained were analyzed for kinetics and adsorption isotherm studies. The pH value was optimized at pH 6 giving maximum Cd removal of 84 and 75.2% with GAC and A‐clay, respectively. The adsorbent dosage was optimized and was found to be 5 g/L for GAC and 10 g/L for A‐clay. Batch adsorption studies were carried out with initial adsorbate (Cd) concentration of 100 mg/L and adsorbent dosage of 10 g/L at pH 6. The optimum contact time was found to be 5 h for both the adsorbents. Kinetic studies showed Cd removal a pseudo second order process. The isotherm studies revealed Langmuir isotherm to better fit the data than Freundlich isotherm.  相似文献   
298.
Granulites are important component of high-grade metamorphic rocks reflecting intense conditions observed for crustal rocks in terms of temperature, and pressure. This review paper demonstrates how these high-grade granulites are critical to understanding the evolution of the lower continental crust with special reference to southern India. Geothermobarometric traverse across different granulite blocks in southern India shows wide ranging P-T conditions of metamorphism (700–1000 ° C, and 5–10 kbar). The sapphirine-, orthopyroxene-sillimanite, and spinel -bearing quartz-deficient granulites recognised from parts of southern granulite terrain (Ganguvarpatti, Kiranur, and Palani hill ranges etc.) show oriented sillimanite aggregates pseudomorph after course twinned kyanite, staurolite + kyanite assemblages, and corroded blebs of gedrite within orthopyroxene, suggesting a prograde stage of a clockwise P-T evolution. Evidence of ITD history comes from the textures in which an early Mg-rich garnet (XMg 52–60) with orthopyroxene (up to 10% Al2O3) involving sillimanite breakdown forming variety of symplectites having combinations of orthopyroxene, sapphirine, cordierite, and spinel. These spectacular reaction textures, and mineralogic sensors from the high-grade rocks establish a prograde clockwise P-T-t path with notable decompressive history (ITD) in the southern granulite terrain. The inferred P-T-t paths have been further integrated with the recent geochronological, and isotopic data to constrain the timing, and duration of metamorphism, emplacement of the magmatic protolith for characterising the evolution of the granulites, and their bearing on the geodynamic implications. Based on the emerging evidence for Neoproterozoic tectonothermal imprints in the southern granulite terrain, history of the assembly of dispersed fragments is also addressed within the East Gondwana framework.  相似文献   
299.
Competitive sorption of estriol (E3) and 17α‐ethinylestradiol (EE2) was studied on activated charcoal. Better sorption of E3 (88.9%) and EE2 (69.5%) was observed with single‐solute sorption system than with bi‐solute sorption system. Single‐solute sorption kinetics of E3 and EE2 were evaluated with two (Langmuir and Freundlich) and three (dual mode and Song) parameter models. Freundlich model (R2, 0.9915 (E3); 0.9875 (EE2)) showed good prediction compared to other models for single‐solute sorption. Adsorption capacity documented reduced efficacy (86.4% (E3); 65.9% (EE2)) due to induced competitive behavior between the estrogens in aqueous phase. Bi‐solute adsorption kinetics of E3 and EE2 were described by IAST with two and three parameter models. Among these models, IAST‐Freundlich model (R2, 0.9765 (E3); 0.9985 (EE2)) was best in predicting bi‐solute sorption of E3 and EE2 by activated charcoal. All these models showed favorable representation of both single‐ and bi‐solute sorption behaviors.  相似文献   
300.
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