全文获取类型
收费全文 | 43724篇 |
免费 | 4037篇 |
国内免费 | 5609篇 |
专业分类
测绘学 | 2350篇 |
大气科学 | 6019篇 |
地球物理 | 9503篇 |
地质学 | 21744篇 |
海洋学 | 3384篇 |
天文学 | 2544篇 |
综合类 | 4197篇 |
自然地理 | 3629篇 |
出版年
2024年 | 98篇 |
2023年 | 400篇 |
2022年 | 911篇 |
2021年 | 1087篇 |
2020年 | 905篇 |
2019年 | 992篇 |
2018年 | 5558篇 |
2017年 | 4783篇 |
2016年 | 3566篇 |
2015年 | 1160篇 |
2014年 | 1349篇 |
2013年 | 1247篇 |
2012年 | 2072篇 |
2011年 | 3803篇 |
2010年 | 3032篇 |
2009年 | 3326篇 |
2008年 | 2752篇 |
2007年 | 3176篇 |
2006年 | 807篇 |
2005年 | 991篇 |
2004年 | 936篇 |
2003年 | 993篇 |
2002年 | 846篇 |
2001年 | 610篇 |
2000年 | 714篇 |
1999年 | 1014篇 |
1998年 | 829篇 |
1997年 | 884篇 |
1996年 | 817篇 |
1995年 | 686篇 |
1994年 | 564篇 |
1993年 | 514篇 |
1992年 | 395篇 |
1991年 | 291篇 |
1990年 | 232篇 |
1989年 | 182篇 |
1988年 | 174篇 |
1987年 | 126篇 |
1986年 | 107篇 |
1985年 | 76篇 |
1984年 | 53篇 |
1983年 | 46篇 |
1982年 | 37篇 |
1981年 | 49篇 |
1980年 | 60篇 |
1979年 | 28篇 |
1978年 | 15篇 |
1976年 | 17篇 |
1975年 | 14篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
Leonhard Gantner Vera Maurer Norbert Kalthoff Olga Kiseleva 《Boundary-Layer Meteorology》2017,162(3):475-502
A method to simulate characteristics of wind speed in the boundary layer of tropical cyclones in an idealized manner is developed and evaluated. The method can be used in a single-column modelling set-up with a planetary boundary-layer parametrization, or within large-eddy simulations (LES). The key step is to include terms in the horizontal velocity equations representing advection and centrifugal acceleration in tropical cyclones that occurs on scales larger than the domain size. Compared to other recently developed methods, which require two input parameters (a reference wind speed, and radius from the centre of a tropical cyclone) this new method also requires a third input parameter: the radial gradient of reference wind speed. With the new method, simulated wind profiles are similar to composite profiles from dropsonde observations; in contrast, a classic Ekman-type method tends to overpredict inflow-layer depth and magnitude, and two recently developed methods for tropical cyclone environments tend to overpredict near-surface wind speed. When used in LES, the new technique produces vertical profiles of total turbulent stress and estimated eddy viscosity that are similar to values determined from low-level aircraft flights in tropical cyclones. Temporal spectra from LES produce an inertial subrange for frequencies \(\gtrsim \)0.1 Hz, but only when the horizontal grid spacing \(\lesssim \)20 m. 相似文献
982.
Lin-Lin Pan Shu-Hua Chen Dan Cayan Mei-Ying Lin Quinn Hart Ming-Hua Zhang Yubao Liu Jianzhong Wang 《Climate Dynamics》2011,37(9-10):2005-2020
In this study, the influence of climate change to California and Nevada regions was investigated through high-resolution (4-km grid spacing) dynamical downscaling using the WRF (Weather Research & Forecasting) model. The dynamical downscaling was performed to both the GFS (Global forecast model) reanalysis (called GFS-WRF runs) from 2000?C2006 and PCM (Parallel Climate Model) simulations (called PCM-WRF runs) from 1997?C2006 and 2047?C2056. The downscaling results were first validated by comparing current model outputs with the observational analysis PRISM (Parameter-elevation Regressions on Independent Slopes Model) dataset. In general, the dominant features from GFS-WRF runs and PCM-WRF runs were consistent with each other, as well as with PRISM results. The influences of climate change on the California and Nevada regions can be inferred from the model future runs. The averaged temperature showed a positive trend in the future, as in other studies. The temperature increases by around 1?C2°C under the assumption of business as usual over 50?years. This leads to an upward shifting of the freezing level (the contour line of 0°C temperature) and more rain instead of snow in winter (December, January, and February). More hot days (>32.2°C or 90°F) and extreme hot days (>37.8°C or 100°F) are predicted in the Sacramento Valley and the southern parts of California and Nevada during summer (June, July, and August). More precipitation is predicted in northern California but not in southern California. Rainfall frequency slightly increases in the coast regions, but not in the inland area. No obvious trend of the surface wind was indicated. The probability distribution functions (PDF) of daily temperature, wind and precipitation for California and Nevada showed no significant change in shape in either winter or summer. The spatial distributions of precipitation frequency from GFS-WRF and PCM-WRF were highly correlated (r?=?0.83). However, overall positive shifts were seen in the temperature field; increases of 2°C for California and 3°C for Nevada in summer and 2.5°C for California and 1.5°C for Nevada in winter. The PDFs predicted higher precipitation in winter and lower precipitation in the summer for both California and Nevada. 相似文献
983.
2002年西北太平洋和南海热带气旋路径主客观预报评价 总被引:1,自引:2,他引:1
利用目前中央气象台热带气旋路径实时业务预报中使用的各种主客观预报产品资料,对2002年西北太平洋和南海热带气旋路径实时业务预报中的主客观预报进行对比分析检验。结果显示:虽然在整体上主观预报要优于客观模式的结果,但客观模式的预报能力已接近主观预报,有时甚至还好于主观预报,特别是48小时以上时效的客观模式较主观预报具有一定的优势;而在客观模式中,全球模式优于台风模式;热带气旋路径数值模式产品的使用对提高热带气旋路径业务预报水平具有十分重要的作用。 相似文献
984.
Maciej Sadowski 《Climatic change》2008,90(4):443-451
Adopted by COP 10 (Dec 1/CP.10) and approved by the MOP1, the Buenos Aires programme of adaptation and response measures opens
doors to intensify preparations for expected climate change. By this decision the COP, requested the SBSTA to develop a structured
5-year programme of work of the SBSTA on the scientific, technical and socio-economic aspects of impacts of, and vulnerability
and adaptation to, climate change. Consequently, the COP, by its decision 2/CP.11, adopted the “Five-year programme of work
of the Subsidiary Body for Scientific and Technological Advice on impacts, vulnerability and adaptation to climate change”
Finally during COP12 this programme was approved as “Nairobi Work Programme on impacts, vulnerability and adaptation to climate
change”. This programme has fundamental significance not only for developing countries, but also for industrialized nations
in which some sectors of the or social life are particularly vulnerable to climate change, specifically, inter alia EIT countries and new EU Member States. Further development of this adaptation programme economy should contain steps that
provide optimum economic and social effectiveness, risk management, identification of vulnerable sectors and gaps in knowledge,
preparation of a list of policy options, including an analysis of cost effectiveness, selection of the most effective policies,
and a preparedness implementation plan. In Poland the preliminary adaptation programme covered agriculture, water management,
and coastal zone management. For the time being, gaps in knowledge and preparedness measures have been identified. An estimation
of possible impact on these areas was based on chosen GCMs, and sea level rise IPCC scenarios. In conclusion, it was stated
that the results achieved should be seen as a first step forward and a more comprehensive study is necessary to update the
results and cover other sectors of the economy, such as health protection, spatial planning, ecosystems and forestry, and
to develop specific guidelines and recommendations for policy-makers. 相似文献
985.
Summary A three-dimensional, nonhydrostatic numerical model with high spatial resolution, in which a simple energy closure scheme
is employed, has been developed to simulate the spray dispersion over complex terrain. The evaporation, condensation, and
dispersion of the spray and moisture are taken into account in model equations. The term of latent heat due to phase transformation
is considered in detail to account for its effects on the temperature field and airflow. As an application of the model, the
spray concentration and air relative humidity are calculated under neutral condition. The results indicate that under the
neutral condition, the spray is transported to about 0.6 km downwind from the source, and its effects on the air humidity
reach a further distance of 0.9 km downwind from the source.
Attention is given to the dependence of the results upon the various factors influencing the simulation, such as the intensity
of the source, the atmospheric stratification, and the dynamic factor of the terrain. Some numerical tests were carried out
to provide extra insight to the effects of these factors. It has been demonstrated that the simulation results such as relative
humidity and temperature are sensitive to these factors, especially to the thermal stratification. Under unstable conditions,
the effects of the spray source increase significantly, and the variation extent of the temperature, relative humidity and
flow field is larger than that under neutral condition. The effects of dynamic and thermal factors on the air flow field are
discussed through the comparison of the modeling results over complex terrain and flat terrain.
Received June 8, 1998 Revised April 17, 1999 相似文献
986.
Thomas K. Flesch Lowry A. Harper Raymond L. Desjardins Zhiling Gao Brian P. Crenna 《Boundary-Layer Meteorology》2009,132(1):11-30
Inverse-dispersion calculations can be used to infer atmospheric emission rates through a combination of downwind gas concentrations
and dispersion model predictions. With multiple concentration sensors downwind of a compound source (whose component positions
are known) it is possible to calculate the component emissions. With this in mind, a field experiment was conducted to examine
the feasibility of such multi-source inferences, using four synthetic area sources and eight concentration sensors arranged
in different configurations. Multi-source problems tend to be mathematically ill-conditioned, as expressed by the condition
number κ. In our most successful configuration (average κ = 4.2) the total emissions from all sources were deduced to within 10% on average, while component emissions were deduced
to within 50%. In our least successful configuration (average κ = 91) the total emissions were calculated to within only 50%, and component calculations were highly inaccurate. Our study
indicates that the most accurate multi-source inferences will occur if each sensor is influenced by only a single source.
A “progressive” layout is the next best: one sensor is positioned to “see” only one source, the next sensor is placed to see
the first source and another, a third sensor is placed to see the previous two plus a third, and so on. When it is not possible
to isolate any sources κ is large and the accuracy of a multi-source inference is doubtful. 相似文献
987.
关于梅雨研究的回顾与展望 总被引:2,自引:0,他引:2
从梅雨的划分、梅雨的降水分型、梅雨与季风的关系及梅雨的影响因子几个方面,对前人的研究成果进行了回顾和讨论。最后,提出梅雨研究仍需解决的问题:(1)江淮流域梅雨季节的开始至今仍没有一个客观统一划定标准;(2)南海季风、印度季风等季风子系统对梅雨的影响大小及其机制尚需进一步研究讨论;(3)应针对梅雨季节内江淮流域不同的降水分布型,寻找其前期预兆信号进行深入研究;(4)应特别注意特定海温分布型对梅雨的影响,并从中找出影响梅雨的关键区域和影响的关键时段;(5)积冰和雪盖与梅雨异常的关系仍需进一步求证,影响机制还需进一步探索。 相似文献
988.
989.
利用北京近郊地区南苑机场1990-2000年6-8月观测资料,分析了北京夏季对流云出现日数、出现时间、云底高、生命史等基本特征;利用北京站1995-2000年6-8月常规探空资料,分析了北京夏季对流温度和对流凝结高度的特征,尝试用对流温度预报对流云的出现,用对流凝结高度预报对流云的云高。结果表明:对流温度在局地热力对流云的预报中具有一定的指示意义,对流凝结高度能在一定程度上反映出对流云的云高。有对流云时,对流温度与实测温度之差在4℃以内的,占对流云总数的80%。在对流温度与实测温度之差≤4℃的有对流云日内,对流凝结高度与实测对流云云高之差90%以上都是在1200m以内,500m以内的也达到了53%。 相似文献
990.
Statistical estimation of high-resolution surface air temperature from MODIS over the Yangtze River Delta,China 下载免费PDF全文
High-resolution surface air temperature data are critical to regional climate modeling in terms of energy balance, urban climate change, and so on. This study demonstrates the feasibility of using Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) to estimate air temperature at a high resolution over the Yangtze River Delta region, China. It is found that daytime LST is highly correlated with maximum air temperature, and the linear regression coefficients vary with the type of land surface. The air temperature at a resolution of 1 km is estimated from the MODIS LST with linear regression models. The estimated air temperature shows a clear spatial structure of urban heat islands. Spatial patterns of LST and air temperature differences are detected, indicating maximum differences over urban and forest regions during summer. Validations are performed with independent data samples, demonstrating that the mean absolute error of the estimated air temperature is approximately 2.5°C, and the uncertainty is about 3.1°C, if using all valid LST data. The error is reduced by 0.4°C (15%) if using best-quality LST with errors of less than 1 K. The estimated high-resolution air temperature data have great potential to be used in validating high-resolution climate models and other regional applications. 相似文献