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71.
利用中尺度数值模式ARPS进行了理想场的数值模拟,分析研究了水汽和潜热释放对大气层结稳定度的影响以及其在背风波的发展和演变过程中的作用,研究发现,潜热释放对大气层结分布的影响要远大于水汽对大气层结分布的直接影响,如果没有潜热的释放,水汽对背风波的发展和演变的作用非常小,而潜热释放可以使湿层结稳定度急剧下降,迅速破坏原有的层结分布,使这个区域出现非拦截的强烈的垂直运动,波动的崩溃更加迅速和明显。但需要说明的是在试验中,将数值模式里控制潜热释放的参数设为:0、1/2、2的假定情况,则在实际的大气运动过程中是不可能存在的。 相似文献
72.
The broadband diffuse radiation method is improved to retrieve the aerosol refractive index imaginary part (AIP) and broadband (400-1000 nm mean) single scattering albedo (SSA). In this method, four sets of SSA selection criteria are proposed for quality control. The method is used to retrieve AIP, SSA and absorptive optical thickness (AbOT) from routine hourly-exposed pyrheliometer and paranometer measurements over 11 sites (meteorological observatories) in China during 1998-2003. Apart from one suburban site (Ejin Qi), the other urban sites are all located around big or medium cities. As shown in the retrieval results, annual mean SSA during 1998-2003 changes from 0.941 (Wuhan) to 0.849 (Lanzhou), and AIP from 0.0054 to 0.0203. The 11-site average annual mean SSA and AIP are 0.898 and 0.0119, respectively. SSA during winter is smaller for most sites. There is an evidently positive correlation between SSA and aerosol optical thickness (AOT) for all sites. There is also a positive correlation between SSA and relative humidity for most sites, but a negative correlation for a few sites, such as Kashi and ǚrǚmqi in Northwest China. 相似文献
73.
气温日较差研究进展:变化趋势及其影响因素 总被引:6,自引:0,他引:6
从日较差的变化趋势、影响因素以及人类活动对气候变化影响的指示3个方面对日较差的研究进行了总结和概括。观测数据以及气候模式模拟的结果表明,全球气温日较差在近半个多世纪以来呈下降趋势,而这种下降趋势不仅仅是自然变化的结果,还受到人类活动的影响。辐射、云量、气溶胶、下垫面的变化、水汽、降水以及航迹云等因素都能对日较差的变化造成影响。日较差的"周末效应"以及城市化过程中日较差的变化相对于平均气温的变化,能够更有效地指示人类活动对气候变化的影响。 相似文献
74.
The climate–population relationship has long been conceived. Although the topic has been repeatedly investigated, most of
the related works are Eurocentric or qualitative. Consequently, the relationship between climate and population remains ambiguous.
In this study, fine-grained temperature reconstructions and historical population data sets have been employed to statistically
test a hypothesized relationship between temperature change and population growth (i.e., cooling associated with below average
population growth) in China over the past millennium. The important results were: (1) Long-term temperature change significantly
determined the population growth dynamics of China. However, spatial variation existed, whilst population growth in Central
China was shown to be responsive to both long- and short-term temperature changes; in marginal areas, population growth was
only sensitive to short-term temperature fluctuations. (2) Temporally, the temperature–population relationship was obscured
in some periods, which was attributable to the factors of drought and social buffers. In summary, a temperature–population
relationship was mediated by geographic factors, the aridity threshold, and social factors. Given the upcoming threat posed
by climate change to human societies, this study seeks to improve our knowledge and understanding of the climate–society relationship. 相似文献
75.
UV attenuation in the cloudy atmosphere 总被引:1,自引:0,他引:1
Jianhui Bai 《Journal of Atmospheric Chemistry》2009,62(3):211-228
Ultraviolet (UV) energy absorption plays a very important role in the Earth–atmosphere system. Based on observational data
for Beijing, we suggest that some atmospheric constituents utilize or transfer UV energy in chemical and photochemical (C&P) reactions, in addition to those which absorb UV energy directly. These constituents are primarily volatile organic compounds
(VOCs) emitted from both vegetative and anthropogenic sources. The total UV energy loss in the cloudy atmosphere for Beijing
in 1990 was 78.9 Wm−2. This attenuation was caused by ozone (48.3 Wm−2), other compounds in the atmosphere (26.6 Wm−2) and a scattering factor (4.0 Wm−2). Our results for a cloudy atmosphere in the Beijing area show that the absorption due to these other compounds occurs largely
through the mediation of water vapor. This fraction of energy loss has not been fully accounted for in previous models. Observations
and previous models results suggest that 1) a cloudy atmosphere absorbs 25∼30 Wm−2 more solar shortwave radiation than models predict; and 2) aerosols can significantly decrease the downward mean UV-visible
radiation and the absorbed solar radiation at the surface by up to 28 and 23 Wm−2, respectively. Thus, quantitative study of UV and visible absorption by atmospheric constituents involved in homogeneous
and heterogeneous C&P reactions is important for atmospheric models. 相似文献
76.
José Luís Argaín Miguel A. C. Teixeira Pedro M. A. Miranda 《Boundary-Layer Meteorology》2017,165(1):145-160
A method is proposed for estimating the surface-layer depth \((z_s)\) and the friction velocity \((u_*)\) as a function of stability (here quantified by the Obukhov length, L) over the complete range of unstable flow regimes. This method extends that developed previously for stable conditions by Argaín et al. (Boundary-Layer Meteorol 130:15–28, 2009), but uses a qualitatively different approach. The method is specifically used to calculate the fractional speed-up \((\varDelta S)\) in flow over a ridge, although it is suitable for more general boundary-layer applications. The behaviour of \(z_s \left( L\right) \) and \(u_*\left( L\right) \) as a function of L is indirectly assessed via calculation of \(\varDelta S\left( L\right) \) using the linear model of Hunt et al. (Q J R Meteorol Soc 29:16–26, 1988) and its comparison with the field measurements reported in Coppin et al. (Boundary-Layer Meteorol 69:173–199, 1994) and with numerical simulations carried out using a non-linear numerical model, FLEX. The behaviour of \(\varDelta S\) estimated from the linear model is clearly improved when \(u_*\) is calculated using the method proposed here, confirming the importance of accounting for the dependences of \(z_s\left( L \right) \) and \(u_*\left( L \right) \) on L to better represent processes in the unstable boundary layer. 相似文献
77.
Juan Huang Yanli Feng Jian Li Bin Xiong Jialiang Feng Sheng Wen Guoying Sheng Jiamo Fu Minghong Wu 《Journal of Atmospheric Chemistry》2008,61(1):1-20
The levels of carbonyl compounds in Shanghai ambient air were measured in five periods from January 2007 to October 2007 (covering
winter, high-air-pollution days, spring, summer and autumn). A total of 114 samples were collected and eighteen carbonyls
were identified. Formaldehyde, acetaldehyde and acetone were the most abundant carbonyls and their mean concentrations of
19.40 ± 12.00, 15.92 ± 12.07 and 11.86 ± 7.04 μg m−3 respectively, in the daytime for five sampling periods. Formaldehyde and acetaldehyde showed similar diurnal profiles with
peak mixing ratios in the morning and early afternoon during the daytime. Their mean concentrations were highest in summer
and lowest in winter. Acetone showed reversed seasonal variation. The high molecular weight (HMW, ≥C5) carbonyls also showed
obvious diurnal variations with higher concentrations in the daytime in summer and autumn, while they were all not detected
in winter. Formaldehyde and acetaldehyde played an important role in removing OH radicals in the atmosphere, but the contribution
of acetone was below 1%. The carbonyls levels in high-air-pollution days were reported. More carbonyl species with higher
concentrations were found in high-air-pollution days than in spring. These carbonyls were transported with other pollutants
from north and northwest in March 27 to April 2, 2007 and then mixed with local sources. Comparing with Beijing and Guangzhou,
the concentrations of formaldehyde and acetaldehyde in Shanghai were the highest, which indicated that the air pollution in
Shanghai was even worse than expected. 相似文献
78.
论青藏高原隆起作用于大气的临界高度 总被引:11,自引:4,他引:11
在以前工作的基础上,从大气动力学、热力学及气候学的角度,进一步论证了在青茂高原隆起过程中存在一个临界高度hc(-1.5-2km)。当高原隆起突破这一临界高度时才开始对大气产生强烈的作用,从而造成大气环流、大气热力结构、亚洲区域以及全球气候等一系列巨大转变。 相似文献
79.
General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations
without a large extent of ver- tical flow. Vertical flow, however, plays an important role in the formation of local breezes,
such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of
atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a
general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their
high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account
by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model
equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model
nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical
solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach
can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface
energy balance are important further steps towards the practical application of the method. 相似文献
80.
Climatic regime shift and decadal anomalous events in China 总被引:15,自引:0,他引:15
Climatic time series from historical documents and instrumental records from China showed temporal and regional patterns in
the last two to three centuries, including two multidecadal oscillations at quasi-20-year and quasi-70-year timescales revealed
by signal analysis from wavelet transform. Climatic anomalous events on the decadal timescale were identified based on the
two oscillations when their positive (or negative) phases coincide with each other to amplify amplitude. The coldest event
occurred in the decade of 1965–1975 in eastern China, while the periods of 1920–1930, 1940–1950, and 1988–2000 appeared to
be warmer in most parts of China. For the precipitation series in northern China, the dry anomalous event was found in the
late 1920s, while the wet anomalous event occurred in the 1950s. A severe drought in 1927–1929 in northern China coincided
with the anomalous warm and dry decade, caused large-scale famine in nine provinces over northern China. Climatic anomalous
events with a warm-dry or cold-wet association in the physical climate system would potentially cause severe negative impacts
on natural ecosystem in the key vulnerable region over northern China. The spatial pattern of summer rainfall anomalies in
the eastern China monsoon region showed an opposite variations in phase between the Yellow River Valley (North China) and
the mid-low Yangtze River Valley as well as accompanied the shift of the northernmost monsoon boundary. Climatic regime shifts
for different time points in the last 200 years were identified. In North China, transitions from dry to wet periods occurred
around 1800, 1875, and 1940 while the transitions from wet to dry periods appeared around 1840, 1910, and the late 1970s.
The reversal transition in these time points can also be found in the lower Yangtze River. Climatic regime shifts in China
were linked to the interaction of mid- and low latitude atmospheric circulations (the westerly flow and the monsoon flow)
when they cross the Tibetan Plateau in East Asia. 相似文献