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991.
The monthly means of north component X of geomagnetic field from 16 observatories during 1984–1988 were analyzed using the
Sompi spectral analysis technique Most of these observatories are located in China. The analysis of the semiannual variations
indicates that the latitude has no apparent effect on the X component. This clearly implies that the source field mode of
semiannual variations cannot simply be described by using the p
1
0
mode. Using the p
1
0
mode to estimate the inductive scale lengthC in the semiannual period, the value ofC at each observatory would be biased significantly. The purpose of this study is to find which kind of modes is optimal for
estimating the values ofC corresponding to the semiannual variations. The results show that a composite mode, involving five terms P
n
0
(n = 1,, 5), might be a reasonable and acceptable one 相似文献
992.
993.
Julie Weills Ambler 《Estuarine, Coastal and Shelf Science》1985,20(6):743-760
Egg production and hatching success were determined between March 1981 and March 1982 for the copepod Acartia tonsa Dana from East Lagoon, Galveston, Texas. During three-day experiments in the laboratory, field collected females were fed diets of (1) natural particles collected over the water column, (2) some modification of this and (3) the diatom Thalassiosira weissflogii. The latter served to isolate the effects of temperature and salinity from the effects of the natural particle diets on egg production. Specific rates of egg production, i.e. μg egg biomass/μg body biomass/time, were consistently higher per unit carbon than nitrogen.The influence of seasonal factors on egg production was compared. Salinity was inversely correlated with egg production, but had less effect than temperature. Positive correlations with temperature were always higher for specific rates per unit nitrogen than carbon. At 15°C, females produced 0·25 of their body carbon (or nitrogen) as eggs per day, whereas at 28°C, they produced at least their own biomass as eggs per day (up to 1·80). These high rates of A. tonsa were probably due to its reproductive biology and adaptation to the subtropical habitat as well as the high temperatures and food concentrations. The correlation between specific egg production rate and temperature was less with the natural particle diets than with the unialgal diet. This indicated that the quantity or quality of natural particle assemblages in East Lagoon influenced egg production. Egg viability was highest in the spring, but was not related to diet or the percentage of females with spermatophores. 相似文献
994.
南太平洋大气和海洋年代际变化与冷空气关系的研究 总被引:1,自引:0,他引:1
本文分析了美国国家环境预报中心和气象研究中心(NCEP/NCAR)1958—1997年的月平均资料和海表面温度异常资料(JONES,1994),发现南太平洋大气和海洋及赤道东太平洋中存在明显的年代际时间尺度的变化,1972年以前,副热带海区大气旋度场与海表面温度(SST)的变化同步,大气中的变化超前于海洋的变化;1972年以后到90年代初,该海区大气旋度场与海表面温度(SST)的变化趋势相反。研究发现南半球中低纬度之间热量的交换程度与副热带海区年代际时间尺度的变化具有明显的关系,说明南半球大气热通量的经向输送有可能是影响海洋年代际变化的原因之一。相关分析表明,对赤道东太平洋年代际变化的影响海区在南太平洋副热带海区,主要位于南纬20度和25度附近。 相似文献
995.
Jianyu Hu Hiroshi Kawamura Huasheng Hong Fumiaki Kobashi Dongxiao Wang 《Journal of Oceanography》2001,57(1):69-78
Sea surface height (SSH) variations with a period of 36 months (SSH36 variations) in the South China Sea (SCS) and its adjacent ocean are intensively investigated using six years of TOPEX/POSEIDON-derived SSH data. The results show that there appears higher energy of SSH36 variations in the east of the Luzon Strait and in some areas of the SCS, both of which are correlated with each other. The SSH36 variations usually propagate westward in the subtropical region of the northern Pacific Ocean and turn northward in the east of the Luzon Strait while they sometimes propagate into the SCS through the Luzon Strait with the phase speed of about 11–12 cm/s, which may be considered as Rossby waves. It can be inferred that the SSH36 variations are strongly associated with current structures and eddies in the SCS because of their significant intensiveness. The SSH variations with the period of 6 months are more dominant than those with the other periods in the SCS. 相似文献
996.
Eight years of sea surface height data derived from the TOPEX/Poseidon altimeter, are analyzed in order to identify long- and a-periodic behavior of the North Atlantic sea level. For easy interpolation, sea surface height data are converted into sea surface topography data using the geoid derived from EGM96 to degree 360. Principal Component Analysis is used to identify the most dominant spatial and temporal variations. In order to separate dominant periodic signals, a yearly and a half-yearly oscillation, as well as alias effects from imperfect ocean tide corrections, are estimated independently by a Harmonic Analysis and subtracted. The residuals are smoothed by a 90-day moving average filter and examined once again by a PCA, which identifies a low-frequency variation with a period of approximately 6-7 years and an amplitude of about 1 dm, as well as a large sea level change of partially more than ±1 dm within only few months. This sea level change can also be seen in yearly and seasonal sea level residuals. Furthermore, the analysis shows a significant sea level change in 1998 occurring almost over the whole North Atlantic, which is not clearly identified by the PCA. Similar results are obtained by analyzing sea surface temperature and sea level pressure data. 相似文献
997.
998.
The seasonal variations of water properties and the baroclinic flow pattern in the upper layer of Toyama Bay, where the shelf
breaks in the passway of the eastward coastal branch of the Tsushima Warm Current, have been examined using temperature and
salinity data from 26 local stations collected in the 32 years from 1963 through 1994. The results show that the flow pattern
around the bay, as inferred from the distributions of the geopotential anomaly at 300 dbar and saline core water, changes
remarkably from summer to autumn. There are two obvious inflows into Toyama Bay in a year. One is the surface inflow of less
saline water from east of the Noto Peninsula as the coastal-trapped density-driven flow of the coastal branch during the transition
from May to July. In September, this inflow is abruptly weakened by a transient northwestward reversal flow in the intermediate
layer around 100 m depth. This reversal flow is accompanied by the temporary shallowness of the pycnoclines inside the bay.
At that time, another inflow with more saline water of the year occurs in the intermediate layer. From November until January,
this reversal flow disappears and a southeastward passing through-flow gradually intensifies across the bay mouth, accompanied
by deepening of the pycnoclines inside the bay. According to our interannual analysis over the 32-year study period, this
reversal flow has been a stable seasonal phenomenon, except for only 4 years, in which a local warm region or warm eddy developed
just north of the Noto Peninsula. 相似文献
999.
Nutrients, chlorophyll-a, particulate organic carbon (POC), and environmental conditions were extensively investigated in
the northern East China Sea (ECS) near Cheju Island during three seasonal cruises from 2003 to 2005. In spring and autumn,
relatively high concentrations of nitrate (2.6~12.4 μmol kg-1) and phosphate (0.17~0.61 μmol kg-1) were observed in the surface waters in the western part of the study area because of the large supply of nutrients from
deep waters by vertical mixing. The surface concentrations of nitrate and phosphate in summer were much lower than those in
spring and autumn, which is ascribed to a reduced nutrient supply from the deep waters in summer because of surface layer
stratification. While previous studies indicate that upwellings of the Kuroshio Current and the Changjiang (Yangtze River)
are main sources of nutrients in the ECS, these two inputs seem not to have contributed significantly to the build-up of nutrients
in the northern ECS during the time of this study. The lower nitrate:phosphate (N:P) ratio in the surface waters and the positive
correlation between the surface N:P ratio and nitrate concentration indicate that nitrate acts as a main nutrient limiting
phytoplankton growth in the northern ECS, contrary to previous reports of phosphate-limited phytoplankton growth in the ECS.
This difference arises because most surface water nutrients are supplied by vertical mixing from deep waters with low N:P
ratios and are not directly influenced by the Changjiang, which has a high N:P ratio. Surface chlorophyll-a levels showed
large seasonal variation, with high concentrations (0.38~4.14 mg m-3) in spring and autumn and low concentrations (0.22~1.05 mg m-3) in summer. The surface distribution of chlorophyll-a coincided fairly well with that of nitrate in the northern ECS, implying
that nitrate is an important nutrient controlling phytoplankton biomass. The POC:chlorophyll-a ratio was 4~6 times higher
in summer than in spring and autumn, presumably because of the high summer phytoplankton death rate caused by nutrient depletion
in the surface waters. 相似文献
1000.
Climatic causes of ecological and environmental variations in the source regions of the Yangtze and Yellow Rivers of China 总被引:1,自引:0,他引:1
In the source regions of the Yangtze and Yellow Rivers of China, glaciers, frozen ground, the hydrological system, and alpine
vegetation have changed over the past decades years. Climatic causes of these variations have been analyzed using mean monthly
air temperature and monthly precipitation between 1956 and 2000, and monthly evaporation from φ20 evaporation pans between
1961 and 1996. In the source region of the Yangtze River, lower temperature and plentiful precipitation during the 1960s and
continuing into the early 1980s triggered a glacier advance that culminated in the early 1990s, while a robust temperature
increase and precipitation decrease since 1986 has forced glaciers to retreat rapidly since 1995. Permafrost degradation is
another consequence of the climatic warming. The variations in the hydrological system and alpine vegetation are controlled
mainly by the climate during the warm season. Warmer and drier summer climate is the major cause of a degradation of the vegetation,
desiccation of the high-cold marshland, a decrease in the areas and numbers of lakes and rivers in the middle and north source
regions of the Yangtze and Yellow Rivers, and a reduction in surface runoff in the source region of the Yangtze River for
the last 20 years. The causes of eco-environmental change in Dari area, near the outlet from the source area of the Yellow
River, are different from those elsewhere in the study area. A noticeable reduction in runoff in the source region of the
Yellow River and degradation of alpine vegetation in Dari area are closely related to the permafrost degradation resulting
from climate warming. 相似文献