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771.
根据我国温度、降水长期变化规律的分析 ,已持续 1 0多年的暖周期还将持续一段时间 ;其中北方大部分地区气温可能处于下降趋势 ,南方大部分地区可能处于上升趋势 ;冬季温度将趋于下降 ,平均温度将比 2 0世纪 90年代降低 ;夏季温度将趋于上升 ,平均温度可能会比2 0世纪 90年代升高。长江流域将可能由多雨期向少雨期过渡 ,降水将比 2 0世纪 90年代减少 ;华北和黄河流域一带可能向多雨期过渡 ,降水将增加。 相似文献
772.
In this paper, observation data in 25 GPS reference stations of China have been analyzed by calculating GPS position coordinate
time-series with GIPSY. Result shows there is an obvious trend variation in such time-series. The trend variations of time
series along the longitude and latitude coordinate reflect the motion of each position in the global-plate, in which the trend
variation in the vertical direction reveals some large-scale construction information or reflects the local movement around
the positions. The analysis also shows that such time-series have a variation cycle of nearly 1.02 a, but the reason still
remains to be further studied. At the end of this paper, response of the time-series of M
S=8.1 Kunlunshan earthquake was analyzed, and the seismogenic process of M
S=8.1 Kunlunshan earthquake, according to the time proceeding and the feature of anomaly, was divided into 3 phases—changes
in blocks with forces, strain accumulation, quick accumulation and slow release of energy. At the initial stage of seismogenic
process of M
S=8.1 earthquake and at the imminent earthquake, coseismic process as well as during the post earthquake recovery, anomaly
in vertical direction is always in a majority. The anomalous movement in vertical direction at the initial stage resulted
in a blocking between faults, while at the middle stage of seismogenic process, the differential movement between blocks are
in a majority, which is the major reason causing energy accumulating at the blocking stage of faults.
Foundation item: National Natural Science Foundation of China (40074024 and 40304002). 相似文献
773.
On the Measurement of the Tensile Strength of Soft Rocks 总被引:8,自引:4,他引:8
Summary. This paper reports on a comparative study of various types of experimental tests for measuring the tensile strength of rocks and rock-like materials. A critical assessment is presented of some widely used laboratory techniques on the basis of experimental data from the literature and from the laboratory investigation performed in this study.Tests were carried out using a triaxial apparatus recently set up at Milan University of Technology. This was designed to reduce random misalignments between specimen and loading frame, which are typical of conventional triaxial cells with external tie bars. The apparatus was then modified to perform various types of tests for determining the tensile strength of materials. An artificial building stone and a natural calcarenite of the Gravina di Puglia geological formation, sampled at Montescaglioso (Matera-Italy) were tested in this research. The experimental investigation included various types of tests, namely the uni-axial, the Brazilian, the ring, the three and four points bending and the Luong test. Specimens of both materials were also compressed to failure in unconfined conditions and loaded cyclically in unconfined tension and compression, Young’s moduli being measured by means of local instrumentation. 相似文献
774.
The study zone is located in the city of Padova (the Veneto region, NE Italy). The industrial activities present in this area
since 1950 have produced very high concentrations of Pb, Zn, Cu, Pcb and oils until a depth of 7 m. The unsaturated and the
saturated zones are both polluted. Because of the abundance of Pb values it was decided to analyze the lead distribution in
the studied zone. In many studies of the polluted sites, the geometry of the investigated volume is highly anisotropic. Generally
we have an extension of some hectares in the horizontal plane and of a few meters in depth. It is likely that different horizontal
spatial continuity structures in pollution distribution are found at different depths both for the layered nature of the medium
and for the transition between unsaturated and saturated conditions. In such conditions the decision to divide a 3D problem
into 1D and 2D problems can be useful. Initially the studied volume was divided into seven layers up to 5 m in depth; the
study was then approached in two phases. First, the Pb values in the vertical direction were analyzed, considering a derive
along z, and estimating the values using the Kriging with Trend (KT) method. Thus it was possible to increase the data in the z direction, especially in the deeper layers. Second, 500 realizations of the Pb distribution for each of the seven layers
were simulated using the simulated annealing procedure. Finally, results were presented and discussed for each layer in terms
of median and probability maps. 相似文献
775.
776.
Spatial and temporal variations and controlling factors of potential evapotranspiration in China: 1956-2000 总被引:7,自引:0,他引:7
Based on the climatic data of 580 stations in China during 1956 and 2000, potential evapotranspiration are calculated using the Penman-Monteith Method recommended by FAO. The spatial and temporal distributions of the potential evapotranspiration over China and the temporal trends of the regional means for 10 major river basins and whole China are analyzed. Through a partial correlation analysis, the major climate factors which affect the temporal change of the potential evapotranspiration are analyzed. Major results are drawn as follows: 1) The seasonal and annual potential evapotranspiration for China as a whole and for most basins show decline tendencies during the past 45 years; for the Songhua River Basin there appears a slightly increasing trend. 2) Consequently, the annual potential evapotranspirations averaged over 1980-2000 are lower than those for the first water resources assessment (1956-1979) in most parts of China. Exceptions are found in some areas of Shandong Peninsula, western and middle basins of the rivers in Southwest China, Ningxia Hui Autonomous Region as well as the source regions of the Yangtze and Yellow rivers, which may have brought about disadvantages to the exploration and utilization of water resources. 3) Generally, sunshine duration, wind speed and relative humidity have greater impact on the potential evapotranspiration than temperature. Decline tendencies of sunshine duration and/or wind speed in the same period appear to be the major causes for the negative trend of the potential evapotranspiration in most areas. 相似文献
777.
778.
779.
The presented results of cyclic triaxial tests on sand demonstrate that the cumulative effects due to small cycles obey a kind of flow rule. It mainly depends on the average stress ratio about which the cycles are performed. This so-called “cyclic flow rule” is unique and can be well approximated by flow rules for monotonic loading. Amongst others it is shown that the cyclic flow rule is only moderately influenced by the average mean pressure, by the strain loop (span, shape, polarization), the void ratio, the loading frequency, the static preloading and the grain size distribution curve. A slight increase of the compactive portion of the flow rule with increasing residual strain (due to the previous cycles) was observed. These experimental findings prove that the cyclic flow rule is an essential and indispensable concept in explicit (N-type) accumulation models. 相似文献
780.
Scrap tyres can be shredded into chips and can easily be mixed with granular soils. To assess the behaviour of the admixtures,
compressibility and triaxial compression tests were carried out by varying chip size and chip content. The results demonstrated
that sand–tyre chip mixtures up to 20% could be a potential material for highway construction and embankment construction
up to around 10 m height. 相似文献