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141.
We present results for the generation process of a shell current loop by using a three-dimensional ideal MHD code. It is shown that a shell current loop with a diffuse closure current can be generated due to the twisting motions of the loop footpoints. It is also shown that during the generation of a shell current loop, plasma density enhancement propagates along a shell current loop. It is suggested that the generation process of a shell current loop may be related to the movement of soft X-ray enhancement from the footpoints along a loop before onset of a solar flare. 相似文献
142.
Forced magnetic reconnection induced by magnetohydrodynamic (MHD) waves may account for the triggering of explosive solar activities such as flares. Reconnection in a neutral sheet plasma can be driven by the ponderomotive force associated with nonlinear MHD waves accompanying plasma vortex motion. The nonlinear stage of forced reconnection by MHD waves is simulated with a MHD particle-code: Some conditions for fast reconnection are discussed with applications to solar flares. 相似文献
143.
We present a numerical simulation of the fast magnetosonic shock wave formation during a two-current-loop collision by using
a magnetohydrodynamical model. It is shown that the rarefaction waves are generated in the initial stage when the two current
loops start to collide. After the rarefaction waves propagate away from the excited region, the fast magnetosonic waves with
density enhancement can be produced for the simulation when the current strength of the loop is weak. As the current becomes
strong enough, the magnetosonic shock waves can be generated in the direction perpendicular to that of the two-loop collision. 相似文献
144.
Cyclic loading tests were performed on three one‐storey steel frames and four three‐storey concrete‐filled tube (CFT) moment frames reinforced with a new type of earthquake‐resisting element consisting of a steel plate shear wall with vertical slits. In this shear wall system, the steel plate segments between the slits behave as a series of flexural links, which provide fairly ductile response without the need for heavy stiffening of the wall. The steel shear walls and the moment frames behaved in a ductile manner up to more than 4% drift without abrupt strength degradation or loss of axial resistance. Results of these tests and complementary analysis provide a basis for an equivalent brace model to be employed in commercially available frame analysis programs. Test and analytical results suggest that the horizontal force is carried by the bolts in the middle portion of the wall–frame connection, while the vertical forces coupled with the moment in the connection are resisted by the bolts in the edge portion of the connection, for which the friction bolts in the connection should be designed. When sufficient transverse stiffening is provided, full plastic strength and non‐degrading hysteretic behaviour can be achieved for this new type of shear wall. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
145.
The δ18O values of eighteen marine evaporites of Precambrian to Recent ages were found to vary from +8 to 25‰ relative to SMOW, while the δ34S values previously measured by Thode and Monster [2] vary from +10 to +38‰ relative to meteoritic sulfur. The results strongly suggest that the δ18O value of ocean sulfate varied with geologic age with a minimum at the Permian age. 相似文献
146.
147.
Mengnjo Jude Wirmvem Takeshi Ohba Justice Yuven Suila Wilson Yetoh Fantong Nchemty Oscar Bate Seigo Ooki Engome Regina Wotany Asobo Nkengmatia Elvis Asaah Samuel Ndonwi Ayonghe Gregory Tanyileke Joseph Victor Hell 《Environmental Earth Sciences》2014,72(9):3585-3598
Shallow groundwater (>30 mbgl) is an essential source of drinking water to rural communities in the Ndop plain, northwest Cameroon. As a contribution to water management, the effect of seasonal variation on the groundwater chemistry, hydrochemical controls, drinking quality and recharge were investigated during the peaks of the dry (January) and rainy (September) seasons. Field measurements of physical parameters were preceded by sampling 58 groundwater samples during both seasons for major ions and stable isotope analyses. The groundwater, which was barely acidic (mean pH of 6) and less mineralised (TDS < 272 mg/l), showed no significant seasonal variation in temperature, pH and TDS during the two seasons. The order of cation abundance (meq/l) was Na+ > Ca2+ > Mg2+ > K+ and Na+ > Mg2+ > Ca2+ > K+ in the dry and rainy seasons, respectively, but that of anions ( \( {\text{HCO}}_{3}^{ - } \) > \( {\text{NO}}_{3}^{ - } \) > Cl? > \( {\text{SO}}_{4}^{2 - } \) > F?) was similar in both seasons. This suggests a negligible effect of seasonal variations on groundwater chemistry. The groundwater, which was CaMgHCO3 and NaHCO3, is chemically evolved rainfall (CaMgSO4Cl) in the area. Silicate mineral dissolution and cation-exchange were the main controls on groundwater chemistry while there was little anthropogenic influence. The major ions and TDS concentrations classified the water as suitable for human consumption as per WHO guidelines. The narrow cluster of δ18O and δD of same groundwater from both seasons between the δ18O and δD values of May–June precipitation along the Ndop Meteoric Water Line indicates meteoric origin, rapid recharge (after precipitation) and timing of recharge between May and June rainfall. Diffuse groundwater recharge mainly occurs at low altitudes (<1,400 m asl) within the plain. Besides major ions and TDS, the similar δ18O and δD of groundwater from both seasons indicate a consistent groundwater recharge and flow pattern throughout the year and resilience to present day short-term seasonal climatic variations. However, controlled groundwater abstraction is recommended given the increasing demand. 相似文献