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91.
Ground water contaminant transport by nondivergence-free, unsteady and nonstationary velocity fields
Pore flow velocity is assumed to be a nondivergence-free, unsteady, and nonstationary random function of space and time for ground water contaminant transport in a heterogeneous medium. The laboratory-scale stochastic contaminant transport equation is up scaled to field scale by taking the ensemble average of the equation by using the cumulant expansion method. A new velocity correction, which is a function of mean pore flow velocity divergence, is obtained due to strict second order cumulant expansion (without omitting any term after the expansion). The field scale transport equations under the divergence-free pore flow velocity field assumption are also derived by simplifying the nondivergence-free field scale equation. The significance of the new velocity correction term is investigated on a two dimensional transport problem driven by a density dependent flow. 相似文献
92.
Alix Lombard Anny Cazenave Pierre Yves Le Traon Stephanie Guinehut Cécile Cabanes 《Ocean Dynamics》2006,56(5-6):445-451
In this paper, we first discuss the controversial result of the work by Cabanes et al. (Science 294:840–842, 2001), who suggested that the rate of past century sea level rise may have been overestimated, considering the limited and heterogeneous
location of historical tide gauges and the high regional variability of thermal expansion which was supposed to dominate the
observed sea level. If correct, this conclusion would have solved the problem raised by the IPCC third assessment report [Church
et al, Cambridge University Press, Cambridge, pp 881, 2001], namely, the factor two difference between the 20th century observed sea level rise and the computed climatic contributions.
However, recent investigations based on new ocean temperature data sets indicate that thermal expansion only explains part
(about 0.4 mm/year) of the 1.8 mm/year observed sea level rise of the past few decades. In fact, the Cabanes et al.’s conclusion
was incorrect due to a contamination of abnormally high ocean temperature data in the Gulf Stream area that led to an overestimate
of thermal expansion in this region. In this paper, we also estimate thermal expansion over the last decade (1993–2003), using
a new ocean temperature and salinity database. We compare our result with three other estimates, two being based on global
gridded data sets, and one based on an approach similar to that developed here. It is found that the mean rate of thermosteric
sea level rise over the past decade is 1.5±0.3 mm/year, i.e. 50% of the observed 3 mm/year by satellite altimetry. For both
time spans, past few decades and last decade, a contribution of 1.4 mm/year is not explained by thermal expansion, thus needs
to be of water mass origin. Direct estimates of land ice melt for the recent years account for about 1 mm/year sea level rise.
Thus, at least for the last decade, we have moved closer to explaining the observed rate of sea level rise than the IPCC third
assessment report. 相似文献
93.
地质雷达探测工程的几个问题 总被引:1,自引:0,他引:1
地质雷达(GPR)探测技术在浅层地质勘探领域广泛应用,并取得较好的应用效果.文章针对消除干扰的方法、关于防空洞探测、关于公路路面检测和隧道衬砌质量检测、地下岩溶探测等内容进行了探讨. 相似文献
94.
95.
Temperature variations at very long baseline interferometry (VLBI) sites cause thermal deformations of the VLBI antennas and
corresponding displacements of the VLBI reference points. The thermal deformation effects typically contain seasonal and daily
signatures. The amplitudes of the annual vertical motion of the antenna reference point can reach several millimeters, depending
on the design of the antenna structure, on the material, and on the environmental effects such as global station position,
station height and climatology effects. Simple methods to correct this effect use the difference of the environmental temperature
with respect to a defined reference temperature, the antenna dimensions, the elevation of the antenna, the material of antenna
structure. Applying these simple models for thermal deformation in the VLBI data analysis improves the baseline length repeatability
by 3.5%. A comparison of these simple models with local thermal deformation measurements at the antennas in Onsala and Wettzell
show that the local measurements and the modeled corrections agree well when the temperature of the antenna structure is used,
but agree less good when the surrounding air temperatures are used. To overcome this problem we present a method to model
temperature penetration into the antenna structures, that allows to model thermal deformation effects that agree with the
observed vertical deformation of the Onsala and Wettzell radio telescopes with a root mean square deviation of 0.07 and 0.13 mm,
respectively. Possible implementations in the VLBI analysis are presented, and the definition of an adequate reference temperature
is discussed. 相似文献
96.
硫酸盐渍土在多次冻融循环时的盐胀累加规律 总被引:10,自引:3,他引:7
通过室内模拟试验,研究了硫酸盐渍土在历经多次冻融循环时的盐胀累加规律,得出了盐胀累加的不同类型,给出了累加盐胀率与循环次烽之间的关系式,进一步揭示了盐胀累加的 和影响因素。 相似文献
97.
This paper studies the relative motion of satellite formation flying in arbitrary elliptical orbits with no perturbation.
The trajectories of the leader and follower satellites are projected onto the celestial sphere. These two projections and
celestial equator intersect each other to form a spherical triangle, in which the vertex angles and arc-distances are used
to describe the relative motion equations. This method is entitled the reference orbital element approach. Here the dimensionless
distance is defined as the ratio of the maximal distance between the leader and follower satellites to the semi-major axis
of the leader satellite. In close formations, this dimensionless distance, as well as some vertex angles and arc-distances
of this spherical triangle, and the orbital element differences are small quantities. A series of order-of-magnitude analyses
about these quantities are conducted. Consequently, the relative motion equations are approximated by expansions truncated
to the second order, i.e. square of the dimensionless distance. In order to study the problem of periodicity of relative motion,
the semi-major axis of the follower is expanded as Taylor series around that of the leader, by regarding relative position
and velocity as small quantities. Using this expansion, it is proved that the periodicity condition derived from Lawden’s
equations is equivalent to the condition that the Taylor series of order one is zero. The first-order relative motion equations,
simplified from the second-order ones, possess the same forms as the periodic solutions of Lawden’s equations. It is presented
that the latter are further first-order approximations to the former; and moreover, compared with the latter more suitable
to research spacecraft rendezvous and docking, the former are more suitable to research relative orbit configurations. The
first-order relative motion equations are expanded as trigonometric series with eccentric anomaly as the angle variable. Except
the terms of order one, the trigonometric series’ amplitudes are geometric series, and corresponding phases are constant both
in the radial and in-track directions. When the trajectory of the in-plane relative motion is similar to an ellipse, a method
to seek this ellipse is presented. The advantage of this method is shown by an example. 相似文献
98.
基于珞珈一号和DMSP/OLS夜间灯光数据,提取辽宁省城市空间用地信息并监测分析了2003—2018年城市空间扩张特征。结果表明:1)利用辽宁省DMSP/OLS长时间序列夜间灯光数据提出了一种适合校正长时间序列DMSP/OLS数据的校正方法,提高了数据的连续性和可对比性;2)弥补了统计数据在空间属性的不足,消除了过去单纯依靠统计数据分析城市空间扩张的弊端,为其他省市分析城市扩张提供新的遥感监测分析方法;3)在2003—2018年间,辽宁省城市空间扩张存在城市空间扩张与南方省份相比发展比较缓慢及协调性欠佳等问题。 相似文献
99.
The thermo-hydro-elastodynamic model (THED), in which the thermo-osmosis and thermal-filtration phenomenon in a two-phase porous thermoelastic medium can be considered, was previously presented by the authors [Ganbin Liu, Kanghe Xie, Rongyue Zheng. Model of nonlinear coupled thermo-hydro-elastodynamics response for a saturated poroelastic medium. Sci China (Ser E) 2009;52(8):2373–83] and is used in this paper to investigate the thermo-elastodynamic response of a spherical cavity in a saturated poroelastic medium when subjected to a time-dependent non-torsional thermal/mechanical source. The Separated Variable Method is introduced, and the non-zero displacement potentials are expanded in terms of the Legendre polynomial. Solutions for the displacement, temperature increment, pore pressure and stress are obtained in the domain of the Laplace transform. Numerical results are also performed for different modes and are compared with the results of the thermoelastic model (TED) to ascertain the validity and the difference between these two models. 相似文献
100.
通过对钻探过程中井漏的复杂地质因素分析,提出了水化膨胀复合材料体系,并对该体系进行了膨胀性、封堵性及复合桥接堵漏模拟实验。实验结果表明,堵漏材料PAR具有很强的吸水膨胀性能,可膨胀至原体积的几十倍,且时间快有利于形成快速的封堵。材料PAR与稻谷和锯末形成的复合堵漏材料具有很强的堵塞率,可达70%以上。承压堵漏测量装置中测试表明:复合堵漏体系不仅能形成封堵,而且能够承受一定的压差。在云南临仓市勐简乡铅锌矿钻探过程中,运用复合堵漏体系满足了该地区复杂地矿钻探需要。 相似文献