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881.
882.
883.
西南某电站右岸开挖边坡稳定性的FLAC3D分析 总被引:11,自引:2,他引:9
西南某大型水电站引水发电洞进水口边坡顶部在开挖过程中出现带状裂缝 ,引起了多方的极大关注。在对该边坡系统的地质调查基础上 ,确立了其变形破坏模式 ;通过FLAC3D模拟开挖过程 ,客观地验证了实际开挖过程中边坡的变形及其顶部平台出现的裂缝 ;并预测了在采取加固措施后边坡内部变形趋势。经计算 ,开挖面临空方向最大位移量达到 5 .4cm。此后 ,经过有效的锚固处理 ,边坡经过变形和应力的调整 ,总体上趋于稳定 ,为确保进水口隧洞的顺利开挖提供了科学依据 相似文献
884.
城乡结合部土地利用变化的信息提取技术与分析--以无锡市为例 总被引:11,自引:0,他引:11
作为两种截然不同的生态系统过渡区,城乡结合部是土地利用/土地覆被变化最激烈地区之一,城乡结合部的土地利用情况日益受到人们重视.本文以无锡市为例,利用3S技术提取城乡结合部的范围和土地利用/土地覆被状况信息,提出了确定无锡市城乡结合部范围边界的半自动提取模型和结合部土地利用类型半自动提取模型,并对无锡市城乡结合部土地利用结构及其变化进行分析,揭示了无锡市城乡结合部土地利用/土地覆被变化特征,据此提出城乡结合部土地合理利用的建议. 相似文献
885.
L. Hjalmarsdotter A. A. Zdziarski S. Larsson V. Beckmann M. McCollough D. C. Hannikainen O. Vilhu 《Monthly notices of the Royal Astronomical Society》2008,384(1):278-290
The X-ray binary Cygnus X-3 (Cyg X-3) is a highly variable X-ray source that displays a wide range of observed spectral states. One of the main states is significantly harder than the others, peaking at ∼20 keV, with only a weak low-energy component. Due to the enigmatic nature of this object, hidden inside the strong stellar wind of its Wolf–Rayet companion, it has remained unclear whether this state represents an intrinsic hard state, with truncation of the inner disc, or whether it is just a result of increased local absorption. We study the X-ray light curves from RXTE /ASM and CGRO /BATSE in terms of distributions and correlations of flux and hardness and find several signs of a bimodal behaviour of the accretion flow that are not likely to be the result of increased absorption in a surrounding medium. Using INTEGRAL observations, we model the broad-band spectrum of Cyg X-3 in its apparent hard state. We find that it can be well described by a model of a hard state with a truncated disc, despite the low cut-off energy, provided the accreted power is supplied to the electrons in the inner flow in the form of acceleration rather than thermal heating, resulting in a hybrid electron distribution and a spectrum with a significant contribution from non-thermal Comptonization, usually observed only in soft states. The high luminosity of this non-thermal hard state implies that either the transition takes place at significantly higher L / L E than in the usual advection models, or the mass of the compact object is ≳20 M⊙ , possibly making it the most-massive black hole observed in an X-ray binary in our Galaxy so far. We find that an absorption model as well as a model of almost pure Compton reflection also fit the data well, but both have difficulties explaining other results, in particular the radio/X-ray correlation. 相似文献
886.
Douglas O. ReVelle 《Earth, Moon, and Planets》2008,102(1-4):345-356
We have developed a new approach to modeling the acoustic-gravity wave (AGW) radiation from bolide sources. This first effort
involves entry modeling of bolide sources that have available satellite data through procedures developed in ReVelle (Earth
Moon Planets 95, 441–476, 2004a; in: A. Milani, G. Valsecchi, D. Vokrouhlicky (eds) NEO Fireball Diversity: Energetics-based Entry Modeling and Analysis Techniques, Near-earth Objects: Our Celestial Neighbors
(IAU S236), 2007b). Results from the entry modeling are directly coupled to AGW production through line source blast wave theory for the initial
wave amplitude and period at 38_2007_9181_Article_IEq2.gif" alt="$$x=10$$" align="middle" border="0"> (at 10 blast wave radii and perpendicular to the trajectory). The second effort involves the prediction of the formation
and or dominance of the propagation of the atmospheric Lamb, edge-wave composite mode in a viscous fluid (Pierce, J. Acoust.
Soc. Amer. 35, 1798–1807, 1963) as a function of the source energy, horizontal range and source altitude using the Lamb wave frequency that was deduced
directly during the entry modeling and that is used as a surrogate for the source energy. We have also determined that Lamb
wave production by bolides at close range decreases dramatically as either the source energy decreases or the source altitude
increases. Finally using procedures in Gill (Atmospheric-Ocean Dynamics, 1982) and in Tolstoy (Wave Propagation, 1973), we have analyzed two simple dispersion relationships and have calculated the expected dispersion for the Lamb edge-wave
mode and for the excited, propagating internal acoustic waves. Finally, we have used the above formalism to fully evaluate
these techniques for four large bolides, namely: the Tunguska bolide of June 30, 1908; the Revelstoke bolide of March 31,
1965; the Crete bolide of June 6, 2002 and the Antarctic bolide of September 3, 2004. Due to page limitations, we will only
present results in detail for the Revelstoke bolide. 相似文献
887.
Using a 12th order expansion of the perturbative potential in powers of the eccentricities and the inclinations, we study
the secular effects of two non-coplanar planets which are not in mean–motion resonance. By means of Lie transformations (which
introduce an action–angle formulation of the Hamiltonian), we find the four fundamental frequencies of the 3-D secular three-body
problem and compute the long-term time evolutions of the Keplerian elements. To find the relations between these elements,
the main combinations of the fundamental frequencies common to these evolutions are identified by frequency analysis. This
study is performed for two different reference frames: a general one and the Laplace plane. We underline the known limitations
of the linear Laplace–Lagrange theory and point out the great sensitivity of the 3-D secular three-body problem to its initial
values. This analytical approach is applied to the exoplanetary system 3727j4/10569_2007_9113_Article_IEq1.gif" alt="$${\upsilon}$$" align="middle" border="0"> Andromedae in order to search whether the eccentricities evolutions and the apsidal configuration (libration of 3727j4/10569_2007_9113_Article_IEq2.gif" alt="$${\Delta \varpi}$$" align="middle" border="0">) observed in the coplanar case are maintained for increasing initial values of the mutual inclination of the two orbital
planes.
Anne-Sophie Libert is FNRS Research Fellow. 相似文献
888.
Tadross A. L. 《中国天文和天体物理学报》2008,8(3):362-368
As a continuation of a series of work, we aim to refine and re-determine the physical parameters of previously rarely or un-studied open star clusters with good quality CMDs using Near-IR JHK photometry. Here we present a morphological analysis of the 2MASS database (the digital "Two Micron All Sky Survey") for the open cluster Pismis 3. Some of the physical parameters are estimated for the first time, and some others, re-determined. 相似文献
889.
GRB 060124 is the first event that both prompt and afterglow emission were observed simultaneously by the three Swift instruments. Its main peak also triggered Konus-Wind and HETE-II. Therefore, investigation on both the temporal and spectral properties of the prompt emission can be extended to X-ray bands. We perform a detailed analysis on the two well identified pulses of this burst, and find that the pulses are narrower at higher energies, and both X-rays and 3b3;-rays follow the same wȁ3;E relation for an individual pulse. However, there is no a universal power-law index of the wȁ3;E relation among pulses. We find also that the rise-to-decay ratio r/d seems not to evolve with E and the r/d values are well consistent with that observed in typical GRBs. The broadband spectral energy distribution also suggests that the X-rays are consistent with the spectral behavior of the 3b3;-rays. These results indicate that the X-ray emission tracks the 3b3;-ray emission and the emissions in the two energy bands are likely to be originated from the same physical mechanism. 相似文献
890.
Comet 73P-B/Schwassmann-Wachmann 3 was observed with IRCS/Subaru at geocentric distance of 0.074 AU on UT 10 May 2006. Multiple H2O emission lines were detected in non-resonant fluorescence near 2.9 μm. No significant variation in total H2O production rate was found during the (3 h) duration of our observations. H2O rotational temperatures and ortho-to-para abundance ratios were measured for several positions in the coma. The temperatures extracted from two different time intervals show very similar spatial distributions. For both, the rotational temperature decreased from ∼110 to ∼90 K as the projected distance from the nucleus increased from ∼5 to ∼30 km. We see no evidence for OPR change in the coma. The H2O ortho-para ratio is consistent with the statistical equilibrium value (3.0) for all spatially resolved measurements. This implies a nuclear spin temperature higher than ∼45 K. 相似文献