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831.
简述了缺陷的类型及其在新材料制备中的作用,通过实例分析固溶体和非化学计量化合物缺陷对材料物理化学性能的影响,阐明缺陷化学是一种研究新型功能材料的有力手段,根据新材料的发展趋势分析了缺陷化学可能取得的重大突破及新的研究热点。 相似文献
832.
在前文粉末态模拟实验基础上,初步模拟古玉埋藏的酸性以及碱性环境,通过对不同材质玉料的块状形态在酸、碱缓冲溶液中的浸泡实验,并与粉末态玉料的浸泡结果进行对比分析,以深化对古玉器风化机理的认识。 相似文献
833.
Infrared absorbance spectra over ∼100 to 1,800 cm−1 were collected from optically thin films of 21 samples with compositions spanning the forsterite–fayalite binary. Polarization
information from previous specular reflectance data on end-members was used in tracing the peaks across the entire binary.
Peak positions (νi) were constrained by Lorentzian decompositions. Fitting also constrained widths for singlet peaks but for doublets and triplets,
variation in νi with composition among the constituent polarizations alters widths from intrinsic. Because film thicknesses of 0.6–1.4 μm
were estimated, our band strengths are approximate; however, relative intensities should be correct. Only for a few peaks
does νi vary smoothly across the entire binary; instead, distinct linear trends exist for Fe- and Mg-rich olivines. Discontinuities
and kinks in νi(X) occur at X = Mg/(Fe + Mg) = 0.7 and are accompanied by a change in intensity patterns. This interesting behavior was not revealed in
previous spectra of powder dispersions. The contrasting character of IR vibrations for Fe- and Mg-rich olivines is inferred
to arise from structural variations because (1) frequency is related to bond length, (2) other factors affecting frequency
(cation mass and probably bonding type) vary linearly across the binary, and (3) available data on unit cell parameters are
consistent with distinct trends for forsterites and fayalites. Vibrational components of heat capacity (C
V) and enthalpy (H) calculated from νi, were found to be slightly more negative than linear interpolations between values for forsterite and fayalite. Our computations
give smaller negative excesses from ideality in H than do previous calorimetric measurements, but are equal within experimental uncertainties. 相似文献
834.
An unresolved issue in the study of pressure solution in rock materials is the dependence of grain boundary structure and
diffusive properties on the mutual orientation of neighbouring grain lattices. We report electrical measurements yielding
the diffusivity of differently oriented halite–glass and halite–halite contacts loaded in the presence of brine. The halite–glass
contact experiments show pressure solution of the halite and an effect of halite lattice orientation on grain boundary transport.
Post-mortem observations show an orientation-dependent grain boundary texture controlled by the periodic bond chains in the
halite structure. It is inferred that this texture determines the internal grain boundary structure and properties during
pressure solution. In the halite–halite experiments neck-growth occurred, its rate depending on twist-misorientation. The
results imply that deformation by pressure solution may lead to lattice-preferred orientation development, and that polymineralic
rocks may deform faster at lower stresses than monomineralic rocks. 相似文献
835.
Victor L. Vinograd Julian D. Gale Björn Winkler 《Physics and Chemistry of Minerals》2007,34(10):713-725
Static lattice energy calculations (SLEC), based on empirical interatomic potentials, have been performed for a set of 800
different structures in a 2 × 2 × 4 supercell of C2/c diopside with compositions between diopside and jadeite, and with different states of order of the exchangeable Na/Ca and
Mg/Al cations. Excess static energies of these structures have been cluster expanded in a basis set of 37 pair-interaction
parameters. These parameters have been used to constrain Monte Carlo simulations of temperature-dependent properties in the
range of 273–2,023 K and to calculate a temperature–composition phase diagram. The simulations predict the order–disorder
transition in omphacite at 1,150 ± 20°C in good agreement with the experimental data of Carpenter (Mineral Petrol 78:433–440,
1981). The stronger ordering of Mg/Al within the M1 site than of Ca/Na in the M2 site is attributed to the shorter M1–M1 nearest-neighbor
distance, and, consequently, the stronger ordering force. The comparison of the simulated relationship between the order parameters
corresponding to M1 and M2 sites with the X-ray refinement data on natural omphacites (Boffa Ballaran et al. in Am Mineral
83:419–433, 1998) suggests that the cation ordering becomes kinetically ineffective at about 600°C. 相似文献
836.
采用镍锍火试金法结合ICP-MS分析了毛屋斜方辉石岩和石榴二辉岩样品中的Ir、Ru、Rh、Pt和Pd的含量,结果显示其铂族元素(PGE)的含量随岩石类型无规律性的变化,原始地幔标准化后的铂族元素分布模式呈负斜率,Pd、Ir发生了分异。毛屋超镁铁岩铂族元素特征的形成受岩石中铂族元素的存在相制约,PPGE富集在富Cu硫化物,而IPGE以类似残留相、不熔的单硫化物固熔体形式存在,其中地壳混染也起了一定的作用;同时,成岩过程中流体的存在造成了Pt和Pd的活化。因此,单硫化物固熔体和流体的共同作用形成了毛屋超镁铁岩类似残留地幔岩的铂族元素分布特征。 相似文献
837.
838.
839.
V.?S.?Kalantonis V.?V.?Markellos E.?A.?PerdiosEmail author 《Astrophysics and Space Science》2005,298(3):441-451
We consider Newton’s method for computing periodic orbits of dynamical systems as fixed points on a surface of section and
seek to clarify and evaluate the method’s uncertainty of convergence. Several fixed points of various multiplicities, both
stable and unstable are computed in a new version of Hill’s problem. Newton’s method is applied with starting points chosen
randomly inside the maximum possible—for any method—circle of convergence. The employment of random starting points is continued
until one of them leads to convergence, and the process is repeated a thousand times for each fixed point. The results show
that on average convergence occurs with very few starting points and non-converging iterations being wasted. 相似文献
840.
YU Jinhai & ZHANG Chuanding . Institute of Geodesy Geophysics of Chinese Academy of Sciences Wuhan China . Zhengzhou Information Engineering University Zhengzhou China 《中国科学D辑(英文版)》2005,48(3):398-405
Boundary value problem (BVP) plays a funda-mental role in physical geodesy that aims at determin-ing the earth’s shape and its external gravity field. TheMolodensky BVP and the Stokes BVP are typical inphysical geodesy, and the gravity anomaly is a kind ofbasic data. With the wide use of GPS, measurementaccuracy of the earth’s surface can reach one centime-ter, while that of the gravity measurement can reachμgals. Hence, it is necessary to establish a new kind ofBVP which can satisfy… 相似文献