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191.
Shigehiko Tateno Kei Hirose Nagayoshi Sata Yasuo Ohishi 《Physics and Chemistry of Minerals》2006,32(10):721-725
The stability and high-pressure behavior of perovskite structure in MnGeO3 and CdGeO3 were examined on the basis of in situ synchrotron X-ray diffraction measurements at high pressure and temperature in a laser-heated diamond-anvil cell. Results demonstrate that the structural distortion of orthorhombic MnGeO3 perovskite is enhanced with increasing pressure and it undergoes phase transition to a CaIrO3-type post-perovskite structure above 60 GPa at 1,800 K. A molar volume of the post-perovskite phase is smaller by 1.6% than that of perovskite at equivalent pressure. In contrast, the structure of CdGeO3 perovskite becomes less distorted from the ideal cubic perovskite structure with increasing pressure, and it is stable even at 110 GPa and 2,000 K. These results suggest that the phase transition to post-perovskite is induced by a large distortion of perovskite structure with increasing pressure. 相似文献
192.
A. R. Chakhmouradian K. Ross R. H. Mitchell I. Swainson 《Physics and Chemistry of Minerals》2001,28(4):277-284
A series of fluoride perovskites related to neighborite was investigated using X-ray and neutron diffraction techniques, and Rietveld profile refinement of powder diffraction data. The series (Na1? x K x )MgF3 comprises orthorhombic (Pbnm, a?≈? , b?≈? , c?≈?2a p , Z=4) perovskites in the compositional range 0?≤?x?≤?0.30, tetragonal perovkites (P4/mbm, a?≈? , c?≈?a p , Z=2) in the range 0.40?≤?x?≤?0.46, and cubic phases (Pm3¯m, Z=1) for x?>?0.50. The structure of the orthorhombic neighborite is derived from the perovskite aristotype by rotation of MgF6 octahedra about the [110] and [001] axes of the cubic subcell. The degree of rotation, measured as a composite tilt Φ about the triad axis, varies from 18.2° at x=0 to 11.2° at x=0.30 (as determined from the fractional atomic coordinates). Orthorhombic neighborite also shows a significant displacement of Na and K from the “ideal” position (≤0.25?Å). The tetragonal members of the neighborite series exhibit only in-phase tilting about the [001] axis of the cubic subcell (φ) ranging from 4.5° to 4.8° (determined from the atomic coordinates). The solid solution (Na1? x K x )MgF3, shows a regular variation of unit-cell dimensions with composition from 3.8347?Å for the end-member NaMgF3 (reduced to pseudocubic subcell, a p ) to 3.9897?Å for KMgF3. This variation is accompanied by increasing volumes of the A-site polyhedra, whereas the volume of MgF6 octahedra initially decreases (up to x=0.40), and then increases concomitantly with K content. The polyhedral volume ratio, V A /V B , gradually increases towards the tetragonal structural range, in agreement with diminishing octahedral rotation in the structure. The P4/mbm-type neighborite has an “anomalous” polyhedral volume ratio (ca. 5.04) owing to the critical compression of MgF6 polyhedra. 相似文献
193.
利用电磁波在导电媒质界面反射系数的附加相角,导出了电场垂直于入射面的非均匀电磁波在导电介质界面的类全反射横向偏移,并对横向偏移进行了相关计算,绘出了横向偏移随入射角的变化曲线. 结果表明:入射角在相移常数临界角、衰减常数临界角和90°处,横向偏移曲线存在三个间断点. 当入射角等于这三个角时,横向偏移为无穷大,即电磁波将沿界面传播;当入射角在这三个角附近时,横向偏移变得非常大. 相似文献
194.
斜压模,正压模和异常海温时间变化的位相关系 总被引:5,自引:2,他引:3
利用1958-1997共40年NECP/NCAR再分析大气资料和GISST海表温度资料集,研究了大气斜压模、正压模与海表温度变化这三者之间位相关系,并从大气动力学方程组解释了这些位相关系。指出:大气了斜压西风异常时间变化的位相落略微后于SSTA的变化位相,而正压西风异常的变化位相超前于SS-TA变化位相。斜压纬向风异常的变化又超前于正压异常纬向风的变化。斜压纬向风异常与海表温度异常之间存在正相关关 相似文献
195.
S. Ono E. Ito T. Katsura A. Yoneda M. J. Walter S. Urakawa W. Utsumi K. Funakoshi 《Physics and Chemistry of Minerals》2000,27(9):618-622
In situ synchrotron X-ray experiments in the system SnO2 were made at pressures of 4–29 GPa and temperatures of 300–1400 K using sintered diamond anvils in a 6–8 type high-pressure
apparatus. Orthorhombic phase (α-PbO2 structure) underwent a transition to a cubic phase (Pa3ˉ structure) at 18 GPa. This transition was observed at significantly lower pressures in DAC experiments. We obtained the
isothermal bulk modulus of cubic phase K
0 = 252(28) GPa and its pressure derivative K
′=3.5(2.2). The thermal expansion coefficient of cubic phase at 25 GPa up to 1300 K was determined from interpolation of the
P-V-T data obtained, and is 1.7(±0.7) × 10−5 K−1 at 25 GPa.
Received: 7 December 1999 / Accepted: 27 April 2000 相似文献
196.
K. Kuroda T. Irifune T. Inoue N. Nishiyama M. Miyashita K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2000,27(8):523-532
Determination of the phase boundary between ilmenite and perovskite structures in MgSiO3 has been made at pressures between 18 and 24 GPa and temperatures up to 2000 °C by in situ X-ray diffraction measurements
using synchrotron radiation and quench experiments. It was difficult to precisely define the phase boundary by the present
in situ X-ray observations, because the grain growth of ilmenite hindered the estimation of relative abundances of these phases.
Moreover, the slow reaction kinetics between these two phases made it difficult to determine the phase boundary by changing
pressure and temperature conditions during in situ X-ray diffraction measurements. Nevertheless, the phase boundary was well
constrained by quench method with a pressure calibration based on the spinel-postspinel boundary of Mg2SiO4 determined by in situ X-ray experiments. This yielded the ilmenite-perovskite phase boundary of P (GPa) = 25.0 (±0.2) – 0.003
T (°C) for a temperature range of 1200–1800 °C, which is generally consistent with the results of the present in situ X-ray
diffraction measurements within the uncertainty of ∼±0.5 GPa. The phase boundary thus determined between ilmenite and perovskite
phases in MgSiO3 is slightly (∼0.5 GPa) lower than that of the spinel-postspinel transformation in Mg2SiO4.
Received: 19 May 1999 / Accepted: 21 March 2000 相似文献
197.
铁(II)-5-Br-PADAP-乳化剂OP体系析相光度法测定微量铁的应用研究 总被引:5,自引:0,他引:5
研究了铁 (Ⅱ ) 5 Br PADAP 乳化剂OP体系中的析相、显色反应的条件及其吸收光谱的分析特征 ,拟定了直接测定不同种类样品中痕量铁的分析方法。在pH =5 .0的HAC NaAC缓冲溶液中 ,Fe(Ⅱ ) 5 Br PADAP络合物具有两个吸收峰 ,分别位于λ1 =5 6 1nm与λ2 =75 4nm处。本文选择λ =75 4nm进行测定 ,其摩尔吸光系数为 :ε75 4 =3.9× 10 4L·mol- 1 ·cm- 1 。铁含量在 0~ 2 4μg范围内服从比尔定律。此方法用于样品中痕量铁的测定 ,结果准确 相似文献
198.
喜马拉雅造山带核部的变质作用与部分熔融:亚东地区高压泥质麻粒岩的岩石学与年代学研究 总被引:5,自引:4,他引:1
喜马拉雅造山带核部的高喜马拉雅结晶岩系是印度大陆深俯冲到欧亚板块之下经历了高压变质作用的产物,记录了喜马拉雅造山带的形成与演化历史。本文对喜马拉雅造山带中段亚东地区高喜马拉雅结晶岩系中的泥质麻粒岩进行了岩石学和锆石U-Pb年代学研究,结果表明泥质麻粒岩经历了复杂的变质演化和部分熔融,可识别出三期变质矿物组合。早期进变质矿物组合为石榴石+斜长石+钾长石+黑云母+白云母+石英,峰期变质矿物组合为石榴石+斜长石+钾长石+黑云母+蓝晶石+石英,晚期退变质矿物组合为石榴石+斜长石+钾长石+夕线石+黑云母+白云母+石英。相平衡模拟表明,该泥质麻粒岩经历了高温、高压的峰期变质条件为800~835℃和12.8~14kbar,在进变质和峰期变质过程中经历了白云母和黑云母脱水熔融,所形成的熔体量至少为5%~8%。麻粒岩的晚期退变质条件为720~740℃和7.6~8.3kbar。这表明泥质麻粒岩经历了一条以高压麻粒岩相峰期变质和降温、降压退变质为特征的顺时针P-T轨迹。锆石U-Pb定年结果表明,麻粒岩相变质和深熔作用发生在28.5~17.0Ma。本研究表明高喜马拉雅结晶岩系的上部构造层位经历了高压麻粒岩相变质作用,而不是以前认为的以高温、低压变质作用为特征,并为喜马拉雅造山带构造演化的研究提供了新的见解。 相似文献
199.
200.
Thermochemistry of monazite-(La) and dissakisite-(La): implications for monazite and allanite stability in metapelites 总被引:2,自引:2,他引:0
E. Janots F. Brunet B. Goffé C. Poinssot M. Burchard L. Cemič 《Contributions to Mineralogy and Petrology》2007,154(1):1-14
Thermochemical properties have been either measured or estimated for synthetic monazite, LaPO4, and dissakisite, CaLaMgAl2(SiO4)3OH, the Mg-equivalent of allanite. A dissakisite formation enthalpy of ?6,976.5 ± 10.0 kJ mol?1 was derived from high-temperature drop-solution measurements in lead borate at 975 K. A third-law entropy value of 104.9 ± 1.6 J mol?1 K?1 was retrieved from low-temperature heat capacity (C p) measured on synthetic LaPO4 with an adiabatic calorimeter in the 30–300 K range. The C p values of lanthanum phases were measured in the 143–723 K range by differential scanning calorimetry. In this study, La(OH)3 appeared as suitable for drop solution in lead borate and represents an attractive alternative to La2O3. Pseudo-sections were calculated with the THERIAK-DOMINO software using the thermochemical data retrieved here for a simplified metapelitic composition (La = ∑REE + Y) and considering monazite and Fe-free epidotes along the dissakisite-clinozoïsite join, as the only REE-bearing minerals. Calculation shows a stability window for dissakisite-clinozoïsite epidotes (T between 250 and 550°C and P between 1 and 16 kbar), included in a wide monazite field. The P–T extension of this stability window depends on the bulk-rock Ca-content. Assuming that synthetic LaPO4 and dissakisite-(La) are good analogues of natural monazite and allanite, these results are consistent with the REE-mineralogy sequence observed in metapelites, where (1) monazite is found to be stable below 250°C, (2) around 250–450°C, depending on the pressure, allanite forms at the expense of monazite and (3) towards amphibolite conditions, monazite reappears at the expense of allanite. 相似文献