首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   37527篇
  免费   215篇
  国内免费   170篇
测绘学   721篇
大气科学   1737篇
地球物理   7098篇
地质学   14728篇
海洋学   3549篇
天文学   8872篇
综合类   108篇
自然地理   1099篇
  2022年   489篇
  2021年   719篇
  2020年   784篇
  2019年   860篇
  2018年   1710篇
  2017年   1545篇
  2016年   1647篇
  2015年   618篇
  2014年   1417篇
  2013年   2044篇
  2012年   1628篇
  2011年   1907篇
  2010年   1797篇
  2009年   1996篇
  2008年   1775篇
  2007年   1985篇
  2006年   1738篇
  2005年   906篇
  2004年   818篇
  2003年   813篇
  2002年   746篇
  2001年   770篇
  2000年   636篇
  1999年   419篇
  1998年   438篇
  1997年   480篇
  1996年   337篇
  1995年   362篇
  1994年   337篇
  1993年   282篇
  1992年   285篇
  1991年   291篇
  1990年   338篇
  1989年   273篇
  1988年   261篇
  1987年   261篇
  1986年   193篇
  1985年   301篇
  1984年   304篇
  1983年   298篇
  1982年   278篇
  1981年   249篇
  1980年   265篇
  1979年   204篇
  1978年   242篇
  1977年   205篇
  1976年   178篇
  1975年   186篇
  1974年   171篇
  1973年   206篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Geology of Ore Deposits - Rare thallium minerals, avicennite and weissbergite, were found for the first time within the karst zones of the Khokhoy field of the Verkhnyaya Amga gold area, South...  相似文献   
132.
Man's engineering activities are concentrated on the uppermost part of the earth's crust which is called engineering-geologic zone. This zone is characterized by a significant spatialtemporal variation of the physical properties status of rocks, and saturating waters. This variation determines the specificity of geophysical and, particularly, geoelectrical investigations. Planning of geoelectric investigations in the engineering-geologic zone and their subsequent interpretation requires a priori) geologic-geophysical information on the main peculiarities of the engineering-geologic and hydrogeologic conditions in the region under investigation. This information serves as a basis for the creation of an initial geoelectric model of the section. Following field investigations the model is used in interpretation. Formalization of this a priori) model can be achieved by the solution of direct geoelectric problems. An additional geologic-geophysical information realized in the model of the medium allows to diminish the effect of the “principle of equivalence” by introducing flexible limitations in the section's parameters. Further geophysical observations as well as the correlations between geophysical and engineering-geologic parameters of the section permit the following step in the specification of the geolectric model and its approximation to the real medium. Next correction of this model is made upon accumulation of additional information. The solution of inverse problems with the utilization of computer programs permits specification of the model in the general iterational cycle of interpretation.  相似文献   
133.
Continuous high-precision long-term gravity measurements are carried out at the geophysical observatory located in the experimental base of Vladimir State University. The long time series of gravity acceleration and its standard deviation are obtained. The factors responsible for the increases in the studied deviations are analyzed. The recommendations for improving the accuracy of relative gravity measurements are formulated.  相似文献   
134.
135.
Doklady Earth Sciences - Waters at seventeen mud volcanoes of the Kerch–Taman province in the Northwestern Cis-Caucasus region have been analyzed for Sr isotope composition. The 87Sr/86Sr...  相似文献   
136.
137.
The combined use of geophysical and soil gas composition exploration methods allows to rapidly obtain at relative low cost information that might be related to seismic activity conditions. In this study, we carried out geochemical soil gas sampling (222Rn, 220Rn and CO2), electrical resistivity tomography and seismic refraction profiles in two selected zones near the town of Amer in the Spanish Pyrenees, where the presence of recent fractures is evident in the field. Data analysis clearly reveals anomalous values for each gas at specific positions along the electrical imaging transects. Geomorphologic and hydrogeologic data and the integration of geophysical data and soil gas measurements indicate that: (1) endogene gases radon (222Rn) and carbon dioxide (CO2) are released from the meta-sedimentary basement rocks across the main fractured zones with higher permeability values, while lower Cenozoic detrital sedimentary formations act as an impervious boundary; (2) sites with highest radon concentrations (52?kBq?m?3) coincide with the zones in the Amer fault showing more recent geomorphic evidence of activity, and more specifically with those areas covered by thinner surficial formations; (3) the lowest 222Rn values (0.2?C0.4?kBq?m?3) were recorded just on the master active fault plane. This pattern could be explained by a dilution effect resulting from high rates of soil CO2 efflux (267?g?m?2?day?1); (4) soil thoron (220Rn) activity is maximum (143?kBq?m?3) in areas with high surficial fracturing; (5) groundwater pumping may cause important distortions in the natural flow dynamics and in the measured concentrations of gases. The agreement between the different data (geochemical, geophysical, and hydrogeological) and field observations (geology and geomorphology) leads us to propose a preliminary tectonic-gravitational model for the study area.  相似文献   
138.
A series of high structural state plagioclases (Ab-An) was crystallized from glasses. By exchanging Na for K in KCl melts, metastable K-plagioclases (Or-An) were prepared which possess the same structural state as the starting plagioclases. Both series were investigated at 980 K by lead borate solution calorimetry. Continuing the ideas of Carpenter and McConnell (1984) and Carpenter (1992a), the results can be interpreted as follows. In the high plagioclase series, the enthalpies of solution, jHsol, reflect the schemes of Al,Si ordering: (1) analbite-like (C2/m) ordering in the An-poor region 0hXAnА.2, (2) high albite-like (C1¥) ordering in intermediate plagioclases, and (3) anorthite-like (I1¥) ordering in the An-rich region 0.7AnБ. In regions 1 and 2, jHsol decreases as a function of XAn, but increases in region 3 as a consequence of the C1¥MI1¥ ordering reaction. Therefore, it is not a mixing effect but a compositionally restricted ordering effect which causes the excess enthalpies, jHex, to be positive in the plagioclase binary as a whole. Neglecting the existence of phase transitions at XAn=0.2 and XAn=0.7, jHex can be approximated by a two-parameter Margules model yielding WHAnAb=14Dž kJ/mol and WHAbAn=40Dž kJ/mol. jHsol values of I1¥ plagioclases (XAn>0.7) can be "corrected" for the C1¥MI1¥ ordering effect (Carpenter 1992a). When combining the corrected values with the jHsol data which were actually measured on the C1¥ plagioclases (XAn<0.7), negative excess enthalpies are generated in the plagioclase binary. This may be expected when C1¥ ordering occurs relative to topochemically monoclinic reference states of analbite and hypothetical anorthite devoid of I1¥ order. The solution experiments on the K-plagioclases resulted in similar characteristics as those found for the plagioclases. However, in addition to the ordering effects observed in the plagioclase binary, volume mismatch effects contribute to jHex in the K-plagioclase series. jHex can be represented by a Margules model with WHAnOr=60ᆞ kJ/mol and WHOrAn=91ᆢ kJ/mol when the phase transitions at XAn=0.2 and XAn=0.7 are again neglected. The contribution of the volume mismatch effect to jHex is considerable, as appears from the large difference between the K-plagioclase and the plagioclase Margules parameters. Their difference corresponds to a practically symmetrical dependence of jHexvolmism on composition, with WHvolmism=48ᆡ kJ/mol.  相似文献   
139.
140.
The results of experiments on the physical modeling of long-range infrasonic propagation in the atmosphere are given. Such modeling is based on the possible coincidence between the forms of the vertical profiles of the effective sound speed stratification in the atmospheric boundary layer (between 0 and 600 m for the case under consideration) and in the atmosphere as a whole (from the land surface up to thermospheric heights (about 150 km)). The source of acoustic pulses was an oscillator of detonation type. Owing to the detonation of a gas mixture of air (or oxygen) and propane, this generator was capable of producing short, powerful (the maximum acoustic pressure was on the order of 30 to 60 Pa at a distance of 50 to 100 m from the oscillator), and sufficiently stable acoustic pulses with a spectral maximum at frequencies of 40 to 60 Hz and a pulsing period of 20 to 30 s. The sites of acoustic-signal recording were located at different distances (up to 6.5 km) from the source and in different azimuthal directions. The temperature and wind stratifications were monitored in real time during the experiments with an acoustic locator—a sodar—and a temperature profiler. The data on the physical modeling of long-range sound propagation in the atmosphere are analyzed to verify the physical and mathematical models of predicting acoustic fields in the inhomogeneous moving atmosphere on the basis of the parabolic equation and the method of normal waves. A satisfactory agreement between calculated and experimental data is obtained. One more task was to compare the theoretical relations between variations in the azimuths and angles of tilting of sound rays about the horizon and the parameters of anisotropic turbulence in the lower troposphere and stratosphere with the experimental data. A theoretical interpretation of the experimental results is proposed on the basis of the theory of anisotropic turbulence in the atmosphere. The theoretical and experimental results are compared, and a satisfactory agreement between these results is noted.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号