全文获取类型
收费全文 | 18551篇 |
免费 | 4037篇 |
国内免费 | 4387篇 |
专业分类
测绘学 | 781篇 |
大气科学 | 2841篇 |
地球物理 | 6452篇 |
地质学 | 8480篇 |
海洋学 | 3746篇 |
天文学 | 717篇 |
综合类 | 1168篇 |
自然地理 | 2790篇 |
出版年
2024年 | 29篇 |
2023年 | 111篇 |
2022年 | 218篇 |
2021年 | 291篇 |
2020年 | 315篇 |
2019年 | 445篇 |
2018年 | 345篇 |
2017年 | 344篇 |
2016年 | 354篇 |
2015年 | 413篇 |
2014年 | 560篇 |
2013年 | 745篇 |
2012年 | 743篇 |
2011年 | 637篇 |
2010年 | 600篇 |
2009年 | 716篇 |
2008年 | 896篇 |
2007年 | 1298篇 |
2006年 | 1333篇 |
2005年 | 1417篇 |
2004年 | 1446篇 |
2003年 | 1175篇 |
2002年 | 1130篇 |
2001年 | 1068篇 |
2000年 | 1015篇 |
1999年 | 1159篇 |
1998年 | 1352篇 |
1997年 | 924篇 |
1996年 | 920篇 |
1995年 | 852篇 |
1994年 | 766篇 |
1993年 | 854篇 |
1992年 | 664篇 |
1991年 | 569篇 |
1990年 | 362篇 |
1989年 | 230篇 |
1988年 | 197篇 |
1987年 | 104篇 |
1986年 | 35篇 |
1985年 | 54篇 |
1984年 | 37篇 |
1983年 | 54篇 |
1982年 | 29篇 |
1981年 | 20篇 |
1980年 | 26篇 |
1979年 | 18篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
临沧超大型锗矿床有机质与锗矿化的地球化学特征 总被引:10,自引:3,他引:10
临沧锗矿床是一产于第三系含煤岩系中的超大型矿床。矿床的最初锗源与盆地西缘的二云母花岗岩有关。主矿体产于下煤组沉积旋回的早期地层中,每一沉积阶段早期形成的褐煤和碳质泥岩中富含锗,最高含量达1470×10^-6。褐煤和碳质泥岩在矿化过程中平均富集了164-169倍。根据锗含量,褐煤和碳质泥岩可分为锗含量小于12×10^-6的低锗煤(泥岩)和大于90×10^-6的高锗煤(泥岩)。高锗煤中有机质富含氧官能 相似文献
942.
In this paper,the Gutenberg-Richter model is used to generate seismic events.The events that satisfy the random distribution are also generated.With those events,the natural probability distribution of Load and Unload Response Ratio(LURR),which measures quantitatively the degree of instability of a nonlinear system,is discussed.The study is based on stress energy release,which is chosen as the response of nonlinear system F3.The comparative results from the observation catalogue and generating data are also studied.It is revealed that the natural probability of LURR is mostly stable when the sample number is sufficient.The lower the natural probability of LURR,the more the precursory is information it may contain.The influence of Y3 resulting from the sample number and the magnitude range of events is also discussed. 相似文献
943.
Zhou Cuiying Wang Hongwei Wang Mei and Zhang YuxiaSeismological Bureau of Shandong Province Jinan China Center for Analysis Prediction SSB Beijing China 《中国地震研究》1997,(4)
In order to solve the problem of early estimation of moderately strong aftershock duration time in an earthquake sequence,this study has been conducted.First,the definition of the strong aftershock has been given.It is pointed out that there is a difference in the strong aftershock duration time between the main shock type sequence and the strong earthquake swarm sequence.After dividing the three cases,i.e.,a strong aftershock duration time larger than 1 day,smaller than 1 day,and no strong aftershock occurred in a main shock type sequence by using the pattern recognition method,we gave the rough correlation relation between strong aftershock duration time and first large shock magnitude for two types of sequences.Finally,the judgment index and method of estimating strong aftershock duration times for different sequence types have been given. 相似文献
944.
Dong Ruishu Xiang Hongfa Guo Shunmin Ran Hongliu and Fu ChanghongInstitute of Geology SSB Beijing China Institute of Geophysics SSB Beijing China 《中国地震研究》1997,(4)
There have been 12 possible locations of the earthquakes occurring in the South Yellow Sea since 1505.In this paper,the location of the earthquake that occurred in 1505 has been determined by the collection of more historical data of the influenced field,referring the isoseismal data of earthquakes with the epicentral intensityⅨ and combining geophysical field data with tectonic condition,due to its great influence on seismic safety assessment of some significant engineering. 相似文献
945.
Thierry Rolland Stéphanie Fayolle Arlette Cazaubon Stéphane Pagnetti 《Aquatic Sciences - Research Across Boundaries》1997,59(1):57-73
In a sub-alpine river, the Asse, with an unpredictable discharge regime, chlorophyll, density and taxonomic diversity of both
drifting and periphytic communities were studied from a methodical approach. The investigations based on stamping two close
cross-sections to know their spatial distributions in a heterogeneous bed substrate showed a heterogeneous pattern of colonization
mainly influenced by hydrological variables as the current velocity, the size of the substrata (gravel-pebble-boulder). For
the drifting algae, mainly composed with benthic species temporarily unhooked to the substrata, the heterogeneity of the distribution
was reduced in fast flow which induced a mixing of the whole mass of water.
For the periphyton, some results indicated that the greatest diversity and the highest chlorophyll concentration were found
on pebble substratum where the current velocity was moderate. These results have also shown that the classical methods used
to day for investigations were inadequate for most Mediterranean rivers.
It was really difficult to estimate the water quality from classical index created for use in regular large plain rivers. 相似文献
946.
Sm/Nd isotopic age determination showed that Xiongshan dike swarm was at 585.7 Ma ± 30 Ma. The trace element geochemistry
and Sr/Nd/Pb isotope gemhemistry studies indicate that the dike swarm was products of back-arc basin spreading ridge and the
magma originated from the depleted mantle region which was metasomatized by LILE-rich liquids/melts derived from subduction
slab.
Project supported by the National Natural Science Foundation of China. 相似文献
947.
K. Holub 《Pure and Applied Geophysics》1997,150(3-4):435-450
—Mining-induced seismicity associated with longwall face operations in the Ostrava- Karviná coal mines, Czech Republic, has
been investigated in order to establish the conditions leading to a focal zone generation. The study, based on macroseismic
and instrumental observations, proved that seismicity is influenced by natural as well as mining conditions. The first group
includes the influence of faults, washouts and red beds, while the second one is represented by shaft and/or crosscut safety
pillars and various types of remnant pillars. All the cases discussed show that many focal zones are generated in overstressed
strata as a consequence of interaction of natural conditions and/or old workings with the active coal face.
Received June 18, 1996, accepted March 10, 1997 相似文献
948.
By means of barotropic model, the characteristic and initial value problems are investigated to reveal the local two-dimensional
barotropic instability of the nonuniform current to the dynamic mechanism of the formation of the Yangtze-Huaihe River severe
storm in July 1991. Analytical theory and numerical experiment show that (i) the unstable developing modes are chiefly the
two periods of about 44 d and 10 d, which are fundamentally consistent with that of the precipitation change of the Yangtze-Huaihe
River. (ii) The growth rate of the local perturbation is dominated by the meridional wave numbern = 1–5 and zonal wave numberk = 1–12, i.e. the severe storm over the Yangtze-Huaihe River results from the interaction of the systems at different latitudes
and waves of different scales, (iii) The perturbation over the Yangtze-Huaihe River possesses the property of local intensification,
which slowly migrates westward over the lower and middle reaches of the Yangtze-Huaihe River. (iv) The growth rate of the
instability, especially the propagation velocity of the perturbation, is sensitive to the external parameters ū and α.
Project supported by the National Natural Science Foundation of China. 相似文献
949.
Song-Yan Song Xue-Song Zhou Chun-Yong Wang Xian-Kang Zhang Jian-Li Song Yi Gong 《地震学报(英文版)》1997,10(1):15-25
On the basis of S wave information from Tai’an-Xinzhou DSS profile and with reference to the results from P-wave interpretation,
the 2-D structures, including S-wave velocity V
s, ratio γ between V
p and V
s; and Poisson’ s ratio σ, are calculated; the structural configuration of the profile is presented and the relevant inferences are drawn from the
above results. Upwarping mantle districts (V
s≈4.30 km/s) and sloping mantle districts (V
s≈4.50 km/s) of the profile with velocity difference about −4% at the top of upper mantle are divided according to the differences
of V
s, γ and σ in different media and structures, also with reference to the information of their neighbouring regions; the existence of
Niujiaqiao-Dongwang high-angle ultra-crustal fault zone is reaffirmed; the properties of low and high velocity blocks (zones)
including the crust-mantle transitionalzone and the boudary indicators of North China rift valley are discussed. A comprehensive
study is conducted on the relation of the interpretation results with earthquakes. It is concluded that the mantle upwarps,
thermal material upwells through the high-angle fault, the primary hypocenter was located at the crust-mantle juncture 30.0∼33.0
km deep, and additional stress excited the M
S=6.8 and M
S=7.2 earthquakes at specific locations around 9.0 km below Niujiaqiao-Dongwang, the earthquakes took place around the high-angle
ultra-crustal fault and centered in the brittle media and rock strata with low γ and low σ values.
This subject is part of the 85-907-02 key project during the “8th Five-Year Plan” from the State Science and Technology Commission. 相似文献
950.
Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning 总被引:1,自引:0,他引:1
Shufeng Yang Hanlin Chen Jishuang Jiang Guoqiang Zhu Hongshen Xie Wei Hou Yueming Zhang Huigang Xu 《中国科学D辑(英文版)》1997,40(5):470-476
The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure
and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity
change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed
during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth
of “softening”, Vp after “softening” and the percentage of Vp’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km
approximately and Vp after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately
and Vp after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening”
of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting,
these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting
of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related
to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type
granitoid. 相似文献