全文获取类型
收费全文 | 29321篇 |
免费 | 391篇 |
国内免费 | 320篇 |
专业分类
测绘学 | 616篇 |
大气科学 | 1817篇 |
地球物理 | 5246篇 |
地质学 | 11265篇 |
海洋学 | 2963篇 |
天文学 | 6859篇 |
综合类 | 68篇 |
自然地理 | 1198篇 |
出版年
2022年 | 297篇 |
2021年 | 455篇 |
2020年 | 509篇 |
2019年 | 556篇 |
2018年 | 1091篇 |
2017年 | 1040篇 |
2016年 | 1146篇 |
2015年 | 545篇 |
2014年 | 1041篇 |
2013年 | 1686篇 |
2012年 | 1152篇 |
2011年 | 1433篇 |
2010年 | 1282篇 |
2009年 | 1557篇 |
2008年 | 1329篇 |
2007年 | 1395篇 |
2006年 | 1301篇 |
2005年 | 755篇 |
2004年 | 705篇 |
2003年 | 659篇 |
2002年 | 687篇 |
2001年 | 619篇 |
2000年 | 568篇 |
1999年 | 461篇 |
1998年 | 479篇 |
1997年 | 453篇 |
1996年 | 391篇 |
1995年 | 350篇 |
1994年 | 378篇 |
1993年 | 294篇 |
1992年 | 297篇 |
1991年 | 286篇 |
1990年 | 322篇 |
1989年 | 220篇 |
1988年 | 225篇 |
1987年 | 268篇 |
1986年 | 209篇 |
1985年 | 314篇 |
1984年 | 276篇 |
1983年 | 258篇 |
1982年 | 275篇 |
1981年 | 203篇 |
1980年 | 243篇 |
1979年 | 195篇 |
1978年 | 211篇 |
1977年 | 165篇 |
1976年 | 163篇 |
1975年 | 172篇 |
1974年 | 167篇 |
1973年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
Doklady Earth Sciences - The data collected in the course of the drifter experiment within the Rim Current zone allowed preliminary estimates of the thermocline response to a changing current... 相似文献
992.
In 2008, during cruise 24 of the R/V Akademik Vavilov, much of our research work was focused on the central segment (Jaseur and Davis seamounts, Dogaressa Bank) of the Vitoria-Trindade seamount chain (west of the Brazil basin) extending along 20.5° S. Work was conducted to survey the upper part of the sedimentary cover and to perform subbottom profiling. The samples dredged on the seamount slopes are represented by volcanites and Fe-Mn crusts. 相似文献
993.
N. S. Zhatnuev 《Doklady Earth Sciences》2010,430(2):176-180
This study attempts to substantiate a model of magma ascent from deep-seated sources driven by the density difference between magmas and wall rocks in a plastic solid medium via hydraulic fracturing (magma-driven fracturing). The difference between magma and wall rock densities causes overpressure development in the head of a magma column. With increasing height of the column or decreasing magma density, the overpressure can build significantly, which is valid for the case of continuous magma conduit from a deepseated source. The depth of mantle chambers, their vertical extent, and magma densities seem to be the key factors in the formation of volcanoes and intracrustal intrusions. Intermittent (or peripheral) magma chambers under volcanoes and crustal-mantle intrusive bodies may be formed at strength barriers, in the zone of elastoplastic transition and at the mantle-crust boundary. 相似文献
994.
Gold ore districts in the Siberian (North Asian) craton and bordering terranes have been studied. Studies showed the long duration of gold concentration processes (Early Cambrian to Late Mesozoic and Cenozoic) and the influence of structural geological, magmatic, and metallogenic factors on the formation of ore districts. The largest Late Mesozoic (J–K) accumulations of gold deposits in southeastern Russia were discovered in the Aldan–Stanovoi Shield and at the northern margin of the Argun superterrane in the Aldan (Yakutia), Balei (Transbaikalia), and Gonzha (Upper Amur area) ore–placer districts.The geological and geophysical positions of these three districts have been compared. All of them are situated in zones of influence of variously trending long-lived deep faults, bordered by large Precambrian uplifts, and spatially (paragenetically) related to local magma chamber domes of Late Mesozoic (J–K) intrusive, subvolcanic, and extrusive–effusive bodies, dikes, and terrigenous pyroclastic blankets. The areas of Jurassic–Cretaceous volcanoplutonic rocks are related to the influence of the East Asian sublithospheric “superplume.”All this confirms the important ore-controlling role of large long-lived deep faults (in the form of global and regional gravity gradient zones) in the distribution of highly productive precious-metal ore–magmatic systems. This suggests that the junctions between gravity gradient zones of different trends and ranks are important to the identification of gold prospects in metallogenic prediction studies and small-scale prospecting. The Archean–Proterozoic age and the great occurrence depth of the tectonic zones suggest that extensive long-lived mobile zones (before the post-Cambrian breakup of the Siberian craton) significantly affected further evolution of the orogenic belts bordering the craton and their metallogeny, including the distribution of precious- metal deposits. 相似文献
995.
I. V. Pekov N. V. Zubkova N. V. Chukanov A. E. Zadov V. G. Grishin D. Yu. Pushcharovsky 《Geology of Ore Deposits》2010,52(7):584-590
A new mineral, yegorovite, has been identified in the late hydrothermal, low-temperature assemblage of the Palitra hyperalkaline pegmatite at Mt. Kedykverpakhk, Lovozero alkaline pluton, Kola Peninsula, Russia. The mineral is intimately associated with revdite and megacyclite, earlier natrosilite, microcline, and villiaumite. Yegorovite occurs as coarse, usually split prismatic (up to 0.05 × 0.15 × 1 mm) or lamellar (up to 0.05 × 0.7 × 0.8 mm) crystals. Polysynthetic twins and parallel intergrowths are typical. Mineral individuals are combined in bunches or chaotic groups (up to 2 mm); radial-lamellar clusters are less frequent. Yegorovite is colorless, transparent with vitreous luster. Cleavage is perfect parallel to (010) and (001). Fracture is splintery; crystals are readily split into acicular fragments. The Mohs hardness is ~2. Density is 1.90(2) g/cm3 (meas) and 1.92 g/cm3 (calc). Yegorovite is biaxial (?), with α = 1.474(2), β = 1.479(2), and γ = 1.482(2), 2V meas > 70°, 2V calc = 75°. The optical orientation is X ∧ a ~ 15°, Y = c, Z = b. The IR spectrum is given. The chemical composition determined using an electron microprobe (H2O determined from total deficiency) is (wt %): 23.28 Na2O, 45.45 SiO2, 31.27 H2Ocalc; the total is 100.00. The empirical formula is Na3.98Si4.01O8.02(OH)3.98 · 7.205H2O. The idealized formula is Na4[Si4O8(OH)4] · 7H2O. Yegorovite is monoclinic, space group P21/c. The unit-cell dimensions are a = 9.874, b= 12.398, c = 14.897 Å, β = 104.68°, V = 1764.3 Å3, Z = 4. The strongest reflections in the X-ray powder pattern (d, Å (I, %)([hkl]) are 7.21(70)[002], 6.21(72)[012, 020], 4.696(44)[022], 4.003(49)[211], 3.734(46)[(bar 2) 13], 3.116(100)[024, 040], 2.463(38)[(bar 4)02, (bar 2)43]. The crystal structure was studied by single-crystal method, R hkl = 0.0745. Yegorovite is a representative of a new structural type. Its structure consists of single chains of Si tetrahedrons [Si4O8(OH)4]∞ and sixfold polyhedrons of two types: [NaO(OH)2(H2O)3] and [NaO(OH)(H2O)4] centered by Na. The mineral was named in memory of Yu. K. Yegorov-Tismenko (1938–2007), outstanding Russian crystallographer and crystallochemist. The type material of yegorovite has been deposited at the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow. 相似文献
996.
Astronomy Letters - We present our photometric observations of the 15 supernovae (SN) discovered in the period 1997–1999; of these, six are type Ia SN, two are peculiar type Ia SN, three are... 相似文献
997.
Gravitationally lensed QSOs (GLQs) at 1≤z≤2 play a key role in understanding the cosmic evolution of the innermost parts of active galaxies (black holes, accretion
disks, coronas and internal jets), as well as the structure of galaxies at intermediate redshifts. With respect to studies
of normal QSOs, GLQ programmes have several advantages. For example, a monitoring of GLQs may lead to unambiguous detections
of intrinsic and extrinsic variations. Both kinds of variations can be used to discuss central engines in distant QSOs, and
mass distributions and compositions of lensing galaxies. In this context, UV data are of particular interest, since they correspond
to emissions from the immediate surroundings of the supermassive black hole. We describe some observation strategies to analyse
optically bright GLQs at z∼1.5, using ISSIS (CfS) on board World Space Observatory-Ultraviolet. 相似文献
998.
A. S. Buslov Yu. D. Kotov V. N. Yurov M. V. Bessonov P. A. Kalmykov E. M. Oreshnikov A. M. Alimov A. V. Tumanov E. A. Zhuchkova 《Solar System Research》2011,45(3):226-230
This paper deals with the organizational structure of ground-based receiving, processing, and dissemination of scientific
information created by the Astrophysics Institute of the Scientific Research Nuclear University, Moscow Engineering Physics
Institute. Hardware structure and software features are described. The principles are given for forming sets of control commands
for scientific equipment (SE) devices, and statistics data are presented on the operation of facility during flight tests
of the spacecraft (SC) in the course of one year. 相似文献
999.
Radio stars are identified optically with bright stars located in the direction of the cluster A3487 (RA(J) = 11h31m58s, DEC(J) = −31°11’34".8) with an accuracy determined by the refraction of radio waves in the interstellar medium in this direction
of the sky. Within an area of 1 sq. degree, 60% of the strong radio sources with P > 0.004 Jy are identified with stars brighter
than 10 m. 相似文献
1000.
Abstract Merrihueite (K,Na)2(Fe, Mg)5Si12O30 (na < 0.5, fe > 0.5, where na = Na/(Na + K), fe = Fe/(Fe + Mg) in atomic ratio) is a rare mineral described only in several chondrules and irregularly-shaped fragments in the Mezö-Madaras L3 chondrite (Dodd et al., 1965; Wood and Holmberg, 1994). Roedderite (Na,K)2(Mg, Fe)5Si12O30 (na > 0.5, fe < 0.5) has been found only in enstatite chondrites and in the reduced, subchondritic silicate inclusions in IAB irons (Fuchs, 1966; Rambaldi et al., 1984; Olsen, 1967). We describe silica-roedderite-bearing clasts in L/LL3.5 ALHA77011 and LL3.7 ALHA77278, a silica-roedderite-bearing chondrule in L3 Mezö-Madaras, and a silica-merrihueite-bearing chondrule in L/LL3.5 ALHA77115. The findings of merrihueite and roedderite in ALHA77011, ALHA77115, ALHA77278 and Mezö-Madaras fill the compositional gap between previously described roedderite in enstatite chondrites and silicate inclusions in IAB irons and merrihueite in Mezö-Madaras, suggesting that there is a complete solid solution of roedderite and merrihueite in meteorites. We infer that the silica- and merrihueite/roedderite-bearing chondrules and clasts experienced a complex formational history including: (a) fractional condensation in the solar nebula that produced Si-rich and Al-poor precursors, (b) melting of fractionated nebular solids resulting in the formation of silica-pyroxene chondrules, (c) in some cases, fragmentation in the nebula or on a parent body, (d) reaction of silica with alkali-rich gas that formed merrihueite/roedderite on a parent body, (e) formation of fayalitic olivine and ferrosilite-rich pyroxene due to reaction of silica with oxidized Fe on a parent body, and (f) minor thermal metamorphism, possibly generated by impacts. 相似文献