全文获取类型
收费全文 | 84569篇 |
免费 | 1075篇 |
国内免费 | 595篇 |
专业分类
测绘学 | 2230篇 |
大气科学 | 6087篇 |
地球物理 | 16526篇 |
地质学 | 28805篇 |
海洋学 | 7239篇 |
天文学 | 20246篇 |
综合类 | 181篇 |
自然地理 | 4925篇 |
出版年
2021年 | 638篇 |
2020年 | 719篇 |
2019年 | 737篇 |
2018年 | 1745篇 |
2017年 | 1623篇 |
2016年 | 2029篇 |
2015年 | 1209篇 |
2014年 | 2099篇 |
2013年 | 4262篇 |
2012年 | 2178篇 |
2011年 | 3011篇 |
2010年 | 2710篇 |
2009年 | 3675篇 |
2008年 | 3220篇 |
2007年 | 3210篇 |
2006年 | 3016篇 |
2005年 | 2499篇 |
2004年 | 2477篇 |
2003年 | 2290篇 |
2002年 | 2184篇 |
2001年 | 1983篇 |
2000年 | 1884篇 |
1999年 | 1733篇 |
1998年 | 1681篇 |
1997年 | 1657篇 |
1996年 | 1399篇 |
1995年 | 1373篇 |
1994年 | 1283篇 |
1993年 | 1153篇 |
1992年 | 1104篇 |
1991年 | 1078篇 |
1990年 | 1214篇 |
1989年 | 1086篇 |
1988年 | 1015篇 |
1987年 | 1193篇 |
1986年 | 1022篇 |
1985年 | 1320篇 |
1984年 | 1485篇 |
1983年 | 1421篇 |
1982年 | 1318篇 |
1981年 | 1285篇 |
1980年 | 1135篇 |
1979年 | 1070篇 |
1978年 | 1066篇 |
1977年 | 982篇 |
1976年 | 927篇 |
1975年 | 860篇 |
1974年 | 911篇 |
1973年 | 927篇 |
1972年 | 575篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Radiolarians from the lower part of the Karai Formation (upper Albian-middle Cenomanian) are studied in detail for the first time. Among over 50 radiolarian species identified in the formation, there are Acaeniotyle amplissima (Foreman), Savaryella novalensis (Squinabol), S. quadra (Foreman), Vitorfus campbelli Pessagno, Archaeodictyomitra montisserei (Squinabol), Holocryptocanium barbui Dumitrica, Pseudoeucyrtis sp. cf. Ps. spinosa (Squinabol), Stichomitra communis Squinabol, Tubilustrionella transmontanum (O’Dogherty), and others. The discovered radiolarians are divided into the Halesium triacanthum-Orbiculiforma nevadaenis (late Albian-early Cenomanian), Crucella latum-Cryptamphorella micropora (late Albian?-early Cenomanian), and Becus sp. B-Godia concava (terminal Albian-middle Cenomanian) assemblages. In general, the Albian-Cenomanian radiolarians of South India are comparatively less diverse than the concurrent assemblages of the Mediterranean region and California. In taxonomic composition and morphological peculiarities, they are comparable with the Aptian-Albian radiolarians of Western Australia (Ellis, 1993). Consequently it can be postulated that sea basins of South India were situated during the Albian-Cenomanian in the temperate latitudes of the Southern Hemisphere. 相似文献
992.
N. V. Chukanov R. K. Rastsvetaeva S. M. Aksenov I. V. Pekov D. I. Belakovskiy G. Blass G. Möhn 《Geology of Ore Deposits》2013,55(8):663-668
A new mineral, lahnsteinite, has been found in the dump of the Friedrichssegen Mine, Bad Ems district, Rhineland-Palatinate (Rheinland-Pfalz), Germany. Lahnsteinite, occurring as colorless tabular crystals in the cavities of goethite, is associated with pyromorphite, hydrozincite, quartz, and native copper. The Mohs’ hardness is 1.5; the cleavage is perfect parallel to (001). D calc = 2.995 g/cm3, D meas = 2.98(2) g/cm3. The IR spectrum is given. The new mineral is optically biaxial, negative, α = 1.568(2), β = 1.612(2), γ = 1.613(2), 2V meas = 18(3)°, 2V calc = 17°. The chemical composition (wt %, electron microprobe data; H2O was determined by gas chromatography of ignition products) is as follows: 3.87 FeO, 1.68 CuO, 57.85 ZnO, 15.83 SO3, 22.3 H2O, total is 101.53. The empirical formula is (Zn3.3Fe0.27Cu0.11)Σ3.91(S0.98O4)(OH)5 · 3H2.10O. The crystal structure has been studied on a single crystal. Lahnsteinite is triclinic, space group P1, a = 8.3125(6), b = 14.545(1), c = 18.504(2) Å, α = 89.71(1), β = 90.05(1), γ = 90.13(1)°, V = 2237.2(3) Å3, Z = 8. The strong reflections in the X-ray powder diffraction pattern [d, Å (I, %)] are: 9.30 (100), 4.175 (18), 3.476 (19), 3.290 (19), 2.723 (57), 2.624 (36), 2.503 (35), 1.574 (23). The mineral has been named after its type locality near the town of Lahnstein. The type specimen of lahnsteinite is deposited in the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, registration number 4252/1. 相似文献
993.
994.
We present JHKLM photometry of the carbon stars ST And and T Lyn acquired in 2000–2010. Along with brightness variations due to pulsations,
changes on timescales of 2000–3000 days are also observed. Our combined light curves can be satisfactorily represented with
light elements derived from visual observations, but the maxima are delayed relative to the calculated times. A color-index
analysis demonstrates that the dust shell of ST And is fairly weak, and is manifest only episodically, while the presence
of hot dust was always detected for T Lyn. These results confirm models of spherically symmetric stellar dust shells based
on mean-flux data, supplemented with observations in the intermediate IR from the IRAS and AKARI satellites. The visual optical
depth of the relatively cool dust shell of ST And assuming a dust temperature at the inner edge of T
1 = 510 K is very low: τ
V = 0.047. The dust shell of T Lyn is considerably hotter (T
1 = 940 K), with τ
V = 0.95. We estimate the mass-loss rate to be 1.8 × 10−7
M
⊙/year for ST And and 3.7 × 10−7
M
⊙/year for T Lyn. 相似文献
995.
Acta Geotechnica - The paper describes the formulation and simulative potential of a constitutive model for monotonic and cyclic shearing of sands. It is a SANISAND-type model that does not... 相似文献
996.
Acta Geotechnica - In the HADES underground research laboratory in Belgium, a large-scale PRACLAY Heater test and a small-scale ATLAS Heater test are performed to examine the... 相似文献
997.
998.
Yu. N. Zanin G. M. Pisareva A. G. Zamirailova V. G. Eder 《Lithology and Mineral Resources》2009,44(3):267-269
Weathering of pyrite in the core recovered from black shales of the Bazhenovo Formation (Upper Jurassic-Lower Cretaceous) in the West Siberian marine basin promoted the successive formation of melanterite (FeSO4 · 7H2O) and szomolnokite (FeSO4 · H2O). Szomolnokite was detected in West Siberia for the first time. 相似文献
999.
P. A. Fokin V. R. Demidova V. M. Yatsenko P. V. Stavinskii O. V. Lisunova 《Moscow University Geology Bulletin》2008,63(5):304-310
Sedimentologic analysis of cores from wells sunk in the Vankor petroleum field allowed refinement of the accumulation conditions producing the sandy strata of the Nizhnyaya Kheta River (Nizhnekhetsky) Formation accumulated in the coastal marine zone and of the Yakovlevo (Yakovlevsky) Formation accumulated under alluvial-deltaic conditions. Petrographic examination of the sandstones added information on the sources, transport, and accumulation conditions of the terrigenous material in the northeastern marginal part of the West Siberian sedimentation basin. 相似文献
1000.
The Ediacaran Period takes its name from the fossils of the Ediacara biota, which represent the first appearance of large and diverse assemblages of organisms in the fossil record. Although the global record of these distinctive body fossils is now well known, a previously unrecognized megascopic organic record of textured organic surfaces (TOS) occurs in the Ediacara biota. However, TOS is also a feature over a wider range of paleoenvironmental settings, where body fossils are unknown, in Ediacaran siliciclastic successions that have been studied in Australia, Namibia and western North America.Paleoecological analysis of successive bedding planes of strata from the late Ediacaran Rawnsley Quartzite in the Flinders Ranges of South Australia, reveals that TOS represent the most common organic features in bedding-surface assemblages of the Ediacara biota. The TOS consist of preserved, patterned assemblages of textured organic mats, fibers and simple tubular body fossils. Complex Ediacara body fossils while striking for their distinctive body plans, and dominating some of the beds, are relatively minor components of combined overall surface area. Many elements of TOS have previously been miss-diagnosed as trace fossils, which are in practice limited to two or at most three morphotypes that indicate the presence of Bilateria. Although TOS represent a simpler grade of organismic construction than discrete and more complex Ediacara body fossils, they were preserved in a similar manner. Marked variability in all components of the biota between successive surfaces suggests that Ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime. 相似文献