全文获取类型
收费全文 | 39932篇 |
免费 | 785篇 |
国内免费 | 256篇 |
专业分类
测绘学 | 776篇 |
大气科学 | 2675篇 |
地球物理 | 7879篇 |
地质学 | 14474篇 |
海洋学 | 3661篇 |
天文学 | 8919篇 |
综合类 | 103篇 |
自然地理 | 2486篇 |
出版年
2022年 | 261篇 |
2021年 | 456篇 |
2020年 | 515篇 |
2019年 | 595篇 |
2018年 | 1038篇 |
2017年 | 1031篇 |
2016年 | 1099篇 |
2015年 | 616篇 |
2014年 | 1067篇 |
2013年 | 1932篇 |
2012年 | 1240篇 |
2011年 | 1701篇 |
2010年 | 1493篇 |
2009年 | 1856篇 |
2008年 | 1686篇 |
2007年 | 1747篇 |
2006年 | 1604篇 |
2005年 | 1097篇 |
2004年 | 1109篇 |
2003年 | 1139篇 |
2002年 | 1031篇 |
2001年 | 888篇 |
2000年 | 822篇 |
1999年 | 744篇 |
1998年 | 732篇 |
1997年 | 745篇 |
1996年 | 608篇 |
1995年 | 581篇 |
1994年 | 515篇 |
1993年 | 467篇 |
1992年 | 422篇 |
1991年 | 440篇 |
1990年 | 447篇 |
1989年 | 409篇 |
1988年 | 385篇 |
1987年 | 418篇 |
1986年 | 430篇 |
1985年 | 521篇 |
1984年 | 572篇 |
1983年 | 557篇 |
1982年 | 509篇 |
1981年 | 470篇 |
1980年 | 446篇 |
1979年 | 421篇 |
1978年 | 385篇 |
1977年 | 393篇 |
1976年 | 355篇 |
1975年 | 364篇 |
1974年 | 345篇 |
1973年 | 381篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
871.
V. V. Arkad’ev A. A. Fedorova Yu. N. Savel’eva E. M. Tesakova 《Stratigraphy and Geological Correlation》2006,14(3):302-330
The Dvuyakornaya Formation section in the eastern Crimea is described and subdivided into biostratigraphic units based on ammonites, foraminifers, and ostracodes. The lower part of the formation contains first discovered ammonites of the upper Kimmeridgian (Lingulaticears cf. procurvum (Ziegler), Pseudowaagenia gemmellariana Olóriz, Euvirgalithacoceras cf. tantalus (Herbich), Subplanites sp.) and Tithonian (?(Lingulaticeras efimovi (Rogov), Phylloceras consaguineum Gemmellaro, Oloriziceras cf. schneidi Tavera, and Paraulacosphinctes cf. transitorius (Oppel)). Based on the assemblage of characteristic ammonite species, the upper part of the formation is attributed to the Berriasian Jacobi Zone. Five biostratigraphic units (zones and beds with fauna) distinguished based on foraminifers are the Epistomina ventriosa-Melathrokerion eospirialis Beds and Anchispirocyclina lusitanica-Melathrokerion spirialis Zone in the upper Kimmeridgian-Tithonian, the Protopeneroplis ultragranulatus-Siphoninella antiqua, Frondicularia cuspidiata-Saracenaria inflanta zones, and Textularia crimica Beds in the Berriasian. The Cyrherelloidea tortuosa-Palaeocytheridea grossi Beds of the Upper Jurassic and Raymoorea peculiaris-Eucytherura ardescae-Protocythere revili Beds of the Berriasian are defined based on ostracodes. A new biostratigraphic scale is proposed for the upper Kimmeridgian-Berriasian of the eastern Crimea. The Dvyyakornaya Formation sediments are considered as deepwater facies accumulated on the continental slope. 相似文献
872.
873.
874.
875.
Coral reefs worldwide are under stress from a variety of anthropogenic activities that can alter or inhibit recovery from
catastrophic physical disturbances such as hurricanes. On coral reefs off southeast Florida, land-based nutrient pollution
contributed to a successful invasion ofCaulerpa brachypus fornaparvifolia that dominated (up to 90% cover) reefs between January 2003 and August 2004. In September 2004, physical effects from Hurricanes
Frances and Jeanne removed virtually all of theC. brachypus from the affected reefs. In July 2005, small patches ofC. brachypus began to re-emerge and the area was affected again by Hurricane Wilma in October 2005. Although these hurricanes provided
temporary relief from theC. brachypus invasion, the future of these reefs is uncertain because of competition with other opportunistic macroalgae and biota that
may respond to the combination of newly created space and continued nutrient stress. 相似文献
876.
An ephemeral estuarine turbidity maximum (ETM) occurs at high water in the macrotidal Taf estuary (SW Wales, United Kingdom).
A new mechanism of ETM formation, due to resuspension and advection of material by flood tidal currents, is observed that
differs from classical mechanisms of gravitational circulation and tidal pumping. The flood tide advances across intertidal
sand flats in the main body of the estuary, progressively entraining material from the rippled sands. Resuspension creates,
a turbid front that has suspended sediment concentrations (SSC) of about 4,000 mg I−1 by the time it reaches its landward limit which is also the landward limit of salt penetration. This turbid body constitutes
the ETM. Deposition occurs at high slack water but the ETM retains SSC values up to 800 mg I−1, 1–2 orders of magnitude greater than ambient SSC values in the river and estuarine waters on either side. The ETM retreats
down the estuary during the ebb; some material is deposited thinly across emergent intertidal flats and some is flushed out
of the estuary. A new ETM is generated by the next flood tide. Both location and SSC of the ETM scale on Q/R3 where Q is tidal range and R is river discharge. The greatest expression of the ETM occurs when a spring tide coincides with
low river discharge. It does not form during high river discharge conditions and is poorly developed on neap tides. Particles
in the ETM have effective densities (120–160 kg m−3) that are 3–4 times less than those in the main part of the estuary at high water. High chlorophyll concentrations in the
ETM suggest that flocs probably originate from biological production in the estuary, including production on the intertidal
sand flats. 相似文献
877.
878.
The effects of advection, dispersion, and biological processes on nitrogen and phytoplankton dynamics after a storm event
in December 2002 are investigated in an estuary located on the northern New South Wales coast, Australia. Salinity observations
for 16 d after the storm are used to estimate hydrodynamic transports for a one-dimensional box model. A biological model
with nitrogen limited phytoplankton growth, mussel grazing, and a phytoplankton mortality term is forced by the calculated
transports. The model captured important aspects of the temporal and spatial dynamics of the bloom. A quantitative analysis
of hydrodynamic and biological processes shows that increased phytoplankton biomass due to elevated nitrogen loads after the
storm was not primarily regulated by advection or dispersion in spite of an increase in river flow from <1 to 928×103 m3 d−1. Of the dissolved nitrogen that entered the surface layer of the estuary in the 16 d following the storm event, the model
estimated that 28% was lost through exchange with the ocean or bottom layers, while 15% was removed by the grazing of just
one mussel species,Xenostrobus securis, on phytoplankton, and 50% was lost through other biological phytoplankton loss processes.X. securis grazing remained an important loss process even when the estimated biological parameters in the model were varied by factors
of ± 2. The intertidal mangrove pneumatophore habitat ofX. securis allows filtering of the upper water column from the lateral boundaries when the water column is vertically stratified, exerting
top-down control on phytoplankton biomass. 相似文献
879.
The feasibility of using the more sophisticated weighted least-squares (WLS) model, as opposed to the traditional ordinary least-squares (OLS), in linear regressions of BHT data to estimate the static formation temperatures (SFT) was investigated. The most commonly used analytical methods (line-source; spherical and radial heat flow; and cylindrical heat source) were applied. Error propagation equations were derived to calculate errors in the time function of each method. These errors were combined with the BHT measurement errors to compute weighting factors for applying the WLS. Intercept uncertainties were estimated for all regressions using sets of synthetic and actual borehole logs taken from geothermal and oil applications. SFT computed with the spherical and radial heat flow method were generally greater than those from the other two methods. 相似文献
880.
J.D. Martín-Martín J. Tritlla E. Cardellach D. Gmez-Gras 《Journal of Geochemical Exploration》2006,89(1-3):267
Fluid inclusions and clay mineralogy of the Permo-Triassic rocks from the Espina and Espadà Ranges (SE Iberian Chain, Spain) have been investigated to establish their relationship with hydrothermal fluid circulation during the Alpine Orogeny. Primary fluid inclusions in quartz-filled tension gashes in Permo-Triassic sandstones reveal maximum temperatures around 230 °C and very constant salinities of 8.5% wt. eq. NaCl. Secondary fluid inclusions found in quartz from the Santonian Ba–Cu–Hg deposits show similar compositional and thermodynamic characteristics, denoting an Alpine recrystallization. Clay mineral composition of Permo-Triassic mudrocks is characterized by pyrophyillite, indicating low-grade metamorphic conditions. Field observations and experimental data suggest that the crystallization of quartz in tension gashes, the formation of secondary fluid inclusions and the development of the metamorphism are contemporaneous and related to fluid circulation during the Alpine compression. Fluid flow took place along the Hercynian fault system that was reactivated during the Mesozoic rift stage and inverted during the Alpine deformation. 相似文献