全文获取类型
收费全文 | 41714篇 |
免费 | 735篇 |
国内免费 | 355篇 |
专业分类
测绘学 | 1291篇 |
大气科学 | 3059篇 |
地球物理 | 8509篇 |
地质学 | 13807篇 |
海洋学 | 3610篇 |
天文学 | 10246篇 |
综合类 | 114篇 |
自然地理 | 2168篇 |
出版年
2021年 | 331篇 |
2020年 | 363篇 |
2019年 | 450篇 |
2018年 | 973篇 |
2017年 | 899篇 |
2016年 | 1172篇 |
2015年 | 664篇 |
2014年 | 1113篇 |
2013年 | 2015篇 |
2012年 | 1219篇 |
2011年 | 1618篇 |
2010年 | 1475篇 |
2009年 | 2028篇 |
2008年 | 1782篇 |
2007年 | 1803篇 |
2006年 | 1695篇 |
2005年 | 1271篇 |
2004年 | 1299篇 |
2003年 | 1187篇 |
2002年 | 1227篇 |
2001年 | 1090篇 |
2000年 | 1018篇 |
1999年 | 893篇 |
1998年 | 884篇 |
1997年 | 889篇 |
1996年 | 712篇 |
1995年 | 666篇 |
1994年 | 626篇 |
1993年 | 543篇 |
1992年 | 475篇 |
1991年 | 487篇 |
1990年 | 467篇 |
1989年 | 487篇 |
1988年 | 434篇 |
1987年 | 503篇 |
1986年 | 456篇 |
1985年 | 535篇 |
1984年 | 658篇 |
1983年 | 569篇 |
1982年 | 557篇 |
1981年 | 505篇 |
1980年 | 440篇 |
1979年 | 434篇 |
1978年 | 445篇 |
1977年 | 382篇 |
1976年 | 341篇 |
1975年 | 351篇 |
1974年 | 326篇 |
1973年 | 362篇 |
1972年 | 262篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
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
993.
Darren F. Mark John Parnell Simon P. Kelley Sarah C. Sherlock 《Journal of Geochemical Exploration》2006,89(1-3):259
Integration of fluid inclusion analysis with high spatial resolution Ar–Ar dating of K-feldspar cements has been used to resolve and reconstruct palaeo-fluid flow. Fluid inclusion analysis allows discrimination of distinct cement phases, thereby identifying discrete episodes of fluid flow. Ar–Ar dating of the same cements via high spatial resolution laserprobe establishes absolute age constraints on the framework previously constructed. Integration of these two datasets yields temperature–composition–time data. 相似文献
994.
E. Eseme P.A. Abanda C.M. Agyingi J. Foba-Tendo R.E. Hannigan 《Journal of Geochemical Exploration》2006,91(1-3):41-55
Salts produced using brines of the Mamfe Basin were analysed by XRD for their mineral composition and ICP-MS for minor element composition. Halite (NaCl) and dolomite (CaMg (CO3)2) constitute the major minerals with minor impurities from Mo and Cd in the chlorides and Sc and Cu in the carbonates. The mineral composition is evidence of dissolution of evaporites with parent brine of marine origin. Other elements analysed are suggested to be adsorbed to these salts and result from water–rock interaction. The elements partitioned based on their correlation to other elements are suggested to derive from sulphates including barite for Ba, sulphides for Pb, Zn, silicates for Zr, Mn and oxides for V, Cr. The electrical conductance of the brines is related to the salt yield by the equation; M = 9 × 10− 4E− 3.27, and it can be used to estimate salt yield throughout the year. Over 1200 tons of salt consisting dominantly of grade I halite are lost annually as brines across the basin. Purification is required for some minor elements including Ba, Pb, Hg and Cd for use as a condiment. A genetic relation between the parent brine, sulphide minerals and organic matter-rich sediments is proposed. 相似文献
995.
Stable isotope evidence for the atmospheric origin of CO2 involved in carbonation of MSWI bottom ash
Stable isotopes were used to constrain the origin of CO2 involved in the ageing process of municipal solid waste incineration (MSWI) bottom ash under open-air conditions. The δ13C and δ18O values of CaCO3 occurring in MSWI bottom ash samples of variable age and the δ13C of the residual organic matter content were measured, and laboratory assessments made of the isotopic fractionation accompanying CaCO3 neo-formation during accelerated carbonation experiments of bottom ash or pure lime with atmospheric or industrial CO2. The results indicate that stable isotopic compositions exhibited by fresh and aged bottom ash samples reflect non-equilibrium processes resembling those described in the carbonation of concrete and mortar. They also lead to conclusions on the prevalent involvement of atmospheric CO2 in the open-air carbonation of MSWI bottom ash. 相似文献
996.
E.P. Oliveira S.F. Toteu M.N.C. Araújo M.J. Carvalho R.S. Nascimento J.F. Bueno N. McNaughton G. Basilici 《Journal of African Earth Sciences》2006,44(4-5):470
The Yaoundé belt (Cameroon) and the Sergipano belt (NE Brazil) belonged to a major and continuous Neoproterozoic orogen at the northern margin of the ancient Congo-São Francisco craton. The Yaoundé belt comprises schists, quartzites, gneisses and migmatitic gneisses grouped into three domains; the low-grade Mbalmayo Group in south and the medium- to high-grade Yaoundé and Bafia Group in north. The Sergipano belt is divided into six domains, the three southernmost of which are mostly made up of clastic and chemical metasedimentary rocks whereas the others are more diverse with a migmatite–gneiss complex, and two metavolcanicplutonic complexes. In general, the two belts show structural vergence and decrease of metamorphic grade towards the craton; three main deformation phases are recognized in the Sergipano belt in contrast with two described in the Yaoundé belt. The minimum age of Pan-African-Brasiliano collision in the Sergipano belt is constrained at 628 ± 12 Ma on syn-collision granites, whereas in the Yaoundé belt collision took place between 620 and 610 Ma, i.e. the age of granulite facies metamorphism. Sm–Nd isotope geochemistry and U–Pb age dating indicate that most clastic metasedimentary rocks in both belts were derived from sources to the north and, to a lesser degree, from the cratons to the south. 相似文献
997.
998.
999.
1000.
Christopher P. Onuf 《Estuaries and Coasts》2006,29(3):511-518
For more than a decade, inexpensive electronic instruments have made continuous underwater light monitoring an integral part
of many seagrass studies. Although biofouling, if not controlled, compromises the utility of the record. A year-long assessment
of the time course of sensor fouling, in the Laguna Madre of Texas established that light transmitted through the fouling
layer after 2 wk of exposure exceeded 90% except for a 6–8 wk period in May and June. On that basis, a 2-wk interval was chosen
for routine servicing. Subsequent monitoring proved this choice to be grossly in error. The period of sub-90% transmittance
after 2 wk extended to 4–6 mo annually over the next 3 yr. Fouling was strongly correlated with temperature, ambient light,
and year. Since an algal bloom of 7-yr duration finally waned during this study, increased ambient light seemed most likely
to explain increased fouling later in the study. The explanatory value of light was less than temperature or year in multiple
regression, requiring some other explanation of the date effect than change in ambient light. Allelopathic and suspension-feeding
depressant effects of the brown tide are offered as the most likely cause of unusually low fouling in the first year. Biofouling
was so unpredictable and rapid in this study that at least weekly maintenance would be required to assure reliability of the
light monitoring record. 相似文献