全文获取类型
收费全文 | 65700篇 |
免费 | 933篇 |
国内免费 | 602篇 |
专业分类
测绘学 | 1586篇 |
大气科学 | 4547篇 |
地球物理 | 12298篇 |
地质学 | 26529篇 |
海洋学 | 5314篇 |
天文学 | 13437篇 |
综合类 | 255篇 |
自然地理 | 3269篇 |
出版年
2022年 | 304篇 |
2021年 | 483篇 |
2020年 | 557篇 |
2019年 | 649篇 |
2018年 | 3840篇 |
2017年 | 3599篇 |
2016年 | 2716篇 |
2015年 | 830篇 |
2014年 | 1291篇 |
2013年 | 2222篇 |
2012年 | 2399篇 |
2011年 | 4391篇 |
2010年 | 3966篇 |
2009年 | 4505篇 |
2008年 | 3738篇 |
2007年 | 4323篇 |
2006年 | 1879篇 |
2005年 | 1758篇 |
2004年 | 1657篇 |
2003年 | 1776篇 |
2002年 | 1454篇 |
2001年 | 1087篇 |
2000年 | 1023篇 |
1999年 | 883篇 |
1998年 | 863篇 |
1997年 | 862篇 |
1996年 | 726篇 |
1995年 | 696篇 |
1994年 | 592篇 |
1993年 | 535篇 |
1992年 | 480篇 |
1991年 | 505篇 |
1990年 | 508篇 |
1989年 | 469篇 |
1988年 | 422篇 |
1987年 | 488篇 |
1986年 | 476篇 |
1985年 | 563篇 |
1984年 | 606篇 |
1983年 | 605篇 |
1982年 | 563篇 |
1981年 | 525篇 |
1980年 | 499篇 |
1979年 | 454篇 |
1978年 | 400篇 |
1977年 | 430篇 |
1976年 | 393篇 |
1975年 | 387篇 |
1974年 | 367篇 |
1973年 | 403篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
31.
Y.-B. WU S. GAO H.-J. GONG H. XIANG W.-F. JIAO S.-H. YANG Y.-S. LIU H.-L. YUAN 《Journal of Metamorphic Geology》2009,27(6):461-477
U–Pb age, trace element and Hf isotope compositions of zircon were analysed for a metasedimentary rock and two amphibolites from the Kongling terrane in the northern part of the Yangtze Craton. The zircon shows distinct morphological and chemical characteristics. Most zircon in an amphibolite shows oscillatory zoning, high Th/U and 176 Lu/177 Hf ratios, high formation temperature, high trace element contents, clear negative Eu anomaly, as well as HREE-enriched patterns, suggesting that it is igneous. The zircon yields a weighted mean 207 Pb/206 Pb age of 2857 ± 8 Ma, representing the age of the magmatic protolith. The zircon in the other two samples is metamorphic. It has low Th/U ratios, low trace element concentrations, variable HREE contents (33.8 ≥ LuN ≥2213; 14.7 ≤ LuN /SmN ≤ 354) and 176 Lu/177 Hf ratios (0.000030–0.001168). The data indicate that the zircon formed in the presence of garnet and under upper amphibolite facies conditions. The metamorphic zircon yields a weighted mean 207 Pb/206 Pb age of 2010 ± 13 Ma. These results combined with previously obtained Palaeoproterozoic metamorphic ages suggest a c. 2.0 Ga Palaeoproterozoic collisional event in the Yangtze Craton, which may result from the assembly of the supercontinent Columbia. The zircon in two samples yields weighted mean two-stage Hf model ( T DM2 ) ages of 3217 ± 110 and 2943 ± 50 Ma, respectively, indicating that their protoliths were mainly derived from Archean crust. 相似文献
32.
S. ENDO S.WALLIS T. HIRATA R. ANCZKIEWICZ J. PLATT M. THIRLWALL Y. ASAHARA 《Journal of Metamorphic Geology》2009,27(5):371-384
Two distinct age estimates for eclogite-facies metamorphism in the Sanbagawa belt have been proposed: (i) c. 120–110 Ma based on a zircon SHRIMP age for the Western Iratsu unit and (ii) c. 88–89 Ma based on a garnet–omphacite Lu–Hf isochron age from the Seba and Kotsu eclogite units. Despite the contrasting estimates of formation ages, petrological studies suggest the formation conditions of the Western Iratsu unit are indistinguishable from those of the other two units—all ∼20 kbar and 600–650 °C. Studies of the associated geological structures suggest the Seba and Western Iratsu units are parts of a larger semi-continuous eclogite unit. A combination of geochronological and petrological studies for the Western Iratsu eclogite offers a resolution to this discrepancy in age estimates. New Lu–Hf dating for the Western Iratsu eclogite yields an age of 115.9 ± 0.5 Ma that is compatible with the zircon SHRIMP age. However, petrological studies show that there was significant garnet growth in the Western Iratsu eclogite before eclogite facies metamorphism, and the early core growth is associated with a strong concentration of Lu. Pre-eclogite facies garnet (Grt1) includes epidote–amphibolite facies parageneses equilibrated at 550–650 °C and ∼10 kbar, and this is overgrown by prograde eclogite facies garnet (Grt2). The Lu–Hf age of c. 116 Ma is strongly skewed to the isotopic composition of Grt1 and is interpreted to reflect the age of the pre-eclogite phase. The considerable time gap ( c. 27 Myr) between the two Lu–Hf ages suggests they may be related to separate tectonic events or distinct phases in the evolution of the Sanbagawa subduction zone. 相似文献
33.
34.
35.
36.
37.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
39.
Takuya Matsumoto Masahiko Honda Ian McDougall Igor Yatsevich Suzanne Y. O'Reilly 《地学学报》2004,16(1):23-26
Using a Rayleigh distillation fractionation model, we calculate that the maximum isotope fractionation potentially achievable is less than 5% during the early stages of gas release from a sample. Our calculation corrects the erroneous conclusions of Gautheron and Moreira (2003), who re‐interpreted the plume‐like neon isotopic compositions found in metasomatic apatite from a south‐eastern Australian xenolith (Matsumoto et al., 1997) to be the result of Rayleigh‐type isotope fractionation of originally MORB‐type neon during stepheating gas extraction. We stress that the modelling of neon isotopic fractionation by Gautheron and Moreira (2003) is incorrect, and that the finding of a plume‐like neon isotopic composition in the apatite by Matsumoto et al. (1997) remains a quite valid and robust conclusion. 相似文献
40.
Virgil E. Barnes 《Meteoritics & planetary science》1990,25(3):149-159
Abstract— Fifty-odd years of tektite research are reviewed, proceeding from the discovery of the first North American tektites in 1936. This included the early recognition that tektites were terrestrial objects rather than meteorites and that the glassy particles in tektites were fused quartz (lechatelierite). Later, during National Science Foundation-supported research, it was found that some tektites appeared to have formed as puddles of melt, that the content and character of bubbles in lechatelierite can be used as a relative temperature scale, that rayed bubbles in tektites formed from hydrous minerals, that bubbles in tektites formed chiefly from water which was absorbed into the walls of the bubbles leaving vacuums, and that “fingers” in the surficial part of some tektites may have formed by differential volatilization. Some unpublished observations and adventures are briefly reported. 相似文献