全文获取类型
收费全文 | 50384篇 |
免费 | 8600篇 |
国内免费 | 12579篇 |
专业分类
测绘学 | 4178篇 |
大气科学 | 5380篇 |
地球物理 | 10004篇 |
地质学 | 32820篇 |
海洋学 | 5593篇 |
天文学 | 2174篇 |
综合类 | 3420篇 |
自然地理 | 7994篇 |
出版年
2024年 | 290篇 |
2023年 | 756篇 |
2022年 | 1507篇 |
2021年 | 1691篇 |
2020年 | 1787篇 |
2019年 | 2031篇 |
2018年 | 1661篇 |
2017年 | 1897篇 |
2016年 | 2079篇 |
2015年 | 2223篇 |
2014年 | 2717篇 |
2013年 | 2689篇 |
2012年 | 3007篇 |
2011年 | 3153篇 |
2010年 | 2720篇 |
2009年 | 3260篇 |
2008年 | 3228篇 |
2007年 | 3550篇 |
2006年 | 3463篇 |
2005年 | 3057篇 |
2004年 | 2862篇 |
2003年 | 2734篇 |
2002年 | 2449篇 |
2001年 | 2139篇 |
2000年 | 2016篇 |
1999年 | 1849篇 |
1998年 | 1589篇 |
1997年 | 1475篇 |
1996年 | 1303篇 |
1995年 | 1126篇 |
1994年 | 1143篇 |
1993年 | 988篇 |
1992年 | 764篇 |
1991年 | 547篇 |
1990年 | 481篇 |
1989年 | 378篇 |
1988年 | 290篇 |
1987年 | 194篇 |
1986年 | 125篇 |
1985年 | 81篇 |
1984年 | 35篇 |
1983年 | 30篇 |
1982年 | 31篇 |
1981年 | 22篇 |
1980年 | 23篇 |
1979年 | 31篇 |
1978年 | 35篇 |
1977年 | 24篇 |
1975年 | 4篇 |
1954年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Based on the δ13C and δ18O fluctuation of lacustrine carbonate, CaCO3 content and sporo-pollen data, a palaeoclimatic history of Bosten Lake during the Holocene has been outlined, several stages
of climatic changes are divided, and the following result es are obtained: (1) Palaeoclimatic changes revealed by carbonate
isotope around Bosten Lake are basically identical with that revealed by other geological records in Xinjiang. Environmental
changes presented apparent Westlies Style model: during cold period, relative humidity increased, δ18O, δ13C and CaCO3 appeared low; but in warm periods, the dry regime aggravated. (2) The temperature reflected by δ18O exist evident features being increase in the late period during the Holocene. Together with the δ13C, pollen and CaCO3 analyses, several cold and warm phases which are of broad regional significance can be identified. The warm peaks occurred
at about 11.0 ka B.P., 9.4 ka B.P., 7.5 ka B.P., 5.0 ka B.P., 3.0 ka B.P. and 2.0 ka B.P.; the cold peaks at 11.5 ka B.P.,
10.5 ka B.P., 8.8 ka B.P., 5.5 ka B.P., 3.3 ka B.P., 2.2 ka B.P. and 1.5 ka B.P.. (3) Several climatic events with the nature
of “abrupt climatic changes” are revealed in the periods of 11.0 ka B.P. −10.5 ka B.P., 9.4 ka B.P. −8.8 ka B.P., 5.5 ka B.P.
−5.0 ka B.P. and 2.0 ka B.P. −1.5 ka B.P.. (4) The results show that carbonate isotopic record of lacustrine sediment in arid
area is very sensitive to climatic changes, and may be play a very important role in understanding the features and mechanism
of palaeoclimatic changes. 相似文献
32.
33.
韩崇德 《地球科学与环境学报》1992,(4)
洛坝铅锌矿床位于黄诸关韧脆性变形带所波及的范围内,断裂、褶皱、劈理、节理等形态构造类型均很发育,经对小型构造的统计及应力场分析证明,矿区变形主要是在海西—印支期长期存在的南北向古应力场持续作用下形成的。 相似文献
34.
T. H. BELL S. E. JOHNSON B. DAVIS A. FORDE N. HAYWARD C. WILKINS 《Journal of Metamorphic Geology》1992,10(3):295-307
Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens. 相似文献
35.
36.
讨论了应用曲面拟合技术和利用离散的重力观测点的重力变化对特定研究区的重力场变化进行数值模拟以获取该区重力变化空间梯度场图像的具体方法;并应用该方法获得了2004年3月福建安溪3.6级地震前的重力变化空间梯度场图像,发现空间梯度场图像能清晰地反映出地震前重力场群体性变化的差异性;利用此方法对2005年6月~2006年3月间台湾海峡西岸重力场变化进行数值模拟,获得其空间梯度场图像。 相似文献
37.
38.
This paper deals with the formation processes and the palaeoenvironmental significance of relict slope deposits located on the uppermost part of the north Portugal mountains. For this purpose, seven key sites representative of the different lithofacies have been selected and analysed in detail. The data show that three main dynamic processes are responsible for the emplacement of regional fossil slope deposits: runoff, debris flows and dry grain flows. The ubiquity of these processes and the lack of frost‐related features or landforms do not support the existence of severe Pleistocene climates in this part of the lberian Peninsula as postulated by previous work. Pedological data gathered at one of the study sites show that a subalpine environment was probably present at 700–800 m altitude between 29 and 14 kyr. Using data from the Pyrenees Mountains, a 6.5 to 12°C depression in mean annual temperature has been tentatively postulated for this Pleniglacial period. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
39.
40.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra. 相似文献