全文获取类型
收费全文 | 42090篇 |
免费 | 3489篇 |
国内免费 | 5194篇 |
专业分类
测绘学 | 2423篇 |
大气科学 | 5745篇 |
地球物理 | 9444篇 |
地质学 | 20161篇 |
海洋学 | 3579篇 |
天文学 | 2391篇 |
综合类 | 3702篇 |
自然地理 | 3328篇 |
出版年
2024年 | 103篇 |
2023年 | 368篇 |
2022年 | 856篇 |
2021年 | 999篇 |
2020年 | 798篇 |
2019年 | 858篇 |
2018年 | 5456篇 |
2017年 | 4698篇 |
2016年 | 3419篇 |
2015年 | 1087篇 |
2014年 | 1121篇 |
2013年 | 1166篇 |
2012年 | 1954篇 |
2011年 | 3641篇 |
2010年 | 3041篇 |
2009年 | 3234篇 |
2008年 | 2655篇 |
2007年 | 3128篇 |
2006年 | 722篇 |
2005年 | 831篇 |
2004年 | 846篇 |
2003年 | 903篇 |
2002年 | 757篇 |
2001年 | 540篇 |
2000年 | 669篇 |
1999年 | 924篇 |
1998年 | 787篇 |
1997年 | 765篇 |
1996年 | 733篇 |
1995年 | 651篇 |
1994年 | 575篇 |
1993年 | 496篇 |
1992年 | 410篇 |
1991年 | 288篇 |
1990年 | 231篇 |
1989年 | 190篇 |
1988年 | 180篇 |
1987年 | 102篇 |
1986年 | 110篇 |
1985年 | 68篇 |
1984年 | 58篇 |
1983年 | 57篇 |
1982年 | 55篇 |
1981年 | 61篇 |
1980年 | 66篇 |
1979年 | 36篇 |
1978年 | 14篇 |
1976年 | 12篇 |
1974年 | 9篇 |
1958年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
华南阿伦尼格世几丁虫生物地层与古生物地理 总被引:14,自引:0,他引:14
本文系统介绍了湖北宜昌黄花场及浙江常山黄泥塘剖面Arenig统几丁虫分布发育规律,指出华南地区Arening统的几丁虫自下向上可划分为Conochitinasymmetrica,Eremochitinabaculata,Eremochitinabrevis-Conochitinalangei,Conochitinapirum,Rhabdochitinaturgida等生物带。讨论了华南地区这一时期 相似文献
42.
成都大邑花水湾温泉,是一口开采地下热水的人工钻井。位于成都市以西86km,储热构造位于龙门山前陆冲断带的雾中山背斜的南西倾没端。储热层为中三叠统雷口坡组碳酸盐地层。为溶隙-裂隙合水层。传热层埋藏深度在孔深1800-2400m井段,水温68℃,是一处非常有价值的医疗热矿水水源地。该地下热水的发现,结束了成都市域没有温泉的历史。该温泉的发现与开发,对四川盆地,乃至中国其他大型内陆盆地中深部地热资源的开发利用有借鉴作用。 相似文献
43.
膨胀土判别与分类的灰关联分析法 总被引:13,自引:3,他引:13
基于灰色系统理论,给出一种用于膨胀土判别与分类的新方法—灰关联分析法。实际算例表明,该法具有简单方便、结果客观可靠等优点。 相似文献
44.
高岭石与碱剂作用后反应液中硅铝元素变化规律研究 总被引:1,自引:2,他引:1
本文系统地研究了高岭石与碱剂间的作用对反应后的液相参数进行全面测定,以查清温度,反应时间,碱性驱替剂的种类浓度等因素与液相参数和固相参数的关系。提出高岭石的非一致性溶蚀趋势,并探讨高岭石与碱性驱替剂的作用机理,丰富了化学驱油过程中化学剂与矿物作用方面的基础理论。 相似文献
45.
In this paper,the Gutenberg-Richter model is used to generate seismic events.The events that satisfy the random distribution are also generated.With those events,the natural probability distribution of Load and Unload Response Ratio(LURR),which measures quantitatively the degree of instability of a nonlinear system,is discussed.The study is based on stress energy release,which is chosen as the response of nonlinear system F3.The comparative results from the observation catalogue and generating data are also studied.It is revealed that the natural probability of LURR is mostly stable when the sample number is sufficient.The lower the natural probability of LURR,the more the precursory is information it may contain.The influence of Y3 resulting from the sample number and the magnitude range of events is also discussed. 相似文献
46.
47.
Numerical modeling of 3-D terrain effect on MT field 总被引:1,自引:0,他引:1
Using the boundary element method, the numerical modeling problem of three-dimensional terrain effect on magnetotelluric (MT)
field is solved. This modeling technique can be run on PC in the case of adopting special net division. The result of modeling
test for 2-D terrain by this modeling technique is basically coincident with that by 2-D modeling technique, but there is
a great difference between the results of 3-D and 2-D modeling for 3-D terrain.
Project supported by the National Natural Science Foundation of China. 相似文献
48.
Magnetostratigraphy and palaeoclimate of Red Clay sequences from Chinese Loess Plateau 总被引:5,自引:0,他引:5
Two Red Clay profiles near Xi’an and Xifeng were investigated in an attempt to determine magnetostratigraphic and palaeoclimatic
records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma,
and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic
history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5–2.5 Ma. Stepwise
increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the
Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global
ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences
from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan
Plateau, solar radiation, global ice volume, etc.
Project supported by the National Natural Science Foundation of China and the Foundation of Xi’an Laboratory of Loess and
Quaternary Geology, Chinese Academy of Sciences. 相似文献
49.
Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning 总被引:1,自引:0,他引:1
Shufeng Yang Hanlin Chen Jishuang Jiang Guoqiang Zhu Hongshen Xie Wei Hou Yueming Zhang Huigang Xu 《中国科学D辑(英文版)》1997,40(5):470-476
The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure
and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity
change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed
during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth
of “softening”, Vp after “softening” and the percentage of Vp’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km
approximately and Vp after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately
and Vp after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening”
of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting,
these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting
of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related
to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type
granitoid. 相似文献