全文获取类型
收费全文 | 54111篇 |
免费 | 723篇 |
国内免费 | 568篇 |
专业分类
测绘学 | 1461篇 |
大气科学 | 3850篇 |
地球物理 | 10008篇 |
地质学 | 19410篇 |
海洋学 | 4942篇 |
天文学 | 12939篇 |
综合类 | 190篇 |
自然地理 | 2602篇 |
出版年
2022年 | 368篇 |
2021年 | 634篇 |
2020年 | 664篇 |
2019年 | 726篇 |
2018年 | 1593篇 |
2017年 | 1516篇 |
2016年 | 1885篇 |
2015年 | 1004篇 |
2014年 | 1761篇 |
2013年 | 2906篇 |
2012年 | 1869篇 |
2011年 | 2399篇 |
2010年 | 2083篇 |
2009年 | 2692篇 |
2008年 | 2313篇 |
2007年 | 2364篇 |
2006年 | 2210篇 |
2005年 | 1632篇 |
2004年 | 1658篇 |
2003年 | 1565篇 |
2002年 | 1483篇 |
2001年 | 1308篇 |
2000年 | 1224篇 |
1999年 | 999篇 |
1998年 | 1052篇 |
1997年 | 957篇 |
1996年 | 825篇 |
1995年 | 787篇 |
1994年 | 693篇 |
1993年 | 608篇 |
1992年 | 597篇 |
1991年 | 597篇 |
1990年 | 626篇 |
1989年 | 500篇 |
1988年 | 508篇 |
1987年 | 532篇 |
1986年 | 489篇 |
1985年 | 623篇 |
1984年 | 679篇 |
1983年 | 600篇 |
1982年 | 570篇 |
1981年 | 508篇 |
1980年 | 474篇 |
1979年 | 486篇 |
1978年 | 464篇 |
1977年 | 373篇 |
1976年 | 351篇 |
1975年 | 363篇 |
1974年 | 312篇 |
1973年 | 348篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
321.
Comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges 总被引:1,自引:1,他引:1
Süleyman Adanur Ahmet Can Altuni?ik Alemdar Bayraktar Mehmet Akk?se 《Natural Hazards》2012,64(1):593-614
This paper presents a comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges. Bo?azi?i (The First Bosporus) and Fatih Sultan Mehmet (Second Bosporus) suspension bridges built in Istanbul, Turkey, are selected as numerical examples. Both bridges have almost the same span. While Bo?azi?i Suspension Bridge has inclined hangers, Fatih Sultan Mehmet Suspension Bridge has vertical hangers. Geometric nonlinearity including P-delta effects from self-weight of the bridges is taken into account in the determination of the dynamic behavior of the suspension bridges for near-fault and far-fault ground motions. Near-fault and far-fault strong ground motion records, which have approximately identical peak ground accelerations, of 1999 Chi-Chi, 1999 Kocaeli, and 1979 Imperial Valley earthquakes are selected for the analyses. Displacements and internal forces of the bridges are determined using the finite element method including geometric nonlinearity. The displacements and internal forces obtained from the dynamic analyses of suspension bridges subjected to each fault effect are compared with each other. It is clearly seen that near-fault ground motions are more effective than far-fault ground motion on the displacements and internal forces such as bending moment, shear force and axial forces of the suspension bridges. 相似文献
322.
323.
324.
325.
Picroilmenite samples from five kimberlite pipes of the Yakutian kimberlite province have been studied. Point microprobe analyses of two mutually perpendicular profiles of each sample were carried out to study the compositional inhomogeneity of picroilmenite. Thermomagnetic curves were also recorded for each sample. A model for the processing of thermomagnetic curves is proposed on the basis of the relationship between the Curie point of picroilmenite and the content of the hematite end-member. The compositions determined by the thermomagnetic curves and microprobe analysis are rather similar. The conclusion has been drawn that thermomagnetic analysis can be used for the rapid determination of the picroilmenite composition. The possibilities and restrictions of this method are shown. 相似文献
326.
Measurements of the linear polarization of individual pulses at 40, 60, and 103 MHz are presented for ten pulsars. The degree and position angle of a linear polarization were measured with a temporal resolution of 1–7 ms, and the longitudinal distributions of these parameters were constructed for each pulsar at one or more of these frequencies. These are the first such measurements for pulsars B0031-07, B0320 + 39, B0628-28, and B2217 + 47. Apart from B0628-28, all the pulsars are characterized by the simultaneous presence of orthogonal polarization modes in at least one component of the integral profile. The secondary polarization mode increases at frequencies ≤100 MHz for pulsars whose integrated pulses contain pairs of conal components (B0031-07, B0329 + 54, B0834 + 06, B1133 + 16, B2020 + 28). This is manifested both as an expansion of the longitudinal range where the secondary polarization mode is observed and an increase in its contribution to the emission at a given longitude. New data confirming the dependence of the linear polarization of individual pulses on the intensity and mode of the pulsar emission have been obtained. 相似文献
327.
328.
I. S. Krassivskaya E. V. Sharkov N. S. Bortnikov A. V. Chistyakov N. V. Trubkin T. I. Golovanova 《Petrology》2010,18(3):263-277
Altered variolites described for the first time in the axial zone of the Mid-Atlantic Ridge are represented by rounded globules
of andesite (icelandite) composition with light trachyandesite rim embedded in a picrobasaltic matrix. The globules were transferred
with picrobasaltic melt and then floated to the surface of lava flow, while formation of leucocratic rims was presumably related
to thermodiffusion (Soret effect) in a cooling heterogeneous melt. This heterogeneous melt was formed by penetration of ascending
column of picrobasaltic magma in already existing small intracructsal magmatic chamber filled with residual icelanditetype
andesite melt and involvement of the latter into a general upward movement. The rapid ascent of the melts in the oceanic spreading
zones by means of turbulent flowing caused dispersion of the extragenous melt into small drops in a jet of picrobasaltic magma,
without their interaction. Variolites were formed during cooling of such heterogeneous lava flow. No signs of liquid immiscibility
were found in the studied variolites. 相似文献
329.
330.
This paper reports REE data on resin-asphaltene components of oil from six oil-gas-bearing provinces and on bitumoids from
inferred oil-source rocks (domanikites and bazhenites). It was shown that, regardless of geological-tectonic structure of
the regions, oil composition, depth of reservoirs, and host lithologies, oil exhibits significant REE fractionation, and,
unlike bitumoids, positive Eu anomaly. The (Eu/Sm)n ratio increases from asphaltenes to resins and further to oils. Based on REE distribution in oil, source rocks, and bitumoids,
it was concluded that deep-seated fluids were one of the possible sources that defined the trace element composition of oil. 相似文献