全文获取类型
收费全文 | 12402篇 |
免费 | 2436篇 |
国内免费 | 2771篇 |
专业分类
测绘学 | 383篇 |
大气科学 | 1651篇 |
地球物理 | 3909篇 |
地质学 | 6801篇 |
海洋学 | 1104篇 |
天文学 | 94篇 |
综合类 | 1228篇 |
自然地理 | 2439篇 |
出版年
2024年 | 88篇 |
2023年 | 205篇 |
2022年 | 419篇 |
2021年 | 469篇 |
2020年 | 448篇 |
2019年 | 556篇 |
2018年 | 461篇 |
2017年 | 536篇 |
2016年 | 554篇 |
2015年 | 589篇 |
2014年 | 781篇 |
2013年 | 736篇 |
2012年 | 851篇 |
2011年 | 854篇 |
2010年 | 778篇 |
2009年 | 783篇 |
2008年 | 774篇 |
2007年 | 868篇 |
2006年 | 836篇 |
2005年 | 700篇 |
2004年 | 622篇 |
2003年 | 555篇 |
2002年 | 505篇 |
2001年 | 480篇 |
2000年 | 404篇 |
1999年 | 426篇 |
1998年 | 422篇 |
1997年 | 338篇 |
1996年 | 305篇 |
1995年 | 253篇 |
1994年 | 219篇 |
1993年 | 211篇 |
1992年 | 162篇 |
1991年 | 99篇 |
1990年 | 87篇 |
1989年 | 58篇 |
1988年 | 55篇 |
1987年 | 32篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
52.
弧后盆地的形成与演化探讨:以东亚陆缘区为例 总被引:3,自引:2,他引:3
通过对弧后盆地大地构造体制的讨论,作者认为基属活化作用的产物根据地质,地球物理,地球化学等资料的分析,作者提出结论认为,由于东亚岛弧系岩石圈的均衡作用及海沟外侧冷却大洋岩石圈块体的下沉拖曳牵引等作用,使软流圈在岛弧系下方发生分异,这种分异作用带动东亚陆缘向东扩张,从而产生弧后的张开。 相似文献
53.
54.
1989年对白洋淀重新蓄水后的轮虫作了采样调查,共采到轮虫123种,隶属于46属12科,并对鉴定到种的轮虫作了初步分析。 相似文献
55.
56.
Ceramicola S. Rebesco M. De Batist M. Khlystov O. 《Marine Geophysical Researches》2001,22(5-6):445-464
High resolution, single-channel seismic sparker profiles across the Akademichesky Ridge, an intra-basin structural high in Lake Baikal (Russia), reveal the presence of small sediment mounds and intervening moats in the upper part of the sedimentary cover. Such features interrupt the generally uniform and even acoustic facies and are not consistent with the hemipelagic sedimentation, which is expected on such an isolated high and which would produce a uniform sediment drape over bottom irregularities. The influence of turbidity currents is excluded since the ridge is an isolated high elevated more than 600-1000 m above adjacent basins. The mounded seismic facies, including migrating sediment waves and non-depositional/erosional incisions, strongly suggest that sediment accumulation was controlled by bottom-current activity. We interpret the mounds as small-scale (< few tens of km2 in area) lacustrine drifts. Four basic types of geometry are identified: 1) slope-plastered patch sheets; 2) patch drifts; 3) confined drifts; 4) fault-controlled drifts. The general asymmetry in the sedimentary cover of the ridge, showing thicker deposits on the NW flank, and the common location of patch drifts on the northeast side of small basement knolls indicate that deposition took preferentially place at the lee sides of obstacles in a current flowing northward or sub-parallel to the main contours. Deep-water circulation in the ridge area is not known in detail, but there are indications that relatively cold saline water masses are presently flowing out of the Central Basin and plunging into the deep parts of the North Basin across the ridge, a process that appears to be driven mainly by small differences in salinity. We infer that the process responsible for the observed bottom-current-controlled sedimentary features has to be sought in these large-scale water-mass movements and their past equivalents. The age of the onset of the bottom-current-controlled sedimentation, based on an average sedimentation rate of 4.0 cm/ky, is roughly estimated to be as least as old as 3.5 Ma, which is generally regarded as the age of the onset of the last major tectonic pulse of rift basin development in the Baikal region. 相似文献
57.
东太湖茭草区网围养鱼模式试验研究 总被引:5,自引:0,他引:5
根据东太湖茭草区资源及环境特点,开展网围养鱼模式试验,结果表明:(1)经济效益明显,产投比1.2—1.5;(2)有良好生态效应,防治湖泊沼泽化和茭草区水质恶化;(3)社会效益显著,解决湖区剩余劳动力和城市居民吃鱼难的问题;(4)利于湖泊资源管理和保护。 相似文献
58.
An applied Fourier transform computation for the hydrodynamic wave-resistance coefficient is shown, oriented to potential flows with a free surface and infinity depth. The presence of a ship-like body is simulated by its equivalent pressure disturbance imposed on the un-perturbed free surface, where a linearized free surface condition is used. The wave-resistance coefficient is obtained from the wave-height downstream. Two examples with closed solutions are considered: a submerged dipole, as a test-case, and a parabolic pressure distribution of compact support. In the three dimensional case, a dispersion relation is included which is a key resource for an inexpensive computation of the wave pattern far downstream like fifteen ship-lengths. 相似文献
59.
讨论了~936)Cl的成因、~(36)Cl断代法的原理及测试方法。自1987年以来,应用该方法测得柴达木盆地尕斯库勒湖和大浪滩湖石盐的沉积年龄,并与~(14)C,~(230)Th和古地磁测年法所测得的年龄数据进行对比,结果均在误差(1δ)范围内相吻合,表明石盐的~(36)Cl断代法是可行的,获得的年龄数据是可靠的。 相似文献
60.