全文获取类型
收费全文 | 13860篇 |
免费 | 2521篇 |
国内免费 | 3409篇 |
专业分类
测绘学 | 887篇 |
大气科学 | 3197篇 |
地球物理 | 3478篇 |
地质学 | 6788篇 |
海洋学 | 1683篇 |
天文学 | 751篇 |
综合类 | 1332篇 |
自然地理 | 1674篇 |
出版年
2024年 | 45篇 |
2023年 | 187篇 |
2022年 | 554篇 |
2021年 | 621篇 |
2020年 | 544篇 |
2019年 | 635篇 |
2018年 | 681篇 |
2017年 | 634篇 |
2016年 | 792篇 |
2015年 | 683篇 |
2014年 | 815篇 |
2013年 | 797篇 |
2012年 | 770篇 |
2011年 | 781篇 |
2010年 | 888篇 |
2009年 | 744篇 |
2008年 | 720篇 |
2007年 | 668篇 |
2006年 | 538篇 |
2005年 | 523篇 |
2004年 | 423篇 |
2003年 | 458篇 |
2002年 | 522篇 |
2001年 | 547篇 |
2000年 | 487篇 |
1999年 | 662篇 |
1998年 | 543篇 |
1997年 | 505篇 |
1996年 | 493篇 |
1995年 | 435篇 |
1994年 | 367篇 |
1993年 | 347篇 |
1992年 | 277篇 |
1991年 | 220篇 |
1990年 | 165篇 |
1989年 | 143篇 |
1988年 | 141篇 |
1987年 | 72篇 |
1986年 | 60篇 |
1985年 | 52篇 |
1984年 | 34篇 |
1983年 | 29篇 |
1982年 | 40篇 |
1981年 | 32篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1958年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
42.
徐文莉 《中国天文和天体物理学报》1997,(1)
LAMOST的光学系统由反射施密特改正板MA 和球面主镜MB 组成 ,MA 和MB 均为对角径 1 .1m的六角形子镜的拼镜面 .本文计算了星在子午圈上时望远镜观测不同的天区零视场和有视场时的光学系统衍射能量分布 ,还计算了MA 不变MB 改为整块的 6m镜以及MA 和MB 均为对角径 1 .5m的六角形子镜的拼镜面的衍射能量分布 .对这些计算结果进行分析 ,论证了六角形子镜尺寸选择的合理性 相似文献
43.
44.
利用三维有限元模拟两层地球模型(包括弹性层和粘弹性层)介质的横向不均匀和断层错动的复杂性对震后地表位移场的影响,其数值结果包括弹性解和粘弹性解。结果表明,震后位移场的分布特征不仅与粘弹性层的流变特性有关,还与弹性层介质的剪切模量以及断层的同震错动有关。 相似文献
45.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献
46.
For a Hamiltonian that can be separated into N+1(N\geq 2) integrable parts, four algorithms can be built for a symplectic integrator. This research compares these algorithms for the
first and second order integrators. We found that they have similar local truncation errors represented by error Hamiltonian
but rather different numerical stability. When the computation of the main part of the Hamiltonian, H
0, is not expensive, we recommend to use S
* type algorithm, which cuts the calculation of the H
0 system into several small time steps as Malhotra(1991) did. As to the order of the N+1 parts in one step calculation, we found that from the large to small would get a slower error accumulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
47.
广西中三叠统浊流流向及坡向 总被引:1,自引:0,他引:1
通过对广西中三叠统浊积岩系中溢堤流沉积的识别,结合同一鲍马层序Tc段斜层理倾向与其底部槽模走向不一致的分析,以及横向冲刷模、U形障碍冲刷痕等冲蚀构造、大型滑动模等压刻构造的认识,筛选出宽阔水道充填沉积、扇状体及分支水道沉积中底模构造的指向数据,来指示浊流主体流向,并区分出溢堤流流向。从而确定了本区中三叠世时的浊流主体流向为NW向,平均为300°。根据滑塌沉积中滑塌包卷层轴面、滑塌面的测定,确定凤山县金牙处的古坡向平均为322°,与浊流主体流向基本一致。还认为中三叠世时右江盆地沉积物源来自桂东和桂东南蚀源区,海水由其南的越南境内进入。 相似文献
48.
利用上海天文台的照相底片资料,确定了疏散星团NGC6530天区364颗恒星的自行和成员概率,并对有关自行测定的方法、结果和精度等问题作了较为详细的介绍和讨论。使用的底片历元差为87年,全部恒星自行中误差的均方根值为1.09mas/a。 相似文献
49.
The pyroxenite xenoliths in the volcanic rocks of Hoh Xil consist of clinopyroxenes and orthopyroxenes. The mineral composition of these pyroxenes is similar to that of mantle xenoliths including peridotite and pyroxenite from China and abroad, and different from that of granulites. The pyroxenes formed at 1101–1400°C (averaging 1250°C) and under 30–60 kb (averaging 46 kb). We deduced that the magma was derived from the mantle at a depth of more than 150 km, which fits in with the geophysical conclusion that the low-velocity layer existed in the mantle under 150 km.
相似文献50.
We study a model of mergers affecting only the progenitors of present E/SO. We adopt the standard scenarios of star formation as prescribed by Guiderdoni & Rocca-Volmerange. The merging process is parametrized under the assumptions of(1) self-similarity of the Schechter MF and(2) mass conservation. Nine models are discussed. The predictions are compared with counts ofB
J
,U
+,F
+,N
+ bands. E/SO mergers account for the excess of the faintest blue galaxies without causing excess in redder bands. However, as we no longer have enough mergers at brighter magnitudes, a plain E/SO merging model fits less tightly for the redshift and the colour distributions. Detection effect, a steeper slope of LF may be ways to improve. Our models predict acceptable merger frequencies atz = 0.5 although some models predict more interacting galaxies than observation atz = 0. 相似文献