全文获取类型
收费全文 | 11070篇 |
免费 | 2095篇 |
国内免费 | 2852篇 |
专业分类
测绘学 | 491篇 |
大气科学 | 2333篇 |
地球物理 | 2816篇 |
地质学 | 4676篇 |
海洋学 | 2008篇 |
天文学 | 2019篇 |
综合类 | 567篇 |
自然地理 | 1107篇 |
出版年
2024年 | 29篇 |
2023年 | 121篇 |
2022年 | 304篇 |
2021年 | 359篇 |
2020年 | 382篇 |
2019年 | 461篇 |
2018年 | 421篇 |
2017年 | 420篇 |
2016年 | 435篇 |
2015年 | 492篇 |
2014年 | 670篇 |
2013年 | 713篇 |
2012年 | 627篇 |
2011年 | 719篇 |
2010年 | 577篇 |
2009年 | 912篇 |
2008年 | 881篇 |
2007年 | 997篇 |
2006年 | 943篇 |
2005年 | 726篇 |
2004年 | 699篇 |
2003年 | 620篇 |
2002年 | 554篇 |
2001年 | 428篇 |
2000年 | 477篇 |
1999年 | 427篇 |
1998年 | 373篇 |
1997年 | 250篇 |
1996年 | 202篇 |
1995年 | 189篇 |
1994年 | 158篇 |
1993年 | 100篇 |
1992年 | 79篇 |
1991年 | 49篇 |
1990年 | 49篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1971年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
42.
THE SIMULATED STORAGE CAPACITY OF FLOOD AND WATERLOGGING IN THE TYPICAL AGRICULTURAL REGION IN JIANGHAN PLAIN 总被引:2,自引:0,他引:2
1INTRODUCTIONJianghanPlainisoneoftheimportantbasesofChina′sagriculturalproductivitylocatedinthemiddleChangjiangRivervalleyofcentralChina.TheJianghanplainapproximately6.6×104km2inareaandover30millioninpopulationistherenowned“countryoffishandrice"in… 相似文献
43.
向文 《大地测量与地球动力学》1997,(2)
为了根据离散观测数据构制连续空间重力变化图像,分析和讨论了3种数值插值方法,计算结果表明多面函数方法插值精度最高。由于逐步回归分析筛选核函数中心点的计算繁琐,文中提出根据分形理论和Shannon取样定理来确定核函数中心点。对滇西试验场进行模拟试算,插值精度可达到4~5(10-8ms-2)。 相似文献
44.
R. Papoular 《Monthly notices of the Royal Astronomical Society》2005,362(2):489-497
A model is proposed for the formation of water ice mantles on grains in interstellar clouds. This occurs by direct accretion of monomers from the gas, be they formed by gas or surface reactions. The formation of the first monolayer requires a minimum extinction of interstellar radiation, sufficient to lower the grain temperature to the point where thermal evaporation of monomers is just offset by monomer accretion from the gas. This threshold is mainly determined by the adsorption energy of water molecules on the grain material; for hydrocarbon material, chemical simulation places this energy between 0.5 and 2 kcal mol−1 , which sets the (true) visible extinction threshold at a few magnitudes. However, realistic distributions of matter in a cloud will usually add to this an unrelated amount of cloud core extinction, which can explain the large dispersion of observed (apparent) thresholds. Once the threshold is crossed, all available water molecules in the gas are quickly adsorbed, because the grain cools down and the adsorption energy on ice is higher than on bare grain. The relative thickness of the mantle, and, hence, the slope of τ3 ( A v ) depend only on the available water vapour, which is a small fraction of the oxygen abundance. Chemical simulation was also used to determine the adsorption sites and energies of O and OH on hydrocarbons and study the dynamics of formation of water molecules by surface reactions with gaseous H atoms, as well as their chances to stick in situ. 相似文献
45.
46.
We show how the Yarkovsky effect can be understood as a heat engine. The output of the engine, manifested in the rate of change in semimajor axis of the body, has a maximum at an intermediate heat capacity, depending on the rotation rate of the body. This maximum arises because the work output depends on the product of the solar heat absorbed by the body and transported from its morning to evening side (this am-pm heat flux increases with heat capacity) and the Carnot efficiency (which declines with heat capacity). 相似文献
47.
48.
49.
We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae. 相似文献
50.
M. G. Abrahamyan 《Astrophysics》2004,47(4):555-567
The equilibrium of elliptical Riemann disks with a polytropic equation of state and their evolution under the influence of viscosity and gravitational radiation inside spheroidal halos with a relative surface mass density k. The evolutionary trajectory of a disk inside a halo with k<0.5, which is analogous to the evolution of an isolated disk, differs from that of a disk inside a denser halo. 相似文献