全文获取类型
收费全文 | 2243篇 |
免费 | 292篇 |
国内免费 | 523篇 |
专业分类
测绘学 | 251篇 |
大气科学 | 523篇 |
地球物理 | 429篇 |
地质学 | 712篇 |
海洋学 | 229篇 |
天文学 | 532篇 |
综合类 | 113篇 |
自然地理 | 269篇 |
出版年
2024年 | 8篇 |
2023年 | 31篇 |
2022年 | 55篇 |
2021年 | 70篇 |
2020年 | 76篇 |
2019年 | 82篇 |
2018年 | 69篇 |
2017年 | 60篇 |
2016年 | 81篇 |
2015年 | 93篇 |
2014年 | 118篇 |
2013年 | 146篇 |
2012年 | 94篇 |
2011年 | 163篇 |
2010年 | 141篇 |
2009年 | 191篇 |
2008年 | 154篇 |
2007年 | 161篇 |
2006年 | 162篇 |
2005年 | 160篇 |
2004年 | 130篇 |
2003年 | 109篇 |
2002年 | 91篇 |
2001年 | 87篇 |
2000年 | 98篇 |
1999年 | 57篇 |
1998年 | 66篇 |
1997年 | 59篇 |
1996年 | 44篇 |
1995年 | 31篇 |
1994年 | 38篇 |
1993年 | 22篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 1篇 |
排序方式: 共有3058条查询结果,搜索用时 15 毫秒
51.
郭遂红 《广东海洋大学学报》2002,22(2):78-81
随着我国改革开放的进展 ,跨国度、跨文化之间的交往越来越频繁。由于文化因素上的差异 ,交际行为在不同的文化中往往产生不同的意义 ,语用迁移难免会造成理解失误或交际失败。因而外语教学在培养学生整体语言技能的同时 ,应注意文化因素的渗透 ,提高学生的跨文化交际能力 相似文献
52.
The radiance leaving the earth-atmosphere system which can be sensed by a satellite borne radiometer is the sum of radiation emission from the earth surface and each atmospheric level that are transmitted to the top of the atmosphere. The radiation emission from the earth surface and the radiance of each atmospheric level can be separated from the radiance at the top the atmospheric level measured by a satellite borne radiometer. However, it is very difficult to measure the atmospheric radiance, especially the synchronous measurement with the satellite. Thus some atmospheric radiative transfer models have been developed to provide many options for modeling atmospheric radiation transport, such as LOWTRAN, MODTRAN, 6S, FASCODE, LBLRTM, SHARC, and SAMM. Meanwhile, these models can support the detailed detector system design, the optimization and evaluation of satellite mission parameters, and the data processing procedures. As an example, the newly atmospheric radiative transfer models, MODTRAN will be compared with other models after the atmospheric radiative transfer is described. And the atmospheric radiative transfer simulation procedures and their applications to atmospheric transmittance, retrieval of atmospheric elements, and surface parameters, will also be presented. 相似文献
53.
基于IC卡综合换乘信息的公交乘客上车站点推算 总被引:1,自引:0,他引:1
现有研究在缺少公交车运营信息的情况下,利用公交线间正交换乘信息的方法来识别公交车持卡乘客的上车站点,但在实际运用中很多班次无正交换乘的乘客,容易导致公交乘客上车站点匹配困难。因此,本文提出了一种基于IC卡综合换乘信息的公交乘客上车站点推算方法,该方法充分利用IC卡数据中的综合换乘信息(公交线间的正交和非正交换乘信息、地铁和公交线间的换乘信息)与公交网数据确定班次行驶方向,对班次内的乘客进行分组,充分利用综合换乘信息确定基准组及其对应的上车站点;然后,通过最小偏差规则匹配待定组的上车站点,实现公交乘客上车站点的推估。利用换乘信息确定班次行驶方向弥补了现有研究无法确定班次行驶方向的不足,使公交乘客上车站点推算方法更科学;最后,基于2011年8月的“深圳通”IC卡数据进行实例分析,对比只利用正交换乘信息确定的基准组数量和利用综合换乘信息确定的基准组数量,结果表明:该方法可使确定上车站点的组数占总组数的比值提高,克服了只利用正交换乘信息推算上车站点方法中存在的单个班次无基准组从而无法进行站点匹配的困难。本文方法比只利用正交换乘信息匹配站点,具有更高的可行性与准确率。 相似文献
54.
提出一种波纹开缝翅片管换热器,对其传热与流动特性进行三维数值模拟,选择Re范围在1 000到5 000时与平板开缝翅片的模拟相比较。结果表明,在Re小于2 752时,平板开缝比波纹开缝的换热效果好,而Re大于2 752时,波纹开缝比平板开缝换热效果更好,并且波纹开缝翅片管换热器的流动阻力小于平板开缝,因此,Re大于2 752时波纹开缝比平板开缝综合效果更好。 相似文献
55.
We have treated formation of spectral lines in a commoving frame where photoionization is predominant over collisional processes.
We have assumed that the radiation field for causing photoionization is a function of Planck function. We have also considered
the situation in which the continuum contributes to the radiation in the line. In all the models the quantityB/A (ratio of outer to inner radii) is kept equal to 10 and the total optical depth is taken to be 103. The velocity is assumed to be varying according to the lawdV/dτ ∼ < 1/τ whereτ is the optical depth (τ > 0) in the given shell. The velocities at the innermost radius (r =A) are set equal to 0 and at the outermost radius (r =B), the maximum velocities are taken to be 0, 1, 3 and 10 Doppler units. The calculated line profiles are those seen by an observer
at infinity.P Cygni-type profiles are observed in the case of a medium with no continuum absorption. For a medium with continuum absorption
double peaked asymmetric profiles are noticed when the velocities are small; the two emission peaks merge into a single asymmetric
peak for larger velocities. 相似文献
56.
K. N. Nagendra 《Solar physics》1996,164(1-2):67-78
Velocity fields in line formation regions strongly affect the line polarization. The conventionally used observer's frame method of solving the polarized transfer equation becomes expensive and inaccurate for partial redistribution problems, when large amplitude velocity fields have to be considered in the observer's frame. An alternative method of solution is the comoving frame method. Partial redistribution problems are solved using comoving frame formalism for line polarization caused by resonance scattering. 相似文献
57.
58.
59.
60.
We investigate the role of seasonal variations of Titan’s stratospheric composition on the temperature. We use a general circulation model coupled with idealized chemical tracers that reproduce variations of ethane (C2H6), acetylene (C2H2), and hydrogen cyanide (HCN). Enhancement of the mole fractions of these compounds, at high latitudes in the winter hemisphere relative to their equatorial values, induces a relative decrease in temperature above approximately 0.2 mbar, with a peak amplitude around −20 K, and a relative increase in temperature below, around 1 mbar, with a peak amplitude around +7 K. These thermal effects are mainly due to the variations of the cooling to space induced by the varying distributions. The ethane, acetylene, and hydrogen cyanide variations affect the cooling rates in a similar way, with the dominant effect being due to ethane, though its latitudinal variations are small. 相似文献