全文获取类型
收费全文 | 2007篇 |
免费 | 361篇 |
国内免费 | 463篇 |
专业分类
测绘学 | 73篇 |
大气科学 | 403篇 |
地球物理 | 391篇 |
地质学 | 837篇 |
海洋学 | 361篇 |
天文学 | 391篇 |
综合类 | 102篇 |
自然地理 | 273篇 |
出版年
2024年 | 11篇 |
2023年 | 20篇 |
2022年 | 59篇 |
2021年 | 80篇 |
2020年 | 71篇 |
2019年 | 103篇 |
2018年 | 87篇 |
2017年 | 59篇 |
2016年 | 66篇 |
2015年 | 69篇 |
2014年 | 108篇 |
2013年 | 115篇 |
2012年 | 119篇 |
2011年 | 115篇 |
2010年 | 89篇 |
2009年 | 145篇 |
2008年 | 142篇 |
2007年 | 162篇 |
2006年 | 139篇 |
2005年 | 106篇 |
2004年 | 146篇 |
2003年 | 118篇 |
2002年 | 95篇 |
2001年 | 83篇 |
2000年 | 84篇 |
1999年 | 85篇 |
1998年 | 83篇 |
1997年 | 41篇 |
1996年 | 35篇 |
1995年 | 39篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2831条查询结果,搜索用时 31 毫秒
1.
2.
3.
Richard J. Pike 《The Professional geographer》1987,39(2):131-145
Extraterrestrial geography has become a reality, as we move from Earth's moon to the planets. A broad-scale regional physiography is being established on twenty planets and satellites through remote sensing techniques. Spacecraft images yield most of the information on Solar System landscapes. Topographic measurements are extracted by monoscopic image-processing, stereophotogrammetry, and radar analysis. Invisible parts of the spectrum furnish non-topographic data. 相似文献
4.
5.
An approximate Riemann solver for the equations of relativistic magnetohydrodynamics (RMHD) is derived. The Harten–Lax–van Leer contact wave (HLLC) solver, originally developed by Toro, Spruce and Spears, generalizes the algorithm described in a previous paper to the case where magnetic fields are present. The solution to the Riemann problem is approximated by two constant states bounded by two fast shocks and separated by a tangential wave. The scheme is Jacobian-free, in the sense that it avoids the expensive characteristic decomposition of the RMHD equations and it improves over the HLL scheme by restoring the missing contact wave.
Multidimensional integration proceeds via the single step, corner transport upwind (CTU) method of Colella, combined with the constrained transport (CT) algorithm to preserve divergence-free magnetic fields. The resulting numerical scheme is simple to implement, efficient and suitable for a general equation of state. The robustness of the new algorithm is validated against one- and two-dimensional numerical test problems. 相似文献
Multidimensional integration proceeds via the single step, corner transport upwind (CTU) method of Colella, combined with the constrained transport (CT) algorithm to preserve divergence-free magnetic fields. The resulting numerical scheme is simple to implement, efficient and suitable for a general equation of state. The robustness of the new algorithm is validated against one- and two-dimensional numerical test problems. 相似文献
6.
7.
INTRODUCTIONTriploidanimalsareusefulbecausetheyaresterile ,characterizedbypositivegrowthinthere productiveseason ,usefulfortesting ,forintroductionofnon nativespecies ,andforprotectionofde velopedstrains.Theinductionoftriploidyhadbeenreportedinmanyaquaculturespecies .Triploidshavebeensuccessfullyinducedinshrimpusingtemperatureshockorchemicalshock (CB ,6 DMAP)in 4species :Sicyoniaingentis (Xiangetal.,1 991 ) ,Fenneropenaeuschinensis (Xiangetal.,1 992 ;Daietal.,1 993;Baoetal.,1 993;Li… 相似文献
8.
A short summary of recent progress in measuring and understanding turbulence during magnetic reconnection in laboratory plasmas
is given. Magnetic reconnection is considered as a primary process to dissipate magnetic energy in laboratory and astrophysical
plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical
theories, such as the Sweet–Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is
conjectured to be enhanced by turbulence to accelerate reconnection rates either in the context of the Sweet–Parker model
or by facilitating setup of the Pestchek model. Measurements at a dedicated laboratory experiment, called MRX or Magnetic
Reconnection Experiment, have indicated existence of strong electromagnetic turbulence in current sheets undergoing fast reconnection.
The origin of the turbulence has been identified as right-hand polarized whistler waves, propagating obliquely to the reconnecting
field, with a phase velocity comparable to the relative drift velocity. These waves are consistent with an obliquely propagating
electromagnetic lower-hybrid drift instability driven by drift speeds large compared to the Alfven speed in high-beta plasmas.
Interestingly, this instability may explain electromagnetic turbulence also observed in collisionless shocks, which are common
in energetic astrophysical phenomena. 相似文献
9.
较详细地研究了无规取向、无吸收椭球体粒子的T-矩阵收敛问题。首先,简要概括了nmax的3种收敛方案和它们的基本特性。然后,应用1993年提出的数学收敛方法(M-方法)和1998年提出和物理收敛方法(P-方法)研究收敛问题。结果表明椭球粒子收敛精度对粒子的尺度参数,纵横比以及椭球体的种类(例如,长/扁椭球)有很强的依赖性。当粒子的尺度参数不太大时,甚至在极端纵横比的条件下,P-收敛方案优于M-收敛方案。 相似文献
10.
Olga Hadz̆ija Mladen Jurac̆ić Marija Luić Maja Tonković Biserka Jeric̆ević 《Estuarine, Coastal and Shelf Science》1985,21(5):701-709
The investigation of mineral, granulometric and chemical composition of sediments of the River Krka estuary (Yugoslavia) were performed in order to elucidate the origin of the sediments and the pattern of sedimentation. Estuarine surface sediments were found to be fine-grained with a bimodal distribution. Environmental conditions in estuarine sediments favour conservation of the organic matter (anoxic conditions). The carbohydrates in the sediments were investigated to determine whether they are of terrigenous or authigenous origin. Glucose, galactose, mannose, xylose, rhamnose, glucosamine and glucuronic acid were detected in the sediments. Their mutual relationship indicates a preferentially terrigenous source of sedimented organic material in estuarine sediments. 相似文献