全文获取类型
收费全文 | 6461篇 |
免费 | 271篇 |
国内免费 | 81篇 |
专业分类
测绘学 | 235篇 |
大气科学 | 512篇 |
地球物理 | 1522篇 |
地质学 | 2160篇 |
海洋学 | 523篇 |
天文学 | 1187篇 |
综合类 | 28篇 |
自然地理 | 646篇 |
出版年
2022年 | 30篇 |
2021年 | 76篇 |
2020年 | 87篇 |
2019年 | 122篇 |
2018年 | 178篇 |
2017年 | 161篇 |
2016年 | 231篇 |
2015年 | 173篇 |
2014年 | 196篇 |
2013年 | 407篇 |
2012年 | 257篇 |
2011年 | 342篇 |
2010年 | 291篇 |
2009年 | 382篇 |
2008年 | 336篇 |
2007年 | 293篇 |
2006年 | 270篇 |
2005年 | 259篇 |
2004年 | 261篇 |
2003年 | 205篇 |
2002年 | 214篇 |
2001年 | 116篇 |
2000年 | 145篇 |
1999年 | 103篇 |
1998年 | 115篇 |
1997年 | 82篇 |
1996年 | 86篇 |
1995年 | 83篇 |
1994年 | 90篇 |
1993年 | 73篇 |
1992年 | 88篇 |
1991年 | 67篇 |
1990年 | 55篇 |
1989年 | 50篇 |
1988年 | 57篇 |
1987年 | 52篇 |
1986年 | 56篇 |
1985年 | 67篇 |
1984年 | 64篇 |
1983年 | 76篇 |
1982年 | 57篇 |
1981年 | 65篇 |
1980年 | 55篇 |
1979年 | 65篇 |
1978年 | 51篇 |
1977年 | 34篇 |
1976年 | 28篇 |
1975年 | 26篇 |
1974年 | 26篇 |
1973年 | 30篇 |
排序方式: 共有6813条查询结果,搜索用时 0 毫秒
831.
The article focuses on the way in which map content reflects the cartographer's World view and system of values. Different
World views are illustrated historically. Examples of topographical, land-use and vegetation maps from different parts of
the World indicate the prevalence of Eurocentric perceptions in cartography. Different geological maps of Norden show how
the visual image depends on the classification system adopted. All maps are mental maps in that their content is culturally
determined and ethnocentric in origin. 相似文献
832.
Many of the non-mare rock types at Apollo 17 can be identified uniquely by their spectral reflectance properties. Mineralogical and textural information is present in the spectral curves of samples from Boulder 1, Station 2. It should be possible to determine the regional extent of rocks similar to the boulder using reflectance spectra from a spacecraft in lunar orbit. 相似文献
833.
834.
Michael Stocking 《Applied geography (Sevenoaks, England)》1983,3(1):63-77
Farming and environmental degradation are inextricably linked through a complex of political, social, economic and physical forces. A connection is drawn between the initiation and maintenance of distinct farming systems (commercial, emergent and subsistence) by largely human influences, and the effect these farming systems have in turn on the environment. There are important implications for the environment through indirect effects on plant cover, cultivation methods and systems of bush fallowing. In many respects subsistence cultivation is probably the safest.A case study from Mkushi District, Central Province exemplifies the influence of external factors on environmental degradation in general, and soil erosion in particular. In the survey, traditional practices show fewer signs of soil erosion than commercial farming because of rational decisions taken by each group of farmers. The implication for conservation strategies is briefly reviewed. 相似文献
835.
836.
W.Michael Reisman 《Marine Policy》1981,5(3):276-277
Appraisers of recent sessions of the Law of the Sea Conference have directed their attention, sometimes at the expense of other critical issues, to the emerging regime to govern seabed mining. For one reason or another, a general Western consensus has emerged that the draft treaty's textual arrangements for traditional and innovative maritime and aerial passage are satisfactory. That complacent consensus may rest on perilously unrealistic assumptions. 相似文献
837.
Parasitic programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. We describe a microprocessor-based automated SETI acquisition system which searches for and records spectra of narrowband signals in the IF band of an observatory receiver. Data taken with this system over 35 days at the Hat Creek Radio Observatory at 1612 MHz are discussed. Out of approximately 105 spectra processed during this period, 4000 were identified by the system as containing narrowband signals and were recorded. Subsequent analysis indicates that over 3900 of these are due to local RF contamination. The remainder are undergoing further investigation. 相似文献
838.
Michael G. Katona 《国际地质力学数值与分析法杂志》1983,7(3):371-384
A simple friction–contact interface element is introduced which simulates frictional slippage, separation, and re-bonding of two bodies initially mating at a common interface and subsequently deforming with an arbitrary static loading schedule. Constraint equations between initially mating node pairs and the general principle of virtual work are used to formulate the interface element for a finite element solution procedure. Some advantages of the interface element include; easy implementation intostandard finite element programs, direct determination of interface forces without round-off problems, and the generality afforded by the virtual work formulation to include other non-conservative models in the system. The application of the interface element to an idealized buried culvert problem illustrates that the model behaves properly. A second application, for a long-span culvert installation with incremental soil loading, demonstrates the importance of modelling slippage at the culvert–soil interface in order to conform with experimental observations. 相似文献
839.
840.
Michael E. Hodgson 《The Professional geographer》1989,41(1):51-61
A widely used method for grid interpretation from a set of discrete sample points is based on the inverse distanceweighted model. This method requires the identification of k-nearest sample points for each grid point, probably the most time-consuming portion of the grid interpolation process. Three searching methods for identifying the k-nearest sample points are discussed and compared. Two of these methods were consistenty faster without sacrificing accuracy than the brute-force searching method, and one method was from one to over 90 times faster than the brute-force searching method. 相似文献