全文获取类型
收费全文 | 6848篇 |
免费 | 937篇 |
国内免费 | 1673篇 |
专业分类
测绘学 | 1732篇 |
大气科学 | 59篇 |
地球物理 | 402篇 |
地质学 | 5826篇 |
海洋学 | 392篇 |
天文学 | 47篇 |
综合类 | 474篇 |
自然地理 | 526篇 |
出版年
2024年 | 23篇 |
2023年 | 94篇 |
2022年 | 273篇 |
2021年 | 235篇 |
2020年 | 284篇 |
2019年 | 302篇 |
2018年 | 190篇 |
2017年 | 355篇 |
2016年 | 333篇 |
2015年 | 314篇 |
2014年 | 411篇 |
2013年 | 492篇 |
2012年 | 416篇 |
2011年 | 449篇 |
2010年 | 358篇 |
2009年 | 356篇 |
2008年 | 440篇 |
2007年 | 428篇 |
2006年 | 385篇 |
2005年 | 324篇 |
2004年 | 289篇 |
2003年 | 282篇 |
2002年 | 250篇 |
2001年 | 303篇 |
2000年 | 229篇 |
1999年 | 228篇 |
1998年 | 205篇 |
1997年 | 181篇 |
1996年 | 157篇 |
1995年 | 149篇 |
1994年 | 157篇 |
1993年 | 116篇 |
1992年 | 94篇 |
1991年 | 70篇 |
1990年 | 60篇 |
1989年 | 52篇 |
1988年 | 38篇 |
1987年 | 44篇 |
1986年 | 29篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1971年 | 3篇 |
排序方式: 共有9458条查询结果,搜索用时 843 毫秒
991.
《The Professional geographer》1988,40(1):106-116
software reviews are in this article BMDP/PC CONCEPTS COMPUTERIZED ATLAS EVALUATION OF ALTERNATE PROPOSALS (EAP) EXTRA: EXPRESS TRANSIT ANALYSIS MATC CAD MOTORS TRANSPORTATION PACKAGE PCMAP: Thematic Mapping Software for the IBM Personal Computer, Version 2.3 PLACE TRANPLAN . US-ATLAS 相似文献
992.
B. M. Yarnal 《Mathematical Geology》1982,14(4):371-386
Three trend surface techniques are used to evaluate the nature and distribution of the surface sediments of a rock glacier. Trend surface analysis, vector trend analysis, and most predictable surface (MPS)mapping suggest that long-term rock glacier creep causes the highly variable debris cover to display crude sorting and orientation patterns. Poorly sorted and randomly oriented surface materials may be the result of insufficient time for slowly evolving rock glacier sediment distributions to be established and/or the site of glacial erosion or deposition. 相似文献
993.
PESQUERA A.; TORRES-RUIZ J.; GIL-CRESPO P. P.; JIANG S.-Y. 《Journal of Petrology》2005,46(5):1013-1044
Tourmaline in the Martinamor antiform occurs in tourmalinites(rocks with >1520% tourmaline by volume), clasticmetasedimentary rocks of the Upper Proterozoic Monterrubio formation,quartz veins, pre-Variscan orthogneisses and Variscan graniticrocks. Petrographic observations, back-scattered electron (BSE)images, and microprobe data document a multistaged developmentof tourmaline. Overall, variations in the Mg/(Mg + Fe) ratiosdecrease from tourmalinites (0·360·75),through veins (0·380·66) to granitic rocks(0·230·46), whereas Al increases in thesame order from 5·846·65 to 6·226·88apfu. The incorporation of Al into tourmaline is consistentwith combinations of xAl(NaR)1 and AlO(R(OH))1exchange vectors, where x represents X-site vacancy and R is(Mg + Fe2+ + Mn). Variations in x/(x + Na) ratios are similarin all the types of tourmaline occurrences, from 0·10to 0·53, with low Ca-contents (mostly <0·10apfu). Based on field and textural criteria, two groups of tourmaline-richrocks are distinguished: (1) pre-Variscan tourmalinites (probablyCadomian), affected by both deformation and regional metamorphismduring the Variscan orogeny; (2) tourmalinites related to thesynkinematic granitic complex of Martinamor. Textural and geochemicaldata are consistent with a psammopelitic parentage for the protolithof the tourmalinites. Boron isotope analyses of tourmaline havea total range of 11B values from 15·6 to 6·8;the lowest corresponding to granitic tourmalines (15·6to 11·7) and the highest to veins (1·9to 6·8). Tourmalines from tourmalinites have intermediate11B values of 8·0 to +2·0. The observedvariations in 11B support an important crustal recycling ofboron in the Martinamor area, in which pre-Variscan tourmaliniteswere remobilized by a combination of mechanical and chemicalprocesses during Variscan deformation, metamorphism and anatexis,leading to the formation of multiple tourmaline-bearing veinsand a new stage of boron metasomatism. KEY WORDS: tourmalinites; metamorphic and granitic rocks; mineral chemistry; whole-rock chemistry; boron isotopes 相似文献
994.
995.
Valentina?MontaldoEmail author Ezio?Faccioli Gaetano?Zonno Aybige?Akinci Luca?Malagnini 《Journal of Seismology》2005,9(3):295-316
In the framework of the 2004 reference seismic hazard map of Italy the amplitude of the strong-motion (expressed in terms
of Peak Horizontal Acceleration with 10% probability of non-exceedence in 50 years, referred to average hard ground conditions)
was computed using different predictive relationships. Equations derived in Italy and in Europe from strong-motion data, as
well as a set of weak and strong-motion based empirical predictive relationships were employed in a logic tree procedure,
in order to capture the epistemic uncertainty affecting ground-motion attenuation. This article describes the adjustments
and conversions required to eliminate the incompatibilities amongst the relations. Particularly significant are distance conversions
and style-of-faulting adjustments, as well as the problems related to the use of regional relations, such as the selection
of a reference depth, the quantification of random variability and the strong-motion prediction. Moreover, a regional attenuation
relationship specific for volcanic areas was also employed, allowing a more realistic evaluation of seismic hazard, as confirmed
by the attenuation of macroseismic intensities. 相似文献
996.
G. Gabert 《Mathematical Geology》1978,10(5):425-432
Based on the results of the Conference on Resource Assessment Techniques of IGCP Project 98 in Loen, Norway, 1976, the importance
of mineral and energy inventories is demonstrated by their long-term objectives which aim at the solution of problems of quantitative
and qualitative mineral and energy reserve and resource assessments, estimates of the exploration potential, supply analysis,
future land-use planning, and national mineral policy. Prior to establishing a mineral and energy inventory it is essential
to clearly define both the long-term and short-term objectives, because they control the scope of an inventory and determine
the approach to and the method of constructing the data base. Only then can questions be answered as to the kind of data required,
the advantages of regional-versus commodity-based inventories, the necessity of computer-processable data files, the availability
of a user-oriented data base management system, and the usefulness of conducting a pilot project. Examples are given for simple
and complex types of mineral and energy inventories. The “Mineral Deposit Inventory” of the Institute for Geosciences and
Natural Resources, Hannover, Federal Republic of Germany, serves mainly as an information and reference system, whereas the
mineral inventory of “Project Manitoba” of the Geological Survey of Canada forms the base for reserve and resource assessment
as well as land-use planning of that province. For developing and industrialized countries alike, mineral and energy inventories
are appropriate tools in planning new exploration activities and decisions on future national mineral policy. Used by the
Regional Mineral Resources Development Centers of ESCAP and ECA, the United Nations economic commissions in Asia and Africa,
these tools could be of great advantage and mutual benefit to the developing countries of those regions.
This paper was presented at the International Geological Correlation Program (IGCP) Project 98: “Standards for Computer Applications
in Resource Studies” held at Taita Hills, Kenya, November 8–15, 1977. 相似文献
997.
Jeremy West 《Mathematical Geology》1985,17(7):743-753
Minerals may be identified by optical inspection and x-ray diffraction analysis. Full and correct identification, however, requires experience and extensive knowledge of mineral characteristics and association. Computer systems designed to approach levels of human expertise in similarly complex identification tasks have become increasingly effective with the application and refinement of various Artificial Intelligence (AI) techniques. These knowledge-based systemsuse the skills, knowledge, and rules of thumb that distinguish the expert from the knowledgeable layman to emulate human expertise. They also may be modified to serve a tutorial role whereby a nonexpert's approach to the task may be compared with that of the expert (system), and criticized accordingly. Such a knowledge-based system capable of identifying minerals from their optical characteristics is being developed at the University of Reading. 相似文献
998.
J. van Kuilenburg 《Mathematical Geology》1986,18(1):75-92
Design of a system which accepts geological maps or soil maps, together with corresponding well logs and produces interpretation maps, is described. The major aim was to get a processing program that would be useful at an operational scale that avoids the use of special purpose graphics hardware. This was achieved by using segment encoding of lines and by treatment of mapped units as basic graphical units (atoms). The system operation was split into an input phase and a processed phase. Input- and file-building require some technical experience, but are a one-time affair, whereas subsequent processing requires less (graphical) resources and experience, but is of a repetitive nature. When writing processing programs, emphasis was placed on ease of adding options. Clever improvements of efficiency (e.g., disk traffic) were not deemed worthwhile or even wise. Two driving forces behind the project required the programs reported here. First was the observation that digital data can be used only if appropriate programs are readily available to produce required results without need for large investments in hardware. Second was the idea that digital tools could be most effective if they allow the end-user (customer) to interact directly with the full base of data without recourse to technical experts. The resulting system is operational and running on a VAX 11/750, coded in FORTRAN. 相似文献
999.
数字地图作为一种新型的地图受到人们越来越广泛的关注。数字地图包含着各种地图数据,为了在多种比例尺范围内能快速地检索地图数据,需要把地图数据分层存贮变焦。作者通过变焦数据模型原理,探讨如何建立多层存贮结构,将数字地图中的大比例尺地图数据库自动导出小比例尺图形。变焦数据模型是一种动态的数据模型, 在该模型中,图形比例尺的变化不是简单的图形尺寸的缩放,而是伴随着各个物体的细节和物体数量而增减。这种基于变焦数据模型建立的数字地图可以提高数据检索与图形表示的灵活性,减少大量不必要的用于重复获取数据而消耗的人力物力,广泛应用于各个领域。 相似文献
1000.
Spline surfaces are interpolated for top of the Dundee Limestone of the central Michigan Basin, USA. The requirement of gridded data render spline functions inappropriate tools for representing many types of geological mapped data. Comparisons are drawn with maps for the same Michigan data based on trend surfaces and spatial filtering. 相似文献