首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   41423篇
  免费   590篇
  国内免费   318篇
测绘学   959篇
大气科学   2944篇
地球物理   8001篇
地质学   14216篇
海洋学   3849篇
天文学   9741篇
综合类   74篇
自然地理   2547篇
  2021年   404篇
  2020年   401篇
  2019年   453篇
  2018年   940篇
  2017年   843篇
  2016年   1090篇
  2015年   608篇
  2014年   1001篇
  2013年   2073篇
  2012年   1133篇
  2011年   1619篇
  2010年   1470篇
  2009年   1983篇
  2008年   1645篇
  2007年   1730篇
  2006年   1587篇
  2005年   1311篇
  2004年   1270篇
  2003年   1241篇
  2002年   1193篇
  2001年   1056篇
  2000年   980篇
  1999年   810篇
  1998年   813篇
  1997年   829篇
  1996年   668篇
  1995年   656篇
  1994年   616篇
  1993年   570篇
  1992年   526篇
  1991年   495篇
  1990年   506篇
  1989年   496篇
  1988年   474篇
  1987年   553篇
  1986年   489篇
  1985年   604篇
  1984年   650篇
  1983年   592篇
  1982年   527篇
  1981年   577篇
  1980年   469篇
  1979年   458篇
  1978年   433篇
  1977年   433篇
  1976年   383篇
  1975年   378篇
  1974年   376篇
  1973年   384篇
  1971年   224篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
721.
722.
This paper critically examines some of the causes and the problems of agricultural development in Nigeria. It also discusses very minimally, the rise and the contribution of the petroleum industry to the Nigerian economy and its effect on the agricultural sector. Finally, some possible suggestions are made in order to ameliorate the situation of agriculture and to overcome the shortage of food production in the country.  相似文献   
723.
724.
Geomagnetism and Aeronomy - The arc-polarized Alfvén waves observed in the near-Earth region of the heliosphere are studied with instruments of the WIND spacecraft in 1995–2011....  相似文献   
725.
Book reviews     
APPLIED GEOGRAPHY: Issues, Questions and Concerns (Geo Journal Library Vol. 15) edited by M. S. Kenzer. 16 × 24 cm, x and 210 pages. Kluwer: Dordrecht 1989 (ISBN 0 7923 04381).

WINE AND THE VINE: An Historical Geography of Viticulture and the Wine Trade by T. Unwin. 16 × 24 cm, xvi and 409 pages. Routledge: London 1991 (ISBN 0 415 13120 6) $A155.00 (hard); distributed by The Law Book Co.

WATERFRONT SYDNEY 1860–1920 by G. Aplin and J. Storey. 26 × 18 cm. 144 pages. Allen & Unwin: Sydney 1991 (first published 1984) (ISBN 1 86373 098 2) $A24.95 (soft).

Australian Geographer 23 (2), November 1992

INDUSTRIAL LOCATION: Principles and Policies (Second Edition) by K. Chapman and D. F. Walker. 15 × 23 cm, xiii and 322 pages. Basil Black‐well: Oxford 1991 (ISBN 0 631 16789 7) $A39.95 (soft).

INTERNATIONALISATION OF AUSTRALIA'S SERVICE INDUSTRIES by J. V. Langdale. 17 × 25 cm, iv and 373 pages. Australian Government Publishing Service, for Department of Industry, Technology and Commerce: Canberra 1991 (ISBN 0 644 13841 6).

TOURISM AND GOLD IN KAKADU: The Impact of Current and Potential Natural Resource Use on the Northern Territory Economy by B. Knapman, O. Stanley and J. Lea. 21 × 29 cm, vi and 49 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1179 4).

ABORIGINAL AUSTRALIA AND THE ‘NEW FEDERALISM’ INITIATIVE (Discussion Paper No. 2) by G. J. Crough. 14 × 21 cm, 42 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1325 8).

AUSTRALIAN NATIONHOOD AND OUTBACK INDIGENOUS PEOPLES (Discussion Paper No. 1) by P. Jull. 14 × 21 cm, 38 pages. North Australia Research Unit, Australian National University: Darwin 1991 (ISBN 0 7315 1309 6).

MIGRATION AND DEVELOPMENT IN THE SOUTH PACIFIC (Pacific Research Monograph No. 24) edited by J. Connell. 17 × 25 cm, xii and 199 pages. National Centre for Development Studies, Australian National University: Canberra 1990 (ISBN 0 07315 0668 5) $A25.00 (soft).

POPIULESIN BLONG HONIARA: Olketa Popiulesin Map Blong 1986 Sensis. HONIARA: 1986 Census Atlas (Statistics Office Occasional Paper No. 4 / Board of Development Studies Monograph No. 1) by A.C. Walsh. 21 × 29 cm, vii and 95 pages. Department of Statistics: Honiara and Board of Development Studies, Massey University: Palmerston North 1990 (ISSN 0114 8834) $NZ34.00 in New Zealand, $NZ38.00 elsewhere (soft).

DOI MOI: Vietnam's Renovation Policy and Performance (Political and Social Change Monograph No. 14) edited by D. K. Forbes, T. H. Hull, D. G. Marr and B. Brogan. 15 × 22 cm, xiv and 263 pages. Department of Political and Social Change, Australian National University: Canberra 1991 (ISBN 0 7315 1303 7).  相似文献   

726.
Bohra DM 《GeoJournal》1979,3(1):63-68
In this research paper attempts have been made to analyze the distribution of 68 urban settlements in 14 regions of the country. The value of near-neighbour statistic (R) shows nearly random pattern of urban settlements in some regions and approachingly uniform distribution of urban settlements in other regions. Regional distribution of urban settlements and their growth have been explained in context of region's geographical, economic and industrial frameworks.  相似文献   
727.
Zusammenfassung Die Zweiachsigkeit von Calciten und Dolomiten wird durch Zwillingslamellen erklärt. Die Größe des Achsenwinkels hängt vom Volumenanteil der gleich orientierten Lamellen und vom Zwillingswinkel ab. Die Doppelbrechung hat nur geringen Einfluß.
Biaxial interference figures in calcite and dolomite
The biaxiality of calcites and dolomites is explained by twin lamellae. The amount of the axial angle depends from the part of volume built up by the lamellae of equal orientation, and from the twin angle. The birefringence is of minor influence.
  相似文献   
728.
Izvestiya, Physics of the Solid Earth - Abstract—Destruction on the Earth’s surface caused by a shock wave is one of the most important and dangerous effects from asteroid and comet...  相似文献   
729.
Publication and citation rates of female engineering faculty (FEF) who work in earthquake engineering are analyzed and compared with a group of leading male engineering faculty (MEF) in the same field. After correcting for the effects of rank and gender, it is found that the future performance of FEF, given the opportunity, can rank as high as the recognized leaders in the field.  相似文献   
730.
Human-wildlife conflict (HWC) is a global conservation issue of increasing concern, and understanding the factors driving conflict is crucial for preventing or mitigating it. In many parts of China, large human populations and increasing development has led to an escalation in HWC with both carnivore and prey species. In this paper we assess herder attitudes toward blue sheep (Pseudaois nayaur, Hodgson, 1833), white lipped deer (Carvus albirostris, Przewalski, 1883), red deer (Cervus elaphus, Linnaeus, 1758), and marmot (Marmota himalayana Hodgson, 1841) through interview-based surveys conducted in 46 households across 8 villages in Qilianshan National Nature Reserve, Gansu, China. We also examine the perceived impact of three ecological-restoration policies (anti-grazing, sustainable grazing, and grass-planting policies) on livelihoods, and how this affects attitudes toward wildlife. Herders reported neutral attitudes toward wildlife species in general, but reported negative attitudes towards blue sheep. Mixed-effects modeling revealed that herder attitudes toward the target species varied significantly across villages, but other socioeconomic variables had limited explanatory power for attitudes. Furthermore, we found that while policy implementation was negatively perceived by herders, anti-grazing policy implementation and total policy implementation were positively correlated with positive attitudes toward wildlife, highlighting a potential gap between perceived threats and actual threats. Finally, we show that the leading cause of reported livestock death is preventable disease, alleviation of which may help improve attitudes toward wildlife.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号