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   7424篇
  免费   386篇
  2023年   40篇
  2020年   126篇
  2019年   181篇
  2018年   247篇
  2017年   226篇
  2016年   287篇
  2015年   186篇
  2014年   169篇
  2013年   2023篇
  2012年   220篇
  2011年   252篇
  2010年   234篇
  2009年   228篇
  2008年   192篇
  2007年   203篇
  2006年   169篇
  2005年   111篇
  2004年   98篇
  2003年   100篇
  2002年   115篇
  2001年   145篇
  2000年   104篇
  1999年   115篇
  1998年   89篇
  1997年   81篇
  1996年   85篇
  1995年   69篇
  1994年   59篇
  1993年   72篇
  1992年   71篇
  1991年   61篇
  1990年   60篇
  1989年   56篇
  1988年   52篇
  1987年   60篇
  1986年   60篇
  1985年   69篇
  1984年   79篇
  1983年   84篇
  1982年   68篇
  1981年   67篇
  1980年   66篇
  1979年   61篇
  1978年   66篇
  1977年   67篇
  1976年   62篇
  1975年   71篇
  1974年   42篇
  1973年   38篇
  1972年   41篇
排序方式: 共有7810条查询结果,搜索用时 31 毫秒
151.
ABSTRACT. This paper examines the socially optimal locations of branch facilities (or small stores) and main facilities (or large stores) on a finite linear market that is uniformly populated from position 0 to position 1. Each consumer has a probability w of finding the desired service (or product) at a branch facility, and a probability 1 of finding the desired service (or product) at a main facility. Two types of consumer search are considered: phone search and visit search. Different assumptions are made about the numbers of branch facilities and main facilities (each involving one or two facilities of each type). Under visit search, the socially optimal locations of branch facilities tend to be closer to main facilities than under phone search, and this tendency is more pronounced for smaller values of w.  相似文献   
152.
153.
ABSTRACT. In this paper a gravity model is formulated to model a hospital patient flow system. Both spatial and nonspatial measures of separation are used to estimate the model. Travel time was found to provide improved fits over linear distance in modeling patient flow behavior. Transformations of travel time (square root and log) were found to improve model performance further. Model diagnostics suggested additional spatial separation measurw, separation measure parameters demonstrated stability over time. The model is used to forecast the effects of health care financing reform and hospital closure on patient flows in an urban hospital market. Universal health coverage was found to dramatically improve access to hospital services for lower income patient populations. Hospitals at risk for closure were forecast to receive increased patient flows. Medical school hospitals are expected to lose patients after implementation of health reform, with important implications for graduate medical education. Hospital closures were shown to have negative effects on access to services in poor neighborhoods, but relatively little effect on access in the system as a whole.  相似文献   
154.
Excavation of Testar del Molí, the only workshop found in the Manises-Paterna area, revealed the existence of a fourteenth-century ceramic workshop covering the remains of the thirteenth-century workshop. This study is concerned with the fourteenth-century production, and forthcoming papers will connect both epochs following the findings of current excavations. The chemical and mineralogical characterization of the ceramic production of this workshop shows the presence of three groups of ceramic pastes which could also be distinguished by, and, thus, related to, their daily use. The raw materials found in the excavation have also been mineralogically and chemically characterized, and a model of possible mixtures of raw materials has also been developed in order to determine their possible use in the manufacture of the pottery previously characterized.  相似文献   
155.
In much contemporary literature the Phineas Gage case is described as contributing to the development of lobotomy and leucotomy but the historical evidence shows this to be an almost completely erroneous view. His case was, however, important in the development of brain surgery itself. I begin this paper by briefly mentioning four early cases of brain surgery and describing the Gage case. I then set out the context of the localisation debate, concentrating particularly on Broca's clinical observations, because Macewen planned the first operation on the brain in the light of Broca's findings. I then turn to that context as it was developed through Jackson's observations and Ferrier's experiments, because Bennett and Godlee used it in planning the first operation for the removal of a brain tumour. It was also in the localisation context that Starr first drew attention to the significance of the changes in Gage for localising frontal tumours. By the turn of the century, several operations had been performed on the frontal lobes and various difficulties with Starr's criteria had become apparent. The reasons for the difficulties will be brought out and I conclude with a brief discussion of the relation between the Gage case and the operations performed by Burckhardt, Moniz, and Freeman.  相似文献   
156.
Book Reviews     
Ken Booth and Steve Smith (eds), International Relations Theory Today, Cambridge: Polity Press, 1995. xii + 367pp. $39.95 (paper).

Christine Sylvester, Feminist Theory and International Relations in a Postmodern Era. Cambridge: Cambridge University Press, 1994. xi + 265pp. $47.50 (paper).

Stephanie Lawson (ed.), The New Agenda for Global Security: Cooperating for Peace and Beyond. St. Leonards: Allen & Unwin/Department of International Relations, RSPAS, Australian National University, 1995. xi + 217pp. $24.95.

Anne O. Krueger, Economic Policies at Cross‐Purposes: The United States and Developing Countries. Washington, DC: Brookings Institution, 1993. xii + 253pp. $US36.95 (cloth).

Robert L. Paarlberg, Leadership Abroad Begins at Home: U.S. Foreign Economic Policy After the Cold War. Washington, DC: Brookings Institution, 1995. xxv + 115pp. $US28.95 (cloth); $US10.95 (paper).

Tony Brenton, The Greening of Machiavelli: The Evolution of International Environmental Politics. London: Royal Institute of International Affairs/Earthscan, 1994. xvii + 282pp. $UK14.95 (paper).

John Charmley, Churchill's Grand Alliance: The Anglo‐American Special Relationship, 1940–1957. London: Hodder & Stoughton, 1995. xv + 427pp. $55.00 (cloth).

Victor A. Kremenyuk, Conflicts In and Around Russia. Nation‐Building in Difficult Times. Westport: Greenwood Press, 1994. xiv + 159pp. $US49.95 (cloth).

Alexander Johnston, Sipho Shezi and Gavin Bradshaw (eds), Constitution‐making in the New South Africa. London and New York: Leicester University Press, 1993. viii + 272pp. $UK 39.50.

Ramesh Thakur, The Politics and Economics of India's Foreign Policy. London: Hurst and Company; New York: St. Martin's Press, 1994. xi + 306pp. No price given.

Francis Seow, To Catch a Tartar: A Dissident in Lee Kuan Yew's Prison (with a foreword by C.V. Devan Nair). Yale Southeast Asia Studies Monograph 42, New Haven: Yale Centre for International and Area Studies, 1994. xxxiii + 293pp. $50.00 (paper).

Brij Lal, Robert Kiste and Kerry Howe (eds), The Tides of History: The Pacific Islands in the 20th Century. St Leonards: Allen & Unwin, 1994. xviii + 475pp. $34.95 (paper).

LaMond Tullis, Unintended Consequences—Illegal Drugs and Drug Policies in Nine Countries. Boulder, CO: Lynne Rienner, 1995. ix + 229pp. $US42.00 (cloth).

The United Nations and Cambodia 1991–1995, The United Nations Blue Books Series, Vol. II. New York: Department of Public Information, United Nations, 1995. 352pp. $US29.95 (paper).

‘Atu Emberson‐Bain (ed.), Sustainable Development or Malignant Growth? Perspectives of Pacific Island Women. Suva, Fiji: Marama Publications, 1994. 290pp. No price given.

Payam Akhavan and Robert Howse (eds), Yugoslavia, the Former and Future: Reflections by Scholars front the Region. Washington, DC and Geneva: The Brookings Institution and The United Nations Research Institute for Social Development, 1995. xxviii + 188pp. $US32.95 (cloth) $US 12.95 (paper).

David Camroux, ‘Looking East’ . . . and Inwards: Internal Factors in Malaysian Foreign Relations during the Mahathir Era 1981–1994. Australia‐Asia Papers No. 72. Griffith University: Centre for the Study of Australia‐Asia Relations, 1994. iii + 62pp. $10.00.  相似文献   

157.
This paper considers the impact of technology on methods used to classify land potential. With developments in new technologies such as Expert Systems (ES) and Geographic Information Systems (GIS), McKeown (1987) proposes a new method by which to explain the decision making process for land classification to an end user. Consideration is given to McKeowns' concept and the literature reviewing both traditional land classification methods and ES and GIS systems.  相似文献   
158.
159.
Lead-glazed pottery from the medieval workshop of Les Olleries Majors (Paterna, Spain) has been studied by Mössbauer spectroscopy, X-ray diffraction, X-ray fluorescence and optical spectroscopy. Yellow, brown and honey-coloured glazes occur on pots glazed on only one surface. They have virtually identical compositions and transmittance spectra, their apparent differences in colour are due to the colours of the underlying pastes. Yellow glazes occur on cream-coloured calcareous bodies, honey-coloured glazes occur on less calcareous bodies with some development of hematite, while brown glazes occur on red siliceous cooking-pots. Green glazes are found on pots glazed on both surfaces; the glazes trapped CO2 evolved by decomposing carbonates, resulting in an internal reducing environment. This caused the reduction of iron to the ferrous state which coloured the glaze green by diffusion.  相似文献   
160.
Glow discharge optical emission spectrometry (GDOES) has been used for obtaining calibration curves for copper, tin, lead, silver, antimony, arsenic, zinc and iron from standards including copper-base alloys (Cu 61.33-99.95%) and from bronze Punic coins. The GDOES results were calibrated using atomic absorption spectroscopy with inductively coupled plasma atomization (ICPAAS) to analyse the standards and coins. For all these materials, the results show that via GDOES it is possible to obtain reliable and reproducible calibration curves for copper, tin, lead, zinc and iron with a linear behaviour as a function of the content. The quantitative GDOES and ICPAAS data for the coins have been also compared with those obtained via X-ray fluorescence (XRF) and it is shown that GDOES, ICPAAS and XRF agree well with one another considering that the bronze coins are inhomogeneous to some degree. As an example of GDOES analytical features, a depth concentration profile through a thin bronze patina is shown and briefly discussed.  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