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   1439896篇
  免费   138552篇
  国内免费   3020篇
  2021年   16769篇
  2019年   16685篇
  2018年   18471篇
  2017年   17039篇
  2016年   28829篇
  2015年   43255篇
  2014年   51542篇
  2013年   77905篇
  2012年   40413篇
  2011年   29233篇
  2010年   44846篇
  2009年   45904篇
  2008年   27149篇
  2007年   25337篇
  2006年   30183篇
  2005年   30941篇
  2004年   30082篇
  2003年   27550篇
  2002年   25314篇
  2001年   38444篇
  2000年   36252篇
  1999年   34440篇
  1998年   24759篇
  1997年   24723篇
  1996年   24125篇
  1995年   23665篇
  1994年   23473篇
  1993年   22661篇
  1992年   30838篇
  1991年   29512篇
  1990年   28117篇
  1989年   28555篇
  1988年   26457篇
  1987年   25214篇
  1986年   24038篇
  1985年   25913篇
  1984年   25049篇
  1983年   22138篇
  1982年   21956篇
  1981年   21202篇
  1980年   19723篇
  1979年   21712篇
  1978年   19783篇
  1977年   18855篇
  1976年   17943篇
  1975年   17828篇
  1974年   18245篇
  1973年   18542篇
  1972年   16092篇
  1971年   14479篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
The NHS reforms have come to mean all things to all men (and women). Identifying a market oriented purchaser-provider split as the conceptual heart of the reforms is still, however, useful. There are important perverse incentives in and around the NHS that are associated with the reforms; furthermore, many reactions to the resulting problems are paradoxical and often counterproductive. Hitherto most criticism of the reforms from the health policy and management community (as opposed to the professions and the public) has been tactical rather than fundamental. There are serious problems for the NHS associated both with the NHS market and with current, often tacit, strategies for the future of the service.  相似文献   
997.
998.
Movements of radio-tagged Common Buzzards Buteo buteo in their first year   总被引:1,自引:1,他引:0  
S. S. WALLS  R. E. KENWARD 《Ibis》1995,137(2):177-182
The movements of 96 radio-tagged juvenile Common Buzzards Buteo buteo were studied during 3 years in Dorset, southern England. Contrary to previous studies which implied that Common Buzzards are territorial, we found that 39% foraged within 1 km of the nest during their first winter, presumably within their parents' home range. Most (72%) of those that did not disperse were recorded making brief excursions during August and September, before opting for a "stay-at-home" strategy. There was no significant difference between the sexes in the tendency to make excursions or disperse, but females dispersed further than males. Buzzards which dispersed early tended to settle significantly farther from their nests than did late dispersers. Long-term radio-tracking has shown that 72% of the dispersing birds returned towards their natal area in the following breeding season. Such philopatry may be an important hindrance to avian recolonization following local extinctions.  相似文献   
999.
1000.
A new failure model is introduced in the form of a four-parameter nonlinear differential equation, with failure probability as the dependent variable and failure time as the independent variable. The first parameter characterizes the location, the second the scale, and the other two the shape of the model. The type of the accompanying hazard function is immediately read off the shape parameters. The new model approximates the classical failure models with rather high precision, but also models cases where the failure density is skewed to the left. It can be used to analyze survival data objectively, based on the shape of the failure distribution. The computation of quantiles and moments is easy and fast. Nonlinear regression methods are used to estimate parameter values.  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