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   41722篇
  免费   4275篇
  国内免费   17篇
  46014篇
  2022年   232篇
  2021年   558篇
  2020年   324篇
  2019年   457篇
  2018年   520篇
  2017年   475篇
  2016年   786篇
  2015年   1234篇
  2014年   1408篇
  2013年   1883篇
  2012年   2235篇
  2011年   2300篇
  2010年   1423篇
  2009年   1378篇
  2008年   2063篇
  2007年   2125篇
  2006年   2030篇
  2005年   2093篇
  2004年   1994篇
  2003年   1984篇
  2002年   1878篇
  2001年   621篇
  2000年   467篇
  1999年   586篇
  1998年   577篇
  1997年   456篇
  1996年   464篇
  1995年   383篇
  1994年   430篇
  1993年   392篇
  1992年   487篇
  1991年   466篇
  1990年   424篇
  1989年   393篇
  1988年   418篇
  1987年   392篇
  1986年   377篇
  1985年   463篇
  1984年   522篇
  1983年   422篇
  1982年   487篇
  1981年   499篇
  1980年   495篇
  1979年   367篇
  1978年   357篇
  1977年   358篇
  1976年   354篇
  1975年   258篇
  1974年   320篇
  1973年   286篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
61.
62.
63.
64.
65.
On 11 May 1985 the main stand of Bradford City Football Club caught fire. Within four minutes the stand was alight from end to end. Fifty three people were burnt to death and about 250 injured; 83 required admission to hospital, and 55 of these were treated by primary excision of their burns and skin grafting. In such disasters the help of staff from other hospitals and areas is essential. Patients should be assessed to see whether they have burns that will ultimately be fatal; if they have they should not be sent to regional burns units, where they would take up beds that could be used for patients with treatable burns. All districts should ensure that their plans for accidents in which burns injuries predominate are adequate.  相似文献   
66.
The Orlando Easterly Wetland (OEW), located near Christmas, Florida, USA, is among the longer-lived treatment wetlands in the United States. It was established in the late 1980s to reduce nitrogen and phosphorus concentrations from tertiary treated wastewater bound for the St. Johns River. A goal of 0.07 mg/l total phosphorus concentration has been set by the regulating agency (St. Johns River Water Management District). In order to understand and define the operating conditions for which this target could be met, a systematic study of historic phosphorus uptake was performed using a traditional first-order model. Phosphorus uptake performance is shown to correlate well with hydraulic performance for two parallel upstream cells. The first-order model is enhanced with predictive capabilities that acknowledge the correlation between the phosphorus uptake rate constant and the hydraulic loading rate observed in the system. Inherent limitations with the first-order modeling approach are addressed and uncertainty in model performance is used to bound predictions.  相似文献   
67.
The movement and polarity of zeatin, a highly active, endogenous cytokinin, through petioles and roots were tested in the classical experimental arrangement using excised 5-mm sections. Zeatin in the receiver cylinders of agar was measured by soybean callus bioassay and by liquid scintillation counting of 14C that had been added in the donor cylinders as [8-14C] zeatin. Both methods agreed in showing movement, but there was no polarity in Coleus #5 petioles. The amounts moved were about one-tenth of the GA-3 movement through petioles of the third pair of leaves of the same clone. Movement of 14C-zeatin through Pisum roots was similarly statistically significant but non-polar; the amounts moved were similar to those previously observed for polar GA-3 movement through Zea roots.  相似文献   
68.
69.
Summary Proponents of Developmental Systems Theory (DST) argue that it offers an alternative to current research programs in biology that are built on the historic disjunction between evolutionary and developmental biology. In this paper I illustrate how DST can be used to account for the acquisition of an important component of moral agency, conscience. Susan Oyama, a major proponent of DST, has set moral issues outside the compass of DST. Thus, I examine her reasons for restricting DST to non-moral matters, and argue that they are not decisive. On the positive side, I argue that DST not only is compatible with attempts to describe and explain moral agency but also aids us in understanding it. In particular, I show how DST can provide a fruitful perspective for viewing some significant current findings and theories in moral developmental psychology about the acquisition of conscience. The familiar dichotomies resisted by DST, those between genes and environment, inherited and acquired, innate and learned, and biological and cultural, have also plagued human developmental psychology, including moral development. By bringing a DST perspective to the study of moral development, I illustrate how a DST perspective might offer a promising way to reconceive that phenomenon, and provide some insights into how further work in understanding the development of moral agency might proceed. Thus, I hope to contribute to the current efforts of proponents of DST to integrate developmental and evolutionary considerations.  相似文献   
70.
The membrane environments in normal and tumor rat tissue and the effect of hyperthermia thereon are studied with 19F-NMR spectroscopy of the general anesthetic halothane. Normal and tumor cell types are clearly differentiated by the halothane resonance. A hydrophobic environment prominent in tumor tissue is more sensitive to heat treatment than the corresponding environments of normal cells. Studies of extracted lipids suggest that this may be due in part to the considerable difference in lipid temperature response which exists between normal and kidney tumor cells.  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