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   11614篇
  免费   1098篇
  国内免费   2篇
  2023年   54篇
  2022年   101篇
  2021年   204篇
  2020年   138篇
  2019年   168篇
  2018年   198篇
  2017年   232篇
  2016年   328篇
  2015年   506篇
  2014年   600篇
  2013年   722篇
  2012年   797篇
  2011年   761篇
  2010年   494篇
  2009年   455篇
  2008年   648篇
  2007年   630篇
  2006年   572篇
  2005年   546篇
  2004年   571篇
  2003年   520篇
  2002年   473篇
  2001年   247篇
  2000年   200篇
  1999年   221篇
  1998年   160篇
  1997年   139篇
  1996年   125篇
  1995年   95篇
  1994年   100篇
  1993年   93篇
  1992年   126篇
  1991年   105篇
  1990年   102篇
  1989年   101篇
  1988年   80篇
  1987年   66篇
  1986年   59篇
  1985年   96篇
  1984年   77篇
  1983年   67篇
  1982年   69篇
  1981年   54篇
  1980年   42篇
  1979年   55篇
  1978年   47篇
  1977年   41篇
  1976年   40篇
  1974年   43篇
  1973年   36篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
121.
122.
123.
In a chromosome study on leucocyte cultures made in 13 patients treated with chlorpromazine, 15 treated with perphenazine, and nine treated with lysergide, a significantly higher frequency of gaps, breaks, and hypodiploid cells in the patients treated with perphenazine and lysergide occurred compared with the 41 controls studied. It is concluded that if some drugs can induce major chromosome abnormalities, and less toxic alternatives are available, the latter should be used in preference.  相似文献   
124.
125.
Summary Experiments with feedback stimulation triggered from the subject's electroencephalogram result in changing the sequential time series of intervals of occipital alpha and intervals of little or no alpha EEG activity. The rate of recurrence of alpha and no-alpha EEG can be changed by regulating the external feedback stimuli or by asking the subject to change his internal state. Four different paradigms were investigated and the results interpreted in terms of the hypothesis that oculomotor functions regulate the occurrence and nonoccurrence of alpha.This work was supported by NIGMS Grants 5 PO1 GM 14940-04 and GM 15006-03.Most of this research was conducted at the Perception Laboratory, Veterans' Administration Hospital, Bedford, Massachusetts, with the cooperation of Dr. Thomas B. Mulholland.  相似文献   
126.
Zusammenfassung Die Schätzung der Varianzkomponenten bei Versuchen mit festen Variabilitätsursachen, z. B. bei der Prüfung von Sorten, Behandlungen usw., ist nur dann sinnvoll, wenn die Varianzkomponenten so definiert sind, daß ihre Summe der Gesamtvarianz gleich ist, d. h. daß sie sich additiv verhalten. Will man die so definierten Varianzkomponenten erwartungstreu schätzen, muß man die Überhöhung der mittleren Quadrate, die durch Division mit Freiheitsgraden statt mit der Gruppenzahl entstanden ist, wieder korrigieren. Diese Korrektion entfällt bei der Schätzung der Varianz von Zufallswirkungen.Die Erwartungswerte der mittleren Quadrate der üblichen varianzanalytischen Zerlegung und die erwartungstreuen Schätzungen der additiv definierten Varianzkomponenten werden am Beispiel eines Versuches mit zwei konstanten Variabilitätsursachen und einer Zufallseinwirkung dargelegt.
Estimating variance components in a fixed model of variance analysis
Summary The partition of a variance into components in experiments with fixed effects, i.e. experiments with varieties, treatment etc., is meaningful only if components are defined as additive parts of a whole. This also demands that the sum of the components of variance be equal to the total variance. Such additivity of the components of variance is achieved by appropriate definitions of the components of variance. Unbiassed estimates of the additively defined components of variance are obtained by a simple correction which eliminates the influence of degrees of freedom on the calculation of mean squares. This correction is not needed for the estimation of variances of random effects.The expected values of mean squares for the partition of variance and formulas for unbiassed estimates of additively defined components of variance are demonstrated in an experiment with two fixed effects and one random effect.
  相似文献   
127.
128.
129.
130.
Summary The cellular localization of biogenic monoamines in crustaceans was studied by means of a highly specific and sensitive fluorescence method devised by Falck and Hillarp. It was found that neurons displaying specific fluorescence in the central nervous system were confined to the protocerebrum, the medulla externa and interna and the ventral nerve cord. The method allows a distinction between the fluorophores of 5-hydroxytryptamine (and 5-hydroxytryptophan), which emit the yellow light, and the fluorophores deriving from the catecholamines (and DOPA), which emit the green light. Green-fluorescent neurons occurred abundantly in the aforementioned parts of the central nervous system while yellow-fluorescent neurons were sparsely present in the same parts.The present work has been carried out at the departments of Histology and Zoology at the University of Lund. The authors take great pleasure in expressing their warmest thanks for laboratory facilities, provided by Professors Erik Dahl (Zoological Institute) and Bengt Falck (Histological Institute).The research reported in this document has been sponsored by the Air Force Office of Scientific Research under Grant AF EOAR 66-14 through the European Office of Aerospace Research (OAR), United States Air Force and by a grant from the Swedish Natural Science Research Council 99-32 (nr 5995).  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