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   52390篇
  免费   257篇
  国内免费   552篇
系统科学   1236篇
丛书文集   154篇
教育与普及   285篇
理论与方法论   520篇
现状及发展   31099篇
研究方法   583篇
综合类   17127篇
自然研究   2195篇
  2013年   806篇
  2012年   561篇
  2011年   2549篇
  2010年   424篇
  2009年   605篇
  2008年   735篇
  2007年   825篇
  2006年   926篇
  2005年   1103篇
  2004年   2207篇
  2003年   1837篇
  2002年   1490篇
  2001年   1239篇
  2000年   768篇
  1999年   884篇
  1998年   644篇
  1997年   772篇
  1996年   532篇
  1994年   681篇
  1993年   688篇
  1992年   838篇
  1991年   725篇
  1990年   792篇
  1989年   605篇
  1988年   603篇
  1987年   601篇
  1986年   657篇
  1985年   810篇
  1984年   707篇
  1983年   630篇
  1982年   784篇
  1981年   810篇
  1980年   884篇
  1979年   1309篇
  1978年   1179篇
  1977年   1194篇
  1976年   1058篇
  1975年   1042篇
  1974年   834篇
  1973年   1125篇
  1972年   1216篇
  1971年   1208篇
  1970年   1239篇
  1969年   1171篇
  1968年   1141篇
  1967年   991篇
  1966年   836篇
  1965年   673篇
  1964年   468篇
  1958年   506篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Recent years have seen an increasing cross-fertilization between the fields of decision analysis and forecasting. Decision-analytic models often require forecasts as inputs, and aspects of the Bayesian decision-theoretic framework underlying decision analysis have proved useful to forecasting, particularly in contexts where subjective judgemental inputs are required. This paper describes the use of decision tree analysis for forecasting and illustrates its use for corporate divisional forecasting and planning. A specialized decision-analytic technique, acts as events, is also described and illustrated to forecast a new product's earnings. Conclusions are drawn about the applicability of decision analysis for forecasting.  相似文献   
82.
Summary Indoxyl derivatives were detected as minor products among the urinary metabolites of two trial drugs, a benzodiazepine (GP 55 129) and a benzophenone (CGP 11 952). Their structures were elucidated by NMR and mass spectroscopy. Presumably, metabolites containing potential aldehyde functions react spontaneously with endogenous indoxyl. Such derivatives have not hitherto been encountered in drug metabolism.  相似文献   
83.
本文提出了精测安培表内阻的新方法,并将其与其它测量方法进行了比较。  相似文献   
84.
本文介绍了在水电工程规划设计时,如何利用三次自然样条插值函数在有限个方案的基础上自动生成无限多个方案,然后采用多目标综合决策模型在其中选择最优方案的一种方法.文中还给出了程序流程,并以某水电站正常蓄水位选择作为实例,对方法进行了验证,结果与专家决策完全吻合.  相似文献   
85.
86.
提出了一种基于径向网络的增量学习算法 ,在对新样本进行学习时 ,通过恢复受干扰样本的方式来尽可能保持已有的知识不变 .模拟实验证明了本算法的正确性和有效性 .  相似文献   
87.
介绍了变电站自动化系统一种基于80C196KB控制CPU设计的新型线路单元测控装置。它能完成一条线路的遥测、遥信、遥控和遥脉功能。模拟量测量采用基于快速傅里叶变换的交流采样算法,测量精度高。与上位机的通信提供多种选择方式,人机交互采用点阵液晶显示及薄膜式键盘,开关量状态、脉冲量的采集以及控制输出都采用二次隔离技术,并采用了先进软件抗干扰技术,遥控操作可靠。  相似文献   
88.
Contemporary developments in economicmethodology have produced a vibrant agenda ofcompeting positions. These include, amongothers, constructivism, critical realism andrhetoric, with each contributing to the Realistvs. Pragmatism debate in the philosophies of thesocial sciences. A major development in theneo-pragmatist contribution to economicmethodology has been Quine's pragmatic assaulton the dogmas of empiricism, which are nowclearly acknowledged within contemporaryeconomic methodology. This assault isencapsulated in the celebrated Duhem-Quinethesis, which according to a number ofcontemporary leading philosophers of economics,poses a particularly serious methodologicalproblem for economics. This problem, asreflected in Hausman's analysis, consists ofthe inability of economics to learn fromexperience, thereby subverting the capacity totest economic theories. In this paper wedispute this position. Our argument is basedon a combination of Quine's holism with VanFraassen's constructive empiricism, especiallythe latter's analysis of empirical adequacy andhis pragmatic approach to explanation. Theresulting reorientation of economic methodologyrestores the capacity of economics to learnfrom experience and reinstates the imperativeof developing alternatives to orthodoxtheorizing in economics.  相似文献   
89.
90.
Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals.In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation.  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