全文获取类型
收费全文 | 23945篇 |
免费 | 275篇 |
国内免费 | 135篇 |
专业分类
教育 | 16367篇 |
科学研究 | 2983篇 |
各国文化 | 197篇 |
体育 | 2206篇 |
综合类 | 16篇 |
文化理论 | 209篇 |
信息传播 | 2377篇 |
出版年
2021年 | 170篇 |
2020年 | 322篇 |
2019年 | 464篇 |
2018年 | 638篇 |
2017年 | 604篇 |
2016年 | 591篇 |
2015年 | 385篇 |
2014年 | 519篇 |
2013年 | 4207篇 |
2012年 | 478篇 |
2011年 | 519篇 |
2010年 | 400篇 |
2009年 | 387篇 |
2008年 | 416篇 |
2007年 | 468篇 |
2006年 | 425篇 |
2005年 | 412篇 |
2004年 | 387篇 |
2003年 | 401篇 |
2002年 | 366篇 |
2001年 | 391篇 |
2000年 | 406篇 |
1999年 | 412篇 |
1998年 | 208篇 |
1997年 | 219篇 |
1996年 | 286篇 |
1995年 | 244篇 |
1994年 | 222篇 |
1993年 | 221篇 |
1992年 | 352篇 |
1991年 | 354篇 |
1990年 | 351篇 |
1989年 | 377篇 |
1988年 | 308篇 |
1987年 | 321篇 |
1986年 | 334篇 |
1985年 | 370篇 |
1984年 | 317篇 |
1983年 | 323篇 |
1982年 | 271篇 |
1981年 | 262篇 |
1980年 | 245篇 |
1979年 | 379篇 |
1978年 | 292篇 |
1977年 | 274篇 |
1976年 | 240篇 |
1975年 | 199篇 |
1974年 | 229篇 |
1973年 | 188篇 |
1971年 | 178篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
In an attempt to clarify the chronological relationship between identity and equivalence conservation, normal preschool-aged children (experiment 1) were exposed to brief videotape demonstrations of a model conserving identity and equivalence, identity only, equivalence only, or neither. Subsequent performances indicate that identity was easier to accelerate than equivalence, and training in both identity and equivalence appeared to be most effective in accelerating conservation. Trainable mentally retarded (TMR) children were then exposed to either the identity-equivalence-conserving or control model (experiment 2). This population, which some have argued remains at a preoperational level of functioning, was more likely to conserve identity than equivalence. In addition, conservation in the training group increased following training, though these gains were not maintained over a 3-week retention interval. 相似文献
93.
The reproducibility of microwave integrated circuits can be improved by employing substrates which are anisotropic. A method is presented which facilitates the computation of the characteristics of distributed integrated microwave circuits of finite conductor thickness on anisotropic and inhomogeneous substrates. The method is variational and it relies on a quasi-static approach which assumes that the charge distribution on each side of the conductor can be represented by a spatially dependent set of exponential functions. 相似文献
94.
It is often desirable to represent carrier distribution systems by networks so that analysis can be made to predict the behavior of these systems. Modeling of two canonical carrier distribution systems, the star-shaped system and the parallel-wire system by networks was carried out in this paper. The representation is given in terms of lumped parameters when the lengths of the carrier lines are short and it is given in terms of lumped and distributed parameters when the lengths of the carrier lines are long. 相似文献
95.
The behavior of narcotics-addicted and nonaddicted newborns on the first 2 days of life was assessed with the Brazelton Neonatal Behavioral Assessment Scale. In addition to classic signs of narcotics abstinence, addicted infants were less able to be maintained in an alert state and less able to orient to auditory and visual stimuli. These deficits were especially pronounced at 48 hours of age. Addicted infants were as capable of self-quieting and responding to soothing intervention as normal neonates, although they were substantially more irritable. These characteristics and addicted infants' greater resistance to cuddling are discussed in terms of their potential impact on early infant-care-giver interaction. 相似文献
96.
G.K. Wertheim 《Journal of The Franklin Institute》1974,298(4):289-298
The principles of X-ray photoelectron spectroscopy are outlined. The application of this technique to the study of the electronic structure of metals, alloys and compounds is illustrated using data in Ag, β-brass, ReO3 and VO2. In the latter a major change in the density of states is observed on passing through the metal-insulator transition. 相似文献
97.
98.
99.
Formulae are derived for the deflection surface of a symmetrically loaded circular plate having several points supports which are situated at equal distances apart on a single concentric circle. There is no restriction on the diameter of the support circle, which may be as large as the diameter of the plate itself. The results of this paper compare favorably with published experimental results. Numerical deflection coefficients for a uniformly loaded plate are provided, and these could be utilized for optimizing the positions and the number of concentrated supports. 相似文献
100.