全文获取类型
收费全文 | 19706篇 |
免费 | 232篇 |
国内免费 | 12篇 |
专业分类
教育 | 14065篇 |
科学研究 | 1912篇 |
各国文化 | 127篇 |
体育 | 1595篇 |
综合类 | 7篇 |
文化理论 | 113篇 |
信息传播 | 2131篇 |
出版年
2021年 | 161篇 |
2020年 | 243篇 |
2019年 | 389篇 |
2018年 | 523篇 |
2017年 | 530篇 |
2016年 | 491篇 |
2015年 | 300篇 |
2014年 | 422篇 |
2013年 | 3583篇 |
2012年 | 429篇 |
2011年 | 492篇 |
2010年 | 348篇 |
2009年 | 331篇 |
2008年 | 459篇 |
2007年 | 363篇 |
2006年 | 401篇 |
2005年 | 288篇 |
2004年 | 265篇 |
2003年 | 253篇 |
2002年 | 295篇 |
2001年 | 420篇 |
2000年 | 398篇 |
1999年 | 370篇 |
1998年 | 182篇 |
1997年 | 199篇 |
1996年 | 231篇 |
1995年 | 228篇 |
1994年 | 196篇 |
1993年 | 210篇 |
1992年 | 325篇 |
1991年 | 294篇 |
1990年 | 281篇 |
1989年 | 333篇 |
1988年 | 309篇 |
1987年 | 273篇 |
1986年 | 271篇 |
1985年 | 304篇 |
1984年 | 252篇 |
1983年 | 291篇 |
1982年 | 240篇 |
1981年 | 214篇 |
1980年 | 214篇 |
1979年 | 286篇 |
1978年 | 244篇 |
1977年 | 213篇 |
1976年 | 203篇 |
1975年 | 158篇 |
1974年 | 157篇 |
1973年 | 162篇 |
1971年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
This paper introduces a polynomial operator called the DT-polynomial as a novel approach to network flow problems. The class of networks dealt with is time-varying in the sense that the capacity, cost, and travel-time of each edge may vary in discrete time. The Dt-polynomial is a polynomial in two operators, D (delay) and T (time), which is used for describing the time-varying transmission characteristics. The paper starts with the mathematics involving the DT-polynomials. A new shortest arrival route algorithm is presented, and its computational complexity is found to be favorable in comparison with others such as Dijkstra's method and the potential method derived from Ford-Fulkerson's technique. Furthermore, a dynamic flow problem is formulated and analyzed in terms of DT-polynomials, and a latest-departure earliest-arrival schedule is given. Finally, a modified DT-polynomial is applied to digital filter networks. 相似文献
73.
To examine the developmental significance of mirrow self-recognition in early childhood, a cross-sectional study with 55 Down's syndrome children was conducted. When their image is altered by rouge on the nose, normal infants by 22 months indicate self-recognition by touching their noses while looking in the mirror. Only a small percentage of Down's syndrome children touched their noses by this age, confirming the expected lag in this development. However, those young Down's syndrome infants with near-normal development quotient did manifest the reaction. In general, when developmental age was equated, the Down's syndrome children showed parallel development to normal children. 相似文献
74.
Victor D Hopper 《Endeavour》1978,2(3):121-126
Measurement of vertical and horizontal wind velocity is of great importance in many contexts, such as investigation of air pollution, weather forecasting, and air-traffic control. In recent years continuously recording acoustic sounders have been developed which give reliable results at reasonable cost: some 200 are now in use in at least 15 countries. 相似文献
75.
D P Biklen 《American annals of the deaf》1975,120(4):382-386
76.
In this paper, the stability equation method is applied to the analysis of nonlinear systems with characteristics equations having complex coefficients. Three types of systems are studied: those with unstable open-loop poles, unstable characteristics roots or an equal number of open-loop poles and zeros. 相似文献
77.
Georges D. Szakasits 《Research Policy》1974,3(1):18-28
The article deals with the results achieved by the adoption of the SAPPHO method (developed by the Science Policy Research Unit of Sussex University) to the conditions of the Hungarian electronics industry. The results coincide to a great extent with those established in the course of the survey made in England, although there are some significant differences. 相似文献
78.
79.
80.
Mary A. Anderson Frank Bowles C. O. Taiwo Jan D. Beckmann L. J. Lewis James R. Liesch Godfrey N. Brown H. L. Elvin Shib K. Mitra Richard F. Behrendt Graeme Kemelfield Hugh W. R. Hawes W. A. Dodd A. L. Tibawi 《International Review of Education/Internationale Zeitschrift für Erziehungswissenschaft/Revue internationale l'éducation》1971,17(2):220-251