全文获取类型
收费全文 | 6803篇 |
免费 | 110篇 |
国内免费 | 7篇 |
专业分类
教育 | 4952篇 |
科学研究 | 514篇 |
各国文化 | 104篇 |
体育 | 537篇 |
综合类 | 8篇 |
文化理论 | 112篇 |
信息传播 | 693篇 |
出版年
2023年 | 25篇 |
2022年 | 37篇 |
2021年 | 94篇 |
2020年 | 170篇 |
2019年 | 230篇 |
2018年 | 255篇 |
2017年 | 301篇 |
2016年 | 269篇 |
2015年 | 175篇 |
2014年 | 223篇 |
2013年 | 1398篇 |
2012年 | 220篇 |
2011年 | 219篇 |
2010年 | 183篇 |
2009年 | 176篇 |
2008年 | 212篇 |
2007年 | 193篇 |
2006年 | 162篇 |
2005年 | 176篇 |
2004年 | 149篇 |
2003年 | 151篇 |
2002年 | 141篇 |
2001年 | 113篇 |
2000年 | 115篇 |
1999年 | 70篇 |
1998年 | 67篇 |
1997年 | 88篇 |
1996年 | 90篇 |
1995年 | 62篇 |
1994年 | 76篇 |
1993年 | 66篇 |
1992年 | 80篇 |
1991年 | 64篇 |
1990年 | 65篇 |
1989年 | 53篇 |
1988年 | 61篇 |
1987年 | 45篇 |
1986年 | 55篇 |
1985年 | 62篇 |
1984年 | 60篇 |
1983年 | 60篇 |
1982年 | 47篇 |
1981年 | 40篇 |
1980年 | 42篇 |
1979年 | 45篇 |
1978年 | 48篇 |
1977年 | 29篇 |
1976年 | 26篇 |
1975年 | 19篇 |
1948年 | 18篇 |
排序方式: 共有6920条查询结果,搜索用时 31 毫秒
141.
Modeling of D-STATCOM in distribution systems load flow 总被引:1,自引:0,他引:1
HOSSEINI Mehdi SHAYANFAR Heidar Ali FOTUHI-FIRUZABAD Mahmud 《浙江大学学报(A卷英文版)》2007,8(10):1532-1542
This paper presents modeling of Distribution STATCOM (D-STATCOM) in load flow calculations for the steady- state voltage compensation. An accurate model for D-STATCOM is derived to use in load flow calculations. The rating of this device as well as the direction of required reactive power injection for voltage compensation in the desired value (1 p.u.) is de- rived and discussed analytically and mathematically by the phasor diagram method. Furthermore, an efficient method for node and line identification used in load flow calculations is presented. The validity of the proposed model is examined by using two standard distribution systems consisting of 33 and 69 nodes, respectively. The best location of D-STATCOM for under voltage problem mitigation approach in the distribution networks is determined. The results validate the proposed model for D- STATCOM in large distribution systems. 相似文献
142.
The monkey’s capacity to extract tonal pattern from a sequence of tones was assessed in four subjects that had the benefit of substantial past experience in discriminating, matching, and remembering acoustic stimuli. In Experiment 1, the monkeys failed to transfer their well-established matching behavior to the matching of two structured sequences of tones that differed primarily in tonal pattern, indicating that for them tonal pattern was not a salient feature of the acoustic stimuli. Experiment 2 was an attempt to encourage tonal pattern perception by employing, within a discrimination paradigm, very simple tonal patterns and multiple exemplars of the positive and negative patterns; the transfer design, borrowed from Hulse and Cynx (1985), was a powerful one for revealing tonal pattern perception. Verifying earlier results from our laboratory, there was little in the monkeys’ transfer performance to indicate that they had extracted tonal pattern from the acoustic stimuli. Major discriminative control seemed to be vested in the first tone of each exemplar. This apparent cognitive limitation may be rather general among animals, perhaps reflecting an intimate connection between the capacity for tonal pattern perception and that for acoustically based language. 相似文献
143.
144.
145.
146.
Prof. Dr. Michael Dowling 《科研管理》2004,25(Z1):106-111
通过对美国及德国的十多年研究表明,对于创新及合作网络的投资有利于促进高技术行业企业不断进步和发展.这些高技术行业包括电信、电脑设备及生物工艺的行业.研究表明政府政策在促进竞争及支持地区合作网络发展中起到了极其重要的作用. 相似文献
147.
In this paper, we focus on the potential innovative benefits to corporate venture capital (CVC), i.e. equity investments in entrepreneurial ventures by incumbent firms. We propose that corporate venture capital programs may be instrumental in harvesting innovations from entrepreneurial ventures and thus an important part of a firm's overall innovation strategy. We hypothesize that these programs are especially effective in weak intellectual property (IP) regimes and when the firm has sufficient absorptive capacity. We analyze a large panel of public firms over a 20-year period and find that increases in corporate venture capital investments are associated with subsequent increases in firm patenting. 相似文献
148.
Real options analysis was often recommended as an emerging valuation technique for high-risk investment projects. Former inter-sectoral surveys have drawn an ambivalent picture of real options usage in general. In addition, there is a lack of sector-specific investigations. In the following article the results of an in-depth analysis of collected empirical data regarding the application of this new tool in the pharmaceutical sector is presented by capturing the internal view from the pharmaceutical companies themselves and the external view from the health care departments of financial service firms. R&D stage specific modi of application, reasons for reluctance in the employment of real options and their assumed future prospects are elucidated. 相似文献
149.
150.