全文获取类型
收费全文 | 3945篇 |
免费 | 105篇 |
国内免费 | 176篇 |
专业分类
系统科学 | 115篇 |
丛书文集 | 129篇 |
教育与普及 | 170篇 |
理论与方法论 | 17篇 |
现状及发展 | 26篇 |
综合类 | 3699篇 |
自然研究 | 70篇 |
出版年
2024年 | 8篇 |
2023年 | 20篇 |
2022年 | 48篇 |
2021年 | 44篇 |
2020年 | 39篇 |
2019年 | 29篇 |
2018年 | 24篇 |
2017年 | 43篇 |
2016年 | 56篇 |
2015年 | 103篇 |
2014年 | 202篇 |
2013年 | 155篇 |
2012年 | 293篇 |
2011年 | 354篇 |
2010年 | 234篇 |
2009年 | 277篇 |
2008年 | 240篇 |
2007年 | 296篇 |
2006年 | 344篇 |
2005年 | 283篇 |
2004年 | 238篇 |
2003年 | 190篇 |
2002年 | 160篇 |
2001年 | 121篇 |
2000年 | 89篇 |
1999年 | 51篇 |
1998年 | 54篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 34篇 |
1994年 | 25篇 |
1993年 | 31篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有4226条查询结果,搜索用时 453 毫秒
161.
论创建节水型城市的建筑节水措施 总被引:1,自引:0,他引:1
邓洁 《湖南城市学院学报(自然科学版)》2007,16(2):25-27
分析了水资源的现状和建筑节水对建设节水型城市的意义,并从推广优质给水管材、节水型卫生器具、采取减压措施等方面,提出了建筑节水等措施. 相似文献
162.
The South Korean species of the genus Exochus are revised. Ten new species, Exochus acostulatus Lee & Choi, sp. nov., Exochus adentatus Lee & Choi, sp. nov., Exochus areolaris Lee & Choi, sp. nov., Exochus carinalis Lee & Choi, sp. nov., Exochus dentisternum Lee & Choi, sp. nov., Exochus depressus Lee & Choi, sp. nov., Exochus nigritulus Lee & Choi sp. nov., Exochus occipitalis Lee & Choi, sp. nov., Exochus orbitalis Lee & Choi, sp. nov. and Exochus propodealis Lee & Choi, sp. nov., are described. Also, 21 species of this genus are reviewed and newly recorded from South Korea, with diagnoses provided. A key to the South Korean species of Exochus and illustrations of external characters are provided.
http://zoobank.org/urn:lsid:zoobank.org:pub:B28700A7-9CA7-4AE7-9816-9C8F4CD46160 相似文献
163.
164.
文章针对广珠城际轨道交通工程施工中450 t提运架设备箱梁架设施工方法、工艺及技术保证措施展开论述。 相似文献
165.
针对员工在应聘、聘用以及解聘后都有可能面临各种隐私泄漏问题,总结目前员工隐私泄露的各种途径,以及隐私泄露对员工和企业所带来的危害,并参考国内外该领域知名学者之前的研究,从四个角度提出员工隐私保护对策. 相似文献
166.
Forecasting VaR models under Different Volatility Processes and Distributions of Return Innovations 下载免费PDF全文
This paper provides clear‐cut evidence that the out‐of‐sample VaR (value‐at‐risk) forecasting performance of alternative parametric volatility models, like EGARCH (exponential general autoregressive conditional heteroskedasticity) or GARCH, and Markov regime‐switching models, can be considerably improved if they are combined with skewed distributions of asset return innovations. The performance of these models is found to be similar to that of the EVT (extreme value theory) approach. The performance of the latter approach can also be improved if asset return innovations are assumed to be skewed distributed. The performance of the Markov regime‐switching model is considerably improved if this model allows for EGARCH effects, for all different volatility regimes considered. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
167.
5G移动通信发展趋势与若干关键技术 总被引:4,自引:0,他引:4
第5代移动通信系统(5G)是面向2020年之后的新一代移动通信系统,其技术发展尚处于探索阶段.结合国内外移动通信发展的最新趋势,本文对5G移动通信发展的基本需求、技术特点与可能发展途径进行了展望,并分无线传输和无线网络两个部分,重点论述了富有发展前景的7项5G移动通信关键技术,包括大规模天线阵列、基于滤波器组的多载波技术、全双工复用、超密集网络、自组织网络、软件定义网络及内容分发网络.本文还概括性地介绍了国内5G移动通信的相关研发活动及其近期发展目标. 相似文献
168.
《Journal of Natural History》2012,46(21-24):1301-1311
The Australian members of the subgenus, Sinella (Coecobrya) Yosii, are revised. A new species from Western Australia, Queensland, and the Northern Territory, Sinella (Coecobrya) tropicalis sp. nov., is described, Sinella (Coecobrya) tenebricosa Folsom, 1902 is recorded from Australia for the first time, and new records of Sinella (Coecobrya) communis Chen and Christiansen, 1997 are documented. Sinella (Coecobrya) caeca Schött, 1896 is considered a dubious record from Australia. A key is provided to the three known Australian species and a summary given of all dorsal and lateral chaetal patterns found on the fourth abdominal segment of subgenera Sinella Brook, 1882 and Coecobrya Yosii, 1956. The biogeography of the subgenus is described. 相似文献
169.
《Journal of Natural History》2012,46(9):1259-1290
Monocotyle is revised and three new species are proposed. Monocotyle corali sp. nov. is described from the gills of the cowtail ray, Pastinachus sephen (Forsskål) (Dasyatididae), and is distinguished from other members of Monocotyle by the large hamuli with a distinct tail on the guard and by the male copulatory organ with three loops and a wing-like accessory piece at the distal end. Monocotyle jordani sp. nov. from the gills of the southern eagle ray, Myliobatis australis Macleay (Myliobatididae), is differentiated by the male copulatory organ with a large, unique accessory piece. Monocotyle youngi sp. nov., from the gills of Himantura fai Jordan and Seale (Dasyatididae), has marginal haptoral papillae armed with 12 to 15 sclerites, a male copulatory organ with 20 loops and a unique accessory piece at the distal end. Monocotyle trygoni (Venkatanarsaiah and Kulkarni, 1980) Timofeeva, 1985 is synonymized with M. spirophallus Tripathi, 1959 and M. spirophallus is redescribed fully. There are now 16 valid species of Monocotyle and a key to species is presented. Additional data and illustrations of important taxonomic characters are provided. The developmental sequence of the male copulatory organ of M. spiremae Measures, Beverley-Burton and Williams, 1990 from juvenile to adult is described. The anterior glands and the type of secretion they contain are also documented for several species of Monocotyle. 相似文献
170.