全文获取类型
收费全文 | 5116篇 |
免费 | 90篇 |
国内免费 | 203篇 |
专业分类
系统科学 | 54篇 |
丛书文集 | 76篇 |
教育与普及 | 70篇 |
理论与方法论 | 123篇 |
现状及发展 | 18篇 |
综合类 | 4942篇 |
自然研究 | 126篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 48篇 |
2021年 | 50篇 |
2020年 | 67篇 |
2019年 | 68篇 |
2018年 | 48篇 |
2017年 | 52篇 |
2016年 | 47篇 |
2015年 | 98篇 |
2014年 | 281篇 |
2013年 | 157篇 |
2012年 | 430篇 |
2011年 | 321篇 |
2010年 | 255篇 |
2009年 | 318篇 |
2008年 | 308篇 |
2007年 | 410篇 |
2006年 | 395篇 |
2005年 | 320篇 |
2004年 | 238篇 |
2003年 | 293篇 |
2002年 | 181篇 |
2001年 | 184篇 |
2000年 | 145篇 |
1999年 | 162篇 |
1998年 | 87篇 |
1997年 | 78篇 |
1996年 | 56篇 |
1995年 | 41篇 |
1994年 | 67篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 29篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 22篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
排序方式: 共有5409条查询结果,搜索用时 15 毫秒
31.
东北地区城市群组城市流强度研究 总被引:5,自引:0,他引:5
采用城市流强度的定量分析方法,对东北三个城市群组"辽中南"、"吉中"、"哈大齐"的区位熵、外向功能量和城市流强度进行了计算分析,并基于此提出了城市群组的城市流强化与城市整合对策.结果显示,东北三个城市群组的中心城市均可以分为三类--高等、中等、低等:沈阳、大连、长春和哈尔滨以较大的城市流强度值成为各自城市群组联系的高等级中心;鞍山、丹东、营口、四平、大庆、绥化分别成为各自的中等级中心;其他城市成为各自群组的低等级中心.东北地区城市群组实现城市流强化和城市整合发展的对策为:网络化发展以解决结构与体制的矛盾,合理定向以实现各群组内部城市的整合发展,分等策略以提升城市群组内部的城市流强度. 相似文献
32.
Cecilia Ferreyra 《Systemic Practice and Action Research》2006,19(6):577-598
In the last few decades, there has been a trend towards increased stakeholder and public participation in natural resource management in North America. To a certain extent, the rationale for this trend is found in the complexity and uncertainty of environmental issues, which confront us with the coexistance of multiple legitimate values and perspectives in society. Recognizing this “epistemological plurality” has important implications for both policy and science. In this paper, I critically reflect on my experiences as a doctoral student engaged in participatory action research (PAR) with a watershed partnership in Ontario, Canada. In providing this biographical account, I seek to make a contribution to ongoing discussions regarding the nature, challenges and benefits of this methodological approach for academic research, as well as to emerging debates on PAR in the context of environmental governance and “post-normal” approaches to natural resource management.
相似文献
Cecilia FerreyraEmail: |
33.
Nine new species of the subgenus Stegana (Oxyphortica) have been discovered from the Oriental Region: S. (O.) chuanjiangi Zhang and Chen, sp. nov., S (O.) dainuo Wang and Chen, sp. nov., S. (O.) dawa Zhang and Chen, sp. nov., S. (O.) laohlie Zhang and Chen, sp. nov., S. (O.) luchun Wang and Chen, sp. nov., S. (O.) mengwan Wang and Chen, sp. nov., S. (O.) triodonta Cheng and Chen, sp. nov. from southern China; S. (O.) dehiscens Cheng and Chen, sp. nov. and S. (O.) spinosa Cheng and Chen, sp. nov. from eastern Malaysia. One newly recorded species from China: S. (O.) maichouensis Sidorenko is re-described. The DNA sequences of the mitochondrial COI gene with BOLD Process ID and GenBank accession numbers are provided for the above seven new species and five known species from China: S. (O.) acutipenis Xu, Gao and Chen, S. (O.) adentata Toda and Peng, S. (O.) hirtipenis Xu, Gao and Chen, S. (O.) latipenis Xu, Gao and Chen, and S. (O.) maichouensis Sidorenko. Intra- and interspecific pairwise K-2P distances among these species are summarized and the phylogenetic relationships are reconstructed based on the neighbour-joining (NJ) analyses.
www.zoobank.org/urn:lsid:zoobank.org:pub:2FA403F6-5535-40A4-9FD0-ADB9913EDE83. 相似文献
34.
《Journal of Natural History》2012,46(20):1759-1778
The species from northern Vietnam described as Rana fansipani Bourret, is shown to be a synonym of the species from northern Thailand described as Rana aenea Smith, . The male secondary sex characters of this species are described in detail for the first time. Combined with a few other characters, they allow this species to be distinguished from the closely related Rana unculuanus Liu, Hu and Yang, 1960 from southern China. Both species should be placed in a subgenus Chaparana (Chaparana), a member of the tribe Paini of the subfamily Dicroglossinae of the Ranidae. In this study, we propose a new statistical method for testing homogeneity of small samples: this consists of considering the values obtained for each specimen and for each regression factor score as morphometric characteristics of this specimen within the frame of this analysis; these values, or some of them, can be used to compare subgroups of specimens by non‐parametric tests such as the Mann–Whitney U test. 相似文献
35.
《Journal of Natural History》2012,46(37-40):2537-2542
The earliest report on radiolarians from the Arctic Ocean (north of the Arctic Circle) was provided by H. B. Brady (1878). He documented the occurrences of 10 genera from soundings in northern Baffin Bay and north of Greenland, but he did not illustrate any specimens in his report. We have re‐examined Brady's original slide collection, housed at the Natural History Museum, London (NHM), in order to refine his radiolarian identifications to species level. We have identified 11 radiolarian taxa in his slides, but some are definitely more characteristic of tropical oceans rather than high northern latitudes. We conclude that this is most likely due to sample contamination or misidentification of samples. Therefore, the actual occurrence of tropically affiliated radiolarians recorded from the Arctic is uncertain and should be regarded with suspicion. 相似文献
36.
《Journal of Natural History》2012,46(33-34):2097-2104
A new eyeless species, Oodinotrechus liyoubangi n. sp, is described from northern Guangxi. All specimens of this interesting species were collected in three limestone caves in Mulun National Nature Reserve of northern Guangxi, southern China. It is the second species for the genus Oodinotrechus Uéno, 1998, distinguished from the type species O. kishimotoi Uéno, 1998 by its visible scutellum and pronotal structure. Several additional diagnostic characters for the genus and a geographical distribution map for both known species are also provided.http://zoobank.org/urn:lsid:zoobank.org:pub:F82E3C03-0A15-4410-B674-BC8EB95607CE 相似文献
37.
38.
《Journal of Natural History》2012,46(5-6):359-373
The Chinese species of the genus Coccobius Ratzeburg (Hymenoptera: Aphelinidae) are reviewed. Sixteen species, C. abdominis Huang, C. annulicornis Ratzeburg, C. azumai Tachikawa, C. chaoi Huang, C. curtifuniculatus Huang, C. flaviceps (Girault & Dodd), C. flavicornis Compere & Annecke, C. fulvus (Compere & Annecke), C. furviflagellatus Huang, C. furvus Huang, C. languidus Huang, C. longialatus Huang, C. longifuniculatus Huang, C. maculatus Huang, C. wuyiensis Huang, and one new species, Coccobius albiscutellum Wang and Huang sp.nov., are treated. A key is provided for the recognition of the females of all Chinese species of Coccobius, and notes are given on their use in biological control of scale insect pests. http://www.zoobank.org/urn:lsid:zoobank.org:pub:F510059B-F176-46BA-B7B5-8252B06BE91F 相似文献
39.
《Journal of Natural History》2012,46(33-34):2083-2096
Two new species of the tetrigid genus Eucriotettix Hebard from China, namely Eucriotettix tridentatus sp. nov. and Eucriotettix torulisinotus sp. nov. are described. The distribution and an updated key to the species of the genus from China is given.http://zoobank.org/urn:lsid:zoobank.org:pub:E7E5EA3B-92ED-450F-9D1C-74569148D4F8 相似文献
40.
《Journal of Natural History》2012,46(17):2183-2209
This paper reviews the Chinese species of Platyplectrus Ferrière. Twelve valid species are recognized from mainland China and a key to species is provided. Trichoplectrus Erdös (1951) is newly synonymized with Metaplectrus Ferrière (1941) and three new combinations are proposed: Metaplectrus szepligetii (Erdös) from Platyplectrus, Platyplectrus bussy (Crawford) from Euplectrus and P. politus (Lin) from Metaplectrus. Four species of Platyplectrus were known previously from China: P. politus (Lin), P. odontogaster (Lin), P. papillata Lin and P. medius Zhu and Huang. Six species, P. bussyi (Crawford), P. laeviscuta (Thomson), P. natadae Ferrière, P. orthocraspedae Ferrière, P. pannonica (Erdös) and P. viridiceps (Ferrière) are newly recorded from China and re-described. Five new species, P. pulcher, P. setulosus, P. peculiaris, P. obtusiclavatus and P. variflagellum are described and compared with related species. Several species are also newly recorded from other regions: P. orthocraspedae Ferrière from the Afrotropical region, P. bussyi (Crawford) and P. laeviscuta (Thomson) from the Australian/Pacific region, P. laeviscuta (Thomson) from the Oriental region and P. viridiceps from the Palearctic region. 相似文献