首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5731篇
  免费   133篇
  国内免费   177篇
系统科学   85篇
丛书文集   157篇
教育与普及   68篇
理论与方法论   56篇
现状及发展   23篇
综合类   5150篇
自然研究   502篇
  2024年   10篇
  2023年   25篇
  2022年   55篇
  2021年   63篇
  2020年   68篇
  2019年   69篇
  2018年   63篇
  2017年   90篇
  2016年   76篇
  2015年   143篇
  2014年   286篇
  2013年   201篇
  2012年   700篇
  2011年   386篇
  2010年   310篇
  2009年   329篇
  2008年   338篇
  2007年   500篇
  2006年   368篇
  2005年   296篇
  2004年   245篇
  2003年   247篇
  2002年   218篇
  2001年   178篇
  2000年   135篇
  1999年   95篇
  1998年   60篇
  1997年   96篇
  1996年   49篇
  1995年   60篇
  1994年   55篇
  1993年   61篇
  1992年   33篇
  1991年   41篇
  1990年   22篇
  1989年   30篇
  1988年   17篇
  1987年   11篇
  1986年   10篇
  1985年   1篇
  1984年   1篇
排序方式: 共有6041条查询结果,搜索用时 296 毫秒
271.
《Journal of Natural History》2012,46(37-38):2237-2253
Four nominal species of the genus Horatia Bourguignat, 1887 were described by Russian authors from Caucasian caves (H. borutzkii Shadin, 1932, H. birsteini Starobogatov, 1962, H. ljovushkini Starobogatov, 1962 and H. sokolovi Starobogatov, 1962). Hitherto all the species were known from type series (presented by empty shells) only. Examination of newly obtained samples from the caves of South Caucasus has shown that the four species actually do not belong to the genus Horatia due to obvious differences in the morphology of the copulatory organs between H. klecakiana Bourguignat, 1887 (the type species of this genus) and the Caucasian snails. Moreover, statistical analysis of conchological variation has revealed that the species H. birsteini, H. ljovushkini, and H. sokolovi are conspecific. Two genera are described: Pontohoratia (includes P. birsteini and P. smyri sp. nov.) and Motsametia (with the single species M. borutzkii comb. nov.). The two genera can be distinguished on the basis of the structure of their copulatory organs. The distribution and ecology of the Caucasian Horatia-like mollusks are briefly outlined.

http://zoobank.org/urn:lsid:zoobank.org:pub:4EDFB2AE-CB1D-4113-8CC7-3A1BBB46D838  相似文献   
272.
Continuing examination of colonial ascidians in museum collections is revealing further diversity in the family Didemnidae, which abounds in the tropical Indo-West Pacific and around the Australian continent (Kott, 2001). From the present work, it is apparent that much remains to be learnt about this fauna. Of the 45 species discussed in this paper, 16 are new. Larvae are described for the first time for Polysyncraton pedunculatum Kott, 2001 and P. rica Kott, 2001. Amongst the synonymy established in this paper Didemnoides tropicum Sluiter, 1909 is found to be a junior synonym of Lissoclinum patella (Gottschaldt, 1898) and Trididemnum vermiforme Kott, 2001 a junior synonym of T. nobile Kott, 2001. Didemnum nekozita Tokioka, 1967 is found to be a valid species distinct from Polysyncraton cuculliferum (Sluiter, 1909). Prolific replication rates, rapid colony growth, flexibility in growth form and a viviparous habit result in convergence tending to small zooid size, and similar large, increasingly complex colonies found in this family contribute to species diversity around the whole of the Australian continent.  相似文献   
273.
针对去方块效应滤波的边界强度判断争滤渡过程计算量大的情况,本文提出了一种新的去方块效应滤波算法,分别对边界强度判断和穗渡过程的算法进行优化。综合两部分的优化算法,通过实验结果得知,降低的算法复杂度乎均值达到了9.82%、峰值信噪比(PSNR)乎均值也增加了0.119dB。该算法既降低了算法的复杂度又改善了压缩后视频的质量。  相似文献   
274.
Japanese fauna of the cimicomorphan family Microphysidae is documented. Four species of the genus Loricula Curtis are recognised, including three new species herein described from Japan, Loricula miyamotoi, L. nikko and L. yakushima, representing the first discovery of new taxa in the twenty-first century for the Asian Microphysidae. A single known species, L. pilosella Miyamoto, is rediagnosed. A key is provided to distinguish both sexes of the Japanese Loricula species.

http://zoobank.org/urn:lsid:zoobank.org:pub:C01445E4-FD3E-4953-932C-7835FC8BDD16  相似文献   

275.
A long-term survey of tritrophic (plant–aphid–parasitoid) associations in the urban ecosystems of Lleida (Catalonia) and Paris (France) resulted in the detection of associations of two bamboo aphids, Takecallis arundinariae (Essig) and Takecallis taiwanus (Takahashi), respectively, with a new aphid parasitoid species. Trioxys remaudierei Starý & Rakhshani sp. nov. is described and illustrated as a unique parasitoid of Takecallis aphids outside the area of their origin. The new species is easily distinguishable from its congeners in having the ventral prongs of the abdomen fused over two-thirds of their length, then bifurcated towards the tip. The only morphologically similar species is Trioxys betulae (Marshall), which exhibits a clearly different prong shape (and has a different host range, Symydobius Mordvilko and Clethrobius Mordvilko). The new species is compared with allied taxa associated with bamboo aphids. The occurrence of Takecallis taiwanus on bamboo is recorded in France for the first time.

www.zoobank.org/urn:lsid:zoobank.org:pub:ED15BA16-E8A9-4CEA-BDA7-FBAB02FEB091  相似文献   

276.
Three unique mirine plant bugs inhabiting typical subalpine vegetation in the Nepalese Himalayas are documented, with their confirmed plant associations. A new genus and new species, Khumbumiris schwartzi, is diagnosed and described, based on a male specimen collected from Abies spectabilis; two additional new species, Lygocoris laligurans (associated with Rhododendron shrubs) and Phytocoris sagarmathanus (Abies spectabilis), are also described. Images of the habitats and live individuals are also provided. The tribal placement of Khumbumiris is discussed in detail.

http:/zoobank.org/urn:lsid:zoobank.org:pub:54E31614-3262-4BF8-8BBB-F81893AF41D2  相似文献   

277.
The present study summarizes additions to the known fauna of Eucharitidae of Saudi Arabia. Cherianella arabica Gadallah &; Soliman sp. nov. and the male of previously known female Eucharis (Psilogastrellus) albipennis Bou?ek, 1956 are described and illustrated. Three new records are also added to the fauna of Saudi Arabia: Eucharis (Eucharisca) intermedia Ruschka, 1924, Eucharis (Psilogastrellus) acuminata Ruschka, 1924 and Eucharis (Psilogastrellus) punctata Förster, 1859.

http:/zoobank.org/urn:lsid:zoobank.org:pub:F1B1C493-AA83-4696-AF8B-3B3F62C09B41  相似文献   
278.
由于可再生能源开发利用的快速发展,世界各国面临着可再生能源如何接入及充分利用等一系列问题,而智能电网则是应对这些挑战的有效战略措施.智能电网具有强大的功能、显著的综合效益和广阔的发展前景,是世界电网发展的趋势.但是智能电网不是一个单纯的技术问题,它涉及许多重要的基本理念.厘清这些理念对于科学高效地实施智能电网、对于技术创新和产业发展至关重要.为此本文从智能电网的特点、智能电网的总体设想和技术内涵、与智能电网相关的技术、智能电网的近期与远期目标以及在实施智能电网时需要注意的事项等方面阐释了智能电网的基本理念.  相似文献   
279.
The taxonomy of the family Raspailiidae has always been controversial. The family was first included in the order Poecilosclerida. It was then allocated to the order Axinellida and later moved back to Poecilosclerida. Currently with the development of molecular tools it has been assigned to the order Axinellida. In this contribution we describe 10 species from the Mexican Pacific Ocean. Seven of them are new to science: Raspailia (Parasyringella) rubra sp. nov., Raspailia (Raspaxilla) hymani (Dickinson 1945 Dickinson, MG. 1945. Sponges on the Gulf of California. Allan Hancock Pac Exp, 11(1): 1251.  [Google Scholar]), Raspailia (Raspaxilla) hyle (de Laubenfels 1930 de Laubenfels, MW. 1930. The sponges of California. (Abstracts of dissertations for the degree of doctor of philosophy). Stanford Univ Bull, 5(98): 2429.  [Google Scholar]), Aulospongus cerebella (Dickinson 1945 Dickinson, MG. 1945. Sponges on the Gulf of California. Allan Hancock Pac Exp, 11(1): 1251.  [Google Scholar]), Aulospongus californianus sp. nov., Aulospongus aurantiacus sp. nov., Eurypon patriciae sp. nov., Eurypon tylospinosum sp. nov., Eurypon diversicolor sp. nov. and Eurypon brunus sp. nov. We discuss the genus Eurypon and include a table for all the species described worldwide with some comments about this genus. http://www.zoobank.org/urn:lsid:zoobank.org:pub:D462084B-EE9C-4C61-884A-C9DB70003B4A  相似文献   
280.
设计了一种新型HSn70-1黄铜合金,其冷拉拔加工率为55%.应用偏光显微镜、X射线衍射仪、扫描电子显微镜、显微硬度计、万能材料试验机和电化学工作站等设备,研究了不同的退火温度对新型合金显微组织和性能的影响.结果表明:加入少量Sn,Al,P,Ni合金元素构成了新型HSn70-1合金,合金元素以固溶体的形式存在于晶粒内部,其组织为α单相;合金在不同温度下保温2 h,200℃时发生应变时效,300~450℃为再结晶过程,450~550℃为晶粒长大阶段,550~600℃晶粒基本完全长大.随着退火温度的升高,合金的硬度、抗拉强度和屈服强度逐渐降低并趋于缓慢,其伸长率变化相反;合金自腐蚀电流密度、失重率逐渐降低并趋于稳定;开路电位逐渐变大,最后趋于稳定,新型HSn70-1黄铜的耐腐蚀性逐渐变好.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号