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   2166篇
  免费   120篇
  国内免费   237篇
  2024年   17篇
  2023年   64篇
  2022年   84篇
  2021年   64篇
  2020年   83篇
  2019年   155篇
  2018年   99篇
  2017年   80篇
  2016年   74篇
  2015年   52篇
  2014年   173篇
  2013年   191篇
  2012年   130篇
  2011年   108篇
  2010年   78篇
  2009年   96篇
  2008年   103篇
  2007年   98篇
  2006年   87篇
  2005年   70篇
  2004年   50篇
  2003年   43篇
  2002年   21篇
  2001年   29篇
  2000年   26篇
  1999年   29篇
  1998年   23篇
  1997年   7篇
  1996年   5篇
  1995年   8篇
  1994年   10篇
  1993年   6篇
  1991年   5篇
  1989年   4篇
  1988年   6篇
  1987年   4篇
  1986年   4篇
  1985年   16篇
  1984年   41篇
  1983年   42篇
  1982年   34篇
  1981年   27篇
  1980年   31篇
  1979年   31篇
  1978年   19篇
  1977年   23篇
  1976年   22篇
  1975年   16篇
  1974年   17篇
  1973年   10篇
排序方式: 共有2523条查询结果,搜索用时 450 毫秒
121.
红外相机监测是了解野生动物多样性现状、动态变化和面临威胁的重要手段。本研究采用网格抽样调查法, 在贵州梵净山国家级自然保护区内选取2个监测样区共40个监测位点布设红外相机, 对区内兽类和鸟类物种进行监测调查。2017年4月至2018年12月间, 红外相机累积监测14,808个相机工作日, 共收集有效照片14,119张, 独立有效物种照片3,199张。共鉴定野生动物9目22科61种, 其中兽类26种, 隶属于4目12科; 鸟类35种, 隶属于5目10科。记录到国家I级重点保护野生动物2种: 黔金丝猴(Rhinopithecus brelichi)和白颈长尾雉(Syrmaticus ellioti), 国家II级重点保护野生动物9种; 被IUCN红色名录评估为濒危(EN)的1种、易危(VU)的5种、近危(NT)的8种。物种的相对多度指数(relative abundance index, RAI)分析结果显示, 藏酋猴(Macaca thibetana, RAI = 28.23)、毛冠鹿(Elaphodus cephalophus, RAI = 15.46)、野猪(Sus scrofa, RAI = 11.82)、小麂(Muntiacus reevesi, RAI = 9.05)、黔金丝猴(RAI = 7.70)为相对多度最高的5种兽类; 紫啸鸫(Myophonus insularis, RAI = 10.33)、红腹角雉(Tragopan temminckii, RAI = 9.59)、红腹锦鸡(Chrysolophus pictus, RAI = 6.96)、白颈长尾雉(RAI = 3.71)、勺鸡(Pucrasia macrolopha, RAI = 1.55)为相对多度最高的5种鸟类。另外, 红外相机还监测到较多的家畜活动(RAI = 11.14)和人为活动(RAI = 12.90), 保护区管理部门仍需采取相应管理措施, 进一步提高周边居民的保护意识, 促进保护区与社区的协调发展。  相似文献   
122.
2017年5-9月,采用红外相机调查祁连山国家公园(青海片区)兽类和鸟类多样性。共布设154个相机位点,累计12 096个相机日,共获得9 675张有效独立照片,鉴定23种野生兽类和50种野生鸟类物种,分别隶属5目10科和9目19科,另记录到家畜5种。相对多度指数最高的前五种野生动物依次为岩羊(Pseudois rnayaur)(18.23)、喜马拉雅旱獭(Marmota himalayarea)(15.98)、灰尾兔(Lepus oiostolus)(5.06)、红嘴山鸦(Pyrrhocorax pyrrhocorax)(3.39)、高原鼠兔(Ochotona curzoniae)(2.49)。中国特有物种有荒漠猫(Felis bieti)、白唇鹿(Ceryus albirostris)、西藏马鹿(Cervus wallichii)、藏原羚(Procapra picticaudata)、红耳鼠兔(Ochotana erythrotis)、蓝马鸡(Crossoptilon auritum)和地山雀(Pseudopocdoces humilis)7种。国家Ⅰ级重点保护野生动物有4种,国家Ⅱ级重点保护野生动物有20种;被中国脊椎动物红色名录评估为极危、濒危、易危、近危的物种分别有1种、6种、3种、14种。红外相机调查结果反映出祁连山国家公园(青海片区)兽类和鸟类现状,为祁连山国家公园体制试点生物多样性保护和管理提供基础数据。  相似文献   
123.
以国家公园为主体的自然保护地体系立法思考   总被引:2,自引:0,他引:2  
实现十九大报告提出的建立以国家公园为主体的自然保护地体系的改革目标需要法治保障。建设自然保护地体系涉及的不同生态系统和多个管理部门、多方利益主体, 是一个巨大的复杂系统, 需要进行整体性、系统性的立法研究。目前, 国家正在推进国家公园体制改革并已将《国家公园法》列入十三届全国人大常委会立法计划。更需要我们从自然保护地立法体系建设的高度, 正确处理《国家公园法》与未来可能制定的《自然保护地法》的关系, 在《国家公园法》制定过程中为今后出台《自然保护地法》预留空间, 并建立相应的衔接机制, 统筹谋划并协同推进国家公园法与自然保护地立法。  相似文献   
124.
《Fungal biology》2022,126(2):101-112
Living organisms can induce deterioration of cultural heritage. Conservation strategies aimed at avoiding damage and aiding restoration, require a comprehensive knowledge of structure, chemical composition, and identity of microorganisms that colonize artworks. The National Theatre of Costa Rica (NTCR), a building with historic architecture, houses several oil paintings from the nineteenth century, some with visible signs of biodeterioration. One of them is a large format painting on canvas called La Danza (size 9.83 × 5.13 m) from 1896 by Italian artist Vespasiano Bignami, located on the ceiling of the theatre's foyer. In the present study, we undertook a physicochemical and microbiological study of La Danza to identify the fungal species that inhabit the artwork and are responsible for the damage observed. Scanning electron microscope (SEM) images and attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectroscopic data indicated that the canvas material is made of hemp, the binder contains linseed oil and lead white, and a material in the inner face of the canvas is mainly composed of beeswax. Fungi were isolated onto potato dextrose agar (PDA) and carboxymethyl cellulose (CMC) agar, and then identified with molecular (BTUB, nrDNA ITS, and TEF1 regions) and morphological methods. Four isolates belonging to the genera Myxospora, Pestalotiopsis, Ustilago, and aff. Penicillium, were obtained. Qualitative tests showed cellulolytic activity in all isolated specimens, confirming their possible role in biodeterioration of the canvas. Phylogenetic and morphological data revealed a new species of Myxospora we name here as Myxospora theatro sp. nov., in reference to NTCR. The findings broaden the knowledge of fungi capable of inhabiting and damaging cultural heritage. They also provide valuable information to develop strategies for conservation and restoration of oil paintings on canvas.  相似文献   
125.
We evaluated the existence of trophic guild structure, considering seasonal and annual variation, in two terrestrial carnivore assemblages: one from Santa Cruz province (Argentinean Patagonia, composed by six carnivore species), and the other from Doñana National Park (SW Spain, composed by five carnivore species). To identify trophic guilds, we first studied seasonal and annual diets of predators, calculated trophic overlap among species pairs, and then constructed overlap matrices (similarity matrices). We determined guild membership objectively by entering the similarity matrices into the clustering technique unweighted pair-group method with arithmetic averaging. Carnivores from both assemblages were grouped, respectively, into four feeding guilds. Lagomorphs and rodents promoted the formation of two feeding guilds in both study sites, although the taxonomic composition of predator species that composed them was different. The ungulates-edentates feeding guild was only present at Santa Cruz, whereas the birds and reptiles feeding guild was only present at Doñana. Invertebrates and fruits were the base for the formation of a guild composed by species of the same taxonomic origin both in Santa Cruz and Doñana. Guild structure of Santa Cruz and Doñana assemblages did not exhibit seasonal or annual variation, although the specific guild composition changed over the two studied periods for both assemblages. This structure probably responded to discontinuities in resource spectra in Santa Cruz and fluctuations in rabbit abundance in Doñana. Our results support the hypothesis that establishes that guilds are originated by opportunistic convergence of species on abundant and energetically rewarding resources.  相似文献   
126.
After the first report of Brucella melitensis infection from a 7-year-old alpine ibex (Capra ibex) buck living in Gran Paradiso National Park (GPNP), further studies demonstrated the presence of the infection in ibex and chamois. Considering that livestock herds keep on sharing pastures with more than 3,500 ibex and 9,000 chamois in the park, our aim was to demonstrate under controlled conditions the possibility of Brucella infection passing from wild ruminants to livestock. A 7-year-old male alpine ibex with clinical signs of brucellosis and serologically positive was released in a 5,000 m2 enclosure together with five goats and two sheep rams. Due to poor condition, ibex was suppressed at day 40, domestic ruminants stayed into the enclosure potentially contaminated by ibex for further 38 days. During this period, we had monitored our animals taking blood from domestic ruminants every 15 days and tested the serum to Rose Bengal agglutination test and Complement Fixation test. Domestic animals tested negative at serology at all sampling time and at isolation, while B. melitensis biovar 3 was isolated from ibex tissues. Our data show that transmission of infection from ibex to livestock is not easy. After 40 days of strict cohabitation and 38 days of permanence in an area where an infected ibex lives, no one of the domestic animals contracted infection. In spite of the limitation of our field trial, we have demonstrated that long direct and indirect contact between alpine ibex and domestic animals will not easily lead to an infection of the latter. Further investigations are needed to confirm our results and evaluate the effective risk of B. melitensis transmission from alpine ibex to livestock.  相似文献   
127.
谢凡  鲁碧耕  油志远  李刚  张惠  杨孔  杨楠 《四川动物》2022,41(1):107-120
鸟类多样性研究是国家级自然保护区的重要工作。2020年6月—2021年5月,采用样线法和样点法,调查了四川格西沟国家级自然保护区的鸟类多样性。结果显示:结合历史文献资料,保护区共有鸟类19目56科249种。其中,国家一级重点保护动物10种,国家二级重点保护动物35种,中国特有种11种。居留型以留鸟为主,共156种(62.65%),其次是夏候鸟60种(24.10%)、旅鸟19种(7.63%)、冬候鸟14种(5.62%)。区系组成以东洋界为主,共116种(46.59%),古北界103种(41.37%)、广布种30种(12.04%)。各生态系统中森林和灌丛生态系统Shannon-Wiener指数最高,其他生态系统最低,森林和灌丛生态系统的Sorenson相似性指数最高;夏、秋季的Shannon-Wiener指数和Pielou均匀度指数最高,冬季最低。建议保护区建立长期监测体系,并持续开展鸟类保护宣传活动,加大巡护和管控力度,降低保护区内的人为干扰,同时注重鸟类所利用栖息地的保护。  相似文献   
128.
该文系统回顾了华南国家植物园近百年来几个关键时期的历史发展、主要成就和社会贡献,从国家、中国科学院、地方政府三个层面分析了华南国家植物园率先设立的缘由,展望了华南国家植物园的未来发展前景,提出了我国国家植物园体系建设的思考和建议。  相似文献   
129.
武夷山国家公园是中国正式设立的第一批国家公园之一, 其所处的武夷山脉在动物地理区划上是东洋区南亚亚区华南小区、东洋区东亚亚区华东小区的分界线。为查明武夷山国家公园及其周边的鱼类区系和多样性现状, 本研究在梳理历史研究资料的基础上, 对调查区域内的崇阳溪、麻阳溪、九曲溪、北溪和铅山河5条河流进行了实地调查, 从物种多样性和功能多样性两个层面对武夷山国家公园及其周边地区鱼类多样性水平进行了分析。结合历史数据, 武夷山国家公园及其周边地区分布的土著鱼类为113种, 隶属于5目17科61属, 其中以鲤形目鱼类为主, 共82种, 占物种总数的72.6%, 其次为鲈形目, 共16种, 占总数的14.2%。受威胁鱼类3种, 包括2种国家II级野生水生保护动物, 即胭脂鱼(Myxocyprinus asiaticus)和花鳗鲡(Anguilla marmorata)。武夷山国家公园的第一优势种为拟腹吸鳅(Pseudogastromyzon fasciatus), 与其周边地区以点纹银鮈(Squalidus wolterstorffi)为第一优势种不同。多样性分析结果显示武夷山国家公园的鱼类物种丰富度指数、多样性指数和均匀度指数均低于周边区域。通过比较调查区域内5条河流的鱼类多样性, 麻阳溪鱼类多样性显著高于其他河流, 铅山河的多样性显著低于其他河流。位于国家公园内的九曲溪鱼类多样性比周边地区的崇阳溪要低。鱼类功能多样性结果显示, 武夷山国家公园的功能丰富度指数显著低于周边地区, 功能离散度和功能均匀度均高于周边地区; 在河流方面, 北溪的功能丰富度显著高于其他河流, 崇阳溪的功能均匀度较高, 九曲溪的功能离散度显著高于其他河流。综合鱼类多样性分析结果, 武夷山国家公园鱼类多样性低主要是自然生境异质性低和人为活动共同作用形成, 而周边地区的河流受到捕捞、水利设施、水质污染等因素的影响。这些干扰改变了鱼类的群落结构, 使得鱼类多样性降低。因此应该加强对该区域的鱼类多样性保护工作, 未来还应进一步开展针对公园内鱼类多样性的调查工作。  相似文献   
130.
Amphibian species are known to carry endoparasitic mites. The infestation probability, prevalence, and intensity of mites vary among species and habitats. Mites of the genus Endotrombicula are known to infest African and Malagasy frogs. However, the factors leading to an increase in the probability of mite infestation are unknown. To test for inter‐ and intraspecific differences in infestation probability and its potential correlation with sex, age, habitat preferences, and/or season within a species‐rich West African leaf‐litter frog assemblage, we examined more than 6,800 individual frogs for the presence of mites throughout two independent time increments, 1999–2000 and 2016–2017. We found only members of the leaf‐litter frog genus Phyrnobatrachus to be infested, while other syntopically occurring genera were not affected. Within Phrynobatrachus, only four out of eight species were infested. Mites prevalence differed between species (highest P. phyllophilus, followed by P. alleni), sex (males higher than females in P. alleni and P. phyllophilus), and age (adults higher than juveniles in P. alleni), as well as season (more mites during wet than dry season in P. phyllophilus). The prevalence of mite infestation did not influence mate choice in P. alleni. Increased humidity showed a clear positive effect on infestation prevalence. We also detected a marked decrease in the prevalence of mites from 1999–2000 to 2016–2017, a period during which climatological changes within the study area have been reported with a tendency toward drier conditions. The decrease in mite infestation prevalence over time might be a signal of increasingly drier conditions.  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