全文获取类型
收费全文 | 1293篇 |
免费 | 86篇 |
国内免费 | 1篇 |
专业分类
林业 | 71篇 |
农学 | 28篇 |
基础科学 | 6篇 |
157篇 | |
综合类 | 275篇 |
农作物 | 59篇 |
水产渔业 | 125篇 |
畜牧兽医 | 538篇 |
园艺 | 45篇 |
植物保护 | 76篇 |
出版年
2024年 | 3篇 |
2023年 | 22篇 |
2022年 | 32篇 |
2021年 | 40篇 |
2020年 | 57篇 |
2019年 | 59篇 |
2018年 | 35篇 |
2017年 | 48篇 |
2016年 | 34篇 |
2015年 | 33篇 |
2014年 | 43篇 |
2013年 | 55篇 |
2012年 | 106篇 |
2011年 | 94篇 |
2010年 | 56篇 |
2009年 | 49篇 |
2008年 | 77篇 |
2007年 | 80篇 |
2006年 | 83篇 |
2005年 | 82篇 |
2004年 | 69篇 |
2003年 | 59篇 |
2002年 | 54篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 4篇 |
1996年 | 11篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 11篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有1380条查询结果,搜索用时 15 毫秒
101.
Genetic structure of human populations 总被引:1,自引:0,他引:1
Rosenberg NA Pritchard JK Weber JL Cann HM Kidd KK Zhivotovsky LA Feldman MW 《Science (New York, N.Y.)》2002,298(5602):2381-2385
We studied human population structure using genotypes at 377 autosomal microsatellite loci in 1056 individuals from 52 populations. Within-population differences among individuals account for 93 to 95% of genetic variation; differences among major groups constitute only 3 to 5%. Nevertheless, without using prior information about the origins of individuals, we identified six main genetic clusters, five of which correspond to major geographic regions, and subclusters that often correspond to individual populations. General agreement of genetic and predefined populations suggests that self-reported ancestry can facilitate assessments of epidemiological risks but does not obviate the need to use genetic information in genetic association studies. 相似文献
102.
Weller GR Kysela B Roy R Tonkin LM Scanlan E Della M Devine SK Day JP Wilkinson A d'Adda di Fagagna F Devine KM Bowater RP Jeggo PA Jackson SP Doherty AJ 《Science (New York, N.Y.)》2002,297(5587):1686-1689
In eukaryotic cells, double-strand breaks (DSBs) in DNA are generally repaired by the pathway of homologous recombination or by DNA nonhomologous end joining (NHEJ). Both pathways have been highly conserved throughout eukaryotic evolution, but no equivalent NHEJ system has been identified in prokaryotes. The NHEJ pathway requires a DNA end-binding component called Ku. We have identified bacterial Ku homologs and show that these proteins retain the biochemical characteristics of the eukaryotic Ku heterodimer. Furthermore, we show that bacterial Ku specifically recruits DNA ligase to DNA ends and stimulates DNA ligation. Loss of these proteins leads to hypersensitivity to ionizing radiation in Bacillus subtilis. These data provide evidence that many bacteria possess a DNA DSB repair apparatus that shares many features with the NHEJ system of eukarya and suggest that this DNA repair pathway arose before the prokaryotic and eukaryotic lineages diverged. 相似文献
103.
104.
Wing SL Harrington GJ Smith FA Bloch JI Boyer DM Freeman KH 《Science (New York, N.Y.)》2005,310(5750):993-996
Rapid global warming of 5 degrees to 10 degrees C during the Paleocene-Eocene Thermal Maximum (PETM) coincided with major turnover in vertebrate faunas, but previous studies have found little floral change. Plant fossils discovered in Wyoming, United States, show that PETM floras were a mixture of native and migrant lineages and that plant range shifts were large and rapid (occurring within 10,000 years). Floral composition and leaf shape and size suggest that climate warmed by approximately 5 degrees C during the PETM and that precipitation was low early in the event and increased later. Floral response to warming and/or increased atmospheric CO2 during the PETM was comparable in rate and magnitude to that seen in postglacial floras and to the predicted effects of anthropogenic carbon release and climate change on future vegetation. 相似文献
105.
Callegari A Theulé P Muenter JS Tolchenov RN Zobov NF Polyansky OL Tennyson J Rizzo TR 《Science (New York, N.Y.)》2002,297(5583):993-995
The intensity of water absorption in the region of the solar spectrum plays a dominant role in atmospheric energy balance and hence strongly influences climate. Significant controversy exists over how to model this absorption accurately. We report dipole moment measurements of highly vibrationally excited water, which provide stringent tests of intensities determined by other means. Our measurements and accompanying calculations suggest that the best currently available potential and dipole surfaces do not accurately model intensities in the optical spectrum of water. 相似文献
106.
107.
Seshadri R Adrian L Fouts DE Eisen JA Phillippy AM Methe BA Ward NL Nelson WC Deboy RT Khouri HM Kolonay JF Dodson RJ Daugherty SC Brinkac LM Sullivan SA Madupu R Nelson KE Kang KH Impraim M Tran K Robinson JM Forberger HA Fraser CM Zinder SH Heidelberg JF 《Science (New York, N.Y.)》2005,307(5706):105-108
108.
Thomas Galewski Ben Collen Louise McRae Jonathan Loh Patrick Grillas Michel Gauthier-Clerc Vincent Devictor 《Biological conservation》2011,(5):1392-1399
Biodiversity loss is unevenly distributed in space and time. Species have reached critically low population sizes in some areas, and remain abundant in others. Similarly, some species may benefit from successful conservation plans, while others still experience severe population depletions driven by negative impacts of human activities. Although several indicators have been proposed to measure the fate of biodiversity, they are generally only implemented globally so their relevance for regional assessment is still unclear. Here, we calculated the first regional trend in the Living Planet Index for the Mediterranean wetlands (Med LPI), an indicator that summarizes the fate of global biological diversity based on the temporal trends in abundance of vertebrate populations. The Med LPI was based on 1641 vertebrate populations of 311 species recorded in Mediterranean wetlands from 1970–2008, in 27 different countries. We investigated whether trends in the Med LPI differed between eastern and western Mediterranean countries, which have different socio-economic contexts. Finally, we assessed whether and how the trend in the Med LPI was robust to changes in the number and identity of species considered. We found that, at the Mediterranean scale, the Med LPI increased steeply, which could be taken at first sight, as a general recovery of wetland biodiversity in this biogeographical region. However, we found highly contrasting spatial trends within the Mediterranean region: the average trend was positive for western and negative for eastern countries. Moreover, we showed that depending on the method used to estimate the trend in Med LPI, it can be sensitive to the number and identity of the species considered. We suggest that understanding the regional discrepancies of the trend in biodiversity indicators as well as their robustness to the species represented in the index will enhance progress assessment towards global and regional conservation strategies. 相似文献
109.
110.
Boscan P Monnet E Mama K Twedt DC Congdon J Eickhoff JC Steffey EP 《Veterinary anaesthesia and analgesia》2011,38(3):260-266
Objective A dog model was developed to study visceral pain by stimulating the ovarian ligament. Study design Prospective experimental trial. Animals Twelve 1‐year old female hound dogs weighing 25.7 ± 3.6 kg. Methods Dogs were anesthetized with sevoflurane. The right ovary was accessed via laparoscopy. A suture was placed around the ovarian ligament and exteriorized through the abdominal wall for stimulation. The noxious stimulus consisted of pulling the ovary and ovarian ligament with a force transducer. The response to noxious stimulation was determined using the anesthetic minimum alveolar concentration requirement (MAC) for sevoflurane. The ovarian MAC was compared to the standardized somatic noxious stimulation tail clamp MAC. The results are depicted as mean ± SD and corrected to sea‐level. Results The stimulus–response curve during ovarian stimulation in three dogs was hyperbolic and best represented by a three‐parameter logistic growth curve model. The curve plateaued at 7.12 ± 4.19 N. From the stimulus‐response curve, we chose 6.61 N to test the consistency and repeatability of the model in nine dogs. The ovarian stimulation MAC for sevoflurane in these dogs was 2.16 ± 0.46%. The ovarian stimulation confidence interval and limits are comparable to the results from tail stimulation MAC. The tail stimulation MACs before and after laparoscopy surgery were not different (1.86 ± 0.28% and 1.77 ± 0.38% respectively; p > 0.05) but lower when compared to the ovarian MAC (p < 0.01). The dogs recovered from anesthesia without complications. Conclusions and clinical relevance The ovarian stimulation model is an adequate and repeatable means of producing visceral stimulation to determine MAC. The model may provide a humane mechanism to study the effectiveness of analgesics for acute ovarian pain. 相似文献