全文获取类型
收费全文 | 780篇 |
免费 | 34篇 |
国内免费 | 4篇 |
专业分类
林业 | 34篇 |
农学 | 14篇 |
基础科学 | 1篇 |
172篇 | |
综合类 | 96篇 |
农作物 | 28篇 |
水产渔业 | 41篇 |
畜牧兽医 | 371篇 |
园艺 | 23篇 |
植物保护 | 38篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 30篇 |
2019年 | 28篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 15篇 |
2014年 | 24篇 |
2013年 | 37篇 |
2012年 | 50篇 |
2011年 | 60篇 |
2010年 | 26篇 |
2009年 | 36篇 |
2008年 | 45篇 |
2007年 | 52篇 |
2006年 | 44篇 |
2005年 | 53篇 |
2004年 | 41篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有818条查询结果,搜索用时 31 毫秒
41.
Submarine thermal sprirngs on the galapagos rift 总被引:2,自引:0,他引:2
Corliss JB Dymond J Gordon LI Edmond JM von Herzen RP Ballard RD Green K Williams D Bainbridge A Crane K van Andel TH 《Science (New York, N.Y.)》1979,203(4385):1073-1083
The submarine hydrothermal activity on and near the Galápagos Rift has been explored with the aid of the deep submersible Alvin. Analyses of water samples from hydrothermal vents reveal that hydrothermal activity provides significant or dominant sources and sinks for several components of seawater; studies of conductive and convective heat transfer suggest that two-thirds of the heat lost from new oceanic lithosphere at the Galápagos Rift in the first million years may be vented from thermal springs, predominantly along the axial ridge within the rift valley. The vent areas are populated by animal communities. They appear to utilize chemosynthesis by sulfur-oxidizing bacteria to derive their entire energy supply from reactions between the seawater and the rocks at high temperatures, rather than photosynthesis. 相似文献
42.
43.
44.
El-Sayed NM Myler PJ Blandin G Berriman M Crabtree J Aggarwal G Caler E Renauld H Worthey EA Hertz-Fowler C Ghedin E Peacock C Bartholomeu DC Haas BJ Tran AN Wortman JR Alsmark UC Angiuoli S Anupama A Badger J Bringaud F Cadag E Carlton JM Cerqueira GC Creasy T Delcher AL Djikeng A Embley TM Hauser C Ivens AC Kummerfeld SK Pereira-Leal JB Nilsson D Peterson J Salzberg SL Shallom J Silva JC Sundaram J Westenberger S White O Melville SE Donelson JE Andersson B Stuart KD Hall N 《Science (New York, N.Y.)》2005,309(5733):404-409
A comparison of gene content and genome architecture of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major, three related pathogens with different life cycles and disease pathology, revealed a conserved core proteome of about 6200 genes in large syntenic polycistronic gene clusters. Many species-specific genes, especially large surface antigen families, occur at nonsyntenic chromosome-internal and subtelomeric regions. Retroelements, structural RNAs, and gene family expansion are often associated with syntenic discontinuities that-along with gene divergence, acquisition and loss, and rearrangement within the syntenic regions-have shaped the genomes of each parasite. Contrary to recent reports, our analyses reveal no evidence that these species are descended from an ancestor that contained a photosynthetic endosymbiont. 相似文献
45.
In higher eukaryotes, the S phase and M phase of the cell cycle are triggered by different cyclin-dependent kinases (CDKs). For example, in frog egg extracts, Cdk1-cyclin B catalyzes entry into mitosis but cannot trigger DNA replication. Two hypotheses can explain this observation: Either Cdk1-cyclin B fails to recognize the key substrates of its S-phase-promoting counterparts, or its activity is somehow regulated to prevent it from activating DNA synthesis. Here, we show that Cdk1-cyclin B1 has cryptic S-phase-promoting abilities that can be unmasked by relocating it from the cytoplasm to the nucleus and moderately stimulating its activity. Subcellular localization of vertebrate CDKs and the control of their activity are thus critical factors for determining their specificity. 相似文献
46.
Houghton J Stoicov C Nomura S Rogers AB Carlson J Li H Cai X Fox JG Goldenring JR Wang TC 《Science (New York, N.Y.)》2004,306(5701):1568-1571
Epithelial cancers are believed to originate from transformation of tissue stem cells. However, bone marrow-derived cells (BMDCs), which are frequently recruited to sites of tissue injury and inflammation, might also represent a potential source of malignancy. We show that although acute injury, acute inflammation, or transient parietal cell loss within the stomach do not lead to BMDC recruitment, chronic infection of C57BL/6 mice with Helicobacter, a known carcinogen, induces repopulation of the stomach with BMDCs. Subsequently, these cells progress through metaplasia and dysplasia to intraepithelial cancer. These findings suggest that epithelial cancers can originate from marrow-derived sources and thus have broad implications for the multistep model of cancer progression. 相似文献
47.
48.
Robert Brus Dalibor Ballian Peter Zhelev Marija Pandža Martin Bobinac Jane Acevski Yannis Raftoyannis Kristjan Jarni 《European Journal of Forest Research》2011,130(4):657-670
We examined leaf and mature seed cone variation of Juniperus oxycedrus L. subsp. oxycedrus in 12 natural populations across the species range in the Balkan Peninsula. We measured 10 morphological traits from a minimum
of 100 leaves in each of 190 individuals, and two morphological traits from 30–50 seed cones in each of 94 females. High phenotypic
variation was found, but no geographical structure or cline across populations was detected for any of the studied traits.
Mean values of comparable leaf and cone morphological traits did not differ considerably from values reported elsewhere. Gender
dimorphism in leaf morphology was detected, but it was not distributed uniformly throughout the studied area. An ANOVA model
with both nested and crossed effects revealed that the largest proportion of the total variation was, as expected, contained
within populations, partly as among-tree variation (18–47%, depending on the trait) and partly as within-tree variation (33–77%),
which was remarkably high. Gender dimorphism explained only 0–3% of the total variation. Differences among populations (2–23%)
were significant for all studied traits except one; however, PCA showed no clear geographical differentiation of the studied
populations. This lack of phylogeographical structure may be the consequence of repeatedly occurring colonisation-retreat
scenarios and suggests the existence of several small refugial populations scattered over a large part of the Balkan Peninsula
in the Pleistocene. Further research including palaeobotanical and molecular genetic studies will be needed to better understand
the forces that shaped current variation patterns of J. oxycedrus L. subsp. oxycedrus in the Balkan Peninsula. 相似文献
49.
Monique L. Sakalidis Jane D. Ray Vincent Lanoiselet Giles E. StJ. Hardy Treena I. Burgess 《European journal of plant pathology / European Foundation for Plant Pathology》2011,130(3):379-391
Members of the Botryosphaeriaceae, in particular Lasiodiplodia theobromae, Neofusicoccum parvum, N. mangiferum and Botryosphaeria dothidea, commonly cause stem cankers, dieback and stem end rot of mangoes worldwide. In the current study, eight taxa of Botryosphaeriaceae
were identified as canker-associated fungi, pathogens, potential pathogens or endophytes of mangoes in the Kimberley, Australia.
These include Neoscytalidium novaehollandiae, Ne. dimidiatum, Pseudofusicoccum adansoniae, P. ardesiacum, P. kimberleyense, Lasiodiplodia sp. 1, L. iraniensis and L. pseudotheobromae. The pathogenicity of a selection of these species toward fruit and branches was tested. All were pathogenic to mango in comparison
to the control, with Lasiodiplodia spp. being the most pathogenic. It appears that either geographic isolation or the unique growing conditions in the Kimberley
may have provided an effective barrier to the acquisition or establishment of known botryosphaeriaceous pathogens. Wounds
caused by mechanical pruning may provide an entry point for infection, whilst severe pruning may increase plant stress. 相似文献
50.
For population viability analysis of endangered orchid populations, it is crucial to disentangle the effects of weather and management from intrinsic orchid dynamics. When doing this, typically several months’ average temperatures and/or sums of precipitations are compared with some characteristics of plant performance. Here we tested, whether short averaging intervals (1-2 weeks) are more closely correlated with orchid performance. We used 5 years of data from five Dactylorhiza majalis populations, and have shown that the improvement of prediction by shortening the interval over which the temperatures are averaged or precipitation summed, even if detectable, is only weak and not significant. This, however, may be due to low weather variability during the study. Regarding the second aspect, the effect of management (presence or absence of mowing), we have found that leaf area of D. majalis at the regularly mown site was larger than that at the sites which were mown only once in 2 years, but we did not detect a significant effect of the absence of mowing on the incidence of flowering. Mowing can affect orchid performance in two ways: by reduced shading of orchids and by reducing competition with other species. Therefore, we have determined the co-occurring species associated with presence or absence of mowing and found that shading significantly affected the length of the flower stalk, the ratio of leaf width to leaf length at the end of the season, but did not affect seed weight and probability of flowering the next year. We conclude that the most appropriate management for D. majalis is mowing at least once a year, ideally at the end of June/beginning of July, after its fruiting. 相似文献