全文获取类型
收费全文 | 26982篇 |
免费 | 748篇 |
专业分类
林业 | 4393篇 |
农学 | 1654篇 |
基础科学 | 181篇 |
4897篇 | |
综合类 | 1090篇 |
农作物 | 2479篇 |
水产渔业 | 2729篇 |
畜牧兽医 | 6188篇 |
园艺 | 1245篇 |
植物保护 | 2874篇 |
出版年
2023年 | 82篇 |
2022年 | 116篇 |
2021年 | 245篇 |
2020年 | 238篇 |
2019年 | 167篇 |
2018年 | 3055篇 |
2017年 | 3028篇 |
2016年 | 1614篇 |
2015年 | 426篇 |
2014年 | 481篇 |
2013年 | 645篇 |
2012年 | 1525篇 |
2011年 | 2733篇 |
2010年 | 2395篇 |
2009年 | 1550篇 |
2008年 | 1820篇 |
2007年 | 2043篇 |
2006年 | 447篇 |
2005年 | 554篇 |
2004年 | 470篇 |
2003年 | 513篇 |
2002年 | 363篇 |
2001年 | 263篇 |
2000年 | 287篇 |
1999年 | 219篇 |
1998年 | 51篇 |
1996年 | 50篇 |
1993年 | 38篇 |
1992年 | 141篇 |
1991年 | 115篇 |
1990年 | 111篇 |
1989年 | 132篇 |
1988年 | 132篇 |
1987年 | 124篇 |
1986年 | 115篇 |
1985年 | 103篇 |
1984年 | 81篇 |
1983年 | 75篇 |
1982年 | 45篇 |
1981年 | 57篇 |
1980年 | 49篇 |
1979年 | 103篇 |
1978年 | 93篇 |
1977年 | 87篇 |
1976年 | 53篇 |
1975年 | 47篇 |
1974年 | 99篇 |
1973年 | 70篇 |
1972年 | 94篇 |
1971年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Insulin and IGF-I receptors and tyrosine kinase activity in carp ovaries: changes with reproductive cycle 总被引:2,自引:0,他引:2
J. Gutiérrez M. Párrizas N. Carneiro J. L. Maestro M. A. Maestro J. Planas 《Fish physiology and biochemistry》1993,11(1-6):247-254
Insulin and insulin-like growth factor I (IGF-I) receptors from carp ovaries were semipurified with wheat germ agglutinin at different moments of the reproductive cycle and their binding characteristics and tyrosine kinase activity were studied. Specific receptors for insulin and IGF-I were found. IGF-I receptors presented higher binding (23.8 ± 1.5%), number of receptors (965 ± 20fm/mg) and affinity (KD 0.24 ± 0.03nM) than those shown for insulin receptors (4.1 ± 1%, 530 ± 85fm/mg and 0.85 ± 0.1nM, respectively). Insulin and IGF-I receptors have a tyrosine kinase activity which is not different from that found in muscle of the same species. Seasonal changes were found in binding, with maximum values for insulin and IGF-I reached at the end of pre-spawning period (June). However, while IGF-I binding was observed in all stages, insulin binding decreased in autumn and disappeared in winter, which suggests a different role for the two peptides in ovarian physiology. 相似文献
32.
ABSTRACT: The present study reports the annual variation in consumption of the sea urchin Strongylocentrotus intermedius by avian predators on a rocky shore where the culture of sea urchins has been conducted. Carrion crow and a few gull species were the most abundant avian predators and consumed a large number of sea urchins. Crows consumed mostly natural sea urchins, approximately 36 kg ww/ha per year on the intertidal rocky bench, but the gull species consumed mostly cultured sea urchins, approximately 100 kg ww/ha per year in the culture area. The seasonal variation in the amount of sea urchins consumed by crows was higher than that by the gull species, presumably because of the difference in foraging behavior in association with the seasonal tidal cycle. The natural sea urchins consumed are an allochthonous input from the subtidal to the intertidal habitat, and thus, crow predation may not affect the natural and the cultured populations of the sea urchin. The gull species consumed much of the cultured sea urchin, and thus, may be regarded as an effective predator causing damage to sea urchin culture. The results suggest that further studies are needed to determine why the gull species selectively feed on cultured sea urchins. 相似文献
33.
Sung Il Lee Kerim Y. Aydin Paul D. Spencer Thomas K. Wilderbuer Chang Ik Zhang 《Fisheries Science》2010,76(3):411-434
We evaluated the role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem using the Ecopath/Ecosim
approach. As basic input data for the Ecopath/Ecosim model, we used estimates of biomass from bottom trawl surveys and age-structured
population models, production/biomass (P/B) ratio, consumption/biomass (Q/B) ratio, diet composition (DC), and fisheries harvests for each component of species or species groups. We estimated the trophic
level of each component, niche overlaps among flatfishes, and the impacts of competition and predation on flatfish species
in the eastern Bering Sea ecosystem. Based on those estimates, we developed the tropho-dynamic structure of the ecosystem,
and the model was used to simulate ecological effects of fishery exploitation patterns. No single flatfish species appeared
to have a profound and uniquely important role in the organization and structure of the ecosystem. Instead, the most important
component among the guild of flatfish species appeared to be yellowfin sole Pleuronectes asper, which had greater biomass than other flatfish and a relatively diverse diet among the small flatfish species. Pacific halibut
Hippoglossus stenolepis, Greenland turbot Reinhardtius hippoglossoides, and arrowtooth flounder Atheresthes stomias were important keystone predators in the eastern Bering Sea ecosystem together with some groups of marine mammals and sea
birds. Intra flatfish complex cannibalism was not observed, however, substantial diet overlaps were common in the flatfish
guild system. 相似文献
34.
Aki Namba Yuya Shigenobu Masahiro Kobayashi Takanori Kobayashi Ichiro Oohara 《Fisheries Science》2010,76(5):873-878
To construct high-quality 16S rDNA clone libraries for microbial communities associated with Porphyra yezoensis and to minimize the detection of rDNA from leafy gametophytes of P. yezoensis, we designed a new 16S rDNA universal primer (75F). Of the clones prepared using 75F, which was designed to distinguish between
bacteria and P. yezoensis, 95% were classified into four groups, namely, β-proteobacteria, γ-proteobacteria, Lentisphaerae, and Flavobacteria. PCR-based analysis of the 16S rDNA primer constructed in this study can be used to implement 16S rDNA-based methodologies
for the investigation of microbial community composition and diversity related to the Porphyra group. 相似文献
35.
Design and validation of a RT‐qPCR procedure for diagnosis and quantification of most types of infectious pancreatic necrosis virus using a single pair of degenerated primers 下载免费PDF全文
Infectious pancreatic necrosis virus (IPNV) is an important virus which affects the salmonid aquaculture industry worldwide; therefore, it is important to develop rapid and reliable methods of diagnosis to detect the disease at early stages. Nowadays, RT‐qPCR is replacing other methods because it provides additional information on the viral load, which is important to have a better understanding of the virus replication level and of the stage of the infection and its risk level. The main problem stems from the high diversity of this virus, which can compromise the reliability of the diagnosis. In this study, we have designed an RT‐qPCR procedure for diagnosis and quantification of IPNV based on a single pair of primers targeted to segment B. The procedure has been validated, in vitro and in vivo, testing two different types of standards against seven reference strains and 23 field isolates from different types. The procedure is reliable for the detection of any type, with a detection limit of 31 TCID50 mL?1, 50 pfu mL?1 or 66 RNA copies mL?1, depending on the standard. All the standard curves showed high reliability (R2 > 0.95). The results support the high reliability of this new procedure for the diagnosis and quantification of IPNV. 相似文献
36.
37.
38.
39.
40.