全文获取类型
收费全文 | 5179篇 |
免费 | 221篇 |
国内免费 | 8篇 |
专业分类
林业 | 309篇 |
农学 | 159篇 |
基础科学 | 44篇 |
782篇 | |
综合类 | 830篇 |
农作物 | 239篇 |
水产渔业 | 436篇 |
畜牧兽医 | 2040篇 |
园艺 | 152篇 |
植物保护 | 417篇 |
出版年
2023年 | 31篇 |
2022年 | 39篇 |
2021年 | 100篇 |
2020年 | 117篇 |
2019年 | 126篇 |
2018年 | 87篇 |
2017年 | 101篇 |
2016年 | 97篇 |
2015年 | 105篇 |
2014年 | 117篇 |
2013年 | 244篇 |
2012年 | 283篇 |
2011年 | 348篇 |
2010年 | 192篇 |
2009年 | 153篇 |
2008年 | 342篇 |
2007年 | 291篇 |
2006年 | 296篇 |
2005年 | 300篇 |
2004年 | 267篇 |
2003年 | 272篇 |
2002年 | 263篇 |
2001年 | 57篇 |
2000年 | 65篇 |
1999年 | 69篇 |
1998年 | 52篇 |
1997年 | 44篇 |
1996年 | 42篇 |
1995年 | 38篇 |
1994年 | 46篇 |
1993年 | 54篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 41篇 |
1989年 | 35篇 |
1988年 | 32篇 |
1987年 | 37篇 |
1986年 | 28篇 |
1985年 | 35篇 |
1984年 | 40篇 |
1983年 | 36篇 |
1982年 | 20篇 |
1981年 | 33篇 |
1980年 | 23篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1975年 | 18篇 |
1974年 | 23篇 |
1973年 | 24篇 |
排序方式: 共有5408条查询结果,搜索用时 15 毫秒
901.
Catfish hatcheries use copper sulphate pentahydrate (CuSO4·5H2O) as an economical control for saprolegniasis on eggs. This study determines hatch rate of channel catfish, Ictalurus punctatus (Rafinesque 1818), eggs in hatching troughs containing 23.8 °C flow‐through well water when treated with 100 mg L?1 CuSO4·5H2O (10 times the proposed therapeutic dose). Eggs were treated daily until the embryos reached the eyed stage. Fry survival in the control and 100 mg L?1 CuSO4·5H2O treatments was significantly different (15% and 71% respectively). This study demonstrates that there is a considerable margin of safety in using CuSO4·5H2O as a catfish egg treatment to control saprolegniasis. 相似文献
902.
Ellis T Berrill I Lines J Turnbull JF Knowles TG 《Fish physiology and biochemistry》2012,38(1):189-199
Mortality has received insufficient attention as a fish welfare topic. Here, we aim to prompt fish farming stakeholders to
discuss fish mortalities in relation to welfare. Mortality in farmed fish populations is due to a variety of biotic and abiotic
causes, although it is often difficult to differentiate between underlying and immediate causes of mortality. Most mortality
appears to occur during episodes associated with disease outbreaks and critical periods (in development or production). Most
causes of mortality can be assumed to be associated with suffering prior to death. As mortality rates in farmed fish populations
are suspected to rank amongst the highest in commonly farmed vertebrate species, mortality should be a principal fish welfare
issue. Long-term mortality rates can be used as a retrospective welfare performance indicator and short-term mortality rates
as an operational welfare indicator. Scrutiny of mortality records and determining causes of death will enable action to be
taken to avoid further preventable mortality. The welfare performance of fish farms should only be judged on levels of predictable
and preventable mortality. Fish farmers will already be monitoring mortality due to commercial and legal requirements. As
profitability in fish farming is directly linked to survival, confronting mortality should ultimately benefit both fish and
farmers. 相似文献
903.
Ken Overturf Roger L. Vallejo Yniv Palti Fredrick T. Barrows James E. Parsons 《Aquaculture International》2012,20(2):213-232
Microarray analysis was conducted using liver samples from two families of rainbow trout that differed in their growth responses
when compared between individuals fed a fishmeal or plant protein-based diet. Differential expression relating to dietary
utilization between the two families found significant changes in expression of 33 expressed sequence tags (ESTs). Eight of
the differentially expressed ESTs had identified mammalian homologs that had been previously researched with identified cellular
interactions and functions. Utilizing pathway analysis software to analyze sequences annotated with known mammalian genes,
we were able to map gene pathways and process interactions. From this information, we were able to infer that the metabolic
changes associated with utilization of plant protein versus fishmeal were associated with differential regulation of genes
related to cell oxidative stress, proliferation, growth and survival. Furthermore, we inferred from the changes we observed
in immune response gene expression that ingestion of this plant-based diet upregulated the expression of genes involved in
immunoregulatory processes. 相似文献
904.
905.
Model organisms such as Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) have proven essential for efficient scientific discovery and development of new methods. With the diversity of plant lineages, some important processes such as C4 photosynthesis are not found in either Arabidopsis or rice, so new model species are needed. Due to their small diploid genomes, short life cycles, self-pollination, small adult statures and prolific seed production, domesticated foxtail millet (Setaria italica) and its wild ancestor, green foxtail (S. viridis), have recently been proposed as novel model species for functional genomics of the Panicoideae, especially for study of C4 photosynthesis. This review outlines the development of these species as model organisms, and discusses current challenges and future potential of a Setaria model. 相似文献
906.
907.
This paper looks at price integration in the aquaculture and wild-harvested African catfish market channels in Uganda. The issue of integration between the two market channels is important because African catfish has become an important traded species in Uganda with exports to regional markets rising even faster than production, yet limited research has been undertaken to understand price formation in the supply chain. The analysis draws on monthly price data from January 2006 to August 2013, and applies threshold autoregressive approaches to test for the existence of a long-run relationship and price asymmetry and to determine the time path needed for shocks to be transmitted from one market channel to the other. The results show that, over the studied period prices in both market channels are linked in the long-run, implying that farm-raised catfish forms part of the same market as wild-harvested catfish in the country. The findings have strong implications for aquaculture producers and artisanal fishers as they can serve as a basis for more efficient farm management and marketing decisions. 相似文献
908.
Stephen F. Omondi David W. Odee George O. Ongamo James I. Kanya Damase P. Khasa 《New Forests》2018,49(1):53-65
Understanding the variation of mating patterns in disturbed habitats provide insight into the evolutionary potential of plant species and how they persist over time. However, this phenomenon is poorly understood in tropical dryland tree species. In the present study, we investigated how Acacia senegal reproduces in two different environmental contexts in Kenya. Open-pollinated progeny arrays of 10 maternal trees from each environmental context were genotyped using 12 nuclear microsatellite markers. Overall, A. senegal displayed a predominantly allogamous mating pattern. However, higher multilocus outcrossing rate (tm) was found in Lake Bogoria (tm = 1.00) than in Kampi ya Moto population (tm = 0.949). Higher biparental inbreeding (t m ? t s = 0.116) and correlation of outcrossed paternity (rp = 0.329) was found in Kampi ya Moto than in Lake Bogoria population (t m ? t s = 0.074, rp = 0.055), showing the occurrence of mating among relatives. Coefficient of coancestry (Θ = 0.208) showed that full-sibs constitute about 21% of the offspring in Kampi ya Moto population compared to about 14% (Θ = 0.136) in Lake Bogoria population. The results demonstrate that low adult tree density of A. senegal may be promoting seed production through consanguineous mating and suggest that man-made disturbance can affect mating patterns of the species. Despite these mating differences, trees from both populations can contribute as seed source for conservational plans, and to support effective genetic conservation and artificial regeneration programs of A. senegal. We suggest collection of seeds from at least 42 and 63 trees in Lake Bogoria and Kampi ya Moto populations, respectively, to retain a progeny array with a total effective population size of 150. 相似文献
909.
Gerald Zvobgo Jonas Lwalaba Wa Lwalaba Shafaque Sehar James Mutemachani Mapodzeke Imran Haider Shamsi 《Communications in Soil Science and Plant Analysis》2018,49(1):50-62
Ninety-four barley genotypes were used to investigate the genotypic differences in arsenic (As) uptake and translocation and their relationships with As tolerance index (TI) and translocation factor (TF). Two As treatments (300 µM and 500 µM) were applied in the initial screening and the confirmatory experiments, respectively. The results showed significant (p < 0.05) differences in tissue biomass, shoot height, root length, As TI and TF among genotypes. Based on As TI, 11 barley genotypes were selected and divided into 3 groups, i.e. tolerant, mildly tolerant and sensitive. There was more As uptake in the roots of the As tolerant genotypes, while the As sensitive genotypes contained more As in shoots, which was further proved by the greater TF. Significantly negative correlation was observed between shoot and root As concentration. The results showed that As tolerant genotypes are able to restrict the upward movement of As, thus developing their tolerance. 相似文献
910.
Abigail Oluremi Ojo Lateef Bamidele Taiwo James Alabi Adediran Adedayo Omowunmi Oyedele IbukunO. Fademi Azarel Caldbak Oladotun Uthman 《Communications in Soil Science and Plant Analysis》2018,49(14):1774-1786
Monitoring the physical, chemical and biological properties during accelerated composting enables concise determination of its stability and maturity. Determination of physical parameters such as pH, moisture and temperature, chemical parameters such as total nitrogen (N), phosphorus (P), potassium (K), organic matter and humic acid as well as biological parameters such as microbial count and carbon dioxide (CO2) evolution was carried out during a four (4) week composting period, The trend observed for pH showed the mesophilic and thermophilic phases and a similar trend was observed for the compost temperature. Intermittent increase and decrease was observed for total N, P, K as well as for the fungal and bacterial population. A direct relationship was observed among the bacterial population, CO2 evolution and humic acid. However, composting for four (4) weeks produced a stable compost, which was evident through the physical observation of the final product and the results obtained for the chemical and biological parameters. 相似文献