全文获取类型
收费全文 | 392篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
林业 | 13篇 |
农学 | 56篇 |
基础科学 | 2篇 |
79篇 | |
综合类 | 30篇 |
农作物 | 20篇 |
水产渔业 | 77篇 |
畜牧兽医 | 116篇 |
园艺 | 5篇 |
植物保护 | 26篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 14篇 |
2018年 | 18篇 |
2017年 | 12篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 22篇 |
2012年 | 19篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 9篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 15篇 |
2003年 | 27篇 |
2002年 | 15篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有424条查询结果,搜索用时 15 毫秒
11.
Y. Yoshiura Y.C. Sohn A. Munakata M. Kobayashi K. Aida 《Fish physiology and biochemistry》1999,21(3):201-210
A cDNA encoding the subunit of thyrotropin (TSH) was isolated from a goldfish (Carassius auratus) pituitary gland cDNA library. By comparing the sequence with other teleost TSHs, a signal peptide of 19 amino acids and a mature hormone of 131 amino acids were predicted for goldfish TSH subunits. The resulting putative mature hormone of 131 amino acids had well-conserved cysteine positions and a putative N-linked glycosylation site; homology was 51–67% with TSHs from other teleosts, 38–43% with tetrapod TSHs, but only 27 and 29% with goldfish GTH-I and -II, respectively. We also examined the effects of thyroid hormones (TH) and thiourea (TU, an inhibitor of TH production) treatments on TSH and GTH subunit gene expressions in the goldfish pituitary gland. After thyroxine (T4) treatment, circulating T4 concentration increased and TSH mRNA level decreased. Supressing the amount of circulating T4 and triiodothyronine (T3) by TU treatment increased the TSH mRNA level. Moreover, T4 replacement therapy (simultaneous treatment of both TU and T4) caused a high level of circulating T4 and a low level of circulating T3, and a decrease in the TSH mRNA level. Thus, changing levels of circulating TH exert a negative feedback on the level of TSH subunit mRNA in goldfish in vivo. On the other hand, GTH subunit mRNA levels were not affected by changes in the levels of circulating TH. 相似文献
12.
H. Yambe A. Munakata S. Kitamura K. Aida N. Fusetani 《Fish physiology and biochemistry》2003,28(1-4):279-280
We investigated the optimum term of 17α-methyltestosterone (MT) -treatment for behavioral test and changes of plasma sex steroids levels in MT-treated immature male masu salmon, Oncorhynchus masou parr. Behavioral responses of MT-treated fish to the urine of ovulated or immature females were observed in an experimental trough. After 5 min of behavioral tests, plasma sex steroids levels were measured by RIAs. MT-treated fish showed specific behavioral responses to the ovulated female urine. MT-treated fish without exposure to the urine showed no clear changes in plasma 17,20β-dihydroxy-4-pregnene-3-one (DHP). However, plasma DHP in MT-treated fish increased when they were exposed to the urine. 相似文献
13.
J.B. Ortiz Delgado N.M. Ruane P. Pouso-Ferreira M.T. Dinis C. Sarasquete 《Aquaculture (Amsterdam, Netherlands)》2006,260(1-4):346-356
A key to success in the culture of marine fish species is the mass production of high quality fry, a process largely dependent on successful first feeding and normal development and growth of fish larvae. In this regard it is important to examine the structural and functional development of the endocrine system (pituitary, thyroid, interrenal glands) during early ontogeny of marine fish. Particularly, the thyroid hormones, thyroxine (T4) and triiodothyronine (T3), influence numerous metabolic processes, such as growth, differentiation, metamorphosis, reproduction, respiration, migratory behaviour, central nervous system activity, seasonal adaptation, etc. Therefore the aim of this study was to describe the development of the thyroid gland and the ontogeny appearance of the thyroid hormones in Solea senegalensis larvae by means of histological and immunohistochemical techniques. The first thyroid follicle was present at 4 days-post-hatch (dph) coinciding with first feeding. During metamorphosis (12–20 dph) the follicles increased in both number and size, and by 30 dph presented the same characteristics as that seen in adult fish. Tissue immunostaining of both thyroid hormones decreased during the endogenous larvae development to nearly undetectable levels at the completion of yolk-sac absorption. During larvae exogenous phase, T3 and T4 immunostaining was first detected by 6 dph and an increase of specific staining for both hormones was detected between 12 and 20 dph, during metamorphosis phase. 相似文献
14.
Pituitary gonadotropin (GTH) secreting cells and brain gonadotropin-releasing hormone (GnRH) secreting neurons are known to be subjected to feedback control by gonadal steroid in teleosts. In masu salmon, Oncorhynchus masou, salmon GnRH (sGnRH) neurons in the ventral telencephalon (VT) and the preoptic area (POA) are involved in the control of GTH cells because sGnRH synthesis in these areas is activated with gonadal maturation. In this study, we attempted to clarify mechanisms of feedback control of sGnRH neurons by gonadal steroids. We examined the effects of 17-methyltestosterone (MT) on sGnRH synthesis in yearling and 2-year-old female fish (which were immature during experimentation in May), and the effects of castration on sGnRH synthesis in underyearling precocious male fish in August. sGnRH synthesis in the POA, but not in the VT, was increased by MT administration in 2-year-old females only, indicating higher sensitivity to MT in the preoptic sGnRH neurons. Castration increased sGnRH synthesis in the VT but not in the POA. These results suggest that sGnRH neurons in the VT and those in the POA are differentially regulated by gonadal steroids. 相似文献
15.
Goldfish,Carassius auratus, spawn several times within a spawning season. A gonadotropin (GtH) surge occurs at the time of ovulation in this cyprinid
species. This ovulatory GtH surge mediates the processes of final oocyte maturation and ovulation, and occurs at the end of
each spawning cycle. Within a cycle, there is a shift in the predominant plasma steroid from estradiol to testosterone, and
finally 17α, 20β-dihydroxy-4-pregnen-3-one at the time of the ovulatory GtH surge. High levels of testosterone were always
observed before ovulation. When ovariectomized or sexually regressed female goldfish were implanted with testosterone, they
exhibited a GtH surge which was similar to those normally observed at ovulation. These results strongly suggest that elevated
plasma testosterone is an important physiological requirement for the occurrence of the GtH surge. 相似文献
16.
This contribution aims at the assessment of the sustainability of a management plan for Lessonia nigrescens in Chilean coastal ecosystems, specially when the harvest pressure could be increased due to that this macroalgae is considered as a food source for the abalon (Haliotis discus hannoi) farming along the Chilean coast. Three qualitative conceptual models were developed and compared; the first and second ones assuming homogeneous and heterogeneous environmental conditions, respectively, and the third expanded one considering eco-social components under the assumption of environmental heterogeneity. For all these models, the factors described by Vásquez [Bot. Mar. 38 (1995) 251] were included in the management plan for the harvesting of brown macroalgae. Based on Levins's Loop Analysis, the system will have a just weakly unstable moving equilibrium if the harvesting activities do not negatively affect the macrophyta's reproduction and recruitment processes. Therefore, coincidence of reproduction and/or recruitment with harvesting must be avoided in a putative management plan. Regarding the qualitative predictions of the system's behaviour after negatively affecting reproduction and recruitment, only an ecological model assuming a heterogeneous environment shows realistic responses in comparison to experimental studies on the same species. This contribution is the first approach considering the dynamical behaviour of L. nigrescens and its surroundings. Nevertheless, further models, based on the same modelling theory, may integrate more variables from social and economical fields in order to improve the scope of this complex system. Further comparative studies should focus on the assessment of the significance of the structural functions of L. nigrescens and other macroalgae for the conservation of this benthic system. 相似文献
17.
Effects of steroid hormones on immunoglobulin M (IgM) in rainbow trout, Oncorhynchus mykiss 总被引:3,自引:0,他引:3
The immunosuppressive effects of steroid hormones were evaluated as the response against implanted steroid hormones, cortisol (F), testosterone (T), estradiol-17 (E2), and 11- ketotestosterone (11-KT), in juvenile rainbow trout. In long term experiments (5 weeks), fish were given a single intraperitoneal implant of F or T. A clear suppressive effect of plasma IgM levels with F and T was not necessarily obtained, although mucus IgM levels were reduced corresponding to the elevated plasma steroid hormone levels. In short term experiments (1 week), intraperitoneal implantation of T, 11-KT and E2 suppressed plasma and mucus IgM levels, although the effects were not dose-dependent. When administered through diet, F and T caused a suppression of plasma IgM levels; F administration at both high and low dosages caused a significant decrease in plasma IgM levels, while only a high dose of T caused the suppression. These results suggest that sex steroid hormones, as well as F, have immunosuppressive functions in rainbow trout. 相似文献
18.
The importance of reduced tillage in sustainable agriculture is well recognized. Reduced-tillage practices (which may or may
not involve retention of crop residues) and their effects differ from those of conventional tillage in several ways: soil
physical properties; shifts in host–weed competition; soil moisture availability (especially when sowing deeply or under stubble);
and the emergence of pathogen populations that survive on crop residues. There may be a need for genotypes suited to special
forms of mechanization (e.g. direct seeding into residues) and to agronomic conditions such as allelopathy, as well as specific
issues relating to problem soils. This article examines issues and breeding targets for researchers who seek to improve crops
for reduced-tillage systems. Most of the examples used pertain to wheat, but we also refer to other crops. Our primary claim
is that new breeding initiatives are needed to introgress favourable traits into wheat and other crops in areas where reduced
or zero-tillage is being adopted. Key traits include faster emergence, faster decomposition, and the ability to germinate
when deep seeded (so that crops compete with weeds and use available moisture more efficiently). Enhancement of resistance
to new pathogens and insect pests surviving on crop residues must also be given attention. In addition to focusing on new
traits, breeders need to assess germplasm and breeding populations under reduced tillage. Farmer participatory approaches
can also enhance the effectiveness of cultivar development and selection in environments where farmers’ links with technology
providers are weak. Finally, modern breeding tools may also play a substantial role in future efforts to develop adapted crop
genotypes for reduced tillage. 相似文献
19.
María Valeria Romagnoli Juan Pablo A. Ortiz Gerardo D. Cervigni Cintia Heisterborg Rubén H. Vallejos 《Euphytica》1996,90(1):89-93
Summary Somatic embryos of genotype R11 of the alfalfa variety Pampeana were produced from embryogenic calli derived from leaf sections. They were induced by an auxin shock and its development was attempted on six different media. The best condition for somatic embryo production was inducing callus on MS medium plus 10 M 2,4-D and 4,6 M KIN and transferring them, after the auxin shock, to MS with 10–20 mM NH4
+ and 30 mM proline. More than 500 somatic embryos per plate were produced. Embryos were grown to plants on MS or half strength MS media and all regenerated plants resembled the original R11 genotype. This technique could be useful in alfalfa Pampeana improvement using genetic modification. 相似文献
20.
Plant regeneration was achieved through anther culture of three wild species of Hordeum (H. murinum, H. marinum and H, bulbosum). Calli or embryoids were formed from microspores in anthers cultured on a medium containing 6-benzylammopurine (BAP) and ficoll. These calli or embryoids regenerated green or albino shoots and roots after transfer to regeneration media. Green plantlets which developed on regeneration media were transferred to soil where they showed further growth. 相似文献