首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   805篇
  免费   40篇
林业   52篇
农学   128篇
基础科学   22篇
  149篇
综合类   53篇
农作物   62篇
水产渔业   36篇
畜牧兽医   265篇
园艺   11篇
植物保护   67篇
  2022年   6篇
  2021年   13篇
  2020年   21篇
  2019年   14篇
  2018年   18篇
  2017年   31篇
  2016年   25篇
  2015年   19篇
  2014年   22篇
  2013年   51篇
  2012年   43篇
  2011年   38篇
  2010年   29篇
  2009年   30篇
  2008年   31篇
  2007年   27篇
  2006年   20篇
  2005年   24篇
  2004年   12篇
  2003年   16篇
  2002年   23篇
  2001年   20篇
  2000年   12篇
  1999年   12篇
  1998年   11篇
  1996年   7篇
  1994年   11篇
  1993年   6篇
  1992年   11篇
  1991年   9篇
  1990年   11篇
  1989年   9篇
  1988年   17篇
  1987年   18篇
  1986年   11篇
  1985年   8篇
  1984年   9篇
  1983年   11篇
  1982年   9篇
  1981年   13篇
  1980年   7篇
  1979年   14篇
  1978年   8篇
  1975年   13篇
  1973年   8篇
  1972年   6篇
  1971年   7篇
  1970年   11篇
  1969年   13篇
  1968年   6篇
排序方式: 共有845条查询结果,搜索用时 15 毫秒
101.
Adiponectin is an adipocyte‐derived hormone regulating energy metabolism, insulin sensitivity and recently found to regulate reproduction. The current study was carried out to investigate gene and protein expression, immunolocalization of adiponectin and its receptors AdipoR1 and AdipoR2 in ovarian follicles of different developmental stages in water buffalo (Bubalus bubalis) and to investigate the effect of adiponectin on steroid production in cultured bubaline granulosa cells. qPCR, western blotting and immunohistochemistry were applied to demonstrate mRNA expression, protein expression and immunolocalization, respectively. The results indicate that adiponectin, AdipoR1 and AdipoR2 were present in granulosa cells (GC) and theca interna (TI) of ovarian follicles and the expression of adiponectin, AdipoR1, AdipoR2 in GC and AdipoR1 and AdipoR2 in TI increased with increase in follicle size (p < .05). Expression of adiponectin was high in small and medium size follicles in TI. The adiponectin and its receptors were immunolocalized in the cytoplasm of GC and TI cells. Further, in the in‐vitro study, GCs were cultured and treated with recombinant adiponectin each at 0, 1 and 10 µg/ml alone or with follicle stimulating hormone (FSH) at 30 ng/ml) or Insulin‐like growth factor I (IGF‐I) at 10 ng/ml for 48 hr after obtaining 75%–80%s confluency. Adiponectin at 10 µg/ml increased IGF‐I‐induced estradiol (E2) and progesterone (P4) secretion and FSH‐induced E2 secretion from GC and also increased the abundance of factors involved in E2 and P4 production (cytochrome P45019A1 [CYP19A1] and 3‐beta‐hydroxysteroid dehydrogenase [3β‐HSD]). In conclusion, this study provides novel evidence for the presence of adiponectin and its receptors in ovarian follicles and modulatory role of adiponectin on steroid production in buffalo.  相似文献   
102.
A field study on assessment of crop establishment methods on yield, economics and water productivity of rice cultivars under upland and lowland production ecologies was conducted during wet seasons (June–November) of 2012 and 2013 in Eastern Indo-Gangetic Plains of India. The experiment was laid-out in a split-plot design (SPD) and replicated four times. The main-plot treatments included three crop establishment methods, viz. dry direct-seeded rice (DSR), system of rice intensification (SRI) and puddled transplanted rice (PTR). In sub-plots, five rice cultivars of different groups like aromatic (Improved Pusa Basmati 1 and Pusa Sugandh 5), inbreds (PNR 381 and Pusa 834) and hybrid (Arize 6444) were taken for their evaluations. These two sets of treatments were laid-out simultaneously in two production ecologies, upland and lowland during both years. In general, lowland ecology was found favourable for rice growth and yield and resulted in 13.2% higher grain yield as compared to upland ecology. Rice grown with SRI method produced 19.4 and 7.0% higher grain yield in 2012 and 20.6 and 7.1% higher in 2013, over DSR and PTR. However, PTR yielded 13.1 and 14.5% higher grain over DSR during 2012 and 2013, respectively. On an average, Arize 6444 produced 26.4, 26.9, 28.9 and 54.7% higher grain yield as compared to PS 5, P 834, PNR 381 and IPB1, respectively. Further, the interaction of production ecologies × crop establishment methods revealed that, in upland ecology, SRI recorded significantly higher grain yield as compared to PTR and DSR, but in lowland, grain yield resulting from SRI was similar to the yield obtained with PTR and significantly higher than DSR. The latter two methods (PTR and DSR) yielded alike in lowland ecology in both study years. The production ecologies × crop establishment methods × cultivars interaction on grain yield showed that the growing of Arize 6444 cultivar using SRI method in upland ecology resulted in the higher grain yield (8.87 t/ha). But the cost of production was also highest in SRI followed by PTR and DSR across production ecologies and cultivars. Cultivation of hybrid (Arize 6444) involved higher cost of production than all other cultivars. Irrespective of crop establishment methods and cultivars, gross returns, net returns and B:C ratio were significantly higher in lowland compared to upland ecology. Owing to higher grain yield, SRI method fetched significantly higher gross returns and net returns over PTR and DSR. Average increase in net return with Arize 6444 was 68.8, 41.0, 37.7 and 33.1% over IPB 1, PNR 381, P 834 and PS 5, respectively. There was a saving of 30.7% water in SRI and 19.9% in DSR over PTR under upland ecology. Similarly in lowland ecology, water saving of 30.2% was observed in SRI and 21.2% in DSR over PTR. Due to higher yield and saving on water, SRI returned significantly higher total water productivity (TWP) (5.9 kg/ha-mm) as compared to DSR (3.5 kg/ha-mm) and PTR (3.6 kg/ha-mm) under upland ecology. In lowland ecology, also SRI (6.2 kg/ha-mm) resulted in higher TWP as compared to other two methods. However, DSR gave significantly higher TWP as compared to PTR. Among cultivars, hybrid Arize 6444 recorded the highest TWP in both upland and lowland production ecologies across crop establishment methods. Hence, growing of hybrid Arize 6444 with SRI method can enhance rice productivity and water-use efficiency in lowland and upland production ecologies of Eastern Indo-Gangetic Plains and in other similar regions.  相似文献   
103.
Phytohormones are involved in the regulation of plant responses to biotic stress. How a limited number of hormones differentially regulate defence responses and influence the outcome of plant–biotic interactions is not fully understood. In recent years, cytokinin (CK) was shown to induce plant resistance against several pathogens. In the present study, we investigated the effect of CK in inducing tomato resistance against the hemibiotrophic pathogenic bacteria Xanthomonas campestris pv. vesicatoria (Xcv) and Pseudomonas syringae pv. tomato (Pst). We demonstrate that CK enhances tomato resistance to Xcv and Pst through a process that relies on salicylic acid and ethylene signalling. CK did not directly affect the growth or biofilm formation ability of these pathogens in vitro. Overall, our work provides insight into the underlying mechanisms of CK-induced immune responses against bacterial pathogens in tomato.  相似文献   
104.
105.
The nontarget effects of three plant growth stimulants (gibberellic acid, Siapton and triacontanol) and two plant growth retardants (chlormequat chloride and mepiquat chloride) on the survivorship and developmental parameters of Spilarctia obliqua Walker (Lepidoptera: Arctiidae) were studied. For each compound, various concentrations (0.125×, 0.25×, 0.5×, × , 2× and 4×; × = labeled dose) bracketing the labeled dose were prepared by serial dilution and mixed with an artificial diet for the insect. Gibberellic acid caused an increase in the larval period at × − 4×, but no marked difference was observed in the pupal period or in larval survival at any concentration. Siapton induced a significant increase in larval period at the two highest doses but caused significant reduction in pest survival at × − 4×. Interestingly, triacontanol induced a significant reduction in pest survivorship at almost all doses. The LC50 for triacontanol was 0.206% and LT50 was 266.5 hours at the labeled dose. However, triacontanol did not cause any significant difference in larval or pupal periods at any dose tested. Chlormequat chloride and mepiquat chloride caused significant reduction of larval survivorship at concentrations higher than the labeled doses, and no effect on the larval period. Intriguingly, a significant reduction in pupal period was observed with chlormequat chloride at × and 0.25×. Based on the marked effect of triacontanol on pest survivorship, this study suggests incorporating triacontanol in integrated pest management modules for S. obliqua. Caution in the use of gibberellic acid and Siapton for pest infestations is also indicated.  相似文献   
106.
Six blast‐resistant pearl millet genotypes, ICMB 93333, ICMB 97222, ICMR 06444, ICMR 06222, ICMR 11003 and IP 21187‐P1, were crossed with two susceptible genotypes, ICMB 95444 and ICMB 89111 to generate F1s, F2s and backcrosses, BC1P1 (susceptible parent × F1) and BC1P2 (resistant parent × F1) for inheritance study. The resistant genotypes were crossed among themselves in half diallel to generate F1s and F2s for test of allelism. The F1, F2 and backcross generations, and their parents were screened in a glasshouse against Magnaporthe grisea isolates Pg 45 and Pg 53. The reaction of the F1s, segregation pattern of F2s and BC1P1 derived from crosses involving two susceptible parents and six resistant parents revealed the presence of single dominant gene governing resistance in the resistant genotypes. No segregation for blast reaction was observed in the F2s derived from the crosses of resistant × resistant parents. The resistance reaction of these F2s indicated that single dominant gene conferring resistance in the six genotypes is allelic, that is same gene imparts blast resistance in these genotypes to M. grisea isolates.  相似文献   
107.
This study was conducted with Aloe barbadensis in order to investigate the efficacy of four phosphate-solubilizing bacteria (PSB), Pseudomonas synxantha 10223, Burkholderia gladioli 10242, Enterobacter hormaechei 10240 and Serratia marcescens 10241 to solubilize Mussorie rock phosphate (MRP) and to evaluate its effects on growth, soluble P content and P uptake compared with control, i.e. uninoculated plants. Pot experiments were conducted in a greenhouse, in soil supplemented with MRP. Each PSB treatment showed different effects on different plant growth parameters. The maximum increase in leaf length (23.7%), total number of leaves (33.33%) and dry rind weight (69.10%) was observed in plants treated with P. synxantha 10223 compared with control. Whereas, maximum increase in root length (23.43%), fresh leaves weight (79.03%), dry gel weight (113.08%) and total gel volume (112.10%), was observed in plants treated with S. marcescens 10241 compared with uninoculated plants. Maximum increase in aloin-A content [114.92% (per g dry gel weight) and 322.32% (per plant dry gel weight)] was observed in plants treated with P. synxantha 10223 compared with control plants. Root colonization by inoculated PSB as estimated by RAPD technique showed that all PSB were able to survive in the rhizosphere of Aloe plants.  相似文献   
108.
In irrigated agriculture of arid and semiarid regions waterlogging coupled with salinity is a serious problem. Experimental evidence at several locations has led to the realization that subsurface drainage is an essential intervention to reverse the processes of land degradation responsible for the formation of waterlogged saline lands. This paper presents the results of a study conducted from 1995 to 2000 to evaluate the impacts of subsurface drainage on soil properties, groundwater‐table behaviour and crop productivity in a waterlogged saline area of 2200 ha. A subsurface drainage system was installed at 1·6 m depth with 60 m drain spacing covering an area of 1200 ha (23 blocks) during 1997–99 and compared with an undrained block of 1000 ha. Subsurface drainage facilitated the reclamation of waterlogged saline lands and a decrease in the soil salinity (ECe, dS m−1) that ranged from 16·0 to 66·3 per cent in different blocks. On average, 35·7 per cent decrease in salt content was observed when compared with the initial value. Provision of subsurface drainage controlled the water‐table below the root zone during the monsoon season and helped in bringing the soil to optimum moisture content for the sowing of winter crops. In the drained area, the increase in yields of different crops ranged from 18·8 to 27·6 per cent. However, in the undrained area the yield of different crops decreased due to the increased waterlogging and soil salinity problems. Overall the results indicated that investment in subsurface drainage is a viable option for reversing the land degradation of waterlogged saline lands in a monsoon climate. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
109.
Tropical Animal Health and Production - The rise of antibiotic resistance and its global outreach has recently become a subject of increasing importance in veterinary research with an objective to...  相似文献   
110.
Worldwide, the nitrogen use efficiency (NUE) for crop plants is of great concern. The burgeoning world population needs crop genotypes that respond to higher nitrogen and show a direct relationship to yield with use of nitrogen inputs, i.e. high nitrogen-responsive genotypes. However, for fulfilling the high global demand of organic produce, it requires the low nitrogen responsive genotypes with greater NUE and grain yields. The lack of knowledge about precise regulatory mechanisms to explain NUE in crop plants hampers the goal of agricultural productivity. Understanding the molecular basis of NUE will enable to provide handle for crop improvement through biotechnological means. With the advent of modern genomics and proteomics approaches such as subtractive hybridization, differential display, and microarray techniques are revolutionizing to identify the candidate genes which play a pivotal role in the regulation of NUE. Beside it, quantitative real-time polymerase chain reaction technology is also being used to establish marker-trait association for NUE. The identification of potential candidate genes/proteins in the regulation of NUE will serve as biomarker(s) for screening genotypes for their nitrogen responsiveness for optimization of nitrogen input in agriculture. This paper describes the molecular basis of NUE with respect to nitrogen metabolism and its intimate relationship with carbon metabolism, use of molecular-physiological-genetics approaches for understanding the role of various genes/proteins, and their validation to use as biomarker(s) for determining genotypic potential for NUE. Since NUE in plants is a complex trait which not only involves the primary process of nitrogen uptake and assimilatory pathways but also a series of events, including metabolite partitioning, secondary remobilization, C-N interactions, as well as molecular signalling pathways and regulatory control outside the metabolic cascades. Therefore, identification of novel nitrogen responsive genes and their cis- and trans-acting gene elements is essential. Thus, fishing out a single gene, biomarker or a master regulator controlling complex trait of NUE could serve as an appropriate strategy for nitrogen management in agriculture.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号