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   3651篇
  免费   114篇
林业   232篇
农学   212篇
基础科学   144篇
  919篇
综合类   343篇
农作物   402篇
水产渔业   289篇
畜牧兽医   742篇
园艺   107篇
植物保护   375篇
  2025年   46篇
  2024年   121篇
  2023年   80篇
  2022年   122篇
  2021年   159篇
  2020年   195篇
  2019年   235篇
  2018年   246篇
  2017年   221篇
  2016年   213篇
  2015年   116篇
  2014年   137篇
  2013年   352篇
  2012年   171篇
  2011年   213篇
  2010年   150篇
  2009年   107篇
  2008年   167篇
  2007年   104篇
  2006年   79篇
  2005年   65篇
  2004年   54篇
  2003年   41篇
  2002年   34篇
  2001年   28篇
  2000年   35篇
  1999年   20篇
  1998年   21篇
  1997年   16篇
  1996年   19篇
  1995年   14篇
  1994年   11篇
  1993年   9篇
  1992年   12篇
  1991年   11篇
  1990年   15篇
  1989年   10篇
  1988年   5篇
  1987年   13篇
  1986年   9篇
  1985年   12篇
  1984年   15篇
  1983年   9篇
  1981年   6篇
  1979年   7篇
  1975年   3篇
  1973年   4篇
  1972年   3篇
  1971年   4篇
  1967年   4篇
排序方式: 共有3765条查询结果,搜索用时 15 毫秒
951.
The effect of Prohexadione Calcium (Pro-Ca) and daminozide was observed on the growth characteristics and endogenous gibberellin contents of Chrysanthemum morifolium R. cv Monalisa White. Three concentrations viz. 100, 200 and 400 ppm of Pro-Ca and a single concentration of daminozide (800 ppm) were applied three times with 7 days interval on three weeks old plant under greenhouse condition. Pro-Ca suppressed the plant length up to 30.7% while daminozide inhibited up to 27.12% at optimum concentration. The chlorophyll contents and stem diameter were higher than control, while the fresh weight and flower number insignificantly reduced with such treatments. Gibberellin (GA) analysis showed that Pro-Ca and daminozide application significantly lowered bioactive GA1 content, although the amount of its immediate precursor GA20 was fractionally higher. Bioactive GA4 content was slightly higher than the control while significant difference in GA9 was found between the plants treated with Pro-Ca and daminozide. Current study showed that both early C13 hydroxylation and non-C13 hydroxylation pathways of GA biosynthesis are operational in C. morifolium.  相似文献   
952.
Excessive and inappropriate use of fertilizers is a key factor of low sugarcane yield and degradation of soil. A two-year (2013–14 and 2014–15) field study was conducted to assess the impact of combined application of organic and inorganic fertilizers on sugarcane at research farm of Shakarganj Sugar Research Institute, Jhang, Pakistan. Experiment was conducted under randomized complete block design with three replications. Treatments were used as control (no exogenous application), spent wash (160 t ha?1), (nitrogen, phosphorus and potassium) NPK (168:112:112 kg ha?1), spent wash (120 t ha?1) + NPK (42:28:28 kg ha?1), spent wash (80 t ha?1) + NPK (84:56:56 kg ha?1), spent wash (40 t ha?1) + NPK (126:84:84 kg ha?1), and spent wash (160 t ha?1) + NPK (42:28:28 kg ha?1). Application of spent wash @ 80 t ha?1 + NPK @ 84:56:56 kg ha?1 resulted maximum crop growth rate (11.35 g m?2 d?1), leaf area index (7.78), and net assimilation rate (2.53 g m?2 d?1). Maximum number of millable canes (14), weight per stripped cane (0.90 kg), stripped cane yield (117.60 t ha?1) and unstripped cane yield (141.25 t ha?1) were observed with spent wash @ 80 t ha?1 + NPK @ 84:56:56 kg ha?1, followed by sole fertilizer application @ 168:112:112 kg NPK ha?1 and spent wash @160 t ha?1 + NPK @ 42:28:28 kg ha?1. Similar trend was observed regarding quality parameters. The maximum benefit–cost ratio (1.80) was achieved with integrated application of spent wash @ 80 t ha?1 + NPK @ 84:56:56 kg ha?1.  相似文献   
953.
Purpose

Rapid industrialization in China accelerated environmental pollution by xenophores and trace metals particularly cadmium. Numerous studies have been conducted to address soil contamination using organic and inorganic amendments under pot or incubation conditions, but few were performed under field conditions, particularly in the wheat-growing areas. This study aims to investigate the effectiveness of pre-applied soil amendments for Cd immobilization, changes in soil pH, and metal uptake by wheat.

Materials and methods

In this study, 12 treatments, i.e., control (CK), lime, DaSan Yuan (DASY), DiKang No. 1 (DEK1), biochar, Fe-biochar, Yirang, CaMgP, and green stabilizing agents (GSA-1, GSA-2, GSA-3, and GSA-4), were evaluated for Cd immobilization in incubation and field experiments. Changes in soil pH and available metal content with amendments were monitored from 30 to 150 days of incubation. Single extraction method and DTPA-extractable and sequential extraction procedures were employed to assess the variations in available Cd contents of field soil. The impact of soil amendments on Cd uptake and bioaccumulation in food part of wheat was measured at harvesting stage in a contaminated site.

Results and discussion

Lime treatment increased soil pH by 32% and reduced available Cd to 0.213 mg kg?1, as compared to CK (control) in the incubation experiment (0.343 mg kg?1). Effects of the amendments on wheat growth, soil pH, and Cd phytoavailability were reported. Wheat biomass was highest in treatment GSA-2 (13,880 kg ha?1) and GAS-4 resulted in an increase in grain yield (5350 kg ha?1). Soil pH of the treated field at harvesting stage increased up to 6.50, 6.50, and 6.47 by application of GSA-4, GSA-2, and lime, respectively. Cadmium contents in wheat grain were declined significantly in the treatments of GSA-2, GSA-4, and lime.

Conclusions

Results of this study revealed a significant decrease in available Cd concentration with the application of amendments. Composite amendments were more effective in terms of metal uptake and bioaccumulation in wheat. In addition, our results indicate the effectiveness of composite amendments in stabilizing Cd in contaminated soil.

  相似文献   
954.
Abstract

Among major constraints to crop production, salt stress affects the morphological structure and yield in crop plants. Nano-fertilizers, have made their hierarchy to supplement the traditional fertilizers in mitigating the effect of abiotic stress due to their slow release and efficiency. Three products were tested namely lithovit®-standard(LITHO), monopotassium-phosphate(MKP:0-52-34), and aspirin(ASP) on salt-stressed tomato crop. These products were applied through foliar spraying (foliar) or fertigation (ferti) on tomato plants irrigated with 4 saline solutions (4, 6, 8 and 10dS/m). Control plants were subjected to five salinity levels (0, 4, 6, 8 and 10dS/m) without any treatments. Results showed that increasing in salinity levels adversely affected all parameters in the control plants. The ameliorating effect of MKP-ferti was prominent in plant height, stem diameter, number of fruits, fruit weight and yield/plant at 4 and 6S/m. Whereas, the effect of salinity was mitigated by LITHO-foliar regarding flowers number and total chlorophyll content at all salinity level. Leaf N, P and K contents were accumulated higher when MKP-ferti was used whereas, Ca2+ and Mg2+ contents were accumulated higher in the plants treated with LITHO-foliar. The cellular leakage of electrolyte was reduced at 4, 6 and 10dS/m with MKP-ferti and at 8dS/m with LITHO-foliar application. Among the two methods of application, foliar spraying of LITHO and ASP, and fertigation of MKP improved plant performance more than their complementary methods of application. The better performance of MKP necessitates the use of phosphorous and potassium-based nano-fertilizers. It can reduce the production cost of vegetables using conventional fertilizers.  相似文献   
955.
Journal of Soils and Sediments - Tailings are generally characterized by severe physicochemical conditions that limit the establishment of vegetation. The present study aimed to select suitable...  相似文献   
956.
An HPLC method was developed and validated for the quantification of sesaminol triglucoside and a sesaminol diglucoside in sesame seeds. These two lignans were isolated, and their structures were characterized by mass and nuclear magnetic resonance spectroscopy. Defatted sesame flour was extracted first with 85% ethanol for 5 h followed by 70% ethanol for 10 h at room temperature using naringenin as internal standard. Analysis of 65 different samples of sesame seeds indicated that the content of sesaminol triglucoside ranged from 36 to 1560 mg/100 g of seed (mean 637 +/- 312) and that of sesaminol diglucoside ranged from 0 to 493 mg/100 g of seed (mean 75 +/- 95). No significant difference was found between sesaminol glucoside contents in black and white seeds.  相似文献   
957.
Boron (B) is one of the important micronutrient required for rice in particular during reproductive growth. A laboratory study was conducted to explore the potential of boron nutripriming in improving the germination and early seedling growth of rice. Seeds of fine grain aromatic rice cultivar Super Basmati were primed in aerated B solution (0.001, 0.01, 0.1 and 0.5% w/v) while untreated dry seeds were taken as control. Seed priming in 0.001 and 0.1% B solutions improved the time to 50% germination, germination energy, final germination percentage, mean germination time, and germination index. Beyond this concentration either there was no effect or an adverse effect on rice seeds. In the cases of radicle length, plumule length and secondary roots priming more diluted B solution, i.e., 0.001% proved better than rest of the treatments as suppression in these three traits was observed by other B treatments than control. Seed priming in relatively concentrated B solution, i.e., 0.5% completely suppressed the germination and growth.  相似文献   
958.
High temperature has deleterious impacts on tomato growth and development and limits its production. Acetyl salicylic acid (ASA) and 24-epibrassinolide (EBL) have been widely reported as stress-ameliorating agents. The effect of exogenous application of varying levels of EBL (0.75, 1.5, and 3 µM) and ASA (0.25, 0.75, and 1.25 mM) on root activity (RA) in terms of 2,3,5 triphenyl tetrazolium chloride (TTC) reduction and root morphological features was evaluated in four-week-old tomato seedlings (cultivar: Mei Jie Lo) grown under high-temperature stress (46°C/4 h per day) for 21 days. The daily heat stress treatment almost ceased the root growth of chemically untreated seedlings. However, both EBL and ASA significantly attenuated the deleterious impacts of heat stress to different extents regarding root activity, total root length, surface area, volume, and number of nodes and connections. Different concentrations demonstrated signature effects. EBL (3 µM) was over all the best treatment to improve root activity whereas ASA (0.25 mM) best enhanced root architecture (net length, volume, and area) as compared to the untreated heat-stressed controls. However, EBL (3 µM) and ASA (1.25 mM) slightly inhibited mean root diameter. It is concluded that under high-temperature conditions, the exogenous EBL and ASA in studied doses improve root morphological features and root activity, hence enhance heat stress tolerance. Both chemical agents can be potential candidates in practical agriculture for extension of tomato growth period in summer by virtue of their heat stress amelioration ability.  相似文献   
959.
With the aim to select powerful microbial strains to be used for the enhancement of maize yield and resistance to abiotic and biotic stresses, we tested five endophytic bacterial strains previously isolated from maize roots. A range of different laboratory assays in regard to potential plant growth promotion was performed and strains were further evaluated for improving growth of five maize cultivars under axenic and natural soil conditions. Endophytic colonization was an additional component in our selection process as it is of high importance for an inoculant strain to efficiently colonize the plant environment. All strains had the potential to improve maize seedling growth under axenic conditions. Enterobacter sp. strain FD17 showed both the highest growth-promoting activity under axenic conditions as well as colonization capacity. FD17 was therefore selected for further plant tests in a net house, in which two different maize cultivars were grown in large pots until ripening and subjected to outdoor climatic conditions. Results showed that inoculation significantly increased plant biomass, number of leaves plant?1, leaf area, and grain yield up to 39 %, 14 %, 20 %, and 42 %, respectively, as compared to the un-inoculated control. Similarly, inoculation also improved the photochemical efficiency of photosystem II (PSII) of maize plant and reduced the time needed for flowering. We also confirmed that strain FD17 is able to colonize the rhizosphere, roots and stems. Based on rigorous testing, Enterobacter sp. strain FD17 showed the highest potential to promote growth and health of maize grown under natural conditions. This study suggested that in vitro plant growth-promoting traits and potential of maize seedling growth promotion by bacterial endophytes could be used for the selection of potential inoculant strains subjected for further testing as bio-inoculant under field conditions.  相似文献   
960.
The effects of phosphate processing wastewater (PPWW) on heavy metal accumulation in a Mediterranean soil (Tunisia, North Africa) were investigated. Moreover, the residual toxicities of PPWW-irrigated soils extracts were assessed. Results showed that heavy metal accumulation was significantly higher in PPWW-irrigated soil extracts than in control soil. The heavy metal accumulation increased over time in treated soil samples and their average values followed the following order: Iron (Fe 252.72 mg l?1) > Zinc (Zn 152.95 mg l?1) > Lead (Pb 128.35 mg l?1) > Copper (Cu 116.82 mg l?1) > Cadmium (Cd 58.03 mg l?1). The residual microtoxicity and phytotoxicity of the various treated soil samples extracts were evaluated by monitoring the bioluminescence inhibition (BI %) of Vibrio ficheri and the measurement of the germination indexes (GI %) of Lepidium sativum and Medicago sativa seeds. The results showed an important increase of residual toxicities of PPWW-treated soil extracts over time.  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