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   3214篇
  免费   197篇
  国内免费   19篇
林业   223篇
农学   204篇
基础科学   68篇
  869篇
综合类   285篇
农作物   391篇
水产渔业   264篇
畜牧兽医   665篇
园艺   106篇
植物保护   355篇
  2023年   36篇
  2022年   111篇
  2021年   149篇
  2020年   164篇
  2019年   214篇
  2018年   244篇
  2017年   221篇
  2016年   204篇
  2015年   115篇
  2014年   134篇
  2013年   348篇
  2012年   167篇
  2011年   210篇
  2010年   145篇
  2009年   100篇
  2008年   163篇
  2007年   102篇
  2006年   77篇
  2005年   64篇
  2004年   52篇
  2003年   39篇
  2002年   33篇
  2001年   26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
  1980年   3篇
  1979年   7篇
  1976年   3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3430条查询结果,搜索用时 31 毫秒
991.
Three plant growth-promoting rhizobacteria strains containing ACC-deaminase (Pseudomonas jessenii, Pseudomonas fragi, and Serratia fonticola) and Rhizobium leguminosarum were selected and characterized by conducting some experiments under axenic condition. The selected isolates had the potential to improve the growth of lentil seedlings under axenic conditions. Pot and field experiments were conducted to evaluate the potential of these selected strains for improving growth and yield of lentil under natural conditions. A classical triple response (reduction of stem elongation, swelling of hypocotyle, and change in the direction of growth) bioassay was also conducted to evaluate the effect of high ethylene concentration on the growth of etiolated lentil seedlings, and the performance of coinoculation was evaluated to reduce the classical triple response in comparison with cobalt (Co2+), a chemical inhibitor of ethylene. Results showed that coinoculation of Pseudomonas and Serratia sp. with R. leguminosarum significantly increased the growth and yield of lentil. However, synergistic/coinoculation effect of P. jessenii with R. leguminosarum was more pronounced compared to that with P. fragi and S. fonticola. It increased the number of pods per plant, number of nodules per plant, dry nodule weight, grain yield, and straw yield up to 76%, 196%, 109%, 150%, and 164% under pot and up to 98%, 98%, 100%, 82%, and 78%, respectively, under field conditions as compared to uninoculated control. Similarly, combined inoculation significantly increased N concentration of grains under both pot and field conditions. The results from classical triple response assay showed that the effects of classical triple response decreased due to coinoculation in etiolated lentil seedlings and due to a decrease in the ethylene concentration. It is suggested that the strategy adopted by Pseudomonas sp. containing ACC-deaminase with Rhizobium to promote nodulation and yield by adjusting ethylene levels could be exploited as an effective tool for improving growth, nodulation, and yield of lentil.  相似文献   
992.
Changes in total organic C (C T), water-soluble organic C (C WS), microbial biomass C (C MB), C mineralization, particulate organic C (C P), labile organic C (C L), C management index (CMI), and C storage in surface Hapli-Ustic Cambisol (0–20 cm) under straw incorporation after both 2- and 10-year durations were investigated in a maize (Zea mays L.) field experiment in northeast China, in order to examine the effectiveness of these active C fractions and CMI as early indicators for total C change. The treatments included straw removal (0%S), 50% of straw incorporation (50%S), and 100% of straw incorporation (100%S). Under the straw incorporation, C T concentration and C storage did not significantly change under 2-year duration, while were significantly increased under 10-year duration. However, C MB, total C mineralization (C TM), C P, and C L, and CMI were significantly increased under the straw incorporation even after only 2-year duration, and the responses were more significant after 10-year duration. There were positive correlations between all these C indicators with each other. Our findings demonstrate that the measured active C fractions (except for C WS) and CMI can provide an early indication of change in total soil organic C induced by straw incorporation.  相似文献   
993.
The aim of this study was to determine if hypoxia and the hypoxia mimetic cobalt chloride regulate the activity of matrix metalloproteinase (MMP)-2 and -9 in cultures of equine hoof keratinocytes. These effects were assessed in primary cultures of laminar keratinocytes using gelatin zymography. Incubation of keratinocytes with cobalt chloride significantly increased the levels of active MMP-2 compared to untreated controls. Hypoxia significantly increased the expression of active MMP-2 and -9 in keratinocyte cultures. This up-regulation was observed after 6h and peaked at 24h. The study findings provide novel evidence of a potential link between hypoxia within the hoof and up-regulation of MMPs which may in turn result in damage to the lamellar basement membrane.  相似文献   
994.
995.
Twenty one date palm (Phoenix dactylifera L.) accessions originated from different date palm groves were studied to assess the overall degree of polymorphism, detect similarities between genotypes and assess important agronomic traits. Thirty vegetative and reproductive variables were scored and subjected to multivariate analysis. Results showed a considerable phenotypic diversity among local date palm germplasm. Principal component analysis (PCA) revealed that characters related to leaflets length and spine, fruit and seed sizes accounted for a large proportion of the observed variability. Cluster analysis (CA) showed a typically continuous phenotypic diversity among date palm accessions and little associations between accessions from same geographic origin. Also, some heterogeneity within accessions that received the same denomination was evidenced.  相似文献   
996.
In this study, in order to know the variability for a rootstock breeding program genetic diversity and relationships among 55 Iranian almond genotypes and seven related Prunus species were investigated. Morphological and molecular analyses were used. Principal component analysis showed that three components explained 67.6% of the total morphological variation for the first year and 68.06% for the second year of the study. Leaf traits were predominant in the first component and contributed most of the total variation. Leaf length and width, as well as, leaf area were highly correlated with each other and correlated to vigor. Also a negative correlation was found between leaf length/width ratio and vigor. Ward's method was used to construct cluster from morphological data which allocated individuals into their respective species. Out of 100 pre-screened RAPD primers, 16 with reproducible bands and maximum polymorphism were selected. Two-hundred and sixty bands were scored of which 250 of them were polymorphic. Average value of polymorphism per primer was 95.81% and maximum value for polymorphism (100%) was obtained from TIBMBA-14, TIBMBA-17, TIBMBB-05, TIBMBB-08, TIBMBD-09, and TIBMBD-10. On the other hand, the minimum value was obtained from TIBMBB-16 (86%). Primer TIBMBB-5 gave the maximum number of bands (25 fragments) and the minimum obtained from TIBMBE-18 (11 fragments). Genetic similarity based on Jaccard's coefficient ranged from 0.28 to 0.79 with an average of 0.53. Molecular analysis revealed a high degree of separation among samples regarding their geographical origin. Correlation between two approaches was low (R = −0.38). High molecular and morphological variability indicated that this collection includes rich and valuable plant materials for almond rootstock breeding.  相似文献   
997.
The aim of this study was to investigate the anatomy of the arterial supply and branches of the thoracic limb of the porcupine. With this aim, five (three male and two female) adult porcupines were used. The vascular tree of the thoracic limb was injected through the common carotid arteries with coloured latex. The a. thoracica externa arose from the a. axillaris at the level of the fourth rib. It divided into two branches and went to the m. cutaneus trunci and the m. pectoralis ascendens. The a. subscapularis came off the a. thoracodorsalis. Later, the a. circumflexa humeri caudalis et cranialis, the three muscular branches and the a. circumflexa scapulae arose from the a. subscapularis. The a. profunda brachii arose together with the a. bicipitalis from the same truncus. The a. collateralis ulnaris left from the a. brachialis independently. Rete carpi dorsale was formed by the a. radialis. the r. carpeus dorsalis of the a. collateralis ulnaris and the a. interossea caudalis. Arcus palmaris profundus was formed by the r. profundus of the a. interossea caudalis and the r. palmaris profundus of the a. radialis. In conclusion, despite a partial resemblance to that in the rat, the distribution of the thoracic limb arteries in the porcupine was found to be completely different from that of other mammals. These findings represent, to our knowledge, the first study on the distribution of thoracic limb arteries in the porcupine.  相似文献   
998.
In the very large areas of arid highlands in West Asia, of which land over 1000 m in Balochistan is typical, as a result of rapidly increasing numbers of small ruminants and subsequent overgrazing of natural rangelands, severe shortages in animal feed are being experienced. To address this problem the And Zone Research Institute (AZRI) have been evaluating annual forage legume germplasm for adaptability to the harsh climatic conditions of highland Balochistan. Due to the marginality of the environment for sustained crop production an unconventional germplasm evaluation strategy has been adopted which emphasizes the introduction of landraces, particularly of the genus Vicia. The substantial risk of crop failure from either cold or drought, in any year, makes continuity of seed supply of selected lines a major problem. Support from ICARDA in Syria for re-supply of seed is a major advantage to the AZRI program.
In the last three years some tangible progress has been made in selection. V. villosa ssp. dasycarpa Ace. 683 has with autumn sowing shown sufficient cold tolerance and is highly productive in wet years. V. ervilia Ace. 2542 has shown some potential for drought tolerance which could be exploited for spring sowing.  相似文献   
999.
Hydatidosis was seen in 38.90% of cattle, 33.06% of buffaloes and 58.9% of camels slaughtered at a local abattoir. No statistically significant seasonal difference in prevalence was observed. Most cysts (63.14%) were infertile. Protein and carbohydrate contents of fluid from fertile and infertile cysts did not differ significantly. Sensitivity, specificity and efficiency of indirect haemagglutination test and enzyme-linked immunosorbent assay were low.  相似文献   
1000.
Phenylbutazone was administered intravenously and intramuscularly at a dosage rate of 4.4 mg/kg to a group of 6 female camels in a two-period crossover study. After intravenous (i.v.) administration, disposition was characterised by a two-compartment open model, with a low volume of distribution (0.174 l.kg–1), and distribution and elimination half-lives of 0.43 and 12.51 h, respectively. After intramuscular (i.m.) dosing absorption was relatively rapid with absorption half-time and time of maximal concentration values of 1.14 and 3.95 h, respectively. Plateau concentrations of phenylbutazone in plasma were obtained between 2 and 12 h and mean bioavailability was 97%, although this was subject to wide inter-animal differences. Plasma concentrations of the phenylbutazone metabolite, oxyphenbutazone, were low after iv dosing and generally undetectable after im administration, indicating that it is unlikely to contribute significantly to the pharmacological effects produced by phenylbutazone administration. An indication was obtained that phenylbutazone inhibited the ex vivo synthesis of serum thromboxane B2 (TxB2) for 24 h after i.v. dosing, but this finding requires confirmation.  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