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   5756篇
  免费   345篇
  国内免费   2篇
林业   1044篇
农学   167篇
基础科学   13篇
  1232篇
综合类   540篇
农作物   154篇
水产渔业   222篇
畜牧兽医   2186篇
园艺   128篇
植物保护   417篇
  2023年   35篇
  2022年   44篇
  2021年   86篇
  2020年   81篇
  2019年   51篇
  2018年   201篇
  2017年   181篇
  2016年   166篇
  2015年   140篇
  2014年   156篇
  2013年   383篇
  2012年   327篇
  2011年   359篇
  2010年   169篇
  2009年   153篇
  2008年   288篇
  2007年   318篇
  2006年   314篇
  2005年   273篇
  2004年   253篇
  2003年   272篇
  2002年   217篇
  2001年   181篇
  2000年   174篇
  1999年   103篇
  1998年   36篇
  1997年   35篇
  1996年   46篇
  1995年   74篇
  1994年   44篇
  1993年   23篇
  1992年   25篇
  1991年   21篇
  1990年   22篇
  1989年   16篇
  1988年   23篇
  1987年   14篇
  1986年   30篇
  1985年   31篇
  1984年   25篇
  1983年   21篇
  1982年   15篇
  1980年   26篇
  1977年   23篇
  1973年   16篇
  1966年   14篇
  1961年   13篇
  1955年   14篇
  1941年   14篇
  1857年   13篇
排序方式: 共有6103条查询结果,搜索用时 546 毫秒
131.
The specificity of the infection of maize, wheat and rice roots by N2-fixing Azospirillum spp was studied in four greenhouse experiments using pots with unsterilized soil and in two field experiments. In all experiments A. lipoferum was most frequently isolated from externally sterilized roots of maize, and A. brasilense nir? (nitrite reductase negative) from wheat and rice. In pot experiments, A. brasilense nir+ was isolated with moderate frequency from within maize roots but rarely from within wheat or rice roots. Inoculation of the pots with a mixture of representative strains of the three Azospirillum groups had no effect on the proportion of strains recovered from each plant species. In the field experiments, inoculation with spontaneous streptomycin-resistant mutants of two of the representative strains confirmed the apparent specificity of A. lipoferum for maize roots and of A. brasilense for wheat but the results were partially obscured by the unexpectedly high proportion of streptomycin-resistant strains isolated from within the roots of uninoculated plants.  相似文献   
132.
133.
A technique for assessing the metabolically-active fungal biomass by means of fluorescein diacetate (FDA) staining was recently described (Söderström, 1977). In this note some practical details in the application of this technique to studies of FDA-active fungal biomass in the soil are discussed.  相似文献   
134.
135.
136.
Ohne Zusammenfassung  相似文献   
137.
In this research, the mineral and organic composition of the seminal plasma, physical spermatological parameters and their physiological relationships were investigated in grass carp (Ctenopharyngodon idella). The seminal plasma contained 98.14±5.23 mM L?1 (Na+), 380.85±25.95 mM L?1 (K+), 30.25±4.96 mg dL?1 (Ca2+), 19.16±1.70 mEq L?1 (Mg2+), 1.36±0.11 mg dL?1 glucose, 0.37±0.08 g dL?1 total protein, 12.02±1.18 mg dL?1 cholesterol, 14.85±1.50 mg dL?1 triglyceride and 43.5±9.56 mg dL?1 urea. The following spermatological parameters were found: sperm volume 14.44±1.16 mL, sperm motility 80.60±1.55%, movement duration 67.68±4.32 s, density 15.43±0.72 × 109 mL?1, total density 337.43+45.86 × 109 and pH 7.24±0.17. The Na+ and Ca2+ ions correlated negatively with spermatozoa motility (r=?0.453, P>0.05 and r=?0.192, P>0.05) respectively. The K+ ion correlated positively with spermatozoa motility (r=0.545, P>0.05). But a statistically significant correlation was not observed between sperm motility and seminal plasma parameters. The following correlations were observed between mineral and organic components. The Mg2+ was positively correlated with glucose and cholesterol (r=0.692, P<0.05 and r=0.680, P<0.05) respectively. A highly significant positive relationship was also found between Mg2+ and total protein (r=0.837, P<0.01). On the other hand, a significantly negative relationship was found between Ca2+ and triglyceride (r=?0.639, P<0.05). These parameters should be considered when developing procedures for either artificial fertilization or for cryopreservation of grass carp sperm.  相似文献   
138.
Laminarin is a β‐glucan from the brown algae Laminaria digitata (J.V. Lamour), which can activate innate immune responses. With the aim of developing a strategy to evaluate specific phenotypical parameters of the effects of laminarin in trout innate immunity, we (i) fed fish with laminarin‐supplemented diet (0.2 g kg?1 day?1) for 21 days and (ii) treated fish with a single dose of intraperitoneal injected laminarin (0.08 g kg?1 fish). The evaluation of cellular and humoral immune parameters was established at phenotypic level by the phagocytic activity of headkidney macrophages and detection of inflammatory cytokines in head kidney and gill tissue by indirect ELISA. Results showed that both delivery methods of laminarin produce an increase in the phagocytic activity in head kidney macrophages and a significant increase in the production of TNFα and IL‐8 in gill tissue at day 21. Additionally, some of these parameters were significantly correlated (P < 0.025), which places them as new potential combined markers to detect activation of trout defense mechanisms by laminarin. These results highlight the importance of developing new protocols to quantitate immune parameters, in order to evaluate immunostimulants in fish farming.  相似文献   
139.
The current study investigated the effects of oyster mushroom Pleurotus ostreatus, extract on immunological and hematological parameters of rainbow trout, Oncorhynchus mykiss. The fish were fed diets containing 0 (control), 1, and 2% supplementation of the oyster mushroom extract for 6 wk. Blood samples were collected weekly for the first 6 weeks. After 6 wk of feeding, the fish were challenged with Lactococcus garvieae and mortality was recorded. The results of this study showed that feeding rainbow trout an oyster mushroom extract–supplemented diet stimulated phagocytic activity of phagocytic cells, lysozyme activity, and myeloperoxidase activity in serum, but it did not significantly affect the total serum immunoglobulin level. At the same time, a significant increase was found in the number of neutrophils, monocytes, and total white blood cells. Fish fed the diet supplemented with oyster mushroom extract showed reduced mortalities following L. garvieae infection compared with controls. These results show that supplementation of fish diets with oyster mushroom extract at 1 and 2% concentrations significantly imrpoves hematological parameters and modulates the immune response against L. garvieae in rainbow trout.  相似文献   
140.
Im Statischen Düngungsversuch Bad Lauchstädt werden nach Erweiterung der Versuchsfrage seit 1978 die Prüffaktoren: Stalldung (2 Stufen), Corg‐Gehalt im Boden (6 Stufen) und Mineral‐N‐Mengen (5 Stufen) in der Fruchtfolge Kartoffeln, Winterweizen, Zuckerrüben, Sommergerste geprüft. Nur bei Sommergerste konnte eine Ertragswirkung des Stalldungs im Vergleich zu ausschließlicher Mineraldüngung nachgewiesen werden. Die jährlichen Veränderungen der Corg‐ und Nt‐Gehalte im Boden betrugen bei jeweils extremen Änderungen des Düngungsregimes bis zu 0, 012% Corg bzw. 0,0013% Nt.  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