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   255篇
  免费   14篇
林业   10篇
农学   4篇
基础科学   2篇
  39篇
综合类   63篇
农作物   24篇
水产渔业   10篇
畜牧兽医   100篇
园艺   5篇
植物保护   12篇
  2023年   3篇
  2021年   3篇
  2020年   6篇
  2018年   3篇
  2017年   6篇
  2016年   6篇
  2015年   3篇
  2013年   6篇
  2012年   19篇
  2011年   10篇
  2010年   6篇
  2009年   3篇
  2008年   15篇
  2007年   16篇
  2006年   10篇
  2005年   12篇
  2004年   5篇
  2003年   7篇
  2000年   3篇
  1999年   5篇
  1995年   4篇
  1992年   3篇
  1990年   4篇
  1989年   3篇
  1988年   4篇
  1987年   3篇
  1986年   4篇
  1985年   4篇
  1981年   3篇
  1979年   5篇
  1978年   2篇
  1977年   3篇
  1976年   2篇
  1975年   3篇
  1974年   3篇
  1973年   4篇
  1972年   6篇
  1971年   4篇
  1970年   2篇
  1969年   4篇
  1968年   2篇
  1948年   2篇
  1947年   4篇
  1946年   3篇
  1945年   2篇
  1944年   3篇
  1943年   5篇
  1935年   2篇
  1933年   2篇
  1911年   2篇
排序方式: 共有269条查询结果,搜索用时 328 毫秒
181.
Effect of sericea lespedeza [SL; Lespedeza cuneata (Dum-Cours.) G. Don.] leaf meal feeding was evaluated in two experiments in indoor reared goats with experimental infection of Haemonchus contortus larvae. In the first experiment, ten 8-10 month old male Spanish and Alpine cross kids pair matched for body weight and age were fed SL or bermudagrass [BG; Cynodon dactylon (L.) Pers.] hay one week before infection and were infected with 5000 H. contortus L(3). The animals were maintained on the same diet for the remaining period and were slaughtered 28 days post-infection (DPI) to determine the establishment of incoming infective larvae. Goats fed SL had lower establishment (P<0.05) of H. contortus larvae than that of the control goats fed BG hay. In the second experiment, twenty-five 8-10 months old male Alpine cross, Saanen, Nubian×Saanen and Spanish kids reared in confinement on BG were experimentally infected with 5000 H. contortus L(3). On 35 DPI, the animals were allocated to two groups after blocking by fecal egg count (FEC), and one group was fed SL leaf meal (n=13), and another control group remained on BG (n=12). Four goats/group were slaughtered successively on days 7, 14, and 28 days post SL feeding, except on day 7, when five SL fed goats were slaughtered. Fecal egg counts and blood packed cell volume (PCV) were measured at weekly intervals and worm count, female worm fecundity, worm length and mucosal eosinophils, mast cells and globule leucocytes were measured after slaughter. Goats fed SL had a lower FEC (P<0.05) one week after feeding, as compared to those fed on BG, and the values remained at low level thereafter. Similarly, PCV was also significantly affected by feeding (P<0.01), and feeding and time interaction (P<0.05). However, worm burden, female worm fecundity, parasite length, and mucosal inflammatory cell count were similar between the groups. Feeding SL reduced the establishment of infective larvae and FEC of H. contortus in experimental studies and this plant could be used for biological control of parasite infection under field conditions to limit the harmful effects of the parasites in goats.  相似文献   
182.
OBJECTIVES: To estimate the intakes of cereal and dairy products and their contribution to nutrient intakes in men and women from the Republic of Ireland with a view to formulating food-based dietary guidelines. DESIGN: The North/South Ireland Food Consumption Survey established a database of habitual food and drink consumption using a 7-day food diary. From this database all cereal and dairy products from recipes and identifiable sources were identified and a new database was generated from which analysis of the role of cereal and dairy products in the diet was carried out. RESULTS: Almost 100% of the population consumed cereal and dairy products over the course of the survey week. In general, men consumed significantly more cereal and dairy products than did women (P<0.05). Cereal products made an important contribution to the mean daily intakes of energy (26%), protein (21%), fat (13%), carbohydrate (41%), fibre (45%), iron (43%) and folate (27%). Dairy products also contributed largely to the mean daily intakes of energy (11%), protein (14%), fat (17%), calcium (48%), phosphorus (24%) and vitamin A (27%). Analysis of nutrient intakes across tertiles of cereal and dairy consumption showed that high consumers of wholemeal bread, breakfast cereals, reduced-fat milk and yoghurt had lower fat and higher carbohydrate, fibre and micronutrient intakes than low consumers of these foods. CONCLUSIONS: Findings from the present study could be used to develop effective health strategies to implement changes in cereal and dairy consumption that could alter fat, fibre and micronutrient intakes in the diet.  相似文献   
183.
Many adhesive interactions are mediated by Arg-Gly-Asp (RGD) sequences within adhesive proteins. Such RGD sequences are frequently recognized by structurally related heterodimers that are members of the integrin family of adhesion receptors. A region was found in the platelet RGD receptor, gpIIb/IIIa, to which an RGD peptide becomes chemically cross-linked. This region corresponds to residues 109 to 171 of gpIIIa. This segment is conserved among the beta subunits of the integrins (76 percent identity of sequence), indicating that it may play a role in the adhesive functions of this family of receptors.  相似文献   
184.
Prioritizing climate change adaptation needs for food security in 2030   总被引:8,自引:0,他引:8  
Investments aimed at improving agricultural adaptation to climate change inevitably favor some crops and regions over others. An analysis of climate risks for crops in 12 food-insecure regions was conducted to identify adaptation priorities, based on statistical crop models and climate projections for 2030 from 20 general circulation models. Results indicate South Asia and Southern Africa as two regions that, without sufficient adaptation measures, will likely suffer negative impacts on several crops that are important to large food-insecure human populations. We also find that uncertainties vary widely by crop, and therefore priorities will depend on the risk attitudes of investment institutions.  相似文献   
185.
The correlation among a variety of physiological properties and the histochemical characteristics of muscle fibers belonging to single motor units in a mixed mammalian muscle is directly demonstrated. The population of motor units making up the cat gastrocnemius was classified into three nonoverlapping groups on the basis of a combination of physiological parameters. The muscle fibers belonging to motor units of each physiological type exhibited a distinctive histochemical profile, such that the three basic histochemical "fiber types" exactly matched the three physiologically defined groups. Within each individual motor unit, the muscle fibers were histochemically uniform.  相似文献   
186.
Serums showing complement-dependent cytotoxic reactions to acute lymphocytic leukemia cells were detected in three normal unimmunized subjects. These serums were reactive with tumor cells from 514 (514 tested) acute lymphocytic leukemia patients, and three (12 tested) patients with acute myelocytic leukemia; they did not react with tumor cells from patients with acute monocytic leukemia (two tested), with chronic lymphocytic leukemia (two tested) or with leukolymphosarcoma (two tested); nor did they react with normal lymphocytes from 52 different donors. These reactive serums appear to recognize antigens primarily associated with acute lymphocytic leukemia.  相似文献   
187.
Fragments of exogenous DNA that range in size up to several hundred kilobase pairs have been cloned into yeast by ligating them to vector sequences that allow their propagation as linear artificial chromosomes. Individual clones of yeast and human DNA that have been analyzed by pulsed-field gel electrophoresis appear to represent faithful replicas of the source DNA. The efficiency with which clones can be generated is high enough to allow the construction of comprehensive libraries from the genomes of higher organisms. By offering a tenfold increase in the size of the DNA molecules that can be cloned into a microbial host, this system addresses a major gap in existing experimental methods for analyzing complex DNA sources.  相似文献   
188.
There is increasing interest in good agriculture practices that address the issues of sustainability, reduction in inputs such as fertilizers and pesticides while maintaining crop yield and soil fertility. It is important that soil microbial diversity and function are not impaired by altered agricultural practice. In this study, as indicators of soil quality, the bacterial community structure was evaluated from a long-term field trial managed with conventional and low-input fertilization/pesticide regimes. The low-input plots under study received approximately one fifth less N fertilizer than the conventional-input plots, a maximum of half the recommended application rates of fungicides and pesticides and no externally added P source. A non-culturable approach was taken using polymerase chain reaction–denaturing gradient gel electrophoresis analysis of 16S rRNA and alkaline phosphomonoesterase [phosphatase] (ALP) genes in an attempt to relate bacterial community structure to respective field management regimes. To identify the ALP bacteria in these plots, randomly selected ALP clones were sequenced. The results based on Shannon diversity indices and community structure analysis of ALP genes suggest differences in community diversity and structure under conventional and low-input barley sites in most sampling seasons. We conclude that soil fertilization management affects the ALP bacteria in the barley rhizosphere, while the overall changes in bacterial community in these sites are prominently due to seasonal variation compared to crop or input regimes. The randomly selected ALP sequences identified from these sites were mostly from the Alpha and Gamma classes of Proteobacteria.  相似文献   
189.

Background

Root growth is highly responsive to temporal changes in the environment. On the contrary, diel (24 h) leaf expansion in dicot plants is governed by endogenous control and therefore its temporal pattern does not strictly follow diel changes in the environment. Nevertheless, root and shoot are connected with each other through resource partitioning and changing environments for one organ could affect growth of the other organ, and hence overall plant growth.

Results

We developed a new technique, GROWMAP-plant, to monitor growth processes synchronously in leaf and root of the same plant with a high resolution over the diel period. This allowed us to quantify treatment effects on the growth rates of the treated and non-treated organ and the possible interaction between them. We subjected the root system of Nicotiana tabacum seedlings to three different conditions: constant darkness at 22°C (control), constant darkness at 10°C (root cooling), and 12 h/12 h light–dark cycles at 22°C (root illumination). In all treatments the shoot was kept under the same 12 h/12 h light–dark cycles at 22°C. Root growth rates were found to be constant when the root-zone environment was kept constant, although the root cooling treatment significantly reduced root growth. Root velocity was decreased after light-on and light-off events of the root illumination treatment, resulting in diel root growth rhythmicity. Despite these changes in root growth, leaf growth was not affected substantially by the root-zone treatments, persistently showing up to three times higher nocturnal growth than diurnal growth.

Conclusion

GROWMAP-plant allows detailed synchronous growth phenotyping of leaf and root in the same plant. Root growth was very responsive to the root cooling and root illumination, while these treatments altered neither relative growth rate nor diel growth pattern in the seedling leaf. Our results that were obtained simultaneously in growing leaves and roots of the same plants corroborate the high sensitivity of root growth to the environment and the contrasting robustness of diel growth patterns in dicot leaves. Further, they also underpin the importance to carefully control the experimental conditions for root growth analysis to avoid or/and minimize artificial complications.  相似文献   
190.
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