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   877篇
  免费   55篇
林业   70篇
农学   12篇
基础科学   8篇
  146篇
综合类   90篇
农作物   28篇
水产渔业   72篇
畜牧兽医   420篇
园艺   16篇
植物保护   70篇
  2022年   9篇
  2021年   10篇
  2020年   15篇
  2019年   17篇
  2018年   27篇
  2017年   21篇
  2016年   22篇
  2015年   20篇
  2014年   28篇
  2013年   60篇
  2012年   41篇
  2011年   48篇
  2010年   27篇
  2009年   33篇
  2008年   49篇
  2007年   49篇
  2006年   24篇
  2005年   38篇
  2004年   35篇
  2003年   36篇
  2002年   19篇
  2001年   13篇
  2000年   21篇
  1999年   11篇
  1998年   10篇
  1997年   7篇
  1995年   6篇
  1994年   6篇
  1993年   6篇
  1992年   17篇
  1991年   14篇
  1990年   10篇
  1989年   15篇
  1988年   6篇
  1987年   5篇
  1986年   15篇
  1985年   10篇
  1984年   9篇
  1982年   5篇
  1980年   7篇
  1979年   9篇
  1978年   6篇
  1976年   5篇
  1974年   5篇
  1973年   5篇
  1972年   4篇
  1970年   8篇
  1966年   4篇
  1868年   4篇
  1864年   5篇
排序方式: 共有932条查询结果,搜索用时 0 毫秒
41.
Growth, gravidity and lactation put high demands on the performance of the myocardium. The aim of this study, which was performed in 40 female and 20 male bovines ranging from 1 to 4.5 years old, was to determine gross and microscopic morphometric data of bovine myocardium to establish a comparative measure of myocardial growth during juvenile development. During the developmental stage of young adulthood, age‐related increases in female myocardial characteristics included cardiac mass, left and right ventricular mass and the ratio of cardiac mass to loose connective tissue. Age‐related decreases were observed in the number of myocyte nuclei per mm² and the thickness of the right ventricular wall. Sex differences in these parameters were found between 2‐year‐old bulls (N = 20) and 2‐year‐old heifers (N = 10), with males having heavier hearts, thicker ventricular walls, less myocytes in the left ventricle and less connective tissue in both ventricles. Age and sex had no influence on the ratio of capillaries to myocytes, estimated at 0.98 in the adult bovine. Capillary density does not change during juvenile development, but cross‐sectional capillary area does adapt to myocyte cross‐sectional area, accounting for this relatively constant ratio.  相似文献   
42.
The detection of ChIFN production after ex vivo antigenic-stimulation of T-lymphocytes has been evaluated for the first time, as a tool to assess cell-mediated immunity (CMI) after avian influenza (AI) infection in 10-day-old SPF chickens. Preliminarily, recall antigens have been produced either by concentrating and inactivating the whole virus or by dissociating the viral proteins. Biologically and structurally intact forms of the viral proteins were isolated by non-ionic detergents while heating, chemical agents and ionic detergent used for virus inactivation altered the antigenic viral components. The n-octyl-B-D-gluco-pyranoside treatment at low temperature was very efficient to produce AI antigenic proteins used for evaluation of ChIFN production after ex vivo antigenic-stimulation of splenic and peripheral lymphocytes. In addition, protocols to isolate lymphocytes from the respiratory tract - the trachea and the lung - have been adapted for local CMI evaluation after similar ex vivo recall assay. Specific AI CMI in the spleen, the blood and the lung was detected for 5 weeks after low pathogenic AI (LPAI) infection in chickens, while further development is needed for tracheal CMI measurement.  相似文献   
43.
Stenotrophomonas rhizophila DSM14405T is of high biotechnological interest as plant growth stimulator, especially for salinated conditions. The objective of this study was to determine the effect of plant species (cotton, tomato, and sweet pepper) on colonisation and plant growth promotion of this beneficial bacterium in gnotobiotic systems and in non-sterile soil. All plant structures (leaves, stems, and roots) were densely colonised by DSM14405T reaching up to 109 cells g?1 fresh weight; under gnotobiotic conditions the abundances were 4–5 orders of magnitude higher than in non-sterile soil. Under non-sterile conditions and ambient humidity, tomato shoots were more densely colonised than shoots of sweet pepper and cotton. S. rhizophila DSM14405T was shown to grow endophytically and colonise the vicinity of root hairs of tomato. Plant growth promotion was particularly apparent in tomato. In general, the impact of plant species on colonisation and plant growth promotion was more pronounced in soil than under gnotobiotic conditions and likely due to the control of diseases and deleterious microorganisms. S. rhizophila DSM14405T was shown to control diseases in sweet pepper and in cotton. Molecular profiling via single strand conformation polymorphism of internal transcribed spacers and 16S rRNA genes (PCR-single strand conformational polymorphism (SSCP)) revealed that S. rhizophila DSM14405T strongly affected fungal, but not bacterial communities in the rhizosphere of tomato and sweet pepper. Major SSCP bands related to uncultured fungi and Candida subhashii, disappeared in tomato rhizosphere after Stenotrophomonas treatment. This suggests an indirect, species-specific plant growth promotion effect of S. rhizophila via the elimination of deleterious rhizosphere organisms.  相似文献   
44.
Economic growth in China’s agricultural sector lags behind growth in industry and services, creating an ever widening rural–urban income gap. Development of the non-agricultural sectors offers new opportunities for farmers in China’s more advanced provinces such as Zhejiang. Increased income in the urban sector creates markets for new products, and migrating farmers rent their land to those staying. Until now, the prevailing rice-based systems have been managed mainly using manual labour and animal traction, but the larger farms resulting from migration may facilitate, or even require mechanization. In this study, we use a simulation model of the farm household to analyse the effects of increasing farm size and the transition from rice to vegetable production, while also studying the effects of mechanization.  相似文献   
45.
To improve genetic gain of breeding programs for village poultry production, breeding schemes with observations obtained in village production systems using individual (VIO) and group recording (VGO) were examined under different levels of genotype-by-environment-interactions (GxE). GxE was modeled by varying the correlation between traits measured in the breeding station and village environments for bodyweight (rg_BW) and egg production (rg_EP). Relative and absolute genetic gains obtained from VIO and VGO were used for comparison between the schemes. Results showed that village observations significantly improved genetic gains compared to the scheme without birds tested in the village. The improvement was only slightly larger with individual observations than with group observations. Higher rg_BW and rg_EP led to lower relative genetic gain, but a higher absolute gain of VIO and VGO. It is recommended to apply a breeding scheme using group recording of village performance when strong GxE in breeding for village poultry is expected.  相似文献   
46.
47.
Sixty-one dogs with appendicular osteosarcoma were treated with amputation and chemotherapy of cisplatin and doxorubicin. Serum samples were obtained before and after treatment for determination of total alkaline phosphatase (TALP) activity as well as the activities of the constituent bone (BALP), liver (LALP), and corticosteroid-induced (CALP) isoenzymes. The relationship between alkaline phosphatase activities and survival was examined by Cox proportional hazards regression analysis and Kaplan-Meier log rank analysis. Mean activity of TALP, BALP, and LALP decreased significantly after treatment (P < .001). TALP and LALP activities before treatment were significantly correlated with survival (P = .006 and .001, respectively). The correlation between BALP activity before treatment and survival approached significance (P = .054). CALP activity and TALP, BALP, and LALP activities after treatment were not significantly correlated with survival. Dogs with normal pretreatment TALP and BALP activities survived significantly longer than dogs with increased pretreatment activities (P = .001 and .003, respectively). Median survival times for dogs with normal or increased TALP activities before treatment were 12.5 and 5.5 months, respectively; and median survival times for dogs with normal or increased BALP activities before treatment were 16.6 and 9.5 months, respectively. In the design of future clinical trials involving dogs with osteosarcoma, consideration should be given to stratifying the randomization according to alkaline phosphatase activity. In addition, alkaline phosphatase activity should be a factor considered by clinicians attempting to tailor the aggressiveness of adjuvant chemotherapy to the needs of individual patients or owners.  相似文献   
48.
49.
tests, based on the polymerase chain reaction ( ), were developed for the detection of two breed-specific mutations responsible for the autosomal recessive disorder bovine α-mannosidosis. The tests involve separate amplification of two exons of the lysosomal α-mannosidase gene followed by restriction enzyme digestion of the amplicons. We demonstrate that one of the mutations, the 662G→A transition, is responsible for α-mannosidosis in Galloway cattle. The other mutation, the 961T→C transition, is uniquely associated with α-mannosidosis in Angus, Murray Grey and Brangus cattle from Australia. The 961T→C mutation was also detected in Red Angus cattle exported from Canada to Australia as embryos. All 39 animals classified as heterozygotes on the basis of biochemical assays were heterozygous for one of the two mutations. None of 102 animals classified as homozygous-normal on the basis of biochemical assays possessed the mutations. Our results indicate that the two breed-specific mutations may have arisen in Scotland and by the export of animals and germplasm disseminated to America, New Zealand and Australia.  相似文献   
50.
AZD3783, a cationic amphiphilic drug and a potent inhibitor of the 5-hydroxytryptamine (5-HT1B) receptor, was explored as a potential treatment for depression. To support clinical trials, repeat dose toxicity studies in rats and dogs were conducted. Here we report toxicity findings in dogs after dosing from 1 to 3 months. In the 1-month study, there were minimal neuronal vacuolation in the brain, a marked increase in liver enzymes accompanied by hepatocellular degeneration/necrosis and phospholipidosis (PLD), and PLD/cholecystitis in the gallbladder of animals dosed at 47 mg/kg/day. In the 3-month study, neurotoxicity resulted in euthanasia of one animal dosed at 30 mg/kg/day after 86 days. Extensive pathologic changes were seen in all animals in retina epithelium (inclusion bodies), brain (neuronal vacuolation, degeneration, or necrosis and nerve fiber degeneration), spinal ganglia (vacuolation, degeneration, or necrosis), as well as sciatic and optic nerves (degeneration). Pigment-laden macrophages were observed in the lung, kidney, liver, gallbladder, bone marrow, gastrointestinal tract, and lymphoid tissues. Also seen were vitrel and retinal hemorrhage in the eyes. A brain concentration and pathology study showed that the concentration of AZD3783 in the brain was approximately 4 times higher than in the plasma after 4 weeks of dosing, however, they were similar in all regions examined, and did not correlate with areas with pathologic findings. Our findings with AZD3783 in dogs have not been reported previously with other CNS compounds that effect through serotonergic pharmacology.  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