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   394篇
  免费   30篇
林业   19篇
农学   23篇
基础科学   1篇
  67篇
综合类   48篇
农作物   12篇
水产渔业   15篇
畜牧兽医   194篇
园艺   13篇
植物保护   32篇
  2023年   5篇
  2022年   5篇
  2021年   11篇
  2020年   12篇
  2019年   3篇
  2018年   8篇
  2017年   9篇
  2016年   8篇
  2015年   12篇
  2014年   12篇
  2013年   14篇
  2012年   17篇
  2011年   30篇
  2010年   14篇
  2009年   20篇
  2008年   19篇
  2007年   29篇
  2006年   23篇
  2005年   23篇
  2004年   19篇
  2003年   15篇
  2002年   21篇
  2001年   4篇
  2000年   2篇
  1998年   5篇
  1997年   6篇
  1996年   2篇
  1995年   6篇
  1994年   5篇
  1993年   2篇
  1991年   4篇
  1989年   2篇
  1988年   3篇
  1987年   2篇
  1986年   2篇
  1985年   2篇
  1984年   3篇
  1983年   6篇
  1981年   7篇
  1980年   4篇
  1979年   2篇
  1978年   2篇
  1974年   4篇
  1973年   3篇
  1972年   2篇
  1970年   2篇
  1969年   2篇
  1966年   3篇
  1955年   1篇
  1903年   1篇
排序方式: 共有424条查询结果,搜索用时 15 毫秒
41.
A separation system has been developed to permit the simultaneous analysis of major anthocyanins and stilbenes from berries of Vitis species in <1 h. The system makes use of separation by HPLC and detection by UV-visible absorption and fluorescence, for anthocyanins and stilbenes, respectively, with the two detection systems linked in series. Monitoring the absorption at 520 nm permits ready identification and quantification of major anthocyanins. Chromatograms derived from fluorescence (330 nm excitation/374 nm emission) produce less clear data for the piceids and resveratrols, which are present in much lower amounts; peaks for these compounds can be verified by means of external or internal standards.  相似文献   
42.
43.
Selected primitive and modern wheat species were evaluated on the basis of their carotenoid composition and effects of the genotype and environment on lutein using spectrometry and liquid chromatography. Carotenoids in the wheat extracts were identified and confirmed on the basis of their UV/vis and mass spectra compared with those of authentic standards. The protonated molecule (M + 1)+ at m/z 569 was the predominant ion for zeaxanthin compared to the fragment ion at m/z 551 for lutein. A similar carotenoid profile was obtained for the wheat species investigated, but significant differences were observed in the concentration of carotenoids. Einkorn (Triticum monococcum) exhibited the highest level of all-trans-lutein, averaging 7.41 microg/g with small amounts of all-trans-zeaxanthin, cis-lutein isomers, and beta-carotene. Durum, Kamut, and Khorasan (Triticum turgidum) had intermediate levels of lutein (5.41-5.77 microg/g), while common bread or pastry wheat (Triticum aestivum) had the lowest content (2.01-2.11 microg/g). Lutein in einkorn appeared to be influenced significantly by environmental growing conditions.  相似文献   
44.
45.
ObservationsA 26-year-old male white rhinoceros (Ceratotherium simum), weighing approximately 2000 kg was anesthetized for an exploratory celiotomy. Sedation was achieved with intramuscular butorphanol (0.04 mg kg?1) and detomidine (0.025 mg kg?1) and induction of anesthesia with intravenous glyceryl guaiacolate (50 g) and three intravenous boluses of ketamine (200 mg, each); the trachea was then intubated and anesthesia maintained with isoflurane in oxygen using a circle breathing system. Positioning in dorsal recumbency for the surgery and later in sternal recumbency for the recovery represented challenges that added to the prolonged anesthesia time and surgical approach to partially correct an impaction. The rhinoceros recovered uneventfully after 10.4 hours of recumbency.ConclusionsAnesthetic management for an exploratory celiotomy with a midline approach is possible in rhinoceroses, although planning and extensive staff support is necessary to adequately position the patient.  相似文献   
46.
Considerable attention has focussed on the potential of indigenous agricultural knowledge for sustainable development. Drawing upon fieldwork on the soil and water management principles of rice farming systems in Senegambia, this paper examines the potential of the traditional system for a sustainable food security strategy. Problems with pumpirrigation are reviewed as well as previous efforts in swamp rice development. It is argued that sustainability depends on more than ecological factors and in particular, requires sensitivity to socio-economic parameters such as the labor demands of the food security strategy, the sexual division of labor, and food pricing policies.  相似文献   
47.
The objective of this retrospective study was to determine the occurrence of joint-related complications after elective arthroscopy of the tibiotarsal joint (TTJ) in 329 horses, and the association with specific clinical parameters. Data were collected from medical records of horses undergoing elective tibiotarsal joint arthroscopy for fragment removal. Exact conditional univariate regression was used to determine significant risk factors for joint-related post-operative complications.Of 485 joints, 2 (0.4%) developed surgical site infection, 4 (0.8%) developed septic arthritis, 1 (0.2%) developed synovial fistula. There was a significantly increased odds of having septic arthritis as height and length of the distal intermediate ridge of the tibia (DIRT) lesion increased. The median height and length of the DIRT fragments in affected cases was 13.5 mm and 18.0 mm, respectively. For each unit (1 mm) increase in height, there was a 42% increase in the risk of septic arthritis occurrence (P = 0.0042), and a 15% increase for each unit increase in length (P = 0.035). Horses were significantly less likely to develop septic arthritis when suture smaller than USP 0 was used.Horses with larger osteochondritis dissecans lesions of the DIRT region have an increased risk of developing septic arthritis following fragment removal.  相似文献   
48.
Small nuclear RNAs (snRNAs) are essential factors in messenger RNA splicing. By means of homozygosity mapping and deep sequencing, we show that a gene encoding U4atac snRNA, a component of the minor U12-dependent spliceosome, is mutated in individuals with microcephalic osteodysplastic primordial dwarfism type I (MOPD I), a severe developmental disorder characterized by extreme intrauterine growth retardation and multiple organ abnormalities. Functional assays showed that mutations (30G>A, 51G>A, 55G>A, and 111G>A) associated with MOPD I cause defective U12-dependent splicing. Endogenous U12-dependent but not U2-dependent introns were found to be poorly spliced in MOPD I patient fibroblast cells. The introduction of wild-type U4atac snRNA into MOPD I cells enhanced U12-dependent splicing. These results illustrate the critical role of minor intron splicing in human development.  相似文献   
49.
Novel, low-abundance microbial species can be easily overlooked in standard polymerase chain reaction (PCR)-based surveys. We used community genomic data obtained without PCR or cultivation to reconstruct DNA fragments bearing unusual 16S ribosomal RNA (rRNA) and protein-coding genes from organisms belonging to novel archaeal lineages. The organisms are minor components of all biofilms growing in pH 0.5 to 1.5 solutions within the Richmond Mine, California. Probes specific for 16S rRNA showed that the fraction less than 0.45 micrometers in diameter is dominated by these organisms. Transmission electron microscope images revealed that the cells are pleomorphic with unusual folded membrane protrusions and have apparent volumes of <0.006 cubic micrometer.  相似文献   
50.
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