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   1693篇
  免费   68篇
  国内免费   2篇
林业   53篇
农学   28篇
基础科学   4篇
  246篇
综合类   177篇
农作物   53篇
水产渔业   67篇
畜牧兽医   1045篇
园艺   38篇
植物保护   52篇
  2023年   9篇
  2022年   9篇
  2021年   21篇
  2020年   24篇
  2019年   31篇
  2018年   29篇
  2017年   25篇
  2016年   28篇
  2015年   25篇
  2014年   36篇
  2013年   55篇
  2012年   91篇
  2011年   144篇
  2010年   77篇
  2009年   54篇
  2008年   107篇
  2007年   130篇
  2006年   137篇
  2005年   128篇
  2004年   126篇
  2003年   116篇
  2002年   107篇
  2001年   16篇
  2000年   18篇
  1999年   26篇
  1998年   19篇
  1997年   17篇
  1996年   10篇
  1995年   16篇
  1994年   14篇
  1993年   12篇
  1992年   7篇
  1991年   20篇
  1990年   10篇
  1989年   9篇
  1988年   4篇
  1987年   7篇
  1985年   10篇
  1984年   3篇
  1983年   4篇
  1982年   3篇
  1981年   3篇
  1980年   6篇
  1979年   4篇
  1976年   3篇
  1974年   3篇
  1973年   1篇
  1970年   1篇
  1968年   1篇
  1965年   2篇
排序方式: 共有1763条查询结果,搜索用时 0 毫秒
61.
The polyacetylene falcarinol, isolated from carrots, has been shown to be protective against chemically induced colon cancer development in rats, but the mechanisms are not fully understood. In this study CaCo-2 cells were exposed to falcarinol (0.5-100 microM) and the effects on proliferation, DNA damage, and apoptosis investigated. Low-dose falcarinol exposure (0.5-10 microM) decreased expression of the apoptosis indicator caspase-3 concomitantly with decreased basal DNA strand breakage. Cell proliferation was increased (1-10 microM), whereas cellular attachment was unaffected by <10 microM falcarinol. At concentrations above 20 microM falcarinol, proliferation of CaCo-2 cells decreased and the number of cells expressing active caspase-3 increased simultaneously with increased cell detachment. Furthermore, DNA single-strand breakage was significantly increased at concentrations above 10 microM falcarinol. Thus, the effects of falcarinol on CaCo-2 cells appear to be biphasic, inducing pro-proliferative and apoptotic characteristics at low and high concentrations of falcarinol, respectively.  相似文献   
62.
The next generation of biotechnology-derived products with the combined benefit of herbicide tolerance and insect protection (MON 88017) was developed to withstand feeding damage caused by the coleopteran pest corn rootworm and over-the-top applications of glyphosate, the active ingredient in Roundup herbicides. As a part of a larger safety and characterization assessment, MON 88017 was grown under field conditions at geographically diverse locations within the United States and Argentina during the 2002 and 2003-2004 field seasons, respectively, along with a near-isogenic control and other conventional corn hybrids for compositional assessment. Field trials were conducted using a randomized complete block design with three replication blocks at each site. Corn forage samples were harvested at the late dough/early dent stage, ground, and analyzed for the concentration of proximate constituents, fibers, and minerals. Samples of mature grain were harvested, ground, and analyzed for the concentration of proximate constituents, fiber, minerals, amino acids, fatty acids, vitamins, antinutrients, and secondary metabolites. The results showed that the forage and grain from MON 88017 are compositionally equivalent to forage and grain from control and conventional corn hybrids.  相似文献   
63.
ABSTRACT A novel whitefly-transmitted member of the family Potyviridae was isolated from a squash plant (Cucurbita pepo) with vein yellowing symptoms in Florida. The virus, for which the name Squash vein yellowing virus (SqVYV) is proposed, has flexuous rod-shaped particles of approximately 840 nm in length. The experimental host range was limited to species in the family Cucurbitaceae, with the most dramatic symptoms observed in squash and watermelon, but excluded all tested species in the families Amaranthaceae, Apocynaceae, Asteraceae, Chenopodiaceae, Fabaceae, Malvaceae, and Solanaceae. The virus was transmitted by whiteflies (Bemisia tabaci) but was not transmitted by aphids (Myzus persicae). Infection by SqVYV induced inclusion bodies visible by electron and light microscopy that were characteristic of members of the family Potyviridae. Comparison of the SqVYV coat protein gene and protein sequences with those of recognized members of the family Potyviridae indicate that it is a novel member of the genus Ipomovirus. A limited survey revealed that SqVYV also was present in watermelon plants suffering from a vine decline and fruit rot recently observed in Florida and was sufficient to induce these symptoms in greenhouse-grown watermelon, suggesting that SqVYV is the likely cause of this disease.  相似文献   
64.
Journal of Pest Science - Over the past three decades, highly increased whitefly (Bemisia tabaci) populations have been observed on the staple food crop cassava in eastern Africa and associated...  相似文献   
65.
Recent investigations by the Australian Department of Agriculture, Fisheries and Forestry into high mortalities on live export voyages from Australia to the Middle East during the Northern hemisphere summer suggest that animal welfare may be compromised by heat stress. The live export industry has generated a computer model that aims to assess the risk of heat stress and to contain mortality levels on live export ships below certain arbitrary limits. Although the model must be complied with under Australian law, it is not currently available for independent scientific scrutiny, and there is concern that model and the mandated space allowances are inadequate. This review appraises the relevant literature on heat stress in sheep and cattle, including laboratory studies aimed at mimicking the ambient temperatures and humidity levels likely to be encountered on live export voyages. Animal welfare is likely to be very poor as a result of heat stress in some shipments.  相似文献   
66.
67.
The development to the veliger stage of fertilised ova of the Pacific oyster, Crassostrea gigas, was compared in raw natural sea water and in sea water pre-treated with various substances. Significantly higher veliger yields were obtained when the water was pre-treated with 1 mg l?1 EDTA. Combinations of EDTA and 20 mg l?1 sodium metasilicate, or 20 mg l?1 alumina, or 50 mg l?1 magnesium trisilicate or 150 mg l?1 Fuller's earth also enhanced development.  相似文献   
68.
Novel wheat lines with altered flour compositions can be used to decipher the roles of specific gluten proteins in flour quality. Grain proteins from transgenic wheat lines in which genes encoding the omega-5 gliadins were silenced by RNA interference (RNAi) were analyzed by quantitative 2-dimensional gel electrophoresis (2-DE). The precise effects of the genetic modifications on the proteome were assessed in four homozygous lines generated with the same RNAi construct. Two of the lines showed >80% decreases in omega-5 gliadins with only small changes in the levels of other gluten proteins. In the other two lines, omega-5 gliadins were not detectable by 2-DE. However, there were notable reductions in all omega-1,2 gliadins. Small decreases in several other gluten proteins were also detected in one of the lines. The other line showed notable decreases in three HMW-GS and an s-type LMW-GS, increases in two m-type LMW-GS and several alpha gliadins, as well as increases in both serpins and triticin. The study demonstrates that the same RNAi construct can have differential effects on the wheat grain proteome and highlights the importance of detailed proteomic analyses of transgenic grain prior to selecting lines for further assessment of flour quality and allergenic potential.  相似文献   
69.
Antibiotic resistance among pathogenic microorganisms is becoming ever more common. Unfortunately, the development of new antibiotics which may combat resistance has decreased. Recently, however the oceans and the marine animals that reside there have received increased attention as a potential source for natural product discovery. Many marine eukaryotes interact and form close associations with microorganisms that inhabit their surfaces, many of which can inhibit the attachment, growth or survival of competitor species. It is the bioactive compounds responsible for the inhibition that is of interest to researchers on the hunt for novel bioactives. The genus Pseudovibrio has been repeatedly identified from the bacterial communities isolated from marine surfaces. In addition, antimicrobial activity assays have demonstrated significant antimicrobial producing capabilities throughout the genus. This review will describe the potency, spectrum and possible novelty of the compounds produced by these bacteria, while highlighting the capacity for this genus to produce natural antimicrobial compounds which could be employed to control undesirable bacteria in the healthcare and food production sectors.  相似文献   
70.
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