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   661篇
  免费   29篇
  国内免费   73篇
  2024年   8篇
  2023年   23篇
  2022年   25篇
  2021年   32篇
  2020年   22篇
  2019年   26篇
  2018年   19篇
  2017年   30篇
  2016年   40篇
  2015年   32篇
  2014年   37篇
  2013年   38篇
  2012年   37篇
  2011年   22篇
  2010年   15篇
  2009年   31篇
  2008年   21篇
  2007年   30篇
  2006年   32篇
  2005年   36篇
  2004年   26篇
  2003年   23篇
  2002年   17篇
  2001年   23篇
  2000年   19篇
  1999年   18篇
  1998年   8篇
  1997年   6篇
  1996年   11篇
  1995年   9篇
  1994年   8篇
  1993年   7篇
  1992年   2篇
  1991年   7篇
  1990年   4篇
  1989年   4篇
  1988年   3篇
  1987年   4篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1982年   2篇
  1981年   1篇
  1979年   1篇
排序方式: 共有763条查询结果,搜索用时 15 毫秒
181.
黄芩的生物学研究进展   总被引:11,自引:0,他引:11  
药用黄芩为唇形科(Labiatae)黄芩属(Scutellaria)多年生草本植物黄芩(Scutellaria baicalensisGeorgi)的干燥根,是我国大宗中药材之一,药用历史悠久。我们对其原植物黄芩的种质资源、形态结构、生长发育、繁殖方式等方面的研究进展,以及黄芩药材的解剖学研究和显微鉴定等进行了系统考察和总结,可为深入进行原植物黄芩的生物学研究及药用黄芩的真伪鉴别和提高药用部分的质量和产量提供依据和资料。  相似文献   
182.
Summary In vitro-stored plant germplasm is usually evaluated by visual analysis of the plant based on subjective characters. To reduce the variability in these evaluations, we developed a digital-image evaluation system for in vitro-stored plantlets. This study compares the standard visual evaluation system with a digital analysis system to determine if digital analysis can effectively quantify the health of diverse Humulus germplasm. Eight cultivars of Humulus lupulus L. were stored on standard Murashige and Skoog (MS) medium with iron alone (EDTA chelated) and on MS iron with 100 or 200 mgl−1 sequestrene 138 iron (EDDHA chelated). Digital images of the upper two nodes of each plantlet were evaluated for red, green, blue, green/red ratio, and modified normalized difference vegetation index (MNDVI=R-G/R+G). Evaluation of each plantlet for MNDVI values showed consistent significant differences for all treatments only at the upper node. Significant differences for visual and the MNDVI values among the three iron treatments were observed at the upper node of most of the eight hop cultivars. Regression analysis of the upper node MNDVI values vs. whole-plant visual ratings showed positive correlations for most cultivars. Effects of iron treatments on storage duration were also analyzed for both visual and digital systems. There were significant differences among MNDVI values for plantlets stored on medium with standard MS iron alone (EDTA chelated) and with the addition of sequestrene 138 iron. In general, the MNDVI value of the upper node correlated well with visual ratings and could be used to determine the health of in vitro stored hops.  相似文献   
183.
An investigation was made of the phylogenetic relationships among wild accessions of Lima bean (Phaseolus lunatus) and wild allies of Mesoamerican and Andean origins, using electrophoresis of seed storage proteins and isozymes. Mesoamerican wild species are phylogenetically more distant fromP. lunatus than Andean species, and apparently belong to the tertiary gene pool of Lima bean. The Andean wild species, which are investigated for the first time, reveal a high similarity to the Lima bean, and particularly with its Mesoamerican gene pool. These Andean species probably constitute a secondary gene pool of Lima bean, and are thus of considerable interest in the context of genetic improvement of the crop. Based on these observations, an Andean origin is suggested for the Andean wild species and forP. lunatus. These results point out the importance of collecting and conserving AndeanPhaseolus germplasm.  相似文献   
184.
我国杜鹃花资源的保护与开发利用   总被引:16,自引:0,他引:16  
我国拥有世界最丰富的杜鹃花资源。我国栽培杜鹃花有悠久的历史,但开发利用水平却很低。保护我国杜鹃花生物多样性,并在此基础上开发利用我国的杜鹃花资源具有非常重要的意义。  相似文献   
185.
Ownership of intellectual and tangible property (IP/TP) rights in agricultural biotechnology (ag-biotech) and transgenic plants has become critically important. For scientists in all institutions, whether industrialized or developing country, public or private sector, an understanding of IP/TP rights is fundamental in both research and development. Transgenic plants and ag-biotech products embody numerous components and processes, each of which may have IP/TP rights attached. To identify these rights, a transgenic plant or ag-biotech product must be dissected into its essential components and processes, with each 'piece' analysed under the IP/TP 'microscope'. This product deconstruction is an integral step in product clearance (PC) analysis leading to freedom to operate (FTO). To facilitate a PC analysis, the following points are important: (1) knowing what one has and where it's from, (2) organizing material transfer agreements and licences, (3) researching scientific and patent databases and relevant literature, (4) instituting a laboratory notebook policy, (5) keeping track of ownership of germplasm and plant genetic resources, and (6) promoting ongoing IP/TP management, awareness and training. However, a FTO opinion does not solve the IP/TP issues of releasing a transgenic plant or ag-biotech product; rather, it is a management tool for assessing the risks of litigation. When transferring transgenic plants or ag-biotech to developing nations, scientists from industrialized countries have the heightened responsibility of verifying that IP/TP issues are fully addressed and documented. Successful technology transfer goes beyond research, development and licensing; it is an holistic package leading to long-term partnerships in international development. Managing IP/TP requires capacity-building in scientists and technology transfer offices, in both industrialized and developing countries.  相似文献   
186.
Seedling raised elites of Dendrocalamus hamiltoniiNees et Arn. Ex Munro were chosen as the source of nodal explants from precocious branches. While axillary bud break was accomplished in hormone free 1/2MS medium containing sucrose (3%, w/v), BA supplementation was required for shoot proliferation. A variety of hormonal combinations induced rooting in clumps of shoots. Somatic embryogenesis was also obtained in callus cultures raised in 2,4-D supplemented MS medium and plantlets derived from somatic embryos were hardened for field transfer. Comparative growth performances of plants raised from nodal cuttings of field-grown plants, those from single node cuttings of precocious branches and from somatic embryos indicated that growth performance of the tissue culture raised plants was relatively better than those from nodal cuttings. Improved protocols for efficient micropropagation are visualized to provide an impetus to raising of bamboo nurseries of elite genotypes in bamboo growing areas of western Himalayas.  相似文献   
187.
Determining the ploidy of plant germplasm is a necessary step in breeding or genetic studies in species. The purpose of this research was to determine the presence of ploidy level differentiation of hairy vetch (Vicia villosd) germplasm. Flow cytometry and root tip chromosome squashing methods were employed to assess 45 accessions labeled V. villosa available through the USDA germplasm collection. Flow cytometry determined that 43 of the accessions were 2C, one accession was 4C, and one accession was 6C. Analysis of accessions by root tip chromosome counts indicated that all accessions were diploid. The 2C accession contains 14 chromosomes and their chromosomes were approximately one-half and one-third in size as compared to the chromosomes of the 4C and 6C accessions, respectively. The 4C accession was observed to have 16 chromosomes and the 6C accession was observed to have 14 chromosomes. The large-scale differences in DNA amounts were due to chromosomal size variability as opposed to ploidy differences. This revealed the incidence of species misidentification of these two V. villosa accessions to be Vicia pannonica. All the V. villosa accessions were observed to be diploid and have similar DNA amounts. Flow cytometry proved to be useful in the efficient assessment of these accessions.  相似文献   
188.
Groundnut rosette, a virus disease of groundnut (Arachis hypogaea) transmitted by the aphid, Aphis craccivora Koch, reduces yield in susceptible cultivars by 30–100%. Additional sources were sought in germplasm accessions involving 2301 lines from different sources and from 252 advanced breeding lines derived from crosses involving earlier identified sources of resistance to rosette. The lines were evaluated in field screening trials using an infector row technique during 1996 and 1997 growing seasons. Among the germplasm lines, 65 accessions showed high levels of resistance while 134 breeding lines were resistant. All rosette disease resistant lines were susceptible to groundnut rosette assistor virus. This work identified germplasm and breeding lines that will contribute to an integrated management of groundnut rosette disease. These new sources also provide an opportunity to eliminate yield losses due to the rosette disease.  相似文献   
189.
Medium-term conservation of mature embryos of coconut   总被引:1,自引:0,他引:1  
Optimal conditions for the medium-term conservation of zygotic embryos of coconut were developed. After 6 months of storage on a medium devoid of sucrose and containing 2 g l–1 activated charcoal, 100% of the embryos developed into whole plantlets within 5 months after transfer to the recovery medium. After a 12-month storage period on medium containing 15 g l–1 sucrose and devoid of activated charcoal, 51% of the embryos germinated within 2 months after transfer to the recovery medium.  相似文献   
190.
该文系统综述了我国杂粮种质资源保存、鉴定评价、创新利用、基因资源挖掘研究现状, 以及基础研究存在的问题和挑战, 并提出杂粮研究的重点和发展方向。  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