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   6572篇
  免费   617篇
  国内免费   584篇
  2024年   13篇
  2023年   119篇
  2022年   114篇
  2021年   181篇
  2020年   245篇
  2019年   287篇
  2018年   207篇
  2017年   216篇
  2016年   220篇
  2015年   219篇
  2014年   233篇
  2013年   437篇
  2012年   289篇
  2011年   285篇
  2010年   252篇
  2009年   307篇
  2008年   269篇
  2007年   353篇
  2006年   301篇
  2005年   318篇
  2004年   265篇
  2003年   246篇
  2002年   185篇
  2001年   206篇
  2000年   179篇
  1999年   160篇
  1998年   180篇
  1997年   153篇
  1996年   137篇
  1995年   139篇
  1994年   116篇
  1993年   108篇
  1992年   108篇
  1991年   93篇
  1990年   77篇
  1989年   66篇
  1988年   62篇
  1987年   46篇
  1986年   47篇
  1985年   70篇
  1984年   68篇
  1983年   33篇
  1982年   32篇
  1981年   30篇
  1980年   25篇
  1979年   18篇
  1978年   12篇
  1977年   8篇
  1976年   16篇
  1974年   7篇
排序方式: 共有7773条查询结果,搜索用时 15 毫秒
81.
Cassava fertility and seed viability are frequently low, which can be a disadvantage in a breeding programme. An embryo culture method is described whereby embryonic axes are excised from mature seeds and placed on a culture medium containing 1.23 M indolebutyric acid (IBA) at 30°C under continuous light. The number of plants recovered by embryo culture was much greater than the number recovered from conventional seed germination procedures.  相似文献   
82.
In a succession of seed harvests of carrot, the highest percentage and most rapid germination was obtained from seed harvested 51 days after anthesis (DAA) when dried by conditioning at 25°C and 60% RH for one week and from seeeds harvested 65 or 79 DAA with or without conditioning treatment. Seed from these harvests had reached maximum weight when dried, had embryos of maximum length and were considered mature. The germinaton of seed from these treatments was unaffected by a mixture of the gibberellins A4 and A7 (GA4/7) applied in the incubation medium. Seed harvested 37 DAA also gave maximum percentage germination when it was both conditioned and incubated in GA4/7 solution. Seed harvested earlier than this germinated poorly. Germination times of both mature and immature seed were reduced after storage for 18 months but there was no response to GA4/7.Abbreviations ABA abscisic acid - DAA days after anthesis - GA gibberellin  相似文献   
83.
Extract of alfalfa seed (ethanolic 50 % v/v) prevents the development of plaque formation and hyperlipidaemia in cholesterol fed rabbits. It inhibits the elevation of serum total cholesterol, triglycerides, phospholipids, LDL-cholesterol and total cholesterol/phospholipid ratio, while HDL-cholesterol/total cholesterol ratio increases, which is associated with a reduced incidence of atherosclerosis. Further reduction in total cholesterol and phospholipid contents of liver and heart muscle are suggestive of a beneficial role of the seed extract. The possible mechanisms of action are discussed.  相似文献   
84.
Six closely related taxa of the sect.Eusideritis of the genusSideritis (S. leucantha, S. pusilla, S. flavovirens, S. granatensis, S. biflora andS. osteoxylla) are analysed to elucidate their phylogenetic relationships and position within the sect.Eusideritis. Meiotic behaviour, karyotype features, size and fertility of pollen grains, DNA amounts and seed protein profiles are reviewed. A polyploid origin of the group (from x = 7) and the further diversification through dysploidy and chromosome repatterning is postulated.S. osteoxylla is apparently of hybrid origin.  相似文献   
85.
Seed protein electrophoresis of four chromosomes races ofFestuca arundinacea, F. mairei and their progenitors showed variation in banding patterns. High protein similarities betweenF. arundinacea, F. mairei, F. scariosa, andF. pratensis indicate close phylogenetic relationships of these species. The ancestry ofF. arundinacea cytotypes could be narrowed to three diploid species:F. scariosa, F. pratensis, andF. rubra or to their close relatives.  相似文献   
86.
The mode of germination of representatives of 89 genera of the Cactaceae, 4 genera of Portulacaceae and 1 genus of Phytolaccaceae was studied. Most of the species of the Cactaceae germinate by means of a seed lid (operculum). In the Cactaceae studied 11 kinds of germination could be distinguished, 3 of which were with, and 8 without, operculum formation.
Opercula are restricted in their occurrence to the subfamilies Cactoideae (Cereoideae) and Pereskioideae and are not found in the subfamily Opuntioideae. Within the subfamily Cactoideae operculum formation was found to occur in all tribes and in all investigated subtribes. Opercula were also found in two genera of the related family of the Portulacaceae. In the Phytolaccaceae no operculum formation was observed.  相似文献   
87.
A hitherto unknown hydroxy acid has been isolated from Blepharis sindica seed oil has been characterized as 9-hydroxydodecanoic acid by IR, NMR and mass spectral studies. The structure of this acid was further supported by its chemical transformations.  相似文献   
88.
The fat of the seeds from the West African tree Pycnanthus kombo contains ca 20% of a hitherto undescribed compound. This compound was identified as 16(2′,5′-dihydroxy-3′-methylphenyl)-2,6,10,14-tetramethyl-2,6,10,14-hexadecatetraenoic acid, for which the name kombic acid is proposed.  相似文献   
89.
Guinea fowl were inoculated rectally with Histomonas meleagridis to produce histomoniasis. The birds were infected readily by this unnatural route. Severe cecal involvement was frequent and long-lasting but liver lesions and death were rare. Turkeys given the same inoculum had high levels of liver involvement and mortality. Guinea fowl responded much less severely to infection with H. meleagridis when infected by a natural route (ingestion of a vector) rather than by rectal inoculation. Thus, naturally acquired infections with H. meleagridis appear to be of small consequence in the guinea fowl.  相似文献   
90.
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