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   10733篇
  免费   973篇
  国内免费   789篇
  2024年   25篇
  2023年   178篇
  2022年   169篇
  2021年   284篇
  2020年   383篇
  2019年   432篇
  2018年   327篇
  2017年   346篇
  2016年   351篇
  2015年   343篇
  2014年   395篇
  2013年   722篇
  2012年   435篇
  2011年   417篇
  2010年   385篇
  2009年   515篇
  2008年   482篇
  2007年   568篇
  2006年   499篇
  2005年   483篇
  2004年   443篇
  2003年   396篇
  2002年   357篇
  2001年   362篇
  2000年   297篇
  1999年   265篇
  1998年   287篇
  1997年   260篇
  1996年   234篇
  1995年   222篇
  1994年   164篇
  1993年   186篇
  1992年   154篇
  1991年   155篇
  1990年   116篇
  1989年   91篇
  1988年   84篇
  1987年   84篇
  1986年   79篇
  1985年   105篇
  1984年   100篇
  1983年   49篇
  1982年   53篇
  1981年   53篇
  1980年   39篇
  1979年   24篇
  1978年   21篇
  1977年   13篇
  1976年   27篇
  1975年   11篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
121.
Breeding vervet monkeys in a closed environment   总被引:1,自引:0,他引:1  
A breeding group of vervet monkeys produced 95 offspring over five years. Fetal wastage for 114 pregnancies was 16.7%. Uterine sizes were recorded for 103 pregnancies in various stages of gestation. This enabled diagnosis of pregnancy, estimation of stage of gestation, and prediction of parturition to within two weeks. Detailed observations were made on dental eruption, pelage development, and growth of 57 infants.  相似文献   
122.
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   
123.
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   
124.
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   
125.
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   
126.
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   
127.
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   
128.
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   
129.
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   
130.
Gray-cheeked mangabeys live in multimale social groups. Two groups of these monkeys were studied extensively over a period of 22 months, and a further eight groups were observed opportunistically. Data on the occurrence of sexual swelling infernales were collected and the different phases of swelling and deflation are described in detail together with data on their duration. The data were found to agree broadly with those presented by other workers on captive animals. Pre and postpartum swellings are described. The majority of copulations was observed to occur at peak swelling and a specific gesture, the head flag, was noted as a solicitation. The data on initiation of copulations show that the males initiated more copulations than the females. However, female-initiated copulations ended in ejaculation more often than male-initiated copulations. The behaviors of the mangabeys during precopulation and copulation were found to be broadly similar to those of the macaque. Copulations were observed most often on the day of peak swelling;however, adult males were the only animals to copulate prior to peak swelling. Subadult male copulations were most often after peak swelling. Masturbation was observed to ejaculation on two occasions. The data show gestation periods of between 184 and 189 days. A mean interbirth interval was calculated to be 33.33 ± 15.87 months.  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