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   821篇
  免费   38篇
  国内免费   60篇
  2023年   10篇
  2022年   11篇
  2021年   16篇
  2020年   18篇
  2019年   16篇
  2018年   12篇
  2017年   24篇
  2016年   14篇
  2015年   20篇
  2014年   31篇
  2013年   42篇
  2012年   29篇
  2011年   23篇
  2010年   22篇
  2009年   44篇
  2008年   54篇
  2007年   48篇
  2006年   36篇
  2005年   38篇
  2004年   33篇
  2003年   26篇
  2002年   30篇
  2001年   17篇
  2000年   21篇
  1999年   26篇
  1998年   25篇
  1997年   13篇
  1996年   20篇
  1995年   18篇
  1994年   18篇
  1993年   12篇
  1992年   18篇
  1991年   20篇
  1990年   13篇
  1989年   11篇
  1988年   10篇
  1987年   17篇
  1986年   11篇
  1985年   7篇
  1984年   8篇
  1983年   4篇
  1982年   5篇
  1981年   1篇
  1980年   6篇
  1979年   3篇
  1978年   3篇
  1977年   11篇
  1976年   1篇
  1975年   1篇
  1973年   1篇
排序方式: 共有919条查询结果,搜索用时 15 毫秒
91.
黑龙江省通河乌龙狩猎场野猪冬季食性的初步研究   总被引:12,自引:3,他引:9  
王文  马建章  李健  王志平 《兽类学报》2005,25(4):407-409
野生动物食性的研究,在野生动物保护和管理方面具有重要的基础理论意义。野猪(Sus scrofa)是一种经济价值较高的有蹄类动物。国内对野猪食性的报道,仅见综述性献(巫露平,1980;李振营和罗泽殉,1983;杨伯然,1984),野猪食性方面的研究尚未多见;国外对野猪食性的研究主要集中在食物组成的定量分析和食物营养质量的评价(Eriksson and Petrov,1995;Foumier-chambrillon et al.,1995;朝日念,1985)。因此,作从2000~2001年,分别在黑龙江省通河乌龙狩猎场收集粪样,利用粪便显微组织学分析方法并结合野外掘食痕迹对野猪冬季食性进行了初步研究。  相似文献   
92.
胡杨、灰叶胡杨开花生物学特性研究   总被引:12,自引:0,他引:12  
从居群水平研究了胡杨、灰叶胡杨不同居群的开花物候特征.结果表明:胡杨、灰叶胡杨各居群均表现为雄株开花物候早于雌株,一般可授期开始较散粉期晚1~4 d,结束较散粉期晚2~5 d,并且居群散粉期和可授期的重叠期较长.在同一居群内,胡杨、灰叶胡杨同性单株间开花期的不一致性较高.两个种相比较,胡杨居群的开花进程比灰叶胡杨居群早2~5 d,并且从每日开花株数累积分布来看,胡杨散粉期、可授期为双峰型,灰叶胡杨为单峰型.  相似文献   
93.
Important agronomic traits such as fruit quality, harvesting efficiency or production largely depend on flowering time. We have analysed the effect of the overexpression of the Arabidopsis APETALA1 MADS-box gene on vegetative and reproductive growth of tomato. Constitutive expression of APETALA1 in tomato plants has major effects on the length of their growth cycle as well as on their growth habit. Transgenic tomato plants initiated flowering after the production of 6 vegetative nodes as compared to 11 nodes for the wild type plants. Most of tomato 35S:AP1 plants also showed determinate growth habit, similar to the phenotype of self pruning tomato mutants, as well as an initial reduction of their axillary growth. Moreover, development and fertility of flowers were not affected in plants expressing AP1. Consequently, fruit formation in transgenic plants grown under greenhouse conditions occurred normally, which permitted a similar fruit yield compared to control plants. Since traits conferred by AP1 expression are dominant, its expression in tomato breeding lines could provide advantages for the development of new hybrid varieties with shorter generation time, determinate growth, and reduced pruning requirements.  相似文献   
94.
太行山猕猴的食性   总被引:6,自引:0,他引:6  
猕猴 (Macacamulatta)是世界上地理和生态地位分布最广泛的非人灵长类。我国是唯一的地跨热带、亚热带、暖温带均有猕猴分布的国家。直到1987年 ,亚洲最北部的猴群在河北兴隆绝灭以后[12 ] ,自然分布于河南省与山西省交界处的太行山及中条山南段的猕猴就成为亚洲猕猴分布的最北界 ,位于N35°11'~ 35°17',E112°0 3'~ 112°33',地处暖温带。经 1981年以来的调查研究发现 ,太行山猕猴在形态、生理、生态等方面与其它地区的猕猴不同 ,是最具研究意义的种群[5] 。猕猴同其它动物一样 ,通过食物与其它动物 ,周围环境及人类物质…  相似文献   
95.
蔺草开花与温光条件关系的数学分析及模拟模型   总被引:1,自引:1,他引:0  
本文对蔺草开花与温光条件关系作了分析研究.根据浙江宁波市郊区1992-2000年的农业气候资料的分析计算表明,影响蔺草冈山3号草茎开花率(SFR)的主要气象因子为12月下旬、2月中旬的平均气温,2月下旬的日照时数和3月下旬的雨量.依据春化作用的机理和上述影响因子的分析,得SFR的模拟模型为:SFR=其中∑j相似文献   
96.
Podophyllum hexandrum Royle, an important alpine herb, is the source of highly valued podophyllotoxin. The effect of some plant growth substances (GA3, BAP & ABA), uniconazole (an inhibitor of GA biosynthesis), and a combination of GA3 and uniconazole were examined in respect to influence on sprouting in rhizomes of P. hexandrum and on induction of flowering at a lower altitude. Amongst the various chemicals tested, GA3 had a marked effect resulting in uniform sprouting and also induced flowering in about half of the treated rhizomes. While BAP also promoted early sprouting, delayed sprouting was seen in rhizomes treated with ABA. Uniconazole treatment, either alone or with GA3 was found to inhibit flowering and also resulted in reduced plant height. GA3 treatment of rhizomes from plants that was maintained for up to 30 months at a lower altitude also induced flowering thus replacing the normal chilling requirement of plants. These results suggest that treatment of GA3 could be effectively used for inducing uniform sprouting and flowering in rhizomes of P. hexandrum grown at lower altitudes.  相似文献   
97.
In 1997 and 1998, we sampled the Missouri River, North Dakota to determine if anthropogenic disturbances had influenced catostomid species composition and feeding ecology. We compared two distinct river segments, the Missouri River between the mouth of the Yellowstone River and Lake Sakakawea (the Yellowstone–Sakakawea segment (YSS)), a moderately altered segment and the Missouri River between Garrison Dam and Lake Oahe (the Garrison–Oahe segment (GOS)), a highly altered segment. The segments exhibited greatly different sucker communities. Bigmouth buffalo, Ictiobus cyprinellus, smallmouth buffalo, Ictiobus bubalus, and river carpsucker, Carpiodes carpio, represented 94% of the sucker catch in the YSS, whereas in the GOS, white sucker, Catostomus commersoni, and longnose sucker, Catostomus catostomus, constituted 98% of the sucker catch. In the YSS, high zooplankton densities led to greater sucker zooplanktivory and food niche overlap than in the GOS. Intense anthropogenic disturbances to the GOS are associated with the differences in sucker species composition, prey density and composition, and sucker feeding ecology between the two segments.  相似文献   
98.
Three species of mangroves, Rhizophora stylosa, Rhizophora mangle (synonym R. samoensis) and Bruguiera gymnorhiza in the family Rhizophoraceae were studied to understand the flowering pattern, propagule development and the propagule size at maturity prior to dispersal from the mother plant. The study was conducted in the Wet and the Dry zones over two seasons in Viti Levu, the Main Island of Fiji. The flower number, number of propagules and propagule size at maturity were significantly different among three species and within species in the Dry and the Wet zones. Only 1–2% of total flowers in each species became mature propagules. This percentage was significantly lower in the Dry zone for all three species. Rhizophora stylosa produced the biggest size of propagules followed by Rhizophora mangle and Bruguiera gymnorhiza. Relatively longer and heavier propagules were recorded in the Wet zone and shorter and lighter in the Dry zone. Inter-seasonal differences were not significant for these characters. This could be mainly due to almost similar amount of rainfall, relative humidity and temperature regimes over two seasons within each zone.  相似文献   
99.
绿鹭的繁殖习性观察   总被引:2,自引:0,他引:2  
2001年4-9月在合肥市对绿鹭(Butorides striatus)的繁殖习性进行了观察。绿鹭营巢生境主要选择在建筑物附近的高大阔叶树上,常一树一巢,未见与其他鹭类混群营巢。每巢产3-5枚卵,孵卵期21d,育雏期41d,42日龄后幼鸟离巢飞走,出飞存活率62.5%。育雏期雏鸟主要食物为小型鱼类。在4所大学校园及1处公园统计到有效巢56个,推算绿鹭224只。绿鹭在合肥繁殖属首次记录。  相似文献   
100.
Winter survival is an important characteristic of oilseedBrassica that is seeded in the fall in northern climates,and it may be affected by genetic variation for other cold-regulated traits,such as freezing tolerance and vernalization responsive flowering time. Weanalyzed immortalized populations of oilseed Brassica rapa(recombinant inbred lines) and B. napus (double haploidlines) derived from crosses of annual and biennial types in order to comparethe map positions and effects of quantitative trait loci controlling wintersurvival, nonacclimated and acclimated freezing tolerances, and flowering time.The B. napus population was evaluated in multiple winters,and six of the 16 total significant QTL for winter survival were detected inmore than one winter. Correspondence in the map positions of QTL controllingdifferent traits within species provided evidence that some alleles causinggreater acclimated freezing tolerance and later flowering time also contributedto increased winter survival. Correspondence in the map positions of QTLbetween species provided evidence for allelic variation at homologous loci inB. rapa and B. napus. The potentialrole of some candidate genes in regulating these traits is discussed.  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