全文获取类型
收费全文 | 821篇 |
免费 | 38篇 |
国内免费 | 60篇 |
出版年
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
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.
93.
Expression of Arabidopsis APETALA1 in tomato reduces its vegetative cycle without affecting plant production 总被引:2,自引:0,他引:2
Ellul Philippe Angosto Trinidad García-Sogo Begoña García-Hurtado Noemí Martín-Trillo Mar Salinas María Moreno Vicente Lozano Rafael Martínez-Zapater José M. 《Molecular breeding : new strategies in plant improvement》2004,13(2):155-163
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.
96.
Hemant Pandey Shyamal K. Nandi Bhuwan Chandra Mohammad Nadeem Lok Man S. Palni 《Acta Physiologiae Plantarum》2001,23(4):467-474
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.
Anand Prakash Tyagi 《Wetlands Ecology and Management》2003,11(3):167-174
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.
100.
Kole C. Thormann C.E. Karlsson B.H. Palta J.P. Gaffney P. Yandell B. Osborn T.C. 《Molecular breeding : new strategies in plant improvement》2002,9(3):201-210
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