全文获取类型
收费全文 | 2919篇 |
免费 | 193篇 |
国内免费 | 157篇 |
专业分类
3269篇 |
出版年
2024年 | 3篇 |
2023年 | 32篇 |
2022年 | 44篇 |
2021年 | 66篇 |
2020年 | 67篇 |
2019年 | 77篇 |
2018年 | 74篇 |
2017年 | 62篇 |
2016年 | 95篇 |
2015年 | 108篇 |
2014年 | 109篇 |
2013年 | 183篇 |
2012年 | 95篇 |
2011年 | 121篇 |
2010年 | 99篇 |
2009年 | 154篇 |
2008年 | 141篇 |
2007年 | 166篇 |
2006年 | 141篇 |
2005年 | 142篇 |
2004年 | 140篇 |
2003年 | 112篇 |
2002年 | 96篇 |
2001年 | 73篇 |
2000年 | 94篇 |
1999年 | 76篇 |
1998年 | 84篇 |
1997年 | 62篇 |
1996年 | 60篇 |
1995年 | 58篇 |
1994年 | 55篇 |
1993年 | 47篇 |
1992年 | 46篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 39篇 |
1988年 | 25篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 1篇 |
排序方式: 共有3269条查询结果,搜索用时 9 毫秒
121.
Phenotypic variation in 11 floral and reproductive traits was studied in cloned plants of Campanula rapunculoides replicated in three discrete environments. Using an ANOVA approach, we determined the relative influence of genotype (G), environment (E), G × E interaction, and ontogeny (position on the raceme) on the 11 traits. Two traits, duration of flowering and pollen size, showed no significant variation. All nine remaining traits had significant genotypic variation, accounting for 21-38% of the total phenotypic variation. Correlations among variant traits in seven genotypes were predominantly positive, but several significant correlations in one environment changed sign or were nonsignificant in another environment. Ovule number was negatively correlated with most male function traits: the negative correlation between ovule and pollen number was particularly strong and consistent across environments. Six traits varied significantly across environments, including number of flowers, number of ovules per flower, and duration of the male phase, but pollen traits did not show a significant environmental main effect. The G × E interaction was significant for flower number, corolla size, nectar quality, duration of the male phase, pollen viability, and ovule number. The contribution of interaction variance to the total phenotypic variation (5-14%) was comparable to that of the environment alone (7-21%). Ovule number decreased in flowers on the upper part of the raceme by nearly 25%, but other traits did not vary significantly by floral position. These results suggest that (1) pollen traits are buffered against environmental change more than ovule number or other floral characters, (2) a male-female trade-off exists and is complicated by ontogenic factors, (3) G × E interactions are common but may have small effects, and (4) specific correlation patterns among floral traits can be dependent upon the environment under which they develop. 相似文献
122.
We estimated selection on three morphological characters in the hermaphroditic, hawkmoth-pollinated orchid Platanthera bifolia and explored selection surfaces through male and female function. The work was carried out in northern Sweden during two flowering seasons (1994 and 1995) in one natural population and one season (1995) in another natural population. Fitness was estimated as number of pollinia removed (male function) and number of fruits produced (female function). We detected directional selection towards larger inflorescence size (flower number) through both sex functions in both populations in 1995. In 1994, with an unusually dry growing season, 78% of the individuals failed to set any fruit, and there was selection for larger inflorescences only through male function. In this year, there was selection towards longer flower spurs, which could be a direct or indirect effect of spurs being shortened by drought. The results demonstrate that selection patterns may vary temporally and spatially, and that the 'male function hypothesis' may be applicable as female function is more resource dependent than male function. 相似文献
123.
描述了产于中国广西、云南和福建的2种蟹蛛,锡兰瘤蟹蛛Phrynarachne ceylonica(O.P.-Cambridge,1884)和贵州耙蟹蛛Strigoplus guizhouensis Song et Chai,1990,前1种系中国新纪录,后1种的雄性系首次发现.标本保存在河北大学博物馆. 相似文献
124.
The genus Stichillus in Japan is revised. Three species are recognized: S. japonicus (Matsumura), S. spinosus Liu and Chou and S. cylindratus sp. nov. Stichillus brunneicornis Beyer is excluded from the Japanese fauna. These Japanese species are described and keyed. The male genitalia and the female terminalia are illustrated. Some unique characters of the male genitalia in the genus are reported, and morphology of the male genitalia and the female terminalia is discussed. 相似文献
125.
利用分子标记定位农垦58S的光敏核不育基因 总被引:17,自引:0,他引:17
对农垦58S(Oryzasativasp.japonica)/大黑矮生标记基因系FL2组合组建可育集团和不育集团,并以亲本为对照进行了RFLP、RAPD和双引物RAPD分析,结果第12染色体上的一个单拷贝标记G2140与光敏核不育基因连锁遗传,二者间的遗传图距为14.1cM(centimorgan)。在筛选过的1040个随机单引物和190个双引物中,仅引物OPAU10扩增出与光敏核不育基因连锁的1.5kbDNA片段,回收、克隆该DNA片段并制备探针,将其转换成共显性的RFLP标记并命名为OPAU101500。分离群体连锁分析表明该标记与标记G2140紧密连锁,将农垦58S的一对光敏核不育基因定位于第12染色体上。 相似文献
126.
127.
描述簇毛巨螯螨Maerocheles penicilliger(Berlese,1904)雄螨。 相似文献
128.
Manipulation of male attractiveness induces rapid changes in avian maternal yolk androgen deposition
Kingma Sjouke A.; Komdeur Jan; Vedder Oscar; von Engelhardt Nikolaus; Korsten Peter; Groothuis Ton G.G. 《Behavioral ecology》2009,20(1):172-179
Avian eggs contain maternal androgens that may adjust offspringdevelopment to environmental conditions. We review evidenceand functional explanations for the relationship between androgenconcentrations in avian eggs and male attractiveness. Experimentalstudies in captive birds show generally positive relationships,but results from correlational and experimental field studiesare less consistent, perhaps because they lack a within-femaledesign to control for confounding between-female variation.We analyzed the effect of male attractiveness on yolk levelsof maternal androgens in a wild bird, using a correlationaland experimental approach with a within-female design. We manipulatedthe sexually selected UV coloration of the crown feathers ofmale blue tits (Cyanistes caeruleus) after their female hadlaid the second egg and measured the subsequent effect on androgenconcentrations (testosterone and androstenedione) in the fifth,seventh, and ninth eggs relative to that in the second egg.Levels of testosterone, but not androstenedione, in eggs 5 and7 were higher for control (attractive) than for UV-reduced (unattractive)males. This effect disappeared in the ninth egg, coincidingwith the recovery of UV coloration after manipulation. Thissuggests that females are capable of rapid adjustments of testosteronedeposition in response to changes in their mate's ornamentalplumage. However, androgen concentrations in the second eggand pretreatment male crown coloration were not correlated.Possibly, the combination of relatively small variation in UVcoloration before treatment and the influence of unknown confoundingvariables in the correlative approach resulted in insufficientstatistical power to detect such a correlation. 相似文献
129.
130.