全文获取类型
收费全文 | 86473篇 |
免费 | 9552篇 |
国内免费 | 44篇 |
出版年
2021年 | 1040篇 |
2020年 | 641篇 |
2019年 | 773篇 |
2018年 | 1010篇 |
2017年 | 993篇 |
2016年 | 1648篇 |
2015年 | 2861篇 |
2014年 | 3266篇 |
2013年 | 4445篇 |
2012年 | 4890篇 |
2011年 | 4916篇 |
2010年 | 3485篇 |
2009年 | 3242篇 |
2008年 | 4363篇 |
2007年 | 4440篇 |
2006年 | 4318篇 |
2005年 | 4213篇 |
2004年 | 4288篇 |
2003年 | 3883篇 |
2002年 | 3905篇 |
2001年 | 1044篇 |
2000年 | 745篇 |
1999年 | 1082篇 |
1998年 | 1471篇 |
1997年 | 1108篇 |
1996年 | 1100篇 |
1995年 | 1036篇 |
1994年 | 1012篇 |
1993年 | 974篇 |
1992年 | 877篇 |
1991年 | 870篇 |
1990年 | 851篇 |
1989年 | 858篇 |
1988年 | 810篇 |
1987年 | 766篇 |
1986年 | 698篇 |
1985年 | 822篇 |
1984年 | 959篇 |
1983年 | 847篇 |
1982年 | 964篇 |
1981年 | 988篇 |
1980年 | 940篇 |
1979年 | 693篇 |
1978年 | 755篇 |
1977年 | 713篇 |
1976年 | 674篇 |
1975年 | 586篇 |
1974年 | 626篇 |
1973年 | 613篇 |
1970年 | 416篇 |
排序方式: 共有10000条查询结果,搜索用时 506 毫秒
171.
172.
173.
F. Slansky Jr. 《Entomologia Experimentalis et Applicata》1985,39(1):47-60
Over 80% of the values of approximate digestibility (AD), efficiency of conversion of assimilated food to biomass (ECD) and efficiency of conversion of ingested food (ECI) calculated using energy terms are greater than the corresponding dry weight (DW) values, based on data for over 65 species (38 studies; number of comparative values: AD=139, ECD=128 and ECI=169). Largest positive differences (energy > DW values) are 30 (AD, ECD) and 24 (ECI) percentage points and largest negative differences (energy < DW values) are 9 (AD), 11 (ECD) and 8 (ECI) percentage points. These differences generally are least for ECI (71% of the differences fall between 0 and +5 percentage points), and AD (68%), followed by ECD (only 47% fall between 0 and +5), and they may vary with temperature, food and other factors. The differences tend to increase (esp. for ECD and ECI) when comparing later with earlier instars. Energy > DW efficiency values are commonly expected for AD because of the generally greater energy content of food than feces, and for ECD and ECI because of the generally greater energy content of insect biomass than ingested and assimilated food. Deviations from predicted differences in surveyed literature data are discussed in terms of possible methodological sources of error.
Résumé Plus de 80% des valeurs de la digestibilité approchée (AD), de l'efficacité de la conversion de la nourriture assimilée en biomasse (ECD) et de l'efficacité de la conversion de l'aliment ingéré (ECI), calculées en termes énergétiques, et obtenus à partir de données sur 65 espèces, sont supérieures aux valeurs des poids secs correspondants (DW): 38 études; valeurs comparatives: AD=139, ECD=128, ECI=169. Les plus importantes différences positive (énergie>valuers DW) sont de 30 (AD, ECD) et de 24 (ECI) centièmes (les différences négatives les plus fortes = 9 (AD), 11 (ECD) et 8 (ECI); ces différences sont moindres pour ECI (71% des différences tombent à 0 et +5 centièmes), et AD (68%), suivi de ECD (seulement 47% tombent entre 0 et +5). Ces différences peuvent varier avec la température, l'alimentation et d'autres facteurs; les différences tendent à croître (particulièrement pour ECD et ECI) quant on les compare plus tard avec des stades plus précoces. Energie > aux valeurs d'efficacité DW sont généralement attendues pour AD par suite du contenu énergétique supérieur de l'aliment à celui des excréments, et pour ECD et ECI par suite du contenu énergétique généralement plus élevé pour la biomasse de l'insecte que pour l'aliment ingéré et assimilé. Les écarts par rapport aux différences prédites dans les données de la littérature examinée sont analysées en considérant les sources possibles d'erreurs méthodologiques.相似文献
174.
175.
Summary Two siblings with a short-limb dwarfing condition which we call acromesomelic dysplasia, Hunter-Thompson type are reported. Abnormalities are limited to the limbs and limb joints in this severe form of dwarfism. The middle and distal
segments of the limbs are most affected. The lower limbs are more affected than the upper. We are aware of one previously
published case of this entity reported by A. G. W. Hunter and M. W. Thompson in 1976. Dislocations of the elbows and ankles
were present in all three patients and dislocations of the hips and knees in two. One of the siblings who did not have hip
and knee dislocations clinically resembled Grebe chondrodysplasia, another severe acromesomelic dwarfing condition. However,
radiological analysis suggests that while acromesomelic dysplasia, Hunter-Thompson type and Grebe chondrodysplasia are related,
they are not identical. Grebe chondrodysplasia has been established as an autosomal recessive trait. It appears probable that
the entity we describe has the same mode of genetic transmission. 相似文献
176.
177.
178.
179.
Douglas G. Gilmour Walter M. Collins Tom L. Fredericksen Willard E. Urban Jr. Paul F. Ward Nancy L. DiFronzo 《Immunogenetics》1986,23(1):1-6
Chickens of Regional Poultry Research Laboratory (RPRL) inbred line 63 regress sarcomas induced by Bryan high-titer Rous sarcoma virus to a greater extent than chickens of line RPRL 100, although these lines are identical for the major histocompatibility B complex. They differ, however, at three independent autosomal loci: Ly-4 and Th-1 determine the surface alloantigens of partly overlapping subsets of T lymphocytes, and Bu-1 determines a surface alloantigen of B lymphocytes. The association of genotypes at these loci with quantitative variation in their ability to regress Rous sarcomas was tested in segregating F4 generation progeny derived from crosses of lines 100 and 63. The Ly-4 and Bu-1 genotypes showed association with Rous sarcoma regression, but the Th-1 genotype did not. Chickens of the Ly-4
a/Ly-4
a, Bu-1
b/Bu-1
b and Ly-4
b/Ly-4
b, Bu-1
a/Bu-1
a genotypes had a significantly higher regressor ability than the other two double homozygous genotypes. These results indicate that higher regression is associated with (1) interaction between the Ly-4 and Bu-1 loci, and (2) complementation between either the line 6 Ly-4
a allele and the line 100 Bu-1
b allele, or the line 100 Ly-4
b allele and the line 6 Bu-1
a allele. 相似文献
180.
A new species,Acanthocephaloides cyrusi, is described from the fishesSolea bleekeri andPomadasys commersoni from Lake St. Lucia, Natal, South Africa. It is distinguished from the other species in the genus by the more marked sexual dimorphism in length, the arrangement of hooks, the proboscis with the longest hooks at the anterior-most extremity and the greater size of the proboscis hooks and body spines. An acanthella, which may represent this species, was found in the tanaidApseudes digitalis. 相似文献