全文获取类型
收费全文 | 1540篇 |
免费 | 145篇 |
国内免费 | 1篇 |
出版年
2023年 | 9篇 |
2022年 | 25篇 |
2021年 | 60篇 |
2020年 | 24篇 |
2019年 | 27篇 |
2018年 | 41篇 |
2017年 | 30篇 |
2016年 | 43篇 |
2015年 | 80篇 |
2014年 | 85篇 |
2013年 | 92篇 |
2012年 | 105篇 |
2011年 | 114篇 |
2010年 | 69篇 |
2009年 | 46篇 |
2008年 | 67篇 |
2007年 | 62篇 |
2006年 | 75篇 |
2005年 | 65篇 |
2004年 | 33篇 |
2003年 | 26篇 |
2002年 | 35篇 |
2001年 | 29篇 |
2000年 | 31篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 30篇 |
1991年 | 30篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1972年 | 7篇 |
排序方式: 共有1686条查询结果,搜索用时 15 毫秒
1.
A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing. 相似文献
2.
3.
Cloning and nucleotide sequence of the isoamylase gene from Pseudomonas amyloderamosa SB-15 总被引:3,自引:0,他引:3
A Amemura R Chakraborty M Fujita T Noumi M Futai 《The Journal of biological chemistry》1988,263(19):9271-9275
The gene (iam) coding for isoamylase (glycogen 6-glucanohydrolase) of Pseudomonas amyloderamosa SB-15 was cloned. Its nucleotide sequence contained an open reading frame of 2313 nucleotides (771 amino acids) encoding a precursor of secreted isoamylase. The precursor contained a signal peptide of 26 amino acid residues at its amino terminus and three regions homologous with those conserved in alpha-amylases (1,4-alpha-D-glucan 4-glucanohydrolase) of species ranging from prokaryotes to eukaryotes. These homologous regions were also found in another debranching enzyme, pullulanase (pullulan 6-glucanohydrolase) from Klebsiella aerogenes. Sequences of the isoamylase also showed significant homology with those between positions 300 and the carboxyl terminus of pullulanase. The regions required for the specificity of isoamylase were discussed on the basis of a comparison of its amino acid sequence with those of alpha-amylases, cyclomaltodextrin glucanotransferases, and pullulanase. 相似文献
4.
Experimental infection of hamsters with Leishmania donovani caused visceral leishmaniasis in which hematological changes occurred. The infected hamsters were anemic and reticulocyte counts were high. No significant change in the serum erythropoietin level was noted. Red cell membrane Na(+)-K(+)-ATPase and acetylcholinesterase activities increased. Osmotic fragility of the erythrocytes from infected animals increased. The level of 2,3-diphosphoglycerate of the red cells increased with the degree of anemia. 相似文献
5.
6.
On binding toVicia faba lectin, the fluorescence of 4-methylumbelliferyl-α-D-glucoPyranoside was quantitatively quenched showing that the interaction
of 4-methylumbelliferyl-α-D-glucoPyranoside took Place in a binding environment. The binding of the fluorescent sugar was
saccharide sPecific as evidenced by the reversal of 4-methylumbelliferyl-α-D-glucoPyranoside fluorescence quenching by D-fructose.
The association constant,K
a, values for the 4-methylumbelliferyl-α-D-glucoPyranoside was determined by comPetition study emPloying reversal of fluorescence
quenching of 4-methylumbelliferyl-α-D-glucoPyranoside by D-fructose. TheK
a value obtained for D-fructose was 1.07 ±0.03 X 104 M-1 and for 4-methylumbelliferyl-α-D-glucoPyranoside was 1.60 ±0.05 X 104 M-1 at 15°C. TheK
a values of 2.51 ±0.06 X 104M-1, l.26 ±0.02 X 104 M-1 and 0.56 ±0.01 X 104M-1, resPectively at 10°, 20° and 30°C were obtained from the ChiPman equation. The relative fluorescence quenching, ΔF
a, at infinite concentration of the free saccharide sites ofVicia faba lectin [P′] was 93.5% at 30°C and the binding constant for 4-methylumbelliferyl-α-D-glucoPyranoside lectin interaction as derived by
Yank and Hanaguchi equation was 0.63 ±0.01 X 104M-1. 相似文献
7.
The primary structure of Klebsiella serotype K10 capsular polysaccharide has been investigated using mainly the techniques of methylation, partial hydrolysis, and 1H and 13C NMR spectroscopy. The polysaccharide was found to consist of hexasaccharide repeating units having the following structure: (formula; see text) 相似文献
8.
Effect of erythropoietin on the glucose transport of rat erythrocytes and bone marrow cells 总被引:1,自引:0,他引:1
J Ghosal M Chakraborty T Biswas C K Ganguly A G Datta 《Biochemical medicine and metabolic biology》1987,38(2):134-141
The effect of Ep on radioactive glucose and methyl-alpha-D-glucoside transport by rat erythrocytes and bone marrow cells were studied. There is initial linearity followed by saturation kinetics of [14C]glucose transport by the erythrocytes of starved and starved plus Ep-treated rats at different concentrations of glucose. Starvation caused slight inhibition of glucose transport which increased markedly on Ep administration to starved rats. Normal animals failed to show any significant change in glucose transport after Ep treatment. Methyl-alpha-D-glucoside inhibited the Ep-stimulated glucose transport significantly. Ep also stimulated the transport of radioactive methyl-alpha-D-glucoside which was competitively inhibited in presence of D-glucose. Glucose transport in erythrocytes was found to be sensitive to metabolic inhibitors like azide and DNP. A sulfhydryl reagent and ouabain also inhibited the transport process. Ep stimulated glucose and methyl-alpha-D-glucoside transport in the bone marrow cells of starved rats. The sugar analog competitively inhibited the glucose transport in bone marrow cells and vice versa. 相似文献
9.
The spiro attachment of an epoxide group to a tetrahydropyran ring in the trichothecene mycotoxins has prompted this study of the mutagenicity and alkylation rates of the trichothecene, anguidine, and 5 related model oxaspiro compounds. While the model compounds were weak alkylating agents of 4-(4-nitrobenzyl)pyridine as a test nucleophile, anguidine lacks such activity. Also, while mutagenicity was not established for anguidine in Salmonella TA100, 3 of the oxaspiro compounds were weakly mutagenic and 2 compounds were toxic to the bacteria. The toxicity and mutagenicity of the model compounds are more related to their polarity than to their alkylation rates. 相似文献
10.
R. Chakraborty 《International Journal of Anthropology》1990,5(1):33-42
Simple heritability estimators of continuous as well as discrete traits from twin data are known to overestimate the degree
of genetic determination of the measured traits for several reasons. Errors of zygosity determination will, however, underestimate
the true heritability. The bias due to wrong assignment of dizygous twin pairs into monozygous type is evaluated here, and
the results indicate that this negative bias has a compensatory effect on the estimate of the degree of genetic determination
when other factors of similarity between twin pairs are taken into account. It is shown that when an estimate of zygosity
error is available, the bias due to this factor can be evaluated quantitatively, and hence the adjustment for zygosity error
can be incorporated in the estimation of the degree of genetic determination of a trait.
Although this theory is explicitly developed here for twin studies, the general principle also applies for other types of
errors of determining the degree of biological relationships for estimation of heritability, in which case this type of error
may be more important than the simple zygosity error. 相似文献