全文获取类型
收费全文 | 1140篇 |
免费 | 87篇 |
出版年
2021年 | 14篇 |
2020年 | 10篇 |
2018年 | 22篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 24篇 |
2014年 | 36篇 |
2013年 | 46篇 |
2012年 | 51篇 |
2011年 | 47篇 |
2010年 | 31篇 |
2009年 | 35篇 |
2008年 | 45篇 |
2007年 | 41篇 |
2006年 | 33篇 |
2005年 | 51篇 |
2004年 | 36篇 |
2003年 | 44篇 |
2002年 | 31篇 |
2001年 | 28篇 |
2000年 | 27篇 |
1999年 | 25篇 |
1998年 | 10篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 10篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 16篇 |
1972年 | 15篇 |
1971年 | 14篇 |
1970年 | 11篇 |
1932年 | 9篇 |
排序方式: 共有1227条查询结果,搜索用时 15 毫秒
51.
52.
Abbott RJ 《Trends in ecology & evolution》1992,7(12):401-405
Interspecific hybridization between a native and an invading plant species, or two invading species, sometimes results in a new, sexually reproducing taxon. Several examples of such taxa have been confirmed by recent molecular and isozyme analyses. Further study of these new taxa, when recognized soon after their origin, should aim to elucidate the factors that influence their subsequent establishment and spread, thus leading to a better understanding of the processes that lead to successful speciation. Plant hybrids formed following a plant invasion provide great potential for the study of ‘evolution in action’. 相似文献
53.
J Watkins E C Abbott C N Hensby J Webster C T Dollery 《BMJ (Clinical research ed.)》1980,281(6242):702-705
The effects of 100 mg indomethacin daily for three weeks on blood pressure and urinary excretion of prostaglandin F2 alpha were studied in a double-blind, placebo-controlled comparison of two groups of patients with essential hypertension, eight receiving propranolol and seven thiazide diuretics. Compared with placebo, adding indomethacin to the patients'' established antihypertensive treatment increased blood pressure by 14/5 Hg supine and 16/9 mm Hg erect in the patients receiving propranolol, and by 13/9 mm Hg supine and 16/9 mm Hg erect in the patients receiving thiazide diuretics (all p less than or equal to 0.05). The excretion of the major urinary metabolite of prostaglandin F2 alpha was reduced by 67% in the propranolol-treated patients and by 57% in those receiving a thiazide diuretic. Body weight increased by 0 . 8 kg (propranolol) and 1 . 1 kg (thiazide diuretic) when indomethacin was given, but there were no significant changes in creatinine clearance, urinary sodium excretion, or packed cell volume in either treatment group. These results suggest that products formed by the arachidonic acid cyclo-oxygenase contribute to the regulation of blood pressure during treatment with both propranolol and thiazide diuretics. Inhibition of the cyclo-oxygenase with indomethacin partially antagonises the hypotensive effect of these drugs. 相似文献
54.
One question which is unresolved in developmental immunology is whether cortical thymocytes are the precursor cells which give rise to medullary thymocytes and peripheral T cells. Cortical thymocytes display a characteristic surface antigen phenotype (high TL and Thy-1, low H-2, no Qa-2, no Qa-3), are agglutinated by peanut agglutinin (PNA), and are unresponsive to concanavalin A (Con-A). The functionally more mature medullary thymocytes express a surface phenotype more closely resembling peripheral T cells (no TL, low Thy-1, high H-2, and some Qa-2), are not agglutinated by PNA, and are responsive to Con-A. An in vitro induction system has been devised in which mouse thymocytes undergo quantitative changes in surface antigens in less than 24 hr and increase their mitogen response to Con-A. The phenotypic changes are characterized by a decrease of TL and Thy-1 and an increase in H-2, Qa-2, and Qa-3. Studies in which thymocytes were fractionated on BSA gradients and by PNA agglutination demonstrate that the inducible cells have the properties of cortical thymocytes. Our data show that a subpopulation of cortical thymocytes can acquire phenotypic characteristics similar to medullary thymocytes and peripheral T cells. 相似文献
55.
Growth and nitrate reductase activity were measured in Paul's Scarlet rose cell suspensions, cultured in media purified from molybdenum and containing nitrate or urea as sole nitrogen source with or without added Mo. Urea could replace nitrate to yield 80% of the fresh weight in nitrate medium. Nitrate reductase activities were compared by in vivo and in vitro assays. The latter varied due to inactivation during extraction. Compared with activities in cells in complete NO3
- medium, activity in NO3
--Mo cells was reduced to 30% and, in urea-grown cells, to trace amounts. Increases in nitrate reductase activity were found when NO3
- alone was added to NO3
- or urea+Mo cultures. In NO3
--Mo cultures, Mo alone or with NO3
- caused a similar increase in activity, whereas urea-Mo cultures required both NO3
- and Mo for enzyme induction.Abbreviations FAD
flavin adenine dinucleotide
- Mo
molybdenum
- NADH
reduced nicotinamide adenine dinucleotide
- NO3
-+Mo
standard MX1 culture medium
- NO3
--Mo
MX1 medium purified of Mo and used for continuous subculture with nitrate
- NR
nitrate reductase
- PSR
Paul's Scarlet rose
- PVP
polyvinylpyrrolidone
- U
urea
- U+Mo
MX1 medium containing urea instead of nitrate
- U-Mo
MX1 medium containing urea instead of nitrate and also purified of Mo 相似文献
56.
M. M. Abbott H. A. Himel B. S. Leibel C. A. Markson S. P. Starkman H. A. Stein 《CMAJ》1964,90(12):726-730
The planning of a diabetic control program in a home and hospital for the aged prompted a survey of the incidence, severity and number of complications of diabetes mellitus in this population. Twenty-eight per cent of the total population of 265 persons were found to be diabetic. In most of them the onset of diabetes was late in life and in the majority the disease was controlled by dietary measures alone. Of interest was the low incidence of gallbladder disease, hypercholesterolemia, ocular disease, myocardial and peripheral vascular disease. Neurological complications were minimal. The measures adopted to achieve biochemical stabilization in diabetes mellitus are discussed and the absence of acidosis and ketosis in this group is noted. The high incidence of diabetes, the need for detection of undiagnosed cases, and the low rate of complications are discussed. 相似文献
57.
58.
Jessica K. Abbott Adam K. Chippindale Edward H. Morrow 《Journal of evolutionary biology》2020,33(6):738-750
Due to its hemizygous inheritance and role in sex determination, the X‐chromosome is expected to play an important role in the evolution of sexual dimorphism and to be enriched for sexually antagonistic genetic variation. By forcing the X‐chromosome to only be expressed in males over >40 generations, we changed the selection pressures on the X to become similar to those experienced by the Y. This releases the X from any constraints arising from selection in females and should lead to specialization for male fitness, which could occur either via direct effects of X‐linked loci or trans‐regulation of autosomal loci by the X. We found evidence of masculinization via up‐regulation of male‐benefit sexually antagonistic genes and down‐regulation of X‐linked female‐benefit genes. Potential artefacts of the experimental evolution protocol are discussed and cannot be wholly discounted, leading to several caveats. Interestingly, we could detect evidence of microevolutionary changes consistent with previously documented macroevolutionary patterns, such as changes in expression consistent with previously established patterns of sexual dimorphism, an increase in the expression of metabolic genes related to mito‐nuclear conflict and evidence that dosage compensation effects can be rapidly altered. These results confirm the importance of the X in the evolution of sexual dimorphism and as a source for sexually antagonistic genetic variation and demonstrate that experimental evolution can be a fruitful method for testing theories of sex chromosome evolution. 相似文献
59.
60.
R. Abbott D. Albach S. Ansell J. W. Arntzen S. J. E. Baird N. Bierne J. Boughman A. Brelsford C. A. Buerkle R. Buggs R. K. Butlin U. Dieckmann F. Eroukhmanoff A. Grill S. H. Cahan J. S. Hermansen G. Hewitt A. G. Hudson C. Jiggins J. Jones B. Keller T. Marczewski J. Mallet P. Martinez‐Rodriguez M. Möst S. Mullen R. Nichols A. W. Nolte C. Parisod K. Pfennig A. M. Rice M. G. Ritchie B. Seifert C. M. Smadja R. Stelkens J. M. Szymura R. Väinölä J. B. W. Wolf D. Zinner 《Journal of evolutionary biology》2013,26(2):229-246
Hybridization has many and varied impacts on the process of speciation. Hybridization may slow or reverse differentiation by allowing gene flow and recombination. It may accelerate speciation via adaptive introgression or cause near‐instantaneous speciation by allopolyploidization. It may have multiple effects at different stages and in different spatial contexts within a single speciation event. We offer a perspective on the context and evolutionary significance of hybridization during speciation, highlighting issues of current interest and debate. In secondary contact zones, it is uncertain if barriers to gene flow will be strengthened or broken down due to recombination and gene flow. Theory and empirical evidence suggest the latter is more likely, except within and around strongly selected genomic regions. Hybridization may contribute to speciation through the formation of new hybrid taxa, whereas introgression of a few loci may promote adaptive divergence and so facilitate speciation. Gene regulatory networks, epigenetic effects and the evolution of selfish genetic material in the genome suggest that the Dobzhansky–Muller model of hybrid incompatibilities requires a broader interpretation. Finally, although the incidence of reinforcement remains uncertain, this and other interactions in areas of sympatry may have knock‐on effects on speciation both within and outside regions of hybridization. 相似文献