全文获取类型
收费全文 | 2339篇 |
免费 | 193篇 |
专业分类
2532篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 33篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 38篇 |
2015年 | 108篇 |
2014年 | 94篇 |
2013年 | 117篇 |
2012年 | 180篇 |
2011年 | 161篇 |
2010年 | 112篇 |
2009年 | 114篇 |
2008年 | 146篇 |
2007年 | 160篇 |
2006年 | 145篇 |
2005年 | 133篇 |
2004年 | 149篇 |
2003年 | 168篇 |
2002年 | 124篇 |
2001年 | 34篇 |
2000年 | 12篇 |
1999年 | 38篇 |
1998年 | 40篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 33篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 9篇 |
1989年 | 22篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有2532条查询结果,搜索用时 15 毫秒
131.
Intraspecific sexual selection on a speciation trait, male coloration, in the Lake Victoria cichlid Pundamilia nyererei 总被引:3,自引:0,他引:3
Maan ME Seehausen O Söderberg L Johnson L Ripmeester EA Mrosso HD Taylor MI van Dooren TJ van Alphen JJ 《Proceedings. Biological sciences / The Royal Society》2004,271(1556):2445-2452
The haplochromine cichlids of Lake Victoria constitute a classical example of explosive speciation. Extensive intra- and interspecific variation in male nuptial coloration and female mating preferences, in the absence of postzygotic isolation between species, has inspired the hypothesis that sexual selection has been a driving force in the origin of this species flock. This hypothesis rests on the premise that the phenotypic traits that underlie behavioural reproductive isolation between sister species diverged under sexual selection within a species. We test this premise in a Lake Victoria cichlid, by using laboratory experiments and field observations. We report that a male colour trait, which has previously been shown to be important for behavioural reproductive isolation between this species and a close relative, is under directional sexual selection by female mate choice within this species. This is consistent with the hypothesis that female choice has driven the divergence in male coloration between the two species. We also find that male territoriality is vital for male reproductive success and that multiple mating by females is common. 相似文献
132.
Many chromosomal rearrangements are detected each year in France on young boars candidates for reproduction. The possible use of these animals requires a good knowledge of the potential effect of the rearrangements on the prolificacy of their mates. This effect can be estimated by an accurate determination of the rate of unbalanced spermatozoa in the semen of boars which carry the rearrangements. Indeed, these spermatozoa exhibiting normal fertilizing ability are responsible for an early embryonic mortality, and then, for a decrease of the litter sizes. The "spermFISH" technique, i.e. fluorescent in situ hybridization on decondensed sperm heads, has been used on several occasions in Man, in this perspective. In livestock species, this method was formerly used mainly for semen sexing purposes. We used it, for the first time, to estimate the rates of imbalance in the semen of four boars carrying chromosomal rearrangements: two reciprocal translocations, rcp(3;15)(q27;q13) and rcp(12;14)(q13;q21), as well as two independent cases of trisomy 18 mosaicism. The rates of unbalanced gametes were relatively high for the two reciprocal translocations (47.83% and 24.33%, respectively). These values differed from the apparent effects of the rearrangements estimated using a limited number of litters: a decrease in prolificacy of 23% (estimation obtained using the results of 6 litters) and 39% (57 litters), respectively for the 3/15 and 12/14 translocations. The imbalance rates were much lower for the trisomy mosaics (0.58% and 1.13%), suggesting a very moderate effect of this special kind of chromosomal rearrangement. 相似文献
133.
Ziegler DR Ribeiro LC Hagenn M Siqueira IR Araújo E Torres IL Gottfried C Netto CA Gonçalves CA 《Neurochemical research》2003,28(12):1793-1797
Ketogenic diets have been used in the treatment of refractory childhood epilepsy for almost 80 years; however, we know little about the underlying biochemical basis of their action. In this study, we evaluate oxidative stress in different brain regions from Wistar rats fed a ketogenic diet. Cerebral cortex appears to have not been affected by this diet, and cerebellum presented a decrease in antioxidant capacity measured by a luminol oxidation assay without changes in antioxidant enzyme activities—glutathione peroxidase, catalase, and superoxide dismutase. In the hippocampus, however, we observed an increase in antioxidant activity accompanied by an increase of glutathione peroxidase (about 4 times) and no changes in lipoperoxidation levels. We suggest that the higher activity of this enzyme induced by ketogenic diet in hippocampus might contribute to protect this structure from neurodegenerative sequelae of convulsive disorders. 相似文献
134.
Schmidt JM Mercure J Tremblay GB Pagé M Feher M Dunn-Dufault R Peter MG Redden PR 《Bioorganic & medicinal chemistry》2003,11(7):1389-1396
There is still a strong need for additional diversity and new chemical scaffolds to allow for the exploration of improved tissue selectivity and finding better selective estrogen receptor modulators (SERMs). Using a de novo design technology a diphenylnaphthyl propylene scaffold, exemplified by (E)-9b, with ER antagonist activity has been generated. It was prepared by alkylating 1-[4-methoxyphenyl)-2-(4-(2-chloroethoxy)phenyl]-1-propanone under metal halogen exchange conditions with 1-iodo-6-methoxy-naphthalene. Following dehydration and cleavage of the methoxy groups, (E)-9b was formed by displacement of the chloro group with pyrrolidine. (E)-9b binding to ER generated calculated K(i) values of 3.7 nM for hER(alpha) and 72 nM for hER(beta). The antagonism of (E)-9b was demonstrated in cell transfection assays using the ERE from the vitA2 promotor and the natural ER-responsive pS2 promotor. With increasing concentrations of (E)-9b, the E(2)-dependent response was efficiently inhibited demonstrating that (E)-9b could function as an anti-estrogen in these assays. Interestingly, ER(alpha) activity was inhibited even below basal levels suggesting that ligand-independent activity of ER(alpha) was also inhibited. Computational docking studies suggest that the placement of the hydroxyl group on the naphthalene group may not be optimal and we are currently exploring additional analogues. 相似文献
135.
Day FH Zhang Y Clair P Grabstein KH Mazel M Rees AR Kaczorek M Temsamani J 《Journal of immunology (Baltimore, Md. : 1950)》2003,170(3):1498-1503
Linear peptides (SynB vectors) with specific sequence motifs have been identified that are capable of enhancing the transport of a wide range of molecules into cells. These peptide vectors have been used to deliver exogenous peptides and protein Ags across the cell membrane and into the cytoplasm of cells. Specifically, in vitro analysis indicated that these SynB peptides enhanced the uptake of two 9-mer peptide Ags, NP(147-155) and Mtb(250-258) (T cell epitopes of influenza nucleoprotein and Mycobacterium tuberculosis, respectively) and the M. tuberculosis Ag Mtb8.4 protein, into K562 cells when covalently linked to the respective Ags. Furthermore, selected SynB vectors, when conjugated to these same Ags and used as immunogens, resulted in considerably enhanced Ag-specific CTL responses. Several SynB vectors were tested and resulted in varying levels of cellular uptake. The efficiency of uptake correlated with the ability of the SynB construct to deliver each epitope in vivo and induce specific CTL responses in mice. These data suggest that peptide vectors, such as SynB that transport target Ags across the cell membrane in a highly efficient manner, have significant potential for vaccine delivery. 相似文献
136.
137.
Chatel G Montiel G Pré M Memelink J Thiersault M Saint-Pierre B Doireau P Gantet P 《Journal of experimental botany》2003,54(392):2587-2588
138.
In vivo impact of CpG1826 oligodeoxynucleotide on CD8 T cell primary responses and survival 总被引:3,自引:0,他引:3
Beloeil L Tomkowiak M Angelov G Walzer T Dubois P Marvel J 《Journal of immunology (Baltimore, Md. : 1950)》2003,171(6):2995-3002
CpG oligodeoxynucleotide (ODN) promotes maturation of APCs in vivo and induces strong type 1 T cell responses in mice. In this study, we have investigated the ability of CpG1826 to modulate peptide-specific CD8 T cell responses in a context where CD4 T cells are likely to play a minor role. The effects of CpG1826 were evaluated in a system where a population of NP68-specific F5 TCR transgenic CD8 T cells is diluted into a polyclonal host following adoptive transfer into C57BL/10 syngeneic recipients. Using this approach, we found that CpG1826 enhanced the ability of F5 CD8 T cells to undergo multiple divisions in vivo, to express IFN-gamma ex vivo, and to up-regulate memory-associated cell surface markers such as CD122 (IL-2Rbeta) and Ly-6C. Moreover, CpG1826 greatly increased in vivo cytotoxic activity. Using tetramer detection, we found that CpG1826 promoted long-term survival of Ag-specific CD8 T cells after immunization while no NP68-specific cells were detected when the cognate peptide was injected alone. These results indicate that CpG1826 acts as an adjuvant which increases CD8 T cell effector responses and promotes long-term survival of NP68 peptide-specific cells in vivo. They also suggest that this adjuvant can modulate CD8 T cell responses in a system which is likely to be independent of CD4 T cell help. 相似文献
139.
140.
Identification of a new simian immunodeficiency virus lineage with a vpu gene present among different cercopithecus monkeys (C. mona, C. cephus, and C. nictitans) from Cameroon 下载免费PDF全文
Courgnaud V Abela B Pourrut X Mpoudi-Ngole E Loul S Delaporte E Peeters M 《Journal of virology》2003,77(23):12523-12534
During a large serosurvey of wild-caught primates from Cameroon, we found 2 mona monkeys (Cercopithecus mona) out of 8 and 47 mustached monkeys (Cercopithecus cephus) out of 302 with human immunodeficiency virus (HIV)-simian immunodeficiency virus (SIV) cross-reactive antibodies. In this report, we describe the full-length genome sequences of two novel SIVs, designated SIVmon-99CMCML1 and SIVmus-01CM1085, isolated from one mona (CML1) and one mustached (1085) monkey, respectively. Interestingly, these viruses displayed the same genetic organization (i.e., presence of a vpu homologue) as members of the SIVcpz-HIV type 1 lineage and SIVgsn isolated from greater spot-nosed monkeys (Cercopithecus nictitans). Phylogenetic analyses of SIVmon and SIVmus revealed that these viruses were genetically distinct from other known primate lentiviruses but were more closely related to SIVgsn all across their genomes, thus forming a monophyletic lineage within the primate lentivirus family, which we designated the SIVgsn lineage. Interestingly, mona, mustached, and greater spot-nosed monkeys are phylogenetically related species belonging to three different groups of the genus Cercopithecus, the C. mona, C. cephus, and Cercopithecus mitis groups, respectively. The presence of new viruses closely related to SIVgsn in two other species reinforces the hypothesis that a recombination event between ancestral SIVs from the family Cercopithecinae is the origin of the present SIVcpz that is widespread among the chimpanzee population. 相似文献