全文获取类型
收费全文 | 5753篇 |
免费 | 442篇 |
国内免费 | 3篇 |
出版年
2023年 | 38篇 |
2022年 | 78篇 |
2021年 | 185篇 |
2020年 | 157篇 |
2019年 | 175篇 |
2018年 | 220篇 |
2017年 | 199篇 |
2016年 | 269篇 |
2015年 | 324篇 |
2014年 | 381篇 |
2013年 | 412篇 |
2012年 | 457篇 |
2011年 | 376篇 |
2010年 | 256篇 |
2009年 | 248篇 |
2008年 | 305篇 |
2007年 | 259篇 |
2006年 | 226篇 |
2005年 | 202篇 |
2004年 | 192篇 |
2003年 | 144篇 |
2002年 | 147篇 |
2001年 | 109篇 |
2000年 | 108篇 |
1999年 | 88篇 |
1998年 | 47篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 42篇 |
1994年 | 16篇 |
1993年 | 23篇 |
1992年 | 36篇 |
1991年 | 24篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 41篇 |
1987年 | 30篇 |
1986年 | 27篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 15篇 |
1972年 | 13篇 |
1971年 | 10篇 |
排序方式: 共有6198条查询结果,搜索用时 218 毫秒
51.
Molecular evolution of voltage-sensitive ion channel genes: on the origins of electrical excitability 总被引:14,自引:0,他引:14
We have analyzed nucleic acid and amino acid sequence alignments of a
variety of voltage-sensitive ion channels, using several methods for
phylogenetic tree reconstruction. Ancient duplications within this family
gave rise to three distantly related groups, one consisting of the Na+ and
Ca++ channels, another the K+ channels, and a third including the cyclic
nucleotide-binding channels. A series of gene duplications produced at
least seven mammalian homologues of the Drosophila Shaker K+ channel;
clones of only three of these genes are available from all three mammalian
species examined (mouse, rat, and human), pointing to specific genes that
have yet to be recovered in one or another of these species. The
Shaw-related K+ channels and the Na+ channel family have also undergone
considerable expansion in mammals, relative to flies. These expansions
presumably reflect the needs of the high degree of physiological and
neuronal complexity of mammals. Analysis of the separate domains of the
four-domain channels (Ca++ and Na+) supports their having evolved by two
sequential gene duplications and implies the historical existence of a
functional two-domain channel.
相似文献
52.
mtDNA diversity in rhesus monkeys reveals overestimates of divergence time and paraphyly with neighboring species 总被引:4,自引:0,他引:4
Reconstructions of the human-African great ape phylogeny by using
mitochondrial DNA (mtDNA) have been subject to considerable debate. One
confounding factor may be the lack of data on intraspecific variation. To
test this hypothesis, we examined the effect of intraspecific mtDNA
diversity on the phylogenetic reconstruction of another Plio- Pleistocene
radiation of higher primates, the fascicularis group of macaque (Macaca)
monkey species. Fifteen endonucleases were used to identify 10 haplotypes
of 40-47 restriction sites in M. mulatta, which were compared with similar
data for the other members of this species group. Interpopulational,
intraspecific mtDNA diversity was large (0.5%- 4.5%), and estimates of
divergence time and branching order incorporating this variation were
substantially different from those based on single representatives of each
species. We conclude that intraspecific mtDNA diversity is substantial in
at least some primate species. Consequently, without prior information on
the extent of genetic diversity within a particular species, intraspecific
variation must be assessed and accounted for when reconstructing primate
phylogenies. Further, we question the reliability of hominoid mtDNA
phylogenies, based as they are on one or a few representatives of each
species, in an already depauperate superfamily of primates.
相似文献
53.
da Cunha Cruz Yasmini Scarpa Ana Lívia Martins Díaz Alejandro Sandria Pereira Marcio Paulo de Castro Evaristo Mauro Pereira Fabricio José 《Journal of plant research》2023,136(5):665-678
Journal of Plant Research - Precipitation is an important climatic element that defines the hydrological regime, and its seasonal variation produces annual dry and wet periods in some areas. This... 相似文献
54.
55.
Mapping of resistance to the potato cyst nematode Globodera rostochiensis from the wild potato species Solanum vernei 总被引:1,自引:0,他引:1
Jeanne M. E. Jacobs Herman J. van Eck Karin Horsman Paul F. P. Arens Brigitte Verkerk-Bakker Evert Jacobsen Andy Pereira Willem J. Stiekema 《Molecular breeding : new strategies in plant improvement》1996,2(1):51-60
A population of diploid potato (Solanum tuberosum) was used for the genetic analysis and mapping of a locus for resistance to the potato cyst nematode Globodera rostochiensis, introgressed from the wild potato species Solanum vernei. Resistance tests of 108 genotypes of a F1 population revealed the presence of a single locus with a dominant allele for resistance to G. rostochiensis pathotype Ro1. This locus, designated GroV1, was located on chromosome 5 with RFLP markers. Fine-mapping was performed with RAPD and SCAR markers. The GroV1 locus was found in the same region of the potato genome as the S. tuberosum ssp. andigena H1 nematode resistance locus. Both resistance loci could not excluded to be allelic. The identification of markers flanking the GroV1 locus offers a valuable strategy for marker-assisted selection for introgression of this nematode resistance.Abbreviations BSA
bulked segregant analysis
- RAPD
random-amplified polymorphic DNA
- RFLP
restriction fragment length polymorphism
- SCAR
sequence-characterized amplified region 相似文献
56.
Cardoso RA Filho AA Melo MC Lyerly DM Wilkins TD Lima AA Ribeiro RA Souza GE 《Mediators of inflammation》1996,5(3):183-187
This study investigated the ability of Clostridium difficile toxin B, isolated from the VPI 10463 strain, to induce fever and neutrophilia in rats. Intravenous injection of toxin B (0.005-0.5 mug/kg) evoked a dose-dependent increase in body temperature. The febrile response to 0.5 mug/kg of the toxin started in 2.5 h, peaked at 5 h, and subsided fully within 24 h. Toxin B also induced a dosedependent neutrophilia. Pretreatment with indomethacin (2 mg/kg, i.p.) did not affect the neutrophilia induced by toxin B, but significantly reduced the febrile response measured 4 to 8 h after toxin B injection. Dexamethasone (0.5 mg/ kg) also markedly diminished the febrile response induced by toxin B. These results show that Clostridium difficile toxin B induced a febrile response susceptible to inhibition by dexamethasone and indomethacin. Furthermore, they suggest that prostaglandins are not involved in the neutrophilia caused by this toxin. 相似文献
57.
Measurements of anther (length, width, depth), pollen grain (percent fertility, polar diameter, equatorial diameter, polar diameter/equatorial diameter ratio, volume) and pistil (stigma length, style length, ovary length, total pistil length, stigma width, style width, ovary width) were taken on 12 diverse sesame (Sesamum indicum L.) genotypes on each of four collection dates in 1994. Highly significant differences among genotype means were obtained for all characters except polar diameter. Highly significant differences among environment (collection date) means were found for ten of the 15 characters measured. Highly significant genotype x environment interactions were obtained for all characters except anther length. For the anther characters measured, relatively high repeatability values were found, ranging from 99.8% for length to 87.6% for depth. For the pollen grain characters measured, the repeatability values ranged from 67.6% for percent fertility to 23.1% for polar diameter. For the pistil characters measured, the repeatability values ranged from 94.0% for style width to 49.6% for total pistil length. These results indicate that genotype and environment influence anther, pollen grain and pistil characters. Variation in some of these morphological aspects could influence the consistency and interpretation of male transmission studies on both the applied and evolutionary levels. 相似文献
58.
A genetic map of potato (Solanum tuberosum) integrating molecular markers,including transposons,and classical markers 总被引:2,自引:0,他引:2
J. M. E. Jacobs H. J. Van Eck P. Arens B. Verkerk-Bakker B. te Lintel Hekkert H. J. M. Bastiaanssen A. El-Kharbotly A. Pereira E. Jacobsen W. J. Stiekema 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(2):289-300
A genetic map of potato (Solanum tuberosum L.) integrating molecular markers with morphological and isozyme markers was constructed using a backcross population of 67 diploid potato plants. A general method for map construction is described that differs from previous methods employed in potato and other outbreeding plants. First, separate maps for the female and male parents were constructed. The female map contained 132 markers, whereas the male map contained 138 markers. Second, on the basis of the markers in common the two integrated parental maps were combined into one with the computer programme JoinMap. This combined map consisted of 175 molecular markers, 10 morphological markers and 8 isozyme markers. Ninety-two of the molecular markers were derived from DNA sequences flanking either T-DNA inserts in potato or reintegrated maize transposable elements originating from these T-DNA constructs. Clusters of distorted segregation were found on chromosomes 1,2,8 and 11 for the male parent and chromosome 5 for both parents. The total length of the combined map is 1120 cM. 相似文献
59.
José A. A. Sant''Ana Pereira Arnold De Haan Andy Wessels Antoon F. M. Moorman Anthony J. Sargeant 《The Histochemical journal》1995,27(9):715-722
Summary In the present study we report a novel histochemical method which, by sequential pre-incubations in alkaline and acidic media,
selectively differentiates muscle fibres expressing myosin heavy chain IIX, on the basis of a specific profile for myofibrillar
actomyosin ATPase (mATPase) activity. The enzyme reactions were tested for specificity by means of anti-myosin heavy chain
monoclonal antibodies, which were characterized on Western blots of muscle homogenates. Enzyme histochemical reactions with
the traditional pH buffers were compared to those of the new method and, in conjunction with the immunoreactions, used to
confirm the relationship between MyHC expression and the distinct profiles for mATPase. Imrnunohistochemical reactions demonstrated
that the new method only differentiates those fibres expressing myosin heavy chain IIX. The method revealed a continuum in
which the intermediate staining intensities corresponded to hybrid fibres expressing myosin heavy chain IIX in combination
with either the IIA or IIB forms. Quantitative histochemistry and immunohistochemistry (by image analysis), used to examine
the relationship between staining intensities for mATPase and amounts of myosin heavy chain IIX expression, revealed that
the new method discriminates well between hybrid fibres expressing variable amounts of the IIX isoform (r2 = 0.93). 相似文献
60.
Inês A. C. Pereira Jean LeGall António V. Xavier M. Teixeira 《Journal of biological inorganic chemistry》1997,2(1):23-31
The high-molecular-mass cytochromes c (Hmcs) from the sulfate-reducing bacteria Desulfovibrio gigas and Desulfovibrio vulgaris (Hildenborough) were found to be strongly bound to the cytoplasmic membrane. After detergent solubilization they were shown to be water soluble and to be similar to those previously isolated from the soluble fractions in terms of N-terminal sequence, molecular mass, UV-visible and EPR spectroscopies. In D. gigas, higher amounts of Hmc can be obtained from the membranes than from the soluble fraction. This enabled further characterization of both cytochromes. The apparent heme reduction potentials of both Hmcs, determined at pH 7.5 through visible and EPR redox titrations, span a large range of redox potentials, approximately between 0 and –280?mV, and can be roughly divided into three groups: four to five hemes have E 0s of –30?mV to –100?mV, three to four hemes have E 0s around –170?mV, and seven to eight hemes have a lower E 0 of –250 to –280?mV. Several of these redox potentials are strongly pH dependent. Mössbauer studies of oxidized and reduced D. vulgaris Hmc show that this protein contains two high-spin hemes in both oxidation states. The rate of reduction of both Hmcs with the periplasmic hydrogenases from the corresponding organisms is extremely slow. 相似文献