全文获取类型
收费全文 | 192篇 |
免费 | 23篇 |
国内免费 | 9篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 11篇 |
2010年 | 14篇 |
2009年 | 12篇 |
2008年 | 4篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1969年 | 2篇 |
1955年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有224条查询结果,搜索用时 15 毫秒
1.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
2.
3.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献
4.
Molecular phylogeny and divergence times of drosophilid species 总被引:32,自引:15,他引:17
The phylogenetic relationships and divergence times of 39 drosophilid
species were studied by using the coding region of the Adh gene. Four
genera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (from
Hawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, and
Sophophora--were included. After conducting statistical analyses of the
nucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNA
genes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophila
as the outgroup. The phylogenetic tree obtained showed that the first major
division of drosophilid species occurs between subgenus Sophophora (genus
Drosophila) and the group including subgenera Drosophila and Engiscaptomyza
plus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is then
divided into D. willistoni and the clade of D. obscura and D. melanogaster
species groups. In the other major drosophilid group, Zaprionus first
separates from the other species, and then D. immigrans leaves the
remaining group of species. This remaining group then splits into the D.
repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila,
Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightly
clustered. Each of the D. repleta, D. obscura, and D. melanogaster groups
is monophyletic. The splitting of subgenera Drosophila and Sophophora
apparently occurred about 40 Mya, whereas the D. repleta group and the
Hawaiian drosophilid cluster separated about 32 Mya. By contrast, the
splitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya,
suggesting that Scaptomyza experienced a rapid morphological evolution. The
D. obscura and D. melanogaster groups apparently diverged about 25 Mya.
Many of the D. repleta group species studied here have two functional Adh
genes (Adh-1 and Adh-2), and these duplicated genes can be explained by two
duplication events.
相似文献
5.
Charged residues are major determinants of the transmembrane orientation of a signal-anchor sequence 总被引:12,自引:0,他引:12
J P Beltzer K Fiedler C Fuhrer I Geffen C Handschin H P Wessels M Spiess 《The Journal of biological chemistry》1991,266(2):973-978
Uncleaved signal-anchor sequences of membrane proteins inserted into the endoplasmic reticulum initiate the translocation of either the amino-terminal or the carboxyl-terminal polypeptide segment across the bilayer. Which topology is acquired is not determined by the apolar segment of the signal but rather by the hydrophilic sequences flanking it. To study the role of charged residues in determining the membrane topology, the insertion of mutants of the asialoglycoprotein receptor H1, a single-spanning protein with a cytoplasmic amino terminus, was analyzed in transfected COS-7 cells. When the charged amino acids flanking the hydrophobic signal were mutated to residues of opposite charge, half the polypeptides inserted with the inverted orientation. When, in addition, the amino-terminal domain of the mutant protein was truncated, approximately 90% of the polypeptides acquired the inverted topology. The transmembrane orientation appears to be primarily determined by the charges flanking the signal sequence but is modulated by the domains to be translocated. 相似文献
6.
Sulfate reduction and S-oxidation in a moorland pool sediment 总被引:3,自引:2,他引:1
In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO4
2– reduction rates in the sediment, (2) depletion of SO4
2– in the overlying water column and (3) release of35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO4
2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core35SO4
2– injection. Rates of SO4
2– consumption in the overlying water were estimated by changes in SO4
2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m–2 d–1. Rates of SO4
2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m–2 d–1 (November) to 0.43–1.81 mmol m–2 d–1 (July, August and April). Maximum rates of oxidation to SO4
2– in July 1990 estimated by combination of SO4
2– reduction rates and rates of in situ SO4
2– uptake in the enclosed water column were 10.3 and 10.5 mmol m–2 d–1 at an organic rich and at a sandy site respectively.Experiments with35S2– and35SO4
2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO4
2– and (2) the presence of mainly non SO4
2–-S derived from reduced S transported from the sediment into the overlying water. A35S2– tracer experiment showed that about 7% of35S2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author 相似文献
7.
Effects of exogenous 1,3-diaminopropane and spermidine on senescence of oat leaves : I. Inhibition of protease activity, ethylene production, and chlorophyll loss as related to polyamine content 总被引:3,自引:3,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Excision and dark incubation of oat (Avena sativa L., var. Victory) leaves cause a sharp increase in protease activity, which precedes Chl loss. Both these senescence processes are inhibited by exogenously applied 1,3-diaminopropane (Dap), which occurs naturally in leaf segments. The inhibition of protease activity is much greater in vivo than in vitro, suggesting inhibition of protease synthesis as well as protease action by Dap. Chl breakdown in leaves of radish and broccoli, which also senesce rapidly in the dark, is only slightly inhibited by DaP. These differences between cereal and dicotyledonous plants are correlated with the natural occurrence of Dap in cereals. In the light, Dap promotes, rather than retards, the loss of Chl in oat leaves. This resembles previously described effects of other polyamines. Addition of Mg2+ to the medium does not antagonize this effect. In the dark, the accumulated Dap also inhibits ethylene production and decreases titer of other polyamines. Addition of Ca2+ to the incubation medium containing Dap competitively reduces the effects of Dap. Thus, Dap, like other polyamines, seems to require an initial attachment to a membrane site shared with Ca2+ before exerting its antisenescence action. 相似文献
8.
H Koprowski Z Steplewski K Mitchell M Herlyn D Herlyn P Fuhrer 《Somatic cell genetics》1979,5(6):957-971
Hybridoma cells which secrete colorectal carcinoma-specific antibodies have been produced and used to study the antigenic structure of these tumor cells. Nineteen antibodies have been studied in detail, and 15 of these are colorectal carcinoma specific. Only two antibodies reactive with carcinoembryonic antigen (CEA) have been discovered and five other antibodies that react with distinct epitopes on the cell surface have been defined. Several antigens with distinct molecular characteristics have been shown to exist by use of hybridoma antibodies. Six hybridoma antibodies have been shown to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). 相似文献
9.
JOSEP PIÑOL XAVIER ESPADALER NÚRIA CAÑELLAS JORDI MARTÍNEZ‐VILALTA JOSÉ A. BARRIENTOS DANIEL SOL 《Ecological Entomology》2010,35(3):367-376
1. Predation‐exclusion experiments have highlighted that top‐down control is pervasive in terrestrial communities, but most of these experiments are simplistic in that they only excluded a single group of predators and the effect of removal was evaluated on a few species from the community. The main goal of our study was to experimentally establish the relative effects of ants and birds on the same arthropod assemblage of canopy trees. 2. We conducted 1‐year long manipulative experiments in an organic citrus grove intended to quantify the independent effects of bird and ant predators on the abundance of arthropods. Birds were excluded with plastic nets whereas ants were excluded with sticky barriers on the trunks. The sticky barrier also excluded other ground dwelling insects, like the European earwig Forficula auricularia L. 3. Both the exclusion of ants and birds affected the arthropod community of the citrus canopies, but the exclusion of ants was far more important than the exclusion of birds. Indeed, almost all groups of arthropods had higher abundance in ant‐excluded than in control trees, whereas only dermapterans were more abundant in bird‐excluded than in control trees. A more detailed analysis conducted on spiders also showed that the effect of ant exclusion was limited to a few families rather than being widespread over the entire diverse spectrum of spiders. 4. Our results suggest that the relative importance of vertebrate and invertebrate predators in regulating arthropod populations largely depends on the nature of the predator–prey system. 相似文献
10.
目的:早期液体复苏对感染性休克患者血流动力学的影响。方法:选取2012年2月-2013年2月我院ICU收治的26例感染性休克患者作为研究对象,随机分为对照组和试验组,各13例。两组患者均采用PICCO监测,并根据早期复苏目标导向(Earlygoaldirectedtherapy,EGDT)进行早期液体复苏治疗。对照组和试验组复苏液分别为林格液和6%羟乙基淀粉130/0.4氯化钠溶液。分别于复苏开始时(Oh)、8h和24h收集患者的血流动力学参数。结果:两组患者CO及PAWP水平均随着时间的延长下降,而CI、CVP及SVR水平均随着时间的增加上升。除对照组CI外,与开始复苏(oh)相比较试验组和对照组的C0、CI、CVP、SVR及PAWP与开始复苏(O小时)相比较均有显著差异(P值均〈0.05)。经重复测量资料的.方差分析进行比较发现,与对照组相比较,试验组CVP和SVR上升水平及PAWP下降水平明显,差异具有统计学意义(P值均〈0.05)。结论:感染性休克患者使用6%羟乙基淀粉130/0.4氯化钠溶液进行复苏,能更好的改善患者的血流动力学指标。 相似文献