全文获取类型
收费全文 | 626篇 |
免费 | 92篇 |
国内免费 | 1篇 |
出版年
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 29篇 |
2012年 | 25篇 |
2011年 | 39篇 |
2010年 | 24篇 |
2009年 | 22篇 |
2008年 | 27篇 |
2007年 | 27篇 |
2006年 | 26篇 |
2005年 | 27篇 |
2004年 | 23篇 |
2003年 | 21篇 |
2002年 | 29篇 |
2001年 | 22篇 |
2000年 | 26篇 |
1999年 | 15篇 |
1998年 | 5篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 11篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1966年 | 2篇 |
1946年 | 3篇 |
排序方式: 共有719条查询结果,搜索用时 15 毫秒
1.
Exposure to 2.0 micrograms/ml cytochalasin B causes loss of viability in Friend erythroleukaemia cells. This effect is only observed however in cells undergoing mitosis. 相似文献
2.
3.
Summary Production of trace levels of carbon monoxide was consistently observed in the off-gas of a laboratory anaerobic digester fed Waste Activated Sludge. Inocula from this digester was enriched for acetate and methanol utilizing methanogenic populations. These enriched inocula were then monitored in batch assays for carbon monoxide and hydrogen production. Results demonstrated that carbon monoxide is produced during methanogenesis on both substrates. Subsequent utilization of CO was observed to occur after methane production was essentially complete for the assays conducted with methanol. Carbon monoxide evolution during methanogenesis on acetate displayed a markedly different trend from that observed from methanol. 相似文献
4.
JoAnne S. Richards Gerard J. Hickey Shiuan Chen John E. Shively Peter F. Hall Dana Gaddy-Kurten Richard Kurten 《Steroids》1987,50(4-6):393-409
To determine the molecular basis for changes in aromatase (P450arom) activity in rat ovarian follicles and corpora lutea, seven clones for rat P450arom cDNA have been identified and isolated from a rat granulosa cell λgtll cDNA expression library using a 62 mer deoxyoligonucleotide probe (derived from an amino acid sequence of purified human placental aromatase) and a human placental P450arom cDNA probe. One of the rat P450arom cDNA clones contained an insert 1.2 kb in size. Both the human 1.8 kb cDNA and the rat 1.2 kb cDNA probes hybridized to a single species of P450arom mRNA that was 2.6 kb in size. Northern blot analysis revealed that corpora lutea isolated on day 15 of pregnancy contained high amounts of P450arom mRNA, whereas granulosa cells of antral follicles of hormonally primed, hypophysectomized rats (i.e., those from which mRNA was isolated to construct the cDNA library) contained only low amounts of P450arom mRNA. The lower amounts of P450arom in granulosa cells of preovulatory follicles in the estradiol-follicle-stimulating hormone primed hypophysectomized rats were unexpected because follicles incubated in medium containing testosterone substrate produce more estradiol than do corpora lutea isolated on day 15 of pregnancy and incubated under similar conditions. Additional studies will determine the hormonal events responsible for the elevated amounts and constitutive maintenance of P450arom mRNA and aromatase activity in luteal cells in vivo and in vitro. 相似文献
5.
Replacement of the invariant lysine 77 by arginine in yeast iso-1-cytochrome c results in enhanced and normal activities in vitro and in vivo 总被引:10,自引:0,他引:10
D Holzschu L Principio K T Conklin D R Hickey J Short R Rao G McLendon F Sherman 《The Journal of biological chemistry》1987,262(15):7125-7131
Oligonucleotide-directed mutagenesis of the yeast Saccharomyces cerevisiae was used to generate an abnormal iso-1-cytochrome c having an Arg-77 replacement of the normal Lys-77; this Lys-77 residue is evolutionarily conserved in most eukaryotic cytochromes c and is trimethylated in fungal and plant cytochromes c. Examination of strains having a single chromosomal copy of the gene encoding the Arg-77 protein indicated that the altered protein was synthesized at the normal rate and that it had normal or near normal activity in vivo. Examination of enzymatic activities in vitro with cytochrome b2, cytochrome c peroxidase, and cytochrome c oxidase indicated that the altered iso-1-cytochrome c has equal or enhanced catalytic efficiencies. Thus, replacement of the evolutionarily conserved residue Lys-77 produces no or only minor effects both in vivo and in vitro. 相似文献
6.
Donal A. Hickey Bernhard F. Benkel Poppo H. Boer Yves Genest Sumaia Abukashawa Gerard Ben-David 《Journal of molecular evolution》1987,26(3):252-256
Summary We constructed a cDNA library for the beetle,Tribolium castaneum. This library was screened using a cloned amylase gene fromDrosophila melanogaster as a molecular probe. Beetle amylase cDNA clones were isolated from this bank, and the nucleotide sequence was obtained for a cDNA clone with a coding capacity for 228 amino acids. Both the nucleotide sequence and predicted amino acid sequence were compared to our recent results forD. melanogaster alpha-amylases, along with published sequences for other alpha-amylases. The results show that animal alpha-amylases are highly conserved over their entire length. A borader comparison, which includes plant and microbial alpha-amylase sequences, indicates that parts of the gene are conserved between prokaryotes, plants, and animals. We discuss the potential importance of this and other enzyme-coding genes for the construction of molecular phylogenies and for the study of the general question of molecular clocks in evolution. 相似文献
7.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
8.
9.
D Dudley D M Baker M J Hickey D D Hickstein 《Biochemical and biophysical research communications》1989,160(1):346-353
We characterized the surface antigen and mRNA expression for the CD11c (alpha X, p150) subunit of the human leukocyte adherence receptor family during hematopoietic cell differentiation. The CD11c subunit antigen and mRNA are constitutively expressed in undifferentiated HL-60 promyelocytic leukemia cells, and levels increase markedly with differentiation along the monocyte/macrophage pathway using phorbol myristate acetate. Human monocyte-derived macrophages and human alveolar macrophages express elevated levels of the CD11c subunit antigen and mRNA, indicating that the changes observed in vitro are present in vivo. Dot blot analysis of immature and mature lymphoid and myeloid cells and cell lines demonstrate equivalent levels of CD11c mRNA expression. We conclude that CD11c gene expression is selectively increased during hematopoietic cell differentiation along the monocyte/macrophage pathway. 相似文献
10.
Amylase gene expression in intraspecific and interspecific somatic transformants of Drosophila. 总被引:1,自引:0,他引:1
The Amylase locus in Drosophila melanogaster normally contains two copies of the structural gene for alpha-amylase, a centromere-proximal copy, Amy-p, and a distal copy, Amy-d. Products of the two genes may display discrete electrophoretic mobilities, but many strains known to carry the Amy duplication are characterized by a single amylase electromorph, e.g., Oregon-R, which produces the mobility variant AMY-1. A transient expression assay was used in somatic transformation experiments to test the functional status of the Amy genes from an Oregon-R strain. Plasmid constructs containing either the proximal or distal copy were tested in amylase-null hosts. Both genes produced a functional AMY-1 isozyme. Constructs were tested against an AMY-3 reference activity produced by a coinjected plasmid that contains the Amy-d3 allele from a Canton-S strain. With reference to the internal control, the Amy-p and Amy-d genes from Oregon-R expressed different relative activity levels for AMY-1 in transient assays. The transient expression assay was successfully used to test the functional status of Amy-homologous sequences from strains of other species of Drosophila characterized by a single amylase elctromorph, namely, Drosophila pseudoobscura ST and Drosophila miranda S 204. The amylase-null strain of D. melanogaster provided the hosts for these interspecific somatic transformation experiments. 相似文献