全文获取类型
收费全文 | 639篇 |
免费 | 75篇 |
国内免费 | 1篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 20篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 17篇 |
2016年 | 19篇 |
2015年 | 26篇 |
2014年 | 34篇 |
2013年 | 52篇 |
2012年 | 47篇 |
2011年 | 62篇 |
2010年 | 33篇 |
2009年 | 29篇 |
2008年 | 26篇 |
2007年 | 41篇 |
2006年 | 37篇 |
2005年 | 20篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1969年 | 6篇 |
1968年 | 3篇 |
排序方式: 共有715条查询结果,搜索用时 93 毫秒
11.
Compact, friable and embryogenic calli were initiated from immature inflorescences and young leaf bases of one week old seedlings of Paspalum scrobiculatum cultured on MS medium supplemented with 2,4-D. A stable, embryogenic suspension culture was initiated from these calli and maintained in a liquid version of the same MS medium. Embryogenic calli and somatic embryos were obtained by plating suspension culture cells onto semi-solid medium containing 2,4-D. Complete, normal plantlets developed on 2,4-D free medium at a high frequency from somatic embryos. NAA and BAP in the medium promoted plant development.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- NAA
1-naphthaleneacetic acid
- BAP
6-benzylaminopurine
- ABA
Abscisic acid
- MS
Murashige and Skoog (1962)
- CM
Coconut milk 相似文献
12.
R Nayak 《Biochemical and biophysical research communications》1992,184(1):467-470
5-Fluoro-2'-deoxyuridine is incorporated into DNA of mouse breast tumour in vivo. The incorporation is inhibited by thymidine. Part of the fluorodeoxyuridine is cleaved to fluorouracil and is incorporated into RNA. This incorporation is enhanced by thymidine. The result suggests that the major mechanism of action of the fluorouracil is due to its incorporation into RNA. 相似文献
13.
Influenza virus polymerase basic protein 1 interacts with influenza virus polymerase basic protein 2 at multiple sites. 总被引:2,自引:2,他引:0 下载免费PDF全文
Three polymerase proteins of influenza type A virus interact with each other to form the active polymerase complex. Polymerase basic protein 1 (PB1) can interact with PB2 in the presence or absence of polymerase acidic protein. In this study, we investigated the domains of PB1 involved in complex formation with PB2 in vivo, using coexpression and coimmunoprecipitation of the PB1-PB2 complex with monospecific antibodies. Results show that PB1 possesses at least two regions which can interact independently and form stable complexes with PB2. Both of these regions are located at the NH2 terminus of PB1; the COOH-terminal half of PB1 is not involved in interacting with PB2. Deletion analysis further demonstrated that the interacting regions of PB1 encompass amino acids (aa) 48 to 145 and aa 251 to 321. Linker insertions throughout the PB1 sequences did not affect complex formation with PB2. Deletion and linker-insertion mutants of PB1 were tested for polymerase activity in vivo. For this analysis, we developed a simplified assay for viral polymerase activity that uses a reporter chloramphenicol acetyltransferase gene containing the 5' and 3' ends of influenza viral promoter and nontranslating regions (minus sense) of the NS gene joined to a hepatitis delta virus ribozyme at its 3' end. This assay demonstrated that all deletion mutants of PB1 exhibited either background or greatly reduced polymerase activity irrespective of the ability to interact with PB2 and that all linker-insertion mutants except one at the extreme COOH end (L-746) of PB1 were also negative for viral polymerase activity. These results show that compared with complex formation of PB1 with PB2, the polymerase activity of PB1 was extremely sensitive to structural perturbation. 相似文献
14.
Three genotypes of chickpea ICCV-1, ICCV-6 and a Desi (local) variety were tested for plant regeneration through multiple shoot production. The embryo axis was removed from mature seeds, the root meristem and the shoot apex were discarded. These explants were cultured on medium containing MS macro salts, 4X MS micro salts, I35 vitamins, 3.0 mg/1 BAP, 0.004 mg/1 NAA, 3% (w/v) sucrose and incubated at 260C. The explants were transformed withAgrobacterium tumefaciens strain LBA4404 with binary vector pBI121 containing theuidA andnptIl genes. Multiple shoots were repeatedly selected with kanamycin. The selected kanamycin resistant shoots were rooted on MS medium supplemented with 0.05 mg/1 113A. The presumptive transformants histochemically stained positive for GUS. Additionally, nptll assay confirmed the expression ofnptII in kanamycin resistant plants. Transgenic plants were transferred to soil and grown in the green house.Abbreviations BAP
6-benzylamino purine
- 2,4-D
2,4dichlorophenoxy acetic acid
- IAA
Indole acetic acid
- IBA
Indole butaric acid
- NAA
Naphthalene acetic acid 相似文献
15.
Enhanced production and accumulation of free and conjugated polyamines as well as increased activities of their biosynthetic enzymes in plants have been associated with heat stress. Perchloric acid-soluble free, as well as conjugated polyamines, and their metabolic enzymes were studied under 45°C heat stress in callus raised from heat-tolerant and -sensitive rice cultivars. The levels of free and conjugated polyamines, as well as arginine decarboxylase (EC 4.1.1.19) and polyamine oxidase (EC 1.4.34) activities were higher in tolerant than in sensitive callus under non-stressed conditions. Heat stress caused greater accumulation of free and conjugated polyamines in callus of the heat-tolerant cultivar N22 than in that of the heat-sensitive cultivar IR8. In particular, the uncommon polyamines norspermidine and norspermine were detected in cv. N22, which increased appreciably during stress, but they were not detected in callus of cv. IR8. Arginine decarboxylase and polyamine oxidase activities increased to a larger extent in N22 than in IR8 callus during stress, activities that were well correlated with the increased levels of common and uncommon polyamines. Increased levels of transglutaminase activity indicated the high titre of conjugated polyamines. 相似文献
16.
Analysis of the signals for polarized transport of influenza virus (A/WSN/33) neuraminidase and human transferrin receptor, type II transmembrane proteins. 总被引:4,自引:2,他引:2 下载免费PDF全文
In polarized MDCK cells influenza virus (A/WSN/33) neuraminidase (NA) and human transferrin receptor (TR), type II glycoproteins, when expressed from cloned cDNAs, were transported and accumulated preferentially on the apical and basolateral surfaces, respectively. We have investigated the signals for polarized sorting by constructing chimeras between NA and TR and by making deletion mutants. NATR delta 90, which contains the cytoplasmic tail and transmembrane domain of NA and the ectodomain of TR, was found to be localized predominantly on the apical membrane, whereas TRNA delta 35, containing the cytoplasmic and transmembrane domains of TR and the ectodomain of NA, was expressed preferentially on the basolateral membrane. TR delta 57, a TR deletion mutant lacking 57 amino acids in the TR cytoplasmic tail, did not exhibit any polarized expression and was present on both apical and basolateral surfaces, whereas a deletion mutant (NA delta 28-35) lacking amino acid residues from 28 to 35 in the transmembrane domain of NA resulted in secretion of the NA ectodomain predominantly from the apical side. These results taken together indicate that the cytoplasmic tail of TR was sufficient for basolateral transport, but influenza virus NA possesses two sorting signals, one in the cytoplasmic or transmembrane domain and the other within the ectodomain, both of which are independently able to transport the protein to the apical plasma membrane. 相似文献
17.
Ribonucleoproteins (RNPs) isolated from infectious and defective interfering (DI) influenza virus (WSN) contained three major RNP peaks when analyzed in a glycerol gradient. Peak I RNP was predominant in infectious virus but was greatly reduced in DI virus preparations. Conversely, peak III RNP was elevated in DI virus, suggesting a large increase in DI RNA in this fraction. Labeled [(32)P]RNA was isolated from each RNP region and analyzed by electrophoresis on polyacrylamide gels. Peak I RNP contained primarily the polymerase and some HA genes, peak II contained some HA gene but mostly the NP and NA genes, and peak III contained the M and NS genes. In addition, peak III RNP from DI virus also contained the characteristic DI RNA segments. Interference activity of RNP fractions isolated from infectious and DI virus was tested using infectious center reduction assay. RNP peaks (I, II, and III) from infectious virus did not show any interference activity, whereas the peak III DI RNP caused a reduction in the number of infectious centers as compared to controls. Similar interference was not demonstrable with peak I RNP of DI virus nor with any RNP fractions from infectious virus alone. The interference activity of RNP fractions was RNase sensitive, suggesting that the DI RNA contained in DI RNPs was the interfering agent, and dilution experiments supported the conclusion that a single DI RNP could cause interference. The interfering RNPs were heterogeneous, and the majority migrated slower than viral RNPs containing M and NS genes. These results suggest that DI RNP (or DI RNA) is also responsible for interference in segmented, negative-stranded viruses. 相似文献
18.
Immune response to human influenza virus hemagglutinin expressed in Escherichia coli 总被引:9,自引:0,他引:9
Cloned DNA fragments coding for parts of strain WSN (H1N1) influenza virus hemagglutinin (HA) were fused to a bacterial leader DNA derived from the Escherichia coli trp operon. Fusion proteins produced consisted of 190 amino acids of trpLE' protein at the amino terminus, and HA amino acids, either 1-308, 1-396, or 1-548 (complete HA), at the carboxyl terminus. These proteins were expressed at high levels (10-20% of total protein) in E. coli starved for tryptophan. A CNBr fragment (HA1-211) was derived from HA-308. Each of the proteins was purified and used for immunizing mice and rabbits. The antibody produced was shown to bind to (i) the HA fusion proteins, (ii) detergent-treated viral HA, (iii) HA, on intact virions, and (iv) the HA on the surface of cells infected with influenza virus. This shows that the HA fusion proteins expressed in bacteria can elicit antibodies that recognize at least some determinants of the native viral HA, and probably could lead to development of an anti-influenza vaccine. 相似文献
19.
Nuclear retention of M1 protein in a temperature-sensitive mutant of influenza (A/WSN/33) virus does not affect nuclear export of viral ribonucleoproteins. 下载免费PDF全文
We investigated the properties of ts51, an influenza virus (A/WSN/33) temperature-sensitive RNA segment 7 mutant. Nucleotide sequence analysis revealed that ts51 possesses a single nucleotide mutation, T-261----C, in RNA segment 7, resulting in a single amino acid change. Phenylalanine (position 79) in the wild-type M1 protein was substituted by serine in ts51. This mutation was phenotypically characterized by dramatic nuclear accumulation of the M1 protein and interfered with some steps at the late stage of virus replication, possibly affecting the assembly and/or budding of viral particles. However, although M1 protein was retained within the nucleus, export of the newly synthesized viral ribonucleoprotein containing the minus-strand RNA into the cytoplasm was essentially the same at both permissive and nonpermissive temperatures. The roles of M1 in the export of viral ribonucleoproteins from the nucleus into the cytoplasm and in the virus particle assembly process are discussed. 相似文献
20.
Construction and characterization of a bacterial clone containing the hemagglutinin gene of the WSN strain (HON1) of influenza virus 总被引:12,自引:0,他引:12
A synthetic dodecadeoxynucleotide primer has been used to prepare a double-stranded DNA form of the hemagglutinin (HA) gene of a human influenza virus (WSN strain, HON1). This DNA has been inserted in plasmid pBR322 and cloned in bacterial cells. The insert contains nearly the complete hemagglutinin gene. A restriction map of this insert has been determined and structurally important areas of the HA gene have been sequenced. Amino acid sequences of several regions of the HA protein were deduced from the DNA sequences and compared to the known amino acid sequences of other influenza A viruses. WSN HA shows extensive homology to all influenza A viruses in a few regions, namely the first 17 amino acids of the N-terminus of HA1 (N-terminal polypeptide of HA) and the first 24 amino acids of the N-terminus of HA2 (C-terminal polypeptide of HA). The sequence diverges extensively from other influenza A viruses in most other areas. The sequence of WSN virus HA is similar to that of other HON1 viruses with the exception of the C-terminus of the HA1 peptide. The change in this area may contribute to some of the unique properties of WSN virus among the HON1 viruses. In addition, WSN HA contains a 17-amino-acid precursor before the N-terminus of HA1 and a single amino acid, arginine, connecting HA1 and HA2. 相似文献