全文获取类型
收费全文 | 4387篇 |
免费 | 376篇 |
国内免费 | 5篇 |
出版年
2023年 | 18篇 |
2022年 | 20篇 |
2021年 | 67篇 |
2020年 | 44篇 |
2019年 | 48篇 |
2018年 | 60篇 |
2017年 | 50篇 |
2016年 | 111篇 |
2015年 | 180篇 |
2014年 | 196篇 |
2013年 | 227篇 |
2012年 | 324篇 |
2011年 | 305篇 |
2010年 | 185篇 |
2009年 | 181篇 |
2008年 | 261篇 |
2007年 | 273篇 |
2006年 | 228篇 |
2005年 | 248篇 |
2004年 | 226篇 |
2003年 | 224篇 |
2002年 | 214篇 |
2001年 | 58篇 |
2000年 | 62篇 |
1999年 | 78篇 |
1998年 | 59篇 |
1997年 | 40篇 |
1996年 | 33篇 |
1995年 | 51篇 |
1994年 | 53篇 |
1993年 | 39篇 |
1992年 | 44篇 |
1991年 | 45篇 |
1990年 | 38篇 |
1989年 | 44篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 21篇 |
1985年 | 38篇 |
1984年 | 23篇 |
1983年 | 29篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1979年 | 19篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1973年 | 13篇 |
1971年 | 14篇 |
1967年 | 8篇 |
1965年 | 9篇 |
排序方式: 共有4768条查询结果,搜索用时 15 毫秒
61.
Michel Monod Giuseppe Togni Bernhard Hube Dominique Sanglard 《Molecular microbiology》1994,13(2):357-368
The secreted aspartic proteinases (SAP) of Candida sp. are presumed to be potential virulence factors. In the opportunistic pathogen Candida albicans the proteinase genes identified to date, SAP1, SAP2, SAP3 and SAP4, constitute a multigene family. Before addressing the possible role of each proteinase in virulence, we sought to isolate all the members of this multigene family by screening a genomic library with a SAP1 probe for additional C. albicans SAP genes using low-stringency hybridization conditions. Three putative new members, SAP5, SAP6 and SAP7 were isolated and sequenced. The N-terminal segments of the deduced amino acid sequences of SAP5 and SAP6 contained secretion signal sequences similar to those of other Candida SAPs. Upon comparison and alignment with the other reported SAP amino acid sequences, SAP7 is not only the most divergent protein but also exhibits a much longer putative pro-sequence with a single Lys-Lys putative processing site. Using SAP1 to SAP7 as probes, the overall number of SAP genes in C. albicans was tentatively estimated by low-stringency hybridization to EcoRI-digested genomic DNA. While each isolated SAP gene could be assigned to distinct EcoRI bands, the existence of two additional genes not isolated after screening of the C. albicans gene library was inferred. Furthermore, evidence was obtained for the existence of SAP muttigene families in other Candida species such as C. tropicalis, C. parapsilosis and C. guiller-mondii. 相似文献
62.
Cloning and nucleotide sequence analysis of the Lactobacillus delbrueckii ssp. lactis DSM7290 cysteine aminopeptidase gene pepC 总被引:1,自引:0,他引:1
Abstract A genomic library of Lactobacillus delbrueckii ssp. lactis DSM7290 in the low copy number vector pLG339, was screened for the presence of peptidase genes. Using the chromogenic substrate gly-ala-β-naphthylamide, which is not a substrate for any of the recently cloned peptidases of DSM7290, and the multiple peptidase deficient Escherichia coli strain CM89, allowed the isolation of clones, which contained the equivalent hydrolytic activity. To identify genes encoding the conserved catalytic active site of cysteine proteases, partial nucleotide sequencing with a degenerate oligonucleotide was performed on recombinant plasmids isolated from such clones. This allowed to identify two out of nine clones to carry the Lactobacillus pepC gene. A total of 2026 nucleotides were determined, and sequence analysis revealed a gene with strong homology to the recently cloned Lb. helveticus (73.2%) and Lactococcus lactis (51.03%) pepC genes, and the derived protein showed homology with the active site of a large number of cysteine proteases. The predicted open reading frame consists of 449 codons, coding for a protein of 50 909 Da. The enzyme is functional and extremely overexpressed in E. coli . 相似文献
63.
Bernhard M. Riegl Samuel J. Purkis Peter Houk Genevieve Cabrera Richard E. Dodge 《Coral reefs (Online)》1994,13(1):40-40
International Society for Reef Studies 相似文献
64.
Frank Bernhard David L. Coplin Klaus Geider 《Molecular & general genetics : MGG》1993,239(1-2):158-168
A large ams gene cluster required for production of the acidic extracellular polysaccharide (EPS) amylovoran by the fire blight pathogen Erwinia amylovora was cloned. Tn5 mutagenesis and gene replacement were used to construct chromosomal ams mutants. Five complementation groups, essential for amylovoran synthesis and virulence in E. amylovora, were identified and designated amsA-E. The ams gene cluster is about 7 kb in size and functionally equivalent to the cps gene cluster involved in EPS synthesis by the related pathogen Erwinia stewartii. Mucoidy and virulence were restored to E. stewartii mutants in four cps complementation groups by the cloned E. amylovora ams genes. Conversely, the E. stewartii cps gene cluster was able to complement mutations in E. amylovora ams genes. Correspondence was found between the amsA-E complementation groups and the cpsB-D region, but the arrangement of the genes appears to be different. EPS production and virulence were also restored to E. amylovora amsE and E. stewartii cpsD mutants by clones containing the Rhizobium meliloti exoA gene. 相似文献
65.
Sieghart Sopper Susanne Hemm Jürgen Meixensberger Cheik Coulibaly Christiane Stahl-Hennig Gerhard Hunsmann Bernhard Fleckenstein Volker ter Meulen Rüdiger Drries 《Journal of medical primatology》1993,22(2-3):138-146
Paired sera and CSF samples were collected from SIVmac-infected macaques. Animals infected with SIVmac251 maintained low gag and high env-specific antibody levels in plasma. Increasing env-specific antibody titers in CSF were associated in one animal with strong intrathecal synthesis. SIVmac239-infected monkeys revealed high antibody titers of gag and env-specificity, in one animal accompanied by weak intrathecal synthesis of virus-specific antibodies. In all animals, the CD4/CD8 ratio in CSF decreased faster compared to blood. 相似文献
66.
Bernd Johannsen Bernhard Noll Peter Leibnitz Günter Reck Steffi Noll Hartmut Spies 《Inorganica chimica acta》1993,210(2)
The reaction of mercaptoacetyl diglycine (MAG2) with technetium(V) gluconate in aqueous solution produced [TcO(MAG2)]−. A single X-ray structure determination was carried out for the tetraphenylarsonium salt. The dark brown crystals are monoclinic, space group P2(1)/n, with a=12.478(5), b=14.922(5), c=17.183(9) Å and Z=4. The [TcO(MAG2)]− ion has a square pyramidal geometry with the technetium atom displaced by 0.756 Å towards the oxo ligand from the plane formed by the equatorial S,N,N,O atoms. The rhenium complex AsPh4[ReO(MAG2)] was prepared analogously starting from Re(V) gluconate and characterized. 相似文献
67.
The preparation and X-ray structure of [Ag(9-EtGH-N7)2]NO3·H2O(9-EtGH=neutral 9-ethylguanine) is reported. The compound crystallizes in the triclinic system, space group P
with a=7.063(6), b=7.153(3), c=11.306(10) Å, α=83.36(6), β=76.66(7), γ=81.44(6)°. The cation is centrosymmetric with Ag(I) coordinated via two N7 positions and Ag---N7 bond lengths of 2.11(1) Å. Applying 109Ag NMR spectroscopy, complex formation constants for both the 1:1 complex (log β1=0.6) and the title compound (log β2=1.6) in Me2SO have been determined. 相似文献
68.
69.
Glutamate Dehydrogenase Is Not Essential for Glutamate Formation by Corynebacterium glutamicum
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Elke R. Brmann-El Kholy Bernhard J. Eikmanns Marcella Gutmann Hermann Sahm 《Applied microbiology》1993,59(7):2329-2331
Two Corynebacterium glutamicum strains, one being glutamate dehydrogenase (GDH) negative and the other possessing 11-fold-higher specific GDH activity than the parental wild type, were constructed and used to analyze the role of GDH in C. glutamicum. The results indicate (i) that GDH is dispensable for glutamate synthesis required for growth and (ii) that although a high level of GDH increases the intracellular glutamate pool, the level of GDH has no influence on glutamate secretion. 相似文献
70.
Biochemical studies on anaerobic phenylme-thylether cleavage by homoacetogenic bacteria have been hampered so far by the complexity of the reaction chain involving methyl transfer to acetyl-CoA synthase and subsequent methyl group carbonylation to acetyl-CoA. Strain TMBS 4 differs from other demethylating homoacetogenic bacteria in using sulfide as a methyl acceptor, thereby forming methanethiol and dimethylsulfide. Growing and resting cells of strain TMBS 4 used alternatitively CO2 as a precursor of the methyl acceptor CO for homoacetogenic acetate formation. Demethylation was inhibited by propyl iodide and reactivated by light, indicating involvement of a corrinoid-dependent methyltransferase. Strain TMBS 4 contained ca. 750 nmol g dry mass-1 of a corrinoid tentatively identified as 5-hydroxybenzimidazolyl cobamide. A photometric assay for measuring the demethylation activity in cell extracts was developed based on the formation of a yellow complex of Ti3+ with 5-hydroxyvanillate produced from syringate by demethylation. In cell extracts, the methyltransfer reaction from methoxylated aromatic compounds to sulfide or methanethiol depended on reductive activation by Ti3+. ATP and Mg2+ together greatly stimulated this reductive activation without being necessary for the demethylation reaction itself. The specific activity of the transmethylating enzyme system increased proportionally with protein concentration up to 3 mg ml-1 reaching a constant level of 20 nmol min-1 mg-1 at protein concentrations 10 mg ml-1. The specific rate of activation increased in a non-linear manner with protein concentration. Strain TMBS 4 degraded gallate, the product of sequential demethylations, to 3 acetate through the phloroglucinol pathway as found earlier with Pelobacter acidigallici.Abbreviations BV
benzyl viologen
- CTAB
cetyltrimethylammonium bromide
- H4folate
tetrahydrofolate
- MOPS
3-[N-morpholino]propanesulfonic acid
- MV
methyl viologen
- NTA
nitrilotriacetate
- td
doubling time
- TMB
3,4,5-trimethoxybenzoate 相似文献