全文获取类型
收费全文 | 7775篇 |
免费 | 754篇 |
国内免费 | 1篇 |
专业分类
8530篇 |
出版年
2021年 | 85篇 |
2020年 | 51篇 |
2019年 | 66篇 |
2018年 | 89篇 |
2017年 | 72篇 |
2016年 | 142篇 |
2015年 | 269篇 |
2014年 | 254篇 |
2013年 | 363篇 |
2012年 | 433篇 |
2011年 | 419篇 |
2010年 | 313篇 |
2009年 | 265篇 |
2008年 | 421篇 |
2007年 | 411篇 |
2006年 | 418篇 |
2005年 | 419篇 |
2004年 | 389篇 |
2003年 | 361篇 |
2002年 | 356篇 |
2001年 | 136篇 |
2000年 | 118篇 |
1999年 | 117篇 |
1998年 | 99篇 |
1997年 | 84篇 |
1996年 | 78篇 |
1995年 | 64篇 |
1994年 | 79篇 |
1993年 | 91篇 |
1992年 | 108篇 |
1991年 | 93篇 |
1990年 | 106篇 |
1989年 | 77篇 |
1988年 | 80篇 |
1987年 | 71篇 |
1986年 | 63篇 |
1985年 | 86篇 |
1984年 | 87篇 |
1983年 | 68篇 |
1982年 | 57篇 |
1981年 | 59篇 |
1980年 | 72篇 |
1979年 | 59篇 |
1978年 | 63篇 |
1977年 | 54篇 |
1976年 | 68篇 |
1975年 | 64篇 |
1974年 | 64篇 |
1972年 | 53篇 |
1971年 | 53篇 |
排序方式: 共有8530条查询结果,搜索用时 11 毫秒
41.
The intracellular growth of pathogenic mycobacteria has been linked to the presence of an electron transparent zone (ETZ or capsule), which surrounds the phagocytized bacteria and prevents the diffusion of lysosomal enzymes in infected macrophages. Recently, it was suggested that this capsule may be a bacterial structures, even being present in test tube-grown pathogenic mycobacteria (FEMS Microbiol. Lett. 1988, 56, 225-230). In the present paper, we show that under special fixation and embedding conditions, this capsule was clearly observed among 7 strains of mycobacteria grown in axenic media and also in M. leprae extracted and purified from experimentally infected armadillo or nude mice. In the case of bacteria treated likewise but subject to a prior dehydration step, this capsular structure disappeared suggesting its lipidic nature. Ultrathin sections of M. intracellular after immunolabelling showed for the first time that this capsule obtained mycobacterial antigens confirming its mycobacterial origin. It is suggested that the mycobacterial capsule may be formed of inert lipids, in which surface antigens are embedded. 相似文献
42.
Acid shock proteins of Escherichia coli 总被引:19,自引:0,他引:19
Synthesis of total cellular proteins of Escherichia coli was studied after transfer of cultures from pH 6.9 to pH 4.3. Proteins induced by such an external pH shift down were identified by mono- and bi-dimensional electrophoresis. 30 to 45 min after an acid shift, a group of at least sixteen polypeptides was markedly induced. Four of these polypeptides corresponded to the well known heat shock proteins GroEL, DnaK, HtpG and HtpM. Their pH induction was RpoH-dependent. Three other pH-induced proteins were previously identified as stress proteins induced either by osmolarity or aerobiosis or low temperature (proteins 32 (defined in this paper), C70.0 and C62.7). Seven other proteins were specifically induced after an acid shift and were called acid shock proteins (ASP). The induction of one of these proteins was RpoH-dependent, whereas that of others was RpoH-independent. 相似文献
43.
44.
P De Togni H Niman V Raymond P Sawchenko I M Verma 《Molecular and cellular biology》1988,8(5):2251-2256
We have generated monoclonal antibodies by using a synthetic peptide corresponding to amino acid positions 4 to 17 of the human fos protein. The antibodies detected both v- and c-fos proteins by immunoprecipitation, immunoblotting, and indirect immunofluorescence. The monoclonal antibodies not only identified the fos protein complex with the cellular 39-kilodalton protein, but also recognized the modified forms of the mouse, rat, and human fos proteins. In day-17 rat embryos, nuclear-staining fos protein could be identified in the cartilage by immunohistochemical staining. 相似文献
45.
Raymond Hellio Dr. Claude Fréhel Jean-Yves Rauzier Nalin Rastogi 《Current microbiology》1988,17(4):235-242
Cytochemical characterization of mycobacterial surfaces was carried out on virulent (H37Rv) and avirulent (H37Ra) strains ofMycobacterium tuberculosis. The results were quantified and compared with those obtained with three colony types of the opportunistic pathogenMycobacterium avium. Mycobacterium aurum, a rapidly growing, nonpathogenic species, served as a model for the cytochemical methods. Concanavalin A (ConA) reacted with -d-mannose and -d-glucose residues, whereas negative charged residues were detected with either the ionized ferritin (CF) or the colloidal ferric hydroxide (CIH) method. Strongly acidic sulfate groups were detected by their selective blockage with alcian blue (AB) at pH 1 prior to the CIH labeling at pH 1.8. Weakly acidic groups were demonstrated by AB blockage at pH 2.5 prior to staining with CF stain. Except forM. aurum, all other strains showed a marked heterogeneity in regard to the abundance of their surface labeling. Accessible sulfate groups were present on the cell surface of the virulent H37Rv strain ofM. tuberculosis, but not on the avirulent strain H37Ra. Distribution of ConA receptors, on the other hand, was unrelated to the virulence or pathogenicity of the bacterial strain. 相似文献
46.
Aromatase, the important regulatory enzyme that converts androgens to estrogens, is found in relatively high levels in the human placenta. However, since the ovary is the major source of the estrogens in females, we undertook studies to compare the rodent ovarian enzyme with that from human placenta. Pregnant mare's serum gonadotropin (PMSG) markedly increases aromatase activity in the ovaries of immature rats, and this model was used in order to reproducibly obtain high enzyme levels. An injection of PMSG resulted in a specific stimulation of aromatase activity 12 times the increase in ovarian weight in 48 h. Kinetic studies demonstrated that, although the PMSG-stimulated ovarian microsomes had one-tenth the specific activity of the human placenta, the Km values were similar (about 33 and 44 nM, respectively). The potent inhibitor of placenta aromatase, 10-propargylestr-4-ene-3,17-dione, was used to further characterize the enzyme. It inhibited the rat aromatase with an I50 of 36 nM and exhibited time-dependent inhibition with a half-life of inactivation of 16 min and a Ki of 15 nM. These values are similar to those we obtained with the human enzyme (10 nM, 12 min, and 5 nM, respectively). The enzyme parameters in the presence and absence of the inhibitor suggest that the enzymes from the two sources are kinetically quite similar. 相似文献
47.
Summary Plant cell suspension cultures producing secondary metabolites have been permeabilized for product release by electroporation. The two cell cultures studied, i.e. Thalictrum rugosum and Chenopodium rubrum, require about 5 and 10 kV cm–1, respectively, for complete permeabilization (release of all the intracellularly stored product). The number of electrical pulses and capacitance used had a relatively limited effect on product release while the viability of the cells was strongly influenced by the latter. Conditions for complete product release resulted in total loss of viability of the cells after treatment. The release of product from immobilized cells was also achieved by electroporation. Cells entrapped in alginate required less voltage for permeabilization than free or agarose entrapped cells. 相似文献
48.
Minor lamin polypeptides from rat liver nuclei can be cross-linked into heteropolymers by disulfide bridges 总被引:1,自引:0,他引:1
The peripheral lamina of rat liver nuclei is characterized by the presence of three major polypeptides called lamins A, B, and C. Recent studies have identified in rat liver lamina two quantitatively minor polypeptides that have some of the biochemical and immunological properties of the lamins and were tentatively called minor lamin species. We have further characterized these minor lamin polypeptides. Both minor lamin species copurified quantitatively with the major lamins in dissociation-reassociation experiments and shared epitopes with all three major lamins as well as with intermediate filament proteins, including an epitope involved in coiled-coil interactions in lamina and filaments. Minor lamins generated partial peptide maps very similar to each other but completely different from those of lamins A, B, and C. The two minor lamin species could be cross-linked into heteropolymers containing a constant ratio of both polypeptides by exposure to O-phenanthroline - cupric ion complexes, although they did not appear to be cross-linked by disulfide bonds in the native envelope. Preliminary results suggest that the cross-linked minor lamins could be preferentially associated with lamin B. It therefore appears that in addition to the network of lamins A, B, and C, the peripheral lamina is characterized by the presence of two closely juxtaposed minor lamin polypeptides. The molecular interactions between these various polypeptides and their respective roles remain to be identified. 相似文献
49.
K99 lectin fromEscherichia coli was purified and biotinylated via its carboxyl groups using biocytin hydrazide and a water soluble carbodiimide. Biotinylation of two out of the nine carboxyl groups was sufficient to permit detection of the lectin by avidin and did not cause any loss of the haemagglutinating activity. It was demonstrated that the biotinylated K99 lectin retained other important properties of native K99 and that it will probably become a very sensitive detecting reagent. Indeed, it was able to bind to HeLa cells, as do intact bacteria carrying K99 fimbriae, and also to recognizeN-glycolyl-neuraminyl-lactosyl-ceramide in an overlay binding assay.
Abbreviations: NeuAc,N-acetylneuraminic acid; NeuGc,N-glycolylneuraminic acid; PBS, phosphate buffered saline (0.9% NaCl containing 150mm sodium phosphate, pH 7.2); LPS, lipopolysaccharide; BCHZ, biocytin hydrazide; EDC, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; BSA, bovine serum albumin; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; DMEM, Dulbecco's modified Eagle medium. For the gangliosides, trivial names and structures are given according to the recommendations in [43]. NeuAc2-3Gal1-4Glc1-1Cer (NeuAc-GM3); NeuGc2-3Gal1-4Glc1-1Cer (NeuGc-GM3); GalNAc1-4(NeuAc2-3)Gal1-4Glc1-1Cer (GM2); NeuAc2-8NeuAc2-3Gal1-4Glc1-1Cer (GD3); Gal1-3GalNAc1-4(NeuAc2-3)Gal1-4Glc1-1Cer (GM1); NeuAc2-3Gal1-3GalNAc1-4(NeuAc2-3)Gal1-4Glc1-1Cer (GD1a); Gal1-3GalNAc1-4(NeuAc2-8NeuAc2-3)Gal1-4Gle1-1Cer (GD1b); NeuAc2-3Gal1-3GalNAc1-4(NeuAc2-8NeuAc2-3) Gal1.-4Glc1-1Cer (GT1b). NeuGc2-3Gal1-4GleNAc1-4Gal1-4Glc1-1Cer (NeuGc-SPG). 相似文献
50.
Sabine Lhernould Yannis Karamanos Sylvain Bourgerie Gerard Strecker Raymond Julien Henri Morvan 《Glycoconjugate journal》1992,9(4):191-197
We have previously isolated mannoside and xylomannoside oligosaccharides with one or two terminal reducingN-acetylglucosamine residues from the extracellular medium of white campion (Silene alba) suspension culture. We have now demonstrated the presence of peptide-N
4-(N-acetylglucosaminyl)asparagine amidase (PNGase) activity in cell extracts as well in the culture medium that could explain the production of those compounds. An additional xylomannoside, (GlcNAc)Man3(Xyl)GlcNAc(Fuc)GlcNAc, was characterized, and1H- and13C-NMR assignments for the oligosaccharide Man3(Xyl)GlcNAc(Fuc)GlcNAc were obtained using homonuclear and heteronuclear spectroscopy (COSY).Abbreviations Endo
endo--N-acetylglucosaminidase
- Fuc
fucose
- GlcNAc
N-acetylglucosamine
- Man
mannose
- NMR
nuclear magnetic resonance
- PNGase
peptide-N
4-(N-acetylglucosaminyl)asparagine amidase
- Xyl
xylose 相似文献