全文获取类型
收费全文 | 772篇 |
免费 | 62篇 |
专业分类
834篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 22篇 |
2017年 | 14篇 |
2016年 | 16篇 |
2015年 | 44篇 |
2014年 | 38篇 |
2013年 | 64篇 |
2012年 | 61篇 |
2011年 | 59篇 |
2010年 | 40篇 |
2009年 | 35篇 |
2008年 | 29篇 |
2007年 | 43篇 |
2006年 | 36篇 |
2005年 | 36篇 |
2004年 | 27篇 |
2003年 | 28篇 |
2002年 | 26篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 8篇 |
1971年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有834条查询结果,搜索用时 15 毫秒
1.
Recently numerous attempts have been made to reduce the use of vertebrate animals in laboratory experiments to evaluate general and acute toxicity, mutagenesis and teratogenesis of new drugs or chemicals. One common approach is to use established, proliferating cell lines that preserve differentiated functions such as the competence to metabolize xenobiotics. To this end a continuous Chinese hamster epithelial liver cell line (CHEL cells) was established, cultured as used for mutagenesis studies. Structurally different promutagens, such as 7,12-dimethylbenz[a]anthracene (7,12-DMBA), benzo[a]pyrene (B(a)P), aflatoxin B1 (AB1) and cyclophosphamide (CP), were used in order to check and validate the test system. anti-Chrysene-1,2-diol 3,4-epoxide (CDE) and mitomycin C (MMC) were taken as representatives of direct mutagens. The genetic change induced by the mutagens was quantified by measuring mutation frequencies at the HGPRT locus. Several parameters, such as mutant expression time for each chemical, cell density for selection of mutants and enzymatic characterization for HGPRT phenotype, were examined to establish the optimal assay conditions. All promutagens analyzed significantly affected either the cloning efficiency and/or the mutant frequency of CHEL cells after 24 h of exposure. In addition, various enzyme activities involved in the metabolism of the promutagens were determined in CHEL cells, under the experimental conditions of chemical exposure used in the mutagenesis assay. The enzyme activities were compared with those found in uninduced Chinese hamster liver. 相似文献
2.
Valerio Vidotto Giuseppe Picerno Stefano Caramello Giovanna Paniate 《Mycopathologia》1988,104(3):129-135
The passage between the yeast and mycelial forms of Candida albicans B 311-10 was studied by using the minimal syntehtic medium of Shepherd et al. [19] modified without biotin and with low glucose concentrations. It was observed that biotin, aminoacids and particularly pH are not important factors in the dimorphism of C. albicans. The only factor of notable importance in the passage of yeast form to mycelial form in C. albicans was glucose concentration. 相似文献
3.
Arginyl residues in BamHI endonuclease were examined because of their alleged role in proteins that contain nucleotide- or phosphate-binding sites. Butanedione, an arginine-specific reagent, inhibited the endonuclease in the presence of sodium borate. The inhibition was decreased by preliminary incubation of the enzyme with DNA or competitive inhibitors which were the 5'-phosphoryl deoxydinucleotide subsets of the BamHI recognition sequence. The dinucleotide pdGpdG protected the enzyme most efficiently against the butanedione modification. Dinucleotides that were unrelated to the recognition sequence failed to protect the enzyme from inactivation. These studies indicate that arginine residues may reside in the enzyme's active site and might function in the sequence-specific recognition of the BamHI palindrome. 相似文献
4.
Summary Kidney cells from primary cultures of 15-day old mouse embryos were incubated for 2, 5 or 10 min with H3-uridine, then either fixed immediately or incubated again for various periods in a chase medium containing an excess of unlabeled uridine and cytidine. The number of grains over the non-nucleolar part of the nucleus (chromatin), the nucleolus and the cytoplasm were counted on the autoradiograms.The grain count showed that both chromatin and nucleolus incorporate very rapidly H3-uridine from the medium, whereas a time lag elapses before any H3-radioactivity above background is detected in the cytoplasm. Incorporation of H3-uridine into the RNA of the nucleus and the nucleolus is not immediately blocked after chase, suggesting that the labeled precursor pool is not completely washed out from the living cell, or diluted by the excess of unlabeled uridine present in the medium. The grain count over the nucleus and the nucleolus rises for a certain time after chase and then gradually declines; H3-radioactivity appears in the cytoplasm 10 min after chase and keeps rising through a 110-min interval. The experiment, then — even though it suggests that the bulk of cellular RNA is synthesized in the chromatin and the nucleolus and then continuously released into the cytoplasm — does not rule out the possibility that some RNA fraction, characterized by a low turnover rate, is synthesized independently in the cytoplasm.Synthesis of RNA is a continuous process throughout the cell cycle, except during metaphase and anaphase. It ceases at prometaphase after the disappearance of the nucleolus and disintegration of the nuclear membrane, and resumes in early telophase. Part of the chromosomal RNA does not remain associated with the chromosomes through division, but is suddenly released into the cytoplasm when the cell enters metaphase. 相似文献
5.
6.
7.
Gloria Giacomini Santo V. Nicosia Beatriz O. Saunders Caroline Fultz X. Sun Valerio M. Jasonni 《In vitro cellular & developmental biology. Animal》1995,31(4):300-309
Summary The ovarian mesothelium (OM) represents the tissue of origin of ovarian epithelial cancer. To gain insight into the regulation
of this tissue, OM organoids and submesothelial ovarian stromal cells (SC) were isolated from New Zealand White rabbits by
a stepwise tissue dispersal technique, while granulosa cells (GC) were aspirated from mature follicles (14±4 groups/animal).
OM and SC dispersal were sequentially accomplished by: a) 1-h incubation in collagenase type I (300 U/ml), gentle scraping
of the ovarian surface, and 1 g sedimentation of OM organoids (equivalent to 0.93±0.40 × 106 cells/animal) on 5% bovine serum albumin (BSA); b) 2-h incubation in pronase-collagenase (0.5%–300 U/ml) under periodical
resuspension and gentle scraping of SC (1.40±0.25 × 106/animal) from OM-denuded ovaries. After a week-long in vitro expansion, OM cells (OMC) were cultured alone and with SC or
GC within monocameral vessels or bicameral transfilter vessels in serumless, fibronectinrich (4μg/ml) HL-1 medium. After 7
d of contact cell-cell interaction, cytokeratin-positive OMC became surrounded by fibroblastoid, vimentin-positive SC or by
cytokeratin and vimentin-weakly positive GC. Filter-bound OMC humorally interacting with underlying SC or GC displayed a biphasic,
epithelioid and spindle, morphology with universal cytokeratin expression. Bromo-2′-deoxyuridine (BrdU) immunoperoxidase revealed
mean cell proliferation indices of 14.88% for OMC cultured alone, 11.21% and 19.39% for OMC cultured with GC or SC in monocameral
dishes, and 15.25% or 22.47% for OMC cultured in bicameral vessels over GC or SC, respectively. This model provides an experimental
tool for investigating the unexplored role of stromal-mesothelial interaction in OM pathobiology. 相似文献
8.
Maura Turriani Rossana Pesi Antonella Nardone Gino Turchi Francesco Sgarrella Pier Luigi Ipata Maria Grazia Tozzi 《Journal of biochemical and molecular toxicology》1994,9(1):51-57
Nucleoside phosphotransferase acting on inosine and deoxyinosine has been partially purified from cultured Chinese hamster lung fibroblasts (V79). The activity is associated with a cytosolic 5′-nucleotidase acting on IMP and deoxyIMP. The transfer of the phosphate group from IMP to inosine catalyzed by this enzyme was activated by ATP and 2,3-bisphosphoglycerate. Inosine, deoxyinosine, guanosine, deoxyguanosine, and the nucleoside analogs 2′,3′-dideoxyinosine and 8-azaguanosine are substrates, while adenosine and deoxyadenosine are not. IMP, deoxyIMP, GMP, and deoxyGMP are the best phosphate donors. The cytosolic 5′-nucleotidase/phosphotransferase substrate, 8-azaguanosine, was found to be very toxic for cultured fibroblasts (LD50 = 0.32 μM). Mutants resistant to either 8-azaguanosine and the correspondent base 8-azaguanine were isolated and characterized. Our results indicated that the 8-azaguanosine-resistant cells were lacking both cytosolic 5′-nucleotidase and hypoxanthine-guanine phosphoribosyltransferase, while 8-azaguanine resistant cells were lacking only the latter enzyme. Despite this observation, both mutants displayed 8-azaguanosine resistance, thus indicating that cytosolic 5′-nucleotidase is not essential for the activation of this nucleoside analog. 相似文献
9.
R. M. Valerio A. M. Bray N. J. Maeji P. O. Morgan J. W. Perich 《Letters in Peptide Science》1995,2(1):33-40
Summary The synthesis of two model Tyr(P)-containing peptides using Fmoc-Tyr(PO3
tBu2)-OH, Fmoc-Tyr(PO3Bzl2)-OH and Fmoc-Tyr(PO3H2)-OH established that the t-butylphosphate-protected derivative was the preferred derivative for use in Fmoc solid-phase peptide synthesis, since it afforded phosphopeptides in high purity and with the lowest amount of Tyr-peptide contamination. In addition, this study confirmed that commercially available Fmoc-Tyr(PO3H2)-OH is also suitable for use in Fmoc solid-phase synthesis but gives less pure phosphopeptides, along with the generation of 1–4% of the tyrosine-containing peptide for the model sequences studied. In view of the good performance of Fmoc-Tyr(PO3
tBu2)-OH, a large-scale three-step synthetic procedure was developed which involved phenacyl protection of the carboxyl group, phosphite-triester phosphorylation of the tyrosyl hydroxyl using di-t-butyl N,N-diethylphosphoramidite, and final removal of the phenacyl group by zinc reduction in acetic acid.Abbreviations BOP
benzotriazol-1-yl-oxy-tris(dimethylamino)phosphonium hexafluorophosphate
-
tBu
t-butyl
- Bzl
benzyl
- DBU
1,8-diazabicyclo[5,4,0]undec-7-ene
- DMF
N,N-dimethylformamide
- EDT
ethanedithiol
- Fmoc
9-fluorenylmethoxycarbonyl
- HOBt
N-hydroxybenzotriazole
- HPLC
high performance liquid chromatography
- NMM
N-methylmorpholine
- Pac
phenacyl
- TFA
trifluoroacetic acid
- THF
tetrahydrofuran
- Tyr(P)
O-phosphotyrosine 相似文献
10.
Isolation ofYersinia enterocolitica andYersinia enterocolitica-like organisms from raw milk in Italy
Thirty samples of raw milk, originating from individual producers in the Turin area, were examined for the presence ofYersinia enterocolitica. A cold enrichment method with phosphate-buffered saline (PBS) 1/15M, pH 7.6, and sorbitol-bile-salts broth (SB) was used. After 7, 14, or 21 days at 4°–5°C, plating was performed on selective agar media directly (MacConkey agar andSalmonella-Shigella agar) after the alkali method was used. Six strains ofY. enterocolitica (biotype 1) and 32 strainsY. enterocolitica-like (threeY. fredericksenii; nineYersinia rhamnose-, melibiose+, -methyl-d-glucoside+, raffinose+, probablyYersinia intermedia biotype rhamnose-; and 20Y. intermedia) were isolated.Yersinia strains were found in 11 samples of raw milk, andY. enterocolitica in four samples. 相似文献