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121.
122.
W. Y. Chan T. B. Ng Joyce S. Y. Lam Jack H. Wong K. T. Chu P. H. K. Ngai S. K. Lam H. X. Wang 《Applied microbiology and biotechnology》2010,85(4):985-993
Earlier investigations disclose that some plant ribosome-inactivating proteins (RIPs) adversely affect mouse embryonic development.
In the present study, a mushroom RIP, namely lyophyllin from Lyophyllum shimeji, was isolated, partially sequenced, and its translation inhibitory activity determined. Its teratogenicity was studied by
using a technique entailing microinjection and postimplantation whole-embryo culture. It was found that embryonic abnormalities
during the period of organogenesis from E8.5 to E9.5 were induced by lyophyllin at a concentration as low as 50 μg/ml, and
when the lyophyllin concentration was raised, the number of abnormal embryos increased, the final somite number decreased,
and the abnormalities increased in severity. The affected embryonic structures included the cranial neural tube, forelimb
buds, branchial arches, and body axis, while optic and otic placodes were more resistant. Lyophyllin at a concentration higher
than 500 μg/ml also induced forebrain blisters within the cranial mesenchyme. When the abnormal embryos were examined histologically,
an increase of cell death was found to be associated with abnormal structures, indicating that cell death may be one of the
underlying causes of teratogenicity of the mushroom RIP. This constitutes the first report on the teratogenicity of a mushroom
RIP. 相似文献
123.
Lizbeth Castro-Concha Victor M. Loyola-Vargas José L. Chan Manuel L. Robert 《Plant Cell, Tissue and Organ Culture》1990,22(2):147-151
Agave tequilana stem explants were used to produce adventitious shoots under a set of different water potentials induced by different concentrations of gelrite in the medium. At high water potentials all shoots were vitrified; as the medium water potential became more negative the degree of vitrification decreased but the number of shoots per explant also diminished. The enzymes NADH and NAD-GDH (EC. 1.4.1.2) were measured along the water potential gradient. GDH activity was high in the non-vitrified tissues and decreased significantly in the vitrified ones.Abbreviations GDH
glutamate dehydrogenase
- MS
Murashige and Skoog medium
- MSO
methionine sulfoximine
- PVP
polyvinylpolypyrrolidone
- GS
glutamine synthetase
- GOGAT
glutamine: oxoglutarate amino transferase 相似文献
124.
Cytotoxic activities of Coriolus versicolor (Yunzhi) extract on human leukemia and lymphoma cells by induction of apoptosis 总被引:3,自引:0,他引:3
Coriolus versicolor (CV), also known as Yunzhi, is one of the commonly used Chinese medicinal herbs. Although recent studies have demonstrated its antitumour activities on cancer cells in vitro and in vivo, the exact mechanism is not fully elucidated. Hence, the objective of this study was to examine the in vitro cytotoxic activities of a standardized aqueous ethanol extract prepared from Coriolus versicolor on a B-cell lymphoma (Raji) and two human promyelocytic leukemia (HL-60, NB-4) cell lines using a MTT cytotoxicity assay, and to test whether the mechanism involves induction of apoptosis. Cell death ELISA was employed to quantify the nucleosome production resulting from nuclear DNA fragmentation during apoptosis. The present results demonstrated that CV extract at 50 to 800 microg/ml dose-dependently suppressed the proliferation of Raji, NB-4, and HL-60 cells by more than 90% (p < 0.01), with ascending order of IC50 values: HL-60 (147.3 +/- 15.2 microg/ml), Raji (253.8 +/- 60.7 microg/ml) and NB-4 (269.3 +/- 12.4 microg/ml). The extract however did not exert any significant cytotoxic effect on normal liver cell line WRL (IC50 > 800 microg/ml) when compared with a chemotherapeutic anticancer drug, mitomycin C (MMC), confirming the tumour-selective cytotoxicity. Nucleosome productions in HL-60, NB-4 and Raji cells were significantly increased by 3.6-, 3.6- and 5.6-fold respectively upon the treatment of CV extract, while no significant nucleosome production was detected in extract-treated WRL cells. The CV extract was found to selectively and dose-dependently inhibit the proliferation of lymphoma and leukemic cells possibly via an apoptosis-dependent pathway. 相似文献
125.
Infection by echoviruses 1 and 8 depends on the alpha 2 subunit of human VLA-2. 总被引:4,自引:10,他引:4 下载免费PDF全文
J M Bergelson N St John S Kawaguchi M Chan H Stubdal J Modlin R W Finberg 《Journal of virology》1993,67(11):6847-6852
Anti-VLA-2 antibodies protected HeLa cells from infection by echoviruses 1 and 8 but not from infection by other echovirus serotypes. Echoviruses 1 and 8 bound to and infected nonpermissive hamster cells transfected with the alpha 2 subunit of human VLA-2. These results indicate that the human alpha 2 subunit is critical for infection by echoviruses 1 and 8 but that other echovirus serotypes must bind receptors other than VLA-2. 相似文献
126.
Transferred nuclear Overhauser effects were used to determine the conformations of ATP, CTP, and ITP bound to the regulatory site of aspartate transcarbamylase. The results are in accord with the predictions of the London-Schmidt model [London, R. E., & Schmidt, P. G. (1972) Biochemistry 11, 3136] and show that ATP and CTP bind in the anti conformation while ITP binds in the syn conformation. 相似文献
127.
V J Hruby H I Mosberg T K Sawyer J J Knittel T W Rockway J Ormberg P Darman W Y Chan M E Hadley 《Biopolymers》1983,22(1):517-530
Efforts to understand the chemical-physical basis for peptide hormone and neurotransmitter action requires integration of conformational parameters and biological properties. Since most peptide hormones are conformationally flexible, the question arises as to which of the manifold of conformations is of biological significance. In molecular terms, it is necessary to carefully distinguish chemical-physical features important to binding (the binding message) from those involved in transduction (the biological activity message). One approach to this involves the design, synthesis, and conformational analysis of semirigid hormone analogs. The distinction between binding and transduction can best be examined by evaluation of full biological profiles of partial agonists, antagonists, and analogs with prolonged biological activity. Using this multidisciplinary approach, we have prepared several semirigid [Pen1]-oxytocin antagonist analogs and evaluated their conformational properties and biological activities. Specific conformational features can be related to inhibitory activities in several cases. On the basis of structure–activity relationships and conformational considerations, we have designed a series of conformationally restricted cyclic and acyclic analogs of the linear peptide α-melanotropin. Some of these peptides have exceptionally prolonged in vivo activity (weeks), and others exhibit superagonist potency (10,000 times the native hormone). We have evidence that potency and prolonged activity have different structural and conformational requirements. It is suggested that potency is primarily a function of receptor recognition (the binding message), whereas prolonged activity is related to transduction (the biological activity message). 相似文献
128.
Robert Chan Madaline Gilbert Kristin M. Thompson H. Nicholas Marsh David M. Epstein P. Shannon Pendergrast 《Nucleic acids research》2006,34(5):e36
The specific down-regulation of gene expression in cells is a powerful method for elucidating a gene's function. A common method for suppressing gene expression is the elimination of mRNA by RNAi or antisense. Alternatively, oligonucleotide-derived aptamers have been used as protein-directed agents for the specific knock-down of both intracellular and extracellular protein activity. Protein-directed methods offer the advantage of more closely mimicking small molecule therapeutics' mechanism of activity. Furthermore, protein-directed methods may synergize with RNA-directed methods since the two methods attack gene expression at different levels. Here we have knocked down a well-characterized intracellular protein's activity, NFκB, by expressing either aptamers or small interfering RNAs (siRNAs). Both methods can diminish NFκB's activity to similar levels (from 29 to 64%). Interestingly, expression of both aptamers and siRNAs simultaneously, suppressed NFκB activity better than either method alone (up to 90%). These results demonstrate that the expression of intracellular aptamers is a viable alternative to siRNA knock-down. Furthermore, for the first time, we show that the use of aptamers and siRNA together can be the most effective way to achieve maximal knock-down of protein activity. 相似文献
129.
The core prerequisites for an efficient proteome-scale analysis of mammalian membrane proteins are effective isolation, solubilization, digestion and multidimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS). This protocol is for analysis of the mammalian membrane proteome that relies on solubilization and tryptic digestion of membrane proteins in a buffer containing 60% (vol/vol) methanol. Tryptic digestion is followed by strong cation exchange (SCX) chromatography and reversed phase (RP) chromatography coupled online with MS/MS for protein identification. The use of a methanol-based buffer eliminates the need for reagents that interfere with chromatographic resolution and ionization of the peptides (e.g., detergents, chaotropes, inorganic salts). Sample losses are minimized because solubilization and digestion are carried out in a single tube avoiding any sample transfer or buffer exchange between these steps. This protocol is compatible with stable isotope labeling at the protein and peptide level, enabling identification and quantitation of integral membrane proteins. The entire procedure--beginning with isolated membrane fraction and finishing with MS data acquisition--takes 4-5 d. 相似文献
130.
Wen-Tai Li Anirban Mahapatra David G. Longstaff Gang Zhao Michael K. Chan Joseph A. Krzycki 《Journal of molecular biology》2009,385(4):1156-1164
Pyrrolysine, the 22nd amino acid, is encoded by amber (TAG = UAG) codons in certain methanogenic archaea and bacteria. PylS, the pyrrolysyl-tRNA synthetase, ligates pyrrolysine to tRNAPyl for amber decoding as pyrrolysine. PylS and tRNAPyl have potential utility in making tailored recombinant proteins. Here, we probed interactions necessary for recognition of substrates by archaeal PylS via synthesis of close pyrrolysine analogs and testing their reactivity in amino acid activation assays. Replacement of the methylpyrroline ring of pyrrolysine with cyclopentane indicated that solely hydrophobic interactions with the ring-binding pocket of PylS are sufficient for substrate recognition. However, a 100-fold increase in the specificity constant of PylS was observed with an analog, 2-amino-6-((R)-tetrahydrofuran-2-carboxamido)hexanoic acid (2Thf-lys), in which tetrahydrofuran replaced the pyrrolysine methylpyrroline ring. Other analogs in which the electronegative atom was moved to different positions suggested PylS preference for a hydrogen-bond-accepting group at the imine nitrogen position in pyrrolysine. 2Thf-lys was a preferred substrate over a commonly employed pyrrolysine analog, but the specificity constant for 2Thf-lys was 10-fold lower than for pyrrolysine itself, largely due to the change in Km. The in vivo activity of the analogs in supporting UAG suppression in Escherichia coli bearing genes for PylS and tRNAPyl was similar to in vitro results, with l-pyrrolysine and 2Thf-lys supporting the highest amounts of UAG translation. Increasing concentrations of either PylS substrate resulted in a linear increase in UAG suppression, providing a facile method to assay bioactive pyrrolysine analogs. These results illustrate the relative importance of the H-bonding and hydrophobic interactions in the recognition of the methylpyrroline ring of pyrrolysine and provide a promising new series of easily synthesized pyrrolysine analogs that can serve as scaffolds for the introduction of novel functional groups into recombinant proteins. 相似文献