全文获取类型
收费全文 | 3146篇 |
免费 | 262篇 |
国内免费 | 2篇 |
专业分类
3410篇 |
出版年
2023年 | 12篇 |
2022年 | 43篇 |
2021年 | 64篇 |
2020年 | 33篇 |
2019年 | 49篇 |
2018年 | 78篇 |
2017年 | 54篇 |
2016年 | 119篇 |
2015年 | 174篇 |
2014年 | 182篇 |
2013年 | 206篇 |
2012年 | 289篇 |
2011年 | 266篇 |
2010年 | 167篇 |
2009年 | 156篇 |
2008年 | 189篇 |
2007年 | 210篇 |
2006年 | 167篇 |
2005年 | 164篇 |
2004年 | 130篇 |
2003年 | 122篇 |
2002年 | 131篇 |
2001年 | 26篇 |
2000年 | 11篇 |
1999年 | 28篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1974年 | 6篇 |
1971年 | 4篇 |
1969年 | 4篇 |
1960年 | 4篇 |
1957年 | 5篇 |
1953年 | 4篇 |
1946年 | 4篇 |
排序方式: 共有3410条查询结果,搜索用时 15 毫秒
1.
2.
3.
Immunotargeting of daunomycin to localized and metastatic human colon adenocarcinoma in athymic mice
Esther Hurwitz Ruth Adler Daniel Shouval Hiroshi Takahashi Jack R. Wands Michael Sela 《Cancer immunology, immunotherapy : CII》1992,35(3):186-192
Summary A monoclonal antibody (designated SF25), which recognizes a protein antigen expressed on a large number of human colon carcinomas, was used for drug targeting. Daunomycin-antibody conjugates were prepared by two previously described procedures. In one, the drug was bound to the antibody through a spacer of small molecular mass (cis-aconitic acid), while in the other a dextran bridge served as the link between drug and antibody. High substitution rates of drug to antibody were obtained using the latter binding procedure. Both conjugates were tested in vitro against two human colon carcinoma cell lines, LS180 and KM-12. The efficacy of a daunomycin-dextran-SF25 antibody conjugate was tested against colon carcinoma LS180 tumors transplanted at different sites into athymic mice. The specific conjugate was significantly more inhibitory to a subcutaneous tumor growth than its components or their mixture. SF25 antibody alone showed antitumoral effects against all three forms of transplanted tumor tested, namely, local, metastatic or intrahepatic, whereas daunomycin, on its own, was effective only against the subcutaneous tumor. Binding of daunomycin to dextran partially improved its inhibitory activity against the metastatic tumor. The conjugate, daunomycin-dextran-SF25 antibody reduced the number of metastatic foci, increased the survival rate and delayed death. Yet against lymph node metastases it was not significantly better than a mixture of both constituents. However, results obtained with an intrahepatic tumor, a model that mimics the natural progression of the disease, resembled those described with the subcutaneous tumor. Daunomycin-dextran-SF25 antibody was significantly more effective than all components separately and than a mixture of drug and antibody, provided a highly drug-substituted conjugate was used. 相似文献
4.
Release of Inorganic Phosphate from Irradiated Yeast: Radiation Biodosimetry and Evaluation of Radioprotective Compounds 下载免费PDF全文
When cells of bakers' yeast, Saccharomyces cerevisiae, were irradiated with ionizing radiation, inorganic phosphate, ninhydrin-reactive material, and substances absorbing at 260 mmu were released into the suspending medium. The amount of inorganic phosphate released depended on the radiation dose and on the temperature and pH during irradiation. The concentration of yeast cells did not affect the phosphate yield per milligram of yeast. It is suggested that the release of phosphate may serve as an index of the total radiation environment (i.e., as a biodosimeter) where radiation inactivation of microrganisms is of primary importance, e.g., in radiation preservation of foods. The somewhat limited range of the yeast biodosimeter (ca. 0.5 to 1.75 Mrad) may be extended by use of other more resistant microorganisms, such as bacterial spores. Compounds which have been reported as protecting microorganisms and mammals against the lethal effect of ionizing radiation also inhibited the radiation-induced release of inorganic phosphate from yeast. This phosphate release system is proposed as the basis for an economical, rapid supplement to screening procedures in the evaluation of radioprotective compounds. 相似文献
5.
Jos M. Torn Luisa Moysset Inmaculada Claparols Esther Simn 《Physiologia plantarum》1996,98(2):413-418
The effects of photoperiod and end-of-day phytochrome control on somatic embryogenesis and polyamine (PA) content in Araujia sericifera petals have been studied. Petals from immature flowers were cultured under 16- and 8-h photoperiods. Far red (FR), red (R) and FR followed by R light treatments were applied at the end of the photoperiods for three weeks. The number of somatic embryos, callus weight and the levels of free and bound PAs in the cultured petal explants were determined 40 days after the beginning of light treatments. Long day (LD) promoted somatic embryogenesis but did not have any significant effect on PA content. Short day (SD) reduced somatic embryogenesis and enhanced total PAs, mainly in the form of bound spermidine. End-of-day FR treatment increased PA content and inhibited somatic embryogensis under LD but had no significant effect under SD. This effect of FR on PA levels was cancelled by R and was independent of the presence of silver thiosulphate in the medium. End-of-day R treatment reduced the total PA content under SD. However, end-of-day R increased or reduced somatic embryogenesis under SD depending on the presence or absence of silver in the medium. The results suggest a photoperiodic control of somatic embryogenesis and PA content in A. sericifera. The effects of end-of-day R and FR treatments depend on the length of the photoperiod. This finding and the FR/R photoreversibility of end-of-day treatments indicate that phytochrome may be involved in both somatic embryogenesis and accumulation of PA. 相似文献
6.
7.
A family of dispersed repetitive sequences (Hch1) which is present in the genome of the wild barley Hordeum chilense was studied in detail. Hch1 sequences are found both as part of short tandem arrays and dispersed throughout the H. chilense chromosomes. Subcloning of sections of the sequence reveals that it is composed of unrelated classes of sequences which can also be found separately in other genomic locations. Analysis of these sequences in the genomes of wheat and two other wild barley species strongly suggests that specific amplifications and arrangements of the repeated sequences have taken place during speciation. Nucleotide sequence analysis fails to detect, in their entirity, the features shown by plant transposons. 相似文献
8.
The intermediary cell: Minor-vein anatomy and raffinose oligosaccharide synthesis in the Scrophulariaceae 总被引:7,自引:0,他引:7
Minor-vein anatomy, sugar content, sugar synthesis, and translocation were studied in mature leaves of nine members of the Scrophulariaceae to determine if there is a correlation between companion-cell type and class of sugar translocated. Three types of companion cell were found: intermediary cells with extensive plasmodesmatal connections to the bundle sheath; transfer cells with wall ingrowths and few plasmodesmata; and ordinary companion cells with few plasmodesmata and no wall ingrowths. Alonsoa warscewiczii Regal., Verbascum chaixi Vill., and Mimulus cardinalis Dougl. ex. Benth. have intermediary cells and ordinary companion cells in the minor veins. These plants synthesize large amounts of raffinose and stachyose as well as sucrose. Nemesia strumosa Benth., and Rhodochiton atrosanguineum Zucc. have both intermediary cells and transfer cells and make proportionately less raffinose oligosaccharide than the species above. In N. strumosa, a single sieve element may abut both an intermediary cell and a transfer cell. The minor veins of Asarina scandens (Cav.) Penn. have transfer cells and what appear to be modified intermediary cells that have fewer plasmodesmata than other species, and occasional wall ingrowths. Asarina scandens synthesizes little raffinose or stachyose. Cymbalaria muralis P. Gaertn et al. and Linaria maroccana Hook.f. have only transfer cells and Digitalis grandiflora Mill. has only ordinary companion cells; these species make a trace of galactinol and raffinose, but no stachyose. Translocation experiments indicate that there is long-distance movement of raffinose oligosaccharide in these plants, even when it is synthesized in very small quantities in the leaves. We conclude that intermediary cells are as distinct a cell type as the transfer cell. In contrast to transfer cells, which are specialized for uptake of solute from the apoplast, intermediary cells are specialized for symplastic transfer of photoassimilate from the mesophyll and for synthesis of raffinose oligosaccharide. This supports our contention that raffinose oligosaccharide synthesis and symplastic phloem loading are mechanistically linked (Turgeon and Gowan 1990, Plant Physiol. 94, 1244–1249). Minor-vein anatomy and sugar synthesis may be useful characters in determining the phylogenetic relationships of plants in this family.We thank Andrea Wolfe and Wayne Elisens for helpful discussions on the taxonomy of the Scrophulariaceae. This research was supported by National Science Foundation grant DCB-9104159, U.S. Department of Agriculture Competetive Grant 92-37306-7819, and Hatch funds. 相似文献
9.
Recognition of pathogenic Yersinia enterocolitica by crystal violet binding and polymerase chain reaction 总被引:3,自引:1,他引:2
Cefsulodin-Irgasan-Novobiocin (CIN) agar is used for the selective isolation and enumeration of Yersinia enterocolitica from clinical specimens and food. The medium contains crystal violet and about 1 mmol l-1 calcium and can be used for the phenotypic characterization of strains that carry a virulence plasmid. At 32°C, irrespective of pathogenicity, colonies are translucent with a pale pink centre surrounded by a transparent border ('bullseye'), while at 37°C pathogenic strains grow as calcium-dependent microcolonies which, because of crystal violet binding, are intensely coloured. These results were confirmed by the polymerase chain reaction with primers directed at the vir F gene, which is present only in pathogenic strains of Y. enterocolitica. Pathogenic strains of Y. enterocolitica can be recognized by growth at 37°C on Yersinia selective agar. 相似文献
10.