全文获取类型
收费全文 | 2861篇 |
免费 | 219篇 |
国内免费 | 9篇 |
出版年
2022年 | 19篇 |
2021年 | 56篇 |
2020年 | 28篇 |
2019年 | 36篇 |
2018年 | 49篇 |
2017年 | 37篇 |
2016年 | 65篇 |
2015年 | 90篇 |
2014年 | 121篇 |
2013年 | 170篇 |
2012年 | 213篇 |
2011年 | 194篇 |
2010年 | 128篇 |
2009年 | 109篇 |
2008年 | 140篇 |
2007年 | 138篇 |
2006年 | 129篇 |
2005年 | 109篇 |
2004年 | 123篇 |
2003年 | 129篇 |
2002年 | 100篇 |
2001年 | 33篇 |
2000年 | 34篇 |
1999年 | 35篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 23篇 |
1995年 | 26篇 |
1994年 | 25篇 |
1993年 | 32篇 |
1992年 | 44篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1988年 | 19篇 |
1987年 | 25篇 |
1986年 | 16篇 |
1985年 | 22篇 |
1984年 | 14篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1973年 | 14篇 |
1972年 | 15篇 |
1970年 | 21篇 |
1965年 | 13篇 |
排序方式: 共有3089条查询结果,搜索用时 31 毫秒
1.
D. Pangallo K. Chovanov H. Drahovska F. De Leo C. Urzì 《International biodeterioration & biodegradation》2009,63(7):868-872
The aim of this work was the evaluation of fluorescence ITS-PCR (f-ITS) as a molecular tool to analyze the microbial community involved in the biodeterioration of cultural heritage surfaces. As a case study we analyzed by f-ITS ninety-two bacterial strains isolated from a medieval fresco and the surrounding air environment. The internal transcribed spacer between the 16S and 23S rRNA genes was amplified, and then the fluorescently labeled PCR products were separated by capillary electrophoresis. Bacterial strains were identified by 16S rDNA sequencing. The f-ITS electropherograms showed different profiles coherent with the affiliation of the strains at the genus and species levels. Among the isolates obtained from the fresco surface, those belonging to the genus Bacillus were the most prevailing exhibiting 8 different f-ITS profiles. The airborne bacilli exhibited only 2 of these 8 profiles. Staphylococcus were mostly isolated from air and produced 4 different profiles. Pseudomonas isolates presented 3 different profiles, and one of them was typical of Pseudomonas putida. Members of the other genera produced their distinctive profiles. Our results show that f-ITS is a promising molecular tool for the rapid selection and clustering of strains isolated from different sources. 相似文献
2.
We here report the second record of a developmentally aberrant strain of a cellular slime mold from natural populations and demonstrate that this Dictyostelium mucoroides variant is capable of undergoing normal morphogenesis in the presence of the phycomycete fungus, Mucor hiemalis. The synergism is induced by an extracellular product(s) which is diffusable through thin agar membranes and is released by the fungus. The presence of the fungus not only induces stalk formation in this stalkless variant, but also increases the rate of sorocarp formation in 3 of 5 additional species of cellular slime molds assayed. 相似文献
3.
4.
Different pathways of alcohol metabolism, the alcohol dehydrogenase pathway, the microsomal ethanol-oxidizing system and the catalase pathway are discussed. Alcohol consumption leads to accelerated ethanol metabolism by different mechanisms including an increased microsomal function. Microsomal induction leads to interactions of ethanol with drugs, hepatotoxic agents, steroids, vitamins and to an increased activation of mutagens/carcinogens. A number of ethanol-related complications may be explained by the production of its first metabolite, acetaldehyde, such as alterations of mitochondria, increased lipid peroxidation and microtubular alterations with its adverse effects on various cellular activities, including disturbances of cell division. Nutritional factors in alcoholics such as malnutrition are discussed especially with respect to its possible relation to cancer. 相似文献
5.
Amy P. N. Skubitz Aristidis S. Charonis Effie C. Tsilibary Leo T. Furcht 《Experimental cell research》1987,173(2):349-369
Monoclonal antibodies were prepared to localize the domain(s) of laminin to which tumor cells adhere. Rat Y3-Ag 1.2.3 myeloma cells were fused with spleen cells from a rat immunized with a purified 440-kDa fragment of chymotrypsin-digested laminin. Three monoclonal antibodies (AL-1 to AL-3) that bound to intact laminin in a solid-phase radioimmunoassay were chosen for further analysis. The epitopes recognized by these antibodies were characterized by radioimmunoassays, immunoblotting, radioimmunoprecipitation, and immunoaffinity chromatography. In cell adhesion assays, monoclonal antibody AL-2 inhibited the binding of the highly metastatic melanoma cell line, K-1735-M4, to both intact laminin and the 440-kDa fragment of laminin. Electron microscopic examination of laminin-monoclonal antibody interactions showed that monoclonal antibody AL-2 reacted with the long arm of laminin directly below the cross-region. Two monoclonal antibodies that failed to inhibit tumor cell adhesion to laminin reacted with epitopes on the lateral short arms or cross-region of laminin as seen by electron microscopy. These results suggest that a new tumor cell binding domain of laminin may be located close to the cross-region on the long arm of laminin. 相似文献
6.
Leo S. Luckinbill Michael J. Clare Walter L. Krell William C. Cirocco Paula A. Richards 《Evolutionary ecology》1987,1(1):37-46
Summary Although many different physiological and biochemical changes characterize the process of senescence, little is understood of the genetic elements that determine its age of onset. We provide here the first estimates of the number of genetic factors that extend longevity inDrosophila melanogaster. Life span was measured in F1, F2 and backcrosses of true-breeding long and short-lived stocks ofD. melanogaster, established by selection. Estimates of the number of effective factors delaying senescence range from about 0.3 to 1.5, indicating control by a single factor. The distribution of longevity shows this to arise as selection acts on the short-lived parental stock. Life span is extended at the cost of early fecundity. 相似文献
7.
Summary M1 is a virulent bacteriophage of Methanobacterium thermoautotrophicum strain Marburg. Restriction enzyme analysis of the linear, 30.4 kb phage DNA led to a circular map of the 27.1 kb M1 genome. M1 is thus circularly permuted and exhibits terminal redundancy of approximately 3 kb. Packaging of M1 DNA from a concatemeric precursor initiates at the pac site which was identified at coordinate 4.6 kb on the circular genome map. It proceeds clockwise for at least five packaging rounds. Headful packaging was also shown for M2, a phage variant with a 0.7 kb deletion at coordinate 23.25 on the map. 相似文献
8.
A Miceli D Traversi P De Leo 《Bollettino della Società italiana di biologia sperimentale》1989,65(12):1141-1147
In this study the amount of glucose, sucrose and fructose was determined in the water soluble fraction while cellulose, hemicellulose, pectin and lignin contents were determined in the alcohol insoluble fraction after hydrolysis. Stalks of sweet sorghum (Sorghum vulgare L., var. saccharatum) cv. Vespa, Soave, Roce and MN 1500 at the physiological ripeness stage were used. The results of the analysis of variance with the least significant difference method (LSD, = 0.05) show that cv. Vespa and Roce have a significantly higher total amount of glucose, fructose and sucrose and at the same time, a lower cellulose, pectin, hemicellulose and lignin content then cv. Soave and cv. MN 1500. 相似文献
9.
Conditional expression of RPA190, the gene encoding the largest subunit of yeast RNA polymerase I: effects of decreased rRNA synthesis on ribosomal protein synthesis. 总被引:16,自引:9,他引:7
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M Wittekind J M Kolb J Dodd M Yamagishi S Mémet J M Buhler M Nomura 《Molecular and cellular biology》1990,10(5):2049-2059
The synthesis of ribosomal proteins (r proteins) under the conditions of greatly reduced RNA synthesis were studied by using a strain of the yeast Saccharomyces cerevisiae in which the production of the largest subunit (RPA190) of RNA polymerase I was controlled by the galactose promoter. Although growth on galactose medium was normal, the strain was unable to sustain growth when shifted to glucose medium. This growth defect was shown to be due to a preferential decrease in RNA synthesis caused by deprivation of RNA polymerase I. Under these conditions, the accumulation of r proteins decreased to match the rRNA synthesis rate. When proteins were pulse-labeled for short periods, no or only a weak decrease was observed in the differential synthesis rate of several r proteins (L5, L39, L29 and/or L28, L27 and/or S21) relative to those of control cells synthesizing RPA190 from the normal promoter. Degradation of these r proteins synthesized in excess was observed during subsequent chase periods. Analysis of the amounts of mRNAs for L3 and L29 and their locations in polysomes also suggested that the synthesis of these proteins relative to other cellular proteins were comparable to those observed in control cells. However, Northern analysis of several r-protein mRNAs revealed that the unspliced precursor mRNA for r-protein L32 accumulated when rRNA synthesis rates were decreased. This result supports the feedback regulation model in which excess L32 protein inhibits the splicing of its own precursor mRNA, as proposed by previous workers (M. D. Dabeva, M. A. Post-Beittenmiller, and J. R. Warner, Proc. Natl. Acad. Sci. USA 83:5854-5857, 1986). 相似文献
10.
Leo S. Melchers Dave V. Thompson Ken B. Idler Saskia T. C. Neuteboom Ruud A. de Maagd Rob A. Schilperoort Paul J. J. Hooykaas 《Plant molecular biology》1988,11(2):227-237
The virulence loci play an essential role in tumor formation by Agrobacterium tumefaciens. Induction of vir gene expression by plant signal molecules is solely dependent on the virulence loci virA and virG. This study focused on the virA locus of the octopine type Ti plasmid pTi15955. The nucleic acid sequence of a 5.7-kilobase fragment encompassing virA was determined. Genetic analysis of this region revealed that virA contains one open reading frame coding for a protein of 91 639 daltons. Immunodetection with antibodies raised against a 35-kDa VirA fusion protein produced in E. coli identified the VirA product in wild-type Agrobacterium cells. Moreover, it is shown that the VirA protein is located in the cytoplasmic membrane fraction of Agrobacterium. These data confirm the proposed regulatory function of VirA whereby VirA acts as a membrane sensor protein to identify plant signal molecules in the environment. The proposed sensory function of VirA strikingly resembles the function of the chemotaxis receptor proteins of E. coli. 相似文献