全文获取类型
收费全文 | 3676篇 |
免费 | 237篇 |
专业分类
3913篇 |
出版年
2023年 | 23篇 |
2022年 | 40篇 |
2021年 | 77篇 |
2020年 | 53篇 |
2019年 | 56篇 |
2018年 | 94篇 |
2017年 | 75篇 |
2016年 | 137篇 |
2015年 | 187篇 |
2014年 | 197篇 |
2013年 | 262篇 |
2012年 | 296篇 |
2011年 | 299篇 |
2010年 | 179篇 |
2009年 | 180篇 |
2008年 | 223篇 |
2007年 | 206篇 |
2006年 | 176篇 |
2005年 | 187篇 |
2004年 | 166篇 |
2003年 | 158篇 |
2002年 | 150篇 |
2001年 | 28篇 |
2000年 | 36篇 |
1999年 | 41篇 |
1998年 | 27篇 |
1997年 | 36篇 |
1996年 | 33篇 |
1995年 | 26篇 |
1994年 | 30篇 |
1993年 | 26篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 9篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 7篇 |
1971年 | 5篇 |
1969年 | 5篇 |
1946年 | 5篇 |
排序方式: 共有3913条查询结果,搜索用时 15 毫秒
1.
Lucia Di Giambattista P. Grimaldi S. Gaudenzi D. Pozzi M. Grandi S. Morrone I. Silvestri A. Congiu Castellano 《European biophysics journal : EBJ》2010,39(6):929-934
We have made a preliminary analysis of the results about the effects on tumoral cell line (lymphoid T cell line Jurkat) induced
by UVB radiation (dose of 310 mJ/cm2) with and without a vegetable mixture. In the present study, we have used two techniques: Fourier transform infrared spectroscopy
(FTIR) and flow cytometry. FTIR spectroscopy has the potential to provide the identification of the vibrational modes of some
of the major compounds (lipid, proteins and nucleic acids) without being invasive in the biomaterials. The second technique
has allowed us to perform measurements of cytotoxicity and to assess the percentage of apoptosis. We already studied the induction
of apoptotic process in the same cell line by UVB radiation; in particular, we looked for correspondences and correlations
between FTIR spetroscopy and flow cytometry data finding three highly probable spectroscopic markers of apoptosis (Pozzi et
al. in Radiat Res 168:698–705, 2007). In the present work, the results have shown significant changes in the absorbance and
spectral pattern in the wavenumber protein and nucleic acids regions after the treatments. 相似文献
2.
The assembly of a large physical map of genomes requires simultaneous analysis of many cosmid clones for overlapping regions. The search for overlapping regions may be achieved by various means. High-performance liquid chromatography (HPLC) provides an alternative to gel electrophoresis since microgram amounts of each DNA fragment may be collected into individual test tubes for further analysis. HPLC has been used to identify overlapping cosmid clones from a pool of cosmid DNA containing the terminal portion of the long arm of the human X chromosome (Xq24-qter). Among 400 cosmids analyzed, 3 were shown to overlap. 相似文献
3.
4.
Lucia Lioi 《Biologia Plantarum》1987,29(1):49-53
Relationships among storage proteins in seeds from cultivars and primitive accessions of the four economically most important
species ofPhaseolus — P. vulgaris, P. coccineus, P. acutifolius andP. lunatus — were studied.
Analysis of SDS-polyacrylamide gel electrophoretic patterns of storage seed proteins revealed common characteristics in the
major groups of polypeptides forP. vulgaris, P. coccineus andP. acutifolius, while clear differences existed between thesePhaseolus species and P.lunatus. 相似文献
5.
Bruna Tedeschi Patrizia Vernole M.Lucia Sanna Benedetto Nicoletti 《Human genetics》1992,89(5):543-547
Summary Chromosome fragile sites are inducible by aphidicolin in cultured human lymphocytes. To assess the frequency and distribution of these common fragile sites in the general population, a cytogenetic survey was performed on 126 subjects, 59 males and 67 females, whose age ranged from 1 day to 72 years. Common fragile sites, induced by aphidicolin, were widespread and showed a remarkably different sensitivity among individuals; age influenced the overall frequency of fragile sites. Moreover, both age and sex seemed to modulate the expression of specific fragile sites. In our population, the most common fragile sites were: 3p14, 16q23, Xp22, 6q26, 1p31, 4q31, 1p22, 7q22, 2q33, 3q27, 2q31, 7q32, 14q24, 10q22, 5q31, 2q37, 6p21. 相似文献
6.
No correlation exists between the conjugative transfer of the autotrophic character and that of plasmids in Nocardia opaca strains 总被引:4,自引:0,他引:4
A new isolate of Nocardia opaca was obtained by enrichment culture for aerobic lithoautotrophic growth on CO2 and H2. This strain, MR22, is very similar to N. opaca MR11 (formerly 1b) in functioning as a donor for genetic information determining the ability to grow lithoautotrophically (Aut character) in matings with Aut- strains of N. opaca or closely related heterotrophic species. The strain contains a plasmid, pHG33 of about 110 kb. A mutant was isolated from strain MR22 which was plasmid-free, and had lost the Aut character, resistance to 50 microM-thallium salt and susceptibility to the nocardia-specific bacteriophage phi B1. As a recipient of the Aut character, this plasmid-free mutant was as well suited as plasmid-bearing Aut- strains of N. opaca. In matings with the mutant as recipient the frequency of Aut+ transconjugants per donor was 3 X 10(-4) with N. opaca MR11 (pHG31-a, Aut+, Tlr, Strs, phi B1s) and 2 X 10(-3) with N. opaca MR22 (pHG33, Aut+, Tlr, Strs, phi B1r) as donor. Phenotypic characterization of the transconjugants, which had been selected for the Aut marker, revealed that in many cases the Aut marker had been transferred without plasmid transfer. Furthermore, plasmid-free, Aut+ transconjugants functioned as donors for the Aut marker. Both plasmid-free and plasmid-bearing transconjugants transferred the Aut marker to the Aut- strains of N. opaca with a frequency which was one or two orders of magnitude higher than that of the wild-type strains. The plasmids pHG31-a and pHG33 code for thallium resistance (50 microM-thallium acetate). The frequency of thallium-resistant transconjugants was 10(-1) to 10(-2) per donor; all thallium-resistant transconjugants contained the donor plasmid. We conclude that the plasmids pHG31-a of strain MR11 and pHG33 of strain MR22 of N. opaca carry the genetic information for thallium resistance but not the Aut character. As plasmid-free Aut+ strains can function as donors the Aut character is assumed to reside on the chromosome and to function as an independent self-transmissible genetic element. 相似文献
7.
B P Griffith S R McCormick C K Fong J T Lavallee H L Lucia E Goff 《Journal of virology》1985,55(2):402-409
The development of cytomegalovirus (CMV) infection in the placenta was studied in Hartley guinea pigs inoculated at midgestation, and its role in determining the outcome of fetal CMV infection was assessed. A hematogenous spread of CMV from the mother to the placenta occurred early during the course of the infection. However, the virus remained present in placental tissues long after CMV had been cleared from maternal blood (i.e., 3 and 4 weeks postinoculation). At that time, the virus was able to replicate in placental tissues in the presence of specific maternal antibodies. Viral nucleocapsids were seen within nuclei of trophoblastic cells, and virions were present surrounding infected cells. In addition, typical CMV-induced histopathological lesions bearing CMV antigens were consistently localized at the transitional zone between the capillarized labyrinth and the noncapillarized interlobium. Whenever CMV infection of the fetus occurred, virus was isolated from the associated placenta. Among placental-fetal units with CMV-infected placentas, only 27% of the fetuses were found to be infected. In addition, there was a delay in the establishment of the infection in the fetus in relation to the placenta, although frequencies of virus isolation in placental and fetal tissues peaked at 3 weeks after CMV inoculation. These results suggest that during primary CMV infection of pregnant guinea pigs, the placenta not only serves as a reservoir for CMV but also acts to limit transmission of the virus to the fetus. 相似文献
8.
9.
Recently isolated coryneform hydrogen bacteria were investigated under taxonomical aspects. Strains 7 C, RH 10, and 14 g are characterized by the snapping type of cell division, 68.5 to 69.7% GC content, dl-diaminopimelic acid in the cell wall, content of metachromatic granules, weak utilization of sugars and inhibitory effect of citrate. The strains are placed to the group 1—genus Corynebacterium—of the classification of coryneform bacteria of Yamada and Komagata (1972) and the name Corynebacterium autotrophicum sp.nov. is proposed.Strains 11 X and RH 12 are characterized by the bending type of cell division, a GC content of 70.2 and 70.5%, ll-diaminopimelic acid in the cell wall, absence of metachromatic granules, utilization of several sugars and no changes in cell morphology by citrate. The strains have to be placed to group 6 of coryneform bacteria. 相似文献
10.
Mixed infection of Rickettsiella phytoseiuli and Coxiella burnetii was investigated in hemolymph and organs of experimentally infected females of Dermacentor reticulatus ticks. Following intracoelomic infection, both agents, with the exception of Gene's organ, multiplied well in the cells of the tick host's organs. Two out of six developmental stages of R. phytoseiuli, i.e., crystal-forming and small dark particles, in dual infection with C. burnetii revealed marked morphological alterations. C. burnetii in the presence of R. phytoseiuli penetrated into the cortical layer of the synganglion and into the alveoli of the second and third type of salivary glands, but did not occur in the single infection. 相似文献