全文获取类型
收费全文 | 2181篇 |
免费 | 201篇 |
出版年
2023年 | 8篇 |
2022年 | 20篇 |
2021年 | 46篇 |
2020年 | 29篇 |
2019年 | 61篇 |
2018年 | 73篇 |
2017年 | 65篇 |
2016年 | 75篇 |
2015年 | 123篇 |
2014年 | 136篇 |
2013年 | 164篇 |
2012年 | 153篇 |
2011年 | 204篇 |
2010年 | 126篇 |
2009年 | 69篇 |
2008年 | 133篇 |
2007年 | 120篇 |
2006年 | 144篇 |
2005年 | 120篇 |
2004年 | 91篇 |
2003年 | 91篇 |
2002年 | 66篇 |
2001年 | 16篇 |
2000年 | 8篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 15篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1970年 | 7篇 |
排序方式: 共有2382条查询结果,搜索用时 15 毫秒
981.
P García E García C Ronda R Lopez R Z Jiang A Tomasz 《Journal of general microbiology》1986,132(5):1401-1405
Two mutants of Streptococcus pneumoniae deficient in autolysin activity produced a protein that showed immunological identity with the N-acetyl-muramyl-L-alanyl-amidase present in the wild-type strain, when tested with antiserum obtained against this enzyme. The protein was produced by the mutant cultures grown either at 37 degrees C or at 30 degrees C, although only the cell extracts obtained at 30 degrees C showed significant cell wall hydrolysing activity. In contrast to the lysis resistance of these bacteria grown at 37 degrees C, mutant cultures grown at 30 degrees C exhibited significant degrees of autolysis when treated with detergent or cell wall inhibitors. Extracts of the mutant cultures contained a cell wall hydrolysing activity that was rapidly inactivated during incubation at 37 degrees C. 相似文献
982.
Maria Tomasz 《Chemico-biological interactions》1976,13(1):89-97
Reduction of mitomycin C by NaBH4 or by NADPH in the presence of a cell extract followed by exposure to air results in the generation of H2O2. This phenomenon occurs not only with free mitomycin but also with mitomycin irreversibly bound to DNA. In view of these findings, the antibiotic activity of mitomycin was tested in two bacterial systems: a facultative aerobic bacterium grown in the presence or absence of oxygen and an obligate anaerobic bacterium. No oxygen effect could be demonstrated in either case in the growth-inhibitory and bactericidal activity of the drug. Nevertheless, the H2O2 generating capacity of mitomycin-DNA complexes inside the nucleus may play a role in the drug-induced biological damage to the genetic material of cells. 相似文献
983.
Długosz-Pokorska Angelika Pięta Marlena Janecki Tomasz Janecka Anna 《Molecular biology reports》2019,46(6):5831-5839
Molecular Biology Reports - Overexpression of ATP-binding cassette (ABC) transporters causing multidrug resistance (MDR) in cancer cells is one of the major obstacles in cancer chemotherapy. The... 相似文献
984.
Tomasz W. Pyrcz Haydon Warren-Gash Jadwiga Lorenc-Brudecka Dieuwko?Knoop Philippe Oremans Szabolcs Sáfián 《ZooKeys》2013,(298):1-37
Updated data on the distribution, ecology and taxonomy of Euphaedra cyparissa (Cramer) and Euphaedra sarcoptera (Butler) are presented. Three new subspecies of Euphaedra cyparissa and one of Euphaedra sarcoptera are described and their geographic distribution is presented. The monophyly of the genus Euphaedra sensu Hecq is assessed based on morphological, in particular male and female genitalia, and behavioural traits. Possible evolutionary reasons for the convergence of colour pattern between the sympatric subspecies of Euphaedra cyparissa and Euphaedra sarcoptera are discussed. 相似文献
985.
986.
Gamasid mites are important regulators of soil food webs in forest ecosystems. Wildfire is a dominant disturbance factor in forest ecosystems. We assessed the impact of fire on the species composition of soil gamasid mites at mountain sites following fires of four different degrees of severity and at one control site (5 years post-fire). In total, 14 families, 28 genera, and 54 species or species complexes were found. The abundance and richness were poor in severely burned sites compared to the less damaged sites. The different species compositions, especially in the medium-burned site, require further ecological study to improve our understanding. The fire response and recovery processes of selected species are also discussed. 相似文献
987.
Synthesis of 4-hydroxyborauracil and 4-hydroxy-3-methylborauracil, the first boron analogues of uracil, and comparison of their 1H and 13C NMR properties with those of uracil, are presented. The analyses of NMR-monitored boron compound-alcohol and boron compound-amine interactions pointed to the existence of sp3-hybridized, B,B-bis-methoxyborauracils and pyridine-/n-butylamine-borauracils ate-complexes in solution. 相似文献
988.
In various contexts, animals rely on acoustic signals to differentiate between conspecifics. Currently, studies examining vocal signatures use two main approaches. In the first approach, researchers search for acoustic characteristics that have the potential to be individual specific. This approach yields information on variation in signal parameters both within and between individuals and generates practical tools that can be used in population monitoring. In the second approach, playback experiments with natural calls are conducted to discern whether animals are capable of discriminating among the vocal signatures of different individuals. However, both approaches do not reveal the exact signal characteristics that are being used in the discrimination process. In this study, we tested whether an individual-specific call characteristic – namely the length of the intervals between successive maximal amplitude peaks within syllables (PPD) – is crucial in neighbour-stranger discrimination by males of the nocturnal and highly secretive bird species, the corncrake (Crex crex). We conducted paired playback experiments in which corncrakes (n = 47) were exposed to artificial calls with PPD characteristics of neighbour and stranger birds. These artificial calls differed only in PPD structure. The calls were broadcast from a speaker, and we recorded the birds'' behavioural responses. Although corncrakes have previously been experimentally shown to discriminate between neighbours and strangers, we found no difference in the responses to the artificial calls representing neighbours versus strangers. This finding demonstrates that even if vocal signatures are individual specific within a species, it does not automatically mean that said signatures are being crucial in discrimination among individuals. At the same time, the birds'' aggressive responses to the artificial calls indicated that the information transmitted by PPDs is important in species-specific call recognition and may be used by males and/or females to evaluate sender quality, similarly like sound frequency in some insect species. 相似文献
989.
990.
Bogdan Malkowski Maciej Harat Agnieszka Zyromska Tomasz Wisniewski Aleksandra Harat Rita Lopatto Jacek Furtak 《PloS one》2015,10(10)
Gliomas are common brain tumours, but obtaining tissue for definitive diagnosis can be difficult. There is, therefore, interest in the use of non-invasive methods to diagnose and grade the disease. Although positron emission tomography (PET) with 18F-fluorethyltyrosine (18F-FET) can be used to differentiate between low-grade (LGG) and high-grade (HGG) gliomas, the optimal parameters to measure and their cut-points have yet to be established. We therefore assessed the value of single and dual time-point acquisition of 18F-FET PET parameters to differentiate between primary LGGs (n = 22) and HGGs (n = 24). PET examination was considered positive for glioma if the metabolic activity was 1.6-times higher than that of background (contralateral) brain, and maximum tissue-brain ratios (TBRmax) were calculated 10 and 60 min after isotope administration with their sums and differences calculated from individual time-point values. Using a threshold-based method, the overall sensitivity of PET was 97%. Several analysed parameters were significantly different between LGGs and HGGs. However, in a receiver operating characteristics analysis, TBR sum had the best diagnostic accuracy of 87% and sensitivity, specificity, and positive and negative predictive values of 100%, 72.7%, 80%, and 100%, respectively. 18F-FET PET is valuable for the non-invasive determination of glioma grade, especially when dual time-point metrics are used. TBR sum shows the greatest accuracy, sensitivity, and negative predictive value for tumour grade differentiation and is a simple method to implement. However, the cut-off may differ between institutions and calibration strategies would be useful. 相似文献