全文获取类型
收费全文 | 961篇 |
免费 | 57篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 25篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 22篇 |
2017年 | 21篇 |
2016年 | 33篇 |
2015年 | 54篇 |
2014年 | 53篇 |
2013年 | 52篇 |
2012年 | 84篇 |
2011年 | 80篇 |
2010年 | 51篇 |
2009年 | 44篇 |
2008年 | 55篇 |
2007年 | 72篇 |
2006年 | 58篇 |
2005年 | 41篇 |
2004年 | 53篇 |
2003年 | 51篇 |
2002年 | 30篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1018条查询结果,搜索用时 31 毫秒
51.
Kálvin B Fekésházy A Lengyel Z Szakáll S Agoston P Lengyel E Székely J Galuska L Trón L Esik O 《Magyar onkologia》2002,46(3):203-223
The authors have reviewed the financial considerations of oncological FDG PET examinations by the guidelines of the Health Care Financing Administration (USA). By critical assessment of large number of clinical investigations,the cost-effectiveness of FDG PET scans has been confirmed in the following cases: differential diagnosis of solitary pulmonary nodule, diagnosis,staging and restaging of non-small cell lung cancer, colorectal cancer, malignant lymphomas, melanoma malignum, esophageal neoplasms and cancers of the head and neck. The role of this method in breast cancer is currently under intensive investigation. Due to the correct staging, PET examinations in these indications enable the clinicians to choose the optimal treatment ensuring the maximum probability of recovery and being cost-effective as unnecessary medical interventions become avoidable. 相似文献
52.
Warmlander S Sponer JE Sponer J Leijon M 《The Journal of biological chemistry》2002,277(32):28491-28497
Sequences of four or more AT base pairs without a 5'-TA-3' step, so-called A-tracts, influence the global properties of DNA by causing curvature of the helix axis if phased with the helical repeat and also influence nucleosome packaging. Hence it is interesting to understand this phenomenon on the molecular level, and numerous studies have been devoted to investigations of dynamical and structural features of A-tract DNA. It was early observed that anomalously slow base pair-opening kinetics were a striking physical property unique to DNA A-tracts (Leroy, J. L., Charretier, E., Kochoyan, M., and Gueron, M. (1988) Biochemistry 27, 8894-8898). Furthermore, a strong correlation between DNA curvature and anomalously slow base pair-opening dynamics was found. In the present work it is shown, using imino proton exchange measurements by NMR spectroscopy that the main contribution to the dampening of the base pair-opening fluctuations in A-tracts comes from the C5 methylation of the thymine base. Because the methyl group has been shown to have a very limited effect on the DNA curvature as well as the structure of the DNA helix, the thymine C5 methyl group stabilizes the helix directly. Empirical potential energy calculations show that methylation of the tract improves the stacking energy of a base pair with its neighbors in the tract by 3-4 kcal/mol. 相似文献
53.
Bak J Billington RA Genazzani AA 《Biochemical and biophysical research communications》2002,295(4):806-811
Nicotinic acid adenine dinucleotide phosphate (NAADP) has been shown to be a powerful Ca2+ release agent in numerous systems, including echinoderms, plants, and mammalian cells. NAADP has been shown to release Ca2+ via a separate mechanism to IP3 and ryanodine receptors, and specific binding sites have recently been characterised. However, functional studies have shown that there is a functional interplay between the NAADP-sensitive mechanism and the other two. In particular, it appears that activation of the NAADP receptor might act as a trigger to facilitate responses from IP3 and ryanodine receptors. To further characterise this interplay, we have investigated the effects of luminal and cytosolic Ca2+ on the NAADP receptor in sea urchin egg homogenates. We report that neither cytosolic nor luminal Ca2+ appears to influence NAADP binding. Conversely, emptying of stores significantly amplifies NAADP-induced fractional Ca2+-release, providing a mechanism of self-adjustment independent of store loading. 相似文献
54.
The spectroscopy of horseradish peroxidase with and without the substrate analogue benzohydroxamic acid (BHA) was monitored in different solvents as a function of the temperature in the interval from 10 to 300 K. Thermal broadening of the Q(0,0) optical absorption band arises mainly from interaction of the electronic pi --> pi transition with the heme vibrations. In contrast, the width of the IR absorption band of CO bound to heme is controlled by the coupling of the CO transition moment to the electric field of the protein matrix. The IR bandwidth of the substrate free enzyme in the glycerol/H2O solvent hardly changes in the glassy matrix and strongly increases upon heating above the glass transition. Heating of the same enzyme in the trehalose/H2O glass considerably broadens the band. The binding of the substrate strongly diminishes the temperature broadening of the CO band. This result is consistent with the view that the BHA strongly reduces the amplitude of vibrations of the heme pocket environment. Unusually strong thermal broadening of the CO band above the glass transition is interpreted to be caused by thermal population of a very flexible excited conformational substate. The thermal broadening of the same band in the trehalose glass is caused by an increase of the protein vibrational amplitude in each of the conformational substates, their population being independent of the temperature in the glassy matrix. 相似文献
55.
The effect of mannitol on different genotypes of potato was studied in callus and plantlet culture. In vitro responses of five potato genotypes with well-known field behaviour to water deficit were analysed. After a 4-week-long cultivation on media containing mannitol up to 0.8 M, different morpho-physiological parameters were determined and statistically analysed. The useful concentration of mannitol for in vitro screening the osmotic tolerance of different genotypes depended on the type of culture; it was 0.4 M in plantlet-test and 0.8 M in callus-test. In callus-test the relative increase of callus mass was a useful parameter for determination of osmotic tolerance of genotypes at cellular level. In plantlet culture, stress index calculated from the rate of surviving in vitro shoots, number and length of roots per surviving explant and the rate of rooted explants were applicable to determine three groups according to the tolerant, medium tolerant and sensitive categories in agreement with the field behaviour of these genotypes. Under in vitro stress conditions we were able to distinguish the examined genotypes with different drought tolerance. 相似文献
56.
57.
Stadler K Jenei V von Bölcsházy G Somogyi A Jakus J 《Free radical biology & medicine》2003,35(10):1240-1251
The levels of different reactive species, especially those of nitric oxide and peroxynitrite, were determined in streptozotocin-induced diabetic rat tissues, before the development of histopathological damages. Significantly higher steady state free radical concentrations were found in the liver 3 weeks after the onset of diabetes compared to age-matched control groups. Increased nitric oxide levels in diabetic vasculature and kidney decreased the production of detectable reactive oxygen species. High peroxynitrite generation suggested the onset of processes characteristic to premature aging of the endothelium. According to the histopathological results, there were no signs of late complications in the tissues up to 7 weeks after induction of diabetes. These results support the idea that oxidative stress is increased at a very early stage of diabetes and, in particular, that high levels of nitric oxide and peroxynitrite could play a decisive role in the development of late complications in the diabetic vasculature and kidney. 相似文献
58.
Moldvay J 《Magyar onkologia》2000,44(3):195-202
Primary bronchial cancer is the most common cause of cancer death worldwide, and it shows a steadily increasing incidence. Beside classical histological typing and grading, immunohistochemical, cytometric, and molecular biological parameters are highly needed to assist light microscopy investigations to better characterize primary bronchial cancers. In this work the author summarizes the main tumor markers and prognostic factors in lung cancer studied intensively at present. Serum markers as well as different tissue markers, such as cell proliferation markers, oncogenes, growth factors, apoptosis markers and vascularisation markers, tumor suppressor genes and markers of drug resistance are discussed in details. The methods currently used in this field are also mentioned and the data of the literature is often completed with results of the author's own investigations. An overview is given about the role of tumor markers in the early detection of lung cancer, in the assessment of tumor aggressiveness, and in therapy of lung cancer. The aim of this work is to create a bridge between the research laboratory in which lung cancer is studied sometimes using very sophisticated techniques and the bedside with all its practical, difficult but very important questions. Getting closer the theory and the practice can be very promising in the establishment of a fruitful collaboration in order to be more effective in the fight against lung cancer. 相似文献
59.
Christian Schobert Lucian Baker Judit Szederkényi Pia Großmann Ewald Komor Hiroaki Hayashi Mitsuo Chino William J. Lucas 《Planta》1998,206(2):245-252
The mature, functional sieve-tube system in higher plants is dependent upon protein import from the companion cells to maintain
a functional long-distance transport system. Soluble proteins present within the sieve-tube lumen were investigated by analysis
of sieve-tube exudates which revealed the presence of distinct sets of polypeptides in seven monocotyledonous and dicotyledonous
plant species. Antibodies directed against sieve-tube exudate proteins from Ricinus communis L. demonstrated the presence of shared antigens in the phloem sap collected from Triticum aestivum L., Oryza sativa L., Yucca filamentosa L., Cucurbita maxima Duch., Robinia pseudoacacia L. and Tilia platyphyllos L. Specific antibodies were employed to identify major polypeptides. Molecular chaperones related to Rubisco-subunit-binding
protein and cyclophilin, as well as ubiquitin and the redox proteins, thioredoxin h and glutaredoxin, were detected in the
sieve-tube exudate of all species examined. Actin and profilin, a modulator of actin polymerization, were also present in
all analyzed phloem exudates. However, some proteins were highly species-specific, e.g. cystatin, a protease-inhibitor was
present in R. communis but was not detected in exudates from other species, and orthologs of the well-known squash phloem lectin, phloem protein
2, were only identified in the sieve-tube exudate of R. communis and R. pseudoacacia. These findings are discussed in terms of the likely roles played by phloem proteins in the maintenance and function of the
enucleate sieve-tube system of higher plants.
Received: 12 February 1998 / Accepted: 16 March 1998 相似文献
60.
Gabriella Juhasz Xenia Gonda Gabor Hullam Nora Eszlari David Kovacs Judit Lazary Dorottya Pap Peter Petschner Rebecca Elliott John Francis William Deakin Ian Muir Anderson Peter Antal Klaus-Peter Lesch Gyorgy Bagdy 《PloS one》2015,10(3)