全文获取类型
收费全文 | 859篇 |
免费 | 72篇 |
出版年
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 21篇 |
2017年 | 11篇 |
2016年 | 30篇 |
2015年 | 34篇 |
2014年 | 46篇 |
2013年 | 49篇 |
2012年 | 59篇 |
2011年 | 54篇 |
2010年 | 49篇 |
2009年 | 42篇 |
2008年 | 32篇 |
2007年 | 50篇 |
2006年 | 39篇 |
2005年 | 32篇 |
2004年 | 18篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 19篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1970年 | 4篇 |
1966年 | 3篇 |
1961年 | 3篇 |
排序方式: 共有931条查询结果,搜索用时 15 毫秒
101.
Ilona Schonn Jana Hennesen Dorothee C. Dartsch 《Apoptosis : an international journal on programmed cell death》2010,15(2):162-172
The topoisomerase IIα inhibitor etoposide is a ‘broad spectrum’ anticancer agent and a potent inducer of DNA double strand
breaks. DNA damage response of mammalian cells usually involves cell cycle arrest and DNA repair or, if unsuccessful, cell
death. We investigated these processes in the human colon cancer cell line HT-29 treated with three different etoposide regimens
mimicking clinically relevant plasma concentrations of cancer patients. Each involved a period of drug-free incubation following
etoposide exposure to imitate the decline of plasma levels between the cycles of chemotherapy. We found a massive induction
of double strand breaks that were rapidly and nearly completely fixed long before the majority of cells underwent apoptosis
or necrosis. An even greater percentage of cells lost clonogenicity. The occurrence of double strand breaks was accompanied
by a decrease in the levels of Ku70, Ku86 and DNA-PKcs as well as an increase in the level of Rad51 protein. Twenty-four hours after the first contact with etoposide we found a
pronounced G2/M arrest, regardless of the duration of drug exposure, the level of double strand breaks and the extent of their repair.
During the subsequent drug-free incubation period, the loss of clonogenicity correlated well with the preceding G2/M arrest as well as with the amount of cell death found several days after exposure. However, it correlated neither with
early apoptosis or necrosis nor with any of the other investigated parameters. These results suggest that the G2/M arrest is an important determinant in the cytostatic action of etoposide and that the removal of DNA double strand breaks
is not sufficient to ensure cell survival. 相似文献
102.
103.
104.
105.
106.
H Schimmelpenning K Hamper U G Falkmer J Caselitz G Seifert G U Auer 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》1989,11(6):379-383
The image cytometric nuclear DNA assessments on paraffin-embedded tissue sections and on Cytospin preparations of disaggregated specimens from the same cases were compared in 98 salivary gland tumors, including 21 acinic cell carcinomas, 29 mucoepidermoid carcinomas, 21 adenocarcinomas and 27 adenoid cystic carcinomas. The histogram type (diploid, tetraploid or aneuploid) and the number of cells with DNA values greater than 2.5c (expressed in relative units) were considered as variables in the correlation. A high correlation between the results in different specimens was found in acinic cell carcinomas, mucoepidermoid carcinomas and adenocarcinomas; the histogram type and the number of cells with DNA values greater than 2.5c were essentially the same between specimen types in these three tumor entities. The cases of adenoid cystic carcinomas showed a considerably lower degree of correlation: in 8 of the 27 cases, the Cytospin preparations yielded diploid histograms, while the tissue sections yielded aneuploid histograms. The number of cells with DNA values greater than 2.5c was notably lower in the Cytospin preparations from adenoid cystic carcinoma; the reasons for this exceptional behavior of the cells of adenoid cystic carcinoma are discussed. These findings demonstrate that paraffin-embedded specimens of different tumor entities, even from the same organ, can be affected differently by disaggregation procedures. While retrospective studies on disaggregated paraffin-embedded specimens can yield reliable results, comparative assessments using both DNA analysis techniques, as in this study, should be performed before a large number of cases is evaluated. 相似文献
107.
C Kremser W Lutz A Auer C Schmiedauer S Felber E Hochmair F Aichner 《Biomedizinische Technik》1999,44(10):265-271
The accurate localization of specific intracranial blood vessels is a major difficulty with transcranial Doppler sonography (TCD). It was the purpose of this study to develop a system enabling stereotactic navigation during a TCD examination on the basis of high-resolution three-dimensional magnetic resonance angiographic (MRA) data. During TCD, the examiner is provided--on a computer screen--with a projected view of the respective intracranial vessel anatomy. With the aid of an optoelectronic localization system, the spatial orientation and localization of the US probe is determined in real time, and correlated with the patient's MRA data using a dedicated stereotactic mask. Subsequently, the US beam and the points of insonation are displayed on the screen overlaid on the vessel anatomy. In this way the examiner gains real time control of the localization of the respective intracranial vessel insonated. Points of insonation can be stored and recalled for follow-up examinations. In addition to the successful verification of the system, it was shown that, in comparison with conventional TCD, stereotactic navigation distinctly improves the reproducibility of repeat TCD examinations. 相似文献
108.
Markus Auer Clemens Gruber Marzia Bellei Katharina F. Pirker Marcel Zamocky Daniela Kroiss Stefan A. Teufer Stefan Hofbauer Monika Soudi Gianantonio Battistuzzi Paul G. Furtmüller Christian Obinger 《The Journal of biological chemistry》2013,288(38):27181-27199
Reconstructing the phylogenetic relationships of the main evolutionary lines of the mammalian
peroxidases lactoperoxidase and myeloperoxidase revealed the presence of novel bacterial heme
peroxidase subfamilies. Here, for the first time, an ancestral bacterial heme peroxidase is shown to
possess a very high bromide oxidation activity (besides conventional peroxidase activity). The
recombinant protein allowed monitoring of the autocatalytic peroxide-driven formation of covalent
heme to protein bonds. Thereby, the high spin ferric rhombic heme spectrum became similar to
lactoperoxidase, the standard reduction potential of the Fe(III)/Fe(II) couple shifted to more
positive values (−145 ± 10 mV at pH 7), and the conformational and thermal stability
of the protein increased significantly. We discuss structure-function relationships of this new
peroxidase in relation to its mammalian counterparts and ask for its putative physiological
role. 相似文献
109.
In vivo magnetic resonance imaging of the reproductive organs in a passerine bird species 总被引:1,自引:0,他引:1
For researchers working on the reproductive anatomy of birds, the standard tool has been the scalpel. We demonstrate that magnetic resonance imaging (MRI) allows us to study non-invasively the testes and ovaries of small birds. Thus, repeated measurements of the same individual can be obtained at different life-history stages or before and after experimental treatment with a minimum of harm done to the birds. We present cross-sectional images of male and female Garden Warblers Sylvia borin at different stages of their gonadal maturation cycle to illustrate the high resolution that can be achieved through MRI. Volumetric analyses enabled us to determine the total testicular volume with high accuracy. 相似文献
110.