全文获取类型
收费全文 | 900篇 |
免费 | 66篇 |
出版年
2023年 | 5篇 |
2021年 | 7篇 |
2019年 | 7篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 19篇 |
2015年 | 16篇 |
2014年 | 12篇 |
2013年 | 68篇 |
2012年 | 55篇 |
2011年 | 70篇 |
2010年 | 52篇 |
2009年 | 39篇 |
2008年 | 42篇 |
2007年 | 37篇 |
2006年 | 44篇 |
2005年 | 34篇 |
2004年 | 50篇 |
2003年 | 40篇 |
2002年 | 37篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1971年 | 6篇 |
1955年 | 8篇 |
1954年 | 27篇 |
1953年 | 8篇 |
1952年 | 9篇 |
1951年 | 9篇 |
1950年 | 7篇 |
1949年 | 7篇 |
排序方式: 共有966条查询结果,搜索用时 171 毫秒
161.
The constraint-based reconstruction and analysis (COBRA) framework has been widely used to study steady-state flux solutions in genome-scale metabolic networks. One shortcoming of current COBRA methods is the possible violation of the loop law in the computed steady-state flux solutions. The loop law is analogous to Kirchhoff's second law for electric circuits, and states that at steady state there can be no net flux around a closed network cycle. Although the consequences of the loop law have been known for years, it has been computationally difficult to work with. Therefore, the resulting loop-law constraints have been overlooked. Here, we present a general mixed integer programming approach called loopless COBRA (ll-COBRA), which can be used to eliminate all steady-state flux solutions that are incompatible with the loop law. We apply this approach to improve flux predictions on three common COBRA methods: flux balance analysis, flux variability analysis, and Monte Carlo sampling of the flux space. Moreover, we demonstrate that the imposition of loop-law constraints with ll-COBRA improves the consistency of simulation results with experimental data. This method provides an additional constraint for many COBRA methods, enabling the acquisition of more realistic simulation results. 相似文献
162.
The direct tracking of cellular reactions in vivo has been facilitated with recent technologies that strongly enhance NMR signals in substrates of interest. This methodology can be used to assay intracellular reactions that occur within seconds to few minutes, as the NMR signal enhancement typically fades on this time scale. Here, we show that the enhancement of (13)C nuclear spin polarization in deuterated glucose allows to directly follow the flux of glucose signal through rather extended reaction networks of central carbon metabolism in living Escherichia coli. Alterations in central carbon metabolism depending on the growth phase or upon chemical perturbations are visualized with minimal data processing by instantaneous observation of cellular reactions. 相似文献
163.
Amundsen BH Ericsson M Seland JG Pavlin T Ellingsen Ø Brekken C 《Laboratory animals》2011,45(1):31-37
Non-invasive imaging methods like echocardiography and magnetic resonance imaging (MRI) are very valuable in longitudinal follow-up studies of cardiac function in small animals. To be able to compare results from studies using different methods, and explain possible differences, it is important to know the agreement between these methods. As both self-gated high-field MRI and high-frequency echocardiography (hf-echo) M-mode are potential methods for evaluation of left ventricular (LV) function in healthy mice, our aim was to assess the agreement between these two methods. Fifteen healthy female C57BL/6J mice underwent both self-gated MRI and hf-echo during the same session of light isoflurane anaesthesia. LV dimensions were estimated offline, and agreement between the methods and reproducibility for the two methods assessed using Bland-Altman methods. In summary, hf-echo M-mode had better inter-observer repeatability than self-gated MRI for all measured parameters. Compared with hf-echo, systolic posterior wall thicknesses were significantly higher when measured by MRI, while diastolic anterior wall thicknesses were found to be significantly smaller. MRI measurements of diastolic LV diameter were also higher using MRI, resulting in larger fractional shortening values compared with the values obtained by hf-echo. In conclusion, hf-echo M-mode is easy to apply, has high temporal and spatial resolution, and good reproducibility. Self-gated MRI might be advantageous in cases of abnormal LV geometry and heterogeneous regional myocardial function, especially with improvements in spatial resolution. The moderate agreement between the methods must be taken into account when comparing studies using the two modalities. 相似文献
164.
Houen G Struve C Søndergaard R Friis T Anthoni U Nielsen PH Christophersen C Petersen BO Duus JØ 《Bioorganic & medicinal chemistry》2005,13(11):3783-3796
The oxidation of spermidine or homospermidine with bovine serum amine oxidase (BSAO) was monitored in situ, using proton nuclear magnetic resonance spectroscopy in water with 10% D(2)O. NMR assignments were performed by spin decoupling and COSY spectra or by comparison with data from synthetic aminoaldehydes. The results represent the first in situ characterisation of the highly reactive aminoaldehydes and showed oxidation at the N(1) amino group of spermidine and homospermidine. Comparison of homospermidine with a variety of substrates revealed that among straight chain di- and polyamines both an aminopropyl group and two primary amino groups separated by seven (norspermidine) or eight (spermidine) carbon atoms were required for optimal substrate ability. However, highest activity was seen with the substrate N-(4-aminobutyl)hexahydropyrimidine, showing that the substrate channel of BSAO has a dual substrate preference, with moderately bulky substituents at the distal end of a diamine contributing equally well as an alkyl amino group. Cytotoxic investigations of a variety of substrates for BSAO, confirmed previous results, that cytotoxicity is primarily linked to polyamines encompassing the aminopropyl moiety. No acrolein was observed at any time during the oxidation showing that it reacts very fast with available amino groups forming a variety of derivatives. 相似文献
165.
Sabine Buurgaard Sørensen Bjarne Larsen Jihad Orabi Marian Ørgaard 《Nordic Journal of Botany》2014,32(4):503-510
During the past centuries Danish populations of Primula farinosa have seriously declined in number. We investigated the genetic structure and genetic diversity of plants of seven populations from two different regions, Zealand and Bornholm in Denmark, using three AFLP markers. Two populations from nearby Scania, Sweden were included as reference. We found 54 unambiguously polymorphic loci. The genetic structure analysis suggested division of the 268 plants into three distinct groups, to a large extent matching the geographical distribution of the populations. Analysis of molecular variance (AMOVA) indicated significant genetic differentiation of 67% within populations and 33% among the populations. Our results suggest that genetic differentiation among regions and unique local genetic diversity should carefully be considered in future conservation attempts if we are to maintain as much genetic variation as possible. We present a historical overview of the decline in Danish populations and discuss conservation management and restoration strategies. 相似文献
166.
Chen Ying Klingen Tor A Wik Elisabeth Aas Hans Vigeland Einar Liestøl Knut Garred Øystein Mæhlen Jan Akslen Lars A Lømo Jon 《Diagnostic pathology》2014,9(1):1-2
Squamous cell carcinomas (SCCs) are uncommon, high-grade tumors, predominantly composed of round cells in the prepuce. The aim of this study is to better define the clinicopathologic features of this neoplasm. We conducted cyto-histopathologic analysis on the manifestations of the prepuce SCC by H &; E staining in a terrier mix dog. Grossly, tumor was large, multiple erythematous patch, and ulcerated masses frequently affecting the prepuce and deeply invading to distal prepuce out from the ventro-lateral of penis and the tumor covered by a necrotic discharge. Cytological evaluation of fine-needle aspirates from the cutaneous mass from the prepuce comprised of round nuclei, coarse chromatin pattern, distinct nucleoli and nuclear pleomorphism. Furthermore, the neoplastic cells were pleomorphic, round to caudate in shape, exhibiting prominent anisokaryosis and anisocytosis with rare mitotic features. Microscopically, the lesions were predominantly composed of atypical round cells disposed in interlacing fascicles. Frequent findings include keratin formation, horn pearls, mitoses and cellular atypia. The cells showed distinct borders, ranged from polygonal to round or elongate and had moderate amounts of eosinophilic cytoplasm. The histopathologic features coupled with the cytopathology findings led to a diagnosis of squamous cell carcinoma. To the authors’ knowledge, this is the first time that multiple erythematous plaques have undergone malignant transformation in a terrier mix dog. The virtual slide(s) for this article can be found here:
http://www.diagnosticpathology.diagnomx.eu/vs/5748771971272873 相似文献
167.
Yang Ning Huang Bin Tsinkalovsky Oleg Brekkå Narve Zhu Huaiyang Leiss Lina Enger Per Øyvind Li Xingang Wang Jian 《Cancer cell international》2014,14(1):1-7
The anticancer effects of ceramide have been reported in many types of cancers but less in lung cancer. In this study, we used C2-ceramide to further investigate its possible anticancer effects and mechanisms on non-small cell lung cancer (NSCLC) H1299 cells. The result of cell proliferation in terms of trypan blue assay showed high dose of C2-ceramide inhibited cell survival after 24 h treatment. The flow cytometry-based assays indicated the effect of apoptosis, chromatin condensation, and G1 arrest in terms of Annexin V/propidium iodide (PI), DAPI, and PI stainings, respectively. Moreover, the decreased protein level of p-Akt, p-NFκB, survivin and cyclin A2 were detected by Western blot assay. Taken together, these results indicated the antiproliferative effect of C2-ceramide is majorly responsible for cell apoptosis in lung cancer H1299 cells. 相似文献
168.
Ingibjörg E. Einarsdóttir Kjell J. Nilssen Svein O. Øren Martin Iversen 《Polar Biology》2000,23(4):231-235
In order to elucidate the immune responses of Arctic charr in relation to temperature, groups were acclimated to a moderate
(9°C) and a cold temperature regime (4°C), as well as subjected to a temperature decrease (from 9 to 4°C) immediately prior
to an immunization with sheep red blood cells. The charr kept at 9°C responded with increased primary and secondary antibody
titres, as seen by direct haemagglutination, while fish at 4°C, as well as the fish subjected to a temperature reduction,
displayed lower and lowest antibody titres, respectively, and only after a second immunization. It is concluded that Arctic
charr can respond to a cellular antigen with a humoral immune response typical for other teleosts, but that the immune response
is delayed and diminished at low temperatures. This temperature-induced immune suppression is intensified if the fish have
not been acclimated to cold water prior to immunization.
Accepted: 10 October 1999 相似文献
169.
170.
Summary Hyperosmolality adversely affects growth of murine hybridoma cells. Addition of low concentrations of betaine to the growth medium will protect the hyperosmotically stressed cells. The protective effect is observed as increased growth rate and cell density of the stressed cell cultures. The cellular production of monoclonal antibody is related to growth rate in an inverse fashion. 相似文献