全文获取类型
收费全文 | 2104篇 |
免费 | 218篇 |
出版年
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 25篇 |
2019年 | 17篇 |
2018年 | 25篇 |
2017年 | 22篇 |
2016年 | 38篇 |
2015年 | 53篇 |
2014年 | 56篇 |
2013年 | 113篇 |
2012年 | 109篇 |
2011年 | 108篇 |
2010年 | 74篇 |
2009年 | 54篇 |
2008年 | 83篇 |
2007年 | 76篇 |
2006年 | 78篇 |
2005年 | 74篇 |
2004年 | 61篇 |
2003年 | 65篇 |
2002年 | 81篇 |
2001年 | 46篇 |
2000年 | 52篇 |
1999年 | 44篇 |
1998年 | 33篇 |
1997年 | 33篇 |
1996年 | 32篇 |
1995年 | 27篇 |
1994年 | 31篇 |
1993年 | 27篇 |
1992年 | 54篇 |
1991年 | 58篇 |
1990年 | 44篇 |
1989年 | 44篇 |
1988年 | 40篇 |
1987年 | 42篇 |
1986年 | 45篇 |
1985年 | 40篇 |
1984年 | 43篇 |
1983年 | 28篇 |
1982年 | 21篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 21篇 |
1976年 | 16篇 |
1975年 | 19篇 |
1974年 | 16篇 |
1973年 | 15篇 |
1971年 | 17篇 |
排序方式: 共有2322条查询结果,搜索用时 15 毫秒
981.
A method has been developed to replace segments of a protein backbone by other segments with standard peptide units and given (φ, ψ) angles. Restrictions were imposed by fixed orientations of the N- and C-terminals and by the absence of steric hindrance between non-bonding atoms. This procedure was applied to the prediction of three dimensional backbone conformations of antibody combining sites based on the amino acid sequences of the six complementarity determining regions. In particular, the detailed backbone structure around the combining site of immunoglobulin MOPC-315 was predicted. Atomic co-ordinates of all non-hydrogen backbone atoms including Cβ of the predicted structure were given so that future comparisons with experimental data and other predictions could be made. 相似文献
982.
983.
James W. Atkinson 《Invertebrate Biology》2003,122(4):326-333
Abstract. The ability of an olfactory-dominant organism, the land snail Anguispira alternata , to negotiate an odor-permeable barrier to obtain food in still air was tested. Thirty-nine snails were challenged with a "V"-shaped wire mesh fence that allowed them to get within 1 cm of their food but required them to turn away from the food to move around the fence. Fifteen snails were tested under the same conditions but without a food odor source present. Of the 39 snails tested with food, 22 moved up the odor gradient directly toward the food. Twentyone of these snails altered their foraging behavior by moving away from the odor source after they encountered the barrier. Twelve of these 21 moved along the fence to the food. The other 9 snails moved away from the fence and wandered about within the arena. Of the 39 snails tested, 17 did not move toward the food but by-passed the fence by either following the arena edge or moving toward the gap between the fence and the arena wall. Since some of these snails obtained the food without encountering the fence, a second experiment challenged 19 snails with a "J"-shaped fence in which one of the possible detour paths was blocked. There was no difference in the number of snails taking the blocked path vs. snails taking the open path. Therefore it is unlikely that these snails were able to detect the fence and plot a path around it before actually moving. In the 2 experiments, 91% of the snails that followed the odor gradient directly toward the food subsequently switched their foraging behavior. The ability of these snails to switch their foraging behavior was unexpected in an olfactory-dominant animal and suggests that their behavior is based on a significant amount of sensory processing. 相似文献
984.
Victoria C. Warwick-Evans Philip W. Atkinson Leonie A. Robinson Jonathan A. Green 《PloS one》2016,11(3)
During the breeding season seabirds are constrained to coastal areas and are restricted in their movements, spending much of their time in near-shore waters either loafing or foraging. However, in using these areas they may be threatened by anthropogenic activities such as fishing, watersports and coastal developments including marine renewable energy installations. Although many studies describe large scale interactions between seabirds and the environment, the drivers behind near-shore, fine-scale distributions are not well understood. For example, Alderney is an important breeding ground for many species of seabird and has a diversity of human uses of the marine environment, thus providing an ideal location to investigate the near-shore fine-scale interactions between seabirds and the environment. We used vantage point observations of seabird distribution, collected during the 2013 breeding season in order to identify and quantify some of the environmental variables affecting the near-shore, fine-scale distribution of seabirds in Alderney’s coastal waters. We validate the models with observation data collected in 2014 and show that water depth, distance to the intertidal zone, and distance to the nearest seabird nest are key predictors in the distribution of Alderney’s seabirds. AUC values for each species suggest that these models perform well, although the model for shags performed better than those for auks and gulls. While further unexplained underlying localised variation in the environmental conditions will undoubtedly effect the fine-scale distribution of seabirds in near-shore waters we demonstrate the potential of this approach in marine planning and decision making. 相似文献
985.
Nucleotide sequence of the thymidylate synthetase gene (thyP3) from the Bacillus subtilis phage phi 3T 总被引:6,自引:0,他引:6
The thyP3 gene, encoding thymidylate synthetase, from the Bacillus subtilis phage phi 3T has been cloned and the nucleotide sequence determined. The derived amino acid sequence indicates a subunit Mr of 32 748. The primary amino acid sequence is compared with the sequences of the analogous proteins specified by Escherichia coli (thyA), Lactobacillus casei, (thyA) and phage T4 (td). Extensive conservation exists in all four sequences implying a shared tertiary structure. 相似文献
986.
Morgan Hepburn Daniel J. Saltzberg Linda Lee Shujuan Fang Claire Atkinson Natalie C.J. Strynadka Andrej Sali Susan P. Lees-Miller David C. Schriemer 《Structure (London, England : 1993)》2021,29(5):467-478.e6
- Download : Download high-res image (312KB)
- Download : Download full-size image
987.
Stefan J. Kempf Sonja Buratovic Christine von Toerne Simone Moertl Bo Stenerl?w Stefanie M. Hauck Michael J. Atkinson Per Eriksson Soile Tapio 《PloS one》2014,9(10)
Patients suffering from brain malignancies are treated with high-dose ionising radiation. However, this may lead to severe learning and memory impairment. Preventive treatments to minimise these side effects have not been possible due to the lack of knowledge of the involved signalling pathways and molecular targets. Mouse hippocampal neuronal HT22 cells were irradiated with acute gamma doses of 0.5 Gy, 1.0 Gy and 4.0 Gy. Changes in the cellular proteome were investigated by isotope-coded protein label technology and tandem mass spectrometry after 4 and 24 hours. To compare the findings with the in vivo response, male NMRI mice were irradiated on postnatal day 10 with a gamma dose of 1.0 Gy, followed by evaluation of the cellular proteome of hippocampus and cortex 24 hours post-irradiation. Analysis of the in vitro proteome showed that signalling pathways related to synaptic actin-remodelling were significantly affected at 1.0 Gy and 4.0 Gy but not at 0.5 Gy after 4 and 24 hours. We observed radiation-induced reduction of the miR-132 and Rac1 levels; miR-132 is known to regulate Rac1 activity by blocking the GTPase-activating protein p250GAP. In the irradiated hippocampus and cortex we observed alterations in the signalling pathways similar to those in vitro. The decreased expression of miR-132 and Rac1 was associated with an increase in hippocampal cofilin and phospho-cofilin. The Rac1-Cofilin pathway is involved in the modulation of synaptic actin filament formation that is necessary for correct spine and synapse morphology to enable processes of learning and memory. We suggest that acute radiation exposure leads to rapid dendritic spine and synapse morphology alterations via aberrant cytoskeletal signalling and processing and that this is associated with the immediate neurocognitive side effects observed in patients treated with ionising radiation. 相似文献
988.
989.
990.