全文获取类型
收费全文 | 4054篇 |
免费 | 255篇 |
国内免费 | 8篇 |
专业分类
4317篇 |
出版年
2024年 | 12篇 |
2023年 | 40篇 |
2022年 | 126篇 |
2021年 | 168篇 |
2020年 | 165篇 |
2019年 | 264篇 |
2018年 | 233篇 |
2017年 | 155篇 |
2016年 | 189篇 |
2015年 | 194篇 |
2014年 | 277篇 |
2013年 | 353篇 |
2012年 | 368篇 |
2011年 | 334篇 |
2010年 | 183篇 |
2009年 | 148篇 |
2008年 | 165篇 |
2007年 | 200篇 |
2006年 | 141篇 |
2005年 | 119篇 |
2004年 | 86篇 |
2003年 | 107篇 |
2002年 | 87篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1966年 | 3篇 |
1961年 | 2篇 |
排序方式: 共有4317条查询结果,搜索用时 0 毫秒
991.
992.
Reza Zamiri Hossein Abbastabar Ahangar Ajay Kaushal Azmi Zakaria Golnoosh Zamiri David Tobaldi J. M. F. Ferreira 《PloS one》2015,10(4)
A template-free precipitation method was used as a simple and low cost method for preparation of CeO2 nanoparticles. The structure and morphology of the prepared nanoparticle samples were studied in detail using X-ray diffraction, Raman spectroscopy and Scanning Electron Microscopy (SEM) measurements. The whole powder pattern modelling (WPPM) method was applied on XRD data to accurately measure the crystalline domain size and their size distribution. The average crystalline domain diameter was found to be 5.2 nm, with a very narrow size distribution. UV-visible absorbance spectrum was used to calculate the optical energy band gap of the prepared CeO2 nanoparticles. The FT-IR spectrum of prepared CeO2 nanoparticles showed absorption bands at 400 cm-1 to 450 cm-1 regime, which correspond to CeO2 stretching vibration. The dielectric constant (εr) and dielectric loss (tan δ) values of sintered CeO2 compact consolidated from prepared nanoparticles were measured at different temperatures in the range from 298 K (room temperature) to 623 K, and at different frequencies from 1 kHz to 1 MHz. 相似文献
993.
Hamid Tanzadehpanah Massoud Saidijam Jamshidkhan Chamani Hanie Mahaki 《Journal of biomolecular structure & dynamics》2013,31(14):3803-3818
Bioactive peptides have been defined as specific protein fragments that have numerous biological activities. The aim of this study was to introduce three multifunctional peptides. Hence, we used rabbit lung angiotensin converting enzyme (ACE) inhibitor peptide AFKDEDTEEVPFR to prepare two analogous peptides KDEDTEEVP and KDEDTEEVH. ACE inhibitory, antioxidant, and antimicrobial activities of three synthetic peptides were investigated. Among the three peptides, KDEDTEEVP exhibited the highest ACE inhibitory activity with IC50 value of 69.63 ± 2.51 μM. Furthermore, the results of fluorescence spectroscopy and molecular modeling showed that KDEDTEEVP had more affinity to ACE than other peptides. The peptide of KDEDTEEVH showed the strongest antioxidant scavenging capacity on DPPH radicals (EC50 = 135 ± 9.62 μM), hydroxyl radicals (EC50 = 144 ± 8.73 μM), and ABTS radicals (EC50 = 62 ± 4.52%). Moreover, it showed the highest activity in iron-chelating test (EC50 = 226 ± 14.13 μM) and could also effectively inhibit the peroxidation of linoleic acid. The antimicrobial activity results showed that KDEDTEEVH had higher efficiency against Gram-positive than Gram-negative bacteria with MIC values of higher than 205 ± 10.75 μM. Although there was not a direct correlation between ACE inhibitor and antioxidant activity for analogous peptides, both analogous peptides exhibited more efficiency than the mother peptide. Thus, they can be considered as multifunctional peptides and would be beneficial ingredient to be used in food and drug industry. 相似文献
994.
Jamshid Faraji Nabiollah Soltanpour Seyed Yaghoob Jafari Reza Moeeini Shiva Pakdel Alireza Moharreri Gerlinde A.S. Metz 《Hormones and behavior》2014
Stress affects psychomotor profiles and exploratory behavior in response to environmental features. Here we investigated psychomotor and exploratory patterns induced by stress in a simple open-field arena and a complex, multi-featured environment. Groups of rats underwent seven days of restraint stress or no-stress conditions and were individually tested in three versions of the ziggurat task (ZT) that varied according to environmental complexity. The hyperactivity of the hypothalamic–pituitary–adrenal (HPA) axis due to stress procedure was evaluated by the pre- and post-stress levels of circulating corticosterone (CORT). Horizontal activity, exploration, and motivation were measured by the number of fields entered, the time spent in the central fields, path length and speed, and stop duration. In addition, vertical exploratory behavior was measured by the times rats climbed onto ziggurats. Stress-induced psychomotor changes were indicated by reduced path length and path speed and increased duration of stops only within the complex arena of the ZT. Rats in stress groups also showed a significant decline in the vertical movements as measured by the number of climbing onto ziggurats. No stress-induced changes were revealed by the simple open-field arena. The exploratory patterns of stressed animals suggest psychomotor inhibition and reduced novelty-seeking behaviors in an environment-dependent manner. Thus, multi-featured arenas that require complex behavioral strategies are ideally suited to reveal the inhibitory effects of stress on psychomotor capabilities in rodents. 相似文献
995.
Mohammad Tajfard Seyedeh Belin Tavakoly Sany Amir Avan Latiffah A. Latiff Hamid Reza Rahimi Mohsen Moohebati Mehdi Hasanzadeh Hamideh Ghazizadeh Habibollah Esmaeily Hassan Doosti Ali Taghipour Majid Ghayour-Mobarhan Gordon A. Ferns Marzie Emamian Mohd Sokhini Bin Abd Mutalib 《Journal of cellular physiology》2019,234(7):10289-10299
Serum high-sensitivity C-reactive protein (hs-CRP) is predictive of coronary artery disease (CAD). The aim of this study was to examine the possible association of hs-CRP with presence and severity of CAD and traditional CAD risk factors. This case-control study was carried out on 2,346 individuals from September 2011 to May 2013. Of these 1,187 had evidence of coronary disease, and were subject to coronary angiography, and the remainder were healthy controls (n = 1,159). Characteristics were determined using standard laboratory techniques and serum Hs-CRP levels were estimated using enzyme-linked immunosorbent assay (ELISA) kits, and severity of CAD was assessed according to the score of obstruction in coronary artery. Serum hs-CRP levels were higher in those with severe coronary disease, who had stenosis ≥ 50% stenosis of at least one coronary artery (all p < 0.001 vs. individuals in healthy control), and correlated significantly with the score for coronary artery disease (all p < 0.01). After adjustment for conventional risk factors, regression analysis revealed that smoking habits, fasting blood glucose, total cholesterol, high-density lipoprotein, hs-CRP, blood pressure, anxiety, dietary intake of vitamin E, and cholesterol remained as independent determinants for angiographic severity of CAD. The area under the receiving operating characteristic (ROC) curve for serum hs-CRP was 0.869 (CI 95% 0.721–0.872, p < 0.001). The optimal values for the cut-off point was a serum hs-CRP of 2.78 mg/l (sensitivity 80.20%, specificity 85%) to predict severity of CAD. Increased serum hs-CRP levels are significantly associated with angiographic severity of CAD, suggesting its value as a biomarkers for predicting CAD. 相似文献
996.
Elias Ebrahimzadeh Mohammad Shams Ali Rahimpour Jounghani Farahnaz Fayaz Mahya Mirbagheri Naser Hakimi Lila Rajabion Hamid Soltanian-Zadeh 《Cognitive neurodynamics》2021,15(2):207
Precise localization of epileptic foci is an unavoidable prerequisite in epilepsy surgery. Simultaneous EEG-fMRI recording has recently created new horizons to locate foci in patients with epilepsy and, in comparison with single-modality methods, has yielded more promising results although it is still subject to limitations such as lack of access to information between interictal events. This study assesses its potential added value in the presurgical evaluation of patients with complex source localization. Adult candidates considered ineligible for surgery on account of an unclear focus and/or presumed multifocality on the basis of EEG underwent EEG-fMRI. Adopting a component-based approach, this study attempts to identify the neural behavior of the epileptic generators and detect the components-of-interest which will later be used as input in the GLM model, substituting the classical linear regressor. Twenty-eight sets interictal epileptiform discharges (IED) from nine patients were analyzed. In eight patients, at least one BOLD response was significant, positive and topographically related to the IEDs. These patients were rejected for surgery because of an unclear focus in four, presumed multifocality in three, and a combination of the two conditions in two. Component-based EEG-fMRI improved localization in five out of six patients with unclear foci. In patients with presumed multifocality, component-based EEG-fMRI advocated one of the foci in five patients and confirmed multifocality in one of the patients. In seven patients, component-based EEG-fMRI opened new prospects for surgery and in two of these patients, intracranial EEG supported the EEG-fMRI results. In these complex cases, component-based EEG-fMRI either improved source localization or corroborated a negative decision regarding surgical candidacy. As supported by the statistical findings, the developed EEG-fMRI method leads to a more realistic estimation of localization compared to the conventional EEG-fMRI approach, making it a tool of high value in pre-surgical evaluation of patients with refractory epilepsy. To ensure proper implementation, we have included guidelines for the application of component-based EEG-fMRI in clinical practice. 相似文献
997.
S. Akram Shirdel Khosro Khajeh S. Mohsen Asghari Hamid‐Reza Karbalaei‐Heidari 《Engineering in Life Science》2014,14(2):229-234
Neutral proteases are inactivated at higher temperatures because of autolysis. It appears that autolysis involves some specific solvent‐exposed regions that become prone to local unfolding as temperature increases. Accordingly, we designed surface‐located mutations at the N‐terminal loops (A56P and T73F) of the neutral protease from Salinivibrio proteolyticus and compared the thermostability and autolysis as well as structural properties of wild‐type (WT) and mutant proteins. Circular dichroism in far‐UV region and intrinsic fluorescence data indicated that compactness of protein increases upon mutation. It was revealed that the catalytic efficiency (kcat/Km) of the enzyme is improved in mutants and optimum temperature of mutants increases relative to WT enzyme. It was also shown that the mutant enzymes are more resistant against autolysis and their thermostability and kinetic parameters are also changed compared to WT protein. This study shows that the stability of enzyme against autolysis and temperature may be increased even by changing only a single amino acid, which in turn is important from application point of view. 相似文献
998.
999.
1000.
A gain-field encoding of limb position and velocity in the internal model of arm dynamics 总被引:1,自引:1,他引:1
Adaptability of reaching movements depends on a computation in the brain that transforms sensory cues, such as those that indicate the position and velocity of the arm, into motor commands. Theoretical consideration shows that the encoding properties of neural elements implementing this transformation dictate how errors should generalize from one limb position and velocity to another. To estimate how sensory cues are encoded by these neural elements, we designed experiments that quantified spatial generalization in environments where forces depended on both position and velocity of the limb. The patterns of error generalization suggest that the neural elements that compute the transformation encode limb position and velocity in intrinsic coordinates via a gain-field; i.e., the elements have directionally dependent tuning that is modulated monotonically with limb position. The gain-field encoding makes the counterintuitive prediction of hypergeneralization: there should be growing extrapolation beyond the trained workspace. Furthermore, nonmonotonic force patterns should be more difficult to learn than monotonic ones. We confirmed these predictions experimentally. 相似文献