全文获取类型
收费全文 | 4507篇 |
免费 | 328篇 |
出版年
2023年 | 23篇 |
2022年 | 54篇 |
2021年 | 128篇 |
2020年 | 79篇 |
2019年 | 96篇 |
2018年 | 132篇 |
2017年 | 107篇 |
2016年 | 175篇 |
2015年 | 253篇 |
2014年 | 265篇 |
2013年 | 369篇 |
2012年 | 407篇 |
2011年 | 388篇 |
2010年 | 236篇 |
2009年 | 234篇 |
2008年 | 301篇 |
2007年 | 252篇 |
2006年 | 216篇 |
2005年 | 224篇 |
2004年 | 200篇 |
2003年 | 183篇 |
2002年 | 145篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 24篇 |
1998年 | 23篇 |
1997年 | 28篇 |
1996年 | 29篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有4835条查询结果,搜索用时 31 毫秒
971.
Chiara Giverso Alessandro Arduino Luigi Preziosi 《Bulletin of mathematical biology》2018,80(5):1017-1045
In order to move in a three-dimensional extracellular matrix, the nucleus of a cell must squeeze through the narrow spacing among the fibers and, by adhering to them, the cell needs to exert sufficiently strong traction forces. If the nucleus is too stiff, the spacing too narrow, or traction forces too weak, the cell is not able to penetrate the network. In this article, we formulate a mathematical model based on an energetic approach, for cells entering cylindrical channels composed of extracellular matrix fibers. Treating the nucleus as an elastic body covered by an elastic membrane, the energetic balance leads to the definition of a necessary criterion for cells to pass through the regular network of fibers, depending on the traction forces exerted by the cells (or possibly passive stresses), the stretchability of the nuclear membrane, the stiffness of the nucleus, and the ratio of the pore size within the extracellular matrix with respect to the nucleus diameter. The results obtained highlight the importance of the interplay between mechanical properties of the cell and microscopic geometric characteristics of the extracellular matrix and give an estimate for a critical value of the pore size that represents the physical limit of migration and can be used in tumor growth models to predict their invasive potential in thick regions of ECM. 相似文献
972.
Alessandro Agostini Jens Niklas Tim Schulte Marilena Di Valentin Marco Bortolus Eckhard Hofmann Wolfgang Lubitz Donatella Carbonera 《BBA》2018,1859(8):612-618
The peridinin–chlorophyll-a protein (PCP) is a water-soluble light harvesting protein of the dinoflagellate Amphidinium carterae, employing peridinin (Per) as the main carotenoid to fulfil light harvesting and photo-protective functions. Per molecules bound to the protein experience specific molecular surroundings which lead to different electronic and spectral properties. In the refolded N89?L variant PCP (N89?L-RFPCP) a significant part of the intensity on the long wavelength side of the absorption spectrum is shifted to shorter wavelengths due to a significant change in the Per-614 site energy. Since Per-614 has been shown to be the main chlorophyll (Chl) triplet quencher in the protein, and the relative geometry of pigments is not affected by the mutation as verified by X-ray crystallography, this variant is ideally suited to study the dependence of the triplet-triplet energy transfer (TTET) mechanism on the pigment site energy. By using a combination of Optically Detected Magnetic Resonance (ODMR), pulse Electron Paramagnetic Resonance (EPR) and Electron Nuclear DOuble Resonance (ENDOR) we found that PCP maintains the efficient Per-614-to-Chl-a TTET despite the change of Per-614 local energy. This shows the robustness of the photoprotective site, which is very important for the protection of the system. 相似文献
973.
Fatal primary diffuse large B‐cell lymphoma of the maxillary sinus initially treated as an infectious disease in an elderly patient: A clinicopathologic report 下载免费PDF全文
Mayara Santos de Castro Cínthia Magalhães Ribeiro Marina Lara de Carli Alessandro Antônio Costa Pereira Felipe Fornias Sperandio Oslei Paes de Almeida João Adolfo Costa Hanemann 《Gerodontology》2018,35(1):59-62
Objective
To report a case of primary diffuse large B‐cell lymphoma (DLBCL) of the maxillary sinus in an 82‐year‐old Caucasian woman.Background
Diffuse large B‐cell lymphoma of the maxillary sinus has non‐specific signs and symptoms that may be confused with benign inflammatory conditions and upper respiratory infections.Methods
An incisional biopsy was performed. CD20+/CD3–/Ki‐67: 95% cells were observed.Conclusion
A good medical history, clinical and imaging evaluations and immunohistochemical reactions are crucial to establish a correct and early diagnosis of DLBCL. 相似文献974.
Alessandro Jedlowski 《Visual Anthropology: Published in cooperation with the Commission on Visual Anthropology》2018,31(3):236-252
This article analyzes the ways in which a Nigerian video film about human trafficking is received by Nigerian women who have themselves experienced trafficking in their migration to Italy. This contextualized case study is used as a methodological “lockpick” to open up new lines of enquiry into the relationship that southern Nigerian video films create with their audiences. The essay argues that, by virtue of their specific “addressivity,” the genre of Nigerian video films that focus on female migration and prostitution participates in the creation of moral publics that are concerned with the definition of the postcolonial subject’s responsibility in shaping his/her own destiny. 相似文献
975.
Mattia Mori Davide Deodato Mohan Kasula Davide M. Ferraris Adriana Sanna Alessandro De Logu Menico Rizzi Maurizio Botta 《Bioorganic & medicinal chemistry letters》2018,28(4):637-641
Sixteen 3-(carboxymethyl)rhodanines, and twelve aminothiazoles as rhodanine-mimetics were designed, synthesized and tested as inhibitors of the Zmp1 enzyme from Mycobacterium tuberculosis (Mtb). Almost all rhodanines (5a–d, 5f–n, and 7a–b) exhibited Zmp1 inhibition with IC50 values in the range 1.3–43.9?µM, whereas only aminothiazoles 12b and 12d proved active with IC50 values of 41.3 and 35.7?µM, respectively. Structure-activity relationships (SAR) were coupled with molecular modeling studies to highlight structural determinants for Zmp1 inhibition. Moreover, rhodanines 5a and 5c induced 23.4 and 53.8% of Mtb growth inhibition in THP-1 infected cells, respectively, at the non-toxic concentration of 10?µg/ml. This work represents a step forward in targeting Zmp1 by small molecules. 相似文献
976.
Assessing and modeling seed germination of Mediterranean wildflowers for low input landscape restoration 下载免费PDF全文
Stefania Toscano Daniela Romano Alessandro Tribulato Valeria Cavallaro 《Restoration Ecology》2018,26(3):525-536
Native species are recommended for use in landscape restoration because they adapt well to the local pedo‐climatic conditions. Despite the high biodiversity in the Mediterranean, the use of native plants is hampered by the limited knowledge of their seed germination. This is particularly true for a number of plants which are appropriate for creating species‐rich herbaceous communities. In this study, seeds of 35 species were collected in different roadside and degraded sites in rural and urban areas. Two experiments were carried out to determine the influence of light and thermal conditions on seed germination. In the first experiment, seeds of 17 species were tested at different temperatures (5, 15, and 25°C). At 15°C, seed germination was tested under both dark and light conditions. In the second experiment, the germination of 30 species was tested under alternating temperatures (25/15°C) and dark/light conditions. The responses of the various species differed in relation to thermal levels and light conditions, e.g., Bartsia trixago did not germinate in the dark at constant temperatures (5, 15, and 25°C), while in the light (15°C) and at alternating temperatures (25/15°C) in light and dark conditions, germination was over 60%. In both experiments, Tragopogon porrifolius and Triticum ovatum showed the highest germination rate (≥88%). With the sole exception of Medicago orbicularis, all members of the Fabaceae showed no or low germination. The definition of the germination requirements of some Mediterranean species, highlighted in these experiments, provides useful information for the creation of low input green areas and environmental restoration using these species. 相似文献
977.
Massimiliano Tattini Riccardo Gucci Annalisa Romani Alessandro Baldi John D. Everard 《Physiologia plantarum》1996,98(1):117-124
Self-rooted olive ( Olea europaea L.) plants were grown in hydroponics at various NaCl concentrations (from 0 to 200m M ) for 28 to 32 days followed by 28 to 30 days of relief from salinity over two growing seasons. Olive leaves accumulated both glucose and mannitol during the period of salinity stress. The concentrations of fructose, myo -inositol, galactose, galactinol, sucrose, raffinose, and stachyose were not significantly affected by salinity. Starch content was decreased by salinity. The mannitol/glucose and mannitol/soluble carbohydrates ratios increased as the external NaCl concentration was increased, but returned to the control levels during the relief period. The increase in mannitol or glucose molar concentrations, expressed on a leaf tissue water basis, was partially due to a reduction in leaf tissue water content under salinity stress. However, an increase in mannitol concentration was also observed when expressed on a dry weight basis. The accumulation of mannitol in leaf tissue preceded any reduction in leaf area rate or net assimilation rate. The increase in leaf mannitol or glucose concentration was positively correlated with the increasing level of salinity at the root zone, but not with the accumulation of Na+ in the shoot. The role of mannitol. a potential osmoregulator in leaf mesophyll during salinity stress, is discussed in relation to the complex carbohydrate composition of olive leaves. 相似文献
978.
979.
980.
Alfredo Brusco Umberto Cariota Andrea Bottaro Cleide Boccazzi Alessandro Plebani Alberto G. Ugazio Renzo Galanello Maria G. Guerra Angelo O. Carbonara 《Human genetics》1995,95(3):319-326
The Immunoglobulin Heavy chain Constant region (IGHC) locus is a multigene family composed of highly homologous segments often involved in unequal crossings over that lead to deleted and duplicated haplotypes. The frequencies of these haplotypes in 558 individuals from Lombardy, Veneto, Puglia and Sardinia were determined by Pulsed Field Gel Electrophoresis (PFGE), followed by Southern blotting with four IGHC probes, and compared with those observed in 110 subjects from Piedmont. Twenty deletions and 60 duplications were characterized, all in heterozygous individuals except for 2 homozygous deletions. The differences in frequency between the five populations were not significant. The deletions/duplications involved one or more genes: GP-A2, A1-E and G4 duplications, and A1-E and GP-A2 deletions were the most common. Four new duplications are described: three, involving the genes from GP to A2, from G2 to G4, and G4, are counterparts of known deletions. The fourth duplication spans from GP to G2. A G1 deleted heterozygous individual never previously described in Italy is reported. All the rearranged haplotypes seem to be the result of unequal crossing over. The difference between the number of duplications and deletions was significant in Sardinia, Lombardy, Puglia and in the total of 668 subjects (P < 0.001). This may be due to selection or genetic drift. 相似文献