全文获取类型
收费全文 | 545篇 |
免费 | 52篇 |
国内免费 | 66篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 18篇 |
2016年 | 14篇 |
2015年 | 21篇 |
2014年 | 35篇 |
2013年 | 35篇 |
2012年 | 38篇 |
2011年 | 43篇 |
2010年 | 28篇 |
2009年 | 20篇 |
2008年 | 30篇 |
2007年 | 24篇 |
2006年 | 32篇 |
2005年 | 25篇 |
2004年 | 27篇 |
2003年 | 25篇 |
2002年 | 29篇 |
2001年 | 23篇 |
2000年 | 12篇 |
1999年 | 27篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 1篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1965年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有663条查询结果,搜索用时 15 毫秒
71.
自1950s以来,我国玉米(Zea
mays L.)产量以年递增幅度为126kg 相似文献
72.
The cell polarity protein ASIP/PAR-3 directly associates with junctional adhesion molecule (JAM). 总被引:20,自引:0,他引:20
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
K Ebnet A Suzuki Y Horikoshi T Hirose M K Meyer Zu Brickwedde S Ohno D Vestweber 《The EMBO journal》2001,20(14):3738-3748
The establishment and maintenance of cellular polarity are critical for the development of multicellular organisms. PAR (partitioning-defective) proteins were identified in Caenorhabditis elegans as determinants of asymmetric cell division and polarized cell growth. Recently, vertebrate orthologues of two of these proteins, ASIP/PAR-3 and PAR-6, were found to form a signalling complex with the small GTPases Cdc42/Rac1 and with atypical protein kinase C (PKC). Here we show that ASIP/PAR-3 associates with the tight-junction-associated protein junctional adhesion molecule (JAM) in vitro and in vivo. No binding was observed with claudin-1, -4 or -5. In fibroblasts and CHO cells overexpressing JAM, endogenous ASIP is recruited to JAM at sites of cell-cell contact. Over expression of truncated JAM lacking the extracellular part disrupts ASIP/PAR-3 localization at intercellular junctions and delays ASIP/PAR-3 recruitment to newly formed cell junctions. During junction formation, JAM appears early in primordial forms of junctions. Our data suggest that the ASIP/PAR-3-aPKC complex is tethered to tight junctions via its association with JAM, indicating a potential role for JAM in the generation of cell polarity in epithelial cells. 相似文献
73.
Expression and localization of P-glycoprotein in human heart: effects of cardiomyopathy. 总被引:7,自引:0,他引:7
Konrad Meissner Bernhard Sperker Christiane Karsten Henriette Meyer Zu Schwabedissen Ute Seeland Michael B?hm Sandra Bien Peter Dazert Christiane Kunert-Keil Silke Vogelgesang Rolf Warzok Werner Siegmund Ingolf Cascorbi Michael Wendt Heyo K Kroemer 《The journal of histochemistry and cytochemistry》2002,50(10):1351-1356
ABC-type transport proteins, such as P-glycoprotein (P-gp), modify intracellular concentrations of many substrate compounds. They serve as functional barriers against entry of xenobiotics (e.g., in the gut or the blood-brain barrier) or contribute to drug excretion. Expression of transport proteins in the heart could be an important factor modifying cardiac concentrations of drugs known to be transported by P-gp (e.g., beta-blockers, cardiac glycosides, doxorubicin). We therefore investigated the expression and localization of P-gp in human heart. Samples from 15 human hearts (left ventricle; five non-failing, five dilated cardiomyopathy, and five ischemic cardiomyopathy) were analyzed for expression of P-gp using real-time RT-PCR, immunohistochemistry, and in situ hybridization. Immunohistochemistry revealed expression of P-gp in endothelium of both arterioles and capillaries of all heart samples. Although P-gp mRNA was detected in all samples, its expression level was significantly reduced in patients with dilated cardiomyopathy. We describe variable expression of P-gp in human heart and its localization in the endothelial wall. Thus, intracardiac concentrations of various compounds may be modified, depending on the individual P-gp level. 相似文献
74.
75.
H Ballina-Gomez E Ruiz-Sanchez W Chan-Cupul L Latournerie-Moreno L Hernández-Alvarado I Islas-Flores J J Zuñiga-Aguilar 《Neotropical Entomology》2013,42(2):205-210
Bemisia tabaci Genn. biotype B is a widely distributed plant pest that represents one of the major constraints for horticultural crop production. The purpose of the present work was to evaluate the oviposition preference, survivorship, and development of B. tabaci biotype B on semi-cultivated genotypes of Capsicum annuum from southeast Mexico. In free-choice experiments to evaluate the oviposition preference, lower number of eggs laid by B. tabaci biotype B was observed in the genotypes Maax and Xcat´ik relative to that in the commercial genotype Parado. Egg hatchability was significantly lower in Pico Paloma, Bolita, Blanco, Chawa, Payaso, and Xcat´ik than in the rest of the genotypes, including the commercial genotype Jalapeño. Likewise, survivorship of nymphs was significantly lower in Pico Paloma, Bolita, and Blanco than in the remaining genotypes. Nymph developmental time and the period of development from egg to adult were the shortest in Amaxito. Therefore, sources of resistance to B. tabaci biotype B by antibiosis (accumulation of plant defense compounds) might be found in the semi-cultivated genotypes Pico Paloma, Bolita, and Blanco. 相似文献
76.
Iván González-Chavarría Rita P. Cerro Natalie P. Parra Felipe A. Sandoval Felipe A. Zu?iga Valeska A. Omazábal Liliana I. Lamperti Silvana P. Jiménez Edelmira A. Fernandez Nicolas A. Gutiérrez Federico S. Rodriguez Sergio A. Onate Oliberto Sánchez Juan C. Vera Jorge R. Toledo 《PloS one》2014,9(8)
Altered expression and function of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) has been associated with several diseases such as endothelial dysfunction, atherosclerosis and obesity. In these pathologies, oxLDL/LOX-1 activates signaling pathways that promote cell proliferation, cell motility and angiogenesis. Recent studies have indicated that olr1 mRNA is over-expressed in stage III and IV of human prostatic adenocarcinomas. However, the function of LOX-1 in prostate cancer angiogenesis remains to be determined. Our aim was to analyze the contribution of oxLDL and LOX-1 to tumor angiogenesis using C4-2 prostate cancer cells. We analyzed the expression of pro-angiogenic molecules and angiogenesis on prostate cancer tumor xenografts, using prostate cancer cell models with overexpression or knockdown of LOX-1 receptor. Our results demonstrate that the activation of LOX-1 using oxLDL increases cell proliferation, and the expression of the pro-angiogenic molecules VEGF, MMP-2, and MMP-9 in a dose-dependent manner. Noticeably, these effects were prevented in the C4-2 prostate cancer model when LOX-1 expression was knocked down. The angiogenic effect of LOX-1 activated with oxLDL was further demonstrated using the aortic ring assay and the xenograft model of tumor growth on chorioallantoic membrane of chicken embryos. Consequently, we propose that LOX-1 activation by oxLDL is an important event that enhances tumor angiogenesis in human prostate cancer cells. 相似文献
77.
BpH1, the Bordetella pertussis H1 homolog, interacts with chromosomal DNA. With DNase I protection assays, we demonstrate in this study that BpH1 binds DNA in a nonspecific manner and that it may cover DNA fragments from end to end. Although the binding was shown to be nonspecific, preferential binding sites and sites resistant to BpH1 binding were identified within and upstream of the pertussis toxin promoter sequence. In the presence of DNA ligase, BpH1 favored the formation of multimeric DNA fragments of various sizes and prevented ring closures, suggesting a diminished flexibility of the DNA fragments and thus indicating that BpH1 acts as a macromolecular crowding agent. 相似文献
78.
Nonlinear responses of productivity and diversity of alpine meadow communities to degradation北大核心CSCD
下载免费PDF全文
![点击此处可从《植物生态学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Chen N. Zhang Y.-J. Zhu J.-T. Li J.-X. Liu Y.-J. Zu J.-X. Cong N. Huang K. Wang L. 《植物生态学报》2018,(1):50-65
Aims The alpine meadow degradation could have profound effects on the grassland productivity. The aim of our study is to clarify the dynamic response of community productivity and species diversity in the process of alpine meadow degradation. Methods In the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Northern Tibetan Grassland Ecosystem Research Station (Nagqu station), we conducted stages experiments with multiple degradation levels: control, mild degraded meadow, moderate degraded meadow, severe degraded meadow and serious sandy meadow. Important findings The response of aboveground biomass to alpine meadow degradation showed a linear or nonlinear increased response patterns, but the belowground biomass and total biomass decreased nonlinearly. As observed in measurement of aboveground biomass, Margalef index, Simpson index, Shannon-Wiener index and Pielou evenness index also exhibit a nonlinear increased response to degradation. The results of structural equation models showed that belowground biomass has a positive relationship with soil carbon content (p < 0.05) and volume water content (p < 0.1). However, soil nutrient and soil physical properties had no significant impact on aboveground biomass (p < 0.1). Compared with soil physical properties, soil nutrition is an important factor influencing the diversity index. In our study, the nonlinear responses of productivity and diversity of alpine meadow were described by using the multiple levels of degradation in space. The results suggested that aboveground productivity cannot interpret the degree of degradation of alpine meadow, and by contrast, alpine meadow degradation should be measured by the change of plant functional groups, such as edible grasses and poisonous forbs. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved. 相似文献
79.
Resistance-related physiological response of rice leaves to the compound stress of enhanced UV-B radiation and Magnaporthe oryzae 总被引:1,自引:0,他引:1
Yongmei He Xiang Li Fangdong Zhan Chunmei Xie Yanqun Zu Yuan Li 《Journal of Plant Interactions》2018,13(1):321-328
An enhanced UV-B radiation (5.0?kJ?m?2) was supplied before, during, and after Magnaporthe oryzae infection. The effects of single and compound stress of the UV-B radiation and M. oryzae on the resistance physiology and gene expression of rice leaves were examined. Results revealed that UV-B radiation given before M. oryzae infection (UV-B?→?M.) significantly increased the pathogenesis-related proteins (PRs) activities of phenylalanine ammonialyase (PAL), lipoxygenase (LOX), chitinase (CHT), and β-1,3-glucanase, the resistance-related substances (flavonoids and total phenols) content, and resistance-related genes (OsPAL and OsCHT) expression, thereby improving the disease resistance of rice leaves. Simultaneous exposure to UV-B radiation and M. oryzae (UV-B/M.) significantly increased the OsLOX2 expression and the PRs activities. Exposure to UV-B radiation after M. oryzae infection (M.?→?UV-B) decreased the flavonoid content, did not improve the PRs activity, and increased OsLOX2 expression. Compound treatments of UV-B?→?M., UV-B/M., and M.?→?UV-B reduced the disease index by 62.3%, 40.2%, and 26.6%, respectively, indicating UV-B radiation inhibited the occurrence of M. oryzae disease, but its inhibitory effect weakened when it was provided after M. oryzae infection. Hence, rice responded to the compound stress of UV-B radiation and M. oryzae through a resistance-related physiological mechanism associated with the sequence of stress occurrence. 相似文献
80.
Xiaofeng Zu Ping Liu Shunxi Wang Lei Tian Zhiqiang Tian Yanhui Chen Liuji Wu 《Plant Molecular Biology Reporter》2018,36(2):310-325
Histidine triad nucleotide-binding protein 1 (HINT1) is highly conserved in many species and plays important roles in various biological processes. However, little is known about the responses of HINT1 to abiotic stress in plants. Salt and drought stress are major limiting factors for plant growth and development, and their negative effects on crop productivity may threaten the world’s food supply. Previously, we identified a maize gene, Zm-HINT1, which encodes a 138-amino-acid protein containing conserved domains including the HIT motif, helical regions, and β-strands. Here, we demonstrate that overexpression of Zm-HINT1 in Arabidopsis confers salt and drought tolerance to plants. Zm-HINT1 significantly regulated Na+ and K+ accumulation in plants under salt stress. The improve tolerance characteristics of Arabidopsis plants that were overexpressing Zm-HINT1 led to increased survival rates after salt and drought treatments. Compared with control plants, those plants that overexpressed Zm-HINT1 showed increased proline content and superoxide dismutase activity, as well as lower malondialdehyde and hydrogen peroxide accumulation under salt and drought treatments. The expression patterns of stress-responsive genes in Arabidopsis plants that overexpressed Zm-HINT1 significantly differed from those in control lines. Taken together, these results suggest that Zm-HINT1 has potential applications in breeding and genetic engineering strategies that are designed to produce new crop varieties with improved salt and drought tolerance. 相似文献