全文获取类型
收费全文 | 2403篇 |
免费 | 255篇 |
国内免费 | 15篇 |
出版年
2022年 | 26篇 |
2021年 | 54篇 |
2020年 | 22篇 |
2019年 | 34篇 |
2018年 | 57篇 |
2017年 | 50篇 |
2016年 | 70篇 |
2015年 | 116篇 |
2014年 | 108篇 |
2013年 | 125篇 |
2012年 | 155篇 |
2011年 | 165篇 |
2010年 | 94篇 |
2009年 | 114篇 |
2008年 | 102篇 |
2007年 | 114篇 |
2006年 | 114篇 |
2005年 | 118篇 |
2004年 | 90篇 |
2003年 | 85篇 |
2002年 | 84篇 |
2001年 | 61篇 |
2000年 | 59篇 |
1999年 | 52篇 |
1998年 | 17篇 |
1997年 | 26篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 23篇 |
1993年 | 14篇 |
1992年 | 31篇 |
1991年 | 33篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 37篇 |
1985年 | 20篇 |
1984年 | 26篇 |
1983年 | 16篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1973年 | 13篇 |
1971年 | 11篇 |
1970年 | 10篇 |
1968年 | 15篇 |
1967年 | 19篇 |
排序方式: 共有2673条查询结果,搜索用时 640 毫秒
101.
Eunice Sok Ping Leong Yan Jun Liu Chan Choy Chum Jing Hua Teng 《Plasmonics (Norwell, Mass.)》2013,8(2):1221-1226
Optical magnetic responses were demonstrated in subwavelength Ag–MgF2–Ag grating structures for transverse magnetic-polarized light. The subwavelength Ag–MgF2–Ag grating structures were fabricated using e-beam lithography followed by a lift-off process. By fixing the Ag–MgF2–Ag strip dimension, the effect of the stripe width on the magnetic resonances was compared for two different grating pitches. With further reduced grating pitch, we pushed the optical magnetic resonances to near UV (deep blue). Numerical simulations confirmed our experimental observations and were in good agreement with the experimental results. 相似文献
102.
Yee-Shan Ku Nicolas Siu-Chung Koo Francisca Wing-Yen Li Man-Wah Li Hongmei Wang Sau-Na Tsai Feng Sun Boon Leong Lim Wing-Hung Ko Hon-Ming Lam 《PloS one》2013,8(10)
Inositol polyphosphatases are important regulators since they control the catabolism of phosphoinositol derivatives, which are often signaling molecules for cellular processes. Here we report on the characterization of one of their members in soybean, GmSAL1. In contrast to the substrate specificity of its Arabidopsis homologues (AtSAL1 and AtSAL2), GmSAL1 only hydrolyzes inositol-1,4,5-trisphosphate (IP3) but not inositol-1,3,4-trisphosphate or inositol-1,4-bisphosphate.The ectopic expression of GmSAL1 in transgenic Arabidopsis thaliana led to a reduction in IP3 signals, which was inferred from the reduction in the cytoplasmic signals of the in vivo biomarker pleckstrin homology domain–green florescent protein fusion protein and the suppression of abscisic acid-induced stomatal closure. At the cellular level, the ectopic expression of GmSAL1 in transgenic BY-2 cells enhanced vacuolar Na+ compartmentalization and therefore could partially alleviate salinity stress. 相似文献
103.
Van Lun Low Chee Dhang Chen Han Lim Lee Tiong Kai Tan Chin Fong Chen Cherng Shii Leong Yvonne Ai Lian Lim Phaik Eem Lim Yusoff Norma-Rashid Mohd Sofian-Azirun 《PloS one》2013,8(11)
Background
There has been no comprehensive study on biochemical characterization of insecticide resistance mechanisms in field populations of Malaysian Culex quinquefasciatus. To fill this void in the literature, a nationwide investigation was performed to quantify the enzyme activities, thereby attempting to characterize the potential resistance mechanisms in Cx. quinquefasciatus in residential areas in Malaysia.Methodology/Principal Findings
Culex quinquefasciatus from 14 residential areas across 13 states and one federal territory were subjected to esterases, mixed function oxidases, glutathione-S-transferase and insensitive acetylcholinesterase assays. Enzyme assays revealed that α-esterases and β-esterases were elevated in 13 populations and 12 populations, respectively. Nine populations demonstrated elevated levels of mixed function oxidases and glutathione-S-transferase. Acetylcholinesterase was insensitive to propoxur in all 14 populations. Activity of α-esterases associated with malathion resistance was found in the present study. In addition, an association between the activity of α-esterases and β-esterases was also demonstrated.Conclusions/Significance
The present study has characterized the potential biochemical mechanisms in contributing towards insecticide resistance in Cx. quinquefasciatus field populations in Malaysia. Identification of mechanisms underlying the insecticide resistance will be beneficial in developing effective mosquito control programs in Malaysia. 相似文献104.
105.
Masaru Matsumoto Myo Zaw Seint San Aye 《Archives Of Phytopathology And Plant Protection》2013,46(13-16):777-784
A modified baiting technique was conducted for selective isolation, fungal DNA diagnosis and fungal cell lipid assay derived from Myanmar isolates of Rhizoctonia spp., causal agents of rice sheath diseases by trapping selective plant stem segments. Bait plant materials of rice, mat rush and cotton were successfully used to isolate R. solani AG1-IA, R. oryzae and R. oryzae-sativae. Moreover, the three plant materials were also effectively used to detect genomic DNA derived from all Rhizoctonia spp. obtained from Myanmar. Rice segment was the most successful materials for detection of fungal cell lipids including palmitic, stearic and linoleic acids. The results of this experiment demonstrate that bait plant materials of rice, mat rush and cotton were the best useful tools for not only direct isolation, but also fungal DNA diagnosis and cell lipid assay of Myanmar soil environmental conditions. 相似文献
106.
Biao Wang Zhaoliang Liu Mingfeng Zhang Xiuying San Yanding Zhang Weiqiang Zhang Meishui Wang 《Molecular biology reports》2013,40(2):1463-1471
To investigate the intervention therapy effect on the growth of malignant melanoma, we have made an observation of expression levels of Ang2 in malignant melanoma cells, which was transduced by small interfering RNA (Ang2-siRNA) of Ang2 in vitro and in vivo. We successfully constructed Ang2-siRNA lent virus, and constructed nude mice model by transplanting malignant melanoma. Ang2-siRNA lent virus inhibited Ang2 mRNA of malignant melanoma in vitro and in vivo, and inhibited malignant melanoma tumor growth at the same time. Ang2-siRNA lent virus can interfere expression levels of Ang2 in malignant melanoma cells, inhibit tumor growth, and silent Ang2 gene expression, which may pave a new way for clinical gene therapy of malignant melanoma. 相似文献
107.
Claudia Quezada Wallys Garrido Carlos Oyarzún Katia Fernández Rodrigo Segura Rómulo Melo Paola Casanello Luis Sobrevia Rody San Martín 《Journal of cellular physiology》2013,228(3):602-608
Glioblastoma multiforme (GBM) cells are characterised by their extreme chemoresistance. The activity of multiple‐drug resistance (MDR) transporters that extrude antitumor drugs from cells plays the most important role in this phenomenon. To date, the mechanism controlling the expression and activity of MDR transporters is poorly understood. Activity of the enzyme ecto‐5′‐nucleotidase (CD73) in tumor cells, which hydrolyses AMP to adenosine, has been linked to immunosuppression and prometastatic effects in breast cancer and to the proliferation of glioma cells. In this study, we identify a high expression of CD73 in surgically resected samples of human GBM. In primary cultures of GBM, inhibition of CD73 activity or knocking down its expression by siRNA reversed the MDR phenotype and cell viability was decreased up to 60% on exposure to the antitumoral drug vincristine. This GBM chemosensitization was caused by a decrease in the expression and activity of the multiple drug associated protein 1 (Mrp1), the most important transporter conferring multiple drug resistance in these cells. Using pharmacological modulators, we have recognized the adenosine A3 receptor subtype in mediation of the chemoresistant phenotype in these cells. In conclusion, we have determined that the activity of CD73 to trigger adenosine signaling sustains chemoresistant phenotype in GBM cells. J. Cell. Physiol. 228: 602–608, 2013. © 2012 Wiley Periodicals, Inc. 相似文献
108.
Divyendu Singh Rongsu Qi Jarrat L. Jordan Lani San Mateo C. Cheng Kao 《The Journal of biological chemistry》2013,288(12):8258-8268
LL-37 is an antimicrobial peptide produced by human cells that can down-regulate the lipopolysaccharide-induced innate immune responses and up-regulate double-stranded (ds) RNA-induced innate responses through Toll-like receptor 3 (TLR3). The murine LL-37 ortholog, mCRAMP, also inhibited lipopolysaccharide-induced responses, but unlike LL-37, it inhibited viral-induced responses in mouse cells. A fluorescence polarization assay showed that LL-37 was able to bind dsRNA better than mCRAMP. In the human lung epithelial cell line BEAS-2B, LL-37, but not mCRAMP, colocalized with TLR3, and the colocalization was increased in the presence of dsRNA. The presence of poly(I:C) increased the accumulation of LL-37 in Rab5 endosomes. Signaling by cells induced with both LL-37 and poly(I:C) was sensitive to inhibitors that affect clathrin-independent trafficking, whereas signaling by poly(I:C) alone was not, suggesting that the LL-37-poly(I:C) complex trafficked to signaling endosomes by a different mechanism than poly(I:C) alone. siRNA knockdown of known LL-37 receptors identified that FPRL1 was responsible for TLR3 signaling induced by LL-37-poly(I:C). These results show that LL-37 and mCRAMP have different activities in TLR3 signaling and that LL-37 can redirect trafficking of poly(I:C) to effect signaling by TLR3 in early endosomes in a mechanism that involves FPRL1. 相似文献
109.
Jenifer L. Smith Kassandra I. Rossiter Christopher M. Semko Ying-Zi Xu David A. Quincy Jacek Jagodzinski Michael S. Dappen Andrei W. Konradi Christopher Vandevert Caroline Garrido Wenxian Mao F. Bong San Pablo Brian Wipke Lilibeth Dofiles Angie Wadsworth Eric Peterson Carlos Lorenzana Stellanie Simmonds Ted A. Yednock 《Bioorganic & medicinal chemistry letters》2013,23(14):4117-4119
Mitsunobu reactions were employed to link t-butyl esters of α4 integrin inhibitors at each of the termini of a three-arm, 40 kDa, branched PEG. Cleavage of the t-butyl esters using HCO2H provided easily isolated PEG derivatives, which are potent α4 integrin inhibitors, and which achieve sustained levels and bioactivity in vivo, following subcutaneous administration to rats. 相似文献
110.
Karl P. Phillips Tove H. Jorgensen Kevin G. Jolliffe San‐Marie Jolliffe Jock Henwood David S. Richardson 《Molecular ecology》2013,22(8):2301-2312
Postcopulatory sperm storage can serve a range of functions, including ensuring fertility, allowing delayed fertilization and facilitating sexual selection. Sperm storage is likely to be particularly important in wide‐ranging animals with low population densities, but its prevalence and importance in such taxa, and its role in promoting sexual selection, are poorly known. Here, we use a powerful microsatellite array and paternal genotype reconstruction to assess the prevalence of sperm storage and test sexual selection hypotheses of genetic biases to paternity in one such species, the critically endangered hawksbill turtle, Eretmochelys imbricata. In the majority of females (90.7%, N = 43), all offspring were sired by a single male. In the few cases of multiple paternity (9.3%), two males fertilized each female. Importantly, the identity and proportional fertilization success of males were consistent across all sequential nests laid by individual females over the breeding season (up to five nests over 75 days). No males were identified as having fertilized more than one female, suggesting that a large number of males are available to females. No evidence for biases to paternity based on heterozygosity or relatedness was found. These results indicate that female hawksbill turtles are predominantly monogamous within a season, store sperm for the duration of the nesting season and do not re‐mate between nests. Furthermore, females do not appear to be using sperm storage to facilitate sexual selection. Consequently, the primary value of storing sperm in marine turtles may be to uncouple mating and fertilization in time and avoid costly re‐mating. 相似文献