全文获取类型
收费全文 | 5562篇 |
免费 | 542篇 |
国内免费 | 796篇 |
出版年
2024年 | 9篇 |
2023年 | 71篇 |
2022年 | 172篇 |
2021年 | 303篇 |
2020年 | 223篇 |
2019年 | 250篇 |
2018年 | 210篇 |
2017年 | 182篇 |
2016年 | 222篇 |
2015年 | 351篇 |
2014年 | 415篇 |
2013年 | 469篇 |
2012年 | 558篇 |
2011年 | 468篇 |
2010年 | 328篇 |
2009年 | 334篇 |
2008年 | 352篇 |
2007年 | 323篇 |
2006年 | 249篇 |
2005年 | 260篇 |
2004年 | 220篇 |
2003年 | 204篇 |
2002年 | 167篇 |
2001年 | 105篇 |
2000年 | 83篇 |
1999年 | 76篇 |
1998年 | 89篇 |
1997年 | 46篇 |
1996年 | 29篇 |
1995年 | 24篇 |
1994年 | 23篇 |
1993年 | 13篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有6900条查询结果,搜索用时 31 毫秒
991.
该研究以‘红玉石籽’(Punica granatumcv.Hongyushizi)石榴为试验材料,采用RACE和RT-PCR方法,获得与木质素的合成相关基因PgMYB308。PgMYB308基因cDNA全长792bp,编码263个氨基酸。分子量为29.56kD,理论等电点为9.07。序列比对和功能域分析发现,PgMYB308包含R2和R3保守域,以及C1、C2、C4和锌指基序。系统进化树分析显示,PgMYB308与其他物种起源相同,而与桉树EgMYB308亲缘关系最近。荧光定量PCR分析表明,PgMYB308在茎、叶和种子等组织中均有表达,其中茎中表达量最高,叶片中表达量最低;PgMYB308在‘突尼斯软籽’中表达最高,而在‘红玉石籽’和‘白玉石籽’中表达量较低;PgMYB308在‘红玉石籽’籽粒的不同时期均有表达,但在花后20d相对表达量最高,以后随发育进程呈现逐渐下降的趋势。 相似文献
992.
993.
Ruyin?Liu Rong?Qi Juan?Wang Yu?ZhangEmail author Xinchun?Liu Simona?Rossetti Valter?Tandoi Min?Yang 《Applied microbiology and biotechnology》2017,101(16):6495-6504
Sludge bulking, a notorious microbial issue in activated sludge plants, is always accompanied by dramatic changes in the bacterial community. Despite large numbers of phages in sludge systems, their responses to sludge bulking and phage-host associations during bulking are unknown. In this study, high-throughput sequencing of viral metagenomes and bacterial 16S rRNA genes were employed to characterize viral and bacterial communities in a sludge plant under different sludge conditions (sludge volume index (SVI) of 180, 132, and 73 ml/g). Bulking sludges (SVI > 125 ml/g) taken about 10 months apart exhibited similar bacterial and viral composition. This reflects ecological resilience of the sludge microbial community and indicates that changes in viral and bacterial populations correlate closely with each other. Overgrowth of “Candidatus Microthrix parvicella” led to filamentous bulking, but few corresponding viral genotypes were identified. In contrast, sludge viromes were characterized by numerous contigs associated with “Candidatus Accumulibacter phosphatis,” suggesting an abundance of corresponding phages in the sludge viral community. Notably, while nitrifiers (mainly Nitrosomonadaceae and Nitrospiraceae) declined significantly along with sludge bulking, their corresponding viral contigs were identified more frequently and with greater abundance in the bulking viromes, implying that phage-mediated lysis might contribute to the loss of autotrophic nitrifiers under bulking conditions. 相似文献
994.
Wen L. Bai Jiao J. Wang Rong H. Yin Yun L. Dang Ze Y. Wang Yu B. Zhu Yu Y. Cong Liang Deng Dan Guo Shi Q. Wang Shu H. Yang Hui L. Xue 《Genetica》2017,145(1):115-126
Homeobox protein Hox-C8 (HOXC8) is a member of Hox family. It is expressed in the dermal papilla of the skin and is thought to be associated with the hair inductive capacity of dermal papilla cells. In the present study, we isolated and characterized a full-length open reading frame of HOXC8 cDNA from the skin tissue of Liaoning cashmere goat, as well as, established a phylogenetic relationship of goat HOXC8 with that of other species. Also, we investigated the effect of methylation status of HOXC8 exon 1 at anagen secondary hair follicle on the cashmere fiber traits in Liaoning cashmere goat. The sequence analysis indicated that the obtained cDNA was 1134-bp in length containing a complete ORF of 729-bp. It encoded a peptide of 242 amino acid residues in length. The structural analysis indicated that goat HOXC8 contained a typical homeobox domain. The phylogenetic analysis revealed that Capra hircus HOXC8 had a closer genetic relationship with that of Ovis aries, followed by Bos Taurus and Bubalus bubalis. The methylation analysis suggested that the methylation degree of HOXC8 exon 1 in anagen secondary hair follicle might be involved in regulating the growth of cashmere fiber in Liaoning cashmere goat. Our results provide new evidence for understanding the molecular structural and evolutionary characteristics of HOXC8 in Liaoning cashmere goat, as well as, for further insight into the role of methylation degree of HOXC8 exon 1 regulates the growth of cashmere fiber in goat. 相似文献
995.
996.
Song?Gao Zhiying?Zhao Rong?Wu Yuecan?Zeng Zhenyong?Zhang Jianing?Miao Zhengwei?YuanEmail author 《Radiation and environmental biophysics》2017,56(1):63-77
Radiotherapy is an effective form of therapy for most thoracic malignant tumors. However, myocardial injury resulting from the high doses of radiation is a severe complication. Here we aimed to study the possibility of reducing radiation-induced myocardial injury with mesenchymal stem cell (MSC) transplantation. We used MSCs extracted from bone marrow (BMSCs) to transplant via the tail vein into a radiation-induced heart injury (RIHI) rat model. The rats were divided into six groups: a Sham group, an IRR (irradiation) group, and four IRR + BMSCs transplantation groups obtained at different time points. After irradiation, BMSC transplantation significantly enhanced the cardiac function in rats. By analyzing the expression of PPAR-α, PPAR-γ, TGF-β, IL-6, and IL-8, we found that BMSC transplantation alleviated radiation-induced myocardial fibrosis and decreased the inflammatory reaction. Furthermore, we found that expression of γ-H2AX, XRCC4, DNA ligase4, and TP53BP1, which are associated with DNA repair, was up-regulated, along with increased secretion of growth factors SDF-1, CXCR4, VEGF, and IGF in rat myocardium in the IRR + BMSCs transplantation groups compared with the IRR group. Thus, BMSC transplantation has the potential to improve RIHI via DNA repair and be a new therapeutic approach for patients with myocardial injury. 相似文献
997.
Ming Liu Ai-Jun Zhang Xiao-Guang Chen Rong Jin Hong-Min Li Zhong-Hou Tang 《Acta Physiologiae Plantarum》2017,39(9):211
Potassium (K+) deficiency is an important abiotic stress which has severe influence on the growth and development of sweet potato. To investigate the difference on root morphology, ultrastructure and antioxidant enzyme system at early growth stage, two representative sweet potato cultivars (Ipomoea batatas [L.] Lam.) with different K+ deficiency tolerance capacities were hydroponically cultivated under normal K+ (control) and K+ deficiency (?K) treatments. The results showed that after 14 days of treatment, the root length, surface area, volume, and average diameter of Ningzishu 1 (sensitive to K+ deficiency) were significantly decreased under ?K treatment, by comparison, those corresponding decreases of Xushu 32 (tolerant to K+ deficiency) were lower and not significant (except for root length). In addition, the proportion of fine roots (diameter <0.5 mm) and thick root (d > 1.0 mm) of Xushu 32 seedlings increased significantly under condition of K+ deficiency. Through transmission electron microscopy observations, it can be found that Xushu 32 seedlings showed a more complete root cellular structure and slighter oxidative damage than Ningzishu 1 under ?K treatment. Moreover, the hydrogen peroxide content and malondialdehyde content in the root of Xushu 32 seedlings was significantly lower than that of Ningzishu 1, and the variations of superoxide dismutase, peroxidase, and catalase activities were pronouncedly less than those of Ningzishu 1. These differences between the two cultivars indicated that the stronger root morphology and nutrients absorption ability, and the better root cellular structure and physiological role of Xushu 32 seedlings could alleviate the damage of K+ deficiency stress. Thus, it might be a potential mechanism for cultivar tolerance to low K+ in sweet potato. 相似文献
998.
Bo Xiong Shuang Ye Xia Qiu Ling Liao Guochao Sun Jinyu Luo Lin Dai Yi Rong Zhihui Wang 《Acta Physiologiae Plantarum》2017,39(4):98
The role of exogenous spermidine (Spd) in alleviating fruit granulation in the grafted seedlings of a Citrus cultivar (Huangguogan) was investigated. Granulation resulted in increased electrical conductivity, cell membrane permeability, and total pectin, soluble pectin, cellulose, and lignin contents. However, it decreased the activities of superoxide dismutase, peroxidase, and catalase, as well as the (Spd + Spm):Put ratio. The application of exogenous Spd onto Huangguogan seedlings significantly increased proline and ascorbate contents, but decreased the H2O2 and O 2 ?· levels, which suggested that exogenous Spd provided some protection from oxidative damage. In addition, exogenous Spd decreased cell membrane permeability and MDA content, and increased the (Spd + Spm):Put ratio. The activities of antioxidant enzymes, such as catalase, peroxidase, and superoxide dismutase, were increased in Spd-treated seedlings affected by fruit granulation, resulting in a decrease in oxidative stress levels. The protective effects of Spd were reflected by a decrease in superoxide levels through osmoregulation, increased proline and ascorbate contents, and increased antioxidant activities. Our observations reveal the importance of exogenous Spd in alleviating citrus fruit granulation. 相似文献
999.
Aun Raza Shumaila Bano Xiuquan Xu Rong Xian Zhang Haider Khalid Furqan Muhammad Iqbal Changkun Xia Jian Tang Zhen Ouyang 《Biological trace element research》2017,178(1):160-169
The rutin–nickel (II) complex (RN) was synthesized and characterized by elemental analysis, UV–visible spectroscopy, IR, mass spectrometry, 1H NMR, TG-DSC, SEM, and molar conductivity. The low molar conductivity value investigates the non-electrolyte nature of the complex. The elemental analysis and other physical and spectroscopic methods reveal the 1:2 stoichiometric ratio (metal/ligand) of the complex. An antioxidant study of rutin and its metal complex against DPPH radical showed that the complex has more radical scavenging activity than free rutin. The interaction of complex RN with DNA was determined using fluorescence spectra and agarose gel electrophoresis. The results showed that RN can intercalate moderately with DNA, quench a strong intercalator ethidium bromide (EB), and compete for the intercalative binding sites. The complex showed significant cleavage of pBR 322 DNA from supercoiled form (SC) to nicked circular form (NC), and these cleavage effects were dose-dependent. Moreover, the mechanism of DNA cleavage indicated that it was a hydrolytic cleavage pathway. These results revealed the potential nuclease activity of the complex to cleave DNA. 相似文献
1000.
【目的】从锡盟地区酸马奶酒分离的乳酸菌中筛选出高产信号分子自体诱导物2(Autoinducer-2,AI-2)的乳酸菌,通过优化其重组蛋白Pfs的诱导条件体外合成信号分子AI-2。【方法】利用生物学发光法对不同乳酸菌产信号分子AI-2的产量进行比较,以高产信号分子AI-2乳酸菌基因组DNA为模板,扩增其S-腺苷高半胱氨酸核苷酶(S-adenosylhomocysteine nucleosidase,Pfs)基因,构建原核表达载体。利用异丙基-β-D-硫代吡喃半乳糖苷(IPTG)进行重组蛋白的诱导表达,通过优化培养基、诱导温度、诱导前菌体密度、IPTG浓度以及诱导时间得到高表达的Pfs蛋白,使其与底物作用最终体外合成信号分子AI-2。【结果】10株乳酸菌均可产信号分子AI-2,其中屎肠球菌8-3分泌信号分子AI-2的产量明显高于其他菌株;重组蛋白的最佳诱导条件为:选取SOC(Super optimal broth with catabolite repression)作为诱导表达培养基,菌液OD600为0.5–0.7时加入终浓度为0.1 mmol/L的IPTG,37°C诱导12 h;利用最优诱导条件获得了浓度为4.08 g/L的纯化Pfs蛋白,体外合成了信号分子AI-2。【结论】酸马奶酒中分离出的10株乳酸菌均可产生信号分子AI-2,且屎肠球菌8-3可通过Pfs基因的作用生成信号分子AI-2。 相似文献