全文获取类型
收费全文 | 4139篇 |
免费 | 390篇 |
国内免费 | 238篇 |
出版年
2024年 | 5篇 |
2023年 | 47篇 |
2022年 | 126篇 |
2021年 | 211篇 |
2020年 | 123篇 |
2019年 | 160篇 |
2018年 | 176篇 |
2017年 | 130篇 |
2016年 | 173篇 |
2015年 | 284篇 |
2014年 | 288篇 |
2013年 | 342篇 |
2012年 | 358篇 |
2011年 | 347篇 |
2010年 | 206篇 |
2009年 | 175篇 |
2008年 | 235篇 |
2007年 | 194篇 |
2006年 | 152篇 |
2005年 | 160篇 |
2004年 | 114篇 |
2003年 | 118篇 |
2002年 | 88篇 |
2001年 | 84篇 |
2000年 | 69篇 |
1999年 | 69篇 |
1998年 | 43篇 |
1997年 | 38篇 |
1996年 | 40篇 |
1995年 | 39篇 |
1994年 | 28篇 |
1993年 | 20篇 |
1992年 | 24篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有4767条查询结果,搜索用时 15 毫秒
71.
利用固体淀粉筛选培养基,从安阳市郊区面粉厂附近的土壤里分离筛选出1株产淀粉酶的菌株,编号为MF-3-2.经过菌株形态、革兰氏染色、16S rDNA鉴定及系统进化树分析,初步确定其为枯草芽孢杆菌(Bacillus subtilis).摇瓶培养后对其酶学性质研究发现,该菌株淀粉酶的最适温度为65℃,最适pH值为6.0,在pH值4.8~6.0范围内仍能残余70%以上的酶活力.该菌株的最适生长温度为40℃,最适生长pH值为6.5.产酶条件优化结果表明:最适碳源为马铃薯淀粉,最适氮源为豆粕粉,最适碳氮比为1∶15,发酵温度30℃,发酵pH值6.0,装液量10%,种龄10h,接种量5%,转速200 r/min,48 h达到产酶高峰.通过发酵产酶条件优化,其淀粉酶活性达到86.8 U/mL,是优化前的35倍.另外,在酸性条件下还具有较好的活性.因此,该菌株的淀粉酶具有潜在的工业应用前景. 相似文献
72.
Fangqiao Wei Xiangyu Sun Yufeng Gao Haoyu Dou Yang Liu Lili Su Haofei Luo Ce Zhu Qian Zhang Peiyuan Tong Wen Ren Zhe Xun Ruochun Guo Yuanlin Guan Shenghui Li Yijun Qi Junjie Qin Feng Chen Shuguo Zheng 《蛋白质与细胞》2021,12(6):502-510
Dear Editor,
A series of studies had focused on the ecological stability of human microbiome (Lozupone et al.,2012;Faith et al.,2013;Moya and Ferrer,2016).Despite the continuous perturbation and the highly personalized composition within the human microbiome (Human Microbiome Project,2012),healthy adults stably maintain their microbial communities in terms of space and time (Faith et al.,2013;Moya and Ferrer,2016;Oh et al.,2016).This stability is proved to be critical for the well-being of human body (Lozupone et al.,2012).On the contrary,major shifts in microbial community composition are often related to diseases (Lynch and Pedersen,2016). 相似文献
73.
Ma Bohan Liu Zhanzhu Yan Wei Wang Lixue He Haobo Zhang Aijing Li Zeyuan Zhao Qiuzhu Liu Mingming Guan Shuyan Liu Siyan Qu Jing Yao Dan Zhang Jun 《Functional & integrative genomics》2021,21(3):435-450
Functional & Integrative Genomics - Soybean oil is composed of fatty acids and glycerol. The content and composition of fatty acids partly determine the quality of soybean seeds. Circular RNAs... 相似文献
74.
75.
皂苷类药物普遍分子量比较大,水溶性好,但不易透过细胞膜难以被人体吸收,因此口服制剂体内生物利用度较低.近年来对单体皂苷及总皂苷类药物制剂方面的研究越来越多,随着新型的给药系统和新辅料的出现,皂苷类药物在体内的生物利用度大大提高.本文主要介绍以单体皂苷或总皂苷活性部位为主药的制剂研究进展,以期为该类成分的进一步研究提供思路. 相似文献
76.
Cyclic shedding of the endometrium is unique to menstruating species. The status of the decidua in mouse menstrual-like models seems to differ from that of the predecidua in humans before endometrial breakdown. The aim of this study was to determine how this difference in decidual status is related to endometrial breakdown. A mouse menstruallike model was generated by pharmacological progesterone withdrawal. Histomorphological analysis and reticular fiber staining were used to evaluate endometrial status. In situ zymography was used to determine the localization of active collagenase and gelatinase. The functional endometrial layer containing the mature decidual-like zone (MDZ) and predecidual-like zone (PZ) underwent breakdown. The reticular fibers underwent disruption and fragmentation and became loose or disappeared at 12 h in the PZ, where active collagenase and gelatinase were limited. The reticular fibers were visibly reduced at 24 h in the MDZ, where active collagenase was detected. A few reticular fibers remained; however, the functional layer had sloughed into the lumen of the uterus. The results showed that reticular fibers of the PZ are actively degraded during endometrial shedding.Key words: mouse menstrual-like model, predecidual-like zone, reticular fiber, gelatinase, collagenase 相似文献
77.
Xiangxiang Shan Yufeng Miao Rengen Fan Changzhi Song Guangzhou Wu Zhengqiang Wan Jian Zhu Guan Sun Wenzhang Zha Xiangming Mu Guangjun Zhou Yan Chen 《In vitro cellular & developmental biology. Animal》2013,49(8):576-582
In this study, we aimed to study the role of growth factor receptor-bound protein 2 (Grb2) in palmitic acid-induced steatosis and other “fatty liver” symptoms in vitro. HepG2 cells, with or without stably suppressed Grb2 expression, were incubated with palmitic acid for 24 h to induce typical clinical “fatty liver” features, including steatosis, impaired glucose metabolism, oxidative stress, and apoptosis. MTT and Oil Red O assays were applied to test cell viability and fat deposition, respectively. Glucose uptake assay was used to evaluate the glucose utilization of cells. Quantitative polymerase chain reaction and Western blot were used to measure expressional changes of key markers of insulin signaling, lipid/glucose metabolism, oxidative stress, and apoptosis. After 24-h palmitic acid induction, increased fat accumulation, reduced glucose uptake, impaired insulin signaling, enhanced oxidative stress, and increased apoptosis were observed in HepG2 cells. Suppression of Grb2 in HepG2 significantly reduced fat accumulation, improved glucose metabolism, ameliorated oxidative stress, and restored the activity of insulin receptor substrate-1/Akt and MEK/ERK pathways. In addition, Grb2 deficiency attenuated hepatic apoptosis shown by reduced activation of caspase-3 and fluorescent staining. Modulation of Bcl-2 and Bak1 also contributed to reduced apoptosis. In conclusion, suppression of Grb2 expression in HepG2 cells improved hepatic steatosis, glucose metabolism, oxidative stress, and apoptosis induced by palmitic acid incubation partly though modulating the insulin signaling pathway. 相似文献
78.
Zhanyong Wang Jing Zhang Tingting Su Zhuanfei Guan Man Ji 《Preparative biochemistry & biotechnology》2013,43(3):278-286
Saccharomyces cerevisiae LN-17 was selected from 26 kinds of primary yeast strains that belong to different genera and species. The iron- and zinc-enriched capability of strain LN-17 was higher than the others. The highest iron and zinc contents of the strain were obtained when the strain grew up under the following conditions: The strain was incubated (5%, v/v) in 50 mL wort medium (pH 6.0) with 100 mg/L Fe ion and 120 mg/L Zn ion. The medium was loaded into a 250-mL Erlenmeyer flask and shaken in a rotary shaker (200 rpm) at 30°C for 60 h. Ferrous sulfate and zinc sulfate were chosen as the source of Fe and Zn. The Fe and Zn contents of the dry cells were determined by atomic absorption spectrum analysis. Under the optimized cultivation conditions, the Fe and Zn contents reached 7.854 mg/g dry cells and 4.976 mg/g dry cells. 相似文献
79.
Xiaolei Zhu Lan Ye Huiming Ge Ling Chen Nan Jiang Lai Qian Lingling Li Rong Liu Shen Ji Su Zhang Jiali Jin Dening Guan Wei Fang Renxiang Tan Yun Xu 《Aging cell》2013,12(1):85-92
Increasing evidence demonstrates that amyloid beta (Aβ) elicits mitochondrial dysfunction and oxidative stress, which contributes to the pathogenesis of Alzheimer's disease (AD). Identification of the molecules targeting Aβ is thus of particular significance in the treatment of AD. Hopeahainol A (HopA), a polyphenol with a novel skeleton obtained from Hopea hainanensis, is potentially acetylcholinesterase‐inhibitory and anti‐oxidative in H2O2‐treated PC12 cells. In this study, we reported that HopA might bind to Aβ1–42 directly and inhibit the Aβ1–42 aggregation using a combination of molecular dynamics simulation, binding assay, transmission electron microscopic analysis and staining technique. We also demonstrated that HopA decreased the interaction between Aβ1–42 and Aβ‐binding alcohol dehydrogenase, which in turn reduced mitochondrial dysfunction and oxidative stress in vivo and in vitro. In addition, HopA was able to rescue the long‐term potentiation induction by protecting synaptic function and attenuate memory deficits in APP/PS1 mice. Our data suggest that HopA might be a promising drug for therapeutic intervention in AD. 相似文献
80.
Qingtian Guan Xiaohan Guo Ting Han Mengwei Wei Meiling Jin Fan Zeng Lin Liu Zhe Li Yuhan Wang Gang-Won Cheong Shihong Zhang Baolei Jia 《Process Biochemistry》2013,48(5-6):878-884
Thermostable amylopullulanases can catalyse the hydrolysis of both α-1,4 and α-1,6 glucosidic bonds and are of considerable interest in the starch saccharification industry. In this study, the gene Apu-Tk encoding an extracellular amylopullulanase was cloned from an extremely thermophilic anaerobic archaeon Thermococcus kodakarensis KOD1. Apu-Tk encodes an 1100-amino acid protein with a 27-residue signal peptide, which has a predicted mass of 125 kDa after signal peptide cleavage. Sequence alignments showed that Apu-Tk contains the five regions conserved in all GH57 family proteins. Full-length Apu-Tk was expressed in Escherichia coli and purified to homogeneity. The purified enzyme displayed both pullulanase and amylase activity. The optimal temperature for Apu-Tk to hydrolyse pullulan and soluble starch was >100 °C. Apu-Tk was also active at a broad range of pH (4–7), with an optimum pH of ~5.0–5.5. Apu-Tk also retained >30% of its original activity and partially folded globular structure in the presence of 8% SDS or 10% β-mercaptoethanol. The high yield, broad pH range, and stability of Apu-Tk implicate it as a potential enzyme for industrial applications. 相似文献