全文获取类型
收费全文 | 98299篇 |
免费 | 777篇 |
国内免费 | 880篇 |
专业分类
99956篇 |
出版年
2022年 | 31篇 |
2021年 | 78篇 |
2020年 | 45篇 |
2019年 | 48篇 |
2018年 | 11893篇 |
2017年 | 10723篇 |
2016年 | 7572篇 |
2015年 | 773篇 |
2014年 | 511篇 |
2013年 | 556篇 |
2012年 | 4551篇 |
2011年 | 13146篇 |
2010年 | 12228篇 |
2009年 | 8441篇 |
2008年 | 10080篇 |
2007年 | 11675篇 |
2006年 | 507篇 |
2005年 | 818篇 |
2004年 | 1247篇 |
2003年 | 1307篇 |
2002年 | 1073篇 |
2001年 | 298篇 |
2000年 | 212篇 |
1999年 | 97篇 |
1998年 | 114篇 |
1997年 | 100篇 |
1996年 | 71篇 |
1995年 | 65篇 |
1994年 | 73篇 |
1993年 | 91篇 |
1992年 | 72篇 |
1991年 | 88篇 |
1990年 | 58篇 |
1989年 | 58篇 |
1988年 | 51篇 |
1987年 | 58篇 |
1986年 | 42篇 |
1985年 | 32篇 |
1984年 | 44篇 |
1983年 | 58篇 |
1982年 | 45篇 |
1981年 | 38篇 |
1980年 | 49篇 |
1979年 | 22篇 |
1977年 | 21篇 |
1975年 | 30篇 |
1974年 | 18篇 |
1972年 | 256篇 |
1971年 | 285篇 |
1962年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Anna Antecka Michał Blatkiewicz Marcin Bizukojć Stanisław Ledakowicz 《Biotechnology letters》2016,38(4):667-672
Objective
This work is the first application of a morphological engineering technique called microparticle-enhanced cultivation (MPEC) aimed at the facilitation of laccase production in the submerged cultures by two basidiomycetes species Cerrena unicolor and Pleurotus sapidus.Results
The positive effect of the applied 10 μm Al2O3 microparticles at concentrations from 5 to 30 g Al2O3 l?1 was shown. Laccase activity increased 3.5-fold for C. unicolor and 2-fold for P. sapidus at 15 g Al2O3 l?1 on 9 and 14 day of the cultivation, respectively, compared to the control culture without microparticles. The increase of laccase activity in the cultivation broths was caused by the action of Al2O3 microparticles on the agglomeration of hyphae. It led to the decrease of the size of the pellets, (on average by 2 mm for C. unicolor), the change of their shape (star-shaped pellets for C. unicolor) and the change of their structure (more compact pellets for P. sapidus).Conclusions
Application of MPEC for the submerged cultures of two laccase-producing basidiomycetes proved successful in increasing of enzyme production.972.
Yonghong Meng Guiru Dong Chen Zhang Yuanyuan Ren Yuling Qu Weifeng Chen 《Biotechnology letters》2016,38(4):673-679
Objective
To study the effect of Ca2+ on glutamate dehydrogenase (GDH) and its role in poly-γ-glutamic acid (γ-PGA) synthesis in Bacillus natto HSF 1410.Results
When the concentration of Ca2+ varied from 0 to 0.1 g/l in the growth medium of B. natto HSF 1410, γ-PGA production increased from 6.8 to 9.7 g/l, while GDH specific activity and NH4Cl consumption improved from 183 to 295 U/mg and from 0.65 to 0.77 g/l, respectively. GDH with α-ketoglutarate as substrate primarily used NADPH as coenzyme with a K m of 0.08 mM. GDH was responsible for the synthesis of endogenous glutamate. The specific activity of GDH remained essentially unchanged in the presence of CaCl2 (0.05–0.2 g/l) in vitro. However, the specific activity of GDH and its expression was significantly increased by CaCl2 in vivo. Therefore, the regulation of GDH and PGA synthesis by Ca2+ is an intracellular process.Conclusion
Calcium regulation may be an effective approach for producing γ-PGA on an industrial scale.973.
Mohamed Elshikh Syed Ahmed Scott Funston Paul Dunlop Mark McGaw Roger Marchant Ibrahim M. Banat 《Biotechnology letters》2016,38(6):1015-1019
Objectives
To develop and validate a microdilution method for measuring the minimum inhibitory concentration (MIC) of biosurfactants.Results
A standardized microdilution method including resazurin dye has been developed for measuring the MIC of biosurfactants and its validity was established through the replication of tetracycline and gentamicin MIC determination with standard bacterial strains.Conclusion
This new method allows the generation of accurate MIC measurements, whilst overcoming critical issues related to colour and solubility which may interfere with growth measurements for many types of biosurfactant extracts.974.
Wojciech Barczak Pawel Golusiński Lukasz Luczewski Wiktoria M. Suchorska Michal M. Masternak Wojciech Golusiński 《Biotechnology letters》2016,38(10):1665-1672
Head and neck squamous cell carcinoma is the sixth leading cause of cancer worldwide. The most common risk factors are carcinogens (tobacco, alcohol), and infection of the human papilloma virus. Surgery is still considered as the treatment of choice in case of head and neck cancer, followed by a reconstructive surgery to enhance the quality of life in the patients. However, the widespread use of artificial implants does not provide appropriate physiological activities and often cannot act as a long-term solution for the patients. Here we review the applicability of multiple stem cell types for tissue engineering of cartilage, trachea, vocal folds and nerves for head and neck injuries. The ability of the cells to self-renew and maintain their pluripotency state makes them an attractive tool in tissue engineering. 相似文献
975.
Xiaobo Dong Haiyun Li Yucheng Jiang Mancheng Hu Shuni Li Quanguo Zhai 《Biotechnology letters》2016,38(9):1483-1491
Objectives
To degrade enzymatically bisphenol A (BPA) that causes serious environmental concerns and is difficult to be degraded by chemical or physical methods.Results
BPA (150 mg l?1) was completely degraded by chloroperoxidase (CPO)/H2O2 within 7 min at room temperature, atmospheric pressure with the enzyme at 6 μg CPO ml?1. The degradation products were identified by HPLC–MS, which suggested involvement of multiple steps. Enzymatic treatment followed by existing bioremediation technologies (activated sludge) enhanced removal of COD from 9 to 54 %. Using an ecotoxicity evaluation with Chlorella pyrenoidosa, the degradation products had a lower toxicity than BPA.Conclusion
BPA can be degraded rapidly and efficiently under mild conditions with chloroperoxidase at 6 μg ml?1. The degradation products had a lower toxicity than BPA.976.
Long Jin Hai-Ying Zhu Qing Guo Xiao-Chen Li Yu-Chen Zhang Guang-Lei Zhang Xiao-Xu Xing Mei-Fu Xuan Qi-Rong Luo Xi-Jun Yin Jin-Dan Kang 《Biotechnology letters》2016,38(9):1433-1441
Objective
To examine the effect of PCI-24781 (abexinostat) on the blastocyst formation rate in pig somatic cell nuclear transferred (SCNT) embryos and acetylation levels of the histone H3 lysine 9 and histone H4 lysine 12.Results
Treatment with 0.5 nM PCI-24781 for 6 h significantly improved the development of cloned embryos, in comparison to the control group (25.3 vs. 10.5 %, P < 0.05). Furthermore, PCI-24781 treatment led to elevated acetylation of H3K9 and H4K12. TUNEL assay and Hoechst 33342 staining revealed that the percentage of apoptotic cells in blastocysts was significantly lower in PCI-24781-treated SCNT embryos than in untreated embryos. Also, PCI-24781-treated embryos were transferred into three surrogate sows, one of whom became pregnant and two fetuses developed.Conclusion
PCI-24781 improves nuclear reprogramming and the developmental potential of pig SCNT embryos.977.
Xiaojie Duan Mingming Zheng Yu Liu Zhengqiang Jiang Shaoqing Yang 《Biotechnology letters》2016,38(12):2127-2135
Objectives
To identify novel cold-active lipases from fungal sources and improve their production by heterologous expression in Pichia pastoris.Results
A novel cold-active lipase gene (ReLipB) from Rhizomucor endophyticus was cloned. ReLipB was expressed at a high level in Pichia pastoris using high cell-density fermentation in a 5-l fermentor with the highest lipase activity of 1395 U/ml. The recombinant lipase (RelipB) was purified and biochemically characterized. ReLipB was most active at pH 7.5 and 25 °C. It was stable from pH 4.5–9.0. It exhibited broad substrate specificity towards p-nitrophenyl (pNP) esters (C2–C16) and triacylglycerols (C2–C12), showing the highest specific activities towards pNP laurate (231 U/mg) and tricaprylin (1840 U/mg), respectively. In addition, the enzyme displayed excellent stability with high concentrations of organic solvents including cyclohexane, n-hexane, n-heptane, isooctane and petroleum ester and surfactants.Conclusions
A novel cold-active lipase from Rhizomucor endophyticus was identified, expressed at a high level and biochemically characterized. The high yield and unique enzymatic properties make this lipase of some potential for industrial applications.978.
Jingbo Wu Feng Liu Rulin Zhan Guoping Li Yanlong Zhao Chang Jinmei Yanbiao He 《Biotechnology letters》2016,38(5):835-840
Objectives
To develop a sensitive and specific molecular assay for detection of mango malformation disease (MMD), which is caused primarily by Fusarium mangiferae.Results
We screened 100 ISSR primers and identified one (UBC888) that directed the stable amplification of a specific gene fragment of 479 bp (GenBank accession number KJ526382). Based on the DNA sequence of this fragment, a pair of SCAR primers (W342 and W1772) were designed to amplify another gene fragment of 1376 bp (GenBank accession number KJ526383), demonstrating the successful conversion of an ISSR marker to a SCAR marker. An effective and simple detection assay for MMD was established based on this pair of PCR primers, with a high level of specificity and sensitivity to the DNA of F. mangiferae and other species of Fusarium both in vitro and in vivo. It can detect as little as 10 pg fungal DNA from the DNA of mango’s tissues.Conclusions
Our assay provides a practical method for the early diagnosis so that proper prevention of the mango malformation disease can be developed.979.
980.
Ángel Alberto Puig-Lagunes Domingo Canales-Espinosa Ariadna Rangel-Negrín Pedro Américo D. Dias 《International journal of primatology》2016,37(6):656-670
It is essential to document habitat occupancy patterns and population structure to facilitate the survival of primates in areas of anthropogenic disturbance. The overlapping of the Nearctic and Neotropical regions in the Olmec region of Mexico make this area particularly important as part of a natural biological corridor that harbors a high number of endemic species and connects the Atlantic and Pacific coastal plains. We surveyed Alouatta palliata mexicana (Mexican mantled howlers) in a 300-km2 area to determine if fragment occupation and subpopulation structure were related to the spatial attributes of the fragments. We measured the fragment size and shape as well as the distances to the nearest road, human settlement, agricultural field, and nearest neighboring fragment. During 1 year (ca. 4500 fieldwork hours) we surveyed 48 fragments, 17 of which were occupied, and counted 198 howlers. Larger fragments that were farther from agricultural activities were more likely to be occupied. Subpopulation size and number of individuals in all age–sex classes increased in larger fragments that were closer to other fragments. We found more females and juveniles, as well as more females per male in fragments that were farther from roads and we found fewer immatures per female, females per male, and individuals per area in more irregular fragments. In addition, more males and immatures per female occurred in fragments that were farther from agricultural fields. The Olmec Region is located at the center of the geographic distribution of mantled howlers in Mexico, and could therefore play a fundamental role in maintaining the contact between different populations. However, our study suggests that mantled howlers are highly threatened by anthropogenic habitat disturbance in this area, mainly through the loss of their habitat and contact with humans. 相似文献