全文获取类型
收费全文 | 3418篇 |
免费 | 357篇 |
国内免费 | 1篇 |
出版年
2022年 | 35篇 |
2021年 | 70篇 |
2020年 | 22篇 |
2019年 | 55篇 |
2018年 | 57篇 |
2017年 | 51篇 |
2016年 | 87篇 |
2015年 | 148篇 |
2014年 | 147篇 |
2013年 | 167篇 |
2012年 | 260篇 |
2011年 | 252篇 |
2010年 | 177篇 |
2009年 | 132篇 |
2008年 | 185篇 |
2007年 | 168篇 |
2006年 | 177篇 |
2005年 | 161篇 |
2004年 | 149篇 |
2003年 | 122篇 |
2002年 | 142篇 |
2001年 | 55篇 |
2000年 | 61篇 |
1999年 | 67篇 |
1998年 | 53篇 |
1997年 | 35篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 23篇 |
1993年 | 23篇 |
1992年 | 31篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 31篇 |
1988年 | 29篇 |
1987年 | 27篇 |
1986年 | 30篇 |
1985年 | 29篇 |
1984年 | 33篇 |
1983年 | 29篇 |
1982年 | 30篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 25篇 |
1976年 | 24篇 |
1975年 | 17篇 |
1974年 | 21篇 |
1973年 | 21篇 |
排序方式: 共有3776条查询结果,搜索用时 46 毫秒
51.
Barindra Sana Ke Ding Jia Wei Siau Rupali Reddy Pasula Sharon Chee Sharad Kharel Jean-Baptise Henri Lena Eunice Goh Lakshminarayanan Rajamani Yeng Ming Lam Sierin Lim John F. Ghadessy 《Biotechnology and bioengineering》2023,120(11):3200-3209
Polyethylene terephthalate (PET) hydrolase enzymes show promise for enzymatic PET degradation and green recycling of single-use PET vessels representing a major source of global pollution. Their full potential can be unlocked with enzyme engineering to render activities on recalcitrant PET substrates commensurate with cost-effective recycling at scale. Thermostability is a highly desirable property in industrial enzymes, often imparting increased robustness and significantly reducing quantities required. To date, most engineered PET hydrolases show improved thermostability over their parental enzymes. Here, we report engineered thermostable variants of Ideonella sakaiensis PET hydrolase enzyme (IsPETase) developed using two scaffolding strategies. The first employed SpyCatcher-SpyTag technology to covalently cyclize IsPETase, resulting in increased thermostability that was concomitant with reduced turnover of PET substrates compared to native IsPETase. The second approach using a GFP-nanobody fusion protein (vGFP) as a scaffold yielded a construct with a melting temperature of 80°C. This was further increased to 85°C when a thermostable PETase variant (FAST PETase) was scaffolded into vGFP, the highest reported so far for an engineered PET hydrolase derived from IsPETase. Thermostability enhancement using the vGFP scaffold did not compromise activity on PET compared to IsPETase. These contrasting results highlight potential topological and dynamic constraints imposed by scaffold choice as determinants of enzyme activity. 相似文献
52.
53.
Mitochondrial DNA was examined in natural and hatchery-reared stocks of brown trout, using different methods of restriction analysis. The methods included the development of a brown trout mt DNA hybridization probe through cloning part of the brown trout mitochondrial genome. In addition, fragments were analysed by ethidium bromide staining and end-labelling. The relative merits of each of these methods in assessing levels of genetic relatedness between the natural and hatchery-reared brown trout stocks were evaluated. In addition, the study revealed a diagnostic mtDNA restriction pattern which could be used as a genetic marker for the discrimination of these two groups of brown trout. 相似文献
54.
Joyce K. Smith J. Jeffrey Peirce 《The International Journal of Life Cycle Assessment》1996,1(2):115-118
The newly emerging LCA standards provide an opportunity to review and improve upon the current LCA methodology. As more industrial practitioners enter the arena, the opportunity arises to not only demand environmental improvement from industrial service and product providers but also to fill LCA data gaps. A framework is suggested for improvement in the current LCA framework that focuses on the business relationships of the industrial practitioner. The framework seeks to promote environmental improvement from industrial sectors through the identification of state-of-the-art technologies used throughout a life cycle. Basing LCAs on the best performers in an industry will create a market for a high level of environmental performance, disperse the responsibility of inventory data gathering, and improve upon the advancements already anticipated through the widespread application of LCA. 相似文献
55.
56.
57.
Physical mapping of the Mycoplasma gallisepticum S6 genome with localization of selected genes.
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report the construction of a physical map of the Mycoplasma gallisepticum S6 genome by field-inversion gel electrophoresis of DNA fragments generated by digestion of genomic DNA with rare-cutting restriction endonucleases. The size of the M. gallisepticum S6 genome was calculated to be approximately 1,054 kb. The loci of several genes have been assigned to the map by Southern hybridization utilizing specific gene probes. 相似文献
58.
RNA molecules that are assembled from the four standard nucleotides contain a limited number of chemical functional groups, a characteristic that is generally thought to restrict the potential for catalysis by ribozymes. Although polypeptides carry a wider range of functional groups, many contemporary protein-based enzymes employ coenzymes to augment their capabilities. The coenzymes possess additional chemical moieties that can participate directly in catalysis and thereby enhance catalytic function. In this work, we demonstrate a mechanism by which ribozymes can supplement their limited repertoire of functional groups through RNA-catalyzed incorporation of various coenzymes and coenzyme analogues. The group I ribozyme of Tetrahymena thermophila normally mediates a phosphoester transfer reaction that results in the covalent attachment of guanosine to the ribozyme. Here, a shortened version of the ribozyme is shown to catalyze the self-incorporation of coenzymes and coenzyme analogues, such as NAD+ and dephosphorylated CoA-SH. Similar ribozyme activities may have played an important role in the RNA world, when RNA enzymes are thought to have maintained a complex metabolism in the absence of proteins and would have benefited from the inclusion of additional functional groups.Correspondence to: G.F. Joyce 相似文献
59.
60.
Helminthosporium maydis T Toxin Decreased Calcium Transport into Mitochondria of Susceptible Corn 总被引:7,自引:6,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The effects of purified Helminthosporium maydis T (HmT) toxin on active Ca2+ transport into isolated mitochondria and microsomal vesicles were compared for a susceptible (T) and a resistant (N) strain of corn (Zea mays). ATP, malate, NADH, or succinate could drive 45Ca2+ transport into mitochondria of corn roots. Ca2+ uptake was dependent on the proton electrochemical gradient generated by the redox substrates or the reversible ATP synthetase, as oligomycin inhibited ATP-driven Ca2+ uptake while KCN inhibited transport driven by the redox substrates. Purified native HmT toxin completely inhibited Ca2+ transport into T mitochondria at 5 to 10 nanograms per milliliter while transport into N mitochondria was decreased slightly by 100 nanograms per milliliter toxin. Malate-driven Ca2+ transport in T mitochondria was frequently more inhibited by 5 nanograms per milliliter toxin than succinate or ATP-driven Ca2+ uptake. However, ATP-dependent Ca2+ uptake into microsomal vesicles from either N or T corn was not inhibited by 100 nanograms per milliliter toxin. Similarly, toxin had no effect on proton gradient formation ([14C]methylamine accumulation) in microsomal vesicles. These results show that mitochondrial and not microsomal membrane is a primary site of HmT toxin action. HmT toxin may inhibit formation of or dissipate the electrochemical proton gradient generated by substrate-driven electron transport or the mitochondrial ATPase, after interacting with a component(s) of the mitochondrial membrane in susceptible corn. 相似文献