全文获取类型
收费全文 | 20232篇 |
免费 | 1570篇 |
国内免费 | 11篇 |
出版年
2023年 | 81篇 |
2022年 | 194篇 |
2021年 | 365篇 |
2020年 | 219篇 |
2019年 | 312篇 |
2018年 | 377篇 |
2017年 | 338篇 |
2016年 | 550篇 |
2015年 | 933篇 |
2014年 | 1053篇 |
2013年 | 1320篇 |
2012年 | 1520篇 |
2011年 | 1427篇 |
2010年 | 938篇 |
2009年 | 864篇 |
2008年 | 1122篇 |
2007年 | 1053篇 |
2006年 | 1078篇 |
2005年 | 1044篇 |
2004年 | 981篇 |
2003年 | 859篇 |
2002年 | 904篇 |
2001年 | 257篇 |
2000年 | 205篇 |
1999年 | 243篇 |
1998年 | 268篇 |
1997年 | 200篇 |
1996年 | 218篇 |
1995年 | 194篇 |
1994年 | 211篇 |
1993年 | 207篇 |
1992年 | 182篇 |
1991年 | 144篇 |
1990年 | 120篇 |
1989年 | 132篇 |
1988年 | 133篇 |
1987年 | 93篇 |
1986年 | 93篇 |
1985年 | 113篇 |
1984年 | 139篇 |
1983年 | 100篇 |
1982年 | 130篇 |
1981年 | 102篇 |
1980年 | 97篇 |
1979年 | 81篇 |
1978年 | 76篇 |
1977年 | 72篇 |
1976年 | 48篇 |
1974年 | 48篇 |
1973年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Jan M. Klenk Paulina Dubiel Mahima Sharma Gideon Grogan Bernhard Hauer 《Microbial biotechnology》2019,12(2):377-391
One of the major challenges in chemical synthesis is the selective oxyfunctionalization of non-activated C-H bonds, which can be enabled by biocatalysis using cytochrome P450 monooxygenases. In this study, we report on the characterization of the versatile CYP109Q5 from Chondromyces apiculatus DSM436, which is able to functionalize a wide range of substrates (terpenes, steroids and drugs), including the ring of β-ionone in non-allylic positions. The crystal structure of CYP109Q5 revealed flexibility within the active site pocket that permitted the accommodation of bulky substrates, and enabled a structure-guided approach to engineering the enzyme. Some variants of CYP109Q5 displayed a switch in selectivity towards the non-allylic positions of β-ionone, allowing the simultaneous production of 2- and 3-hydroxy-β-ionone, which are chemically challenging to synthesize and are important precursors for carotenoid synthesis. An efficient whole-cell system finally enabled the production of up to 0.5 g l−1 hydroxylated products of β-ionone; this system can be applied to product identification in further biotransformations. Overall, CYP109Q5 proved to be highly evolvable and active. The studies in this work demonstrate that, using rational mutagenesis, the highly versatile CYP109Q5 generalist can be progressively evolved to be an industrially valuable specialist for the synthesis of specific products. 相似文献
993.
994.
995.
Sybryn L. Maes Michael P. Perring Margot Vanhellemont Leen Depauw Jan Van den Bulcke Guntis Brmelis Jrg Brunet Guillaume Decocq Jan den Ouden Werner Hrdtle Radim Hdl Thilo Heinken Steffi Heinrichs Bogdan Jaroszewicz Martin Kopecký Frantiek Mli Monika Wulf Kris Verheyen 《Global Change Biology》2019,25(1):201-217
Forecasting the growth of tree species to future environmental changes requires a better understanding of its determinants. Tree growth is known to respond to global‐change drivers such as climate change or atmospheric deposition, as well as to local land‐use drivers such as forest management. Yet, large geographical scale studies examining interactive growth responses to multiple global‐change drivers are relatively scarce and rarely consider management effects. Here, we assessed the interactive effects of three global‐change drivers (temperature, precipitation and nitrogen deposition) on individual tree growth of three study species (Quercus robur/petraea, Fagus sylvatica and Fraxinus excelsior). We sampled trees along spatial environmental gradients across Europe and accounted for the effects of management for Quercus. We collected increment cores from 267 trees distributed over 151 plots in 19 forest regions and characterized their neighbouring environment to take into account potentially confounding factors such as tree size, competition, soil conditions and elevation. We demonstrate that growth responds interactively to global‐change drivers, with species‐specific sensitivities to the combined factors. Simultaneously high levels of precipitation and deposition benefited Fraxinus, but negatively affected Quercus’ growth, highlighting species‐specific interactive tree growth responses to combined drivers. For Fagus, a stronger growth response to higher temperatures was found when precipitation was also higher, illustrating the potential negative effects of drought stress under warming for this species. Furthermore, we show that past forest management can modulate the effects of changing temperatures on Quercus’ growth; individuals in plots with a coppicing history showed stronger growth responses to higher temperatures. Overall, our findings highlight how tree growth can be interactively determined by global‐change drivers, and how these growth responses might be modulated by past forest management. By showing future growth changes for scenarios of environmental change, we stress the importance of considering multiple drivers, including past management and their interactions, when predicting tree growth. 相似文献
996.
997.
Henderson Christopher J. Stevens Tim Lee Shing Y. Gilby Ben L. Schlacher Thomas A. Connolly Rod M. Warnken Jan Maxwell Paul S. Olds Andrew D. 《Ecosystems》2019,22(6):1368-1380
Ecosystems - Animals are central to numerous ecological processes that shape the structure and function of ecosystems. It follows that species that are strongly linked to specific functions can... 相似文献
998.
Strejc Jan Kyselova Lucie Cadkova Anna Potocar Tomas Branyik Tomas 《Extremophiles : life under extreme conditions》2019,23(2):219-227
Extremophiles - Acidothermophilic bacteria of the genus Alicyclobacillus are frequent contaminants of fruit-based products. This study is the first attempt to characterize the physico-chemical... 相似文献
999.
Kirsten M. Ellegaard Silvia Brochet German Bonilla‐Rosso Olivier Emery Natasha Glover Noushin Hadadi Kamil S. Jaron Jan R. van der Meer Marc Robinson‐Rechavi Vladimir Sentchilo Florian Tagini Philipp Engel 《Molecular ecology》2019,28(9):2224-2237
Bacteria that engage in long‐standing associations with particular hosts are expected to evolve host‐specific adaptations that limit their capacity to thrive in other environments. Consistent with this, many gut symbionts seem to have a limited host range, based on community profiling and phylogenomics. However, few studies have experimentally investigated host specialization of gut symbionts and the underlying mechanisms have largely remained elusive. Here, we studied host specialization of a dominant gut symbiont of social bees, Lactobacillus Firm5. We show that Firm5 strains isolated from honey bees and bumble bees separate into deep‐branching host‐specific phylogenetic lineages. Despite their divergent evolution, colonization experiments show that bumble bee strains are capable of colonizing the honey bee gut. However, they were less successful than honey bee strains, and competition with honey bee strains completely abolished their colonization. In contrast, honey bee strains of divergent phylogenetic lineages were able to coexist within individual bees. This suggests that both host selection and interbacterial competition play important roles in host specialization. Using comparative genomics of 27 Firm5 isolates, we found that the genomes of honey bee strains harbour more carbohydrate‐related functions than bumble bee strains, possibly providing a competitive advantage in the honey bee gut. Remarkably, most of the genes encoding carbohydrate‐related functions were not conserved among the honey bee strains, which suggests that honey bees can support a metabolically more diverse community of Firm5 strains than bumble bees. These findings advance our understanding of the genomic changes underlying host specialization. 相似文献
1000.
Rolf Holderegger Niko Balkenhol Janine Bolliger Jan O. Engler Felix Gugerli Axel Hochkirch Carsten Nowak Gernot Segelbacher Alex Widmer Frank E. Zachos 《Molecular ecology》2019,28(17):3848-3856
Conservation genetics is a well‐established scientific field. However, limited information transfer between science and practice continues to hamper successful implementation of scientific knowledge in conservation practice and management. To mitigate this challenge, we have established a conservation genetics community, which entails an international exchange‐and‐skills platform related to genetic methods and approaches in conservation management. First, it allows for scientific exchange between researchers during annual conferences. Second, personal contact between conservation professionals and scientists is fostered by organising workshops and by popularising knowledge on conservation genetics methods and approaches in professional journals in national languages. Third, basic information on conservation genetics has been made accessible by publishing an easy‐to‐read handbook on conservation genetics for practitioners. Fourth, joint projects enabled practitioners and scientists to work closely together from the start of a project in order to establish a tight link between applied questions and scientific background. Fifth, standardised workflows simplifying the implementation of genetic tools in conservation management have been developed. By establishing common language and trust between scientists and practitioners, all these measures help conservation genetics to play a more prominent role in future conservation planning and management. 相似文献