全文获取类型
收费全文 | 10966篇 |
免费 | 926篇 |
国内免费 | 3篇 |
专业分类
11895篇 |
出版年
2022年 | 43篇 |
2021年 | 107篇 |
2020年 | 75篇 |
2019年 | 93篇 |
2018年 | 166篇 |
2017年 | 211篇 |
2016年 | 314篇 |
2015年 | 476篇 |
2014年 | 488篇 |
2013年 | 666篇 |
2012年 | 846篇 |
2011年 | 863篇 |
2010年 | 532篇 |
2009年 | 461篇 |
2008年 | 673篇 |
2007年 | 647篇 |
2006年 | 607篇 |
2005年 | 623篇 |
2004年 | 555篇 |
2003年 | 509篇 |
2002年 | 496篇 |
2001年 | 183篇 |
2000年 | 188篇 |
1999年 | 166篇 |
1998年 | 77篇 |
1997年 | 64篇 |
1996年 | 64篇 |
1995年 | 60篇 |
1994年 | 47篇 |
1993年 | 45篇 |
1992年 | 86篇 |
1991年 | 79篇 |
1990年 | 51篇 |
1989年 | 92篇 |
1988年 | 73篇 |
1987年 | 63篇 |
1986年 | 54篇 |
1985年 | 60篇 |
1984年 | 51篇 |
1983年 | 57篇 |
1982年 | 46篇 |
1981年 | 48篇 |
1979年 | 42篇 |
1978年 | 35篇 |
1976年 | 46篇 |
1975年 | 41篇 |
1974年 | 56篇 |
1973年 | 41篇 |
1972年 | 34篇 |
1971年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Pribat A Noiriel A Morse AM Davis JM Fouquet R Loizeau K Ravanel S Frank W Haas R Reski R Bedair M Sumner LW Hanson AD 《The Plant cell》2010,22(10):3410-3422
Tetrahydropterin-dependent aromatic amino acid hydroxylases (AAHs) are known from animals and microbes but not plants. A survey of genomes and ESTs revealed AAH-like sequences in gymnosperms, mosses, and algae. Analysis of full-length AAH cDNAs from Pinus taeda, Physcomitrella patens, and Chlamydomonas reinhardtii indicated that the encoded proteins form a distinct clade within the AAH family. These proteins were shown to have Phe hydroxylase activity by functional complementation of an Escherichia coli Tyr auxotroph and by enzyme assays. The P. taeda and P. patens AAHs were specific for Phe, required iron, showed Michaelian kinetics, and were active as monomers. Uniquely, they preferred 10-formyltetrahydrofolate to any physiological tetrahydropterin as cofactor and, consistent with preferring a folate cofactor, retained activity in complementation tests with tetrahydropterin-depleted E. coli host strains. Targeting assays in Arabidopsis thaliana mesophyll protoplasts using green fluorescent protein fusions, and import assays with purified Pisum sativum chloroplasts, indicated chloroplastic localization. Targeting assays further indicated that pterin-4a-carbinolamine dehydratase, which regenerates the AAH cofactor, is also chloroplastic. Ablating the single AAH gene in P. patens caused accumulation of Phe and caffeic acid esters. These data show that nonflowering plants have functional plastidial AAHs, establish an unprecedented electron donor role for a folate, and uncover a novel link between folate and aromatic metabolism. 相似文献
62.
63.
Pharmacogenetic evidence that cd36 is a key determinant of the metabolic effects of pioglitazone 总被引:4,自引:0,他引:4
Qi N Kazdova L Zidek V Landa V Kren V Pershadsingh HA Lezin ES Abumrad NA Pravenec M Kurtz TW 《The Journal of biological chemistry》2002,277(50):48501-48507
Pioglitazone, like other thiazolidinediones, is an insulin-sensitizing agent that activates the peroxisome proliferator-activated receptor gamma and influences the expression of multiple genes involved in carbohydrate and lipid metabolism. However, it is unknown which of these many target genes play primary roles in determining the antidiabetic and hypolipidemic effects of thiazolidinediones. To specifically investigate the role of the Cd36 fatty acid transporter gene in the insulin-sensitizing actions of thiazolidinediones, we studied the metabolic effects of pioglitazone in spontaneously hypertensive rats (SHR) that harbor a deletion mutation in Cd36 in comparison to congenic and transgenic strains of SHR that express wild-type Cd36. In congenic and transgenic SHR with wild-type Cd36, administration of pioglitazone was associated with significantly lower circulating levels of fatty acids, triglycerides, and insulin as well as lower hepatic triglyceride levels and epididymal fat pad weights than in SHR harboring mutant Cd36. Additionally, insulin-stimulated glucose oxidation in isolated soleus muscle was significantly augmented in pioglitazone-fed rats with wild-type Cd36 versus those with mutant Cd36. The Cd36 genotype had no effect on pioglitazone-induced changes in blood pressure. These findings provide direct pharmacogenetic evidence that in the SHR model, Cd36 is a key determinant of the insulin-sensitizing actions of a thiazolidinedione ligand of peroxisome proliferator-activated receptor gamma. 相似文献
64.
65.
David M. Byers Harold W. Cook Frederick B. St. C. Palmer Matthew W. Spence 《Neurochemical research》1989,14(6):503-509
Distinct sets of cellular proteins were labeled with [3H]myristic and [3H]palmitic acids in primary (rat neurons and astroglia) and continuous (murine N1E-115 neuroblastoma and rat C6 glioma) cell cultures derived from the nervous system. Both soluble and membrane proteins were modified by myristate in a hydroxylamine-stable (amide) linkage, while palmitoylated proteins were esterlinked and almost exclusively membrane bound. Chain elongation of both labeled fatty acids prior to acylation was observed, but no protein amide-liked [3H]myristate originating from [3H]palmitate was detected. Fatty acylation profiles differed considerably among most of the cell lines, except for rat astroglial and glioma cells in which myristoylated proteins appeared to be almost identical based on SDS gel electrophoresis. An unidentified 47 kDa myristoylated protein was labeled to a significantly greater extent in astroglial than in glioma cells; the expression of this protein could be related to transformation or development in cells of glial origin. 相似文献
66.
67.
Multiscale landscape genomic models to detect signatures of selection in the alpine plant Biscutella laevigata 下载免费PDF全文
Kevin Leempoel Christian Parisod Céline Geiser Stéphane Joost 《Ecology and evolution》2018,8(3):1794-1806
Plant species are known to adapt locally to their environment, particularly in mountainous areas where conditions can vary drastically over short distances. The climate of such landscapes being largely influenced by topography, using fine‐scale models to evaluate environmental heterogeneity may help detecting adaptation to micro‐habitats. Here, we applied a multiscale landscape genomic approach to detect evidence of local adaptation in the alpine plant Biscutella laevigata. The two gene pools identified, experiencing limited gene flow along a 1‐km ridge, were different in regard to several habitat features derived from a very high resolution (VHR) digital elevation model (DEM). A correlative approach detected signatures of selection along environmental gradients such as altitude, wind exposure, and solar radiation, indicating adaptive pressures likely driven by fine‐scale topography. Using a large panel of DEM‐derived variables as ecologically relevant proxies, our results highlighted the critical role of spatial resolution. These high‐resolution multiscale variables indeed indicate that the robustness of associations between genetic loci and environmental features depends on spatial parameters that are poorly documented. We argue that the scale issue is critical in landscape genomics and that multiscale ecological variables are key to improve our understanding of local adaptation in highly heterogeneous landscapes. 相似文献
68.
As well as killing pest insects, the rhizosphere competent insect-pathogenic fungus Metarhizium robertsii also boosts plant growth by providing nitrogenous nutrients and increasing resistance to plant pathogens. Plant roots secrete abundant nutrients but little is known about their utilization by Metarhizium spp. and the mechanistic basis of Metarhizium-plant associations. We report here that M. robertsii produces an extracellular invertase (MrInv) on plant roots. Deletion of MrInv (⊿MrInv) reduced M. robertsii growth on sucrose and rhizospheric exudates but increased colonization of Panicum virgatum and Arabidopsis thaliana roots. This could be accounted for by a reduction in carbon catabolite repression in ⊿MrInv increasing production of plant cell wall-degrading depolymerases. A non-rhizosphere competent scarab beetle specialist Metarhizium majus lacks invertase which suggests that rhizospheric competence may be related to the sugar metabolism of different Metarhizium species. 相似文献
69.
Marian Yallop Heike Hirst Martyn Kelly Steve Juggins Jane Jamieson Robin Guthrie 《Aquatic Botany》2009,90(4):289-295
We assessed the feasibility of using herbarium specimens to validate reference conditions in the UK by comparing diatom community composition of river sites with both recent and historic diatom samples. The question of substrate specificity was addressed by comparing epilithon (stone-derived) and epiphyton (plant-derived) samples from a number of rivers. No significant differences were found between the Trophic Diatom Index (TDI), species richness, species diversity, and percentage of motile valves between paired diatom samples (epilithic and epiphytic) from contemporary samples. Significant differences were recorded between a number of indices derived from analysis of the historic diatom samples on plant material sampled pre-1930 compared with diatoms from stones collected post-1990 from the same river location. The TDI, mean species richness, and species diversity and percentage of motile valves and nutrient tolerant valves were all significantly greater in the contemporary samples (p ≤ 0.05). The percentage of nutrient sensitive valves was significantly lower in the contemporary samples (p ≤ 0.05).The relative abundance of Achnanthidium minutissimum and Cocconeis placentula var. lineata was significantly greater on the herbarium material compared to matched contemporary samples. Calculated values for the TDI (43 ± 3) expected at reference conditions were similar to the observed TDI values derived from herbarium material (44 ± 12) showing no significant deviation in ecological status. 相似文献
70.