全文获取类型
收费全文 | 57043篇 |
免费 | 2476篇 |
国内免费 | 2861篇 |
专业分类
62380篇 |
出版年
2023年 | 654篇 |
2022年 | 1035篇 |
2021年 | 1090篇 |
2020年 | 1243篇 |
2019年 | 1510篇 |
2018年 | 1442篇 |
2017年 | 1273篇 |
2016年 | 1295篇 |
2015年 | 1296篇 |
2014年 | 2624篇 |
2013年 | 4178篇 |
2012年 | 1843篇 |
2011年 | 2657篇 |
2010年 | 1901篇 |
2009年 | 2511篇 |
2008年 | 2637篇 |
2007年 | 2674篇 |
2006年 | 2316篇 |
2005年 | 2201篇 |
2004年 | 1812篇 |
2003年 | 1762篇 |
2002年 | 1499篇 |
2001年 | 1154篇 |
2000年 | 1027篇 |
1999年 | 970篇 |
1998年 | 975篇 |
1997年 | 920篇 |
1996年 | 911篇 |
1995年 | 872篇 |
1994年 | 835篇 |
1993年 | 750篇 |
1992年 | 729篇 |
1991年 | 636篇 |
1990年 | 578篇 |
1989年 | 563篇 |
1988年 | 476篇 |
1987年 | 509篇 |
1986年 | 373篇 |
1985年 | 824篇 |
1984年 | 1195篇 |
1983年 | 858篇 |
1982年 | 941篇 |
1981年 | 810篇 |
1980年 | 771篇 |
1979年 | 669篇 |
1978年 | 480篇 |
1977年 | 485篇 |
1976年 | 399篇 |
1975年 | 340篇 |
1974年 | 342篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Saori Oka 《Biochemical and biophysical research communications》2010,395(2):232-7396
GPR35 is a rhodopsin-like G protein-coupled receptor identified in 1998. It has been reported that kynurenic acid, a tryptophan metabolite, may act as an endogenous ligand for GPR35. However, the concentrations of kynurenic acid required to elicit the cellular responses are usually high, raising the possibility that another endogenous ligand may exist. In this study, we searched for another endogenous ligand for GPR35. Finally, we found that the magnitude of the Ca2+ response induced by 2-acyl lysophosphatidic acid in the GPR35-expressing HEK293 cells was markedly greater than that in the vector-transfected control cells. Such a difference was not apparent in the case of 1-acyl lysophosphatidic acid. 2-Acyl lysophosphatidic acid also caused the sustained activation of RhoA and the phosphorylation of extracellular signal-regulated kinase, and triggered the internalization of the GPR35 molecule. These results strongly suggest that 2-acyl lysophosphatidic acid is an endogenous ligand for GPR35. 相似文献
82.
Abstract The bifunctional T-protein (chorismate mutase-T: cyclohexadienyl dehydrogenase) of l -tyrosine biosynthesis was found to be present in all genera making up the enteric bacteria. The dehydrogenase component of the T-protein was active with both prephenate and l -arogenate, showing it to be a cyclohexadienyl dehydrogenase. The dehydrogenase component, but not the mutase component, of the T-protein was feedback-inhibited by l -tyrosine. Unlike some other bifunctional proteins, the T-protein has evolved recently and is not ubiquitous. However, once the biochemical specialization of bifunctionality becomes established, the results indicate that such character states are strongly conserved through evolutionary time. Thus, bifunctional proteins can provide particularly reliable markers for small (recent origin), intermediate, and large (ancient origin) phylogenetic clusters. 相似文献
83.
The effect of caffeine,different fixation regimes and low temperature on microtubules in the cells of higher plants 总被引:2,自引:0,他引:2
Caffeine, (1:3:7-tri-methyl-xanthine), either as a prefixation treatment or included with glutaralde-hyde as the primary fixative, destroys or disorganises the microtubules associated with the formation of secondary walls in fibres from the flowering stem of the grass Lolium temulentum L. There is no observable effect of caffeine treatment on the microtubules associated with primary wall formation in collenchyma and young fibres from L. temulentum or in root cap cells of Zea mays L. and Phaseolus vulgaris L. The microtubules associated with primary wall formation are destroyed by cold treatment but not those associated with secondary wall formation. Tannic acid included in the fixative shows the microtubules associated with secondary wall formation in fibres of L. temulentum to be composed of 13 subunits. Treatment with lanthanum hydroxide does not stain the core or the halo of the microtubules.Abbreviation PIPES
Piperazine N-N- bis 2 ethanol sulphonic acid
The Grassland Research Institute is financed through the Agricultural Research Council 相似文献
84.
85.
The results of a detailed analysis of 100 supernumerary limbs generated by 180° ipsilateral rotation (on the same limb stump) of regeneration blastemas is presented. The limbs were analyzed in terms of their position of origin, frequency, cartilage structure by Victoria blue staining, and muscle structure by serial sections. Single, double, or triple supernumeraries can be produced at no unique position of origin, although the posterodorsal quadrant was preferred. Four classes of supernumerary limbs were generated by such operations—normal; double dorsal or double ventral; part normal/part mirror imaged; part normal/part inverted in approximately equal frequencies. After amputation of these supernumeraries the same muscle patterns are faithfully regenerated. A hypothesis to explain the production of these abnormal limbs is proposed based on the observed phenomenon of fusion of supernumerary blastemata, but their regenerative behaviour presents problems for current models of pattern formation. Similar results have been obtained with developing limb buds and the relation between development and regeneration is discussed. 相似文献
86.
Abstract: Phenylacetic acid, the major metabolite of phenylethylamine, has been identified and quantitated in rat brain regions by capillary column high-resolution gas chromatography mass spectrometry. Its distribution is heterogeneous and correlates with that of phenylethylamine. The values obtained were (ng/g ± SEM): whole brain, 31.2 ± 2.7; caudate nucleus, 64.6 ± 6.5; hypothalamus, 60.1 ± 7.4; cerebellum, 31.3 ± 2.9; brainstem, 33.1 ± 3.3, and the "rest," 27.6 ± 3.0. 相似文献
87.
Novel 2D van der Waals heterostructures with innovative bimetallic oxychloride (Bi‐ and Sb‐based oxychloride) nanosheets that are well dispersed on reduced graphene oxide nanosheets, are established through element engineering for superior potassium ion battery (PIBs) anodes. This material displays an exceptional electrochemical performance, obtaining a discharge capacity as high as 360 mAh g?1 at 100 mA g?1 after running 1000 cycles for over 9 months with a capacity preservation percentage of 88.5% and achieving a discharge capacity as high as 319 mAh g?1 at 1000 mA g?1, in addition to the low charge/discharge plateaus for anodes and promising full cell performance. More significantly, the nature of such 2D van der Waals heterostructures, including the element engineering for morphology control, the function of each component of heterostructures, the mechanism of potassium ion storage, and the process of K+ intercalation accompanied with the lattice distortion and chemical bond breakages, is explored in depth. This study is critical for not only paving the way for the practical application of PIBs but also shedding light on fundamentals of potassium ion storage in 2D van der Waals heterostructures. 相似文献
88.
A possibly physiologically significant inhibition of yeast enolase by fluoride occurs in the absence of inorganic phosphate. The inhibition increases with time, is strongly dependent on fluoride concentration and requires substrate and “catalytic” Mg2+. The inhibition increases more slowly in the presence of product (phosphoenolpyruvate) than substrate (2-phosphoglycerate). The dependence on fluoride concentration and the spans of substrate analogue displacement titrations suggest the inhibition is produced by two moles of fluoride per active site. 相似文献
89.
90.
The shikimate/arogenate pathway: Link between carbohydrate metabolism and secondary metabolism 总被引:2,自引:0,他引:2
Roy A. Jensen 《Physiologia plantarum》1986,66(1):164-168