全文获取类型
收费全文 | 3261篇 |
免费 | 226篇 |
专业分类
3487篇 |
出版年
2023年 | 15篇 |
2022年 | 33篇 |
2021年 | 61篇 |
2020年 | 45篇 |
2019年 | 51篇 |
2018年 | 71篇 |
2017年 | 67篇 |
2016年 | 98篇 |
2015年 | 147篇 |
2014年 | 159篇 |
2013年 | 245篇 |
2012年 | 267篇 |
2011年 | 262篇 |
2010年 | 173篇 |
2009年 | 141篇 |
2008年 | 246篇 |
2007年 | 205篇 |
2006年 | 222篇 |
2005年 | 204篇 |
2004年 | 175篇 |
2003年 | 156篇 |
2002年 | 115篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 23篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1993年 | 7篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 14篇 |
1985年 | 10篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1970年 | 5篇 |
1968年 | 9篇 |
1967年 | 5篇 |
排序方式: 共有3487条查询结果,搜索用时 0 毫秒
1.
2.
Heterologous hybridization of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) restores the enzyme activities 总被引:3,自引:0,他引:3
A Incharoensakdi T Takabe T Takabe T Akazawa 《Biochemical and biophysical research communications》1985,126(2):698-704
The catalytic core (A8) and small subunit (B) of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) were isolated from two species of cyanobacteria (Aphanothece halophytica and Synechococcus ACMM 323) as well as from the photosynthetic purple sulfur bacterium, Chromatium vinosum. The subunit B is essential for the activity of all three enzymes. The heterologous hybridization of RuBisCO molecules from the three organisms was attempted and the reconstitution of the catalytically active hybrid was achieved between A8 derived from either Aphanothece or Synechococcus and subunit B from Aphanothece, Synechococcus or Chromatium. However, reconstitution of the enzymically active hybrid between A8 from Chromatium and B subunits from the cyanobacteria could not be achieved. Experiments by using high performance liquid column chromatography also showed the formation of a heterologous hybrid possessing RuBP carboxylase activity. 相似文献
3.
Centrifugal filtration through a double layer of silicone oil was applied to determine the intermembrane space of organelles enclosed by double envelope membranes, i.e. proplastids, chloroplasts, mitochondria and amyloplasts. The organelles, capable of transporting adenylates by an adenylate translocator located in the inner envelope membrane, were incubated with increasing concentrations of adenylates while maintaining their specific radioactivities constant. Intermembrane spaces were estimated by extrapolation of radioactivities recovered after filtration of the organelles. The values estimated were compared to those obtained employing the classical method measuring the intake of [14C]-sucrose and [14C]-sorbitol which are impermeable to the inner membranes of organelles. The intermembrane space determined by the present method was shown to be uniformly smaller than the sucrose-permeable space which was always smaller than the sorbitol-permeable space. 相似文献
4.
The genetic differentiation among populations of the leaf beetle Chrysolina virgata living in wetlands of Japan was studied based on the sequence data of the mitochondrial cytochrome oxidase subunit I gene region (750 bp). Two distinct lineages of mitochondrial haplotypes were found: one (clade A) consisted of 26 haplotypes distributed over the distribution range of C. virgata between north‐east Honshu and Kyushu, whereas the other (clade B) was monotypic and confined to a small region in north‐east Honshu where it coexisted with clade A. Nested clade analysis for these haplotypes suggested that range expansion and following differentiation due to isolation by distance might have resulted in the present distribution pattern of the haplotypes in clade A. We discuss the evolutionary process leading to the occurrence of two distinct haplotype clades in Japan in terms of repeated colonization from the continent and range expansion and contraction during climatic changes. 相似文献
5.
6.
7.
The anatomical framework of the jawbones is highly conserved among most of the Osteichthyes, including the tetrapods. However, our recent study suggested that the premaxilla, the rostralmost upper jaw bone, was rearranged during the evolution of therian mammals, being replaced by the septomaxilla at least in the lateral part. In the present study, to understand more about the process of evolution from the ancestral upper jaw to the therian face, we re-examined the development of the therian premaxilla (incisive bone). By comparing mouse, bat, goat, and cattle fetuses, we confirmed that the therian premaxilla has dual developmental origins, the lateral body and the palatine process. This dual development is widely conserved among the therian mammals. Cell-lineage-tracing experiments using Dlx1-CreERT2 mice revealed that the palatine process arises in the ventral part of the premandibular domain, where the nasopalatine nerve distributes, whereas the lateral body develops from the maxillary prominence in the domain of the maxillary nerve. Through comparative analysis using various tetrapods, we concluded that the palatine process should not be considered part of the ancestral premaxilla. It rather corresponds to the anterior region of the vomerine bone of nonmammalian tetrapods. Thus, the present findings indicate that the true premaxilla was completely lost during the evolution of the therian mammals, resulting in the establishment of the unique therian face as an evolutionary novelty. Reconsideration of the homological framework of the cranial skeleton based on the topographical relationships of the ossification center during embryonic development is warranted. 相似文献
8.
The intra-chloroplastic distribution of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) between thylakoid membranes and stroma was studied by determining the enzyme activities in the two fractions, obtained by the rapid centrifugation of hypotonically disrupted chloroplast preparations of spinach and pea leaf tissues. The membrane-associated form of RuBisCO was found to increase in proportion to the concentration of MgCl2 in the disrupting medium; with 20 mM MgCl2 approximately 20% of the total RuBisCO of spinach chloroplasts and 10% of that of pea chloroplasts became associated with thylakoid membranes. Once released from membranes in the absence of MgCl2, addition of MgCl2 did not cause reassociation of the enzyme. The inclusion of KCl in the hypotonic disruption buffer also caused the association of RuBisCO with membranes; however, up to 30 mM KCl, only minimal enzyme activities could be detected in the membranes, whereas above 40 mM KCl there was a sharp increase in the membrane-associated form of the enzyme.Higher concentrations of chloroplasts during the hypotonic disruption, as well as addition of purified preparations of RuBisCO to the hypotonic buffer, resulted in an increase of membrane-associated activity. Therefore, the association of the enzyme with thylakoid membranes appears to be dependent on the concentration of RuBisCO. P-glycerate kinase and aldolase also associated to the thylakoid membranes but NADP-linked glyceraldehyde-3-P dehydrogenase did not. The optimal conditions for enzyme association with the thylakoid membranes were examined; maximal association occurred at pH 8.0. The association was temperature-insensitive in the range of 4° to 25° C. RuBisCO associated with the thylakoid membranes could be gradually liberated to the soluble form upon shaking in a Vortex mixer at maximal speed, indicating that the association is loose.Abbreviations DTT
dithiothreitol
- RuBP
ribulose 1,5-bisphosphate
- RuBisCO
ribulose 1,5-bisphosphate carboxylase/oxygenase
- MES
2-(N-morpholino) ethane sulfonic acid 相似文献
9.
Enzymic mechanism of starch breakdown in germinating rice seeds : 11. Ultrastructural changes in scutellar epithelium 总被引:4,自引:2,他引:2 下载免费PDF全文
The ultrastructural changes occurring in the scutellar epithelium cells of rice seeds have been studied during germination and early seedling growth. During this time, several prominent structural changes occur, including (a) formation, development, and proliferation of organelles such as mitochondria, rough endoplasmic reticulum, free ribosomes, and Golgi apparatus; (b) folded structural modification of plasmamembranes in later stages; and (c) conspicuous decrease in lipid-storing spherosomes. Glyoxysome-like electron dense particles are detectable but their formation is much less prominent. It is conceivable that all these structural changes are related to the enhancement of the metabolic activities of the epithelial cells including the synthesis of hydrolytic enzymes such as α-amylase and their secretion into the endosperm tissues. Some enzyme activities characteristic of mitochondria and glyoxysomes have been determined using the crude scutellar extracts, and the results dealing with the low activities of the glyoxylate cycle enzymes and palmitoyl-coenzyme A oxidase appear to indicate that fatty acid breakdown is possibly via mitochondrial β-oxidation, although we reserve a definitive conclusion on the glyoxysomes being nonfunctional in fatty acid oxidation in rice seedlings. 相似文献
10.
Enzymic mechanisms of starch breakdown in germinating rice seeds: 7. Amylase formation in the epithelium 总被引:9,自引:8,他引:1 下载免费PDF全文
The time sequence analysis of the starch digestion pattern of the thin sectioned germinating rice (Oryza sativa L.) seed specimens using the starch film method showed that at the initial stage amylase activity was almost exclusively localized in the epithelium septum between the scutellum and endosperm. Starch breakdown in the endosperm tissues began afterward; amylase activity in the aleurone layers was detectable only after 2 days. Polyacrylamide gel electrofocusing (pH 4 to 6) revealed nearly the same zymogram patterns between endosperm and scutellum extracts, although additional amylase bands appeared in the endosperm extracts at later germination stages (4 to 6 days). These are presumably attributable to the newly synthesized enzyme molecules in the aleurone cells. 相似文献