全文获取类型
收费全文 | 7625篇 |
免费 | 545篇 |
国内免费 | 4篇 |
出版年
2021年 | 70篇 |
2020年 | 43篇 |
2019年 | 62篇 |
2018年 | 104篇 |
2017年 | 64篇 |
2016年 | 97篇 |
2015年 | 188篇 |
2014年 | 215篇 |
2013年 | 475篇 |
2012年 | 333篇 |
2011年 | 329篇 |
2010年 | 226篇 |
2009年 | 221篇 |
2008年 | 329篇 |
2007年 | 354篇 |
2006年 | 304篇 |
2005年 | 323篇 |
2004年 | 332篇 |
2003年 | 312篇 |
2002年 | 303篇 |
2001年 | 269篇 |
2000年 | 271篇 |
1999年 | 241篇 |
1998年 | 113篇 |
1997年 | 93篇 |
1996年 | 81篇 |
1995年 | 87篇 |
1994年 | 84篇 |
1993年 | 88篇 |
1992年 | 179篇 |
1991年 | 146篇 |
1990年 | 159篇 |
1989年 | 162篇 |
1988年 | 129篇 |
1987年 | 144篇 |
1986年 | 99篇 |
1985年 | 132篇 |
1984年 | 109篇 |
1983年 | 83篇 |
1982年 | 70篇 |
1981年 | 57篇 |
1980年 | 48篇 |
1979年 | 67篇 |
1978年 | 42篇 |
1977年 | 58篇 |
1976年 | 40篇 |
1975年 | 40篇 |
1974年 | 52篇 |
1973年 | 48篇 |
1970年 | 57篇 |
排序方式: 共有8174条查询结果,搜索用时 910 毫秒
941.
Shimoda Y Nagata M Suzuki A Abe M Sato S Kato T Tabata S Higashi S Uchiumi T 《Plant & cell physiology》2005,46(1):99-107
We characterized the expression profiles of LjHb1 and LjHb2, non-symbiotic hemoglobin (non-sym-Hb) genes of Lotus japonicus. Although LjHb1 and LjHb2 showed 77% homology in their cDNA sequences, LjHb2 is located in a unique position in the phylogenetic tree of plant Hbs. The 5'-upstream regions of both genes contain the motif AAAGGG at a position similar to that in promoters of other non-sym-Hb genes. Expression profiles obtained by using quantitative RT-PCR showed that LjHb1 and LjHb2 were expressed in all tissues of mature plants, and expression was enhanced in mature root nodules. LjHb1 was strongly induced under both hypoxic and cold conditions, and by the application of nitric oxide (NO) donor, whereas LjHb2 was induced only by the application of sucrose. LjHb1 was also induced transiently by the inoculation with the symbiotic rhizobium Mesorhizobium loti MAFF303099. Observations using fluorescence microscopy revealed the induction of LjHb1 expression corresponded to the generation of NO. These results suggest that non-sym-Hb and NO have important roles in stress adaptation and in the early stage of legume-rhizobium symbiosis. 相似文献
942.
Malquichagua Salazar KJ Delgado Paredes GE Lluncor LR Young MC Kato MJ 《Phytochemistry》2005,66(5):573-579
An extract of leaves and stems of Peperomia villipetiola has been found to contain myristicin (3-methoxy-4,5-methylenedioxy-allylbenzene) and seven chromenes, whose structures are methyl 5-hydroxy-7-methyl-2,2-dimethyl-2H-1-chromene-6-carboxylate (1), methyl 5-methoxy-7-methyl-2,2-dimethyl-2H-1-chromene-8-carboxylate (2), methyl 7-hydroxy-5-methyl-2,2-dimethyl-2H-1-chromene-6-carboxylate (3), methyl 7-methoxy-5-methyl-2,2-dimethyl-2H-1-chromene-6-carboxylate (4), 5-methanol-7-hydroxy-2,2-dimethyl-2H-1-chromene-6-carboxylic acid (5), 5-methanol-7-methoxy-2,2-dimethyl-2H-1-chromene-6-carboxylic acid (6), and methyl 5-acetoxymethanol-7-hydroxy-2,2-dimethyl-2H-1-chromene-6-carboxylate (7). A biosynthetic rationale for 1-7 suggests that orsellinic acid may be a common intermediate. The anti-fungal activities of the chromenes were measured bioautographically against Cladosporium cladosporioides and Cladosporium sphaerospermum: compounds 6 and 7 were found to be the most active. 相似文献
943.
Kageyama H Funahashi H Hirayama M Takenoya F Kita T Kato S Sakurai J Lee EY Inoue S Date Y Nakazato M Kangawa K Shioda S 《Regulatory peptides》2005,126(1-2):67-71
Ghrelin, a novel peptide isolated from stomach tissue of rats and humans, has been identified as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). In addition to its secretion from the stomach, ghrelin is also expressed in the hypothalamic arcuate nucleus, intestine, kidney, placenta, and pancreas. GHS-R mRNA, on the other hand, is expressed in the hypothalamus, pituitary, heart, lung, liver, pancreas, stomach, intestine, and adipose tissue. Ghrelin is considered to have important roles in feeding regulation and energy metabolism as well as in the release of growth hormone (GH). Recent physiological experiments on the pancreas have shown that ghrelin regulates insulin secretion. However, sites of action of ghrelin in the pancreas are yet to be identified. In this study, to gain insight into the role of ghrelin in rat pancreatic islets, we used immunohistochemistry to determine the localization of ghrelin and GHS-R in islet cells. Double fluorescence immunohistochemistry revealed that weak GHS-R-like immunoreactivity was found in B cells containing insulin. GHS-R immunoreactivity overlapped that of glucagon-like immunoreactive cells. Moreover, both ghrelin and GHS-R-like immunoreactivities were detected mostly in the same cells in the periphery of the islets of Langerhans. These observations suggest that ghrelin is synthesized and secreted from A cells, and acts back on A cells in an autocrine and/or paracrine manner. In addition, ghrelin may act on B cells via GHS-R to regulate insulin secretion. 相似文献
944.
Mizuno K Sawa M Harada H Taoka I Yamashita H Oue M Tsujiuchi H Arai Y Suzuki S Furutani Y Kato S 《Bioorganic & medicinal chemistry》2005,13(3):855-868
The synthesis and evaluation of a novel series of 1,7-cyclized indole-based human adrenergic receptor (beta3-AR) agonists are reported. The synthesis of a variety of 1,7-cyclized indole part was accomplished by the Mitsunobu reaction or a ring closing metathesis (RCM) reaction. SAR studies revealed that expansion of the ring size resulted in considerable selectivity against the beta1- and beta2-ARs. Compound 26, an eight-membered ring analogue with a double bond on its 1,7-linker portion, was found to be a potent beta3-AR agonist (EC50 = 0.75 nM, IA = 90%) with extremely high selectivity for the beta3-AR over the beta1- and beta2-ARs. 相似文献
945.
A novel cytochrome P450 is implicated in brassinosteroid biosynthesis via the characterization of a rice dwarf mutant, dwarf11, with reduced seed length 总被引:20,自引:0,他引:20 下载免费PDF全文
Tanabe S Ashikari M Fujioka S Takatsuto S Yoshida S Yano M Yoshimura A Kitano H Matsuoka M Fujisawa Y Kato H Iwasaki Y 《The Plant cell》2005,17(3):776-790
We have characterized a rice (Oryza sativa) dwarf mutant, dwarf11 (d11), that bears seeds of reduced length. To understand the mechanism by which seed length is regulated, the D11 gene was isolated by a map-based cloning method. The gene was found to encode a novel cytochrome P450 (CYP724B1), which showed homology to enzymes involved in brassinosteroid (BR) biosynthesis. The dwarf phenotype of d11 mutants was restored by the application of the brassinolide (BL). Compared with wild-type plants, the aberrant D11 mRNA accumulated at higher levels in d11 mutants and was dramatically reduced by treatment with BL, implying that the gene is feedback-regulated by BL. Precise determination of the defective step(s) in BR synthesis in d11 mutants proved intractable because of tissue specificity and the complex control of BR accumulation in plants. However, 6-deoxotyphasterol (6-DeoxoTY) and typhasterol (TY), but not any upstream intermediates before these compounds, effectively restored BR response in d11 mutants in a lamina joint bending assay. Multiple lines of evidence together suggest that the D11/CYP724B1 gene plays a role in BR synthesis and may be involved in the supply of 6-DeoxoTY and TY in the BR biosynthesis network in rice. 相似文献
946.
A sorting nexin PpAtg24 regulates vacuolar membrane dynamics during pexophagy via binding to phosphatidylinositol-3-phosphate 下载免费PDF全文
Ano Y Hattori T Oku M Mukaiyama H Baba M Ohsumi Y Kato N Sakai Y 《Molecular biology of the cell》2005,16(2):446-457
Diverse cellular processes such as autophagic protein degradation require phosphoinositide signaling in eukaryotic cells. In the methylotrophic yeast Pichia pastoris, peroxisomes can be selectively degraded via two types of pexophagic pathways, macropexophagy and micropexophagy. Both involve membrane fusion events at the vacuolar surface that are characterized by internalization of the boundary domain of the fusion complex, indicating that fusion occurs at the vertex. Here, we show that PpAtg24, a molecule with a phosphatidylinositol 3-phosphate-binding module (PX domain) that is indispensable for pexophagy, functions in membrane fusion at the vacuolar surface. CFP-tagged PpAtg24 localized to the vertex and boundary region of the pexophagosome-vacuole fusion complex during macropexophagy. Depletion of PpAtg24 resulted in the blockage of macropexophagy after pexophagosome formation and before the fusion stage. These and other results suggest that PpAtg24 is involved in the spatiotemporal regulation of membrane fusion at the vacuolar surface during pexophagy via binding to phosphatidylinositol 3-phosphate, rather than the previously suggested function in formation of the pexophagosome. 相似文献
947.
Production of infectious hepatitis C virus in tissue culture from a cloned viral genome 总被引:39,自引:0,他引:39
Wakita T Pietschmann T Kato T Date T Miyamoto M Zhao Z Murthy K Habermann A Kräusslich HG Mizokami M Bartenschlager R Liang TJ 《Nature medicine》2005,11(7):791-796
Hepatitis C virus (HCV) infection causes chronic liver diseases and is a global public health problem. Detailed analyses of HCV have been hampered by the lack of viral culture systems. Subgenomic replicons of the JFH1 genotype 2a strain cloned from an individual with fulminant hepatitis replicate efficiently in cell culture. Here we show that the JFH1 genome replicates efficiently and supports secretion of viral particles after transfection into a human hepatoma cell line (Huh7). Particles have a density of about 1.15-1.17 g/ml and a spherical morphology with an average diameter of about 55 nm. Secreted virus is infectious for Huh7 cells and infectivity can be neutralized by CD81-specific antibodies and by immunoglobulins from chronically infected individuals. The cell culture-generated HCV is infectious for chimpanzee. This system provides a powerful tool for studying the viral life cycle and developing antiviral strategies. 相似文献
948.
Iron regulatory protein 2 (IRP2), a regulator of iron metabolism, is modulated by ubiquitination and degradation. We have shown that IRP2 degradation is triggered by heme-mediated oxidation. We report here that not only Cys201, an invariant residue in the heme regulatory motif (HRM), but also His204 is critical for IRP2 degradation. Spectroscopic studies revealed that Cys201 binds ferric heme, whereas His204 is a ferrous heme binding site, indicating the involvement of these residues in sensing the redox state of the heme iron and in generating the oxidative modification. Moreover, the HRM in IRP2 has been suggested to play a critical role in its recognition by the HOIL-1 ubiquitin ligase. Although HRMs are known to sense heme concentration by simply binding to heme, the HRM in IRP2 specifically contributes to its oxidative modification, its recognition by the ligase, and its sensing of iron concentration after iron is integrated into heme. 相似文献
949.
Faizal I Dozen K Hong CS Kuroda A Takiguchi N Ohtake H Takeda K Tsunekawa H Kato J 《Journal of industrial microbiology & biotechnology》2005,32(11-12):542-547
Pseudomonas putida T-57 was isolated from an activated sludge sample after enrichment on mineral salts basal medium with toluene as a sole source of carbon. P. putida T-57 utilizes n-butanol, toluene, styrene, m-xylene, ethylbenzene, n-hexane, and propylbenzene as growth substrates. The strain was able to grow on toluene when liquid toluene was added to mineral salts basal medium at 10-90% (v/v), and was tolerant to organic solvents whose log P(ow) (1-octanol/water partition coefficient) was higher than 2.5. Enzymatic and genetic analysis revealed that P. putida T-57 used the toluene dioxygenase pathway to catabolize toluene. A cis-toluene dihydrodiol dehydrogenase gene (todD) mutant of T-57 was constructed using a gene replacement technique. The todD mutant accumulated o-cresol (maximum 1.7 g/L in the aqueous phase) when cultivated in minimal salts basal medium supplemented with 3% (v/v) toluene and 7% (v/v) 1-octanol. Thus, T-57 is thought to be a good candidate host strain for bioconversion of hydrophobic substrates in two-phase (organic-aqueous) systems. 相似文献
950.