全文获取类型
收费全文 | 1354篇 |
免费 | 52篇 |
出版年
2021年 | 10篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 18篇 |
2016年 | 13篇 |
2015年 | 39篇 |
2014年 | 32篇 |
2013年 | 42篇 |
2012年 | 68篇 |
2011年 | 76篇 |
2010年 | 38篇 |
2009年 | 35篇 |
2008年 | 54篇 |
2007年 | 43篇 |
2006年 | 52篇 |
2005年 | 55篇 |
2004年 | 62篇 |
2003年 | 47篇 |
2002年 | 63篇 |
2001年 | 48篇 |
2000年 | 61篇 |
1999年 | 47篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 47篇 |
1991年 | 36篇 |
1990年 | 41篇 |
1989年 | 38篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 20篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 20篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1968年 | 5篇 |
1967年 | 8篇 |
排序方式: 共有1406条查询结果,搜索用时 15 毫秒
991.
Kasai S Urushibata S Hozumi K Yokoyama F Ichikawa N Kadoya Y Nishi N Watanabe N Yamada Y Nomizu M 《Biochemistry》2007,46(13):3966-3974
Amyloid fibril formation is associated with several pathologies, including Alzheimer's disease, Parkinson's disease, type II diabetes, and prion diseases. Recently, a relationship between basement membrane components and amyloid deposits has been reported. The basement membrane protein, laminin, may be involved in amyloid-related diseases, since laminin is present in amyloid plaques in Alzheimer's disease and binds to amyloid precursor protein. Recently, we showed that peptide A208 (AASIKVAVSADR), the IKVAV-containing peptide, formed amyloid-like fibrils. We previously identified 60 cell adhesive sequences in laminin-1 using a total of 673 12-mer synthetic peptides. Here, we screened for additional amyloidogenic sequences among 60 cell adhesive peptides derived from laminin-1. We first examined amyloid-like fibril formation by the 60 active peptides with Congo red, a histological dye binding to many amyloid-like proteins. Thirteen peptides were stained with Congo red. Four of the 13 peptides promoted cell attachment and neurite outgrowth like the IKVAV-containing peptide. The four peptides also showed amyloid-like fibril formation in both X-ray diffraction and electron microscopic analyses. The amyloidogenic peptides contain consensus amino acid components, including both basic and acidic amino acids and Ser and Ile residues. These results indicate that at least five laminin-derived peptides can form amyloid-like fibrils. We conclude that the laminin-derived amyloidogenic peptides have the potential to form amyloid-like fibrils in vivo, possibly when laminin-1 is degraded. 相似文献
992.
Masahiro Ichikawa 《Ecological Research》2007,22(3):403-413
Swidden agriculture, commercial logging and plantation development have been considered to be the primary common causes of
degradation and loss of tropical rain forests in Southeast Asia. In this paper, I chose a part of northeastern Sarawak, East
Malaysia as my case study area to analyze the changes in its land-use characteristics. In the study area, as well as primeval
forests, we see that land use began about 100 years ago by a native group called the Iban; commercial logging began in the
1960s, and the development of oil palm plantations began recently. I describe the changes in land use as well as their social
and economic causes by referring to aerial photographs, literature surveys, interviews with government officers and the Iban,
and observation of land use. My analysis of land use demonstrates that on “state land”, where commercial logging and oil palm
plantation development are occurring, large areas of forest have been disturbed in a short period of time. The objective is
to benefit economically in response to the social and economic conditions surrounding the study area. On the other hand, in
the “Iban territory,” where the Iban practice their land use, land conversion has not occurred on a large scale and in a short
period of time, even though the forest has been cut and agricultural fields have been created in response to social and economic
conditions as well. They disperse small agricultural fields throughout their forest land. Therefore, the landscape of the
“Iban territory” is based on secondary forest, composed of patches of forest in various stages and with several types of agricultural
land. Today in Sarawak, monocrop plantations are rapidly expanding and little primeval forest remains. Given these conditions,
the land-use practices of natives such as the Iban will be evaluated from the viewpoint of ecosystem and biodiversity conservation.
It could play an important role in providing habitats for natural wildlife. 相似文献
993.
Sonoda Y Yao SG Sako K Sato T Kato W Ohto MA Ichikawa T Matsui M Yamaguchi J Ikeda A 《The Plant journal : for cell and molecular biology》2007,50(4):586-596
Post-embryonic plant growth is dependent on a functional shoot apical meristem (SAM) that provides cells for continuous development of new aerial organs. However, how the SAM is dynamically maintained during vegetative development remains largely unclear. We report here the characterization of a new SAM maintenance mutant, sha1-1 (shoot apical meristem arrest 1-1), that shows a primary SAM-deficient phenotype at the adult stage. The SHA1 gene encodes a novel RING finger protein, and is expressed most intensely in the shoot apex. We show that, in the sha1-1 mutant, the primary SAM develops normally during the juvenile vegetative stage, but cell layer structure becomes disorganized after entering the adult vegetative stage, resulting in a dysfunctional SAM that cannot initiate floral primordia. The sha1-1 SAM terminates completely at the stage when the wild-type begins to bolt, producing adult plants with a primary inflorescence-deficient phenotype. These observations indicate that SHA1, a putative E3 ligase, is required for post-embryonic SAM maintenance by controlling proper cellular organization. 相似文献
994.
995.
996.
Noguchi R Banno S Ichikawa R Fukumori F Ichiishi A Kimura M Yamaguchi I Fujimura M 《Fungal genetics and biology : FG & B》2007,44(3):208-218
Two-component signal transduction comprising of OS-1 (histidine kinase), OS-4 (MAPKK kinase), OS-5 (MAPK kinase), and OS-2 (MAP kinase) plays an important role in osmotic regulation in Neurospora crassa. To identify the genes regulated downstream of OS-2 MAP kinase, quantitative real-time RT-PCR analysis was conducted in selected genes based on Hog1 MAP kinase regulated genes in yeast. In response to osmotic stress and fludioxonil, expression of six genes that for glycerol synthesis (gcy-1, gcy-3, and dak-1), gluconeogenesis (fbp-1 and pck-1), and catalase (ctt-1) was activated in the wild-type strain, but not in the os-2 mutant. A heat shock treatment also induced their expression in the same way. Consisting with the gene expression, the enzyme activity of glycerol dehydrogenase, but not glycerol-3-phosphate dehydrogenase, was increased in response to osmotic stress and fludioxonil in the wild-type strain. OS-2 was phosphorylated by the OS-1 cascade in response to relatively low osmotic stress and fludioxonil. However, OS-2 phosphorylation by heat shock and a higher osmotic stress was found in the os-1 mutant normally but not in the os-4 and os-5 mutants. These results suggested that non-OS-1 signaling activates OS-2 in an OS-4-dependent manner in such conditions. 相似文献
997.
Nitric oxide synthase (NOS: EC 1.14.13.39) catalyzes L-arginine oxidation to generate nitric oxide (NO) and L-citrulline. Recently, 7-ethoxyresorufin (7-ER), a specific substrate of cytochrome P-4501A1, was used as a cytochrome P-450 inhibitor to study the mechanism underlying the vasodilatation caused by some drugs, and was suggested to inhibit nitric oxide-mediated relaxation. Herein we demonstrate that 7-ER inhibits NO synthesis by uncoupling neuronal nitric oxide synthase (nNOS). 7-ER is a noncompetitive inhibitor of nNOS with respect to L-arginine with a Ki value of 0.76 +/- 0.06 microM. The decrease in NO formation is inversely correlated with an increase in NADPH oxidation. 7-ER binds to nNOS with a Km value of 0.68 +/- 0.07 microM, as calculated from the nNOS-dependent NADPH oxidation in the absence of L-arginine. nNOS catalyzes the reduction of 7-ER at the expense of NADPH. The flavoprotein inhibitor, diphenyleneiodonium chloride (100 microM), completely inhibited nNOS-dependent 7-ER reduction. While nitro-L-arginine (1 mM) and N(G)-nitro-L-arginine methyl ester (1 mM), specific inhibitors of nNOS, and phenylisocyanide (0.1 mM), a specific heme iron ligand, did not affect the reduction of 7-ER. These results indicate that the reductase domain, but not the oxygenase domain, of nNOS is involved in the reduction of 7-ER. 7-ER uncouples nNOS, shunting electrons from the reductase domain to the oxygenase domain of the enzyme. As a consequence, NO synthesis is inhibited. 相似文献
998.
1-O-Acetyl-2,3-dideoxy-3-C-(hydroxymethyl)-4-thiofuranose derivative was synthesized from (S,S)-1,4-bis(benzyloxy)-2,3-epoxybutane derived from (+)-diethyl L-tartrate and the enantiomerically pure (E)-5-(2-bromovinyl)-1-[2',3'-dideoxy-3'-C-(hydroxymethyl)-beta-D-4'- thiopentofuranosyl]uracil 4 was obtained via coupling of silylated uracil followed by palladium-mediated coupling of methyl acrylate. 相似文献
999.
1000.
Bilateral electrolytic lesion of the striatonigral pathways (which convey massive afferents to the substantia nigra) caused a marked lowering of alpha-neo-endorphin (alpha-Neo) and dynorphin A(1-8) [Dyn A(1-8)] levels in the substantia nigra without affecting the alpha-Neo content in the ventral tegmental area. Moreover, unilateral infusion of the axon sparing neurotoxin ibotenate into the striatum, but not into the substantia nigra, decrease these two opioid peptides in the substantia nigra on the side ipsilateral to the lesion, failing to modify the alpha-Neo levels in the ventral tegmental area. Bilateral electrolytic lesion of the habenula augmented alpha-Neo content in the substantia nigra and ventral tegmental area at 8-30 days postlesion without affecting the nigral Dyn A(1-8). These results add further support to the view that alpha-Neo- and Dyn A(1-8)-containing neurons projecting to the substantia nigra originate in the striatum and descend through striatonigral pathways. The present data provide evidence that the habenula may participate in the regulation of the activity of alpha-Neo-immunoreactive neurons in the substantia nigra and ventral tegmental area. 相似文献