全文获取类型
收费全文 | 904篇 |
免费 | 99篇 |
国内免费 | 49篇 |
出版年
2023年 | 15篇 |
2022年 | 22篇 |
2021年 | 18篇 |
2020年 | 34篇 |
2019年 | 58篇 |
2018年 | 51篇 |
2017年 | 33篇 |
2016年 | 44篇 |
2015年 | 40篇 |
2014年 | 50篇 |
2013年 | 85篇 |
2012年 | 43篇 |
2011年 | 49篇 |
2010年 | 53篇 |
2009年 | 49篇 |
2008年 | 36篇 |
2007年 | 49篇 |
2006年 | 23篇 |
2005年 | 44篇 |
2004年 | 29篇 |
2003年 | 38篇 |
2002年 | 30篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1973年 | 1篇 |
排序方式: 共有1052条查询结果,搜索用时 31 毫秒
61.
Shan Huang Yong Xu Wen-Fang Peng Jie Cheng Hui-Hua Li Li-Sha Shen Li-Li Xia 《Journal of cellular biochemistry》2019,120(5):7474-7481
Insulin resistance is associated with impaired glucose uptake and altered protein kinase B (Akt) signaling. Previous studies have suggested asymmetric dimethylarginine (ADMA) and inflammation are two distinguish factors that correlate with insulin resistance (IR). How ADMA and inflammation factors interact and synchronize in the regulation of IR in liver remain to be elucidated. In this study, we systematically investigated whether ADMA is involved in IR using primary hepatocytes, if yes, by via which molecular mechanism. Our results demonstrated that ADMA inhibits insulin sensitivity in a concentration-dependent manner by activating inflammation factors tumor necrosis factor (TNF)-α, interleukin (IL)-1, and IL-6 in primary hepatocytes. Further analysis revealed that mitogen-activated protein kinase (MAPK) signaling pathway act downstream of ADMA and inflammation factors, and inhibition of MAPK pathway rescued the IR. Furthermore, metformin effects has been found which could reverse ADMA-induced IR by suppressing MAPK signaling pathway. To our knowledge, we, for the first time, unveiled the complicated regulatory network and interactions among ADMA, inflammation, and MAPK signaling pathway, which advanced current research on the development and regulation of IR in liver. This study also certainly provided novel insights on comprehensive diagonistics roles of ADMA as a potential biomarker. 相似文献
62.
We have studied the division of postembryonic neuroblasts (Nbs) in the outer proliferation center (OPC) and central brain anlagen of Drosophila. We focused our attention on three aspects of these processes: the pattern of cellular division, the topological orientation of those divisions, and the expression of asymmetric cell fate determinants. Although larval Nbs are of embryonic origin, our results indicate that their properties appear to be modified during development. Several conclusions can be summarized: (i) In early larvae, Nbs divide symmetrically to give rise to two Nbs while in the late larval brain most Nbs divide asymmetrically to bud off an intermediate ganglion mother cell (GMC) that very rapidly divides into two ganglion cells (GC). (ii) Symmetric and asymmetric divisions of OPC Nbs show tangential and radial orientations, respectively. (iii) This change in the pattern of division correlates with the expression of inscuteable, which is apically localized only in asymmetric divisions. (iv) The spindle of asymmetrically dividing Nb is always oriented on an apical-basal axis. (v) Prospero does not colocalize with Miranda in the cortical crescent of mitotic Nbs. (vi) Prospero is transiently expressed in one of the two sibling GCs generated by the division of GMCs. The implications of these results on cell fate specification and differentiation of adult brain neurons are discussed. 相似文献
63.
Sexual selection on plumage and behavior in an avian hybrid zone: experimental tests of male-male interactions 总被引:2,自引:0,他引:2
McDonald DB Clay RP Brumfield RT Braun MJ 《Evolution; international journal of organic evolution》2001,55(7):1443-1451
In western Panama, an unusual hybrid zone exists between white-collared manakins, Manacus candei, and golden-collared manakins, M. vitellinus. Unidirectional introgression of plumage traits from vitellinus into candei has created a region in which all definitively plumaged males have a collar that is lemon-colored. These males are nearly indistinguishable from white-collared candei genetically and morphometrically, but strongly resemble golden-collared vitellinus due to the introgression of secondary sexual plumage traits, particularly the lemon-colored collar. The introgression could be explained by sexual selection for golden-collared traits or by a series of mechanisms that do not invoke sexual selection (e.g., neutral diffusion, dominant allele). Sexual selection on male-male interactions implies behavioral differences among the plumage forms--specifically that golden- and lemon-collared males should be more aggressive than white-collared males. In contrast, the nonsexual hypotheses predict behavioral similarity between lemon- and white-collared males, based on their nearly identical genetics. We tested the sexual selection hypothesis experimentally, by presenting males with taxidermic mounts of the three forms. As response variables, we monitored vocalizations and attacks on the mounts by replicate subject males. Both golden-collared and lemon-collared males were more likely to attack than were white-collared males, as predicted under sexual selection but not by the nonsexual hypotheses. Lemon-collared males were more vocally reactive than either parental form, contrary to the prediction of the nonsexual hypotheses. Our study demonstrates that sexual selection on male-male interactions may play an important role in the dynamics of character evolution and hybrid zones. 相似文献
64.
Sashiwa H Kawasaki N Nakayama A Muraki E Yajima H Yamamori N Ichinose Y Sunamoto J Aiba S 《Carbohydrate research》2003,338(6):557-561
The Michael type reaction of chitosan with ethyl acrylate has been investigated. Although this reaction was quite slow in the case of chitosan, the reiteration of the reaction was an effective means for increasing the degree of substitution (DS) of ethyl ester. The N-carboxyethylchitosan ethyl ester as an intermediate was successfully substituted with various hydrophilic amines, although the simultaneous hydrolysis of the ester to carboxylic acid also occurred. Water-soluble chitosan derivatives were obtained by substitution with hydroxyalkylamines and diamines. 相似文献
65.
1alpha,25-Dihydroxyvitamin D(3) (1alpha,25(OH)2D3) has been shown to modulate not only proliferation and differentiation, but also apoptosis in malignant cells, indicating that it could be useful for the treatment of cancer and psoriasis. However, little information has been available on the binding conformation of the 1alpha,25(OH)2D3 molecule and its analogs with the vitamin D receptor (VDR). Therefore, we synthesized 2alpha-fluorinated A-ring analogs of 19-nor-1alpha,25(OH)2D3 in order to investigate the VDR-binding conformation of the A-rings on the basis of the (19)F NMR analysis. The 2alpha-fluoro-19-nor-1alpha,25-dihydroxyvitamin D3 A-ring analog thus synthesized via a asymmetric catalytic carbonyl-ene cyclization, shows significant activity in transactivation. 相似文献
66.
Tian D Niu C Rose RJ 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2002,104(1):9-16
A regenerable line of Medicago truncatula (Jemalong 2HA) as a recipient species, was fused with the sexually incompatible species Medicago scutellata or Medicago rugosa. The treatments described maintain the chromosome number of the recipient but enable the transfer of small amounts of DNA of
the donor species, probably by intergenomic recombination. Without a chromosome number-change fusion products can readily
regenerate to produce fertile plants; and potentially a library with a diverse array of new genetic material. The selection
of fused cells is based on treatment of the recipient cells with iodoacetamide (IOA), a non-regenerable donor, γ-irradiation
of the donor, and regeneration on a medium favouring the recipient. DNA transfer was demonstrated by amplified fragment length
polymorphism (AFLP), Southern hybridisation and changed morphology.
Received: 21 December 2000 / Accepted: 5 April 2001 相似文献
67.
Axially dissymmetric chiral diimine ligand 2 was prepared from the reaction of (R)-(+)-5,5',6,6',7,7',8,8'-octahydro-[1,1']binaphthyl-2,2'-diamine 1 with 2,6-dichlorobenzaldehyde. The catalytic asymmetric aziridination of alkenes was examined using this novel chiral ligand. Excellent enantioselective aziridination of cinnamates was achieved using C(2)-symmetric chiral ligand 2. 相似文献
68.
The syntheses of new optically active C(2)-symmetrical bis-beta-amino alcohols 1-6 from (S)-2-(1-hydroxy-1,1-diphenylmethyl)-pyrrolidine are described. Especially attention is focused on bridges, which link the two beta-amino alcohol units. These new chiral ligands have been successfully applied in the catalytic enantioselective addition of diethylzinc to aldehydes to give sec-alcohols in good yields with up to 95% enantiomeric excess. 相似文献
69.
Nurrish SJ 《Traffic (Copenhagen, Denmark)》2002,3(1):2-10
It is almost 40 years since Sydney Brenner introduced Caenorhabditis elegans as a model genetic system. During that time mutants with defects in intracellular trafficking have been identified in a diverse range of screens for abnormalities. This should, of course, come as no surprise as it is hard to imagine any biological process in which the regulated movement of vesicles within the cells is not critical at some step. Almost all of these genes have mammalian homologs, and yet the role of many of these homologs has not been investigated. Perhaps the protein that regulates your favorite trafficking step has already been identified in C. elegans? Here I provide a brief overview of those trafficking mutants identified in C. elegans and where you can read more about them. 相似文献
70.
A brief history of Rubisco (ribulose bisphosphate carboxylase oxygenase) research and the events leading to the discovery
and initial characterization of Rubisco activase are described. Key to the discovery was the chance isolation of a novel Arabidopsis photosynthesis mutant. The characteristics of the mutant suggested that activation of Rubisco was not a spontaneous process
in vivo, but involved a heritable factor. The search for the putative factor by 2D electrophoresis identified two polypeptides, genetically
linked to Rubisco activation, that were missing in chloroplasts from the mutant. An assay for the activity of these polypeptides,
which were given the name Rubisco activase, was developed after realizing the importance of including ribulose bisphosphate
(RuBP) in the assay. The requirement for ATP and the subsequent identification of activase as an ATPase came about fortuitously,
the result of a RuBP preparation that was contaminated with adenine nucleotides. Finally, the ability of activase to relieve
inhibition of the endogenous Rubisco inhibitor, 2-carboxyarabinitol 1-phosphate, provided an early indication of the mechanism
by which activase regulates Rubisco.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献