全文获取类型
收费全文 | 4352篇 |
免费 | 389篇 |
国内免费 | 2篇 |
出版年
2023年 | 15篇 |
2022年 | 37篇 |
2021年 | 90篇 |
2020年 | 52篇 |
2019年 | 49篇 |
2018年 | 58篇 |
2017年 | 61篇 |
2016年 | 101篇 |
2015年 | 224篇 |
2014年 | 180篇 |
2013年 | 254篇 |
2012年 | 379篇 |
2011年 | 311篇 |
2010年 | 207篇 |
2009年 | 132篇 |
2008年 | 233篇 |
2007年 | 265篇 |
2006年 | 210篇 |
2005年 | 214篇 |
2004年 | 226篇 |
2003年 | 213篇 |
2002年 | 192篇 |
2001年 | 41篇 |
2000年 | 33篇 |
1999年 | 38篇 |
1998年 | 85篇 |
1997年 | 35篇 |
1996年 | 46篇 |
1995年 | 38篇 |
1994年 | 46篇 |
1993年 | 35篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 37篇 |
1989年 | 36篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 25篇 |
1985年 | 28篇 |
1984年 | 32篇 |
1983年 | 34篇 |
1982年 | 41篇 |
1981年 | 28篇 |
1980年 | 38篇 |
1979年 | 26篇 |
1978年 | 14篇 |
1977年 | 25篇 |
1976年 | 25篇 |
1974年 | 21篇 |
1973年 | 13篇 |
排序方式: 共有4743条查询结果,搜索用时 24 毫秒
81.
Contrasting roles for c-Myc and L-Myc in the regulation of cellular growth and differentiation in vivo. 总被引:8,自引:0,他引:8 下载免费PDF全文
S D Morgenbesser N Schreiber-Agus M Bidder K A Mahon P A Overbeek J Horner R A DePinho 《The EMBO journal》1995,14(4):743-756
Although myc family genes are differentially expressed during development, their expression frequently overlaps, suggesting that they may serve both distinct and common biological functions. In addition, alterations in their expression occur at major developmental transitions in many cell lineages. For example, during mouse lens maturation, the growth arrest and differentiation of epithelial cells into lens fiber cells is associated with a decrease in L- and c-myc expression and a reciprocal rise in N-myc levels. To determine whether the down-regulation of L- and c-myc are required for mitotic arrest and/or completion of differentiation and whether these genes have distinct or similar activities in the same cell type, we have studied the consequences of forced L- and c-myc expression in the lens fiber cell compartment using the alpha A-crystallin promoter in transgenic mice (alpha A/L-myc and alpha A/c-myc mice). With respect to morphological and molecular differentiation, alpha A/L-myc lenses were characterized by a severely disorganized lens fiber cell compartment and a significant decrease in the expression of a late-stage differentiation marker (MIP26); in contrast, differentiation appeared to be unaffected in alpha A/c-myc mice. Furthermore, an analysis of proliferation indicated that while alpha A/L-myc fiber cells withdrew properly from the cell cycle, inappropriate cell cycle progression occurred in the lens fiber cell compartment of alpha A/c-myc mice. These observations indicate that continued late-stage expression of L-myc affected differentiation processes directly, rather than indirectly through deregulated growth control, whereas constitutive c-myc expression inhibited proliferative arrest, but did not appear to disturb differentiation. As a direct corollary, our data indicate that L-Myc and c-Myc are involved in distinct physiological processes in the same cell type. 相似文献
82.
Soo-Kyung Lim Jean-Pascal de Bandt Christian Aussel Pascal Pernet Jacqueline Giboudeau Luc Cynober 《Journal of cellular physiology》1995,162(3):422-426
This study investigates the short-tem effects of glucagon and human recombinant tumor necrosis factor α (TNFα) singly and in association on 2-methylaminoisobutyric acid (MeAIB) transport in hepatocyte monolayers. As expected, glucagon induced a time-dependent stimulation of MeAIB transport. In our experimental conditions, TNFα did not induce cytolysis. A 2 hour exposure to TNFα (0.05–500 ng/I) with or without glucagon (10?9 to 10?6 M) did not modify the basal or glucagon-stimulated MeAIB transport. Varying the duration of exposure to TNFα 5 ng/I up to 6 h was equally ineffective. The presence of hydrocortisone potentiated the glucagon-stimulated transport, but TNFα remained ineffective. Finally, the association of interferon (IFNγ) with TNFα and/or glucagon was unable to modify the transport activity. These data demonstrate that TNFα does not exert a direct effect on MeAIB transport in hepatocytes, at least on a short-term basis. © 1995 Wiley-Liss, Inc. 相似文献
83.
Factors involved in capillary growth in the heart 总被引:6,自引:0,他引:6
Olga Hudlická Margaret D. Brown Helene Walter Jacqueline B. Weiss Anita Bate 《Molecular and cellular biochemistry》1995,147(1-2):57-68
Growth of capillaries in the heart occurs under physiological circumstances during endurance exercise training, exposure to high altitude and/or cold, and changes in cardiac metabolism or heart rate elicited by modification of thyroid hormone levels. Capillary growth in all these conditions can be linked with increased coronary blood flow, decreased heart rate, or both. This paper brings evidence that, although increased blood flow due to long-term administration of coronary vasodilators results in capillary growth, a long-term decrease in heart rate induced by electrical bradycardial pacing in rabbits and pigs, or by chronic administration of a bradycardic drug, alinidine, in rats, stimulates capillary growth with little or no change in coronary blood flow. Decreased heart rate results in increased capillary wall tension, increased end-diastolic volume and increased force of contraction, and thus stretch of the capillary wall. This could lead to release of various growth factors possibly stored in the capillary basement membrane. Correlation was found between capillary density (CD) and the levels of low molecular endothelial cell stimulating angiogenic factor (ESAF) both in rabbit and pig hearts with CD increased by pacing. There was no relation between expression of mRNA for basic fibroblast growth factor and CD in sham-operated and paced rabbit hearts. In contrast, mRNA for TGFß was increased in paced hearts, and the possible role of this factor in the regulation of capillary growth induced by bradycardia is discussed. 相似文献
84.
Genetic and cytological studies were conducted with a new male-sterile, female-fertile soybean [Glycine max (L.) Merr.] mutant. This mutant was completely male sterile and was inherited as a single-recessive gene. No differences in
female or male gamete transmission of the recessive allele were observed between reciprocal cross-pollinations in the F1 or F2 generations. This mutant was not allelic to any previously identified soybean genic male-sterile mutants: ms1, ms2, ms3, ms4, ms5, or ms6. No linkage was detected between sterility and flower color (W1 locus), or between sterility and pubescence color (T1 locus). Light microscopic and cytological observations of microsporogenesis in fertile and sterile anthers were conducted.
The structure of microspore mother cells (MMC) in male-sterile plants was identical to the MMCs in male-fertile plants. Enzyme
extraction analyses showed that there was no callase activity in male-sterile anthers, and this suggests that sterility was
caused by retention of the callose walls, which normally are degraded around tetrads at the late tetrad stage. The tapetum
from male-sterile anthers also showed abnormalities at the tetrad stage and later stages, which were expressed by an unusual
formation of vacuoles, and by accumulation of densely staining material. At maturity, anthers from sterile plants were devoid
of pollen grains.
Received: 13 May 1996 / Revision accepted: 19 August 1996 相似文献
85.
The Loridae are an arboreal family of small primates that are specialized for slow and quiet climbing. This paper examines the relationship between lorid locomotory behaviour and postcranial skeletal morphology. Lorid humeral and femoral diaphyseal geometric cross-sectional properties, articular surface areas, and lengths are compared to those properties in other small primates with less specialized locomotory behaviour. The comparative sample includes both closely related prosimians and more distantly related platyrrhines.
Results indicate that lorids have greater humeral and femoral diaphyseal rigidity than other quadrupedal primates of similar body size, suggesting that lorid limbs are subjected to greater forces. Lorids also have relatively larger humeral and femoral articulations, corresponding to field and laboratory observations which indicate that lorid joints are highly mobilc. In addition, lorids have long humeri relative to femoral length, and compared to humeral length in less specialized prosimians of similar body mass. Long humeral length relative to femoral length is interpreted as a climbing adaptation because similar limb proportions are also seen in many non-primate climbers. Altogether, humeral and femoral diaphyseal cross-sectional properties, articular surface areas, and lengths comprise a suite of characters which have potential for identifying climbing specialists in the fossil record. 相似文献
Results indicate that lorids have greater humeral and femoral diaphyseal rigidity than other quadrupedal primates of similar body size, suggesting that lorid limbs are subjected to greater forces. Lorids also have relatively larger humeral and femoral articulations, corresponding to field and laboratory observations which indicate that lorid joints are highly mobilc. In addition, lorids have long humeri relative to femoral length, and compared to humeral length in less specialized prosimians of similar body mass. Long humeral length relative to femoral length is interpreted as a climbing adaptation because similar limb proportions are also seen in many non-primate climbers. Altogether, humeral and femoral diaphyseal cross-sectional properties, articular surface areas, and lengths comprise a suite of characters which have potential for identifying climbing specialists in the fossil record. 相似文献
86.
Baudin Bruno; Alves Nathalie; Pilon Antoine; Beneteau-Burnat Benedicte; Giboudeau Jacqueline 《Glycobiology》1997,7(4):565-570
We enzymatically deglycosylated pig lung angiotensin I-convertingenzyme (ACE) to study the involvement of its glycanic chainsin its physicochemical and catalytic properties. The effectsof endoglycosidases F2 and H, and of N-glycanase were assessedby ACE mobility in SDS-PAGE. N-Glycanase only was completelyeffective with or without previous denaturation, leading toa shift in ACE Mr from 172 to 135 kDa; endoglycosidase F2 producedthe same shift but only without previous denaturation. DeglycosylatedACE had the same kcat as native ACE for the substrate hippuryl-histidyl-leucine,and an identical Stokes radius as measured by size-exclusionhigh performance liquid chromatography. Neuraminidase had noeffect on ACE Stokes radius but slightly decreased its kcatwhich could be related to variations in ionization of the activesite. The isoelectric point of ACE, as, determined by isoelectricfocusing, increased from 4.54.8 to 5.05.3 aftereither endoglycosidase F2 or neuraminidase digestion, but stillwith microheterogeneities which thus did not seem to be relatedto ACE glycans. Deglycosylated ACE did not bind onto agaroselectinsin contrast to native ACE which bound strongly to concanavalinA showing interactions involving oligomannosidic or biantennaryand sialylated N-acetyl-lactosaminic isoglycans. Finally, tunicamycin,an inhibitor of N-glycosylation, did not modify ACE secretionby endothelial cells. Thus, ACE glycans have no drastic effectson structural and biological properties of the protein, butthey may have a functional role on intracellular targeting ofboth secreted and membrane-bound ACE isoforms, also for theprotection of the soluble plasma form against hepatic lectinsand the maintenance of its hydrosolubility. converting enzyme (peptidyldipeptidase EC.3.4.15.1) endothelium glycosidases lectins 相似文献
87.
Cinnamoyl CoA reductase, the first committed enzyme of the lignin branch biosynthetic pathway: cloning, expression and phylogenetic relationships 总被引:15,自引:3,他引:12
88.
89.
Kenneth J. Snibson David Woodcock Jacqueline M. Orian Malcolm R. Brandon Timothy E. Adams 《Transgenic research》1995,4(2):114-122
We have examined transgene methylation in the DNA from the livers of a pedigree of mice carrying three copies of an integrated MToGH1 transgene. Utilizing the methylation-sensitive isoschizomersMsp I andHpa II, Southern blot analysis revealed that all second generation animals derived from a transgenic female had hypermethylated DNA, whereas first generation animals sired by a transgenic male displayed a range of methylation phenotypes ranging from no methylation to hypermethylation of the transgene sequences. Of the mice that exhibited hypermethylation of the transgene in CpG dinucleotides (CmCGG), a minority of these animals also exhibited apparent CpC methylation (i.e. inhibition ofMsp I cutting, presumably blocked by methylation of the outer C of CCGG). Methylation was also examined in the inner C of CC(A/T)GG sequences in the MToGH1 transgene using the isoschizomer pairBstN I andEcoR II. A minority of MToGH1 animals in the F1 generation showed clear evidence of methylation in these sites as well as in the inner and outer Cs of CCGG sites. An examination of MToGH1 expression in terms of oGH levels in serum revealed that there was a high degree of variation in the levels of circulating oGH between animals of this pedigree. There was a weak inverse relationship between the serum level of oGH and the extent of methylation of the transgene. In particular, mice exhibiting CpC together with CpG methylation were found to have very low levels of circulating oGH. Our results highlight the nature and complexity of epigenetic factors associated with transgene sequences which may ultimately influence expression of introduced genes in the mammalian genome. 相似文献
90.
Jacqueline M. Orian Richard G. Hadikusumo Sangkot Marzuki Anthony W. Linnane 《Journal of bioenergetics and biomembranes》1984,16(5-6):561-581
We have investigated the extent to which the assembly of the cytoplasmically synthesized subunits of the H+-ATPase can proceed in a mtDNA-less (rho°) strain of yeast, which is not capable of mitochondrial protein synthesis. Three of the membrane sector proteins of the yeast H+-ATPase are synthesized in the mitochondria, and it is important to determine whether the presence of these subunits is essential for the assembly of the imported subunits to the inner mitochondrial membrane. A monoclonal antibody against the cytoplasmically synthesized -subunit of the H+-ATPase was used to immunoprecipitate the assembled subunits of the enzyme complex. Our results indicate that the imported subunits of the H+-ATPase can be assembled in this mutant, into a defective complex which could be shown to be associated with the mitochondrial membrane by the analysis of the Arrhenius kinetics of the mutant mitochondrial ATPase activity.This paper is No. 61 in the seriesBiogenesis of Mitochondria. For paper No. 60, see Novitskiet al. (1984). 相似文献