全文获取类型
收费全文 | 584篇 |
免费 | 24篇 |
国内免费 | 54篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 4篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 28篇 |
2012年 | 30篇 |
2011年 | 24篇 |
2010年 | 32篇 |
2009年 | 39篇 |
2008年 | 31篇 |
2007年 | 19篇 |
2006年 | 23篇 |
2005年 | 26篇 |
2004年 | 16篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 17篇 |
2000年 | 7篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1959年 | 8篇 |
1958年 | 16篇 |
1957年 | 13篇 |
1956年 | 25篇 |
1955年 | 14篇 |
1954年 | 10篇 |
1953年 | 20篇 |
1952年 | 13篇 |
1951年 | 15篇 |
1950年 | 14篇 |
排序方式: 共有662条查询结果,搜索用时 15 毫秒
1.
2.
ANDRÉ PICARD JEAN-CLAUDE LABBÉ GÉRARD PEAUCELLIER FRANÇOISE LE BOUFFANT CHRISTIAN LE PEUCH MARCEL DOREE 《Development, growth & differentiation》1987,29(1):93-103
Many studies suggest that MPF activation depends on protein phosphorylation or that MPF is itself a protein kinase. In the present report, cyclic variations of MPF activity have been correlated in vivo with changes in the extent of protein phosphorylation or in vitro with changes of a major protein kinase during the first cell cycles of fertilized starfish eggs. This cycling protein kinase neither requires cAMP nor Ca2+ . Neither colchicine nor aphidicoline, which inhibits cleavage and chromosome replication respectively, was found to suppress the synchronous and cyclic variations of both MPF and protein kinase activities. Protein synthesis was found to be required for both MPF and protein kinase activities to reappear after their simultaneous drop at the time of mitotic or meiotic cleavages. Production of either MPF or protein kinase activities is not the immediate result of protein synthesis since there is a delay at each cell cycle between the time when protein synthesis is required and the time when both MPF and protein kinase activities are produced. This suggests that both MPF and protein kinase activities might involve some post-translational modification of a precursor protein synthesized during the preceeding cell cycle. 相似文献
3.
Receptor activation of G proteins 总被引:6,自引:0,他引:6
E R Weiss D J Kelleher C W Woon S Soparkar S Osawa L E Heasley G L Johnson 《FASEB journal》1988,2(13):2841-2848
G proteins are a highly conserved family of membrane-associated proteins composed of alpha, beta, and gamma subunits. The alpha subunit, which is unique for each G protein, binds GDP or GTP. Receptors such as those for beta- and alpha-adrenergic catecholamines, muscarinic agonists, and the retinal photoreceptor rhodopsin, catalyze the exchange of GDP for GTP binding to the alpha subunit of a specific G protein. G alpha.GTP regulates appropriate effector enzymes such as adenylyl cyclase or the cyclic GMP phosphodiesterase. The beta gamma-subunit complex of G proteins is required for efficient receptor-catalyzed alpha subunit guanine nucleotide exchange and also functions as an attenuator of alpha subunit activation of effector enzymes. Recent elucidation of both receptor and G protein primary sequence has allowed structural predictions and new experimental approaches to study the mechanism of receptor-catalyzed G protein regulation of specific effector systems and the control of cell function including metabolism, secretion, and growth. 相似文献
4.
5.
中国平脉树螽属五新种记述:直翅目:螽斯科:树螽亚科 总被引:2,自引:0,他引:2
本文报道中国平脉树螽属5个新种。每个新种皆有详细的形态描述和形态特征图。所有模式标本存于北京农业大学昆虫标本室。 相似文献
6.
7.
Putative inhibitor of cyclic AMP efflux: chromatography, amino acid composition, and identification as a prostaglandin A1-glutathione adduct 总被引:2,自引:0,他引:2
Avian red cells rapidly and extensively metabolize prostaglandin A1 (PGA1) to a polar form that extracts into 80% ethanol and is quantitatively desalted and recovered over a Waters C18 Sep-Pak. This material co-chromatographs with synthetic PGA1-GSH and with the human red cell PGA1 metabolite on cellulose and silica gel thin layer plates and on normal phase high performance liquid chromatography. Quantitation of the amino acid composition by [35S]cysteine incorporation and by fluorometric amino acid analysis of the material eluting from high performance liquid chromatography indicates the presence of PGA1, cysteine, glutamate, and glycine in equimolar ratios. Base sensitivity of the metabolite indicates that it exists largely (80%) in the 9-hydroxyl form. We conclude that the polar metabolite of PGA1 that acts intracellularly to inhibit cyclic AMP efflux by avian red cells is a glutathione conjugate of PGA1. 相似文献
8.
Prevost, I. and Le PageDegivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.J.exp. Bot. 36: 19001905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radioimmunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability 相似文献
9.
Monitoring the persistence of Laccaria bicolor as an ectomycorrhizal symbiont of nursery-grown Douglas fir by PCR of the rDNA intergenic spacer 总被引:2,自引:0,他引:2
B. HENRION C. DI BATTISTA D. BOUCHARD D. VAIRELLES B. D. THOMPSON † F. LE TACON F. MARTIN 《Molecular ecology》1994,3(6):571-580
The large-scale inoculation of selected beneficial ectomycorrhizal fungi in forest nurseries has generated renewed interest in the ecology of these symbiotic fungi. However, information on the dissemination and persistence of introduced symbionts is scarce due to the limitation of the current identification methods. To identify ectomycorrhizal fungi on single root tips, we investigated the polymorphism of the PCR-amplified ribosomal DNA intergenic spacer (IGS) from a wide range of ectomycorrhizal fungi. To investigate the reliability of this molecular approach in large-scale surveys, the dissemination and persistence on Douglas fir seedlings of the introduced Laccaria bicolor S238N were assessed in a forest nursery in the Massif Central (France). Several hundred ectomycorrhizas and fruiting bodies were sampled from plots where control and L. bicolor inoculated-Douglas fir seedlings were grown for 1.5 years. PCR typing of mycorrhizas indicated that trees inoculated with L. bicolor S238N remained exclusively colonized by that isolate (or sexually derived isolates) for the entire test period. In contrast, control seedlings were infected by indigenous isolates of Laccaria laccata and Thelephora terrestris. The molecular evidence for the persistence of the introduced mycobiont despite the competition from indigenous isolates of the same species provides further illustration of the potential of exotic species for large-scale microbial application. 相似文献
10.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献