全文获取类型
收费全文 | 421篇 |
免费 | 25篇 |
出版年
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 23篇 |
2013年 | 15篇 |
2012年 | 30篇 |
2011年 | 19篇 |
2010年 | 19篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 13篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1897年 | 1篇 |
1887年 | 1篇 |
排序方式: 共有446条查询结果,搜索用时 15 毫秒
1.
Rats treated with chlorpromazine (CPZ) (1 mg/kg/day i.p.) experienced a marked decline in cerebral insulin levels (0.057 +/- 0.01 ng/g wet weight) with respect to a control group (0.38 +/- 0.05 ng/g wet weight), while rats given D-amphetamine bitartrate (AMPH) chronically (20 mg/kg/day p.o.) showed a rise in cerebral insulin (0.55 +/- 0.04 ng/g wet weight). Combined treatment with both drugs at the same dosages produced lower cerebral insulin levels (0.46 +/- 0.10 ng/g wet weight) than in the AMPH animals. In the groups of rats treated with CPZ and with AMPH + CPZ, there was a slight elevation in serum insulin levels. Serum glucose values did not vary. 相似文献
2.
S Sonnino D Acquotti G Fronza L Cantù V Chigorno M Pitto G Kirschner G Tettamanti 《Chemistry and physics of lipids》1988,46(3):181-191
N-Glycolylneuraminic acid containing GM1, GM1(NeuGc), was prepared by semisynthetic procedure. The procedure makes use of GM1 ganglioside deacetylated at the level of sialic acid residue (deAc-GM1) and of 1,3-dioxalan-2,4-dione. DeAc-GM1 is prepared from GM1 by alkaline hydrolysis in the presence of tetramethylammonium hydroxide and the glycolylating compound by reaction of glycolic acid with phosgene in dioxane, followed by cyclization under vacuum. Mass spectrometric and nuclear magnetic resonance spectroscopy analyses clearly indicated the presence, in the neosynthesized ganglioside of a glycolic group in the sialic acid residue. Laser-light scattering measurements show that GM1(NeuGc) aggregates in aqueous media being present in solution as micelles with a molecular weight of 576,000 and a hydrodynamic radius of 62.4 A as determined at 25 degrees C. GM1(NeuGc) promotes neurite outgrowth in N-2a cells to a similar degree as GM1(NeuAc), but shows different behaviour under treatment with sialidase from Arthrobacter ureafaciens. 相似文献
3.
F Rivas D García-Cruz H Rivera M L Plascencia R M González J M Cantú 《Annales de génétique》1985,28(2):113-115
A 2 4/12-year-old girl whith a de novo 46,XX,-22 + der(22), t(19;22)(q13.2;p11) karyotype is described. From this and other eight similar cases previously published, a typical phenotype in distal 19q trisomy is concluded. 相似文献
4.
Forty nine eczematous infants who were still solely and exclusively breast fed and who had never received anything but breast milk were studied for evidence of sensitisation to foods. Thirty four similar infants without eczema formed a control group. The eczematous infants were divided into three groups according to clinical criteria: (1) definite atopic eczema; (2) possible atopic eczema; (3) atopic eczema unlikely. Twenty three infants showed cutaneous hypersensitivity to foods, usually egg and cows'' milk. Seven of 14 infants in group 1 and nine of 20 in group 2 were sensitised compared with four of 15 in group 3 and three of 34 controls (p less than 0.01). Ovalbumin was detected in breast milk from 14 of 19 mothers tested after ingestion of egg, the concentrations being the same for mothers feeding eczematous and normal infants. Breast fed babies developing eczema may be sensitised by foods eaten by their mothers. 相似文献
5.
Thirty seven breast fed infants with eczema were studied to see whether changes in their mothers'' diets affected their skin condition. Nineteen mothers and babies took part in a double blind crossover trial of exclusion of egg and cows'' milk, and 18 took part in open exclusion of 11 foods followed by double blind challenge to those mothers whose infants seemed to respond. Babies were examined at the beginning and end of each dietary period, and the extent and severity of the rash were given a numerical score. The eczema improved in six infants when their mothers avoided egg and cows'' milk and worsened again when these were reintroduced. Two infants suffered gastrointestinal reactions after maternal ingestion of egg and cows'' milk, one developing colitis. Maternal dietary exclusion seems to benefit some breast fed babies with eczema. 相似文献
6.
A new paleoenvironmental proxy, Eucampia Index, was used to trace the Late Pleistocene oscillations of winter ice extent at ODP Leg 119, Site 745B (59° 35.71 S and 85° 51.60 E) on the Kerguelen Plateau. The index is calculated as the ratio of winter terminal to intercalary valves of the diatom Eucampia antarctica sensu lato. During the early Brunhes the winter sea-ice edge was positioned south from Site 745. It started expanding northward, closer to the site location soon after 0.4 Ma and progressed in a manner of a several wide oscillations. For approximately the last 0.1 Ma the winter sea-ice edge oscillated less and retained similar range of oscillations. The ice edge oscillated in periods which correspond closely to that of Milankovitch oscillations of Earth obliquity, although the significance of individual periods appears to vary in time. 相似文献
7.
8.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
9.
Angel García-Gutiérrez Francisco R. Cantón Fernando Gallardo Francisca Sánchez-Jiménez Francisco M. Cánovas 《Plant molecular biology》1995,27(1):115-128
Pine seedlings are able to accumulate chlorophylls and develop green plastids in a light-independent manner. In this work, we have characterized ferredoxin-dependent glutamate synthase (EC 1.4.7.1; Fd-GOGAT), a key enzyme in nitrogen interconversion during this process. Fd-GOGAT has been purified about 170-fold from cotyledons of maritime pine (Pinus pinaster). As occurs in angiosperms, the native enzyme is a single polypeptide with an apparent molecular mass of 163–168 kDa that is confined to the chloroplast stroma. Polyclonal antibodies generated against the purified enzyme were used to immunoscreen a gt11 expression library from Scots pine (Pinus sylvestris) seedlings and partial cDNA clones were isolated and characterized. The clone with the longest cDNA insert (pGOP44) contained the codification for the C-terminal (550 amino acids) of the pine Fd-GOGAT polypeptide. Immunological cross-reactivity and comparative amino sequence analysis revealed that Fd-GOGAT is a well conserved protein in higher plants. Western blot analyses showed that protein was expressed in chloroplast-containing pine tissues and this expression pattern was not affected by exogenously supplied nitrogen. Fd-GOGAT mRNA, polypeptide and enzyme activity accumulated in substantial amounts in dark-grown pine seedlings. The presence of a functional Fd-GOGAT may be important to provide the required glutamate for the biosynthesis of nitrogen compounds during chloroplast biogenesis in the dark. 相似文献
10.