全文获取类型
收费全文 | 1035篇 |
免费 | 72篇 |
国内免费 | 2篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 37篇 |
2015年 | 59篇 |
2014年 | 62篇 |
2013年 | 88篇 |
2012年 | 85篇 |
2011年 | 86篇 |
2010年 | 60篇 |
2009年 | 45篇 |
2008年 | 66篇 |
2007年 | 62篇 |
2006年 | 72篇 |
2005年 | 35篇 |
2004年 | 40篇 |
2003年 | 45篇 |
2002年 | 33篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1949年 | 1篇 |
排序方式: 共有1109条查询结果,搜索用时 187 毫秒
1.
2.
3.
L D'Agostino S Pignata B Daniele R Ventriglia G Ferrari C Ferraro S Spagnuolo P E Lucchelli G Mazzacca 《Biochimica et biophysica acta》1989,993(2-3):228-232
Plasma diamine oxidase (DAO) values are enhanced by intravenous injection of heparin which releases the enzyme, synthesized in small bowel enterocytes, from binding sites located on endothelial cells of the intestinal microvasculature. Intestinal DAO, in analogy with lipoprotein lipase (another heparin-released enzyme), is believed to be electrostatically linked to endothelial binding sites composed of a glycosaminoglycan (GAG) which is presumably heparan sulphate, but the complete mechanism of enzyme release is not known. In this study we assayed in rats the DAO-releasing capability of heparan sulphate, dermatan sulphate, chondroitin sulphate A and hyaluronic acid, all heparin related compounds. Heparan sulphate, a compound with the same hexosamine as heparin but with a lower concentration of sulphated iduronic acid, induced a very high release of DAO (3-fold less than heparin), while the other tested GAGs, composed of higher proportions of non sulphated uronic acid and with galactosamine instead of glucosamine, induced a significantly lower release. In rats treated with 60 mg heparan sulphate the significant decrease in ileal mucosal DAO activity indicates that, in analogy with heparin, the high plasma enzymatic activity induced is of enterocytic origin. It is suggested that the high charge density of the compounds tested, due to the degree of sulphatation, is the decisive factor in promoting the release of intestinal DAO. 相似文献
4.
Rosa Sorrentino Carlo Iannicola Sandro Costanzi Alberto Chersi Roberto Tosi 《Immunogenetics》1991,33(2):118-123
DNA molecules derived from three alleles of the HLA-DRB3 locus and differing from each other at several nucleotide sites were denatured and cross-hybridized. Each allelic combination was found to generate a pair of heteroduplexes of different mobility. Their retardation as compared to homoduplexes was proportional to the number of mismatches. In each heteroduplexes pair the component possessing the highest number of Pyr-Pyr oppositions was the most retarded. The results are those predicted by a theoretical model implying a correlation between base-pair opening and bending of the DNA double helix. These observations introduce a new HLA typing method at the genomic level and indicate an experimental approach to the analysis of the superhelical DNA conformation as related to different types of base oppositions. 相似文献
5.
Niels Gregersen Brage S. Andresen Peter Bross Vibeke Winter Niels Rüdiger Stefan Engst Ernst Christensen Daniel Kelly Arnold W. Strauss Steen Kølvraa Lars Bolund Sandro Ghisla 《Human genetics》1991,86(6):545-551
Summary A series of experiments has established the molecular defect in the medium-chain acyl-coenzyme A (CoA) dehydrogenase (MCAD) gene in a family with MCAD deficiency. Demonstration of intra-mitochondrial mature MCAD indistinguishable in size (42.5-kDa) from control MCAD, and of mRNA with the correct size of 2.4 kb, indicated a point-mutation in the coding region of the MCAD gene to be disease-causing. Consequently, cloning and DNA sequencing of polymerase chain reaction (PCR) amplified complementary DNA (cDNA) from messenger RNA of fibroblasts from the patient and family members were performed. All clones sequenced from the patient exhibited a single base substitution from adenine (A) to guanine (G) at position 985 in the MCAD cDNA as the only consistent base-variation compared with control cDNA. In contrast, the parents contained cDNA with the normal and the mutated sequence, revealing their obligate carrier status. Allelic homozygosity in the patient and heterozygosity for the mutation in the parents were established by a modified PCR reaction, introducing a cleavage site for the restriction endonuclease NcoI into amplified genomic DNA containing G985. The same assay consistently revealed A985 in genomic DNA from 26 control individuals. The A to G mutation was introduced into an E. coli expression vector producing mutant MCAD, which was demonstrated to be inactive, probably because of the inability to form active tetrameric MCAD. All the experiments are consistent with the contention that the G985 mutation, resulting in a lysine to glutamate shift at position 329 in the MCAD polypeptide chain, is the genetic cause of MCAD deficiency in this family. We found the same mutation in homozygous form in 11 out of 12 other patients with verified MCAD deficiency. 相似文献
6.
Vittorio Locatelli Silvano G. Cella Sandro Loche Carlo Pintor Eugenio E. Müller 《Life sciences》1984,35(19):1989-1995
We have investigated the effect of hypothalamo-pituitary disconnection in the rat on the growth hormone (GH) responsiveness to human pancreatic GH-releasing factor (hpGRF). Adult female rats, sham-operated (sham-op) or bearing a complete mechanical ablation of the mediobasal hypothalamus (MBH-A) were challenged, while under urethane anesthesia, with hpGRF-40 (20,100,500 ng/rat i.v.) at different time intervals after surgery. In sham-op rats only 500 ng/rat of hpGRF-40 stimulated GH release, while in 1-and 7-day MBH-A rats the stimulation also occurred with the lower hpGRF doses and the rise in plasma GH was greater than in sham-op controls. Twenty-one and 42 days after the placing of the lesions the GH response to hpGRF-40 was still present at the 500 ng/rat dose, though it was smaller than in sham-op controls. Evaluation of pituitary GH content demonstrated a progressive and rapid decline starting the first day after the placing of the lesions. These data indicate that GH responsiveness to hpGRF is: 1) enhanced in the anterior pituitary shortly after hypothalamo-pituitary disconnection and, 2) despite a striking reduction of the pituitary GH stores, it is maintained after these lesions.The physiologic growth hormone (GH) releaser in the rat is GH-releasing factor and, recently, a group of peptides has been characterized from human pancreatic tumors (hpGRFs) (1,2) which are potent and specific GH-releasers in both animals (3) and man (4). The availability of these peptides, which show a high degree of homology with the physiologic rat hypothalamic GRF (5), offers the unique opportunity to assess somatotrope responsiveness to GRF molecules in rats with hypothalamo-pituitary disconnection.In this study we have first evaluated the GH pituitary responsiveness to increasing doses of hpGRF-40 in rats following mechanical ablation of the mediobasal hypothalamus (6). These rats, by definition, lack the effect of both central nervous system (CNS) inhibitory (e.g. somatostatin) and stimulatory (e.g. GRF) influences to GH release. With the aim to ascertain how the lack of these two opposing inputs reflects on the secretory capacity of the somatotropes, we also investigated the GH response to hpGRF-40 at different time intervals after the lesioning. In a study in rats with electrolytic lesions of the ventromedial-arcuate region of the hypothalamus Tannenbaum et al (7) had shown persistence of the GH response to huge doses of a hpGRF analog. 相似文献
7.
Sandro Pignatti 《Plant Ecology》1969,17(1):83-88
Zusammenfassung Die Häufigkeit des Vorkommens einzelner Familien in Vegetationstabellen scheint einer Gesetzmäßigkeit zu unterliegen. Bei Pioniergesellschaften kommt es vor, daß eine Familie mit weitaus überwiegender Frequenz aufscheint, während klimaxnahe Gesellschaften ein besseres Gleichgewicht der Familienanteile aufzuweisen scheinen.
Summary The frequency of representative species of families in phytosociological tables seems to depend on a general law. Pioneer associations present a family that is largely dominating, while associations near to climax show a better equilibrium.相似文献
8.
Sandro Cavicchi Daniela Guerra Vanna Natali Cristina Pezzoli Gianfranco Giorgi 《Journal of evolutionary biology》1989,2(4):235-251
From a laboratory stock of Drosophila melanogaster (Oregon), reared for more than 20 years at 18° C, a new population was derived and maintained at 28° C for 8 years. The chromosomal and cytoplasmic contribution to genetic divergence between the two populations was estimated. Six body traits and reproductive fitness were taken into account. The third chromosome is responsible for the adaptive difference for temperature between the two lines. Temperature-selected genes which control body size are located on the second and third chromosomes, although the contribution of each chromosome depends on the environment in which the flies develop. The correlation between the chromosomal and cytoplasmic contributions to different traits and fitness, changes with temperature. At 28° C the correlation between fitness and each body trait is proportional to the response to selection exhibited by each of them, but this is not true at 18° C. Body size has, therefore, an adaptive significance in relation to temperature, which is expressed only in the environment where selection occurs. Cytoplasmic genes affect almost all characters to an extent similar to that of chromosomal genes. Inter-chromosomal and nucleo-cytoplasmic interactions are present and also change with temperature. In general, genes selected in a given environment produce greater phenotypic changes in that environment than in another. The population that experienced both temperatures is fitter in both environments, suggesting that the capacity to adapt to warm temperatures depends on genes other than those which are involved in the adaptation to cold. 相似文献
9.
Rosa Sorrentino Carlo Iannicola Sandro Costanzi Giulio Ratti Carolyn Hurley Roberto Tosi Nobuyuki Tanigaki 《Immunogenetics》1990,32(1):8-12
TR81 is a specificity closely related to or identical with DR3. In Caucasoids two amino acids, Tyr at position 26 and Arg at position 74 of HLA class II DR chains, have been found to be associated with the presence of TR81. Recently, a variant of DRBI *03 identified in American Blacks has been shown to possess Arg at position 74 but Phe at position 26. This codon combination is found to be present in four other cell lines where it still specifies the TR81 determinant. This suggests that the TR81 specificity is uniquely dependent on the presence of Arg at position 74. 相似文献
10.
Summary Endoproteinase(s) was isolated from a freeze-dried powder of larvae of Ostrinia nubilalis using reverse micellar solutions. The inhibition of proteinase was studied in reverse micelles with commercial Bowman-Birk soybean trypsin inhibitor and three trypsin inhibitors recently isolated from ripe cruciferous seeds. 相似文献