全文获取类型
收费全文 | 952篇 |
免费 | 71篇 |
国内免费 | 38篇 |
出版年
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 43篇 |
2020年 | 26篇 |
2019年 | 34篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 39篇 |
2015年 | 60篇 |
2014年 | 56篇 |
2013年 | 72篇 |
2012年 | 60篇 |
2011年 | 69篇 |
2010年 | 25篇 |
2009年 | 39篇 |
2008年 | 42篇 |
2007年 | 36篇 |
2006年 | 45篇 |
2005年 | 31篇 |
2004年 | 17篇 |
2003年 | 27篇 |
2002年 | 25篇 |
2001年 | 21篇 |
2000年 | 20篇 |
1999年 | 20篇 |
1998年 | 19篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1968年 | 3篇 |
排序方式: 共有1061条查询结果,搜索用时 328 毫秒
11.
Summary The spatial relationships between the homologous pairs of chromosomes in the normal human colcemid-treated metaphase plate were tested by two different mathematical approaches: (a) determination of the distances between the centromeres of the homologous chromosomes compared to the mean distance of all centromeres of the mitosis in question; (b) measuring the distances of the different chromosomes from the center of the mitosis.The following results were obtained: (1) The arrangement of human metaphase chromosomes does not follow a normal distribution; the distribution is narrower and taller, probably due to an impairment of free chromosome spreading by the cell membrane. We believe that only in membraneless mitotic cells should the chromosome-spread correspond to a normal distribution under the same preparation conditions. (2) There is a positive correlation between decreasing chromosome size and decreasing mean distance between homologous chromosomes. (3) A close positive correlation exists between increasing chromosome size and increasing distance to the barycenter of the mitosis. (4) There is also a close positive correlation between the distance of homologous chromosome pairs and their distance from the center of the mitosis, i.e., with increasing distance from the center of the mitosis, the distance between the homologous partners increases. (5) The following statistically significant deviations from these rules could be established: (a) The large acrocentric chromosomes are closer associated, as one would expect from their size, probably due to their participation in the nucleolus organization; (b) in the female cell one of the two X chromosomes has an extremely peripheral localization; the X chromosomes are furthest apart of all pairs of homologous chromosomes; (c) the chromosome pairs 6 and 8 are relatively close together in spite of their peripheral position, suggesting a truc close association of the homologus partners; (d) the chromosome pair 18 has a more peripheral position than expected, and a relatively large mean distance between the homologous partners; (e) the chromosome pair 1 has a much more central position and a closer association than is expected from its size. 相似文献
12.
Herwig Zang 《Journal of Ornithology》1980,121(4):371-386
Zusammenfassung 1969–1977 wurden in 15 Untersuchungsgebieten des Harzes, die sich auf die Höhenstufen von 100–900 m verteilen, brutbiologische Daten bei Trauerschnäpper, Sumpf-, Blau-, Kohl- und Tannenmeise gesammelt.Die Siedlungsdichte nimmt jeweils auf die Hälfte ab bei einer Höhenzunahme für die Sumpfmeise von 270 m, die Kohlmeise 195 m, die Tannenmeise 178 m und die Blaumeise 101 m (Halbwertshöhe).Die Verzögerung des Legebeginns bzw. des Schlüpftermins beträgt beim Trauerschnäpper 1,72, bei der Tannenmeise 1,68, der Sumpfmeise 1,97, der Kohlmeise 2,19 und der Blaumeise 5,24 Tage/100 m parallel zur vertikalen Verzögerung der Vegetationsentwicklung (Phänologie) von 1,8–2,6 Tage/100 m.Die Gelegegröße von Trauerschnäpper, Sumpf-, Blau- und Kohlmeise nimmt mit zunehmender Höhe linear um 0,14; 0,52; 0,51; und 0,11 Eier/100 m ab. Für die Kohlmeise ergeben sich Unterschiede in Laub- und Nadelwald, für die Tannenmeise zeigt sich eine Tendenz zur Zunahme mit der Höhe.Die Abnahme des Bruterfolges mit der Höhe beträgt beim Trauerschnäpper 0,22 flügge Junge/100 m, bei der Blaumeise 0,57, der Sumpfmeise 0,37, der Tannenmeise 0,23 und der Kohlmeise 0,13 flügge Junge/100 m. Für die Kohlmeise ergeben sich auch hier wieder Unterschiede in Laub- und Nadelwald.Für die Tannenmeise nimmt der Zweibrutanteil mit zunehmender Höhe linear um 3,6 %/100 m ab. Für die Kohlmeise zeigt er ebenfalls fallende Tendenz.Definiert man als vertikale Verbreitungsgrenze einer Art die Höhe, in der sich eine Population im Mittel noch stabil erhalten kann, so lassen sich aus der ermittelten Abnahme des Bruterfolges und den Werten für die Überlebensrate in einer vereinfachten Modellrechnung folgende Grenzen im Harz ermitteln: Blaumeise 500 m, Sumpfmeise 700 m, Kohlmeise 950 m, Trauerschnäpper und Tannenmeise 1000 m. Dies stimmt gut mit der Erfahrung überein.
The altitudinal influence on the population density and on the breeding biology ofFicedula hypoleuca, Parus palustris, P. caeruleus, P. major andP. ater in the Harz Mountains
Summary (a) Between 1967 and 1977, biological breeding data ofFicedula hypoleuca, Parus palustris, P. caeruleus, P. major andP. ater have been collected in 15 study areas of the Harz mountains, at altitude ranging from 100 m to 900 m.(b) The population density decreases by half, as a result of an increase in altitude of 270 m inP. palustris, 195 m inP. major, 178 m inP. ater and 101 m inP. caeruleus (halfvalue altitude).(c) The beginning of egglaying or hatching is delayed by 1.72 days per 100 m inFicedula hypoleuca; 1.68 days inP. ater; 1.97 days inP. palustris; 2.19 days inP. major and 5.24 days inP. caeruleus. These altitudinal retardations are parallel to that of the environmental vegetation (phenology) of 1.8–2.6 days per 100 m.(d) The clutch-size ofFicedula hypoleuca, P. palustris, P. caeruleus andP. major decreases by 0.14; 0.52; 0.51 and 0.11 eggs per 100 m increase of altitude respectively. InP. major, variations occur between deciduous and coniferous forests, and inP. ater the clutch-size tends to increase with an altitudinal increase.(e) The decrease in breeding success amounts to 0.22 fledglings per 100 m increase of altitude inFicedula hypoleuca, 0.57 fledglings inP. caeruleus, 0.37 fledglings inP. palustris, 0.23 fledglings inP. ater and 0.13 fledglings inP. major. Again, in the case ofP. major, differences occur between deciduous and coniferous forests.(f) The percentage of second broods ofP. ater decreases by 3.6 % per 100 m increase of altitude. The percentage of second broods ofP. major shows decreasing tendency, too.(g) When the altitudinal distribution limit of a species is defined as the level at which a population remains stable, the altitudinal decrease of breeding success and the mortality permit to draw up a simplified table of the altitudinal distribution limit. In the Harz these limits are as follows:P. caeruleus 500 m,P. palustris 700 m,P. major 950 m,F. hypoleuca 1000 m, andP. ater 1000 m. These results coincide with the experience.相似文献
13.
Summary The pattern of association of acrocentric chromosomes was examined in ten and five carriers of a 15/21 and a 13/14 Robertsonian translocation, respectively, and was compared with that of the same numbers of relatives with normal karyotypes. In the carriers of 15/21 translocation, the number of large associations (involving more than two acrocentrics) and the association frequencies for individual acrocentric chromosomes, were significantly higher than in the control group. The mean number of associations of the single homologs of the translocation chromosomes was much higher than that of the other acrocentrics. In the carriers of 13/14 translocations, only the association frequency for chromosome 13 was higher than in the normal relatives. The uninvolved chromosomes homologous to those involved in translocations showed an insignificant increase in associations in comparison with the other acrocentrics. These results suggest that some mechanism within the cells compensates for the effect of missing acrocentrics or of acrocentrics lacking NORs on the number of associations. The possible relations of this phenomenon to the activity of the nucleolus organizing regions are discussed. 相似文献
14.
15.
Twelve out of 88 cytogenetically examined meningiomas of female patients showed, in addition to the typical loss of a chromosome 22, a loss of 1 or more chromosomes of group C. Among them 8 tumors had less than 8% cells with Barr-body-like particles, whereas in one tumor 12% and in 3 others over 20% Barr bodies were found, which, based on control studies, were classified as sex-chromatin negative, partly positive, and positive, respectively. In one case the loss of an X chromosome was verified by Giemsa banding. In 6 out of 24 meningiomas of male origin, the chromosomal morphology and association pattern strongly indicated that besides the loss of a chromosome 22, the Y chromosome was also missing. Moreover, the loss of the male sex chromosome could be ascertained in 4 tumors by the conspicuous absence of Y fluorescence in interphase nuclei and in metaphase plates after fluorescence staining. The findings are discussed in connection with the gonosomal loss in other human tumors and in old age. 相似文献
16.
Summary Twelve out of 88 cytogenetically examined meningiomas of female patients showed, in addition to the typical loss of a chromosome 22, a loss of 1 or more chromosomes of group C. Among them 8 tumors had less than 8% cells with Barr-body-like particles, whereas in one tumor 12% and in 3 others over 20% Barr bodies were found, which, based on control studies, were classified as sex-chromatin negative, partly positive, and positive, respectively. In one case the loss of an X chromosome was verified by Giemsa banding.In 6 out of 24 meningiomas of male origin, the chromosoma. morphology and association pattern strongly indicated that besides the loss of a chromosome 22, the Y chromosome was also missing. Moreover, the loss of the male sex chromosome could be ascertained in 4 tumors by the conspicuous absence of Y fluorescence in interphase nuclei and in metaphase plates after fluorescence staining.The findings are discussed in connection with the gonosomal loss in other human tumors and in old age.
Supported by the Deutsche Forschungsgemeinschaft (SFB 51 E 12).
Parts of this work are included in the doctoral thesis (M.D.) of H.S. at the University of Munich, Germany. 相似文献
Zusammenfassung Unter 88 cytogenetisch untersuchten Meningeomen von Frauen wurden 12 Tumoren gefunden, bei denen außer dem für Meningeome typischen Verlust eines Chromosoms 22 auch ein oder mehrere Chromosomen der C-Gruppe verlorengegangen waren. Bei 8 dieser Tumoren konnte in Gewebekulturpräparaten nur in weniger als 8% der untersuchten Zellen Barr-body-ähnliche Kernstrukturen nachgewiesen werden, bei einem Tumor fanden sich 12% und bei 3 über 20% Barr-bodies. Auf Grund von Vergleichsuntersuchungen wurden 8 Tumoren als geschlechtschromatinnegativ, 1 Tumor als teilweise positiv und die übrigen 3 als eindeutig positiv eingestuft. Bei einem Meningeom konnte das Fehlen eines X-Chromosoms direkt mit der Giemsa-Bandentechnik nachgewiesen werden.Bei 6 von 24 Meningeomen männlicher Herkunft konnte auf Grund der Chromosomenmorphologie und des Assoziationsverhaltens sehr wahrscheinlich gemacht werden, daß außer dem Chromosom 22 auch das Y-Chromosom verlorengegangen war. Bei 4 dieser Tumoren konnte eine Fluorescenzfärbung durchgeführt werden, wobei das Fehlen einer Y-Fluorescenz in Interphasezellen und Metaphaseplatten nachweisbar war.Diese Befunde werden im Zusammenhang mit dem Geschlechtschromosomenverlust bei anderen menschlichen Tumoren und im hohen Lebensalter diskutiert.
Supported by the Deutsche Forschungsgemeinschaft (SFB 51 E 12).
Parts of this work are included in the doctoral thesis (M.D.) of H.S. at the University of Munich, Germany. 相似文献
17.
Liangjie Xu Tianxin Geng Guangyao Zang Li Bo Yi Liang Hong Zhou Jinchuan Yan 《Journal of cellular and molecular medicine》2020,24(8):4659-4667
The role of exosomes derived from endothelial cells (ECs) in the progression of atherosclerosis (AS) and inflammation remains largely unexplored. We aimed to investigate whether exosome derived from CD137‐modified ECs (CD137‐Exo) played a major role in AS and to elucidate the potential mechanism underlying the inflammatory effect. Exosomes derived from mouse brain microvascular ECs treated with agonist anti‐CD137 antibody were used to explore the effect of CD137 signalling in AS and inflammation in vitro and vivo. CD137‐Exo efficiently induced the progression of AS in ApoE?/? mice. CD137‐Exo increased the proportion of Th17 cells both in vitro and vivo. The IL‐6 contained in CD137‐Exo which is regulated by Akt and NF‐КB pathway was verified to activate Th17 cell differentiation. IL‐17 increased apoptosis, inhibited cell viability and improved lactate dehydrogenase (LDH) release in ECs subjected to inflammation induced by lipopolysaccharide (LPS). The expression of soluble intercellular adhesion molecule1 (sICAM‐1), monocyte chemoattractant protein‐1 (MCP‐1) and E‐selectin in the supernatants of ECs after IL‐17 treatment was dramatically increased. CD137‐Exo promoted the progression of AS and Th17 cell differentiation via NF‐КB pathway mediated IL‐6 expression. This finding provided a potential method to prevent local and peripheral inflammation in AS. 相似文献
18.
19.
Du Xuemei Fang Ting Liu Yan Huang Liying Wang Xiaoli Zhang Jie Cui Yangbo Zang Maosen Wang Guoying Fu Junjie Liu Yunjun 《In vitro cellular & developmental biology. Plant》2020,56(2):159-168
In Vitro Cellular & Developmental Biology - Plant - Callus induction in plants is similar to pluripotent stem cell induction in animals and can incite global changes in gene expression.... 相似文献
20.
The marker strategy design (MSGD) has been proposed to assess and validate predictive markers for targeted therapies and immunotherapies. Under this design 相似文献