全文获取类型
收费全文 | 753篇 |
免费 | 67篇 |
出版年
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 30篇 |
2015年 | 33篇 |
2014年 | 32篇 |
2013年 | 54篇 |
2012年 | 66篇 |
2011年 | 55篇 |
2010年 | 31篇 |
2009年 | 20篇 |
2008年 | 45篇 |
2007年 | 46篇 |
2006年 | 44篇 |
2005年 | 45篇 |
2004年 | 49篇 |
2003年 | 42篇 |
2002年 | 32篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 10篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 3篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1952年 | 1篇 |
1949年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有820条查询结果,搜索用时 46 毫秒
1.
2.
Danielle L. Laval-Martin Isabelle A. Carr Saverio J. Barbera Leland N. Edmunds 《Chronobiology international》1990,7(2):99-105
-We have previously shown that NAD kinase and NADP phosphatase activities display circadian rhythms, in the soluble (SN) and membrane-bound (P) fractions of crude extracts of the achlorophyllous ZC mutant of the phytoflagellate Euglena gracilis (which displays circadian rhythmicity of cell division). We determined if changes in the affinity of NADP phosphatase and NAD kinase for their substrates, NADP+ and NAD+, were occurring by calculating the ratios 100(velocity found in Km conditions/velocity found in saturating conditions). The rationale was that if the affinity remained unchanged according to circadian time (CI), these values should always equal 50, independently of any changes in enzyme quantity; values greater than 50 should indicate increases in enzyme affinity, and values less than 50 decreases in affinity. Our results indicated that these values calculated for NADP phosphatase exhibited a complex pattern of rhythmicity, while those for NAD kinase displayed circadian variations strongly correlated with the rhythms in enzyme activity. The curves showed troughs at CT 00-04 both in dividing and nondividing cells and peaks at CT 18-20 or at CT 08-14 in cells sampled, respectively, from a dividing or a stationary culture. Such variations are indicative of changes in the kinetic properties of the enzyme, which may reflect modifications in its affinity either for effectors (such as Ca2+-calmodulin) or for its substrate, NAD+. This may be due to (i) the expression of different isoenzymes at different CTs; (ii) different posttranslational modifications of the enzyme; or (iii) concentrations of effectors varying in a circadian manner. 相似文献
3.
Katrin Kausch Clemens R. Müller Tiemo Grimm Kenneth Ricker Marcella Rietschel Sabine Rudnik-Schöneborn Klaus Zerres 《Human genetics》1991,86(3):317-318
Summary Two recent articles have reported the linkage of a gene for recessive spinal muscular atrophy (SMA) on the chromosome region 5q11.2–13.3. Our data show no linkage of the dominantly inherited forms of SMA to this chromosome region. 相似文献
4.
A new iridoid glucoside has been isolated from Stachytarpheta mutabilis and assigned the structure and configuration of 6β-hydroxyipolamiide on the basis of 1H NMR and 13C NMR evidence. The conversion of this compound into penta- acetyllamiol proved the above assignment. 相似文献
5.
Giovanna P. Marziani Longo Marcella Bracale Gianfranca Rossi Claudio P. Longo 《Plant molecular biology》1990,14(4):569-573
Cotyledons were excised from imbibed watermelon seeds, grown for 4 days in darkness on water or 10 M benzyladenine (BA) and then tested for the presence of the light-harvesting chlorophyll a/b protein (LHCP) and its mRNA. LHCP was assayed immunologically by western blotting of SDS gels: the protein was present in plastids, but it was not recovered with the thylakoid fraction. Antibodies directed against LHCP precipitated a 32 kDa polypeptide from translation products of poly(A) RNA of cotyledons only if these had been grown on BA. Taken together the data suggest that in absence of light cytokinins are necessary for the maintenance of a detectable level of LHCP-mRNA as well as for synthesis of the protein. 相似文献
6.
Marcella Carcupino Anna Maria Fausto Maria Luisa Bernardino Ortega Marzio Zapparoli Massimo Mazzini 《Zoomorphology》1996,116(3):103-110
Spermatophore development and ultrastructure of the mature sperm of Craterostigmus tasmanianus were studied using light and electron microscopy. In C. tasmanianus, as in the Scolopendromorpha, the spermatophore develops within the vas deferens. The latter consists of three parts, each
with a different morphology. The first may be involved in guiding the sperm to roll up into typical ring-like structures,
while the other two, which show an evident secretory activity, secrete the acellular wall of the spermatophores. The ultrastructure
of mature spermatozoa showed that a very close similarity exists between Craterostigmomorpha and Lithobiomorpha, especially
regarding the organization of the connecting piece. Based on this similarity, we consider the Craterostigmomorpha together
with the Scolopendromorpha, Geophilomorpha and Lithobiomorpha (=Pleurostigmophora) to be the sister group of the Scutigeromorpha.
Accepted: 2 June 1996 相似文献
7.
Giuliano Callaini Maria Giovanna Riparbelli Marcella Cintorino Sergio Antonio Tripodi Giorgio Bianciardi Piero Tosi Romano Dallai 《Biology of the cell / under the auspices of the European Cell Biology Organization》1994,81(1):39-45
Summary— Immunofluorescence and immunoelectron microscopy indicated that the antibody raised against the nuclear antigen Ki-67 of mammalian cells recognized antigenic determinants of early Drosophila embryos, localized on the outside of the nuclear envelope. Hence, the nuclear envelope of Drosophila appears to share a similar epitope with the chromosome scaffold of mitotic mammalian cells. With the progression of mitosis the antigen persisted around the mitotic spindle region and was also found in the pole regions at metaphase and anaphase. The antibody also stained the equatorial regions of the spindles from anaphase to late telophase. The antibody may therefore be used as a biochemical marker of the nuclear envelope for studying nuclear membrane biogenesis and behavior during the mitotic divisions of the Drosophila embryo. 相似文献
8.
Anna Maria Fausto Marcella Carcupino Massimo Mazzini Franco Giorgi 《Development, growth & differentiation》1994,36(2):197-207
Developing embryos of the stick insect Carausius morosus were examined ultrastructurally with a view to studying vitellophage invasion of the yolk mass during and after germ band formation. Newly laid eggs in C.morosus have a unique yolk fluid compartment surrounded by a narrow fringe of cytoplasm comprising several small yolk granules. Vitellophages originate mainly from a thin layer of stem cells, the so-called yolk cell membrane, interposed between the germ band and the yolk mass. Throughout development, a thin basal lamina separates the yolk cell membrane from the overlying embryo.
Vitellophages extend from the yolk cell membrane with long cytoplasmic processes or filopodia to invade the central yolk mass. Along their route of entrance, filopodia engulf portions of the yolk mass and sequester it into membrane-bounded granules. As this process continues, the yolk mass is gradually partitioned into a number of yolk granules inside the vitellophages.
Later in development, the yolk cell membrane is gradually replaced by the endodermal cells that emerge from the anterior and posterior embryonic rudiments. From this stage of development onwards, vitellophages remain attached to the basal lamina through long filopodia extending between the endodermal cells. Yolk confined in different vitellophagic cells appears heterogeneous both in density and texture, suggesting that yolk degradation may be spatially differentiated. 相似文献
Vitellophages extend from the yolk cell membrane with long cytoplasmic processes or filopodia to invade the central yolk mass. Along their route of entrance, filopodia engulf portions of the yolk mass and sequester it into membrane-bounded granules. As this process continues, the yolk mass is gradually partitioned into a number of yolk granules inside the vitellophages.
Later in development, the yolk cell membrane is gradually replaced by the endodermal cells that emerge from the anterior and posterior embryonic rudiments. From this stage of development onwards, vitellophages remain attached to the basal lamina through long filopodia extending between the endodermal cells. Yolk confined in different vitellophagic cells appears heterogeneous both in density and texture, suggesting that yolk degradation may be spatially differentiated. 相似文献
9.
Numerous studies have demonstrated that several diseases and stress conditions are associated with changes in the levels of zinc in the blood plasma and cellular elements. In this research the association between serum zinc concentrations and other hematic parameters of diagnostic interest has been evaluated. Quantitative determinations of zinc, total plasmatic proteins, albumin, hemoglobin and calculation of mean corpuscular volume were performed on blood samples from 58 males aged 20–61 years. Concentrations measured in our sample are comparable with reference values. Statistically significant correlation coefficients were found between age and albumin (r = - 0.562, P < 0.001), serum zinc and albumin (r = 0.328, P < 0.05), serum zinc and hemoglobin (r = 0.291, P < 0.05), and total plasmatic proteins and albumin (r = 0.463, P < 0.001). These correlation coefficients were significant even after adjustment for age effect. The determination of serum zinc concentration may be useful in the assessment of clinical scenarios. Particularly, it may provide additional information for the diagnosis of specific pathologies, such as hepatic malfunctions. It could also be useful in the identification of different stages of anemia. 相似文献
10.