全文获取类型
收费全文 | 441篇 |
免费 | 5篇 |
国内免费 | 7篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 13篇 |
2014年 | 46篇 |
2013年 | 30篇 |
2012年 | 24篇 |
2011年 | 50篇 |
2010年 | 21篇 |
2009年 | 24篇 |
2008年 | 16篇 |
2007年 | 19篇 |
2006年 | 15篇 |
2005年 | 20篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有453条查询结果,搜索用时 15 毫秒
1.
The results of a detailed analysis of 100 supernumerary limbs generated by 180° ipsilateral rotation (on the same limb stump) of regeneration blastemas is presented. The limbs were analyzed in terms of their position of origin, frequency, cartilage structure by Victoria blue staining, and muscle structure by serial sections. Single, double, or triple supernumeraries can be produced at no unique position of origin, although the posterodorsal quadrant was preferred. Four classes of supernumerary limbs were generated by such operations—normal; double dorsal or double ventral; part normal/part mirror imaged; part normal/part inverted in approximately equal frequencies. After amputation of these supernumeraries the same muscle patterns are faithfully regenerated. A hypothesis to explain the production of these abnormal limbs is proposed based on the observed phenomenon of fusion of supernumerary blastemata, but their regenerative behaviour presents problems for current models of pattern formation. Similar results have been obtained with developing limb buds and the relation between development and regeneration is discussed. 相似文献
2.
Satoshi Baba Toshie Takahashi Takeshi Kasama Haruyuki Shirasawa 《生物化学与生物物理学报:疾病的分子基础》1992,1180(2):195-200
Amyloid A protein (AA), the major fibril protein in AA-amyloidosis, is an N-terminal cleavage product of the precursor protein, serum amyloid A (SAA). Using mass spectrometry and amino-acid sequencing, we identified and characterized two novel AA protein subsets co-deposited as amyloid fibrils in an patient having AA-amyloidosis associated with rheumatoid arthritis. One of the AA proteins corresponded to positions 2–76 (or 75) of SAA2α and the other corresponded to positions 2–76 (or 75) of known SAA1 subsets, except for position 52 or 57, where SAA1α has valine and alanine and SAA1β has alanine and valine in position 52 and 57, respectively, whereas the AA protein had alanine at the both positions. Our findings (1), demonstrate that not only one but two SAA subsets could be deposited together as an AA-amyloid in a single individual and (2), support the existence of a novel SAA1 allotype, i.e., SAA152,57Ala. 相似文献
3.
Studies have been conducted to determine whether the mutagens in fried beef ingested by human subjects are excreted in the urine. Urine samples were collected from individuals on liquid or regular diets before and after a fried beef meal. The mutagenic activity of the samples was tested in the Ames Salmonella/microsome assay system. The results showed that in individuals on liquid diets, most of the urinary mutagenic activity is recovered within 2-6 h after consuming a fried beef meal. In one individual tested, mutagenic activity was found in urine samples obtained 6-15 h after the fried beef meal. No mutagenic activity was detected in any of the urine samples obtained 15-24 h following the meal. In individuals on a regular diet, however, mutagenic activity was frequently observed in urine samples obtained 16-24 h following the fried beef meal, although the mutagenic activity was not as great as that in the preceding 16 h. It appears that the mutagenic agents generated by the frying of beef are ingested, absorbed, and excreted by the human body in biologically detectable quantities. These results suggest that subjects should abstain from fried beef at least one day prior to and during urine mutagenicity screening. 相似文献
4.
To gain insight into the mechanism of formation of chromosomal aberrations by the tumor promoter phorbolmyristate acetate (PMA) in human lymphocytes, we investigated the effect of antioxidants and inhibitors of arachidonic acid metabolism. Among the antioxidants bovine erythrocyte CuZn superoxide dismutase, glutathione peroxidase, mannitol (a scavenger of hydroxyl radicals), butylated hydroxytoluene and butylated hydroxyanisole were anticlastogenic while catalase and dimethylfuran (a scavenger of singlet oxygen) were inactive. These results show that the induction of aberrations by PMA occurs via indirect action, i.e. the intermediacy of superoxide and hydroxyl radicals. The following inhibitors of arachidonic acid metabolism were strongly anticlastogenic: the cyclo-oxygenase inhibitors indomethacin and flufenamic acid and the lipoxygenase inhibitor BN1015. Imidazole, nordihydroguaiaretic acid BN 1048 and 5,8,11,14-eicosatetraynoic acid were moderately active. The inhibitor of phospholipase A2, fluocinolone acetonide, was also anticlastogenic.
We conclude that the oxidative metabolism of arachidonic acid is involved in the induction of chromosomal aberrations by PMA in human lymphocytes. However, because of the limited selectivity of these drugs, it is not yet possible to identify unambiguously the step(s) in the arachidonic acid cascade responsible for PMA clastogenicity. 相似文献
5.
M. Maden 《Developmental biology》1983,98(2):409-416
Previous experiments in which vitamin A has been administered to developing or regenerating limbs have shown that different limb axes are affected. In regenerating axolotl limbs, serial reduplications in the proximodistal axis are produced. In the developing chick limb bud, mirror-imaged reduplications in the anteroposterior axis are produced. Results reported here on Rana temporaria limb buds reveal that vitamin A causes both effects to occur. That is, limbs are both serially reduplicated in the proximodistal axis and mirror imaged in the anteroposterior axis. Time and concentration effects are explored and the significance of these results for our current understanding of axial organisation in limbs is discussed. 相似文献
6.
Genetically stable cell lines of cucumber for the large-scale production of diploid somatic embryos 总被引:2,自引:0,他引:2
Marc Kreuger Wiert van der Meer Erik Postma Rob Abbestee Natasja Raaijmakers Gerrit-Jan van Holst 《Physiologia plantarum》1996,97(2):303-310
For the initiation of embryogenic cucumber ( Cucumis sativus L.) cell lines, from excised radicles, directly in liquid medium, the culture regime, explant density and type and concentration of hormones were adjusted so that pro-embryogenic masses (PEMs) were formed within about 8 weeks. The established cucumber cell lines were maintained tor several years without loss of embryogenic and genetic stability. The ploidy level of somatic embryos from different cucumber eell lines was either diploid or tetraploid and depended on the ploidy level of Ihe cell line. Cucumber cell lines that produced only diploid embryos were obtained by selecting completely diploid explant material and growing it in the dark during the initiation phase. Mixoploid explains could lead to tetraploid or mixoploid ceil lines. Isolation and additional selection and subculturing of single PEMs resulted in either completely diploid or tetraploid cell lines, indicating that all cells of individual PEMs are either diploid or tetraploid. The ernbryogenic cucumber cell Imes, differing only in ploidy level, were indistinguishable in growth rate and embryogetiic potential and were genetically stable over several years. 相似文献
7.
Marie-Dominique Rhoda-Hardy-Dessources René-Serge de Neef Guy Mérault Françoise Giraud 《生物化学与生物物理学报:疾病的分子基础》1993,1181(1):90-96
PtdIns and PtdInsP kinases from normal erythrocyte (AA) membranes and sickle cell anaemia erythrocyte (SS) membranes have been characterized. PtdIns kinase was studied in native membranes under conditions in which PtdInsP kinase and PtdInsP phosphatase do not express any activity. Kinetic analysis of the AA and SS PtdIns kinases indicate similar Km values for PtdIns and ATP but higher Vmax values for SS PtdIns kinase. PtdInsP kinase was partially purified from erythrocyte ghosts by NaCl extraction. The kinetic parameters of PtdInsP kinase determined under these conditions were similar in AA and SS NaCl extracts. These data suggest the presence of some effector of PtdIns kinase in SS cell membranes, resulting in a greater activity of the enzyme. This leads consequently, to increase the PtdInsP pool and to activate PtdInsP kinase, in agreement with our previous observations of a greater [32P]Pi incorporation in both polyphosphoinositides in SS cells relatively to AA cells. 相似文献
8.
Uptake, release and metabolism of docosahexaenoic acid (DHA, c22:6 omega 3) in human platelets and neutrophils 总被引:5,自引:0,他引:5
S Fischer C von Schacky W Siess T Strasser P C Weber 《Biochemical and biophysical research communications》1984,120(3):907-918
Exogenous DHA is converted by human platelets to 14- and 11- HDHE and by human neutrophils mainly to 7- HDHE . Human platelets prelabeled with 14C-DHA, 14C-EPA and 14C-AA and stimulated with thrombin release and metabolize DHA only in trace amounts as compared to EPA and AA. 14C-DHA is incorporated into the 2-position of platelet phospholipids and occurs predominantly in phosphatidylethanolamine. DHA and EPA were also incorporated by dietary means into phospholipids of platelets and neutrophils. In resting platelets free DHA as well as free AA and EPA are not detectable. In platelets stimulated ex vivo with thrombin DHA is not significantly released which is in contrast to EPA and AA. After stimulation, 14- HDHE is found only in trace amounts as compared to 12-HETE and 12- HEPE . In DHA enriched neutrophils formation of HDHEs cannot be demonstrated after stimulation with ionophore A 23187. We conclude that even after dietary enrichment of DHA in phospholipids of platelets and neutrophils the level of free DHA and/or formation of HDHEs might be too low to substantially affect arachidonic acid metabolism and related functions of these cells. 相似文献
9.
月腺大戟根中乙酰基间苯三酚衍生物 总被引:6,自引:0,他引:6
从月腺大戟(Euphorbia ebracteolata Hayata)根中分离出一种新的二苯甲烷化合物-双去甲基伪绵马素-AA和2,4-二羟基-6-甲氧基-3-甲基苯乙酮,并用光谱和化学方法确定前者的结构为3,3-二乙酰基-4,4-二甲氧基-2。25,6-四羟基二苯甲烷 相似文献
10.
Interaction of a spin-labeled 9-aminoacridine with DNA was studied by electron spin resonance spectroscopy. Accurate determination of the binding parameters, equilibrium dissociation constant (KD), and total number of ligand-binding sites was obtained using Scatchard and Lineweaver-Burk plots. The competition between 9-aminoacridine and its spin-labeled derivative was examined by a similar analysis of the spin-label signals. The practical interest of this method lies in the fact that the precision and the simplicity of the measurements allow the quantitative determination of the binding capacity of any intercalative drug which interacts specifically with adenine/thymine bases of DNA. 相似文献