全文获取类型
收费全文 | 3684篇 |
免费 | 288篇 |
国内免费 | 8篇 |
专业分类
3980篇 |
出版年
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 23篇 |
2019年 | 23篇 |
2018年 | 23篇 |
2017年 | 23篇 |
2016年 | 49篇 |
2015年 | 92篇 |
2014年 | 103篇 |
2013年 | 149篇 |
2012年 | 194篇 |
2011年 | 230篇 |
2010年 | 144篇 |
2009年 | 134篇 |
2008年 | 201篇 |
2007年 | 224篇 |
2006年 | 207篇 |
2005年 | 243篇 |
2004年 | 243篇 |
2003年 | 223篇 |
2002年 | 232篇 |
2001年 | 44篇 |
2000年 | 30篇 |
1999年 | 46篇 |
1998年 | 63篇 |
1997年 | 51篇 |
1996年 | 36篇 |
1995年 | 38篇 |
1994年 | 38篇 |
1993年 | 32篇 |
1992年 | 27篇 |
1991年 | 34篇 |
1990年 | 43篇 |
1989年 | 39篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 25篇 |
1985年 | 35篇 |
1984年 | 48篇 |
1983年 | 48篇 |
1982年 | 53篇 |
1981年 | 43篇 |
1980年 | 49篇 |
1979年 | 41篇 |
1978年 | 39篇 |
1977年 | 40篇 |
1976年 | 35篇 |
1975年 | 32篇 |
1974年 | 23篇 |
1973年 | 14篇 |
排序方式: 共有3980条查询结果,搜索用时 8 毫秒
21.
22.
Growth of Octopine-Catabolizing Pseudomonas spp. under Octopine Limitation in Chemostats and Their Potential To Compete with Agrobacterium tumefaciens 总被引:1,自引:1,他引:0 下载免费PDF全文
The growth characteristics of five octopine-catabolizing pseudomonads have been determined in batch and continuous cultures. All five strains belonged to rRNA homology group I and showed a more psychrotrophic growth pattern than did Agrobacterium tumefaciens B6 and ATCC 15955. In chemostats limited by octopine, either as the source of carbon and nitrogen or the sole source of nitrogen, maximum specific growth rates and substrate affinities were lower than those in chemostats limited by glutamate. These growth dynamics were similar to those observed for Agrobacterium strains B6 and ATCC 15955 even though the catabolic genes and pathways are believed to be different in the two genera. An analysis of the yields in octopine-limited chemostats indicated that the use of octopine as the sole source of carbon and nitrogen was grossly inefficient. Octopine and presumably lysopine and octopinic acid provided a better source of nitrogen than of carbon. One of the Pseudomonas fluorescens strains, E175D, was able to produce its highest yield on octopine as a nitrogen source. Competition models formulated on pure culture parameters indicated that two of the Pseudomonas spp. would dominate A. tumefaciens B6 and ATCC 15955 when in simple competition for octopine as a limiting substrate. 相似文献
23.
Johan Stjernschantz Dale Gregerson Larry Bausher Marvin Sears 《Journal of neurochemistry》1982,38(5):1323-1328
A solid phase enzyme-linked immunosorbent assay for quantitation of substance P is presented. The assay measures the capacity of soluble substance P to compete with the solid phase antigen for a limited quantity of specific substance P antibody. The solid-phase antigen consists of a synthetic substance P.poly-D-glutamic acid conjugate coated to polystyrene micro-ELISA plate wells. Soluble substance P and antibodies to substance P are first preincubated together and then added to the wells containing solid-phase antigen. Subsequently the wells are incubated with anti-antibodies conjugated to alkaline phosphatase. The wells are finally incubated with p-nitrophenyl phosphate an the absorbance is read in a spectrophotometer 16--24 hr after the start of the assay. The threshold for detection of substance P was 5--10 pg per well (0.25 ml). Substance P was extracted from rabbit eyes and the values obtained with the present method are compared with previously reported values based on radioimmunoassay. 相似文献
24.
The spin labels, 5-doxylstearate, 12-doxylstearate, 16-doxylstearate and 1-oxyl-2,2,6,6-tetramethyl-4-dodecylphospiperidine, have been incorporated into dodecylphospocholine micelles and mixed dodecylphosphocholine/ glucagon micelles. The EPR spectral parameters for the different spin labels and the 1H- and 13C-NMR relaxation rates for nuclei of the detergent molecules indicated that inclusion of up to one spin label molecule per micelle had little influence on the spatial organization of the micelles. Furthermore, the location and environment of the spin labels in the dodecylphosphocholine micelles were not noticeably affected by the addition of glucagon and the 1H-NMR spectra observed for glucagon in mixed spin label/deuterated dodecylphosphocholine/glucagon micelles showed that the different spin labels had essentially no effect on the conformation of glucagon. Approximate spatial locations within the micelle for the nitroxide moieties of the different spin labels were determined from the NMR relaxation rates observed for different nuclei of dodecylphosphocholine. On this basis, the line broadening of individually assigned glucagon 1H-NMR lines by the different spin labels was used to determine the approximate orientation of the polypeptide chain with respect to the micelle surface. Overall, the data indicate that the glucagon backbone runs roughly parallel to the micelle surface, with the depth of immersion adjusted so that polar and apolar side chains can be oriented towards the surface or interior of the micelle, respectively. 相似文献
25.
C.Stuart Baxter Larry A. Fish 《Biochemical and biophysical research communications》1981,103(1):168-174
Linear saturated fatty acid methyl esters were comitogenic with lectins for mouse lymphocytes, the degree of comitogenicity being strongly dependent on the length of the acyl group, and maximal for methyl tetradecanoate. Lesser effects were found for analogs with 10, 12 or 16 acyl carbon atoms, whereas those with fewer than 10 or more than 16 were inactive. Analogous structure-function relationships have been described for various membrane-active and tumor-promoting phorbol diesters, where there is a similar dependence on ester acyl group length for many activities. The fatty acid esters may therefore represent simple model compounds for studying mechanistic aspects of phorbol diester activity. 相似文献
26.
The partition of cis-parinaric acid (9,11,13,15-cis, trans, trans,cis-octadecatetraenoic acid, cis-PnA) and trans-parinaric acid (9,11,13,15-all-trans-octadecatetraenoic acid, trans-PnA) among aqueous, solid lipid, and fluid lipid phases has been measured by three spectroscopic parameters: absorption spectral shifts, fluorescence quantum yield, and fluorescence polarization. The solid lipid was dipalmitoylphosphatidylcholine (DPPC); the fluid lipid was palmitoyldocosahexaenoylphosphatidylcholine (PDPC). Mole fraction partition coefficients between lipid and water were determined by absorption spectroscopy to be for ci--PnA, 5.3 X 10(5) with a solid lipid and 9 X 10(5) with fluid lipid and, for trans-PnA, 5 X 10(6) with solid lipid and 1.7 X 10(6) with fluid lipid. Ratios of the solid to the fluid partition coefficients (Kps/f) are 0.6 +/- 0.2 for cis-PnA and 3 +/- 1 for trans-PnA. A phase diagram for codispersions of DPPC and PDPC has been constructed from the measurements of the temperature dependence of the fluorescence quantum yield and polarization of cis-PnA and trans-PnA and their methyl ester derivatives. A simple analysis based on the phase diagram and fluorescence data allows additional calculations of Kps/f's which are determined to be 0.7 +/- 0.2 for the cis probes and 4 +/- 1 for the trans probes. The relative preference of trans-PnA for solid phase lipids and its enhanced quantum yield in solid phase lipids make it sensitive to a few percent solid. The trans probes provide evidence that structural order may persist in dispersions of these phospholipids 10 degrees C or more above their transition temperature. It is concluded that measurements of PnA fluorescence polarization vs. temperature are better suited than measurements of quantum yield vs. temperature for determining phospholipid phase separation. 相似文献
27.
Larry A. Jones Diane K. Jordan Kutay Taysi Arnold W. Strauss Joseph K. Toth 《Human genetics》1979,51(1):37-42
Summary A partial duplication of the distal segment of the long arm of chromosome 5 (q31qter) was observed in an infant with congenital malformations and dysmorphic features. The phenotypically normal father had a balanced translocation between the long arm of chromosome 5 and the short arm of chromosome 9: 46,XY,t(5;9)(q31;p24).The clinical and cytogenetic data obtained from six patients with partial duplications of two different long arm segments of chromosome 5 suggest that partial duplication of the distal long arm of chromosome 5 is associated with microcephaly, hypertelorism, epicanthus, strabismus, large upper lip, low-set, dysplastic ears, in addition to growth and psychomotor retardation. Partial duplication of the proximal part of the long arm of chromosome 5, on the other hand, is associated mainly with musculoskeletal abnormalities including muscle hypotrophy and hypotonia, scoliosis, lordosis, pectus carinatum, cubitus valgus, and genu valgum, in addition to psychomotor retardation. The dysmorphic features in this latter group include a bulging forehead, short nose, thick upper lip, low-set protruding ears and tapering, thin fingers. 相似文献
28.
Heritability of Quasi-Continuous Skeletal Traits in a Randombred Population of House Mice 总被引:1,自引:0,他引:1
Heritabilities of 11 quasi-continuous skeletal traits were estimated in randombred house mice of three separate ages (1, 3, and 5 months). Three separate methods—regression, maximum likelihood correlation, and Falconer's Method—were used to obtain heritabilities for each of the separate age groups. Significant differences in the incidences of seven of the skeletal traits were found among ages, but they did not affect the heritability estimates, these estimates being pooled over ages. Heritabilities calculated from female parents were consistently higher (by about 13%) than those from male parents, indicating the presence of maternal effects. Mid-parent estimates made by all three methods gave very similar mean levels (0.17 — 0.20). Although low, this level compared favorably with that expected on the basis of previously estimated rates of accumulation of genetic variance. Maternal effects estimated from full sib correlations averaged 0.08. 相似文献
29.
A modified crossover experiment was conducted to determine the mechanism of arylhydroxylamine rearrangement in the rat. When 1-hydroxy-1-phenyl-3-methylurea was incubated with fractionated liver homogenates or injected intraperitoneally in rats, 1-methylbenzimidazol-2-one was isolated as the major metabolite. Small amounts of the anticipated aminophenol, 1-(o-hydroxylphenyl)-3-methylurea were also isolated. Evidence is presented suggesting that hepatic isomerase-catalyzed rearrangements of hydroxylamines proceed via pathways analogous to those described for chemical model systems. Isomerization appears to be intermolecular involving the generation of a resonance-stabilized nitrenium ion capable of binding to amino acids and nucleotide bases. 相似文献
30.
Siobhan Flaherty Pamela Strauch Mahdi Maktabi Brandon S. Pybus Gregory Reichard Larry A Walker Rosemary Rochford 《Journal of cellular and molecular medicine》2022,26(13):3675
Primaquine (PQ) and Tafenoquine (TQ) are clinically important 8‐aminoquinolines (8‐AQ) used for radical cure treatment of P. vivax infection, known to target hepatic hypnozoites. 8‐AQs can trigger haemolytic anaemia in individuals with glucose‐6‐phosphate dehydrogenase deficiency (G6PDd), yet the mechanisms of haemolytic toxicity remain unknown. To address this issue, we used a humanized mouse model known to predict haemolytic toxicity responses in G6PDd human red blood cells (huRBCs). To evaluate the markers of eryptosis, huRBCs were isolated from mice 24–48 h post‐treatment and analysed for effects on phosphatidylserine (PS), intracellular reactive oxygen species (ROS) and autofluorescence. Urinalysis was performed to evaluate the occurrence of intravascular and extravascular haemolysis. Spleen and liver tissue harvested at 24 h and 5–7 days post‐treatment were stained for the presence of CD169+ macrophages, F4/80+ macrophages, Ter119+ mouse RBCs, glycophorin A+ huRBCs and murine reticulocytes (muRetics). G6PDd‐huRBCs from PQ/TQ treated mice showed increased markers for eryptosis as early as 24 h post‐treatment. This coincided with an early rise in levels of muRetics. Urinalysis revealed concurrent intravascular and extravascular haemolysis in response to PQ/TQ. Splenic CD169+ macrophages, present in all groups at day 1 post‐dosing were eliminated by days 5–7 in PQ/TQ treated mice only, while liver F4/80 macrophages and iron deposits increased. Collectively, our data suggest 8‐AQ treated G6PDd‐huRBCs have early physiological responses to treatment, including increased markers for eryptosis indicative of oxidative stress, resulting in extramedullary haematopoiesis and loss of splenic CD169+ macrophages, prompting the liver to act as the primary site of clearance. 相似文献