全文获取类型
收费全文 | 2270篇 |
免费 | 183篇 |
国内免费 | 128篇 |
出版年
2024年 | 9篇 |
2023年 | 43篇 |
2022年 | 67篇 |
2021年 | 83篇 |
2020年 | 72篇 |
2019年 | 77篇 |
2018年 | 95篇 |
2017年 | 76篇 |
2016年 | 83篇 |
2015年 | 88篇 |
2014年 | 106篇 |
2013年 | 171篇 |
2012年 | 98篇 |
2011年 | 115篇 |
2010年 | 64篇 |
2009年 | 103篇 |
2008年 | 113篇 |
2007年 | 133篇 |
2006年 | 113篇 |
2005年 | 101篇 |
2004年 | 87篇 |
2003年 | 64篇 |
2002年 | 68篇 |
2001年 | 57篇 |
2000年 | 35篇 |
1999年 | 46篇 |
1998年 | 40篇 |
1997年 | 33篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 38篇 |
1993年 | 18篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 22篇 |
1989年 | 26篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 5篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2581条查询结果,搜索用时 234 毫秒
41.
P.J. Thornalley A. Stern 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1984,804(3):308-323
Glyceraldehyde induces changes in the flux of glucose oxidised through the hexose monophosphate pathway, the concentrations of intermediates in the Embden-Meyerhoff pathway, the oxidative status of haemoglobin and levels of reduced and oxidised pyridine nucleotides and glutathione in red cells. Glyceraldehyde autoxidises in the cellular incubations, consuming oxygen and producing glyoxalase I- and II-reactive materials. Major fates of glyceraldehyde in red cells appear to be: (i) adduct formation with reduced glutathione and cellular protein; (ii) autoxidation and reaction with oxyhaemoglobin and pyridine nucleotides, and (iii) phosphorylation of d-glyceraldehyde and entry into the glycolytic pathway as glyceraldehyde 3-phosphate. The production of glycerol from glyceraldehyde by red cell l-hexonate dehydrogenase appears not to be a major reaction of glyceraldehyde in red cells. These results indicate that high concentrations of glyceraldehyde (1–50 mM) may induce oxidative stress in red cells by virtue of the spontaneous autoxidation of glyceraldehyde, forming hydrogen peroxide and α-ketoaldehydes (glyoxalase substrates). The implications of glyceraldehyde-induced oxidative stress for the in vitro anti-sickling effect of dl-glyceraldehyde and for the polyol pathway metabolism of glyceraldehyde are discussed. 相似文献
42.
Matthew J. Friedman Ante M. Krstulović Henri Colin Georges Guiochon Kathleen Pajer 《Analytical biochemistry》1984,142(2):480-486
Described in this paper is a rapid, isocratic assay for serum indole-3-acetic acid (IAA). The sample preparation involves only protein precipitation using sulfosalicylic acid, and the sensitivity of amperometric detection is in the picogram range. The chromatographic analysis time is approximately 4 min. The devised method was used for a longitudinal study of IAA levels in serum samples from control subjects and newly abstinent alcoholics. Dietary variations were eliminated by administering a 2.0-g loading dose of L-Trp to all subjects investigated. The results are presented in the form of cumulative frequency polygons. Preliminary data indicate no differences in IAA levels between newly abstinent alcoholics and control subjects. 相似文献
43.
The chick oviduct in tissue culture. I. Initial characterization of growing primary oviduct tissue cultures 总被引:1,自引:0,他引:1
A simple three-enzyme treatment of collagenase, dispase and hyaluronidase on finely minced chick oviduct yields clumps of 50-150 cells. These cells attach to collagen-treated dishes and survive in culture for at least 2 weeks without subculturing. Oviduct cell cultures can also be induced to grow. Estradiol or epidermal growth factor (EGF) induce a 40% increase in cells in 4 days when cultures are grown in serum levels that do not support growth. Serum from estrogen-stimulated chicks promotes rapid cellular proliferation (doubling times of 1-2 days). Sera from estrogen withdrawn chicks, laying hen or horse do not support as rapid proliferation. The oviduct growth-promoting factors in serum from estrogen-stimulated chicks are not steroids or fibroblast growth factors (FGF). Removal of steroids from these sera by charcoal treatment or delipidization does not decrease the rate of growth. The addition of 1-100 nM estradiol does not increase a serum's ability to promote growth. Purified FGF or platelet-derived growth factor (PDGF) do not induce oviduct proliferation. These results were reproduced in oviduct cell cultures started from estrogen-stimulated and withdrawn chicks as well as laying hens. Thus the factors in serum from estrogen-stimulated chicks that promote rapid oviduct growth are induced by estrogen treatments in vivo, but do not seem to be only steroids. 相似文献
44.
Agonistic behavior was observed in five captive groups of the monogamous monkey Callithrix jacchus jacchus,which normally produces twin offspring every 5 months. Fighting is first recorded when twins are aged 5–10 months. These “twin
fights” determine differences in status between combatants that can be detected 5 months later. From what is known of the
social behavior of the species, it is postulated that an individual’s twin is its most serious rival and that early fighting
is advantageous because injury is minimal while the animal retains its milk dentition. In contrast to twin fights, aggression
between same-sex juveniles and adults does not involve long fights and probably serves to reinforce preexisting differences
in status. It often results in forcing a group member to the periphery, and therefore, its main function may be to drive mature,
same-sexed individuals out of the group. Apart from the relationship between twins, status within the family group is age
related and not normally determined by aggression. 相似文献
45.
Asymptotic solutions for the effectiveness factor and the concentration profile are obtained for mth-order chemical reactions inside a slab catalyst pellet with Robin boundary condition at the pellet's outer surface. Using perturbation analysis in the limit of large reaction order m, the effectiveness factor and the concentration profile are explicitly determined up to O(1/m). Higher-order solutions can be obtained in a systematic way if desired. 相似文献
46.
Free radicals and tissue damage produced by exercise 总被引:11,自引:0,他引:11
K J Davies A T Quintanilha G A Brooks L Packer 《Biochemical and biophysical research communications》1982,107(4):1198-1205
47.
Synthesis of alpha and gamma interferons by a human cutaneous lymphoma with helper T-cell phenotype 总被引:3,自引:0,他引:3
A cloned human cutaneous lymphoma Hut102-B2 with helper T-cell phenotype (Leu1+, Leu2a?, Leu3a+) was found to produce substantial quantities of interferon (IFN) on induction with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). Whereas only trace amounts of IFN were secreted by Hut102-B2 cells spontaneously, up to 8000 laboratory units/ ml of IFN were synthesized under the optimal conditions of TPA induction. Characterization studies including neutralization by specific antisera to IFNs and determination of the activities in human and bovine cells disclosed that the IFN produced by Hut102-B2 cells exposed to TPA was a mixture of immune IFN (IFN-γ) and leukocyte IFN (IFN-α) made in approximately equal amounts in terms of antiviral activity. 相似文献
48.
The hyaline layer (HL) surrounding the sea urchin blastula appears to dissolve in 1 M glycine. However, after this treatment, there persists over the surfaces of the blastomeres a layer of material, referred to here as the apical lamina (AL), that sloughs off as an adhesive convoluted bag upon gradual dissociation of the embryo. Isolated hyaline layers, referred to as HL-AL complexes, were analyzed by urea-SDS-polyacrylamide gel electrophoresis. A major protein of the HL-AL complex, hyalin, bands or precipitates in the stacking gel. Two other major proteins, both strongly PAS positive, migrate with apparent molecular weights of 175K and 145K daltons. As with intact embryos, the glycine wash removes the hyalin protein from the isolated HL-AL complex, leaving the undissolved AL which consists primarily of the 175K- and 145K-dalton proteins. The embryo's own perivitelline-localized cortical granule peroxidase heavily radioiodinates the proteins of the HL-AL complex, further verifying their apical, extracellular location. Unlike hyalin, the AL proteins do not precipitate with calcium ions. Compared to the entire HL-AL complex, the AL contains a greater percentage of carbohydrate. No sialic acid is associated with the HL-AL complex, but the AL contains some sulfate. In contrast to a published report based on ultrastructural staining, no biochemical evidence was found in this study for the presence of collagen or significant glycosaminoglycan within the HL-AL complex. No developmental differences were observed in AL proteins from 1-hr-old embryos compared to those from blastulae. However, there is evidence suggesting heterogeneity and developmental differences in hyalin. The possible organization of hyalin and the AL proteins into separate layers surrounding the embryo is discussed. The influence of the AL proteins in morphogenesis and cell adhesion is considered, and hypothetical roles attributed to the HL and hyalin are critically questioned. 相似文献
49.
Wayne Chris Hawkes Calvin C. Willhite Kimberly A. Craig Stanley T. Omaye Douglas N. Cox Wai Nang Choy Andrew G. Hendrickx 《Biological trace element research》1992,35(3):281-297
Forty pregnant long-tailed macaques were treated daily for 30 d with 0, 25, 150 or 300 μg selenium as L-selenomethionine/kg
body weight. Erythrocyte and plasma selenium and glutathione peroxidase specific activities, hair and fecal selenium, and
urinary selenium excretion were increased by and were linearly related to L-selenomethionine dose. Hair selenium was most
sensitive to L-selenomethionine dose, with an 84-fold increase in the 300 μg selenium/(kg-d) group relative to controls (r=0.917). Daily urinary selenium excretion (80-fold,r=0.958), plasma selenium (22-fold,r=0.885), erythrocyte selenium (24-fold,r=0.920), and fecal selenium (18-fold,r=0.911) also responded strongly to L-selenomethionine. Erythrocyte and plasma glutathione peroxidase specific activities increased
154% and 69% over controls, respectively. Toxicity was associated with erythrocyte selenium >2.3 μg/mL, plasma selenium >2.8
μg/mL, and hair selenium >27 μg/g. Plasma, erythrocyte, and hair selenium concentrations may be useful for monitoring and
preventing the toxicity of L-selenomethionine administered to humans in cancer chemoprevention trials. 相似文献
50.
Pilar Galan Helene Thibault Paul Preziosi Serge Hercberg 《Biological trace element research》1992,32(1-3):421-426
The relationship between iron status and capacity for IL-2 production by lymphocytes was assessed in 81 children from 6 mo
to 3 yr of age selected at random from a population with low socioeconomic status, undergoing free systematic examination
in four children's health centers in the Paris area. Iron deficiency was defined by the existence of at least two abnormal
values among the three indicators of iron status: serum ferritin level ≤12 μg/L, transferrin saturation <12%, and erythrocyte
protoporphyrin concentration >3 μg/g hemoglobin. According to this definition, 53 children were classified as iron deficient
and 28 as iron sufficient. No differences were observed between the iron-deficient and iron-sufficient groups in terms of
the IL-2 concentration without stimulation by PHA. IL-2 production by lymphocytes stimulated with PHA, as well as the stimulation
index (ratio of IL-2 concentration following stimulation by PHA to that of IL-2 concentration without stimulation by PHA)
were significantly lower in iron-deficient children. The reduction in IL-2 production by activated lymphocytes observed in
our study of iron-deficient children may be responsible for impairments in immunity found by other authors, particularly in
cell-mediated immunity. 相似文献