全文获取类型
收费全文 | 3618篇 |
免费 | 333篇 |
国内免费 | 2篇 |
出版年
2023年 | 18篇 |
2022年 | 33篇 |
2021年 | 67篇 |
2020年 | 33篇 |
2019年 | 42篇 |
2018年 | 50篇 |
2017年 | 52篇 |
2016年 | 75篇 |
2015年 | 141篇 |
2014年 | 149篇 |
2013年 | 189篇 |
2012年 | 236篇 |
2011年 | 249篇 |
2010年 | 138篇 |
2009年 | 127篇 |
2008年 | 156篇 |
2007年 | 170篇 |
2006年 | 145篇 |
2005年 | 170篇 |
2004年 | 128篇 |
2003年 | 155篇 |
2002年 | 169篇 |
2001年 | 92篇 |
2000年 | 97篇 |
1999年 | 90篇 |
1998年 | 43篇 |
1997年 | 43篇 |
1996年 | 35篇 |
1995年 | 39篇 |
1994年 | 29篇 |
1993年 | 25篇 |
1992年 | 66篇 |
1991年 | 63篇 |
1990年 | 56篇 |
1989年 | 59篇 |
1988年 | 42篇 |
1987年 | 37篇 |
1986年 | 38篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 36篇 |
1982年 | 25篇 |
1981年 | 27篇 |
1980年 | 15篇 |
1979年 | 27篇 |
1978年 | 31篇 |
1977年 | 17篇 |
1976年 | 21篇 |
1974年 | 25篇 |
1969年 | 16篇 |
排序方式: 共有3953条查询结果,搜索用时 15 毫秒
81.
Significant polymorphism of serum complement components Bf, C2, C3, C6, and C8 in the chimpanzee has been demonstrated. The data are consistent with the hypothesis thatC2 andBf are closely linked toChLA and argue against close linkage ofChLA toC3 or toC8, as in man. In addition, a blank allele for C6 and C6 deficiency was detected in several chimps. 相似文献
82.
1. The stable complex formed between mammalian cytochrome c and phosvitin at low ionic strength was studied by partition in an aqueous two-phase system. Oxidized cytochrome c binds to phosvitin with a higher affinity than reduced cytochrome c. The difference was equivalent to a decrease of the redox potential by 22 mV on binding. 2. Complex-formation with phosvitin strongly inhibited the reaction of cytochrome c with reagents that react as negatively charged species, such as ascorbate, dithionite, ferricyanide and tetrachlorobenzoquinol. Reaction with uncharged reagents such as NNN'N'-tetramethylphenylenediamine and the reduced form of the N-methylphenazonium ion (present as the methylsulphate) was little affected by complex-formation, whereas oxidation of the reduced cytochrome by the positively charged tris-(phenanthroline)cobalt(III) ion was greatly stimulated. 3. A similar pattern of inhibition and stimulation of reaction rates was observed when phosvitin was replaced by other macromolecular polyanions such as dextran sulphate and heparin, indicating that the results were a general property of complex-formation with polyanions. A weaker but qualitatively similar effect was observed on addition of inositol hexaphosphate and ATP. 4. It is suggested that the effects of complex-formation with polyanions on the reactivity of cytochrome c with redox reagents are mainly the result of replacing the positive charge on the free cytochrome by a net negative charge. Any steric effects on polyanion binding are small in comparison with such electrostatic effects. 相似文献
83.
Lars Sottrup-Jensen Torben E. Petersen Staffan Magnusson 《Analytical biochemistry》1980,107(2):456-460
The use of gradient elution with acetate-buffered ethanol for high-performance liquid chromatographic analysis of phenylthiohydantoins (PTHs) is described. The system separates all commonly encountered PTH derivatives in a total analysis time of 20 min on columns of Spherisorb 5 S ODS (4.6 × 250 mm) packed in the laboratory at moderate expense. Experience with routine operation of the method, particularly with regard to column stability is discussed. Ethanol is considerably cheaper and less toxic than previously described solvent systems. 相似文献
84.
Konrad Heintze Karl-Uwe Petersen Peter Olles Sethna H. Saverymuttu John R. Wood 《The Journal of membrane biology》1979,45(1-2):43-59
Summary Fluid transport and net fluxes of Na, K, Cl and HCO3 by guinea pig gallbladder were investigatedin vitro. A perfused gallbladder preparation was devised to simultaneously study unidirectional fluxes of22Na and36Cl. The net Cl flux exceeded the net Na flux during fluid absorption in the presence of HCO3. This Cl excess was counter-balanced by a net HCO3 secretion: a HCO3–Cl exchange. PGE1 reversed the direction of fluid transport and abolished the net Cl flux. The magnitude of the HCO3 secretion remained unchanged, but shifted from a HCO3–Cl exchange to a net secretion of NaHCO3 and KHCO3. Furosemide inhibited both the HCO3–Cl exchange and HCO3 secretion after PGE1 without influencing fluid absorption. Ouabain inhibited the HCO3–Cl exchange as well as fluid absorption; only the effect on the HCO3 secretion was entirely reversible. Secreted HCO3 appeared not to be derived from metabolic sources since HCO3 secretion was abolished in a HCO3-free bathing medium. HCO3 secretion was also dependent on the Na concentration of the bathing fluid. Three lines of evidence are presented in favor of an active HCO3 secretion in guinea pig gallbladder. HCO3 is secreted against: (i) a chemical gradient, (ii) an electrical gradient and (iii) the direction of fluid movement under control conditions. 相似文献
85.
Ionic currents across pancreatic acinar cell membranes and their role in fluid secretion 总被引:1,自引:0,他引:1
O H Petersen Y Maruyama J Graf R Laugier A Nishiyama G T Pearson 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1981,296(1080):151-166
Fluid and enzyme secretion from a number of mammalian exocrine glands is controlled by the action of neurotransmitters and hormones on acinar cell membranes. Sustained stimulation evoking sustained fluid and enzyme secretion also evokes sustained membrane depolarization and increase in conductance. Mouse and rat pancreatic fluid and enzyme secretion, as well as membrane depolarization and conductance increase evoked by sustained stimulation with acetylcholine or cholecystokinin-gastrin peptides, are acutely dependent on extracellular calcium. However, the initial stimulant-evoked conductance increase and secretion appear to be triggered by calcium released from inside the cells. Direct measurement of membrane current during sustained stimulation in voltage-clamp experiments with resolution of the total current into its Na, Cl and K components has allowed calculations of stimulant-evoked Na and Cl uptake into the acinar cells. The NaCl uptake is quantitatively sufficient to account for the stimulant-evoked fluid secretion. The role of the stimulant-evoked transmembrane ionic current appears to be the supply of salt for the fluid secretion. Calcium derived from intracellular sources in the initial phase of secretion, and from the extracellular fluid in the sustained phase, couples fluid and enzyme secretion to hormone-receptor interaction. 相似文献
86.
The nematode Drilomermis leioderma n. gen., n. sp. (Merrnithidae) is described from larvae of Cybister fimbriolatus (Say) (Dytiscidae: Coleoptera) in Louisiana. Diagnostic characters of the genus Drilomermis are: medium-sized nematodes with the cuticle appearing smooth (lacking cross fibers) under the light microscope, six cephalic papillae, without mouth papillae, six hypodermal cords at midbody, 2 extremely long spicules (longer than 10 times body width at anus) which are separate and parallel (not twisted), an S-shaped vagina, medium-sized amphids located near head papillae, and postparasitic juvenile with a tail appendage. D. leioderma possesses a ventrally displaced mouth, very long vagina, and male genital papillae arranged in 3 double rows in the vicinity of the cloacal opening. Even when containing multiple parasites, about 40% of the hosts sulwived emergence of the memithids and lived several more days. In nature, some of these hosts may be able to continue their development, which is unusual since most mermithid-parasitized hosts die soon after the nematode emerges. 相似文献
87.
88.
89.
1. Aldehyde dehydrogenase subcellular distribution studies were performed in a heterogeneous stock (HS) of male and female mice (Mus musculus) with propionaldehyde (5 mM and 50 microM) and formaldehyde (1 mM) and NAD+ or NADP+. 2. The relative percents of distribution were: cytosolic 55-68%, mitochondrial 12-20%, microsomal 9-18% and lysosomal 3-15% for both propionaldehyde concentrations and NAD+. 3. Kinetic experiments using propionaldehyde and acetaldehyde with NAD+ revealed two separate enzymes, Enzyme I (low Km) and Enzyme II (high Km) in the cytosolic and mitochondrial fractions. 4. The kinetic data also indicated a spectrum of cytosolic low Km values that exhibited a bimodal distribution with one congruent to 40 microM and one congruent to 5 microM. 5. It was concluded that there was no significant difference in aldehyde-metabolizing capability between male and female HS mice, compared on a per gram of liver basis. The cytosolic low Km enzyme plays a major role in aldehyde oxidation at moderate to low aldehyde concentrations. 相似文献
90.
G D Li D Milani M J Dunne W F Pralong J M Theler O H Petersen C B Wollheim 《The Journal of biological chemistry》1991,266(6):3449-3457
The mechanism by which extracellular ATP stimulates insulin secretion was investigated in RINm5F cells. ATP depolarized the cells as demonstrated both by using the patch-clamp technique and a fluorescent probe. The depolarization is due to closure of ATP-sensitive K+ channels as shown directly in outside-out membrane patches. ATP also raised cytosolic Ca2+ [( Ca2+]i). At the single cell level the latency of the [Ca2+]i response was inversely related to ATP concentration. The [Ca2+]i rise is due both to inositol trisphosphate mediated Ca2+ mobilization and to Ca2+ influx. The former component, as well as inositol trisphosphate generation, were inhibited by phorbol myristate acetate which uncouples agonist receptors from phospholipase C. This manoeuvre did not block Ca2+ influx or membrane depolarization. Diazoxide, which opens ATP-sensitive K+ channels, attenuated membrane depolarization and part of the Ca2+ influx stimulated by ATP. However, the main Ca2+ influx component was unaffected by L-type channel blockers, suggesting the activation of other Ca2+ conductance pathways. ATP increased the rate of insulin secretion by more than 12-fold but the effect was transient. Prolonged exposure to EGTA dissociated the [Ca2+]i rise from ATP-induced insulin secretion, since the former was abolished and the latter only decreased by about 60%. In contrast, vasopressin-evoked insulin secretion was more sensitive to Ca2+ removal than the accompanying [Ca2+]i rise. Inhibition of phospholipase C stimulation by phorbol myristate acetate abrogated vasopressin but only reduced ATP-induced insulin secretion by 34%. These results suggest that ATP stimulates insulin release by both phospholipase C dependent and distinct mechanisms. The Ca2+)-independent component of insulin secretion points to a direct triggering of exocytosis by ATP. 相似文献