全文获取类型
收费全文 | 2049篇 |
免费 | 226篇 |
国内免费 | 1篇 |
出版年
2021年 | 20篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 40篇 |
2014年 | 50篇 |
2013年 | 66篇 |
2012年 | 74篇 |
2011年 | 88篇 |
2010年 | 50篇 |
2009年 | 65篇 |
2008年 | 69篇 |
2007年 | 71篇 |
2006年 | 85篇 |
2005年 | 78篇 |
2004年 | 68篇 |
2003年 | 58篇 |
2002年 | 58篇 |
2001年 | 54篇 |
2000年 | 59篇 |
1999年 | 62篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 22篇 |
1995年 | 31篇 |
1994年 | 17篇 |
1993年 | 19篇 |
1992年 | 55篇 |
1991年 | 41篇 |
1990年 | 45篇 |
1989年 | 50篇 |
1988年 | 44篇 |
1987年 | 47篇 |
1986年 | 35篇 |
1985年 | 33篇 |
1984年 | 49篇 |
1983年 | 40篇 |
1982年 | 33篇 |
1981年 | 29篇 |
1980年 | 28篇 |
1979年 | 33篇 |
1978年 | 32篇 |
1977年 | 34篇 |
1976年 | 22篇 |
1975年 | 29篇 |
1974年 | 30篇 |
1973年 | 48篇 |
1972年 | 30篇 |
1971年 | 21篇 |
1970年 | 22篇 |
1969年 | 24篇 |
排序方式: 共有2276条查询结果,搜索用时 15 毫秒
81.
82.
Using concentrations of [3H] dihydroergokryptine between 0.1 and 5 nM, saturable binding can be demonstrated in rat cerebral cortical membranes with a dissociation constant (KD) of about 0.8 nM. α-Noradrenergic agonists and antagonists compete for the sites labeled by these low concentrations of [3H] dihydroergokryptine with relative potencies characteristics of classical α-noradrenergic receptors. The very low potency of serotonin in competing for these binding sites indicates that, in contrast to findings with higher concentrations of [3H] DHE, low concentrations do not label serotonin receptors. Moreover, the low potency of dopamine in competing for [3H] dihydroergokryptine binding in both striatal and cortical membranes indicates that no detectable portion of binding is associated with postsynaptic dopamine receptors. 相似文献
83.
Bilateral lesions of the nucleus locus coeruleus in 7 female stumptail monkeys were followed by long lasting hyperphagia and hyperdipsia. The percentage increase in weight at five weeks after lesioning correlated highly with 3-methoxy-4-hydroxy-phenethylene glycol (MHPG) concentration in the cerebral cortex. This relationship suggests that the effects are due to the locus coeruleus system and are not the result of variable destruction of the ventral noradrenergic or adjacent non-noradrenergic pathways. 相似文献
84.
C Gorenstein S H Snyder 《Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)》1980,210(1178):123-132
Enkephalins can be degraded by a variety of peptidases. We have characterized several membrane-associated brain peptidases in an effort to determine which if any are concerned with the physiological inactivation of synaptically released enkephalin. We have distinguished two carboxyl-directed dipeptidylpeptidases, designated enkephalinase A1 and A2, that give rise to the Tyr-Gly-Gly fragment. Both enzymes are physically separable from angiotensin converting enzyme. Regional variations in enkephalinase A1 activity and opiate receptors are similar. A novel amino-terminal-directed dipeptidylpeptidase, enkephalinase B, which generates Tyr-Gly, has been identified. All of these enzymes as well as aminopeptidase have been solubilized from brain membranes by detergent treatment and have been mutually resolved by DEAE column chromatography. Enkephalinase A1 has been purified 1500-fold, to apparent homogeneity. 相似文献
85.
Long-chain alcohols are synthesized in the mouse preputial gland tumor (ESR-586) by NADPH:acyl-CoA oxidoreductase. In this study, a series of labeled acids was tested as substrates for the oxidoreductase in a cell-free system from the tumor, and the distribution of label into alcohols, waxes, and other products was determined. The system contained the labeled acid, an acyl-CoA-generating system, an NADPH-generating system, and tumor homogenate. The highest rates of alcohol synthesis were obtained with palmitic (16:0), heptadecanoic (17:0), stearic (18:0), myristic (14:0), elaidic (18:1 trans), and linoleic (18:2) acids, which yielded, respectively, 151, 124, 102, 76, 65, and 35 pmol alcohol/min per mg protein. Decanoic (10:0), lauric (12:0), oleic (18:1 cis), linolenic (18:3), arachidonic (20:4), and behenic (22:0) acids all gave lower activities. Acyl-CoA formation did not appear to be rate limiting with any of the substrates tested except behenic acid. In addition to the fatty alcohol product, a small amount of fatty aldehyde was formed in the system. Incorporation of the labeled fatty acids into wax esters was examined and the distribution of label between the alcohol and acid components of the waxes was determined. Incubation of [1-(14)C]palmitic acid yielded 3.4% free alcohol, 8.3% alcohol esterified in waxes, and 7.7% palmitoyl groups esterified into waxes, whereas, at the other extreme, [1-(14)C]linolenic acid yielded 0.8%, 0.6%, and 38%, respectively, into the homologous components.-Wykle, R. L., B. Malone, and F. Snyder. Acyl-CoA reductase specificity and synthesis of wax esters in mouse preputial gland tumors. 相似文献
86.
[3H]Mepyramine binds with high affinity to membranes from brain of human, rat, guinea-pig, rabbit and mouse with drug specificity indicating an association with histamine H1receptors. Considerable species differences occur in the affinity of [3H]mepyramine, with guinea-pig and human having 34 times greater affinity than rat, mouse or rabbit. The greater affinity of [3H]mepyramine in guinea-pig than in rat is attributable both to faster association and slower dissociation rates in guinea-pig. Species differences in affinity for H1 receptor sites occur for some antihistamines but not for others. Some tricyclic antidepressant and neuroleptic drugs are extremely potent inhibitors of [3H]mepyramine binding, exceeding in potency any H1 antihistamines examined. The tricyclic antidepressant doxepin and the neuroleptic clozapine are the most potent of all drugs examined in competing for [3H]mepyramine binding. The regional distribution of specific [3H]mepyramine binding differs considerably in the various species examined. 相似文献
87.
Dopamine 3-0-sulfate is present in considerable amounts in mammalian plasma and peripheral tissues. Incubation of dopamine 3-0-sulfate (0.1 μmole) with purified bovine dopamine-β-hydroxylase resulted in the formation of free norepinephrine (7.3 × 10?3 μmole). The conversion to norepinephrine was inhibited by 0.6 mM of fusaric acid, an inhibitor of dopamine-β-hydroxylase. The reaction of dopamine 3-0-sulfate with dopamine-β-hydroxylase followed Michaelis-Menten kinetics. The calculated Km was 17 mM, different from the Km for free dopamine (0.1 mM). The incubation medium does not contain any sulfatase activity. 相似文献
88.
A role in true-late gene expression for the T4 bacteriophage 5' polynucleotide kinase 3' phosphatase. 总被引:5,自引:0,他引:5
Two bacteriophage T4-induced, nucleic acid-modifying activities, 5′ polynucleotide kinase and 3′ phosphatase, are both coded by the pseT gene. Therefore, the product of this gene is an enzyme which can remove phosphates from 3′ termini and add them to 5′-hydroxyl termini and thus could be said to “shuttle” phosphates on polynucleotides. This enzyme is sometimes required for T4 true-late gene expression, probably by helping establish the required intracellular DNA structure. Our data suggest that a host gene product normally can substitute for the product of the pseT gene, making it non-essential for phage multiplication on most laboratory strains of Escherichia coli. 相似文献
89.
A radioreceptor assay for β-adrenergic blocking drugs described here is based on the ability of the blood content of drugs to compete with the binding of 3H-dihydroalprenolol (3H-DHA) to β-adrenergic receptors in calf cerebellar membranes. Plasma protein greatly inhibits the binding of 3H-DHA to β-receptors by binding the 3H-DHA so it is unavailable to the β-receptors. As little as 0.01 ml of human plasma in a final volume of 1 ml reduces binding 25–45%. Assays conducted on plasma dialysates can be performed without such inhibition. The radioreceptor assay is simple to perform as 100 samples can be processed in a morning. It is sensitive, detecting low nanomolar concentrations of plasma propranolol, and it is specific. No drugs clinically employed other than β-blocking agents compete for β-receptor binding. The assay detects all pharmacologically active metabolites of β-blocking drugs as well as the parent drug. 相似文献
90.
When the entire digital web space has been destroyed by burn scarring and there is a contracture of the volar aspect of the web as well as the dorsum, Z-plasties and skin grafts alone seldom produce a satisfactory web space. During the past 3 years, for the release of 46 contracted web spaces in 20 burned patients, we have turned a rectangular flap from the dorsal surface of the web through into an inverted-T incision in the palm. The adjacent sides of the defects have been skin grafted. In all these patients, we obtained satisfactory release of the contracture and restoration of the web space. 相似文献