全文获取类型
收费全文 | 2007篇 |
免费 | 145篇 |
国内免费 | 139篇 |
出版年
2023年 | 33篇 |
2022年 | 75篇 |
2021年 | 91篇 |
2020年 | 76篇 |
2019年 | 112篇 |
2018年 | 157篇 |
2017年 | 118篇 |
2016年 | 68篇 |
2015年 | 70篇 |
2014年 | 104篇 |
2013年 | 222篇 |
2012年 | 115篇 |
2011年 | 72篇 |
2010年 | 35篇 |
2009年 | 58篇 |
2008年 | 56篇 |
2007年 | 71篇 |
2006年 | 50篇 |
2005年 | 27篇 |
2004年 | 24篇 |
2003年 | 20篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 22篇 |
1984年 | 72篇 |
1983年 | 84篇 |
1982年 | 71篇 |
1981年 | 53篇 |
1980年 | 43篇 |
1979年 | 44篇 |
1978年 | 21篇 |
1977年 | 40篇 |
1976年 | 23篇 |
1975年 | 22篇 |
1974年 | 20篇 |
1973年 | 17篇 |
排序方式: 共有2291条查询结果,搜索用时 20 毫秒
71.
72.
Endogenous interfering substances can be detected by applying the techniques of parallel-line analysis of variance to the assay of superoxide dismutase (SOD) activities in crude tissue extracts. The technique also allows expression of specific activities in terms of units of activity as defined by commercially available standards as opposed to definition by the specific assay conditions utilized. This analysis may be broadly applied to many of the indirect SOD assays currently in use. In the current investigation, SOD was assayed by its ability to inhibit the rate of reduction of acetylated ferricytochrome c by superoxide anion () generated via the xanthine-xanthine oxidase reaction. The parallel-line analysis was effective in detecting the presence of interference by exogenous ascorbate in the reaction system, and by unidentified endogenous reactants within extracts of whole blood and ocular choroidal tissues of the rainbow trout, Salmo gairdneri. 相似文献
73.
Chemical quantitation of hemoglobin glycosylation: fluorometric detection of formaldehyde released upon periodate oxidation of glycoglobin 总被引:1,自引:0,他引:1
P M Gallop R Flückiger A Hanneken M M Mininsohn K H Gabbay 《Analytical biochemistry》1981,117(2):427-432
A sensitive fluorometric method for the quantitation of hemoglobin glycosylation, based upon periodate oxidation of the carbohydrate moieties present on both the α- and ?-amino groups of globin is described. The formaldehyde product is measured as the fluorescent 3,5-diacetyl-1,4-dihydrolutidine formed from the condensation of formaldehyde with acetylacetone and ammonia.This method is rigorously designed to assay glycosylated hemoglobin levels and to give a direct measure of the number of glycogroups per milligram of hemoglobin. It requires only 1 mg of protein and may also be used to determine the extent of the nonenzmatic glycosylation of other proteins. 相似文献
74.
F.A. Stephenson M.W. Stelling A.D. Rogol 《Archives of biochemistry and biophysics》1981,209(2):534-538
The effects of acetate and ammonium salts on glucose metabolism, aminoisobutyric acid influx, and radioiodinated insulin binding in isolated thymocytes were studied. Acetate in the concentration range, 0.1–30 mm, was found to inhibit basal and insulin-stimulated CO2 production whereas ammonium chloride at concentrations greater than 0.3 mm was slightly stimulatory. Ammonium salts inhibited glucose incorporation into glycogen and aminoisobutyric acid influx only at high concentration (30 mm). Neither acetate nor ammonium salts had significant effects on glucose incorporation into glycogen or aminoisobutyric acid influx at lower concentrations. No effect on insulin binding was observed. The observation that very low concentrations of acetate can perturb these biological assay systems suggests that other biological functions may be affected by trace amounts of buffer salts carried over from protein isolation steps. 相似文献
75.
76.
An approach to the identification of adenosine''s inhibitory site on adenylate cyclase 总被引:3,自引:0,他引:3
R A Johnson 《FEBS letters》1982,140(1):80-84
The separate and combined effects of molybdate and dithiothreitol on the stability of human uterine 9 S estrogen receptor were studied. Maximal, short-term, protection of the 9 S estrogen receptor was achieved by the joint inclusion of both stabilizing agents in cytosol buffers. This molybdate—dithiothreitol-mediated stability was dependent on reducing agent concentration inferring sulphydryl involvement in 9 S receptor protection by molybdate. The study also showed that molybdate—dithiothreitol could not prevent the gradual decay of the 9 S estrogen receptor to the 4 S form in cytosols stored at 4°C over prolonged periods. 相似文献
77.
Treatment with PGF2α resulted in the termination of pregnancy in 16- and 19-day pregnant rats, but not in 10- or 13-day pregnant rats. Rats that aborted displayed a rapid onset of maternal behavior when tested with foster pups. Aborted rats also displayed sexual receptivity and ovulation: these phenomena resemble the sequence of events following hysterectomy on the same days of pregnancy. Both can be related to the events surrounding normal parturition in the rat. The results are interpreted as due to a pregnancy-induced deactivation of the factor in the uterus that prevents estrogen from stimulating maternal behavior in nonpregnant females. In the absence of this factor, the PGF2α-induced rise in estrogen secretion facilitates maternal behavior and sexual behavior and induces ovulation. 相似文献
78.
79.
Pregnenolone (3β-hydroxy-5-pregnen-20-one) and DHA (3β-hydroxy-5-androsten-17-one), substrates for 3β-hy-droxysteroid dehydrogenase (3β-HSD), with KM values of 15–40 nM, were ineffective inhibitors of 5-ene-3-ketosteroid isomerase (isomerase), with KI values >40 μM in each case. Progesterone and androstenedione (4-androstene-3, 17-dione), 3β-HSD inhibitors with KI values of 5.0 μM and 0.8 μM respectively, were also relatively ineffective inhibitors of isomerase, with KI values of 30 μM and 16.5 μM respectively. Exposure of microsomes to hydrogen peroxide, which significantly increases the KM for pregnenolone as a 3β-HSD substrate, had no effect on the KM for the isomerase substrate 5-pregnene-3, 20-dione.It is concluded that the data do not support the common site concept with regard to the conversion of pregnenolone to progesterone by human placental microsomes. 相似文献
80.
We have investigated alterations in beta-adrenergic receptors in rat myocardial membranes derived from hypothyroid and hyperthyroid animals. (-)Isoproterenol competition curves with (-)[3H]dihydroalprenolol revealed that isoproterenol binds to the beta-adrenergic receptor with two distinct affinity states having high (KH) and low (KL) dissociation constants. In the presence of guanine nucleotides the isoproterenol competition curve steepened and had a higher EC50 (50% displacement). This was due to a transition of the high affinity state to a uniformly low affinity state. Using computer modeling of these competition curves, we have demonstrated that in hyperthyroidism, the isoproterenol curve in the absence of guanine nucleotides is shifted to the left with the EC50 changing from 180 ± 40 to 80 ± 20 nM (p < .02). The fold shift (4 fold) in KH (nM) 30 ± 9 to 7 ± 2 (p < .001) is greater than that (1.6 fold) in KL (nM) 595 ± 56 to 376 ± 34 (p < .001) such that the KL/KH ratio shifted from 20 ± 3 to 54 ± 9 (p < .001). The ratio, KL/KH, for a particular agonist appears to be related to its efficacy in activating adenylate cyclase.There was no significant alteration in any of these parameters in hypothyroid animals. Receptor number was decreased in hypothyroidism, 16 ± 3 fmol/mg protein (p < .03) and increased in hyperthyroidism 44 ± 4 (p < .03) compared to control 26 ± 2.In the rat heart agonist affinity and receptor number are modulated in hyperthyroidism, but only receptor number in hypothryoidism. Thus thyroid hormone can modify not only receptor number but agonist affinity as well. 相似文献