全文获取类型
收费全文 | 394篇 |
免费 | 31篇 |
专业分类
425篇 |
出版年
2021年 | 8篇 |
2020年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 19篇 |
2012年 | 27篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 6篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 17篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1997年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 11篇 |
1971年 | 3篇 |
1970年 | 6篇 |
1967年 | 4篇 |
1964年 | 2篇 |
排序方式: 共有425条查询结果,搜索用时 0 毫秒
1.
2.
The method used here to assess the contribution of liver to plasma acylcarnitine is based on the idea that in rat, shortly after administration of [3H]butyrobetaine the [3H]carnitine appearing in the plasma derives from the liver and so does the acyl moiety of [acyl-3H] carnitine. In the perchloric acid extracts of plasma and liver, the ester fraction of total carnitine was determined by enzymatic analysis and that of [3H]carnitines was determined by high performance liquid chromatography. The ester fraction of total carnitine in the plasma of fed rats was 32.6% while that of [3H]carnitines was 67.9%, 1 h following injection of [3H]butyrobetaine. For 48 h starved rats the equivalent values were 54.2 and 84.0%, respectively. 24 h after the administration of [3H]butyrobetaine, the ester content became the same in the total and [3H]carnitines. That the newly synthesized carnitine was more acylated (67.9 versus 32.6%, fed) indicates that liver exports acyl groups with carnitine as carrier. The observation that the ester fraction in the newly synthesized plasma carnitine increased with fasting (84.0 versus 67.9%) indicates that the surplus plasma acylcarnitine in fasting ketosis derives from the liver. Perfused livers, however, released carnitine with the same ester content (60-61%) whether they were from fed or fasted animals. Probably, the increased plasma [acylcarnitine] in fasting develops not by an increased ester output from the liver but by an altered handling in extrahepatic tissues. 相似文献
3.
4.
5.
E Ronai L Tretter G Szabados I Horvath 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1987,51(4):611-617
The degree of mitochondrial ADP/Fe/NADPH-induced lipid peroxidation was increased up to the fourth day after 9.0 Gy whole body gamma-irradiation. The lipid peroxidation inhibiting effect of succinate added to isolated mitochondria was diminished as a consequence of irradiation. The succinate, administered in vivo prior to irradiation, decreased the amount of malondialdehyde production and protected the succinate dehydrogenase enzyme against inactivation. The mean survival of succinate-pretreated animals was much longer than that of controls. The role of mitochondrial lipid peroxidation in the pathogenesis of radiation injury is discussed. 相似文献
6.
Two-site exchange revisited: a new method for extracting exchange parameters in biological systems. 下载免费PDF全文
R V Mulkern A R Bleier I K Adzamli R G Spencer T Sandor F A Jolesz 《Biophysical journal》1989,55(2):221-232
A new analysis is presented which links real volume fractions, relaxation rates, and intracompartmental exchange rates directly with apparent volume fractions and relaxation rates obtained from biexponential fits of transverse magnetization decay curves. The analysis differs from previous methods in that measurements from two paramagnetic doping levels are used to close the two-site exchange equations. Both the new method and one previously described by Herbst and Goldstein (HG) have been applied to paramagnetically doped whole-blood data sets. Significant differences in the calculated exchange parameters are found between the two methods. A small dependence of the intracellular relaxation rate on extracellular paramagnetic agent concentration, assumed nonexistent with the HG method, is inferred from the new analysis. The analysis was also applied to published data on perfused rat hearts, and we obtained a limited assessment of two-site exchange in this system. 相似文献
7.
Urinary excretion of total carnitine in 48-h fasted rats dropped to 0.30 +/- 0.01 mumol/day from 2.23 +/- 0.4 mumol/day found in fed, control animals (mean +/- SEM). Despite this marked retention, the total carnitine content of the whole body remained constant, about 83 mumol, predicting a slow-down in biosynthesis. The conversion of butyrobetaine into carnitine takes place only in the liver in rats. 48 h of starvation caused a decrease in the liver butyrobetaine level from 11.6 +/- 1.19 nmol/g to 9.30 +/- 1.19 nmol/g, which in whole livers corresponds to a decrease from 138 nmol to 61.3 nmol. The conversion rate of butyrobetaine into carnitine was studied with radiolabelled butyrobetaine. 30 min after injection of [3H]butyrobetaine the carnitine pool in the liver of fasted rats was labelled to about the same extent as that in fed rats, but from a butyrobetaine pool with higher specific radioactivity. Therefore, the conversion rate of butyrobetaine into carnitine was reduced. The newly formed carnitine found in the whole body of fasted rats was estimated to be 59% of controls. We conclude that the biosynthesis of carnitine in fasted rats slows down, for which a decreased availability of butyrobetaine in the liver is responsible. Urinary excretion of butyrobetaine in the fasted group decreased to 74.1 nmol/day from the 222-nmol/day control value while the butyrobetaine content of whole body did not significantly decrease (2.85 mumol vs. 3.04 mumol). Urinary excretion of trimethyllysine was also depressed. 相似文献
8.
R I Christopherson K J Schmalzl E Szabados R J Goodridge M C Harsanyi M E Sant E M Algar J E Anderson A Armstrong S C Sharma 《Biochemistry》1989,28(2):463-470
In mammals, dihydroorotase is part of a trifunctional protein, dihydroorotate synthetase, which catalyzes the first three reactions of de novo pyrimidine biosynthesis. Dihydroorotase catalyzes the formation of a peptide-like bond between the terminal ureido nitrogen and the beta-carboxyl group of N-carbamyl-L-aspartate to yield heterocyclic L-dihydroorotate. A variety of evidence suggests that dihydroorotase may have a catalytic mechanism similar to that of a zinc protease [Christopherson, R. I., & Jones, M. E. (1980) J. Biol. Chem. 255, 3358-3370]. Tight-binding inhibitors of the zinc proteases, carboxypeptidase A, thermolysin, and angiotensin-converting enzyme have been synthesized that combine structural features of the substrates with a thiol or carboxyl group in an appropriate position to coordinate a zinc atom bound at the catalytic site. We have synthesized (4R)-2-oxo-6-thioxohexahydropyrimidine-4-carboxylate (L-6-thiodihydroorotate) and have found that this analogue is a potent competitive inhibitor of dihydroorotase with a dissociation constant (Ki) in the presence of excess Zn2+ ion of 0.17 +/- 0.02 microM at pH 7.4. The potency of inhibition by L-6-thiodihydroorotate in the presence of divalent metal ions decreases in the order Zn2+ greater than Ca2+ greater than Co2+ greater than Mn2+ greater than Ni2+; L-6-thiodihydroorotate alone is less inhibitory and has a Ki of 0.85 +/- 0.14 microM. 6-Thioorotate has a Ki of 82 +/- 8 microM which decreases to 3.8 +/- 1.4 microM in the presence of Zn2+. Zn2+ alone is a moderate inhibitor of dihydroorotase and does not enhance the potency of other inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
9.
10.
In completion of the previously outlined "experimental alcohol blastopathy", the role of acetaldehyde in the induction of preimplantation pathological changes in rat embryos has been controlled. Two experimental models were used: the direct administration of acetaldehyde by gavage and the blockage of acetaldehyde metabolization by ANTALCOL (an aldehyde-dehydrogenase blocking compound). The main results were as follows: The exogenous acetaldehyde in the blood of pregnant animals has an obvious effect upon the developmental rate during the late preimplantation period (retarding segmentation, blastulation), and in one of the experimental models upon the oviductal-uterine migration rate. The increase of the blood acetaldehyde level by blockage of its further metabolization has a more marked effect as compared with the direct intravenous administration of the substance. According to our previous observations the intravenous application of ethanol on the same day (day 4) has no such effect. The direct noxious influence upon the developing preimplantation embryos (fragmentation) of the increased level of acetaldehyde obtained by ANTALCOL treatment is similar but more marked than this effect obtained previously by ethanol administration. The same effect observed after the direct administration of the substance is less marked than the effect of ANTALCOL treatment but more marked than the effect of intravenous ethanol administration. These results attest that acetaldehyde may contribute (alone or together with the effect of ethanol) to the induction of "experimental alcohol blastopathy". The less marked action of the substance proper introduced into the blood stream may be due--in our opinion--to its possible alteration during the period between distillation and application. 相似文献