全文获取类型
收费全文 | 811篇 |
免费 | 72篇 |
出版年
2021年 | 14篇 |
2018年 | 12篇 |
2016年 | 8篇 |
2015年 | 16篇 |
2014年 | 21篇 |
2013年 | 24篇 |
2012年 | 23篇 |
2011年 | 24篇 |
2010年 | 23篇 |
2009年 | 21篇 |
2008年 | 30篇 |
2007年 | 29篇 |
2006年 | 22篇 |
2005年 | 35篇 |
2004年 | 29篇 |
2003年 | 26篇 |
2002年 | 23篇 |
2001年 | 22篇 |
2000年 | 22篇 |
1999年 | 25篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1993年 | 9篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 28篇 |
1989年 | 13篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 14篇 |
1972年 | 9篇 |
1971年 | 8篇 |
1970年 | 9篇 |
1969年 | 10篇 |
1968年 | 7篇 |
1966年 | 6篇 |
1958年 | 6篇 |
排序方式: 共有883条查询结果,搜索用时 328 毫秒
231.
Mechanisms of regulation of liver fatty acid-binding protein 总被引:2,自引:0,他引:2
Raja M. Kaikaus William K. Chan Paul R. Ortiz de Montellano Nathan M. Bass 《Molecular and cellular biochemistry》1993,123(1-2):93-100
Liver fatty acid-binding protein (L-FABP) expression is modulated by developmental, hormonal, dietary, and pharmacological factors. The most pronounced induction is seen after treatment with peroxisome proliferators, which induce L-FABP coordinately with microsomal cytochrome P-450 4A1 and the enzymes of peroxisomal fatty acid -oxidation. These effects of peroxisome proliferators may be mediated by a receptor which has been shown to be activated by peroxisome proliferators in mammalian cell transfection studies. However, the peroxisome proliferators tested thus far do not bind to this receptor, known as the peroxisome proliferator-activated receptor (PPAR), and its endogenous ligand(s) also remain unknown. Peroxisome proliferators inhibit mitochondrial -oxidation, and one hypothesis is that the dicarboxylic fatty acid metabolites of accumulated LCFA, formed via the P-450 4A1 -oxidation pathway, serve as primary inducers of L-FABP and peroxisomal -oxidation. We have tested this hypothesis in primary hepatocyte cultures exposed to clofibrate (CF). Inhibition of P-450 4A1 markedly diminished, via a pre-translational mechanism, the CF induction of L-FABP and peroxisomal -oxidation. In further experiments, long-chain dicarboxylic acids, the final products of the P-450 4A1 -oxidation pathway, but not LCFA, induced L-FABP and peroxisomal -oxidation pre-translationally. These results suggest a role, in part, for long-chain dicarboxylic acids in mediating the peroxisome proliferator induction of L-FABP and peroxisomal -oxidation. We also found that LCFA, which undergo rapid hepatocellular metabolism, could become inducers of L-FABP and peroxisomal -oxidation under conditions where their metabolism was inhibited. The role of the PPAR in mediating these effects is unknown, but clearly warrants further study. The induction of L-FABP and peroxisomal -oxidation by LCFA and/or their -oxidized metabolites may provide a means for limiting the deleterious effects of increased intracellular concentrations of free LCFA, and thus act as an important hepatocellular adaptation to impairment or overload of mitochondrial LCFA oxidation. 相似文献
232.
Michael S. Luck June L. Dahl Michael G. Boyeson Paul Bass 《Cell and tissue research》1993,271(2):363-374
The objective of this study was to examine the effects of two different denervation procedures on the distribution of nerve fibers and neurotransmitter levels in the rat jejunum. Extrinsic nerves were eliminated by crushing the mesenteric pedicle to a segment of jejunum. The myenteric plexus and extrinsic nerves were eliminated by serosal application of the cationic surfactant benzyldimethyltetradecylammonium chloride (BAC). The effects of these two denervation procedures were evaluated at 15 and 45 days. The level of norepinephrine in whole segments of jejunum was initially reduced by more than 76% after both denervation procedures, but by 45 days the level of norepinephrine was the same as in control tissue. Tyrosine hydroxylase (nor-adrenergic nerve marker) immunostaining was absent at 15 days, but returned by 45 days. However, the pattern of noradrenergic innervating axons was altered in the segment deprived of myenteric neurons. Immunohistochemical studies showed protein gene product 9.5 (PGP 9.5)-immunoreactive fibers in whole-mount preparations of the circular smooth muscle in the absence of the myenteric plexus and extrinsic nerves. At 45 days, the number of nerve fibers in the circular smooth muscle increased. Vasoactive intestinal polypeptide (VIP)-immunoreactive fibers, a subset of the PGP 9.5 nerve fibers, were present in the circular smooth muscle at both time points examined. Choline acetyltransferase (CAT) activity and VIP and leucine enkephalin levels were measured in separated smooth muscle and submucosa-musosal layers of the denervated jejunum. VIP and leucine-enkephalin levels were no different from control in tissue that was extrinsically denervated alone. However, the levels of these peptides were elevated two-fold in the smooth muscle 15 and 45 days after myenteric and extrinsic denervation. In the submucosa-mucosa, VIP and leucine enkephalin levels also were elevated two-fold at 15 days, but comparable to control at 45 days. CAT activity was equal to control in the smooth muscle but elevated two-fold in the submucosa-mucosa at both times. These results provide evidence for innervation of the circular smooth muscle by the submucosal plexus. Moreover, these nerve fibers originating from the submucosal plexus proliferate in the absence of the myenteric plexus. Furthermore, the myenteric neurons appear to be essential for normal innervation of the smooth muscle by the sympathetic nerve fibers. It is speculated that the sprouting of the submucosal plexus induced by myenteric plexus ablation is mediated by increased production of trophic factors in the hyperplastic smooth muscle. 相似文献
233.
Richard K. Brantley Andrew H. Bass 《Ethology : formerly Zeitschrift fur Tierpsychologie》1994,96(3):213-232
The plainfin midshipman Porichthys notatus has two male reproductive morphs, ‘Type I’ and ‘Type II’, which are distinguishable by their physical traits alone. Type I males are eight times larger in body mass than Type II males and have a six-fold larger relative sonic (vocal) muscle mass than Type II males. In contrast, the testicles of Type II males are seven times larger than those of Type I males. This study demonstrates morph-specific patterns of reproduction, including acoustic signals, for Type I and II males. Field censuses of nests showed that only Type 1 males maintained nests. Type II males and females transiently appeared in these nests in association with each other. Infra-red video and hydrophone recordings in aquaria showed that Type I males maintained nests and readily vocalized. Long-duration ‘hums’ and sequences of short-duration ‘grunts’ were produced during advertisement and agonistic contexts, respectively. Humming Type I males attracted females to their nests, pair-spawned, and then guarded egg clutches alone. By contrast, Type II males neither acoustically courted females nor maintained available nest sites, but rather ‘sneak-’ or ‘satellite-spawned’ at the nests of Type I males. Type II males infrequently produced low amplitude, short duration grunts that were similar in spectral, temporal and amplitude characteristics to the grunts of females. Type II males appear to be obligate sexual parasites of the nest-building, mate-calling, and egg-guarding Type I males. The dimorphic body and vocal muscle traits of the two male morphs in the plainfin midshipman are thus paralleled by a divergence in their reproductive tactics and the properties of their acoustic signals. 相似文献
234.
In bulls there was no increase in plasma FSH and only a small increase in LH over the first 14 weeks of age. In steers (castrated) plasma LH and FSH were unchanged for the first 3 weeks but increased significantly at 7 and 14 weeks. After 100 micrograms Gn-RH, LH release in bulls was minimal until 7 and 14 weeks and there was no comparable rise for FSH. LH and FSH responded to Gn-RH throughout the trial in the steers. The neonatal calf testes selectively inhibited the release of FSH from the pituitary even when challenged with Gn-RH. 相似文献
235.
A human T-cell line (Molt-4) was shown by viral hemagglutination and infectivity assays to support the replication of rat virus (RV) and H-1 virus. In addition, H-1 virus, but not RV, multiplied in two human B-cell lines, AV-1 and NC-37. The ability to bind radioactively labeled RV was demonstrated for each of the cell lines, but viral adsorption occurred to a greater degree with Molt-4 cells than with either AV-1 or NC-37 cells. After challenge with RV, virus-specific antigens were detected in cells of the B-cell lines by the indirect immunofluorescence technique. Infection of AV-1 or NC-37 cells by RV apparently results in an abortive cycle of virus replication. Differences among the three cell lines that might influence with H-1 virus or RV are discussed. 相似文献
236.
Male Sprague-Dawley rats (8 per group) received 1.25 g/kg ethanol (EtOH) in saline or saline alone i.p. and either saline, 0.1, or 2.0 mg/kg naloxone HC1 (NAL) s.c. five min later. Beginning 15 min after the second injection, rats received five noncontingent 0.5 sec footshocks at each of three intensities (0.6, 0.8, 1.3 mA) in a random order on a variable time 1 min schedule. The amplitude of the startle response, number of audible vocalizations, and extent of overt movements were recorded. EtoH significantly reduced startle response amplitude and overt movements at 0.8 and 1.3 mA; NAL failed to antagonize these indices of EtOH analgesia. NAL was itself without effect upon overt movements but significantly increased startle response amplitude and vocalizations at 1.3 mA. EtOH prevented these NAL-induced increases but this does not appear attributable to ethanol's analgesic or motoric effects. Possible mechanisms of ethanol's effects upon endorphin systems are considered. 相似文献
237.
D H Steven F Bass C J Jansen E J Krane K Mallon C A Samuel A L Thomas P W Nathanielsz 《Quarterly journal of experimental physiology and cognate medical sciences》1978,63(3):221-229
Binucleate cells are a normal component of the ovine chorionic epithelium, but are usually separated from the fetal-maternal interface by a thin layer of cytoplasm derived from the principal or uni-nucleate cells of the trophoblast. They are distinguished not only by two distinct and separate nuclei, but also by conspicuous membrane-bound cytoplasmic inclusions in the form of haloed droplets. After fetal pituitary stalk section binucleate cells move up to and participate in the formation of the fetal-maternal interface; furthermore they extend clear blunt-ended pseudopodia into the maternal epithelial syncytium. These activities do not appear to be supppressed by fetal infusion of cortisol or ACTH. The apparent motility of binucleate cells, together with the presence of haloed droplets within the maternal epithelial syncytium, suggests that after fetal pituitary stalk section binucleate cells invade the uterine syncytium, lose their limiting membranes and discharge their contents into the syncytial cytoplasm. Large molecules such as ovine placental lactogen may be transported from fetal to maternal tissues by this mechanism. 相似文献
238.
Summary Gene marker analyses have been carried out in a patient with 10q(q23qter) duplication. The observed elevation of red cell glutamic oxaloacetic transaminase activity is compatible with earlier somatic cell hybridization studies that mapped the locus to this region. Hexokinase-1 activity in the red cells was normal, which is consistent with its prior assignment to the unaffected part of chromosome 10 (10pterq23). 相似文献
239.
Plasma testosterone, androstenedione and LH concentrations were measured at regular intervals from birth to 500 days of age in bulls; bulls treated with estradiol for 3 weeks after birth; steers and heifers. Behavioural observations were conducted at various periods over 12 months. Apart from a possible quietening effect at 4 months of age, neonatal estrogen administration had no effect on the aggressive behaviour of young bulls. There were no differences among the groups in testosterone levels for the first 60 days but by day 100 the levels in the normal and estrogenized bulls had risen significantly. No differences in androstenedione concentration occurred among the groups. Plasma LH decreased for the first 7 days in the bulls, steers and heifers then rose gradually, however a marked rise occurred in the steers from day 28. The neonatal decline in plasma LH was extended during the period of estrogen administration. 相似文献
240.
J.T. OFlaherty S. Cousart C.L. Swendsen L.R. DeChatelet D.A. Bass S.H. Love C.E. McCall 《生物化学与生物物理学报:生物膜》1981,640(1):223-230
The influence of extracellular Ca2+ and Mg2+ on the transport of 2-deoxy-[3H]glucose into human polymorphonuclear neutrophils was studied. Omission of these cations from the cell suspensions had little effect on resting hexose uptake. Furthermore, the addition of the bivalent cation chelator, EDTA, depressed uptake only slightly. Similarly, neither cation was essential for the enhanced 2-deoxy-D-[3H]glucose uptake stimulated by two chemotactic factors (C5a and ) and arachidonic acid: enhanced uptake was only partially depressed by the omission of Ca2+ and Mg2+ from the suspensions and was still prominent in the presence of EDTA. Two other neutrophil stimulants, the ionophores, A23187 and ionomycin, also enhanced hexose uptake but their actions were heavily dependent upon extracellular bivalent cations and were totally abrogated by EDTA. In all instances, extracellular Ca2+, but not Mg2+, supported optimal enhanced hexose transport induced by stimuli.Activation of 2-deoxy-D-[3H]glucose uptake by each of the five stimuli was totally blocked by cytochalasin B (a blocker of carrier-mediated hexose transport) and D-glucose but not by L-glucose. The data indicate, therefore, that a variety of neutrophil stimulants activate carrier-mediated hexose transport. Although this transport can be triggered by the movement of extracellular Ca2+ into the cell (as exemplified by the action of the two ionophores), such Ca2+ movement is not required for the actions of chemotactic factors or arachidonic acid. Other mechanisms, such as a rearrangement of intracellular Ca2+, may be involved in mediating the activation of hexose transport induced by the latter stimuli. 相似文献