全文获取类型
收费全文 | 1348篇 |
免费 | 31篇 |
国内免费 | 38篇 |
出版年
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 18篇 |
2020年 | 32篇 |
2019年 | 39篇 |
2018年 | 47篇 |
2017年 | 22篇 |
2016年 | 28篇 |
2015年 | 28篇 |
2014年 | 54篇 |
2013年 | 92篇 |
2012年 | 28篇 |
2011年 | 86篇 |
2010年 | 39篇 |
2009年 | 56篇 |
2008年 | 74篇 |
2007年 | 64篇 |
2006年 | 63篇 |
2005年 | 47篇 |
2004年 | 50篇 |
2003年 | 36篇 |
2002年 | 28篇 |
2001年 | 24篇 |
2000年 | 17篇 |
1999年 | 31篇 |
1998年 | 17篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 22篇 |
1994年 | 13篇 |
1993年 | 28篇 |
1992年 | 16篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 22篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 20篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有1417条查询结果,搜索用时 171 毫秒
991.
Simple mixing of acid purified histones H3 and H4 in equimolar quantities at low ionic strength near pH 7 does not yield the tetramer but rather a high Mr aggregate. Dialysis of acid extracted total or core histones into 2 M NaCl 150 mM phosphate (pH 7.4) followed by fractionation of the histone complexes at lower ionic strength (150 mM NaCl) results in an H3H4 tetramer of a structure identical to that derived from salt-extracted histones. Dialysis of acid extracted total or core histones directly into the lower ionic strength buffer with subsequent fractionation, results in H3H4 tetramer of closely similar structure. 相似文献
992.
Abstract: Carbachol or elevated K+ stimulated 45Ca2+ uptake into chromaffin cells two- to fourfold. The uptake was stimulated by cholinergic drugs with nicotinic activity, but not by those with only muscarinic activity. Ca2+ uptake and catecholamine secretion induced by the mixed nicotinic-muscarinic agonist carbachol were inhibited by the nicotinic antagonist mecamylamine, but not by the muscarinic antagonist atropine. Significant Ca2+ uptake occurred within 15 s of stimulation by carbachol or elevated K+ at a time before catecholamine secretion was readily detected. At later times the time course of secretion induced by carbachol or elevated K+ was similar to that of Ca2+ uptake. There was a close correlation between Ca2+ uptake and catecholamine secretion at various concentrations of Ca2+. The concentration dependencies for inhibition of both processes by Mg2+ or Cd2+ were similar. Ca2+ uptake saturated with increasing Ca2+ concentrations, with an apparent Km for both carbachol-induced and elevated K+-induced Ca2+ uptake of approximately 2 mM. The Ca2+ dependency, however, was different for the two stimuli. The studies provide strong support for the notion that Ca2+ entry and a presumed increase in cytosolic Ca2+ concentration respectively initiates and maintains secretion. They also provide evidence for the existence of saturable, intracellular, Ca2+- dependent processes associated with catecholamine secretion. Ca2+ entry may, in addition, enhance nicotinic receptor desensitization and may cause inactivation of voltage-sensitive Ca2+ channels. 相似文献
993.
Summary The influence of gonadotropic hormones on the ultrastructure of rat pinealocytes in short-term organ culture was studied. Human chorionic gonadotropin (HCG), as well as pregnant mare serum gonadotropin (PMSG), caused a marked activation of pinealocytes. An hypothesis is discussed implying the presence of a feedback mechanism between the pineal organ and the hypothalamo-hypophysial system. 相似文献
994.
Abstract: In developing chicken brain Ca2+ /calmodulin-stimulated protein kinase II (CaMPK-II) changes from being primarily cytosolic to being primarily particulate during the protracted maturation period. To investigate whether thyroid hormone levels may be involved in regulating this subcellular redistribution, we raised chickens from 1 day posthatching on food soaked in 0.15% (wt/vol) propylthiouracil (PTU) plus 0.05% (wt/vol) methimazole (MMI). This produced a mild hypothyroidism specifically during the maturation period and resulted in a 67% reduction in the levels of free triiodothyronine (T3 ) at 42 days. The concentrations of α- and β-CaMPK-II in cytosol (S3) and crude synaptic membrane (P2M) fractions from forebrain were measured by three methods: Ca2+ /calmodulin- or Zn2+ -stimulated autophosphorylation or binding of biotinylated calmodulin. By all three methods hypothyroid animals showed a marked retardation of the redistribution of both subunits of CaMPK-II: an increase in the concentration of the enzyme in S3 and a corresponding decrease in P2M with no overall change in the total amount of enzyme and little apparent change in the concentration of other proteins. In both fractions, there was a parallel change in the Ca2+ /calmodulin-stimulated phosphorylation of endogenous protein substrates but no change in the basal or cyclic AMP-stimulated protein phosphorylation. Supplementing the PTU/MMI-treated diet with thyroxine (0.5 ppm) prevented all of the observed changes. 相似文献
995.
脱血红素细胞色素c的构象与其跨膜转运能力是密切相关的。鸡心脱血红素细胞色素c具有较强的自发折叠的能力,在一定条件下可以得到不同解折叠状态的鸡心脱血红素细胞色素c。本文利用疏水层析、与疏水探针1,8—ANS的结合以及色氨酸与结合的ANS之间的荧光共振能量转移,比较了不同解折叠状态的鸡心脱血红素细胞色素c分子的表面性质。结果表明,部分折叠的鸡心脱血红素细胞色素c分子获得了一种高度动态的结构,形成了动态的疏水核心;同时,它也具有较强的凝集倾向。这些性质与鸡心脱血红素细胞色素c分子较强的自发折叠能力是一致的,为进一步分析鸡心脱血红素细胞色素c分子的构象及其在跨膜转运过程中与脂的相互作用奠定了基础。 相似文献
996.
鸡粪中氨基酸利用前景 总被引:2,自引:0,他引:2
通过对鸡饲料鸡粪中蛋白质和氨基酸含量的分析表明:鸡对饲料蛋白质、氨基酸的利用率较低,鸡粪经膨化处理后,仍可用于鸡、猪饲料。鸡粪有着进一步开发利用的好前景。 相似文献
997.
The objective of this experiment was to investigate the effect of rearing density on pecking behaviour and plumage during rearing and throughout the laying period in aviaries. Chicks were reared on sand at high (H; 13 m−2) or low (L; 6.5 m−2) density, in four rearing pens of 390 chicks and eight pens of 195 chicks, respectively, each pen measuring 30 m2. Proportions of chicks per pen performing various types of pecking behaviour were recorded by scan sampling during 16 observation bouts in each rearing pen at 6 weeks of age and during 24 observation bouts at 12 weeks. Individual body weights and plumage condition were recorded. Later, these pullets were housed at 17 hens m−2 in Tiered Wire Floor (TWF; 3 H and 3 L pens of 275 hens) and Laco-Volétage (2 H and 2 L pens of 275 hens) aviaries. At 35 weeks, two samples of eight hens from each aviary pen were observed for pecking behaviour in a test pen. Throughout the laying period, additional records were collected on pecking behaviour, body weight, plumage condition, egg production, and mortality. The L birds had better plumage condition at 6 weeks of age and throughout the laying period. These birds also ground pecked more frequently than H birds during rearing and the laying period. At 12 weeks, L birds feather pecked less than H birds, but no relationship was found between rearing density and feather-pecking behaviour during the laying period. Although TWF hens feather pecked more frequently than Volétage hens, there was no interaction between rearing density and type of aviary for the various pecking behaviours. 相似文献
998.
Backbone 1H, 13C, and 15N chemical shifts are reported for complexes of a perdeuterated glutamate receptor ligand binding domain with kainate, willardiine,
and 5-substituted fluoro-, bromo-, and iodowillardiine. These ligands are partial agonists that induce distinct current responses
at post-synaptic neurons. The chemical shifts pave the way for numerous NMR studies to identify structural and dynamical determinants
of receptor function. 相似文献
999.
The chicken eggshell matrix is a complex mixture of proteins and proteoglycans. It also contains phosphoproteins that are thought to affect mineralization of the matrix. Several of the matrix phosphoproteins, such as the major component osteopontin, have already been identified as phosphoproteins in other tissues, but the phosphorylation status of the eggshell matrix forms was unknown. The phosphopeptides, obtained after cleavage of the matrix proteins with several different cleavage methods, were enriched by anion-exchange chromatography and reversible binding to titanium oxide and identified by LC-MS(n) or pseudo-MS(n) analysis following neutral loss scanning. Altogether we identified 39 phosphorylated matrix proteins, 22 of which were not known to be phosphorylated before. Eight of the proteins were identified as eggshell matrix components for the first time. Together these proteins contained more than 150 different phosphorylation sites, 103 of which were determined with high confidence. Among the major phosphorylated proteins of the chicken eggshell matrix were osteopontin and the eggshell-specific proteins ovocleidin-17, ovocleidin-116, and ovocalyxin-32. 相似文献