全文获取类型
收费全文 | 9393篇 |
免费 | 734篇 |
国内免费 | 434篇 |
出版年
2024年 | 22篇 |
2023年 | 81篇 |
2022年 | 238篇 |
2021年 | 391篇 |
2020年 | 273篇 |
2019年 | 283篇 |
2018年 | 320篇 |
2017年 | 257篇 |
2016年 | 375篇 |
2015年 | 560篇 |
2014年 | 618篇 |
2013年 | 710篇 |
2012年 | 812篇 |
2011年 | 743篇 |
2010年 | 476篇 |
2009年 | 343篇 |
2008年 | 483篇 |
2007年 | 401篇 |
2006年 | 382篇 |
2005年 | 321篇 |
2004年 | 272篇 |
2003年 | 233篇 |
2002年 | 226篇 |
2001年 | 171篇 |
2000年 | 188篇 |
1999年 | 137篇 |
1998年 | 84篇 |
1997年 | 81篇 |
1996年 | 77篇 |
1995年 | 59篇 |
1994年 | 64篇 |
1993年 | 48篇 |
1992年 | 92篇 |
1991年 | 76篇 |
1990年 | 77篇 |
1989年 | 61篇 |
1988年 | 48篇 |
1987年 | 68篇 |
1986年 | 46篇 |
1985年 | 37篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1975年 | 18篇 |
1973年 | 21篇 |
1972年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Tan Agnes; van den Broek Leon; Bolscher Jan; Vermass Dirk Jan; Pastoors Liesbeth; van Boeckel Constant; Ploegh Hidde 《Glycobiology》1994,4(2):141-149
N-Alkylation of the -glucosidase inhibitor 1-deoxynojirimycin(dNM) dramatically increases its inhibitory potency (Tan etal., J. Biol. Chem., 266, 1450414510, 1991). However,the possibility of extending the alkyl chain to N-decyl-dNMis limited by an increase of detergent-like (amphiphilic) propertiesof long-chain alkylated dNM derivatives. Substitution of methylenegroups in the N-decyl chain by oxygen reduced the amphiphilicityof N-decyl-dNM derivatives, while retaining their superior inhibitoryproperties. In intact HepG2 cells, the compound N-7-oxadecyl-dNMwas found to result in the most pronounced retention of glucoseresidues on N-linked glycans. Permeabilization of the plasmamembrane with the bacterial toxin Streptolysin O improves theinhibitory properties of the derivatives N-3,6,9-trioxadecyl-,N-7,10,13-trioxatetradecyl-, N-3-oxadecyl- and N-7-oxadecyl-dNM,but not those of dNM. These observations suggest differencesin the mode of entry of the oxygen-substituted dNM derivativesin comparison with dNM. We observed that the dNM derivativeN-3,6,9-trioxadecyl-dNM, devoid of inhibitory activity in intactcells, was inhibitory in Streptolysh O-permeabilized cells.Thus, the permeability barriers posed by plasma membrane andendoplasmic reticulum membrane are not equivalent. The use ofa permeabilized cell system thus allows the elaboration of inhibitoryprinciples for novel bioactive compounds where study of theisolated enzymes may not be possible, and where intact cellsare not a suitable target due to permeability barriers. -glucosidase inhibition N-linked glycosylation oxygen-substituted N-decyl-dNM derivatives permeabilized cells 相似文献
82.
83.
OBJECTIVE: To determine the rates and outcomes of diabetic end-stage renal disease (ESRD) among registered native people and non-native people in Saskatchewan. DESIGN: Retrospective population-based study using data from the Canadian Organ Replacement Registry. SETTING: Saskatchewan. PATIENTS: All patients with diabetic ESRD diagnosed between Jan. 1, 1981, and Dec. 31, 1990. MAIN OUTCOME MEASURES: Incidence rates of diabetic ESRD in the general population, rates of diabetic ESRD among patients with diabetes mellitus, nature of initial dialysis treatment, length of survival from start of dialysis, cause of death and renal transplant rates. RESULTS: The 10-year incidence rates of diabetic ESRD were higher among all age groups among registered native people than among non-native people. The overall relative risk ratio for native people was 16.2. When a higher prevalence of diabetes among native people was taken into account, native diabetic people were still seven times as likely as non-native diabetic people to manifest diabetic ESRD. The median survival from start of dialysis was under 2 years in both groups, but more native people died of stroke and more non-native people died of heart disease. Non-native diabetic people were more likely than native diabetic people to receive renal transplants. CONCLUSIONS: Although the overall incidence of diabetic ESRD in Saskatchewan is increasing, registered native people have a disproportionate risk for this serious complication. 相似文献
84.
Chong CF Ngoh BL Tan HC Yap EH Singh M Chan L Chan YC 《Clinical and diagnostic virology》1994,1(5-6):335-341
A shortened IgM capture ELISA for the detection of dengue IgM antibodies using simultaneous incubation of antigen and peroxidase-labeled monoclonal antibody was described. The shortened two-step assay was compared with the four-step IgM capture ELISA on sera from dengue patients confirmed by the hemagglutination inhibition (HI) test. When paired acute and convalescent sera were tested, the shortened ELISA showed 100% agreement with HI results. It detected dengue IgM antibodies in the acute sera of 66% of patients with a primary dengue infection, 60% of patients with a secondary infection, and 98% of patients with a presumptive secondary infection. When the results of 151 dengue patients were combined, 75% of the acute sera were positive by the shortened IgM capture ELISA. 相似文献
85.
采用RNA斑点杂交分析,对21例人脑原发性胶质瘤和11例人脑膜瘤中p53,Rb和c-myc基因转录水平的表达进行研究.发现48.4%的肿瘤中p53基因表达减弱,21.9%的肿瘤中Rb基因表达减弱;71.9%的肿瘤中c-myc基因表达增强.在p53基因表达减弱的15例病例中有13例(80%)c-myc基因表达增强.结果表明,p53基因表达减弱和c-myc基因表达增强与人脑原发性肿瘤的发生有关. 相似文献
86.
Stomatal numbers of soybean and response to water stress 总被引:2,自引:0,他引:2
B. R. Buttery C. S. Tan R. I. Buzzell J. D. Gaynor D. C. MacTavish 《Plant and Soil》1993,149(2):283-288
The relationship among stomatal density, photosynthetic rate, leaf conductance, plant growth, bean yield and kaempferol triglucoside (K9) in the leaves of soybean (Glycine max (L.) Merr.) was examined in two field tests. K9 in the leaves was associated with reduced stomatal density, reduced photosynthetic rate, reduced stomatal conductance, reduced plant weight and lower bean yield. Plants with high stomatal frequency (lacking K9) were better able to take advantage of increased water supply by increasing stomatal conductance (upper surface), transpiration and bean yield. Plants with low stomatal frequency (with K9) were unresponsive to irrigation and in this sense were more tolerant of water stress, but their overall yield was low. 相似文献
87.
Growth inhibition of plants suffering from Al toxicity is generally accompanied by impaired root development which can be quantitatively described by reduced specific root length (m g-1 dry root). In addition, the uptake of nutrients such as Mg and Ca is inhibited. Increased supply of either Mg or Ca can significantly diminish the negative effect of Al on root development and improve the Mg or Ca nutrition of the plants. The positive effect of Ca is well established but the effect of Mg has been observed in only a few plan species. Therefore, the effects of increasing Mg and Ca supply on Al toxicity in plants of seven monocots and eight dicots have been now examined in nutrient solution experiments. In general, Mg appears to be more effective than Ca in alleviating Al toxicity with the monocots, whereas the reverse is true for the dicots. Increased concentrations of Mg and Ca in solution seem to protect the plants against Al toxicity by improving the Mg or Ca nutrition and by alleviating the toxic effect of Al on root development. 相似文献
88.
Heavy metals in some Chinese herbal plants 总被引:1,自引:0,他引:1
The concentrations of nine heavy metals, cadmium, cobalt, copper, iron, manganese, nickel, lead, zinc and mercury in 42 Chinese
herbal medicinal plants were determined. Generally, all the samples studied had, relative to the other trace metals, higher
concentrations of iron, manganese, and zinc. The concentration range of the metals determined was comparable to that in many
of the East Asian vegetables and fruits. A few samples were found to contain relatively higher concentrations of the toxic
metals such as cadmium, lead, and mercury. This was probably caused by contamination during air-drying and preservation. 相似文献
89.
载脂蛋白多基因家族分子进化的研究 总被引:2,自引:2,他引:0
与脂质运输有关的载脂蛋白基因构成一个复杂的多基因家族。为探讨这种演化时间长的基因家族的进化规律,本文首先建立了一种在非均衡进化速率条件下计算系统发生树中任意分支长度的简易方法,并可在此基础上算出无根分支系统树中分歧年代的期望值。进一步对本文科10个种属共26种载脂蛋白的系统演作作了实际分析,结果提示:①ApoA-I'ApoA-IV,ApoE及ApoA-II的共同祖先可能在奥陶纪水生脊椎动物中就已存 相似文献
90.
T. R. Soderling S. E. Tan E. McGlade-McCulloh H. Yamamoto K. Fukunaga 《Developmental neurobiology》1994,25(3):304-311
One of the most active areas of neurobiology research concerns mechanisms involved in paradigms of synaptic plasticity. A popular model for cellular leaning and memory is long term potentiation (LTP) in hippocamus. LTP requires postsynaptic influx of Ca2+ which triggers multiple biochemical pathways resulting in pre- and postsynaptic mechanisms enhancing long term synaptic efficiency. This article focuses on an acute postsynaptic Mechanism that can enhance responsiveness of glutamate receptors. Evidence is presented that calcium/calmodulin/dependent protein kinase II, the major potsynaptic density protein at excitatory glutaminergic synapses, can phosphorylate glutamate receptors and enhance ion current flowing through them. 1994 John Wiley & Sons, Inc. 相似文献