首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   246篇
  免费   6篇
  国内免费   5篇
  2023年   1篇
  2022年   3篇
  2021年   3篇
  2020年   1篇
  2019年   7篇
  2018年   3篇
  2017年   1篇
  2016年   5篇
  2015年   1篇
  2014年   10篇
  2013年   7篇
  2012年   6篇
  2011年   17篇
  2010年   14篇
  2009年   19篇
  2008年   15篇
  2007年   27篇
  2006年   11篇
  2005年   13篇
  2004年   9篇
  2003年   7篇
  2002年   7篇
  2001年   2篇
  2000年   1篇
  1999年   6篇
  1998年   3篇
  1997年   4篇
  1996年   8篇
  1995年   5篇
  1994年   2篇
  1993年   7篇
  1992年   1篇
  1987年   2篇
  1986年   5篇
  1984年   1篇
  1983年   2篇
  1982年   5篇
  1980年   1篇
  1979年   6篇
  1978年   4篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1973年   2篇
排序方式: 共有257条查询结果,搜索用时 203 毫秒
1.
本文系统化的综述了当前一个热门的研发领域-疫苗工业,并详细分析了其背景和潜在的市场,以及中国疫苗工业在发展中可能遇到的机遇和挑战。此外,还对中国疫苗工业存在的某些问题提出了解决方法。只有加强中国生物技术公司在高端疫苗领域的技术水平才能在根本上与国外制药业巨头竞争一席之地,向广大民众提供更好的药物。  相似文献   
2.
The synthesis of the open-chain and cyclic polyamines, 1,5,8,12,15,19-hexaazaheptadecane (L1) and 2,6,9,13,16,20-hexaaza[21]-(2,6)-pyridinophane (L2), are described. The protonation constants and interaction constants with Cu(II) have been determined by potentiometric measurements carried out at 298.1 K in 0.15 mol dm−3 NaClO4. The values obtained are discussed as a function of the open-chain or cyclic nature of the ligands and compared with analogous polyamines containing different sets of hydrocarbon chains between the nitrogen donors. Kinetic studies on the acid-promoted dissociation of the Cu(II) complexes indicate that the mono and binuclear complexes of L1 decompose with different kinetics, a behavior unprecedented for open-chain polyamines. In contrast, the dissociation of the first metal ion is accelerated in the binuclear complexes of L2 and so, all the mono and binuclear complexes of L2 decompose with the same kinetics. The voltammetric response of Cu(II)-L1 and Cu(II)-L2 complexes has been studied in order to correlate electrochemical and structural data.  相似文献   
3.
In order to explain the mechanism of the dimerization of 2,6-di-tert-butyl-phenol when catalyzed by the copper-ethylenediamine complexes, a spectrophotometric study of the speciation of copper(II) complexes in methanol of Cu(II), ethylendiamine and Cl or Br was carried out at 303 K. The formation constants obtained for the copper chloride system are: log β101 = 2.90 ± 0.03, log β102 = 6.39 ± 0.03 and log β103 = 8.62 ± 0.04, for the copper bromide system are log β101 = 3.01 ± 0.10, log β102 = 5.50 ± 0.08, for the copper-ethylendiamine complexes are log β110 = 6.13 ± 0.05 and log β120 = 10.54 ± 0.08, and for the ternary copper-ethylenediamine chloride or bromide systems are log β111 = 10.21 ± 0.03 and log β111 = 10.07 ± 0.03, respectively. Knowing the speciation of the copper-ethylenediamine-halide systems, the kinetic studies can be correlated with the species in solution. Comparative studies of the oxidation reaction of 2,6-di-tert-butyl-phenol using different copper(II) complexes with chloride or bromide and ethylenediamine as catalyst are reported. Their catalytic activity in the oxidation of 2,6-di-tert-butyl-phenol was monitored in methanol solution, following the corresponding quinone formation, at 418 nm (ε = 3.95 × 104 mol−1 L cm−1 at 303 K). The results indicate that the most active species are [Cu(en)X]+, where X is bromide or chloride, Both complexes have similar activity.  相似文献   
4.
The previously reported complex [Ru(ttpy)(CN)3] [ttpy = 4′(p-tolyl)-2,2′:6′,2″-terpyridine] is conveniently synthesised by reaction of ttpy with Ru(dmso)4Cl2 to give [Ru(ttpy)(dmso)Cl2], which reacts in turn with KCN in aqueous ethanol to afford [Ru(ttpy)(CN)3] which was isolated and crystallographically characterised as both its (PPN)+ and K+ salts. The K+ salt contains clusters containing three complex anions and three K+ cations connected by end-on and side-on cyanide ligation to the K+ ions. The solution speciation behaviour of [Ru(ttpy)(CN)3] was investigated with both Zn2+ and K+ salts in MeCN, a solvent sufficiently non-competitive to allow the added metal cations to associate with the complex anion via the externally-directed cyanide lone pairs. UV-Vis spectroscopic titration of (PPN)[Ru(ttpy)(CN)3] with Zn(ClO4)2 showed a blue shift of 2900 cm−1 in the 1MLCT absorption manifold due to the ‘metallochromism’ effect; a series of distinct binding events could be discerned corresponding to formation of 4:1, 1:1 and then 1:3 anion:cation adducts, all with high formation constants, as the titration proceeded. In contrast titration of (PPN)[Ru(ttpy)(CN)3] with the more weakly Lewis-acidic KPF6 resulted in a much smaller blue-shift of the 1MLCT absorptions, and the titration data corresponded to formation of 1:1 and then 2:1 cation:anion adducts with weaker stepwise association constants of the order of 104 and then 103 M−1. Although association of [Ru(ttpy)(CN)3] resulted in a blue-shift of the 1MLCT absorptions, the luminescence was steadily quenched, as raising the 3MLCT level makes radiationless decay via a low-lying 3MC state possible.  相似文献   
5.
6.
The interaction of jatrophone with sRNA from Escherichia coli has been investigated through UV, CD, and 1H NMR measurements. The results obtained show that the interaction with jatrophone increases the stability of the polynucleotide. It appears that the optical properties of jatrophone depend upon the jatrophone/nucleotide ratio. The observed behaviour can only be explained by the existence of different types of interaction between jatrophone and sRNA. Even for a jatrophone/nucleotide ratio as low as 0.17 the 1H NMR spectra show a multiplicity of resonances that can only be explained by the simultaneous existence of two different binding modes involving the jatrophone molecules.  相似文献   
7.
Synthesis and stereochemical characterization of enantiomerically pure nucleoside-3′-phosphorothioate esters and salts are reported. Vicinal carbon–phosphorus couplings reflect different predominance of the ? conformation in the isomeric (Rp and Sp) esters, while for the salts the ?t conformation prevails in both stereoisomers. The influence of solvent and temperature on the conformational preferences is also described.  相似文献   
8.
Summary This experiment examined the feasibility of predicting K uptake in white clover by the use of simple and relatively rapid tests that would dispense with the need of knowing the quantity of plant available potassium. Potassium uptake was found to correlate highly (R=>0.9) in linear bivariate regressions using K concentration in the soil solution displaced by centrifuging and an empirical estimate of potassium retention. There was no advantage in determining activity ratios because in at least some of the soils used the ratio law did not apply. Exchangeable potassium alone correlated rather poorly with uptake except at very low soil potassium status. This was not because nonexchangeable potassium was an important source of this nutrient to white clover but because of the large differences in the retention of K amongst the soils used.  相似文献   
9.
目的:研究银杏蜜环口服溶液联合尼可地尔对冠心病患者血清超敏C反应蛋白(High-sensitivity C-reactive protein,Hs CRP)、同型半胱氨酸(Homocysteine,HCY)、缺血修饰白蛋白(Ischemia Modified Albumin,IMA)和脂蛋白相关磷脂酶A2(Lipoprotein-related phospholipase A2,Lp-PLA2)水平的影响。方法:选择2016年11月~2018年11月在我院全科医学科、急诊科收治的80例冠心病患者,根据就诊顺序,用抽签法随机分为两组,每组40例患者。对照组口服尼可地尔治疗,观察组采取银杏蜜环口服溶液联合尼可地尔治疗,两组均持续治疗2周。比较两组治疗前后的血清Hs CRP、HCY、IMA、LP-PLA2水平,左室舒张末径(left ventricular end-diastolic diameter,LVEDD)、心输出量(cardiac output,CO)和左室射血分数(left ventricular ejection fraction,LVEF)等心功能指标的变化。结果:治疗后,观察组的总有效率为92.50%(37/40),明显高于对照组[75.00%(30/40)](P0.05);两组治疗后的血清Hs CRP、HCY、IMA、LP-PLA2水平均较治疗前明显降低(P0.05),且观察组以上指标均明显低于对照组(P0.05);两组治疗后的LVEDD均较治疗前明显降低,而CO和LVEF均较治疗前明显升高(P均0.05),且观察组治疗后的LVEDD与对照组相比明显降低,而CO和LVEF显著升高(P0.05)。结论:银杏蜜环口服溶液联合尼可地尔治疗冠心病的疗效明显优于单独口服尼可地尔治疗,其机制可能与降低血清Hs CRP、HCY、IMA、LP-PLA2水平相关。  相似文献   
10.
医疗设备是医院的重要资产,可在一定程度上反映医院的诊断能力以及现代化程度。新医改政策出台后,各地均大力推进医药卫生信息化建设,随着医疗设备种类的增加,给医院设备管理带来一定的困难,医疗设备信息化管理已成为医院不可或缺的一部分。我国的医疗设备信息化管理起步较晚,尚处于初级研究阶段,从而导致现阶段医疗设备信息化管理问题较多。本文简短叙述了医疗设备信息化管理现状,以及当前医疗设备信息化管理所存在的问题,并对所描述问题提出针对性的解决方案。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号