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   71篇
  免费   2篇
  国内免费   3篇
化学   44篇
晶体学   2篇
综合类   2篇
物理学   2篇
综合类   26篇
  2022年   3篇
  2021年   1篇
  2020年   4篇
  2018年   1篇
  2017年   1篇
  2016年   4篇
  2015年   3篇
  2014年   1篇
  2013年   2篇
  2012年   5篇
  2011年   5篇
  2010年   4篇
  2006年   2篇
  2005年   2篇
  2004年   2篇
  2003年   1篇
  2002年   5篇
  2001年   3篇
  2000年   2篇
  1999年   4篇
  1998年   6篇
  1997年   3篇
  1996年   1篇
  1995年   2篇
  1993年   2篇
  1992年   1篇
  1991年   3篇
  1988年   2篇
  1985年   1篇
排序方式: 共有76条查询结果,搜索用时 15 毫秒
51.
4′,4′-Dimethyl[16α,17α]spiropentanopregn-4-ene-3,20-dione was synthesized. The addition of diazo-2,2-dimethylcyclopropane generated from N-(2,2-dimethylcyclopropyl)-N-nitrosourea to 16,17-didehydropregnenolone acetate occurs regio-and stereospecifically to give 3β-acetoxy-1′,1′-dimethyl-20-oxopregn-5-ene-[16α,17α;7′,6′]-4′, 5′-diazaspiro[2.4]-hept-4′-ene in high yield. Its thermolysis affords a spiropentane-containing steroid, which is transformed into the target diketone. The anti position of the gem-dimethyl group in the fused spiropentane fragment is evident from the X-ray diffraction study of the final product. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2040–2042, November, 2006.  相似文献   
52.
The title compound (C19H26N2O2) is one of a series of novel heteroatom steroidal derivatives recently prepared for testing their antifertility profiles and progesterone binding affinity. It is one of a pair of epimers differing in configuration at position 5. The X-ray analysis has uniquivocally resolved this ambiguity. The compound crystallizes in space group P212121, a = 9.257(3), b = 9.419(3), c = 19.089(5)Å, and Z = 4 and the structure was solved by direct methods. In the steroid skeleton Ring A does not exhibit the chair conformation commonly found in the steroid nucleus, being considerably strained, presumably as a consequence of the fused planar oxadiazole ring E. Rings B and C, however, are chairs and ring D is in an intermediate envelope/half-chair conformation. All rings of the steroid skeleton are trans connected.  相似文献   
53.
Some derivatives of progestins of the pregna-D6-pentarane series have been obtained and examined for their possible hormonal and antihormonal activity in the Clauberg-McPhail assay as well as in the pregnancy maintenance test in ovariectomized rabbits. 16, 17-Cyclohexanoprogesterones of the 19-methyl and 19-nor series (1–4) saturated in ring A, which are inactive as progestins, exhibited a remarkable antiprogesterone effect. They decreased the McPhail index under combined administration with progesterone in a dose-dependable manner and completely inhibited the action of the latter in the pregnancy maintenance test.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 564–567, March, 1995.  相似文献   
54.
该文制备了一种比表面积大、稳定性好的金属有机框架材料(MOF)UiO-67,将其用于复杂牛奶基质中痕量孕激素的富集和净化。结合超高效液相色谱-四极杆/静电场轨道离子阱高分辨质谱(UHPLC-Q-Orbitrap HRMS),建立了同时测定牛奶中7种孕激素残留的检测方法。采用X射线光电子能谱(XPS)对UiO-67吸附孕激素后的元素谱图进行测试分析,通过对比结合能和官能团相对含量的变化证明了UiO-67与孕激素间发生了化学作用,并研究了UiO-67对1 mg/L和5 mg/L孕激素的吸附效果。考察并优化了吸附剂用量、洗脱溶剂类型和pH值等关键参数,评价了基质效应对孕激素质谱信号的影响。优化结果显示,选择吸附剂用量为40 mg,在样品溶液pH值为5时,用5 mL丙酮洗脱目标物就可获得满意的回收率。基质效应在20%之内,可忽略不计。在优化条件下,7种孕激素在1~100μg/L范围内线性相关性良好,相关系数均达到0.99以上,方法的检出限(LOD)和定量限(LOQ)分别为0.06~0.30μg/L和0.19~1.0μg/L;在不同添加水平下,回收率为87.10%~105.58%,相对标准偏差为2.66%~9.64%。方法成功应用于实际牛奶样品中孕激素的测定,结果与SN/T 1980-2007标准得到的结果具有良好的吻合度。相比较已报道的牛奶中孕激素前处理技术和检测方法,该方法具有较高的灵敏度和满意的回收率,为今后这类材料在复杂基质中有毒有害物质的富集检测提供了新的借鉴思路。  相似文献   
55.
Regulation of activin A in cell proliferation as well as hCG and progesterone secretion was investigated using primary cultured cytotrophoblast cells and normal placenta origin cytotrophoblast cell line-NPC cells in serum-free system. It was shown that activin A promoted hCG and progesterone secretion in primary cultured cytotrophoblast cells as well as progesterone secretion in NPC cells, while it had no effect on cell proliferation and hCG secretion in NPC cells. Important evidence is provided for the autocrine regulatory mechanism of activin A on hormone secretion in placental trophoblast cells at early pregnancy.  相似文献   
56.
为了研究不同浓度尼古丁对大鼠卵巢黄体细胞存活情况、在有无hCG支持下分泌孕酮、雌二醇的影响 ,将妊娠第 4天的母鼠卵巢中取出的黄体细胞培养于含 5 %胎牛血清的M199培养基中 ,放置于 37℃、5 %CO2 、饱和湿度的培养箱中培养 .大鼠黄体细胞培养 1~ 2小时后 ,分组加入尼古丁生理盐水溶液 ,最终浓度为 :4mg mL、0 4mg mL、0 0 4mg mL、0 0 0 4mg mL、0 0 0 0 4mg/mL ,将大鼠黄体细胞分为两组 ,一组为基础分泌组 ,另一组为hCG刺檄组 .在大鼠黄体细胞受尼古丁作用 4小时后 ,吸取培养液上清部分以放射性免疫法测定孕酮和雌二醇的含量 ,同时用MTT比色法测定黄体细胞存活情况 .结果发现 ,大鼠黄体细胞在有无hCG的刺激下 ,孕酮 ,雌二醇的分泌量均是随着加药浓度的增加而增加 ,大致呈线形关系 ,但其基础分泌量远远小于hCG刺激下的激素分泌量 .  相似文献   
57.
钕在小鼠体内的分布与蓄积及对孕酮分泌的影响   总被引:15,自引:2,他引:15  
应用核素示踪方法研究147Nd在小鼠体内的分布、蓄积及其对孕酮分泌的影响.一次性腹腔注射200mg@kg-1147Nd在各组织中呈不均匀分布,骨骼中表现出了高度蓄积性,且随时间的延长而增加;在眼睛、血液和大脑中均有一定的蓄积,但因排泄和体内再分配随时间而呈下降趋势;在Nd处理后血清中孕酮浓度显著低于对照组,表现了明显的抑制作用.  相似文献   
58.
液相色谱-串联质谱法测定谷物类饲料中的41种激素   总被引:1,自引:0,他引:1  
Zhang Y  Lan F  Zhang F  Shen J  Chu X 《色谱》2011,29(6):523-534
建立了谷物类饲料中10种雄性激素、11种孕激素、10种糖皮质激素、5种雌性激素以及5种二羟基苯甲酸内酯类药物的液相色谱-串联质谱(LC-MS/MS)检测方法。均质样品经乙酸乙酯提取,以改良的QuEChERS吸附剂分散于提取液中实现快速净化。采用C18色谱柱(150 mm×2.1 mm, 3.0 μm)分离,分别在正、负电喷雾串联质谱多反应监测模式下检测。在优化条件下,41种化合物在5.0~200.0 μg/kg含量范围内有良好的线性相关性,相关系数均不低于0.99,定量限(S/N≥10)为0.123~2.72 μg/kg。在5、40、200 μg/kg或10、40、200 μg/kg 3个添加水平下,豆粕类饲料中各化合物的回收率为70.3%~118.1%,相对标准偏差(RSD)为0.82%~19.5%;玉米类饲料中各化合物的回收率为76.1%~122.8%, RSD为1.3%~15.0%。该方法简便、快速、准确,可用于谷物类饲料中雄性激素、孕激素、糖皮质激素、雌性激素以及二羟基苯甲酸内酯类激素的筛查和测定。  相似文献   
59.
吴庆安  徐志超  柏挺 《合成化学》2016,24(2):174-177
以植物甾醇为原料,分离得豆甾醇(1); 1经沃氏氧化和臭氧化制得中间体孕甾-4-烯-3-酮-22-醛(3); 3经加成缩合并在CuCl催化下经空气氧化合成了黄体酮,总产率69.1%,其结构经1H NMR和ESI-MS确证。  相似文献   
60.
A novel procedure for docking ligands in a flexible binding site is presented. It relies on conjugate gradient minimization, during which nonbonded interactions are gradually switched on. Short Monte Carlo minimization runs are performed on the most promising candidates. Solvation is implicitly taken into account in the evaluation of structures with a continuum model. It is shown that the method is very accurate and can model induced fit in the ligand and the binding site. The docking procedure has been successfully applied to three systems. The first two are the binding of progesterone and 5β-androstane-3,17-dione to the antigen binding fragment of a steroid binding antibody. A comparison of the crystal structures of the free and the two complexed forms reveals that any attempt to model binding must take protein rearrangements into account. Furthermore, the two ligands bind in two different orientations, posing an additional challenge. The third test case is the docking of Nα-(2-naphthyl-sulfonyl-glycyl)-D -para-amidino-phenyl-alanyl-piperidine (NAPAP) to human α-thrombin. In contrast to steroids, NAPAP is a very flexible ligand, and no information of its conformation in the binding site is used. All docking calculations are started from X-ray conformations of proteins with the uncomplexed binding site. For all three systems the best minima in terms of free energy have a root mean square deviation from the X-ray structure smaller than 1.5 Å for the ligand atoms. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 21–37, 1998  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