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   2047篇
  免费   186篇
  国内免费   143篇
化学   1640篇
晶体学   2篇
力学   62篇
综合类   64篇
数学   368篇
物理学   240篇
  2024年   5篇
  2023年   45篇
  2022年   157篇
  2021年   131篇
  2020年   99篇
  2019年   81篇
  2018年   70篇
  2017年   104篇
  2016年   85篇
  2015年   69篇
  2014年   84篇
  2013年   127篇
  2012年   157篇
  2011年   98篇
  2010年   83篇
  2009年   115篇
  2008年   127篇
  2007年   102篇
  2006年   99篇
  2005年   92篇
  2004年   64篇
  2003年   43篇
  2002年   54篇
  2001年   34篇
  2000年   36篇
  1999年   37篇
  1998年   22篇
  1997年   25篇
  1996年   22篇
  1995年   18篇
  1994年   18篇
  1993年   5篇
  1992年   11篇
  1991年   11篇
  1990年   6篇
  1989年   8篇
  1988年   4篇
  1987年   2篇
  1986年   8篇
  1985年   4篇
  1984年   4篇
  1983年   3篇
  1982年   3篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有2376条查询结果,搜索用时 46 毫秒
851.
Adiponectin may affect bone through interactions with two known receptors, adiponectin receptors (ADIPOR) 1 and 2. We examined the association between polymorphisms of ADIPOR1 and ADIPOR2 and bone mineral density (BMD) in postmenopausal Korean women. Six polymorphisms in ADIPOR1 and four polymorphisms in ADIPOR2 were selected and genotyped in all study participants (n = 1,329). BMD at the lumbar spine and femur neck were measured using dual-energy X-ray absorptiometry. Lateral thoracolumbar (T4-L4) radiographs were obtained for vertebral fracture assessment and the occurrence of non-vertebral fractures examined using self-reported data. P values were adjusted for multiple testing using Bonferroni correction (P(corr)). ADIPOR1 rs16850799 and rs34010966 polymorphisms were significantly associated with femur neck BMD (P(corr) = 0.036 in the dominant model; P(corr) = 0.024 and P(corr) = 0.006 in the additive and dominant models, respectively). Subjects with the rare allele of each polymorphism had lower BMD, and association of rs34010966 with BMD showed a gene dosage effect. However, ADIPOR2 single nucleotide polymorphisms and haplotypes were not associated with BMD at any site. Our results suggest that ADIPOR1 polymorphisms present a useful genetic marker for BMD in postmenopausal Korean women.  相似文献   
852.
用阿魏酸与Fe、Co、Ni、Cu、Zn的硝酸盐制备了5种过渡金属配合物,通过红外光谱、热重-差热分析、元素分析、荧光和紫外光谱的方法对配合物进行了表征,确定了配合物的组成。并对配体和配合物进行了全血凝血时间、复钙时间、活化部分凝血活酶时间、凝血酶原时间的测定,结果表明5种配合物具有较好的抗凝血性质。通过荧光光谱、紫外光谱、圆二色谱研究了配合物与人血清白蛋白(HSA)的相互作用,HSA的荧光光谱表明配合物对其有荧光猝灭作用并使其发射峰位置红移,紫外光谱表明配合物的加入导致HSA吸收强度增加且吸收峰位置紫移,圆二色谱表明配合物的存在可引起HSA构象的变化。推测配合物抗凝血作用的起效与其和血清白蛋白之间的相互作用有一定的联系。  相似文献   
853.
采用紫外光谱、荧光光谱和圆二色谱等多种光谱方法研究了三氯生与人类肿瘤相关DNA(抑癌基因p53 DNA和癌基因C-myc DNA)的相互作用,以期为从分子水平上评价三氯生与人类肿瘤发生的危害性提供科学依据。紫外减色效应、KI猝灭受到抑制及圆二色谱正负峰强度减弱等结果表明三氯生以弱嵌插模式与两种DNA发生作用,三氯生与DNA的结合位点数均小于1,以及DNA解链温度小幅升高等结果证实三氯生部分嵌插入DNA的沟区,影响了DNA的双螺旋结构。  相似文献   
854.
《Analytical letters》2012,45(12):2417-2428
Abstract

A simple, sensitive, and specific flow injection fluorimetric method has been developed for the determination of carbamazepine (CBZ). The proposed method is based on use of a solid‐phase reactor containing lead dioxide for on‐line oxidization of CBZ into a strongly fluorescent compound in a medium of phosphoric acid. The product has a green‐yellow fluorescence at a maximum excitation wavelength of 355 nm and an emission wavelength of 478 nm. Under the optimum conditions, the fluorescence intensity is proportional to the concentration of CBZ ranging from 0.0005 to 4.000 µg mL?1. The detection limit is 5.7×10?5 µg mL?1 (2.4×10?10 mol L?1) and the relative standard deviation is 1.4% at the sampling rate of 45 h?1. The proposed method has been applied to clinical estimation of CBZ in real patients' plasma samples with the results compared with those obtained by HPLC method.  相似文献   
855.
《Analytical letters》2012,45(4):561-570
Abstract

A simple reverse‐phase high‐performance liquid chromatographic method for the determination of tenofovir disoproxil fumarate (TDF) in pharmaceutical formulations and human plasma samples has been developed and validated. Piroxicam (PRX) was used as an internal standard. The assay of the drug was performed on a CLC C18 (5 μ, 25 cm×4.6 mm i.d.) with UV detection at 259 nm. The mobile phase consisted of acetonitrile–water mixture in the ratio of 75∶25, and a flow rate of 1 ml/min was maintained. The standard curve was linear over the range of 0.2–10 µg/ml (r 2=0.9966). Analytic parameters have been evaluated. Within‐day and between‐day precision as expressed by relative standard deviation was found to be less than 2%. The method has been applied successfully for the determination of TDF in spiked human plasma samples and pharmaceutical formulations.  相似文献   
856.
《Analytical letters》2012,45(5):806-821
Abstract

The voltammetric behavior of rosiglitazone was studied using direct current (DCt), differential pulse (DPP), and alternating current (ACt) polarography. The drug manifests cathodic waves over a pH range of 2–11.2. In Britton‐Robinson buffer (BRb; pH 4), the diffusion current–concentration relationship was found to be rectilinear over a range of 4–24 µg · mL?1 and 0.1–16 µg · mL?1 using DCt and DPP modes, respectively, with minimum limits of detection (LOD) of 0.15 µg · mL?1 and 0.07 µg · mL?1 using the DCt and DDP modes, respectively. The diffusion‐current constant (I d) was 6.63±0.03 (n=5). The proposed method was successfully applied to the determination of the studied compound both in pure form and in formulations. The mean percentage recoveries in tablets were 100.09±1.18 and 100.85±0.88 (n=5) using DCt and DPP modes, respectively. Furthermore, the proposed method, adopting the DPP mode, was applied to the determination of rosiglitazone in spiked human plasma and the obtained mean percentage recoveries were 99.14±3.29 (n=4).  相似文献   
857.
蒙芳  刘承伟  陈敏  卢昕  赵书林 《色谱》2012,30(10):1056-1061
建立了金纳米粒子富集-高效液相色谱-紫外检测(HPLC-UVD)同时测定人血浆中3种氨基硫醇(半胱氨酸(Cys)、高半胱氨酸(Hcys)、谷胱甘肽(GSH))的新方法。以Tween 20修饰的金纳米粒子作为选择探针萃取富集氨基硫醇。经二硫苏糖醇脱附后,采用SpursilTM C18柱(250 mm×4.6 mm, 5 μm)分离氨基硫醇,以60 mmol/L磷酸盐缓冲溶液(pH 2.0)等度洗脱,检测波长为200 nm。3种氨基硫醇的浓度分别在0.025~350 μmol/L、0.02~60 μmol/L、0.01~50 μmol/L内与峰面积具有良好的线性关系,相关系数均高于0.99。方法检出限(信噪比为3)分别为5.0、6.0和2.5 nmol/L,回收率为92.8%~106.0%。该方法能显著降低血浆样品中内源性物质的干扰,提高HPLC-UVD的选择性和灵敏度。将该方法应用于心血管病人血浆中上述氨基硫醇的分离测定,结果显示: 与对照组相比,疾病组血浆中的Hcys和GSH水平存在显著性差异,Cys不存在显著性差异。  相似文献   
858.
吴晓军  刘国诠 《分析化学》1995,23(5):493-496
研究用分子组氨酸和配体、大孔硅球为基质的拟亲和色谱分离纯化人免疫蛋白G(IgG),认为键合组氨酸具有半抗原体质而与IgG发生免疫亲和作用,以色谱组份重新进样验证了色谱柱对IgG亲和专一性,并用包敷Dextran大孔硅球作基质的拟亲和色谱纯化人血清中的IgG,减少了色谱峰拖尾,缩短了分离时间。  相似文献   
859.
血清中阿斯匹林和水杨酸浓度的快速高效液相色谱法测定   总被引:3,自引:0,他引:3  
孙长海  王敏 《色谱》1996,14(1):64-65
A fast method for determining concentrations of aspirin and salicylic acid in serum using reversedphase high performance liquid chromatography with Spherisorb C18 column,MeOH i H2O: n-BuOH : H3PO4 (300:200 :10 :0. 5,volume ratio) eluent and UV-237 detector was eatablished. The linear range of the method is 1-20μg/mL (r=0. 9996)for aspirin and 2 30μg/mL (r=0. 9981) for salicylic acid. The averagerecoveries are 96. 0 %-106. 0% and 92. 0%-119.5% ,respectively.  相似文献   
860.
液相色谱法测定血浆中三环类抗忧郁药物   总被引:2,自引:0,他引:2  
冯翠玲  刘荫棠  罗毅 《色谱》1996,14(4):282-284
用高效液相色谱法测定了血浆中4种三环类抗忧郁药物:卡马西平、氯氮平、多虑平和阿米替林。方法采用C_(18)色谱柱分离,二极管阵列检测器检测,流动相为甲醇:0.5mol/L三乙胺-0.5mol/L冰醋酸的水溶液(90:10,V/V;pH7.5)。标准曲线的线性范围为0~10mg/L,相关系数在0.99以上。方法的最小检出浓度为10~40μg/L血浆。血中药物经溶剂萃取后,药物的回收率为73.67%~98.24%,血中杂质不影响药物的检测。方法简便、快速,适用于临床中毒样品的分析。  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