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   1007篇
  免费   58篇
  国内免费   63篇
化学   813篇
晶体学   6篇
力学   28篇
综合类   77篇
数学   51篇
物理学   153篇
  2023年   19篇
  2022年   24篇
  2021年   101篇
  2020年   46篇
  2019年   52篇
  2018年   24篇
  2017年   34篇
  2016年   38篇
  2015年   32篇
  2014年   44篇
  2013年   71篇
  2012年   53篇
  2011年   47篇
  2010年   37篇
  2009年   42篇
  2008年   41篇
  2007年   42篇
  2006年   30篇
  2005年   49篇
  2004年   31篇
  2003年   39篇
  2002年   28篇
  2001年   14篇
  2000年   24篇
  1999年   19篇
  1998年   14篇
  1997年   15篇
  1996年   10篇
  1995年   15篇
  1994年   17篇
  1993年   10篇
  1992年   9篇
  1991年   4篇
  1990年   5篇
  1989年   7篇
  1988年   8篇
  1987年   2篇
  1986年   5篇
  1985年   5篇
  1984年   5篇
  1983年   3篇
  1982年   3篇
  1980年   2篇
  1978年   1篇
  1974年   2篇
  1973年   1篇
  1970年   1篇
  1959年   3篇
排序方式: 共有1128条查询结果,搜索用时 104 毫秒
81.
<正>A new dicaffeoyl quinic acid,nannoglottisin A,has been isolated from an endemic plant of Nannoglottis ravida,and the structure of the compound was identified by means of spectroscopic analysis.  相似文献   
82.
建立了微波消解-石墨炉原子吸收光谱法测定植物染发剂中重金属铅、镉和铜的方法.采用L9(34)正交设计讨论了固液比、消解剂体积比、消解时间和消解压力对样品消解效果的影响,最佳的消解条件:固液比(g/mL)为1∶12,HNO3/H2O2(V/V)为4∶1,消解时间为5min,消解压力1.5MPa.在最佳微波消解条件下,进行了精密度实验、回收率实验,相对标准偏差为1.05%~3.35%,回收率为96.67%~105.43%.微波消解法处理植物染发剂样品,试剂用量少、消解完全、快速、简便,而且测定结果的精密度、准确度较好.  相似文献   
83.
Qi Fan  Yuanliang Wang  Peng Sun  Yang Li 《Talanta》2010,80(3):1245-1250
The secondary metabolites of different Ephedra plants are various. Therefore, the discrimination of different Ephedra plants is significant. An objective, easy-to-use, rapid and pollution-free approach is proposed for discriminating Ephedra plants of different species, habitats and picking times on the basis of diffuse reflectance Fourier transform near infrared spectroscopy (FT-NIRS) measurements and multivariate analysis. The Fourier transform near infrared diffuse reflectance spectra (NIRDRS) were acquired from 37 pulverized samples of Ephedra plants put in glass vials in the near infrared (NIR) region between 10 000 and 4000 cm−1, averaging 64 scans per spectrum at a resolution of 4 cm−1. After spectra processing and data pre-processing, spectral data were analyzed respectively with three multivariate analysis techniques: discriminant analysis (DA), self-organizing map (SOM) and back-propagation artificial neural network (BP-ANN). The proposed method could distinguish not only the Ephedra plants of three species and two habitats but also the plants picked at different times of day without special sample treatment and the use of chemical reagents. The performance indexes of the DA model were 84.2-91.9% and the prediction accuracies of both the SOM and the BP-ANN models reached 93.3-100.0%.  相似文献   
84.
一种新型噻二唑Schiff碱的合成及生物活性研究   总被引:1,自引:0,他引:1  
陈传兵  伍海涛  王涛  张荣 《广州化学》2010,35(1):38-40,47
为了寻找具有较高植物生长调节活性的物质,利用生物等排原理和亚结构连接法,对噻二唑母体进行修饰,将2-氨基-1,3,4-噻二唑与2,4-二氯苯甲醛反应,设计并合成了一个新的噻二唑席夫碱,并用FT-IR、1HNMR和元素分析方法确证其结构。合成的化合物具有一定的植物生长调节活性,具有一定的研究开发价值。  相似文献   
85.
A novel analytical reagent 4-(2-hydroxy phenyl ethaminodiol), benzene-1,3-diol(4-2-HPEDB-1,3,D) was synthesized for the determination of molybdenum(VI). The present paper reveals the detailed study of electroanalytical behaviour for [Mo-(4-2-HPEDB-1,3,D)] complex under optimized conditions. The peak obtained for [Mo-(4-2-HPEDB-1,3,D)] prevent the interference of foreign ions which shows the sensitivity of the proposed method. The linearity was maintained at the concentration range of 0.5–200 μg/mL at pH 4.5 with correlation factor 0.9997. The present method was successfully applied for the analysis of molybdenum(VI) in biological fluids and plant material. The results obtained from the proposed method show good agreement with reference method.  相似文献   
86.
Liu W  Kong Y  Zu Y  Fu Y  Luo M  Zhang L  Li J 《Journal of chromatography. A》2010,1217(28):4723-4731
A novel method using liquid chromatography coupled to electrospray ionization mass spectrometry (LC-ESI-MS) has been optimized and established for the qualitative and quantitative analysis of ten active phenolic compounds originating from the pigeon pea leaves and a medicinal product thereof (Tongluo Shenggu capsules). In the present study, the chromatographic separation was achieved by means of a HiQ Sil C18V reversed-phase column with a mobile phase consisting of methanol and 0.1% formic acid aqueous solution. Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) using the selected reaction monitoring (SRM) analysis was employed for the detection of ten analytes which included six flavonoids, two isoflavonoids and two stilbenes. All calibration curves showed excellent coefficients of determination (r(2) ≥ 0.9937) within the range of tested concentrations. The intra- and inter-day variations were below 5.36% in terms of relative standard deviation (RSD). The recoveries were 95.08-104.98% with RSDs of 2.06-4.26% for spiked samples of pigeon pea leaves. The method developed was a rapid, efficient and accurate LC-MS/MS method for the detection of phenolic compounds, which can be applied for quality control of pigeon pea leaves and related medicinal products.  相似文献   
87.
从“福岛第一核电站事故”看我国核能利用的核安全   总被引:1,自引:0,他引:1  
叶奇蓁 《物理》2011,40(7):427-433
文章简要说明了福岛第一核电站事故的起因、发展和后果,并对核电站全厂断电、反应堆压力容器及安全壳超压、氢爆等导致事故恶化的原因作了分析.文章还就导致福岛核事故的相关因素与我国核电站的安全设计及防范对策进行了分析比较.在吸取福岛核事故的经验教训方面,文章提出了若干值得引发关注的启示,作为我国在建和在役核电站的改进,以及新设计核电站的参考.文章还就我国能源的状况,核能发展的必要性,以及核能发展的方针进行了探讨.  相似文献   
88.
植物生长调节剂生物筛选方法的初步构建   总被引:7,自引:0,他引:7       下载免费PDF全文
通过对13种植物生长调节剂的试验,建立了用于筛选植物生长调节剂的生物检测方法,该方法第1步采用萝卜、黄瓜、小麦、油菜4种幼苗生长法联合筛选,第2步采用萝卜子叶扩张法、黄瓜子叶生根法联合筛选,这样能保证有生长调节剂活性的化合物在普筛中不被漏筛,而且方法简便,测试周期短。  相似文献   
89.
《Analytical letters》2012,45(4):567-574
The goal of this study was to develop and validate a high-performance liquid chromatography method for the quantification of two essential oil constituents (myristicin and linalool) from extracts of the three aromatic plants exposed to low-intensity microwave radiation. The analysis was performed by high-performance liquid chromatography using a mobile phase consisting of ultrapure water and acetonitrile. The separations were carried out in the following conditions: isocratic conditions for 30 minutes with 100% acetonitrile and then linear gradient conditions from 100% acetonitrile to 25% acetonitrile for 15 minutes. The developed method was validated in terms of linearity, limits of detection, limits of quantification, precision, accuracy, and robustness. The results show that plants react differently under microwave stress and change their essential oil content as a response.  相似文献   
90.
Fifteen new ferrocene derivatives containing 1H‐1,2,4‐triazole moiety were synthesized in various yields by the condensation of ferrocenecarboxaldehyde with 1‐aryl‐3‐(1H‐1,2,4‐triazo‐1‐yl)‐propen‐1‐ones in toluene. Their structures have been confirmed by 1H NMR, IR, MS and elemental analysis. In addition, the crystal structure of 4l was determined. The antifungal and plant growth regulatory activities of the title compounds are discussed. Copyright © 2005 John Wiley & Sons, Ltd.  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