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   10936篇
  免费   1615篇
  国内免费   1453篇
化学   8741篇
晶体学   461篇
力学   316篇
综合类   72篇
数学   115篇
物理学   4299篇
  2024年   24篇
  2023年   141篇
  2022年   434篇
  2021年   415篇
  2020年   510篇
  2019年   424篇
  2018年   366篇
  2017年   395篇
  2016年   534篇
  2015年   486篇
  2014年   493篇
  2013年   885篇
  2012年   598篇
  2011年   789篇
  2010年   613篇
  2009年   680篇
  2008年   633篇
  2007年   776篇
  2006年   715篇
  2005年   594篇
  2004年   510篇
  2003年   440篇
  2002年   357篇
  2001年   284篇
  2000年   275篇
  1999年   242篇
  1998年   199篇
  1997年   204篇
  1996年   178篇
  1995年   125篇
  1994年   115篇
  1993年   91篇
  1992年   102篇
  1991年   54篇
  1990年   53篇
  1989年   45篇
  1988年   34篇
  1987年   37篇
  1986年   32篇
  1985年   23篇
  1984年   15篇
  1983年   10篇
  1982年   9篇
  1981年   12篇
  1980年   10篇
  1979年   13篇
  1977年   5篇
  1976年   6篇
  1975年   5篇
  1972年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
镉的化学蒸气发生-原子光谱分析法   总被引:6,自引:0,他引:6  
从反应体系、反应机理和应用三方面对镉的化学蒸气发生-原子光谱分析法进行了综述,引用文献34篇。  相似文献   
972.
973.
Measurements of surface-liquid interactions (contact-angle goniometry) and tip-surface adhesion forces (atomic force microscopy) combined with infrared spectroscopic studies have been used to investigate surface-preparation and solution-deposition conditions for the reproducible formation of self-assembled molecular structures on gold-coated tips and substrates for atomic force microscopy. Preliminary data show that surface-saturated self-assembled monolayers form reproducibly on prolonged (>20 h) exposure of gold-coated glass substrates to ethanolic solutions of ω-functionalised alkanethiols in the concentration range 80-160 mmol dm−3. The data also show that exposure for 16 h to alkanethiol concentrations in the range 160-240 mmol dm−3 promote bilayer formation whereas concentrations of 240-320 mmol dm−3 result in the deposition of multilayers, the average orientation of which is parallel to that of the first molecular layer; the use of parent 1-undecanethiol solutions at concentrations of 1-80 mmol dm−3 results in incomplete monolayer coverage.  相似文献   
974.
二氧化钛紫外光在线消解测定COD的研究   总被引:1,自引:0,他引:1  
以TiO2-K2Cr2O7协同光催化氧化体系为基础,结合流动注射分析方法建立了一种快速测定水样中化学需氧量(COD)的简便方法.该方法测试速度快,不需有毒、昂贵的试剂,具有广阔的应用前景.COD含量在10~100mg·L^-1和100~1000mg·L^-1范围内,吸光度与COD含量均呈良好的线性关系;测定30mg·L^-1和300mg·L^-1的COD标准溶液,RSD≤5.1%(n=7);将本系统应用于实际环境水样测定,与国家标准分析方法测定结果相符.  相似文献   
975.
976.
Gold nanostructured screen‐printed carbon electrodes are demonstrated to be suitable transducers for the determination of lead using square‐wave voltammetry. Reproducible gold nanostructures have been obtained by direct electrochemical deposition. A calibration plot from 2.5 to 250 μg/L was obtained in acidic solutions of Pb(II) with a reproducibility of 4% (n=10). The detection limit was 0.09 μg/L of lead. The method is then applied to perform a blood lead analysis by adjusting square‐wave parameters in capillary or venous blood with a minimum sample pretreatment and excellent accuracy and reproducibility.  相似文献   
977.
It was shown that the resonance mixing of states on large molecules can increase the probability of reaction. This effect is similar to a decrease in the activation threshold or the action of an external catalyst.  相似文献   
978.
979.
A mathematical model that describes solution seepage in a porous medium and the processes of mineral dissolving and secondary deposition is proposed. Self-similar solutions describing the motion of the leading and trailing fronts, that is, the boundaries of the complete-dissolving zone, are determined. The main features of the processes under consideration are studied and numerical calculations are performed. It is shown that the model describes well the experimental data on mineral leaching by sulfate solutions. The dynamics of mineral extraction from productive solutions in a medium with a nonuniformacidity distribution are investigated. It is shown that, in the elevated-PH zones, the mineral is dissolved; whereas, in the low-acidity zones, secondary deposition of the mineral occurs. In the latter case, after the work has been completed, the bed may contain more or less considerable mineral resources, depending on the extent of the low-PH zone and its proximity to an extraction well.  相似文献   
980.
The toxicity of ferrocenylethyl benzotriazole ( 1 ) and other ferrocene compounds including ferrocenylmethyl benzimidazoles ( 4,5,6,11 ), ferricenium salts ( 3,9,10 ) and ferrocenylmethyl adenine ( 7 ), was studied. All ferrocene complexes under investigation showed low or medium toxicities. On the basis of an earlier model of chemical carcinogenesis, the antitumor activity of ferrocenylalkyl azoles 1, 8 and ferricenium salts 9, 10 was studied in vivo in the so‐called sub‐capsular test on human tumors. This effectiveness was compared with that of cisplatin. A series of ferrocenylalkyl azoles were synthesized by interacting azoles either with α‐hydroxyalkyl ferrocenes FcC(OH)R1R2 in organic solvent in the presence of aqueous HBF4 in quantitative yields or with trimethyl(aminomethyl)ferrocene iodide in an aqueous‐basic medium in good yields. The X‐ray determinations of molecular and crystal structures of α‐(1‐benzotriazolyl)ethylferrocene ( 1 ) and α‐(1‐naphthatriazolyl)ethylferrocene ( 12 ) were performed. Copyright © 2008 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