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   5019篇
  免费   129篇
  国内免费   7篇
化学   2957篇
晶体学   125篇
力学   168篇
数学   392篇
物理学   1513篇
  2023年   34篇
  2022年   113篇
  2021年   107篇
  2020年   114篇
  2019年   123篇
  2018年   120篇
  2017年   159篇
  2016年   190篇
  2015年   135篇
  2014年   182篇
  2013年   391篇
  2012年   298篇
  2011年   312篇
  2010年   213篇
  2009年   189篇
  2008年   247篇
  2007年   210篇
  2006年   146篇
  2005年   147篇
  2004年   115篇
  2003年   100篇
  2002年   108篇
  2001年   60篇
  2000年   53篇
  1999年   36篇
  1998年   32篇
  1997年   38篇
  1996年   43篇
  1995年   29篇
  1994年   32篇
  1993年   41篇
  1992年   51篇
  1991年   36篇
  1990年   40篇
  1989年   49篇
  1988年   44篇
  1987年   42篇
  1986年   32篇
  1985年   61篇
  1984年   57篇
  1983年   40篇
  1982年   44篇
  1981年   51篇
  1980年   46篇
  1979年   46篇
  1978年   43篇
  1977年   51篇
  1976年   54篇
  1975年   44篇
  1974年   38篇
排序方式: 共有5155条查询结果,搜索用时 0 毫秒
151.
152.
153.
With the aim of understanding the thermochemistry of the introduction of mesoporosity in zeolites by using surfactants, high temperature oxide melt solution calorimetry was used to determine the change in the enthalpy of formation of USY zeolite before and after the introduction of mesoporosity. Our results confirm that this process only slightly destabilizes the zeolite by the additional surface area. However, this can be overcome by the stabilizing effect of the interactions between the surfactant and the zeolite framework.  相似文献   
154.
The combination of acebrophylline (ABP), levocetirizine (LCZ) and pranlukast (PRN) is used to treat allergic rhinitis, asthma, hay‐fever and other conditions where patients experience difficulty in breathing. This study was carried out with the aim of developing and validating a reverse‐phase high‐performance liquid chromatographic bioanalytical method to simultaneously quantitate ABP, LCZ and PRN in rat plasma. The objective also includes determination of the pharmacokinetic interaction of these three drugs after administration via the oral route after individual and combination treatment in rat. Optimum resolution between the analytes was observed with a C18 Kinetex column (250 mm × 4.6 mm × 5 μm). The chromatography was performed in a gradient elution mode with a 1 mL/min flow rate. The calibration curves were linear over the concentration range of 100–1600 ng/mL. The intra‐ and inter‐day precision and accuracy were found to be within acceptable limits as specified in US Food and Drug Administration guideline for bioanalytical method validation. The analytes were stable on the bench‐top (8 h), after three freeze–thaw cycles, in the autosampler (8 h) and as a dry extract (?80°C for 48 h). The statistical results of the pharmacokinetic study in Sprague–Dawley rats showed a significant change in pharmacokinetic parameters for PRN upon co‐administration of the three drugs.  相似文献   
155.
156.
157.
In this paper, the electrical conductivity and relaxation studies in two different temperature regions (T?<?T m and T?>?T m) on plasticized PEO–PMMA blend polymer electrolyte system with AgNO3 salt are reported. The polymer electrolyte system has been prepared by solution cast technique and characterized by X-ray diffraction and differential scanning calorimetry. The conduction and relaxation processes at various temperatures have been investigated in the framework of modulus formalism. The distribution of relaxation times is discussed using Argand plot. Variation in ionic conductivity of polymer blends is discussed with the increase of PEO as well as with temperature.  相似文献   
158.
The synthetic standards for cysteine and valine adducts of sulphur mustard have been synthesized using 2-(2-chloroethylthio) ethanol (half-mustard). These adducts have been recognized as biomarkers for exposure to sulphur mustard. The adducts have been fully characterized using 1 H and 13 C NMR spectroscopy and mass spectrometric techniques.  相似文献   
159.
CaFe2O4 nanocrystalline powders were synthesized through sol–gel treatment in which the stoichiometric mixing of various nitrates involving calcium and iron in presence of citric acid was performed. Subsequently, the as prepared sample was annealed at various temperatures in order to obtain the fine distribution of size including the bulk counterpart. The samples were then characterized using powder X-ray diffraction followed by 57Fe Mössbauer spectroscopy, SQUID as well as vibrating sample magnetometry. The results of spectroanalyses revealed that the samples were formed in single phase cubic spinel structure and exhibits room temperature superparamagnetism, except the bulk one, which crystallizes in characteristic orthorhombic structure of CaFe2O4 and displays trivial coercivity and remanent magnetization at room temperature.  相似文献   
160.
Sharma  Manmohan  Kar  Indrani 《Nonlinear dynamics》2021,104(4):3617-3631
Nonlinear Dynamics - The article proposes a distributed attitude consensus algorithm for multi-agent rigid bodies on the tangent bundle $$\mathrm{TSO}(3)^N$$ . It is assumed that a directed fixed...  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