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   574879篇
  免费   7065篇
  国内免费   1706篇
化学   313145篇
晶体学   8817篇
力学   24632篇
综合类   17篇
数学   65110篇
物理学   171929篇
  2021年   4356篇
  2020年   4872篇
  2019年   5253篇
  2018年   6638篇
  2017年   6479篇
  2016年   10287篇
  2015年   6696篇
  2014年   10072篇
  2013年   25675篇
  2012年   19046篇
  2011年   23570篇
  2010年   16404篇
  2009年   16184篇
  2008年   21563篇
  2007年   21554篇
  2006年   20069篇
  2005年   18074篇
  2004年   16764篇
  2003年   14835篇
  2002年   14584篇
  2001年   16912篇
  2000年   12850篇
  1999年   10186篇
  1998年   8392篇
  1997年   8137篇
  1996年   8011篇
  1995年   7173篇
  1994年   7066篇
  1993年   6822篇
  1992年   7749篇
  1991年   7725篇
  1990年   7472篇
  1989年   7304篇
  1988年   7285篇
  1987年   7185篇
  1986年   6829篇
  1985年   8901篇
  1984年   9107篇
  1983年   7352篇
  1982年   7645篇
  1981年   7544篇
  1980年   7046篇
  1979年   7564篇
  1978年   7930篇
  1977年   7722篇
  1976年   7585篇
  1975年   7122篇
  1974年   7029篇
  1973年   7085篇
  1972年   4951篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
Journal of Structural Chemistry - A new polymorph of the [ReCl3(MeCN)(PPh3)2] complex is synthesized and characterized by single crystal X-ray diffraction (XRD). Its recrystallization from the...  相似文献   
12.
A selective, highly sensitive, precise, and novel bioanalytical method has been developed and validated to quantify sinococuline, an active constituent present in the phytopharmaceutical drug product containing Cocculus hirsutus plant extract, in vivo. Chromatographic separation was achieved on a Luna Omega Polar-C18 bonded analytical column maintained at 45°C. The isocratic mobile phase consisted of methanol and ammonium formate buffer (60:40, v/v) at acidic pH with a low flow rate of 0.250 mL/min. Detection was performed on an API 4000 mass spectrometer using electrospray ionization in positive polarity and multiple reaction monitoring mode to achieve a lower limit of quantification of 1.50 ng/mL. Excellent accuracy and precision were obtained after extracting the analyte from plasma samples using a chemical analogue as an internal standard in the absence of an isotope-labeled compound. The extraction efficacy was evidenced from recovery study, and the analyte was found to be stable in plasma. Validation study demonstrated linearity with coefficient of correlation, r ≥ 0.99, and minimal matrix effect. This bioanalytical method was successfully applied to evaluate pharmacokinetic parameters of sinococuline from a phase I clinical trial of an aqueous extract of C. hirsutus in healthy human volunteers.  相似文献   
13.
Central European Journal of Operations Research - We define a geometric transformation of Euclidean Travelling Salesman Problem (TSP) tours that leads to a new formulation of the TSP. For every...  相似文献   
14.
15.
Aequationes mathematicae - In this paper, we establish a new class of dynamic inequalities of Hardy’s type which generalize and improve some recent results given in the literature. More...  相似文献   
16.
Aqueous self-assembly of short peptides has attracted growing attention for the construction of supramolecular materials for various bioapplications. Herein, we describe how the thermolysin-assisted biocatalytic construction of a dipeptide hydrazide from an N-protected amino acid and an amino acid hydrazide leads to the formation of thermally stable supramolecular hydrogels. In addition, we demonstrate the post-assembly modification of the supramolecular architectures constructed in situ tethering hydrazide groups as a chemical handle by means of fluorescence imaging.  相似文献   
17.
Journal of Structural Chemistry - Atomic and electronic structures of cyclic organosilicon compound 9,9,10,10-tetraethynyl-9,10-dihydrodisilaanthracene are studied by the density functional theory....  相似文献   
18.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  相似文献   
19.
Journal of Analytical Chemistry - The present study reports the development of a magnetic polyethylene glycol nanocomposite based on graphite reinforcement carbon paste electrode for the sensitive...  相似文献   
20.

A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.

  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