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   1524篇
  免费   72篇
  国内免费   15篇
化学   896篇
晶体学   14篇
力学   35篇
数学   378篇
物理学   288篇
  2024年   3篇
  2023年   13篇
  2022年   22篇
  2021年   42篇
  2020年   32篇
  2019年   43篇
  2018年   42篇
  2017年   51篇
  2016年   60篇
  2015年   43篇
  2014年   100篇
  2013年   141篇
  2012年   109篇
  2011年   95篇
  2010年   83篇
  2009年   64篇
  2008年   97篇
  2007年   80篇
  2006年   81篇
  2005年   53篇
  2004年   62篇
  2003年   49篇
  2002年   41篇
  2001年   19篇
  2000年   19篇
  1999年   19篇
  1998年   7篇
  1997年   6篇
  1996年   9篇
  1995年   9篇
  1994年   8篇
  1993年   7篇
  1992年   9篇
  1991年   7篇
  1990年   5篇
  1989年   11篇
  1988年   8篇
  1987年   7篇
  1986年   3篇
  1985年   7篇
  1984年   7篇
  1983年   5篇
  1982年   15篇
  1981年   1篇
  1980年   7篇
  1979年   4篇
  1978年   3篇
  1976年   1篇
  1973年   1篇
  1972年   1篇
排序方式: 共有1611条查询结果,搜索用时 15 毫秒
51.
52.
Tracking signals are used to determine whether a sequence of forecasts is unbiased. We analyse a version of the CUSUM tracking signal that is based on the unsmoothed average mean absolute deviation of forecasting errors. We make the common assumption that demand values in different periods are independently, identically, and normally distributed. We show that, when forecast errors in different periods are also normal iid, this version of the tracking signal can indicate that the sequence is not unbiased even when it is unbiased. We suggest a simple modification to the tracking signal that serves to eliminate this flaw.  相似文献   
53.
Lead scandium phosphate glasses (PbO-Sc2O3-P2O5) containing different concentrations of tungsten oxide (WO3) ranging from 0 to 5 mol% were prepared. A number of studies, viz. differential thermal analysis (DTA), infrared spectra, optical absorption, and electron spin resonance (ESR) spectra, have been carried out. The results of DTA indicated the highest glass forming ability for the glass containing 5 mol% of WO3. The results of spectroscopic studies have been analyzed in light of different oxidation states of tungsten ions.  相似文献   
54.
55.
Quantitation of drugs used for the treatment of chronic lymphocytic leukemia in various biological matrices during both pre-clinical and clinical developments is very important, often in routine therapeutic drug monitoring. The first developed methods for quantitation were traditionally done on LC in combination with either UV or fluorescence detection. However, the emergence of LC with mass spectrometry in tandem in early 1990s has revolutionized the quantitation as it has provided better sensitivity and selectivity within a shorter run time; therefore it has become the choice of method for the analysis of various drugs. In this article, an overview of various bioanalytical methods (HPLC or LC–MS/MS) for the quantification of drugs for the treatment of chronic lymphocytic leukemia, along with applicability of these methods, is given.  相似文献   
56.
Three new metal complexes [Cu(L)2] (1), [Co(L)2] (2) and [Zn(L)2] (3) have been prepared by the reaction of hydrated salts of metal (II) acetate with new Schiff base ligand HL, [2‐((4‐(dimethylamino)phenylimino)methyl)‐4,6‐di‐t‐butylphenol] and characterized by different physico‐chemical analyses such as elemental analysis, single XRD, 1H NMR, FTIR and UV–Vis spectroscopic techniques. Their biomolecular docking, antimicrobial and cytotoxicity studies have also been demonstrated. The proposed structure of Schiff base ligand HL and complex 2 are confirmed by Single crystal X‐ray crystallography study. This analysis revealed that metal (II) complexes remain in distorted tetrahedral coordination environments. The electronic properties such as HOMO and LUMO energies are carried out by gaseous phase DFT/B3LYP calculations using Gaussian 09 program. Complex 1 showed a good binding propensity to the DNA and HSA, during the assessment of docking studies. Schiff base ligand HL and its metal (II) complexes, 1–3 screened for their in vitro antimicrobial activities using the disc diffusion method against selected microbes. Complex 1 shows higher antimicrobial activity than complexes 2, 3 and Schiff base ligand HL. According to the results obtained from the cytotoxic studies, Schiff base ligand HL and its metal (II) complexes 1–3 have better cytotoxicity against MCF‐7 cell lines with potency higher than the currently used chemotherapeutic agent cyclophosphamide.  相似文献   
57.
This paper investigates the existence of positive solutions for a sixth-order differential system with three variable parameters. Using a fixed point theorem and an operator spectral theorem we give some new existence results.  相似文献   
58.
Research on Chemical Intermediates - Eight new series of novel phenothiazine-based chalcone derivatives with various N-substituted rhodanines (10a–g to 17a–g) were synthesized by...  相似文献   
59.
An enantiospecific first total synthesis of metabolite 7a(S)-p-hydroxyphenopyrrozin 2, isolated from the cultured fungi Chromocleista sp. has been achieved starting from readily and abundantly available l-proline. The strategy of synthesis utilizes base mediated cyclization and base mediated oxygenation as the key steps.  相似文献   
60.
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