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   3183篇
  免费   320篇
  国内免费   110篇
化学   829篇
晶体学   1篇
力学   180篇
综合类   109篇
数学   1602篇
物理学   892篇
  2024年   14篇
  2023年   33篇
  2022年   143篇
  2021年   127篇
  2020年   90篇
  2019年   83篇
  2018年   82篇
  2017年   157篇
  2016年   169篇
  2015年   92篇
  2014年   225篇
  2013年   186篇
  2012年   196篇
  2011年   213篇
  2010年   151篇
  2009年   160篇
  2008年   176篇
  2007年   172篇
  2006年   164篇
  2005年   168篇
  2004年   140篇
  2003年   100篇
  2002年   83篇
  2001年   60篇
  2000年   48篇
  1999年   41篇
  1998年   49篇
  1997年   51篇
  1996年   30篇
  1995年   27篇
  1994年   24篇
  1993年   23篇
  1992年   11篇
  1991年   20篇
  1990年   9篇
  1989年   11篇
  1988年   9篇
  1987年   9篇
  1986年   6篇
  1985年   8篇
  1984年   5篇
  1982年   7篇
  1981年   13篇
  1980年   6篇
  1979年   6篇
  1978年   4篇
  1977年   4篇
  1976年   2篇
  1972年   2篇
  1959年   1篇
排序方式: 共有3613条查询结果,搜索用时 15 毫秒
71.
In this study, a fingerprint-activity relationship modeling between chemical fingerprints and antirheumatic activity was established, and multivariate statistical analysis was used to evaluate the quality of Taxilli Herba (TH) from different hosts. Characteristic fingerprints of 20 batches of TH samples were generated by high-performance liquid chromatography coupled with triple quadrupole-time of flight tandem mass spectrometry (HPLC-Triple TOF-MS/MS), and the similarity analysis was calculated based on thirteen common characteristic peaks by hierarchical clustering analysis (HCA). Subsequently, nine efficacy markers were discovered by combining fingerprints and antirheumatic activity through grey correlation analysis (GCA) and bivariate correlation analysis (BCA). Meanwhile, the content of 5 constituents in 9 markers was determined by high-performance liquid chromatography coupled with triple quadrupole-linear ion trap tandem mass spectrometry (HPLC-QTRAP-MS/MS). The comprehensive quality of TH was assessed using multivariate statistical analysis, including principal components analysis (PCA) and technique for order preference by similarity to ideal solution (TOPSIS). The results showed that a high dose of TH extract could markedly ameliorate arthritis damage compared to other doses, with flavonoids playing an important role in the antirheumatic activity. The comprehensive quality of samples from Morus alba L. (SS) was superior to those from Liquidambar formosana Hance (FXS). The present study will demonstrate the markers associated with efficacy, and provide an applicable strategy for more comprehensive quality control and evaluation of TH.  相似文献   
72.
It follows from an analysis of the error levels of TG evaluation methods that it is a conceptual error to disregard the analogies of mass, energy and momentum streams of subordinate partial processes. This error is bypassed by means of the introduced method of dimensionless analysis and by determining the characteristic, constants-like data of thermal processes by using the measured data directly. These methods are very suitable for increasing the consistency of the calculated results by seeking for similarity, even in comparisons of measurements made under very different conditions and for emphasizing the differences too, quantitatively. With this new interpretation of TG processes, the idea of the kinetic compensation effect becomes only a consequence of the discussed conceptual error. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
73.
GC headspace analyses of various aromatizing herbs have been compared with those relating to the essential oils, obtained by steam distillation, of the same plants. In this way it was possible to establish the most significant differences between the composition of a herb flavor and that of its essential oil. In particular, we observed some very volatile compounds in the headspace samples which were absent from the essential oil; these components may make an important contribution to the herb flavor. The identification of these substances is still in progress.  相似文献   
74.
The properties of fluctuations in space in or outside thermal equilibrium are obtained by solving hierarchies of equations derived either from the Liouville or the Master equation. In particular we study the one-, two-, etc., time correlation functions that describe the spatial and temporal behavior of the fluctuations in space. Explicit solutions are obtained for a dilute gas. The Langevin approach is briefly discussed. Our results are compared with those obtained in the extensive literature, which is reviewed in some detail.  相似文献   
75.
《Analytical letters》2012,45(15):2109-2124
Selective and efficient analytical methods for authentication and quality evaluation of herbal medicines are significant and necessary. An expeditious method combining multi-components determination and fingerprinting based on ultra-performance liquid chromatography-photo diode array-tandem mass spectrometry (UPLC-PDA -MS/MS) and chemometrics for authentication and quality evaluation of Cornus Officinalis Sieb. et Zucc was developed. Tandem mass spectrometer operating in multiple reaction monitoring (MRM) was used for determination of three characteristic constituents (morroniside, sweroside, and loganin) in C. Officinalis. Meanwhile, UPLC fingerprint of C. Officinalis was established and the data set was submitted for classification to a suite of chemometrics method. Combing main biologically active components content level and chemometrics analysis, the effects of cultivation area, harvesting, and storage time on the quality of C. Officinalis were investigated. The study reveals that multi-components determination coupled with fingerprinting could be applied for authentication and quality evaluation of C. Officinalis which is accurate, efficient, and reliable.  相似文献   
76.
The purpose of this paper is to design a new extension of the ELECTRE, known as the elimination and choice translating reality method, for multi-criteria group decision-making problems based on intuitionistic fuzzy sets. This method is widely utilized when a set of alternatives should be identified and evaluated with respect to a set of conflicting criteria by reflecting decision makers’ (DMs’) preferences. However, handling the exact data and numerical measure is difficult to be precisely focused because the DMs’ judgments are often vague in real-life decision problems and applications. A more realistic and practical approach can be to use linguistic variables expressed in intuitionistic fuzzy numbers instead of numerical data to model DMs’ judgments and to describe the inputs in the ELECTRE method. The proposed intuitionsitic fuzzy ELECTRE utilizes the truth-membership function and non-truth-membership function to indicate the degrees of satisfiability and non-satisfiability of each alternative with respect to each criterion and the relative importance of each criterion, respectively. Then, a new discordance intuitionistic index is introduced, which is extended from the concept of the fuzzy distance measure. Outranking relations are defined by pairwise comparisons and a decision graph is depicted to determine which alternative is preferable, incomparable or indifferent in the intuitionistic fuzzy environment. Finally, a comprehensive sensitivity analysis is employed to further study regarding the impact of threshold values on the final evaluation, and a comparative analysis is demonstrated with an application example in flexible manufacturing systems between the proposed ELECTRE method and the existing intuitionistic fuzzy technique for order preference by similarity to ideal solution (IF-TOPSIS) method.  相似文献   
77.
A method employing ultra‐high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) for determination of eight components including ferulic acid, senkyunolide A, butylphthalide, ligustilide, butylidenephalide, senkyunolide I, senkyunolide H and levistolide A in Angelica sinensis was established. The separation was carried out using a Waters ACQUITY UHPLC BEH C18 column with gradient elution with 0.1% formic acid aqueous and acetonitrile at a flow rate of 0.4 mL/min. Good linearity was attained with R2 of 0.9983–0.9998 in wide concentration ranges. The method had limit of detection (LOD) and quantitation (LOQ) in the range of 0.42–6.98 ng/mL and 1.39–23.28 ng/mL, respectively. Intra‐ and inter‐day precisions varied with relative standard deviations (RSDs) from 0.33% to 0.88% and 0.37% to 1.04%, respectively. Moreover, the average recoveries were in a satisfactory range of 92.7%–102.1% with RSDs of less than 3.60%. Finally, the method was successfully applied to analyze 19 batches of A. sinensis samples grown in Min County, Gansu province, China, as well as that collected in other regions. The findings indicated that the established method is reliable and may thus be applied as a powerful tool for qualitative and quantitative analysis of components in A. sinensis, which has its implications in quality control of A. sinensis.  相似文献   
78.
The combined use of digital holographic microscopy and computer tomography, here named digital holographic micro-tomography, is used to examine the interior of transparent channels. The proposed method is used to identify internal obstacles inside of transparent troughs having slightly different refractive index. The method is based in the acquisition of a set of digital holograms of the specimen whereas it is axially rotated from 0° to 180°. The phase differences retrieved from the obtained holograms are the inputs to a computerised axial tomography procedure. The technique has been numerically modelled in order to find the optimal tomographic conditions and also to realise the minimum difference of refractive index the method could detect. The obtained results show the feasibility of the proposed method for the non-destructive evaluation of transparent micro-objects.  相似文献   
79.
针对Vague集评价过程中信息容易遗失的问题,提出采用Vague综合评价的思想进行计算.通过定义Vague基本运算法则,以及建立加权综合评价函数构建了新的评价方法.方法体现了Vague集理论描述不确定性问题的优点,反映了项目经理评价的一般特点.最后,通过案例计算,得到了公平公正的评价结果,并验证了计算结果的可靠性.  相似文献   
80.
A regular gradient-holonomic approach to studying the Lax type integrability of the Ablowitz–Ladik hierarchy of nonlinear Lax type integrable discrete dynamical systems in the vertex operator representation is presented. The relationship to the Lie-algebraic integrability scheme is analyzed and the connection with the τ-function representation is discussed.  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