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   6668篇
  免费   816篇
  国内免费   192篇
化学   1016篇
晶体学   29篇
力学   117篇
综合类   104篇
数学   553篇
物理学   1384篇
无线电   4473篇
  2024年   9篇
  2023年   84篇
  2022年   236篇
  2021年   266篇
  2020年   215篇
  2019年   145篇
  2018年   137篇
  2017年   257篇
  2016年   278篇
  2015年   268篇
  2014年   490篇
  2013年   409篇
  2012年   504篇
  2011年   505篇
  2010年   303篇
  2009年   381篇
  2008年   398篇
  2007年   409篇
  2006年   379篇
  2005年   372篇
  2004年   287篇
  2003年   267篇
  2002年   202篇
  2001年   173篇
  2000年   110篇
  1999年   113篇
  1998年   70篇
  1997年   77篇
  1996年   87篇
  1995年   56篇
  1994年   43篇
  1993年   35篇
  1992年   25篇
  1991年   15篇
  1990年   13篇
  1989年   10篇
  1988年   7篇
  1987年   17篇
  1985年   7篇
  1984年   2篇
  1983年   4篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1975年   1篇
  1971年   1篇
  1959年   1篇
排序方式: 共有7676条查询结果,搜索用时 265 毫秒
101.
王永仲 《应用光学》1993,14(5):22-24,21
描述不共轴光学系统计算机优化中坐标变换与逆变换、“入瞳”与光线坐标、像面基准与质量函数定义的一致性问题。  相似文献   
102.
计算机专用实时母系统在VAX/VMS环境下的实现   总被引:3,自引:1,他引:2  
“母系统—子系统”的工作方式是计算机专用实时系统研制中的一次重要尝试,本文闸明计算机专用实时母系统在VAX/VMS环境下的工程实现。  相似文献   
103.
A less labour-intensive method, involving a mixture of 1.0 g MnO2 + 20 mL HCl (11), is proposed for decomposing seven ores and six metallurgical products for accurate and precise estimation of copper, lead, zinc, cobalt and nickel for quality control assessment. Twentyone international reference materials were also analysed. Results of regression analyses are presented and intermethod comparison studies reveal that the probability of results being different compared with a reference method was less than 1%. Sample decomposition is straightforward and the method has been found to be very simple, rapid and easily adaptable, as it involves no separation of the analyte from the matrix elements.  相似文献   
104.
In scientific research laboratories it is rarely possible to use quality assurance schemes, developed for large-scale analysis. Instead methods have been developed to control the quality of modest numbers of analytical results by relying on statistical control: Analysis of precision serves to detect analytical errors by comparing thea priori precision of the analytical results with the actual variability observed among replicates or duplicates. The method relies on the chi-square distribution to detect excess variability and is quite sensitive even for 5–10 results. Interference control serves to detect analytical bias by comparing results obtained by two different analytical methods, each relying on a different detection principle and therefore exhibiting different influence from matrix elements; only 5–10 sets of results are required to establish whether a regression line passes through the origo. Calibration control is an essential link in the traceability of results. Only one or two samples of pure solid or aqueous standards with accurately known content need to be analyzed. Verification is carried out by analyzing certified reference materials from BCR, NIST, or others; their limited accuracy of 5–10% make them less suitable for calibration purposes.  相似文献   
105.
A discrete method of optimal control is proposed in this paper. The continuum state space of a system is discretized into a cell state space, and the cost function is discretized in a similar manner. Assuming intervalwise constant controls and using a finite set of admissible control levels (u) and a finite set of admissible time intervals (), the motion of the system under all possible interval controls (u, ) can then be expressed in terms of a family of cell-to-cell mappings. The proposed method extracts the optimal control results from these mappings by a systematic search, culminating in the construction of a discrete optimal control table.The possibility of expressing the optimal control results in the form of a control table seems to give this method a means to make systems real-time controllable.Dedicated to G. LeitmannThe material is based upon work supported by the National Science Foundation under Grant No. MEA-82-17471. The author is also indebted to Professor G. Leitmann for his many helpful comments.  相似文献   
106.
高效液相色谱指纹图谱应用于地黄的研究   总被引:7,自引:0,他引:7  
曾志  杨东晖  宋力飞  杨挺  刘乡乡  袁敏  曾和平 《分析化学》2003,31(12):1485-1488
利用高效液相色谱建立了地黄的色谱指纹图谱。采用反相C1 8柱 (5 μm ,1 5 0mm× 4.6mm) ,流动相甲醇∶水 (V V =5∶95 ) ,检测波长为 2 80nm ,流速 1 .0mL min进行实验。根据相对保留值和相对面积值对色谱指纹图谱进行分析对比研究 ,建立了控制地黄药材质量的新方法。该法为中药样品的鉴定提供了较全面的信息 ,并为HPLC在复杂组分的样品分析领域开拓了新的应用途径。  相似文献   
107.
 Four inter-comparison exercises on organic elemental analysis were carried out between 1997 and 2001 by the Department of Analytical Chemistry of the University of Barcelona, together with the Microanalysis Service and the Institute of the Marine Sciences, which both belong to the CSIC in Barcelona, and the University of A Coru?a. More than sixty laboratories participated in these exercises. Here we describe the design and characteristics of the trials, the samples and the homogeneity tests applied. We report the results obtained for the analysis of carbon, hydrogen, nitrogen, sulphur and oxygen, their statistical analysis, and the most relevant aspects of the technical discussion meetings. Received December 20, 2001; accepted March 18, 2002; published online July 22, 2002  相似文献   
108.
宋冠群  林金明  屈锋  董文举 《中国化学》2003,21(10):1325-1329
IntroductionTeaisthemostwidelyconsumedbeverageinpeople’slife .Theheightenedpopularityofthisbeveragethroughouttheworldinrecentyearsmaybedueinparttotheevidenceofarelationshipbetweenteaconsumptionandpreventionofcertainformsofhumandisease .Themaincomponentsofteaarepolyphenoliccompounds ,commonlyknownascatechins ,whichrepresentagroupofcom poundsbelongingtotheflavonoidfamily .Thesecom poundsarewidelydistributedinthetealeavesandconsti tuteupto 30 %ofthedryleafweight.1Muchinteresthasbeenfocusedoncat…  相似文献   
109.
The development of theoretical tools for the study of dynamical phenomena of many-particle systems on the quantum level is a fundamental challenge since many decades. A lot of efforts have been invested on Feynman's path integral approach, however, no computationally tractable method for investigating realistic systems could be developed up to now. In this paper we propose an alternative representation of the real-time many-body evolution operator formulated within the framework of the auxiliary field formalism. Our goal is to derive a new auxiliary field functional integral representation, in which the large oscillations of the functional integrand are reduced, in order to render the auxiliary field approach more attractive for real-time computation. This objective is attained using a generalized version of the method of Gaussian equivalent representation of Efimov and Ganbold [Phys. Stat. Sol. 168 (1991) 165], which eliminates the low-order fluctuations of the auxiliary field from the interaction functional.  相似文献   
110.
In this paper, superhigh reproductive rate strains of MEV with titre more than HA8192* or TCID50 log9.7 10 have been achieved both by cultivation in cell lines with different susceptibility to MEV and by isolating and identifying in field by the author. The systematic tests proved that S18 and L12 strains of MEV are the best strains for vaccine preparation. In this study, the best means for the tissue cultivation of MEV and the most advanced technological process for the production and detection of serum-free cell-cultured MEV fluids with super-high HA titre in batches in large quantities have been established for the first time. Optimum conditions for MEV inactivation were determined, and safe and effective inactivated vaccines with mineral oil or A1(OH)3 gel adjuvant were successfully prepared with serum-free cell-cultured MEV fluids. Both vaccines with different adjuvants can be manufactured in batches in large quantities and have been widely used all over China since 1986. The change laws of the imm  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