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   2447篇
  免费   39篇
  国内免费   4篇
电工技术   27篇
化学工业   322篇
金属工艺   27篇
机械仪表   54篇
建筑科学   109篇
矿业工程   5篇
能源动力   39篇
轻工业   121篇
水利工程   18篇
石油天然气   6篇
无线电   195篇
一般工业技术   317篇
冶金工业   974篇
原子能技术   11篇
自动化技术   265篇
  2021年   18篇
  2020年   22篇
  2019年   19篇
  2018年   24篇
  2017年   24篇
  2016年   26篇
  2015年   22篇
  2014年   34篇
  2013年   107篇
  2012年   61篇
  2011年   81篇
  2010年   67篇
  2009年   53篇
  2008年   72篇
  2007年   70篇
  2006年   59篇
  2005年   46篇
  2004年   58篇
  2003年   58篇
  2002年   44篇
  2001年   48篇
  2000年   38篇
  1999年   54篇
  1998年   127篇
  1997年   111篇
  1996年   72篇
  1995年   69篇
  1994年   55篇
  1993年   52篇
  1992年   41篇
  1990年   44篇
  1989年   25篇
  1988年   37篇
  1987年   30篇
  1986年   28篇
  1985年   35篇
  1984年   44篇
  1983年   44篇
  1982年   40篇
  1981年   44篇
  1980年   20篇
  1979年   31篇
  1978年   24篇
  1977年   20篇
  1976年   41篇
  1975年   29篇
  1974年   29篇
  1973年   27篇
  1972年   26篇
  1970年   22篇
排序方式: 共有2490条查询结果,搜索用时 15 毫秒
131.
Generalized procedures are discussed for the accurate calculation of thermodynamic properties of nonpolar and polar fluids and mixtures. It is shown that the concepts of van der Waals for simple fluids can be extended to complex substances, and that the properties of a wide range of fluids can be calculated from a sufficient number of macroscopic parameters defined through the vapor pressure.  相似文献   
132.
The twist in carpet yarns of suitable construction can be adequately set by a continuous treatment with sodium bisulphite in a tape–scouring machine. Different levels of set can be produced by varying the conditions: increasing the bisulphite concentration, the pH of the solution, the dwell time, and the bath temperature all improve the set. Improvements in the colour of the yarn and changes in pH are produced. While the yarn strength and extensibility decrease, the changes are comparable with those produced by the autoclave and water–setting treatments examined. Adverse changes in carpet abrasion resistance may occur when concentrations in excess of 10g/l are used. Bisulphite setting has been found to be more suitable for yarns to be jet–printed than setting in an autoclave or by hot water.  相似文献   
133.
Conditions were investigated to determine the optimum processing parameters for preparation of a protein isolate from the ground, dehulled lupin seeds of Lupinus angustifolius. The extraction variables were: particle size (16–100 mesh); pH (2–11); extraction medium; solvent to lupin ratio (10:1 to 40:1); temperature (20–60oC) and time (15–60 min). The isoelectric point of the lupin protein was found to be pH 4.5 with a protein solubility of greater than 90% above pH 8.0. Using 60–100 mesh ground lupin and extracting at pH 8.5 for 30 min, a protein isolate was obtained on acidification to pH 4.8 which was 89.4% protein compared to 34.0% protein for the original dehulled lupin. This protein isolate represented 19.8% of the starting material and 52% of the starting nitrogen. Similar results were also obtained when hexane defatted lupin was used. In this case the protein isolate had a protein content of 92.5%. The yield of protein isolate could be increased to 25.7% of the starting material if the extraction was repeated. The protein efficiency ratio for the protein isolate was 2.90 when supplemented with methionine.  相似文献   
134.
This paper outlines a computer program especially tailored to the task of deriving explicit equations of motion for structures with point-connected substructures. The special purpose program is written in FORTRAN and is designed for performing the specific algebraic operations encountered in the derivation of explicit equations of motion. The derivation is by the Lagrangian approach. Using an orderly kinematical procedure and a discretization and/or truncation scheme, it is possible to write the kinetic and potential energy of each substructure in a compact vector-matrix form. Then, if each element of the matrices and vectors encountered in the kinetic and potential energy is a known algebraic expression, the computer program performs the necessary operations to evaluate the kinetic and potential energy of the system explicitly. Lagrange's equations for small motions about equilibrium can be deduced directly from the explicit form of the system kinetic and potential energy.  相似文献   
135.
The purpose of this work is to examine the basic foundations, similarities and fundamental differences between the finite element methods (FEM) and the lumped parameter methods (LPM) of analysis for oceanic cables under hydrodynamic load conditions. The continuum method (CM) is presented as a ‘ground truth’ prior to presenting each aspect of the approximate method derivations.  相似文献   
136.
137.
The Rigby-Bethune rapid methods for determining bitterness in beer are compared with Moltke-Meilgaard measurements. A new assay is presented which is suitable for the determination of bitterness in beers flavoured with isohumulone concentrates.  相似文献   
138.
This paper describes a system for structure from motion using vanishing points and three-dimensional lines extracted from omni-directional video sequences. To track lines, we use a novel dynamic programming approach to improve ambiguity resolution, and we use delayed states to aid in the initialization of landmarks. By reobserving vanishing points we get direct measurements of the robots three-dimensional attitude that are independent of its position. Using vanishing points simplifies the representation since parallel lines share the same direction states. We show the performance of the system in various indoor and outdoor environments and include comparisons with independent two-dimensional reference maps for each experiment .  相似文献   
139.
A dynamical model for generating synthetic electrocardiogram signals   总被引:14,自引:0,他引:14  
A dynamical model based on three coupled ordinary differential equations is introduced which is capable of generating realistic synthetic electrocardiogram (ECG) signals. The operator can specify the mean and standard deviation of the heart rate, the morphology of the PQRST cycle, and the power spectrum of the RR tachogram. In particular, both respiratory sinus arrhythmia at the high frequencies (HFs) and Mayer waves at the low frequencies (LFs) together with the LF/HF ratio are incorporated in the model. Much of the beat-to-beat variation in morphology and timing of the human ECG, including QT dispersion and R-peak amplitude modulation are shown to result. This model may be employed to assess biomedical signal processing techniques which are used to compute clinical statistics from the ECG.  相似文献   
140.
The molecular formulas for the structures and substructures of muraymycin antibiotics A1 (C52H90N14O19, MW 1214) and B1 (C49H83N11O18, MW 1113) were determined using electrospray ionization (ESI) Fourier transform mass spectrometry (FTMS). The muraymycin A1 and B1 structures were elucidated by utilizing capillary-skimmer fragmentation with up to five stages of mass spectrometry (MS5). Multi-CHEF, a multiple ion isolation method, was used at each stage of MS(n) to isolate a parent ion and up to four reference ions, for exact-mass calibration. The parent ions were fragmented by SORI-CID and the product ions internally calibrated with average absolute mass errors less than 1 ppm at each stage in the fragmentation processes. Using the top-down/bottom-up approach, the molecular formulas for the antibiotics were determined by summing the elemental formulas of the neutral losses, obtained by measuring the mass differences (<500 Da) between the genetically related sequential parent ion masses in the MS(n) spectra, with the unique elemental formula of the lowest parent ion mass (<500 Da). The structures of 12 additional compounds in the muraymycin complex were elucidated using HPLC ESI capillary-skimmer CID FTMS by correlating their fragmentation patterns with those of muraymycins A1 and B1. Sequential neutral losses of an aminosugar, a valine, a uridine, and an ester fatty acid from the muraymycin parent ions provided diagnostic fragments for characterization.  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