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   32763篇
  免费   1698篇
  国内免费   26篇
电工技术   166篇
综合类   10篇
化学工业   5582篇
金属工艺   420篇
机械仪表   556篇
建筑科学   811篇
矿业工程   52篇
能源动力   507篇
轻工业   5459篇
水利工程   308篇
石油天然气   122篇
武器工业   1篇
无线电   1042篇
一般工业技术   4315篇
冶金工业   11519篇
原子能技术   65篇
自动化技术   3552篇
  2024年   66篇
  2023年   277篇
  2022年   271篇
  2021年   715篇
  2020年   655篇
  2019年   670篇
  2018年   1235篇
  2017年   1206篇
  2016年   1256篇
  2015年   964篇
  2014年   1105篇
  2013年   2296篇
  2012年   1758篇
  2011年   1552篇
  2010年   1266篇
  2009年   1082篇
  2008年   1145篇
  2007年   1049篇
  2006年   665篇
  2005年   560篇
  2004年   537篇
  2003年   504篇
  2002年   429篇
  2001年   323篇
  2000年   259篇
  1999年   481篇
  1998年   3837篇
  1997年   2275篇
  1996年   1425篇
  1995年   754篇
  1994年   616篇
  1993年   690篇
  1992年   127篇
  1991年   166篇
  1990年   128篇
  1989年   136篇
  1988年   157篇
  1987年   157篇
  1986年   133篇
  1985年   140篇
  1984年   64篇
  1983年   46篇
  1982年   70篇
  1981年   104篇
  1980年   97篇
  1978年   47篇
  1977年   261篇
  1976年   519篇
  1975年   46篇
  1973年   38篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
Assessing obesity: classification and epidemiology   总被引:1,自引:0,他引:1  
Obesity is generally defined as a body mass index (BMI) of 30 kg/m2 and higher. Overweight is defined as a BMI between 25 and 30 kg/m2. The prevalence varies considerably between countries, and between regions within countries. It is estimated that more than half of adults aged 35-65 living in Europe are either overweight or obese. Overweight is more common among men than among women but obesity is more common among women. The prevalence of obesity in Europe is probably in the order of 10-20% in men and 15-25% in adult women. In most European countries who have reliable data on time-trends the prevalence of obesity seems to be increasing. In most European countries, obesity is usually inversely associated with socio-economic status, particularly among women. New classifications of overweight may be based on cut-off points for simple anthropometric measures which reflects both total adiposity as well as abdominal fatness.  相似文献   
62.
63.
Distributed and Parallel Databases - Given two datasets of points (called Query and Training), the Group (K) Nearest-Neighbor (GKNN) query retrieves (K) points of the Training with the smallest sum...  相似文献   
64.
Software Quality Journal - Energy consumption of software has been becoming increasingly significant, since it can vary according to how the software has been developed. In recent years, developers...  相似文献   
65.
The different groups and/or classes among phenolic acids and aldehydes identified during the elaboration process of "fino" sherry wine have been studied. The study was carried out using different processes during the elaboration of the wine and we have attempted to establish whether the different treatments of the grape affect these groupings. The study was undertaken by means of cluster and multifactorial analysis on the data obtained by the quantitative determination of phenolic acids and aldehydes during vinification and in experiments carried out on the grape under different mechanical treatments. The analysis of phenolic acids and aldehydes was done with HPLC, using a C-18 mu-Bondapak and a stepwise composite gradient. The samples were previously extracted with ethylic ether.  相似文献   
66.
J. M. Martínez 《Computing》1987,39(4):307-325
We introduce a new method for solving Nonlinear Least Squares problems when the Jacobian matrix of the system is large and sparse. The main features of the new method are the following:
  1. The Gauss-Newton equation is “partially” solved at each iteration using a preconditioned Conjugate Gradient algorithm.
  2. The new point is obtained using a two-dimensional trust region scheme, similar to the one introduced by Bulteau and Vial.
We prove global and local convergence results and we present some numerical experiments.  相似文献   
67.
The conditions for current oscillations in austenitic stainless steel (AISI Type 303) in 1M H2SO4 containing Cl? ions are given. The periodic oscillations are produced in a close potential range determined at the active-passive transition region. It requires a non-homogeneous distribution of inclusions and carbides at the metal surface and a concentration range of Cl? ion where active and passive areas coexist on the metal surface. The constraints at the surface determining these two regions are related to the Cl? ion competitive adsorption and the local accumulation of corrosion products. Electrochemical data and SEM observations are correlated.  相似文献   
68.
Hydrotalcites in the nitrate form were prepared using microwave irradiation in the hydrotreatment step. The surface area (BET) of nitrated hydrotalcites was evaluated. Solids were characterized by atomic absorption, X-ray diffraction and BET analysis. Thermal pretreatment temperature determined the surface area of the hydrotalcites.  相似文献   
69.
The present work analyzes the effect of various factors on the hydration of pentasodium triphosphate. The experimental method is based on application of the hydration test. Technical-quality products with different proportions of phase I and phase II have been used. The variables studied are phase I/phase II ratio, initial temperature, particle size, stirring rate and composition of the slurry (presence of hexahydrate crystals and water hardness). The results have been discussed according to a kinetics model that includes a series of stages of a physical nature (dissolution of anhydrous salt and the crystallization of the hexahydrate), as well as of a chemical nature (solvation of the ions in solution). Crystallization of the hexahydrate may be the controlling stage in the process.  相似文献   
70.
The functional properties of Caryodendron orinocense protein product were investigated and compared with those of soybean (Glycina maxima). The product protein content was 24.47 g/100 g (Nx6.25). Solubility increased at both sides of the isoelectric point (pH 4.0) and with increased NaCl concentration up to 0.5M. Compared with soybean flour (50% protein), the protein product exhibited higher water and oil absorption, but lower emulsifying activity, emulsion stability, foaming capacity, and foam stability, the last one increase at higher pH. Emulsifying activity, foaming capacity, and foam stability were ionic strength dependent. C. orinocense protein product increased its emulsifying activity steadily from 0.05M to 0.75M NaCl, while it remained almost constant for soybean flour. Foaming capacity increased drastically at pH 10. The minimum time and concentration to form a gel was 20% in 4 min and 10% in 8 min for the Caryodendron protein product and soybean flour, respectively. The bulk density was 0.5056+/-0.0041 g/mL.  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