全文获取类型
收费全文 | 117792篇 |
免费 | 19137篇 |
国内免费 | 3974篇 |
专业分类
电工技术 | 5745篇 |
技术理论 | 4篇 |
综合类 | 5337篇 |
化学工业 | 29342篇 |
金属工艺 | 5125篇 |
机械仪表 | 6238篇 |
建筑科学 | 7408篇 |
矿业工程 | 1920篇 |
能源动力 | 3289篇 |
轻工业 | 12527篇 |
水利工程 | 1775篇 |
石油天然气 | 3648篇 |
武器工业 | 597篇 |
无线电 | 16484篇 |
一般工业技术 | 21439篇 |
冶金工业 | 4283篇 |
原子能技术 | 953篇 |
自动化技术 | 14789篇 |
出版年
2024年 | 342篇 |
2023年 | 1336篇 |
2022年 | 2437篇 |
2021年 | 3626篇 |
2020年 | 3772篇 |
2019年 | 5046篇 |
2018年 | 5246篇 |
2017年 | 5685篇 |
2016年 | 6121篇 |
2015年 | 6959篇 |
2014年 | 7577篇 |
2013年 | 9601篇 |
2012年 | 7773篇 |
2011年 | 7997篇 |
2010年 | 7648篇 |
2009年 | 7192篇 |
2008年 | 6681篇 |
2007年 | 6076篇 |
2006年 | 5785篇 |
2005年 | 4929篇 |
2004年 | 4000篇 |
2003年 | 3845篇 |
2002年 | 4058篇 |
2001年 | 3422篇 |
2000年 | 3001篇 |
1999年 | 2212篇 |
1998年 | 1571篇 |
1997年 | 1309篇 |
1996年 | 1158篇 |
1995年 | 976篇 |
1994年 | 827篇 |
1993年 | 603篇 |
1992年 | 448篇 |
1991年 | 357篇 |
1990年 | 274篇 |
1989年 | 222篇 |
1988年 | 189篇 |
1987年 | 116篇 |
1986年 | 100篇 |
1985年 | 72篇 |
1984年 | 54篇 |
1983年 | 34篇 |
1982年 | 34篇 |
1981年 | 42篇 |
1980年 | 35篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 20篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
动态评价技术在塔河碳酸盐岩缝洞型油气藏中的应用 总被引:5,自引:2,他引:3
塔河油田奥陶系油气藏是大型碳酸盐岩溶洞型油气藏,其储渗空间主要为大小不同的溶洞、裂缝带、溶蚀孔隙等组成,该油气藏具有极强的非均质性,单纯用静态资料来认识这类油气藏是非常困难。文章提出利用生产动态资料和信息进行该类型油气藏研究的新思路,利用人工神经网络技术在处理非线性相关参数预测方面的优势,并以渗流理论为基础,结合试井成果,选用已知油井的产量、油嘴、油压、含水率、气油比、原油密度等6个开发动态参数作为样品输入数据,推导出影响油气藏开发的重要参数(地层系数)与生产信息的关系,建立了人工神经网络预测储层参数的结构模型。通过塔里木盆地塔河油气田实例研究,说明了利用动态信息评价油气藏技术在碳酸盐岩缝洞型油气藏储层预测和非均质性分析等方面具有较高的实用价值。 相似文献
3.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
4.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
5.
6.
Effect of modified atmosphere packaging on the shelf-life of coated, whole and sliced mushrooms 总被引:2,自引:0,他引:2
Whole and sliced fresh mushrooms (Agaricus bisporus) were packaged with PVC wrap or two polyolefins (PD-941 and PD-961) films after coating with CaCl2 and chitosan. Package gas composition, color, weight loss and maturity were measured during storage at 12 °C and 80%RH. For PD-961, the highest in-package concentration occurred during the first day of storage regardless of treatments, while wrap and PD-941 showed varying degrees in-package concentration with different processes and coatings. The whiteness of whole mushrooms varied significantly with the type of coating, but not with the type of films. The extent of darkening was greater in coated whole mushrooms than in sliced ones. Weight loss occurred in all packages and varied from 3 (g/100 g) to about 7 (g/100 g) after 6 days of storage. Due to a lower permeability, PD-961 packages had the lowest weight loss. The type of packaging films significantly affected the maturity index, where PD-961 most effectively lowered maturity index for both whole and sliced mushrooms, thus extending the shelf-life. The type of coating did not appear to affect maturity index except for the wrap package where chitosan coating markedly lowered the maturity index of sliced mushrooms. 相似文献
7.
A new excimer laser annealing (ELA) process that uses a floating amorphous-Silicon (a-Si) thin film with a multichannel structure is proposed for high-performance poly-Si thin-film transistors (TFTs). The proposed ELA method produces two-dimensional (2-D) grain growth, which can result in a high-quality grain structure. The dual-gate structure was employed to eliminate the grain boundaries perpendicular to the current flow in the channel. A multichannel structure was adapted in order to arrange the grain boundary to be parallel to the current flow. The proposed poly-Si TFT exhibits high-performance electrical characteristics, which are a high mobility of 504 cm/sup 2//Vsec and a low subthreshold slope of 0.337 V/dec. 相似文献
8.
L. Vu‐Quoc V. Srinivas Y. Zhai 《International journal for numerical methods in engineering》2003,58(3):397-461
We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
9.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
10.
结合工程实例,介绍了我国第一座可拆装高架火炬的基本原理及组成,并对可拆装高架火炬与普通高架火炬在安全、技术、安装、维修、占地面积、投资等方面进行了比较,还分析了高架火炬未来的发展趋势. 相似文献