全文获取类型
收费全文 | 431266篇 |
免费 | 30101篇 |
国内免费 | 9310篇 |
学科分类
工业技术 | 470677篇 |
出版年
2023年 | 3953篇 |
2022年 | 7493篇 |
2021年 | 10795篇 |
2020年 | 9492篇 |
2019年 | 10279篇 |
2018年 | 12360篇 |
2017年 | 13602篇 |
2016年 | 13492篇 |
2015年 | 14028篇 |
2014年 | 17647篇 |
2013年 | 24057篇 |
2012年 | 20887篇 |
2011年 | 22879篇 |
2010年 | 20165篇 |
2009年 | 19802篇 |
2008年 | 19089篇 |
2007年 | 18352篇 |
2006年 | 17949篇 |
2005年 | 15778篇 |
2004年 | 12103篇 |
2003年 | 10900篇 |
2002年 | 10031篇 |
2001年 | 9331篇 |
2000年 | 9775篇 |
1999年 | 10042篇 |
1998年 | 12449篇 |
1997年 | 9598篇 |
1996年 | 8000篇 |
1995年 | 6414篇 |
1994年 | 5411篇 |
1993年 | 4678篇 |
1992年 | 3790篇 |
1991年 | 3537篇 |
1990年 | 3341篇 |
1989年 | 3052篇 |
1988年 | 2846篇 |
1987年 | 2527篇 |
1986年 | 2528篇 |
1985年 | 2487篇 |
1984年 | 2344篇 |
1983年 | 2247篇 |
1981年 | 2292篇 |
1979年 | 2305篇 |
1978年 | 2458篇 |
1977年 | 2450篇 |
1976年 | 3129篇 |
1975年 | 2253篇 |
1974年 | 2317篇 |
1973年 | 2355篇 |
1972年 | 2160篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
V. N. Tsygankov V. V. Safonov A. I. Kozlov V. P. Gavrilov 《Inorganic Materials》2003,39(10):1076-1078
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined. 相似文献
34.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
35.
36.
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
37.
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
38.
39.
In this paper, we propose a routing algorithm called minimum fusion Steiner tree (MFST) for energy efficient data gathering with aggregation (fusion) in wireless sensor networks. Different from existing schemes, MFST not only optimizes over the data transmission cost, but also incorporates the cost for data fusion, which can be significant for emerging sensor networks with vectorial data and/or security requirements. By employing a randomized algorithm that allows fusion points to be chosen according to the nodes' data amounts, MFST achieves an approximation ratio of 5/4log(k + 1), where k denotes the number of source nodes, to the optimal solution for extremely general system setups, provided that fusion cost and data aggregation are nondecreasing against the total input data. Consequently, in contrast to algorithms that only excel in full or nonaggregation scenarios without considering fusion cost, MFST can thrive in a wide range of applications 相似文献
40.
In advancement of Pyrosil®‐technology a new kind of precursor delivery was developed, build and tested on real substrates. A Lab‐demonstrator was build to demonstrate the resources of the technology. 相似文献