全文获取类型
收费全文 | 391444篇 |
免费 | 3686篇 |
国内免费 | 785篇 |
专业分类
电工技术 | 6604篇 |
综合类 | 217篇 |
化学工业 | 61015篇 |
金属工艺 | 21056篇 |
机械仪表 | 14227篇 |
建筑科学 | 7348篇 |
矿业工程 | 4755篇 |
能源动力 | 7880篇 |
轻工业 | 20936篇 |
水利工程 | 5913篇 |
石油天然气 | 16122篇 |
武器工业 | 41篇 |
无线电 | 36832篇 |
一般工业技术 | 91876篇 |
冶金工业 | 59031篇 |
原子能技术 | 13973篇 |
自动化技术 | 28089篇 |
出版年
2021年 | 4039篇 |
2019年 | 3933篇 |
2018年 | 7426篇 |
2017年 | 7676篇 |
2016年 | 8152篇 |
2015年 | 4490篇 |
2014年 | 7645篇 |
2013年 | 16489篇 |
2012年 | 11031篇 |
2011年 | 13950篇 |
2010年 | 11313篇 |
2009年 | 12609篇 |
2008年 | 12848篇 |
2007年 | 12393篇 |
2006年 | 10349篇 |
2005年 | 9323篇 |
2004年 | 8859篇 |
2003年 | 8610篇 |
2002年 | 8341篇 |
2001年 | 8247篇 |
2000年 | 8005篇 |
1999年 | 7523篇 |
1998年 | 16273篇 |
1997年 | 12014篇 |
1996年 | 9128篇 |
1995年 | 7077篇 |
1994年 | 6395篇 |
1993年 | 6684篇 |
1992年 | 5377篇 |
1991年 | 5452篇 |
1990年 | 5383篇 |
1989年 | 5200篇 |
1988年 | 5109篇 |
1987年 | 4797篇 |
1986年 | 4754篇 |
1985年 | 5191篇 |
1984年 | 4964篇 |
1983年 | 4761篇 |
1982年 | 4429篇 |
1981年 | 4459篇 |
1980年 | 4517篇 |
1979年 | 4706篇 |
1978年 | 4827篇 |
1977年 | 5026篇 |
1976年 | 5767篇 |
1975年 | 4445篇 |
1974年 | 4461篇 |
1973年 | 4555篇 |
1972年 | 4052篇 |
1971年 | 3701篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
22.
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
23.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
24.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
25.
26.
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
27.
28.
29.
It is shown that, for the spectrum analysis of digital quasi-periodic signals, one must use a procedure based on approximating the sequence of data readouts by a first-order trigonometric polynomial with a varying frequency of its harmonic functions. 相似文献
30.
Kontogiannopoulos N. Psychalinos C. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(12):1373-1377
In this brief, the well-known switched-current (SI) filtering technique is revisited using the concept of the square-root domain (SRD) filtering. It is proved that SI filters are a subclass of the SRD filters, where sampled-data signal processing is performed. This is achieved by considering typical lossless and lossy SRD sampled-data integrator configurations, using a set of complementary SRD operators which are based on the quadratic I-V relationship of MOS transistor operated in the saturation. Circuit examples are given, where linear-domain integrator and third-order filter configurations were derived using appropriate SRD sampled-data building blocks 相似文献