全文获取类型
收费全文 | 131161篇 |
免费 | 10577篇 |
国内免费 | 5733篇 |
专业分类
电工技术 | 7714篇 |
技术理论 | 10篇 |
综合类 | 8667篇 |
化学工业 | 22011篇 |
金属工艺 | 7205篇 |
机械仪表 | 8605篇 |
建筑科学 | 9644篇 |
矿业工程 | 3677篇 |
能源动力 | 3868篇 |
轻工业 | 8940篇 |
水利工程 | 2175篇 |
石油天然气 | 7785篇 |
武器工业 | 938篇 |
无线电 | 15027篇 |
一般工业技术 | 16776篇 |
冶金工业 | 6256篇 |
原子能技术 | 1478篇 |
自动化技术 | 16695篇 |
出版年
2024年 | 527篇 |
2023年 | 2093篇 |
2022年 | 3684篇 |
2021年 | 5135篇 |
2020年 | 3820篇 |
2019年 | 3406篇 |
2018年 | 3814篇 |
2017年 | 4213篇 |
2016年 | 3808篇 |
2015年 | 5077篇 |
2014年 | 6278篇 |
2013年 | 7675篇 |
2012年 | 8090篇 |
2011年 | 9013篇 |
2010年 | 7937篇 |
2009年 | 7386篇 |
2008年 | 7319篇 |
2007年 | 6920篇 |
2006年 | 6963篇 |
2005年 | 6195篇 |
2004年 | 4321篇 |
2003年 | 4032篇 |
2002年 | 4099篇 |
2001年 | 3505篇 |
2000年 | 3292篇 |
1999年 | 3326篇 |
1998年 | 2793篇 |
1997年 | 2273篇 |
1996年 | 2178篇 |
1995年 | 1866篇 |
1994年 | 1537篇 |
1993年 | 1150篇 |
1992年 | 866篇 |
1991年 | 684篇 |
1990年 | 511篇 |
1989年 | 403篇 |
1988年 | 353篇 |
1987年 | 212篇 |
1986年 | 177篇 |
1985年 | 134篇 |
1984年 | 95篇 |
1983年 | 56篇 |
1982年 | 63篇 |
1981年 | 51篇 |
1980年 | 41篇 |
1979年 | 21篇 |
1977年 | 7篇 |
1976年 | 16篇 |
1975年 | 11篇 |
1970年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Y.H. Sun 《Materials Research Bulletin》2004,39(9):1247-1255
Effects of Ca and Zr substitution upon the dielectric properties of Ba5LaTi3Ta7O30 ceramics were investigated together with the structural characterization. All the samples of Ba5La(ZrxTi1−x)3Ta7O30 formed a filled tungsten-bronze structures, whereas the solid solution limit was determined as x=0.25 in (CaxBa1−x)5LaTi3Ta7O30. Beyond this limit secondary phase of CaTa2O6 was detected and it would become the major phase for the Ca-rich compositions. The temperature coefficient of dielectric constant was improved with increasing Zr content while the dielectric constant decreased and the low dielectric loss varied little (in the order of 10−4). In the case of (CaxBa1−x)5LaTi3Ta7O30, small temperature coefficient of dielectric constant could be obtained with increasing Ca content while the dielectric constant decreased significantly, and a small amount substitution of Ca for Ba induced decrease in dielectric loss. 相似文献
63.
Dongchang Sun Liyong Tong 《International journal for numerical methods in engineering》2004,60(11):1911-1932
A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
64.
Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopy was used to characterize the ferroelectric behavior of a thin poly(vinylidene fluoride–trifluoroethylene) P(VDF–TrFE) copolymer. The lab-built GIRA-FTIR apparatus allowed the heating and corona poling process to be carried out whilst collecting the GIRA spectra of the thin polymer film. The Curie transition from the ferroelectric to paraelectric phase was confirmed from the abrupt change in intensity of the 849 cm−1 band in the RA-FTIR spectrum. It was found that the Curie temperature dropped dramatically when the film thickness was lowered to below a certain critical value of approximately 100 nm. The switching of the CF2 dipoles in the ferroelectric crystals after applying the external electric field could be determined by monitoring the change in the 849 cm−1 band intensity. For the 600 nm thick P(VDF–TrFE) film, the switching of the dipoles appears to occur almost instantaneously, while the kinetics of dipole switching of the 75 nm thick film were significantly retarded. The repeated switchability of the CF2 dipoles upon the application of a bipolar cyclic electric field was also confirmed. The bistability of the film due to remnant polarization was also confirmed from the absorbance of the 849 cm−1 band after removing the applied voltage during corona poling. 相似文献
65.
Du Young Choi Long Mei Jin Dexian Wang Kyung Ho Row 《Korean Journal of Chemical Engineering》2005,22(3):465-469
High-performance frontal analysis (HPFA) was used for a protein binding study of isoflavones (daidzein, genistin, and genistein),
enantiomers of perillyl alcohol and S-ibuprofen to human serum albumin (HSA). The analyses were performed on a Develosil and
Inertsil 100-Diol-5 column (10 cm×4.6mm). Sodium phosphate solution (pH 7.4, ionic strength 0.17) was used as the mobile phase
at a flow rate of 1 ml/min. To ensure the drug to be eluted as a trapezoidal peak with a plateau, injection volumes were each
fixed up the zonal profile with an evident plateau appears. The unbound drug concentration was determined from a plateau height
of the plateau region after that experimental data were fitted by Scatchard equation. The binding constants (K) and total
binding affinities (nK) of drugs to HSA were calculated, respectively. 相似文献
66.
Y. K. Cheung W. G. Jin O. C. Zienkiewicz 《International journal for numerical methods in engineering》1991,32(1):63-78
The application of the Trefftz method for calculating wave forces on offshore structures is presented. Indirect and direct formulations using complete and non-singular systems of Trefftz functions for the Helmholtz equation are posed in this paper. An effective technique using different interpolation functions for the velocity potential and wave force are suggested to improve the computational accuracy of the wave force. The numerical examples show that the present method is highly efficient and accurate. 相似文献
67.
火焰喷涂是激光熔覆前合金粉末的预置方法之一。本文在实验的基础上,探讨了工艺过程,并讨论了影响质量的因素。 相似文献
68.
69.
70.