全文获取类型
收费全文 | 208206篇 |
免费 | 16282篇 |
国内免费 | 7840篇 |
专业分类
电工技术 | 11383篇 |
技术理论 | 14篇 |
综合类 | 11264篇 |
化学工业 | 36299篇 |
金属工艺 | 10620篇 |
机械仪表 | 12128篇 |
建筑科学 | 16496篇 |
矿业工程 | 4961篇 |
能源动力 | 5956篇 |
轻工业 | 12833篇 |
水利工程 | 3238篇 |
石油天然气 | 11099篇 |
武器工业 | 1352篇 |
无线电 | 26165篇 |
一般工业技术 | 27221篇 |
冶金工业 | 11259篇 |
原子能技术 | 2142篇 |
自动化技术 | 27898篇 |
出版年
2024年 | 891篇 |
2023年 | 3283篇 |
2022年 | 5901篇 |
2021年 | 7981篇 |
2020年 | 5859篇 |
2019年 | 5060篇 |
2018年 | 5476篇 |
2017年 | 6270篇 |
2016年 | 5763篇 |
2015年 | 7376篇 |
2014年 | 9662篇 |
2013年 | 12513篇 |
2012年 | 12425篇 |
2011年 | 14075篇 |
2010年 | 11778篇 |
2009年 | 11626篇 |
2008年 | 11039篇 |
2007年 | 10629篇 |
2006年 | 11015篇 |
2005年 | 9721篇 |
2004年 | 6649篇 |
2003年 | 5864篇 |
2002年 | 5322篇 |
2001年 | 4774篇 |
2000年 | 4927篇 |
1999年 | 5695篇 |
1998年 | 5413篇 |
1997年 | 4443篇 |
1996年 | 4029篇 |
1995年 | 3354篇 |
1994年 | 2826篇 |
1993年 | 2229篇 |
1992年 | 1740篇 |
1991年 | 1309篇 |
1990年 | 1053篇 |
1989年 | 909篇 |
1988年 | 701篇 |
1987年 | 514篇 |
1986年 | 406篇 |
1985年 | 353篇 |
1984年 | 227篇 |
1983年 | 205篇 |
1982年 | 170篇 |
1981年 | 153篇 |
1980年 | 136篇 |
1979年 | 102篇 |
1978年 | 71篇 |
1977年 | 69篇 |
1976年 | 85篇 |
1975年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
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
222.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior. 相似文献
223.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
224.
Meng-Cheng Chen 《International Journal of Fracture》2003,121(3-4):133-148
This paper deals with some basic linear elastic fracture problems for an arbitrary-shaped planar crack in a three-dimensional infinite transversely isotropic piezoelectric media. The finite-part integral concept is used to derive hypersingular integral equations for the crack from the point force and charge solutions with distinct eigenvalues s i(i=1,2,3) of an infinite transversely isotropic piezoelectric media. Investigations on the singularities and the singular stress fields and electric displacement fields in the vicinity of the crack are made by the dominant-part analysis of the two-dimensional integrals. Thereafter the stress and electric displacement intensity factor K-fields and the energy release rate G are exactly obtained by using the definitions of stress and electric displacement intensity factors and the principle of virtual work, respectively. The hypersingular integral equations under axially symmetric mechanical and electric loadings are solved analytically for the case of a penny-shaped crack. 相似文献
225.
226.
“两个经常性”工作集中体现了无产阶级性质和全心全意为人民服务的宗旨,反映了企业管理的本质特征和客观规律,是做好管理教育工作应遵循的基本准则。 相似文献
227.
We present a domain decomposition boundary integral equation method for two-dimensional partial differential equations. The overlapping Schwarz method is employed to improve the dual reciprocity boundary element method. The resulting algorithm turns out to be more accurate than a non-overlapping approach previously proposed. Some numerical results showing the improved accuracy and efficiency of the methods are given. 相似文献
228.
229.
230.