全文获取类型
收费全文 | 161008篇 |
免费 | 7621篇 |
国内免费 | 4245篇 |
专业分类
电工技术 | 5655篇 |
技术理论 | 8篇 |
综合类 | 7554篇 |
化学工业 | 24373篇 |
金属工艺 | 8906篇 |
机械仪表 | 8001篇 |
建筑科学 | 7960篇 |
矿业工程 | 2378篇 |
能源动力 | 3307篇 |
轻工业 | 8908篇 |
水利工程 | 2724篇 |
石油天然气 | 4066篇 |
武器工业 | 611篇 |
无线电 | 19244篇 |
一般工业技术 | 26227篇 |
冶金工业 | 6018篇 |
原子能技术 | 1167篇 |
自动化技术 | 35767篇 |
出版年
2024年 | 300篇 |
2023年 | 1180篇 |
2022年 | 2179篇 |
2021年 | 3081篇 |
2020年 | 2237篇 |
2019年 | 2011篇 |
2018年 | 16307篇 |
2017年 | 15483篇 |
2016年 | 12109篇 |
2015年 | 3718篇 |
2014年 | 4068篇 |
2013年 | 4987篇 |
2012年 | 8044篇 |
2011年 | 14748篇 |
2010年 | 12946篇 |
2009年 | 9965篇 |
2008年 | 11213篇 |
2007年 | 11888篇 |
2006年 | 4373篇 |
2005年 | 4915篇 |
2004年 | 3776篇 |
2003年 | 3728篇 |
2002年 | 3300篇 |
2001年 | 2424篇 |
2000年 | 2204篇 |
1999年 | 1928篇 |
1998年 | 1628篇 |
1997年 | 1363篇 |
1996年 | 1274篇 |
1995年 | 1019篇 |
1994年 | 898篇 |
1993年 | 667篇 |
1992年 | 506篇 |
1991年 | 418篇 |
1990年 | 311篇 |
1989年 | 245篇 |
1988年 | 215篇 |
1987年 | 126篇 |
1986年 | 102篇 |
1985年 | 78篇 |
1984年 | 52篇 |
1982年 | 52篇 |
1981年 | 43篇 |
1968年 | 44篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1959年 | 39篇 |
1958年 | 37篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
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
32.
33.
34.
Nguyen An Tien I. Ya. Mittova O. V. Almjasheva S. A. Kirillova V. V. Gusarov 《Glass Physics and Chemistry》2008,34(6):756-761
Nanocrystalline LaFeO3 is prepared by the dehydration of coprecipitated lanthanum and iron(III) hydroxides. It is shown that the behavior of the samples during heating and the size distribution of LaFeO3 nanocrystals can be considerably different depending on the scheme used for coprecipitation of lanthanum and iron hydroxides; independently of the method employed for coprecipitation of the initial compounds, sintering of the samples at 950°C leads to the formation of lanthanum orthoferrite crystals up to 100 nm in size. 相似文献
35.
36.
Eng Leong Tan Ding Yu Heh 《Microwave and Wireless Components Letters, IEEE》2008,18(5):296-298
This letter presents an unconditionally stable alternating direction implicit finite-difference time-domain (ADI-FDTD) method with fourth order accuracy in time. Analytical proof of unconditional stability and detailed analysis of numerical dispersion are presented. Compared to second order ADI-FDTD and six-steps SS-FDTD, the fourth order ADI-FDTD generally achieves lower phase velocity error for sufficiently fine mesh. Using finer mesh gridding also reduces the phase velocity error floor, which dictates the accuracy limit due to spatial discretization errors when the time step size is reduced further. 相似文献
37.
Vjacheslav V. Zuev 《Journal of Polymer Research》2008,15(5):351-356
Functionalized polyanilines containing biphenyl, terphenyl, carbazole, anthracene, and 4-n-hexylphenyl moieties were synthesized though the reaction of polyaniline in emeraldine base form with sodium salt of corresponding
vinylketoaromatics with quantitative yields. Polymers were characterized with Fourier transform infrared spectroscopy, proton
nuclear magnetic resonance spectroscopy, and thermogravimetry. The emission characteristics of these polymers in N-methyl-2-pyrrolidone solution were examined. The functionalized polyanilines exhibited an intense green emission. 相似文献
38.
The effects of key parameters on the preparation and regeneration of protoplast from the β-carotene-producing fungus Blakeslea trispora were discussed in this paper, including the combination of various enzymes, mycelial age, digesting time and temperature,
pH value, osmotic stabilizers, pretreatment, culture medium and culture method. Under the condition of mixed enzymes in osmotic
stabilizer (0.6 M NaCl) combined with 2% lysozyme, 3% cellulase and 3% snailase, the highest protoplast yield, as high as
7.48×106 protoplasts/mL, was obtained when mycelial age was 60 h at pH 5.0–6.0 with digesting for 14–16 h at 28 °C. After
purification of the obtained protoplasts, they were regenerated in PDA regenerative medium using bilayer plate culture method.
To validate the usability of the protoplasts, a novel plasmid with green fluorescent protein (GFP) was used in transformation
for easy visual observation. The results showed that the protoplasts prepared by the optimized method were active and applicable
in further gene manipulation experiments.
This work was presented at 13
th
YABEC symposium held at Seoul, Korea, October 20–22, 2007. 相似文献
39.
Min Chan Kim Dong Won Lee Chang Kyun Choi 《Korean Journal of Chemical Engineering》2008,25(6):1239-1244
When a horizontal homogeneous solid is melted from below, convection can be induced in a thermally unstable melt layer. In
this study the onset of buoyancy-driven convection during time-dependent melting is investigated by using similarly transformed
disturbance equations. The critical Rayleigh numbers based on the melt-layer thickness are found numerically for various conditions.
For small superheats, the present predictions approach the well known results of classical Rayleigh-Bénard problems, that
is, critical Rayleigh numbers are located between 1,296 and 1,708, regardless of the Prandtl number. However, for high superheats
the critical Rayleigh number increases with an increase in phase change rate but with decrease in Prandtl number. 相似文献
40.
Ottavia Colombo Simona Villani Giovanna Pinelli Claudia Trentani Maurizia Baldi Orazio Tomarchio Anna Tagliabue 《Nutrition journal》2008,7(1):5