全文获取类型
收费全文 | 6958篇 |
免费 | 235篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 195篇 |
综合类 | 31篇 |
化学工业 | 1441篇 |
金属工艺 | 184篇 |
机械仪表 | 122篇 |
建筑科学 | 367篇 |
矿业工程 | 54篇 |
能源动力 | 171篇 |
轻工业 | 1231篇 |
水利工程 | 69篇 |
石油天然气 | 22篇 |
无线电 | 429篇 |
一般工业技术 | 941篇 |
冶金工业 | 958篇 |
原子能技术 | 95篇 |
自动化技术 | 898篇 |
出版年
2022年 | 54篇 |
2021年 | 122篇 |
2020年 | 83篇 |
2019年 | 102篇 |
2018年 | 124篇 |
2017年 | 115篇 |
2016年 | 137篇 |
2015年 | 127篇 |
2014年 | 188篇 |
2013年 | 312篇 |
2012年 | 212篇 |
2011年 | 262篇 |
2010年 | 234篇 |
2009年 | 247篇 |
2008年 | 253篇 |
2007年 | 221篇 |
2006年 | 200篇 |
2005年 | 156篇 |
2004年 | 169篇 |
2003年 | 150篇 |
2002年 | 157篇 |
2001年 | 109篇 |
2000年 | 95篇 |
1999年 | 115篇 |
1998年 | 215篇 |
1997年 | 172篇 |
1996年 | 122篇 |
1995年 | 109篇 |
1994年 | 95篇 |
1993年 | 81篇 |
1992年 | 66篇 |
1991年 | 65篇 |
1990年 | 76篇 |
1989年 | 73篇 |
1988年 | 61篇 |
1987年 | 69篇 |
1986年 | 59篇 |
1985年 | 72篇 |
1984年 | 70篇 |
1983年 | 69篇 |
1982年 | 62篇 |
1981年 | 51篇 |
1980年 | 52篇 |
1979年 | 53篇 |
1978年 | 68篇 |
1977年 | 71篇 |
1976年 | 81篇 |
1975年 | 65篇 |
1974年 | 62篇 |
1973年 | 69篇 |
排序方式: 共有7208条查询结果,搜索用时 15 毫秒
51.
52.
The operation of a petroleum refinery at TÜPRA
. Tütünçiftlik was assessed using the pinch-design method. By making use of heat integration in the heat-exchange network, appreciable amounts of energy can be saved as a result of a capital investment having a pay-back period of about 6·5 months. 相似文献
53.
The stability of five major phenolics, namely (−)-epicatechin (EC), procyanidin B2 (PC-B2), chlorogenic acid (ChA), hyperoside (HP) and isoquercitrin (IQ), in hawthorn fruits and a canned hawthorn drink were evaluated during 6 months of storage in the dark at three different temperatures (4, 23 and 40 °C). HPLC with a diode-array detector was used to determine the contents of the individual compounds. The results showed that the studied phenolics in the hawthorn fruits and the drink were both stable at 4 °C and relatively unstable at 23 and 40 °C with varied extents of degradation. At room temperature (23 °C), marked degradations of EC and PC-B2 were observed in both the fruits and the drink with around 50% and 30% decrease after a 6-month storage, respectively. A more significant decrease of the phenolics was observed at 40 °C, especially for EC and PC-B2, which were almost completely degraded after a 6-month storage. HP, IQ and ChA were relatively stable at 23 °C, but unstable at 40 °C. Therefore, low-temperature storage is recommended for maintaining the quality and efficacy of hawthorn fruits and its preparations. 相似文献
54.
Prof. Dipl.-Ing. Dr.techn. Si-min Zeng Prof. Dr. Walter Gretler 《Forschung im Ingenieurwesen》1995,61(11-12):304-315
The aerodynamic behaviour of pressure transients in railway tunnels due to the passage of train are accompanied by the wave reflection between the entrance and exit of the tunnel as well as the tunnel wall and train surface. This study presents a numerical method using the Harten-Yee upwind TVD scheme to simulate compression wave transients and reflection in a railway tunnel. The strength of the compression wave generated by the entrance of a train into a tunnel emerged within the applied calculation procedure, without any special consideration of the boundary condition for the entrance or exit of the tunnel as well as the train nose and tail. Good agreements were obtained when the initial pressure rise at tunnel entrance and the process of pressure variations in a short tunnel, which were calculated by the presented numerical method, were compared with experimental data. The pressure wave reflection at the entrance and exit, the unsteady flow around the train and the transmitted wave at tunnel exit portal were simulated. The transmitted wave at the tunnel exit portal is also discussed. In addition a method to determine the non-reflective boundary condition for multi-dimensional Euler equation is given. 相似文献
55.
Peridynamic modeling of concrete structures 总被引:3,自引:0,他引:3
Walter Gerstle Nicolas Sau Stewart Silling 《Nuclear Engineering and Design》2007,237(12-13):1250-1258
The peridynamic model described in Silling (Silling, S.A., 1998. Reformation of Elasticity Theory for Discontinuous and Long-Range Forces, SAND98-2176. Sandia National Laboratories, Albuquerque, NM), being a central-force model, is limited to modeling materials with a Poisson's ratio of 1/4. In this paper, the peridynamic model is generalized by adding pairwise peridynamic moments to simulate linear elastic materials with varying Poisson's ratios. The new model is called the “micropolar peridynamic model”. The micropolar peridynamic model is placed within a finite element context to enable efficacious application of boundary conditions and efficient computational solutions using an implicit, rather than an explicit solution algorithm. The implicit solution algorithm is suitable for quasistatic simulation of damage and cracking in concrete structures. With this new model, very simple tensile damage mechanisms at the micro structural (peridynamic) level are sufficient to explain a great deal of the microcracking (damage) and fracture mechanics observed in concrete structures. The new implementation appears to be computationally efficient. 相似文献
56.
Thomas Deiß 《International Journal on Software Tools for Technology Transfer (STTT)》2008,10(4):347-352
When deploying TTCN-3 at Nokia, we converted two TTCN-2 test systems to TTCN-3. We explain to which extend we have been able
to do the conversion automatically. The conversion tool used provided a syntactically and semantically correct conversion
of the TTCN-2 code. We define some improvements made on the tool to increase readability and maintainability of the resulting
code. We cover aspects of converting also the non-TTCN-2 parts and describe the experiences we made as a set of lessons learnt. 相似文献
57.
Jens‐Peter Heinß Dr. 《真空研究与实践》2007,19(5):20-23
Hydrogen free amorphous carbon coatings ‐ deposited with plasma‐activated high‐rate evaporation By using the technology of the plasmaactivated electron beam evaporation we deposited hydrogen free amorphous carbon coatings with deposition rates of up to 100 μm/h. The results of the mechanical and tribological investigations show the potential of these layers for the use in case of wear resistance. Hardnesses of up to 16GPa were proved. The actual state of the characterisation of the coatings is described and the outlook onto possibilities of further optimisation is given. 相似文献
58.
Jungho Kim Kondratko P.K. Shun Lien Chuang Walter G. Holonyak N. Jr. Heller R.D. Jr. Zhang X.B. Dupuis R.D. 《Quantum Electronics, IEEE Journal of》2005,41(11):1369-1379
A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation. 相似文献
59.
60.