全文获取类型
收费全文 | 404436篇 |
免费 | 4718篇 |
国内免费 | 1369篇 |
专业分类
电工技术 | 7576篇 |
综合类 | 317篇 |
化学工业 | 60005篇 |
金属工艺 | 16444篇 |
机械仪表 | 13506篇 |
建筑科学 | 8361篇 |
矿业工程 | 2155篇 |
能源动力 | 11587篇 |
轻工业 | 28488篇 |
水利工程 | 4268篇 |
石油天然气 | 7914篇 |
武器工业 | 17篇 |
无线电 | 49306篇 |
一般工业技术 | 83122篇 |
冶金工业 | 74981篇 |
原子能技术 | 9182篇 |
自动化技术 | 33294篇 |
出版年
2022年 | 2595篇 |
2021年 | 3952篇 |
2020年 | 2983篇 |
2019年 | 3849篇 |
2018年 | 6539篇 |
2017年 | 6519篇 |
2016年 | 6955篇 |
2015年 | 4334篇 |
2014年 | 7162篇 |
2013年 | 20081篇 |
2012年 | 11446篇 |
2011年 | 15305篇 |
2010年 | 12186篇 |
2009年 | 13741篇 |
2008年 | 14073篇 |
2007年 | 13842篇 |
2006年 | 12439篇 |
2005年 | 11129篇 |
2004年 | 10514篇 |
2003年 | 10423篇 |
2002年 | 9829篇 |
2001年 | 9734篇 |
2000年 | 9136篇 |
1999年 | 9520篇 |
1998年 | 24327篇 |
1997年 | 16713篇 |
1996年 | 12800篇 |
1995年 | 9517篇 |
1994年 | 8363篇 |
1993年 | 8380篇 |
1992年 | 6054篇 |
1991年 | 5694篇 |
1990年 | 5679篇 |
1989年 | 5317篇 |
1988年 | 5043篇 |
1987年 | 4420篇 |
1986年 | 4299篇 |
1985年 | 4812篇 |
1984年 | 4422篇 |
1983年 | 3994篇 |
1982年 | 3654篇 |
1981年 | 3730篇 |
1980年 | 3429篇 |
1979年 | 3327篇 |
1978年 | 3337篇 |
1977年 | 3750篇 |
1976年 | 4847篇 |
1975年 | 2850篇 |
1974年 | 2663篇 |
1973年 | 2730篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
It is well known that the tearing resistance curve J–Δa is not a material property. A recent approach, based on an energetic critical parameter to model ductile tearing propagation, is used to model 3D effects. The approach considered in this work aims to estimate the dissipated energy in the fracture process during ductile tearing represented by an intrinsic parameter Gfr. A fracture criterion, which accounts for the crack extension length, is defined and lies on a critical energy release rate, noted Gc, which is compared to Gfr. Previously, this parameter was obtained from a numerical local energy release rate, which handicaps the application field of the approach: a fine mesh for the whole propagation area was needed and the criterion allowed only to model 1D propagation. A new manner to estimate Gc is then proposed in this article, based on the J plastic part variation, which allows to model 2D propagation by defining a local criterion. This new calculation method is validated on a CT specimen made in Tu52b ferritic steel, by comparing the results obtained from the two methods of Gc calculation. Then, the 2D crack growth case is studied, by modelling the propagation in a ring, loaded in compression. It is shown that a 3D effect, such as tunnel effect, could be successfully represented with this approach. 相似文献
992.
Mathematical simulation is used to study the dependence of the parameters of an electronuclear system with uranium–plutonium mixed fuel on the amount of plutonium and 240Pu admixture in the fuel. As an example, a 10–20 kW(t) experimental system built at Dubna on the basis of a synchrocyclotron with 660 MeV protons is examined. A 2% admixture of 240Pu decreases the neutron multiplication factor from 0.95 to 0.9 and decreases the neutron yield and heat released by almost a factor of 2. This decrease can be compensated by increasing the plutonium content in the mixed fuel from 25 to 27%. 相似文献
993.
An annual report on meetings of the scientific research seminar on computer algebra is presented. 相似文献
994.
995.
S. Jahanmir 《Wear》1985,102(4):331-349
The effect of additive chain length on friction coefficient and transition temperature is investigated under different test conditions. Carboxylic acids and normal alcohols with 12 – 18 carbon atoms in the chain were used as additives in n-hexadecane base lubricant. It was found that the magnitude of the friction coefficient decreases as the additive chain length is increased. Matching of the additive chain length with the base lubricant had no effect on the friction coefficient. Similarly, the transition temperature at low sliding speeds increased with increasing chain length and was not affected by chain matching. At higher speeds, the acids containing 16 and 18 carbon atoms did not exhibit a transitional behavior within the studied temperature range. These results are discussed in terms of the separation distance between the contacting surfaces, the intermolecular dispersion forces and the structure of adsorbed layers. It is concluded that, at very low speeds, boundary lubrication is controlled by adsorbed monolayers, whereas at higher speeds, where partial elastohydrodynamic conditions prevail, ordered multimolecular layers may influence lubrication. 相似文献
996.
997.
Hydrogenation of canola oil in the presence of nickel and the methyl benzoate-chrome carbonyl complex 总被引:1,自引:0,他引:1
L. J. Rubin S. S. Köseoglu L. L. Diosady W. F. Graydon 《Journal of the American Oil Chemists' Society》1986,63(12):1551-1557
Canola oil was hydrogenated using a mixture of homogeneous methyl benzoate-Cr(CO)3 and heterogeneous nickel catalysts. The effect of the methyl benzoate-Cr(CO)3_to-nickel ratio on the activity, specific isomerization index, linoleate and linolenate selectivities, and fatty acid composition
was evaluated, and the results compared with those obtained with commercial nickel catalyst and methyl benzoate-Cr(CO)3 used individually. At higher chromium-to-nickel ratios the activity of nickel was inhibited and the system behaved essentially
like the pure chrome complex, while at low chromium-to-nickel ratios the characteristics of the nickel predominated. In a
short transition zone relatively high reaction rates were obtained with significantly reducedtrans-isomer levels in the product. In a broader sense, it may be possible to combine a homogeneous and heterogeneous catalyst
while retaining the advantages of both. We may thus be able to design catalyst systems for specific applications. 相似文献
998.
In a high energy electron ring the spins of electrons become spontaneously polarized via the emission of spin-flip synchrotron radiation. By employing a radio frequency radial dipole field kicker, particle spin directions can be rotated slowly over many turns. A model which couples three dimensional spin motion and longitudinal particle motion was constructed to describe nonequilibrium spin dynamics in high energy electron storage rings. The effects of a stochastic synchrotron radiation on the orbital motion in the accelerator synchrotron plane and its influence on the spin motion are studied. The main contributions to the spin motion, the synchrotron oscillations and the stochastic synchrotron radiation, have different influence on the spin polarization reversal in different regions of the parameter space. The results indicate that polarization reversal might be obtained in high energy electron storage rings with a significant noise even with relatively small strengths of a perturbing magnetic field. The only experimental datum available agrees with the model prediction, however further experimental data would be necessary to validate the model. 相似文献
999.
Four experiments of coagulation and flocculation were conducted to investigate the characteristics of colloidal silica removal in a high-tech industrial wastewater treatment plant for reclamation and reuse of the effluent. Experimental results illustrated that poly-aluminium chloride (PACl) showed higher performances on colloidal silica removal than alum. Interestingly, the two coagulants demonstrated the same capacity on silica removal. The specific silica removal capacity was approximately 0.135 mg SiO2/mg Al2O3 when the dosage of coagulants was in the range 30-150 mg/L Al2O3. In addition, the silica was reduced significantly at the condition of pH above 8. Experimental data implied that precipitation of aluminium flocs was the major mechanism for colloid silica removal in PACl and alum coagulation, besides, charge adsorption was also important for improving removal efficiency. Moreover, the addition of polyacrylic acid (PAA) as a flocculant could slightly advance silica removal in the PACl coagulation. The combined PACl/PAA/flocs coagulation was effective for the removal of colloidal silica, soluble COD, and turbidity and also suitable as a pretreatment unit in wastewater reclamation and reuse processes. 相似文献
1000.