全文获取类型
收费全文 | 21494篇 |
免费 | 872篇 |
国内免费 | 150篇 |
专业分类
电工技术 | 355篇 |
综合类 | 34篇 |
化学工业 | 4562篇 |
金属工艺 | 662篇 |
机械仪表 | 771篇 |
建筑科学 | 416篇 |
矿业工程 | 50篇 |
能源动力 | 1447篇 |
轻工业 | 1221篇 |
水利工程 | 171篇 |
石油天然气 | 91篇 |
武器工业 | 1篇 |
无线电 | 2817篇 |
一般工业技术 | 4728篇 |
冶金工业 | 1787篇 |
原子能技术 | 186篇 |
自动化技术 | 3217篇 |
出版年
2024年 | 102篇 |
2023年 | 434篇 |
2022年 | 1020篇 |
2021年 | 1198篇 |
2020年 | 934篇 |
2019年 | 968篇 |
2018年 | 1255篇 |
2017年 | 998篇 |
2016年 | 992篇 |
2015年 | 645篇 |
2014年 | 890篇 |
2013年 | 1656篇 |
2012年 | 963篇 |
2011年 | 1173篇 |
2010年 | 939篇 |
2009年 | 888篇 |
2008年 | 797篇 |
2007年 | 661篇 |
2006年 | 553篇 |
2005年 | 434篇 |
2004年 | 325篇 |
2003年 | 292篇 |
2002年 | 251篇 |
2001年 | 225篇 |
2000年 | 231篇 |
1999年 | 224篇 |
1998年 | 404篇 |
1997年 | 319篇 |
1996年 | 304篇 |
1995年 | 218篇 |
1994年 | 200篇 |
1993年 | 192篇 |
1992年 | 146篇 |
1991年 | 164篇 |
1990年 | 137篇 |
1989年 | 134篇 |
1988年 | 111篇 |
1987年 | 117篇 |
1986年 | 102篇 |
1985年 | 119篇 |
1984年 | 95篇 |
1983年 | 102篇 |
1982年 | 87篇 |
1981年 | 99篇 |
1980年 | 76篇 |
1979年 | 65篇 |
1978年 | 44篇 |
1977年 | 43篇 |
1976年 | 57篇 |
1975年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Poly(vinylbenzyltrimethylammonium chloride)‐graft‐cotton cellulose, an anion‐exchange matrix, was synthesized by a mutual radiation‐induced grafting technique with a 60Co γ‐radiation source. The grafted matrix was characterized by grafting yield estimation, elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The grafting yield decreased with the increase in the dose rate. However, the grafting yield and nitrogen content of grafted samples increased almost linearly with an increase in the total irradiation dose. To evaluate the performance of the grafted anion‐exchange matrix, the protein adsorption and elution behavior were investigated in a continuous column process under various experimental conditions, with bovine serum albumin used as a model protein. The binding and elution behavior of the anion‐exchange matrix depended on different experimental parameters, such as the grafting yield, ionic strength, pH of the medium, and amount of protein loaded. From a breakthrough curve, the equilibrium binding capacity and elution percentage of the grafted anion‐exchange matrix were estimated to be 40 mg/g and 94%, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5512–5521, 2006 相似文献
62.
Xinjian Duan Mukesh Jain David S. Wilkinson 《Metallurgical and Materials Transactions A》2006,37(12):3489-3501
A heterogeneous finite element model with randomly distributed inhomogeneities has been developed for the determination of
the forming limit diagram (FLD) for thin aluminum sheet material based on the prediction of localized necking. The strength
difference between the inhomogeneities and the matrix is ascertained either from the fluctuation of the experimental stress-strain
curve or from a micromechanical analysis that uses a representative particle field. By changing the specimen geometry and
friction conditions, different stress states (or strain paths) are achieved. A plot of the critical Oyane fracture parameter
is used to identify the limit strain state. Also, a plot of equivalent plastic strain rate is used to distinguish the boundary
of intense shear bands and hence to identify where to take the measurement point. Both a plane stress model and a three-dimensional
(3-D) model are adopted to predict the shear banding phenomenon and hence the FLD. The predicted FLD agrees well with the
measurements from a recent round robin experimental FLD involving several independent research laboratories. The Taguchi method
is applied to assess how the various parameters involved in the heterogeneous model affect the calculated forming limit strain. 相似文献
63.
64.
Electrochemical impedance measurements have been used to characterize zinc selenide films prepared by electrochemical co-deposition at a platinum rotating disk electrode. Estimations of capacitance and polarization resistance of variously prepared electrodeposits have been carried out to determine charge carrier density and corrosion rates. 相似文献
65.
M. Jain 《Journal of Materials Science》1992,27(2):399-407
The evolution of dislocation structure during room-temperature, uniaxial, low-cycle fatigue of an overaged Al-Mg-Si alloy is studied. Ageing at 450°C produces a fine dispersion of Mg2Si precipitate particles. During fully reversed strain-controlled cyclic tests, these fine particles restrict deformation to local regions and a stable dislocation substructure is developed early in fatigue life. Substructural observations of hardening and saturation by transmission electron microscopy reveal extensive dislocation band formation on Mg2Si precipitate rods. Various microstructural features such as configuration of tangled dislocations, dislocation cells, precipitate morphologies, sizes, precipitate-free zones, etc., have been examined during cyclic hardening and saturation. The results have been analysed in terms of kinematic and isotropictype microstructural mechanisms. 相似文献
66.
Nirmal Kumar Acharya Young-Dai Lee Jong-Soon Kim 《Canadian Metallurgical Quarterly》2006,20(2):192-195
Design defects are experienced in many projects; the difference is only in the extent of occurrence. This technical note discusses a design error case in a building project in Nepal, where the designer made the wrong assumptions in roof treatment work for waterproofing as well as for heat insulation purposes. From the investigation of the problem, it was found that the waterproofing polymer was not applied directly over concrete slab top. Use of heavy concrete block as a heat insulation material also helped to increase the leakage problem. The problem evoked loss of prestige for project officials, the design consortium, and the contractor. 相似文献
67.
A new discretization method for aggregation equations is developed. It is compared to the fixed pivot technique proposed by Kumar and Ramkrishna (1996a. On the solution of population balance equations by discretization—I. A fixed pivot technique. Chemical Engineering Science 51, 1311-1332). The numerical results for aggregation problems by discretized population balances are consistently overpredicting and diverge before the gelling point in the case of a gelling kernel. The present work establishes a new technique which assigns the particles within the cells more precisely. This is achieved by taking first the average of the newborn particles within the cell and then assigning them to the neighboring nodes such that pre-chosen properties are exactly preserved. The new technique preserves all the advantages of the conventional discretized methods and provides a significant improvement in predicting the particle size distribution (PSD). In addition, it is found that the technique is a powerful tool for the computation of gelling problems. The effectiveness of the technique is illustrated by application to several aggregation problems for suitably selected aggregation kernels including physically relevant kernels. 相似文献
68.
We report a new structure, called the shielded ohmic contact (ShOC) rectifier which utilizes trenches filled with a high-barrier metal to shield an Ohmic contact during the reverse bias. When the device is forward biased, the ohmic contact conducts with a low forward drop. However, when reverse biased, the Ohmic contact is completely shielded by the high-barrier Schottky contact resulting in a low reverse leakage current. Two dimensional numerical simulation is used to evaluate and explain the superior performance of the proposed ShOC rectifier. 相似文献
69.
70.
Undoped and Te-doped gallium antimonide (GaSb) layers have been grown on GaSb bulk substrates by the liquid phase epitaxial
technique from Ga-rich and Sb-rich melts. The nucleation morphology of the grown layers has been studied as a function of
growth temperature and substrate orientation. MOS structures have been fabricated on the epilayers to evaluate the native
defect content in the grown layers from theC-V characteristics. Layers grown from antimony rich melts always exhibitp-type conductivity. In contrast, a type conversion fromp- ton- was observed in layers grown from gallium rich melts below 400 C. The electron mobility of undopedn-type layers grown from Ga-rich melts and tellurium doped layers grown from Sb- and Ga-rich solutions has been evaluated.
Paper presented at the poster session of MRSI AGM VI. Kharagpur. 1995 相似文献