全文获取类型
收费全文 | 485798篇 |
免费 | 89506篇 |
国内免费 | 56544篇 |
专业分类
电工技术 | 45382篇 |
技术理论 | 28篇 |
综合类 | 39664篇 |
化学工业 | 72783篇 |
金属工艺 | 39369篇 |
机械仪表 | 25181篇 |
建筑科学 | 36534篇 |
矿业工程 | 21239篇 |
能源动力 | 16935篇 |
轻工业 | 40113篇 |
水利工程 | 12574篇 |
石油天然气 | 28659篇 |
武器工业 | 5881篇 |
无线电 | 65494篇 |
一般工业技术 | 65715篇 |
冶金工业 | 21784篇 |
原子能技术 | 4671篇 |
自动化技术 | 89842篇 |
出版年
2024年 | 3916篇 |
2023年 | 9279篇 |
2022年 | 14036篇 |
2021年 | 18092篇 |
2020年 | 17792篇 |
2019年 | 24799篇 |
2018年 | 27284篇 |
2017年 | 29496篇 |
2016年 | 28214篇 |
2015年 | 30360篇 |
2014年 | 32169篇 |
2013年 | 34866篇 |
2012年 | 35499篇 |
2011年 | 33556篇 |
2010年 | 29581篇 |
2009年 | 25848篇 |
2008年 | 23874篇 |
2007年 | 22175篇 |
2006年 | 21764篇 |
2005年 | 19259篇 |
2004年 | 17032篇 |
2003年 | 14426篇 |
2002年 | 13493篇 |
2001年 | 12303篇 |
2000年 | 11676篇 |
1999年 | 12376篇 |
1998年 | 10585篇 |
1997年 | 9246篇 |
1996年 | 8638篇 |
1995年 | 7710篇 |
1994年 | 6326篇 |
1993年 | 5223篇 |
1992年 | 4641篇 |
1991年 | 3445篇 |
1990年 | 2669篇 |
1989年 | 2375篇 |
1988年 | 1867篇 |
1987年 | 888篇 |
1986年 | 690篇 |
1985年 | 525篇 |
1984年 | 362篇 |
1983年 | 263篇 |
1982年 | 323篇 |
1981年 | 263篇 |
1980年 | 208篇 |
1978年 | 146篇 |
1976年 | 291篇 |
1975年 | 227篇 |
1972年 | 242篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
N. Balchev D. Kovacheva V. Lovchinov K. Konstantinov K. Petrov 《Journal of Superconductivity》1993,6(1):49-54
The preparation conditions, phase composition, and superconducting properties of Bi-Pb-Sr-Ca-Cu oxide materials from different nominal compositions have been investigated. Nearly single-phase samples from Bi2Pb0.4Sr2Ca3Cu4O
y
, as well as from the proposed compositions Bi1.8Pb0.4Sr2Ca3Cu4O
y
and Bi1.8Pb0.4Sr2Ca2.5Cu3.5O
y
were obtained by a solid-state reaction in air. Samples with the third nominal composition showed the best superconducting properties (T
on=111 K and zero resistance atT
0=103 K). A possible mechanism for the 2223 phase formation in the three investigated compositions has been discussed. 相似文献
82.
The selective reduction of nitrogen oxides by hydrocarbons on a Pt catalyst has been investigated. Some variations are observed between different reductants. However, the most significant result is the observation that no N2O is observed as a by-product when toluene is used as a reductant. 相似文献
83.
Tony Maillet Jacques Barbier Jr. Daniel Duprez 《Applied catalysis. B, Environmental》1996,9(1-4):251-266
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling. 相似文献
84.
In this paper, we investigate the problem of determining the optimal bandwidth allocation for a Dynamic Bandwidth Allocation Scheme (DBAS). The objective is to minimize the total amount of bandwidth required to satisfy the Quality of Service (QoS) requirements of all traffic streams. It is shown that when the performance functions satisfy a certain number of conditions, there exists a unique optimal bandwidth allocation such that, for each traffic stream, either its QoS is just satisfied or its QoS is over-satisfied and it is allocated zero bandwidth. Such an allocation is said to be efficient. It is also shown that there exists a unique efficient allocation in the entire feasible region. An iterative algorithm is developed to compute the efficient allocation employing its special properties. Numerical examples are presented to demonstrate how the algorithm works. Future extensions of this work are also discussed.Partially supported by NSERC of Canada through grants OGP14020 and STRIN-200. 相似文献
85.
Jifu Huang Ke Wu 《Microwave Theory and Techniques》1996,44(8):1508-1511
A generalized transmission line matrix (TLM) algorithm is developed in the frequency domain to tackle arbitrary both reciprocal and nonreciprocal anisotropic waveguiding problems. In particular, the modeling issue for arbitrary planar structures is stressed in this work. A new three-dimensional (3-D) condensed node is used to consider the effect of both electric and magnetic constitutive tensors. Various results indicate how the modal dispersive behavior can be manipulated by changing not only the anisotropic characteristics of the substrate, but also the strip/slot geometry as well as the magnitude and orientation of the applied static magnetic field. The present algorithm is useful for CAD and simulation of a large class of gyrotropic waveguide-based microwave and millimeter-wave circuits 相似文献
86.
地表热释光找油机理的探讨 总被引:4,自引:2,他引:2
油气藏的微渗漏造成的上方放射性元素的局部富集(或贫化)影响地表沙土的天然热释光量,据此探讨了热释光找油的机理。 相似文献
87.
Silicon forms the backbone of the microelectronics industry, and possibly, of the optoelectronics industry, hitherto dominated by III/V materials. One of the remaining goals is to build an optical source in silicon. Erbium exhibits luminescent 1.54 μm intra-4f transitions in both silicon and porous silicon. This paper reviews the work which has been carried out in this field and discusses some possible additional applications of erbium-doped silicon in optoelectronics, such as a novel on-chip temperature sensor. 相似文献
88.
Z. -G. Fan Y. -X. Zhuang G. Yang R. Shao G. -F. Zhang 《Journal of Alloys and Compounds》1993,200(1-2):33-36
The oxygen absorption process in highly aligned YBa2Cu3Ox samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:
(1 − at) ln(1 − at) + at = kDt
The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa2Cu3Ox crystals are discussed. 相似文献
89.
The buckling of plain and discretely stiffened composite axisymmetric shell panels/shells made of repeated sublaminate construction is studied using the finite element method. In repeated sublaminate construction, a full laminate is obtained by repeating a basic sublaminate, which has a smaller number of plies. The optimum design for buckling is obtained by determining the layup sequence of the plies in the sublaminate by ranking, so as to achieve maximum buckling load for a specified thickness. For this purpose, a four-noded 48-dof quadrilateral composite thin shell element, together with fully compatible two-noded 16-dof composite meridional and parallel circle stiffener elements are used. 相似文献
90.
Hsin-Li Chen Ching-Yuan Wu 《Electron Devices, IEEE Transactions on》1998,45(10):2245-2247
An analytical model for the grain-barrier height of the intrinsic poly-Si thin-film transistors (TFTs) is developed, in which the grain-barrier height for the applied gate voltage smaller than the threshold voltage is obtained by solving the charge neutrality equation and the grain-barrier height for the applied gate voltage larger than the threshold voltage is obtained by using the quasi-two-dimensional (2-D) method. Good agreements between experimental and simulation results are obtained for a wide gate voltage range 相似文献