全文获取类型
收费全文 | 159347篇 |
免费 | 14428篇 |
国内免费 | 9216篇 |
专业分类
电工技术 | 12058篇 |
技术理论 | 4篇 |
综合类 | 18384篇 |
化学工业 | 16767篇 |
金属工艺 | 6932篇 |
机械仪表 | 12551篇 |
建筑科学 | 22330篇 |
矿业工程 | 6836篇 |
能源动力 | 5317篇 |
轻工业 | 8624篇 |
水利工程 | 6712篇 |
石油天然气 | 6459篇 |
武器工业 | 2053篇 |
无线电 | 10558篇 |
一般工业技术 | 19597篇 |
冶金工业 | 6126篇 |
原子能技术 | 2428篇 |
自动化技术 | 19255篇 |
出版年
2024年 | 615篇 |
2023年 | 1772篇 |
2022年 | 3375篇 |
2021年 | 4010篇 |
2020年 | 4573篇 |
2019年 | 3872篇 |
2018年 | 3784篇 |
2017年 | 4751篇 |
2016年 | 5409篇 |
2015年 | 5661篇 |
2014年 | 9474篇 |
2013年 | 9061篇 |
2012年 | 12017篇 |
2011年 | 12222篇 |
2010年 | 9446篇 |
2009年 | 9773篇 |
2008年 | 8937篇 |
2007年 | 11211篇 |
2006年 | 9992篇 |
2005年 | 8531篇 |
2004年 | 7047篇 |
2003年 | 6181篇 |
2002年 | 5157篇 |
2001年 | 4236篇 |
2000年 | 3787篇 |
1999年 | 3327篇 |
1998年 | 2607篇 |
1997年 | 2244篇 |
1996年 | 1892篇 |
1995年 | 1685篇 |
1994年 | 1400篇 |
1993年 | 1037篇 |
1992年 | 907篇 |
1991年 | 649篇 |
1990年 | 518篇 |
1989年 | 505篇 |
1988年 | 369篇 |
1987年 | 217篇 |
1986年 | 174篇 |
1985年 | 88篇 |
1984年 | 91篇 |
1983年 | 47篇 |
1982年 | 44篇 |
1981年 | 58篇 |
1980年 | 34篇 |
1979年 | 38篇 |
1978年 | 19篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1959年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The effect of pressure on combustion and heat transfer is analyzed. The research is based on the basic combustion and heat
transfer theorem. A correction for the heat calculation method for pressurized furnace is made on the basis of the normal
pressure case. The correction takes the effect of pressurizing into account. The results show that the correction is reasonable
and the method is applicable to combustion and heat transfer of the marine supercharged boiler. 相似文献
72.
LaNiO3 was synthesized by sol-gel method in which lanthanum nitrate and nickel nitrate were used as start materials and citric acid was used as complex for gel formation.The precursor was dried and subsequently heated at elevated temperature to form the desired product.XRD analysis shows that pure LaNiO3 was synthesized.Electrical conductivity and electrochemical performance of the material were tested.The electrical conductivity decreases from 34.5that there are current peaks in the curve, which is the evidence of the electrochemical activity of LaNiO3. 相似文献
73.
讨论了直流法在线测量钯氢化物电极电阻时的电化学效应,计算了电解液的共导、测量电流与电解电流引起的浓差电池效应以及电极作为集流体引起的电阻贡献。结果表明:当电极具有高的长度与半径比值、粗糙的表面、高的溶液电导以及大的电解电流时容易引起显著的附加电阻。 相似文献
74.
Using boundary element based three dimensional modelling for linear fracture mechanics, we present an analysis of cracking in a homogeneous medium subject to contact load. The proposed iterative solution procedure allows a simultaneous treatment of a reasonable number of partially closed cracks. It is shown that the most probable direction of propagation of a vertical internal crack is strongly dependent on its size compared to the contact radius and its location with respect to the axis of maximum normal load. 相似文献
75.
G. Ranzi M. A. Bradford B. Uy 《International journal for numerical methods in engineering》2004,61(5):657-672
The use of the conventional semi-analytical stiffness method in finite element analysis, in which interpolation polynomials are used to develop the stiffness relationships, leads to problems of curvature locking when beam-type elements are developed for composite members with partial interaction between the materials of which it is comprised. The curvature locking phenomenon that occurs for composite steel–concrete members is quite well reported, and the general approach to minimizing the undesirable ramifications of curvature locking has been to use higher-order polynomials with increasing numbers of internal nodes. This paper presents an alternate formulation based on a direct stiffness approach rather than starting from pre-defined interpolation polynomials, and which does not possess the undesirable locking characteristics. The formulation is based on a more general approach for a bi-material composite flexural member, whose constituent materials are joined by elastic shear connection so as to provide partial interaction. The stiffness relationships are derived, and these are applied to a simply supported and a continuous steel–concrete composite beam to demonstrate the efficacy of the method, and in particular its ability to model accurately both very flexible and very stiff shear connection that causes difficulties when implemented in competitive semi-analytical algorithms. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
76.
Chouping Luo Marek Klisinski 《International journal for numerical methods in engineering》2004,61(2):159-188
The present study is a continuation of our previous work with the aim to reduce problems caused by standard higher order elements in contact problems. The difficulties can be attributed to the inherent property of the Galerkin method which gives uneven distributions of nodal forces resulting in oscillating contact pressures. The proposed remedy is use of piece‐wise linear weight functions. The methods to establish stiffness and/or mass matrix for 8‐node quadrilateral element in 2D are presented, i.e. the condensing and direct procedures. The energy and nodal displacement error norms are also checked to establish the convergence ratio. Interpretation of calculated contact pressures is discussed. Two new 2D 8‐node quadrilateral elements, QUAD8C and QUAD8D, are derived and tested in many examples, which show their good performance in contact problems. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
77.
Youngjean Jung Panayiotis Papadopoulos R. O. Ritchie 《International journal for numerical methods in engineering》2004,60(2):429-460
This work concerns the micromechanical constitutive modelling, algorithmic implementation and numerical simulation of polycrystalline superelastic alloys under multiaxial loading. The model is formulated in finite deformations and incorporates the effect of texture. The numerical implementation is based on the constrained minimization of the Helmholtz free energy with dissipation. Simulations are conducted for thin tubes of Nitinol under tension–torsion, as well as for a simplified model of a biomedical stent. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
78.
Yu. A. Radin I. A. Grishin T. S. Kontorovich O. B. Panshina A. V. Chugin 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2006,40(2):113-119
Problems arising with connecting the second exhaust-heat boiler to the first exhaust-heat boiler under load in the case of
flow circuits of combined-cycle plants of type PGU-450 are considered. Similar problems exist for two-boiler single-turbine
units of type PGU-325 and for two-boiler single-turbine units of traditional steampower plants with an output of 200–300 MW
upon connection of the second furnace of a two-furnace boiler to the operating first furnace. Analysis of the temperature-induced
stressed state and of the cyclic strength of thick-walled elements of the steam-water conduit of PGU-450 and of two-furnace
boilers of two-boiler single-turbine units with an output of 200–300 MW (the check valve, the inlet header of the water economizer)
is used for determining the steam temperature differences in the high-pressure conduits to the steam turbine and the order
of connection of the second exhaust-heat boiler to the operating fist one. Modes of enabling a two-boiler single-turbine unit
of a combined-cycle plant, which are most “rigid” from the standpoint of thermal strength, are determined.
__________
Translated from élektricheskie Stantsii, No. 2, February 2006, pp. 11–17. 相似文献
79.
该文介绍了Mall的产生条件和国内发展概况,并结合实例分析,着重论述建筑设计方面的有关问题。 相似文献
80.
以工业偏钛酸、硫酸锌、氨水为主要原料,用直接沉淀法并进行热处理得到钛酸锌粉体,并用XRD对产物成分进行了检测。结果表明,不同的锌钛比对钛酸锌(ZnO-TiO2)体系的成分有较大影响。 相似文献