全文获取类型
收费全文 | 1430篇 |
免费 | 145篇 |
国内免费 | 47篇 |
专业分类
电工技术 | 65篇 |
综合类 | 74篇 |
化学工业 | 265篇 |
金属工艺 | 48篇 |
机械仪表 | 86篇 |
建筑科学 | 57篇 |
矿业工程 | 35篇 |
能源动力 | 33篇 |
轻工业 | 142篇 |
水利工程 | 23篇 |
石油天然气 | 62篇 |
武器工业 | 4篇 |
无线电 | 204篇 |
一般工业技术 | 181篇 |
冶金工业 | 175篇 |
自动化技术 | 168篇 |
出版年
2024年 | 11篇 |
2023年 | 26篇 |
2022年 | 37篇 |
2021年 | 51篇 |
2020年 | 34篇 |
2019年 | 38篇 |
2018年 | 51篇 |
2017年 | 52篇 |
2016年 | 51篇 |
2015年 | 43篇 |
2014年 | 62篇 |
2013年 | 88篇 |
2012年 | 72篇 |
2011年 | 104篇 |
2010年 | 70篇 |
2009年 | 67篇 |
2008年 | 85篇 |
2007年 | 70篇 |
2006年 | 58篇 |
2005年 | 66篇 |
2004年 | 28篇 |
2003年 | 44篇 |
2002年 | 47篇 |
2001年 | 32篇 |
2000年 | 28篇 |
1999年 | 35篇 |
1998年 | 75篇 |
1997年 | 47篇 |
1996年 | 31篇 |
1995年 | 18篇 |
1994年 | 24篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 1篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有1622条查询结果,搜索用时 31 毫秒
21.
Design sensitivity analysis of flexible multibody systems is important in optimizing the performance of mechanical systems.
The choice of coordinates to describe the motion of multibody systems has a great influence on the efficiency and accuracy
of both the dynamic and sensitivity analysis. In the flexible multibody system dynamics, both the floating frame of reference
formulation (FFRF) and absolute nodal coordinate formulation (ANCF) are frequently utilized to describe flexibility, however,
only the former has been used in design sensitivity analysis. In this article, ANCF, which has been recently developed and
focuses on modeling of beams and plates in large deformation problems, is extended into design sensitivity analysis of flexible
multibody systems. The Motion equations of a constrained flexible multibody system are expressed as a set of index-3 differential
algebraic equations (DAEs), in which the element elastic forces are defined using nonlinear strain-displacement relations.
Both the direct differentiation method and adjoint variable method are performed to do sensitivity analysis and the related
dynamic and sensitivity equations are integrated with HHT-I3 algorithm. In this paper, a new method to deduce system sensitivity
equations is proposed. With this approach, the system sensitivity equations are constructed by assembling the element sensitivity
equations with the help of invariant matrices, which results in the advantage that the complex symbolic differentiation of
the dynamic equations is avoided when the flexible multibody system model is changed. Besides that, the dynamic and sensitivity
equations formed with the proposed method can be efficiently integrated using HHT-I3 method, which makes the efficiency of
the direct differentiation method comparable to that of the adjoint variable method when the number of design variables is
not extremely large. All these improvements greatly enhance the application value of the direct differentiation method in
the engineering optimization of the ANCF-based flexible multibody systems. 相似文献
22.
23.
Yin Ruitong Zhang Shaoshuai Xu Yueyang Xue Jianming Bi Jiaqian Liu Ruijiang 《Journal of Inorganic and Organometallic Polymers and Materials》2021,31(8):3584-3594
Journal of Inorganic and Organometallic Polymers and Materials - Magnetic CoxCu(1–x)Fe2O4 nanoparticles were prepared via an alcohol solution of nitrate combustion and calcination process.... 相似文献
24.
25.
Reactor blends of polyethylene/poly(ethylene-co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and vice versa HMW homopolymer to LMW copolymer. The shear flow characteristics of these polymers in the typical processing range mostly depend on the molecular weight and MWD of the polymer and are independent of the short chain branch content. From oscillatory shear measurements, it was observed that the viscosity of HMW polymers was reduced with the addition of LMW material. For the polymers produced with this two-step polymerization process, the LMW homopolymer and HMW copolymer blends and HMW homopolymer and LMW copolymer blends were melt miscible, despite the large viscosity differences of the pure components. 相似文献
26.
Reactor blends of polyethylene/poly(ethylene-co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and, vice versa, HMW homopolymer to LMW copolymer. The physical properties of the blends were found to be consistent with the nature of the individual components. For the tensile properties, the stiffness decreases with increasing the fraction of the copolymer, regardless of the molecular weight of the homopolymer fraction. For these blends with bimodal microstructures, it was confirmed that the degree of crystallinity governs the stiffness of the polymer. However, the energy dampening properties of the polymers benefit from the presence of the copolymer. A balance of stiffness and toughness can be obtained by altering the composition of the blends. For some blends, the presence of HMW homopolymer can dominate the tensile properties, showing little variation in the stiffness with increased addition of copolymer. It was also demonstrated that the testing conditions and thermal treatment of the polymer greatly influence the resulting elastic and energy dampening properties. Depending on the desired application, annealing these polymers (especially very low density copolymers) not only increases the crystallinity and stiffness, but also changes the frequency response of the dynamic mechanical properties. 相似文献
27.
流域水文模型是水资源评价和管理的重要工具之一,以我国北方的逊毕拉河流域为研究对象,评估了HBV模型在不同资料条件下的区域适用性。结果表明:HBV模型对逊毕拉河流域模拟效果总体较好,Nash系数多在0.6以上;雨量资料的质量对水文模拟效果具有较大的影响,在雨量资料较为充分的条件下模拟效果更好,Nash效率系数超过0.8(吴家堡站);HBV可以较好地适用于资料较好的我国北方寒冷地区进行环境变化影响评估等方面的研究。 相似文献
28.
29.
CuS pineal microspheres congregated from interleaving nanoflakes with thickness of 40 to 200 nm were synthesized by a pyridine-solvothermal process via the reaction between cupric chloride(CuCl2·2H2O) and thioacetamide(TAA,CH3CSNH2).The products were characterized by X-ray diffraction and scanning electron microscopy.UV-Vis absorption spectrum,excitation and photoluminescence spectra of CuS pineal microspheres were obtained at room temperature to investigate their optical properties.A possible growth mechanism on the formation of CuS pineal microspheres is proposed.The factors influencing the evolution of morphologies of CuS crystals including the dosage of the reactants,surfactant,and sulphur-source were also analyzed. 相似文献
30.
The attractiveness of different synthetic host odors and a synthetic aggregation pheromone (grandisoic acid [GA]) to overwintered adult plum curculios (PCs), Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), was examined using two types of traps (sticky panels and black pyramids) placed in border areas surrounding an unsprayed section of an apple orchard in Massachusetts. In 2001, we evaluated the response of PCs to three synthetic fruit volatiles (benzaldehyde [BEN], ethyl isovalerate [EIV], and limonene [LIM]) assessed alone and in combination with GA, as well as the response to GA alone and a no-odor (control) treatment. BEN was the only host volatile that synergized the response of PCs to GA for both trap types. For both trap types, GA was as attractive to PCs as a single component as when in combination with either EIV or LIM. In 2002, four release rates of BEN (0, 2.5, 10, and 40 mg/day) and two release rates of GA (1 and 2 mg/day) were evaluated for attractiveness to PCs using panel and pyramid traps. For panel traps, an increase in amount of GA released (from 1 to 2 mg/day) was associated with a 35% increase in captures. However, PC captures by pyramid traps were similar regardless of the amount of GA released. For panel traps, 10 and 40 mg/day of BEN were the most attractive release rates regardless of the amount of GA released. For pyramid traps baited with GA. PC captures were enhanced by the presence of BEN, regardless of release rate. In 2003, GA at 1 mg/day + BEN at 80 mg/day of release did not enhance PC captures by panel traps relative to lower release rates of BEN. Pyramid traps releasing GA at 1 mg/day performed best when baited with BEN at 10 mg/day of release; a release rate of 80 mg/day of BEN decreased the attractiveness of the binary combination of BEN + GA. Combined results suggest that BEN at 10 mg/day + GA at 1 mg/day of release constitutes an attractive lure that may improve the effectiveness of monitoring traps for PCs. 相似文献