全文获取类型
收费全文 | 1332篇 |
免费 | 113篇 |
国内免费 | 59篇 |
专业分类
电工技术 | 41篇 |
综合类 | 67篇 |
化学工业 | 241篇 |
金属工艺 | 51篇 |
机械仪表 | 77篇 |
建筑科学 | 53篇 |
矿业工程 | 32篇 |
能源动力 | 30篇 |
轻工业 | 130篇 |
水利工程 | 16篇 |
石油天然气 | 48篇 |
武器工业 | 2篇 |
无线电 | 199篇 |
一般工业技术 | 183篇 |
冶金工业 | 177篇 |
自动化技术 | 157篇 |
出版年
2024年 | 10篇 |
2023年 | 17篇 |
2022年 | 33篇 |
2021年 | 38篇 |
2020年 | 21篇 |
2019年 | 30篇 |
2018年 | 48篇 |
2017年 | 45篇 |
2016年 | 46篇 |
2015年 | 38篇 |
2014年 | 50篇 |
2013年 | 81篇 |
2012年 | 69篇 |
2011年 | 92篇 |
2010年 | 72篇 |
2009年 | 69篇 |
2008年 | 81篇 |
2007年 | 71篇 |
2006年 | 62篇 |
2005年 | 67篇 |
2004年 | 24篇 |
2003年 | 43篇 |
2002年 | 42篇 |
2001年 | 25篇 |
2000年 | 29篇 |
1999年 | 32篇 |
1998年 | 75篇 |
1997年 | 47篇 |
1996年 | 32篇 |
1995年 | 19篇 |
1994年 | 22篇 |
1993年 | 13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1504条查询结果,搜索用时 15 毫秒
1.
棋盘格图像在摄像机标定中有非常广泛的应用,对于复杂环境且测量精度要求非常高的场合,会需要特定的且有一定复杂度的算法,但通常情况下,使用这样的标定系统是没有必要的,且会让初次应用的人觉得困难。这里提供一套应用简单,快速,对棋盘格图像具有旋转不变性,良好的鲁棒性,且对非复杂环境具有高精度的标定系统。所有算法均是在前辈们的算法上稍作改变而来,应用效果非常好。 相似文献
2.
本文分析了冷启动却塔风机直接启动方式对风机造成的一些危害。并对冷却循环水风机软启动器改造前、后作了比较 ,重点说明了如何利用软启动器在原冷却塔风机电机上实现限流启动以及改造后在实践过程中存在的一些问题 ,提出了改进措施。 相似文献
3.
U. H. Pi D. H. Kim Z. G. Khim U. Kaiser M. Liebmann A. Schwarz R. Wiesendanger 《Journal of Low Temperature Physics》2003,131(5-6):993-1002
We have studied vortex dynamics in Bi2Sr2CaCu2O8 single crystal with low density columnar defects by using a magnetic force microscope. Single crystal Bi2Sr2CaCu2O8 sample was irradiated by 1.3 GeV uranium ion to form artificial pinning centers along the crystalline c-axis. The irradiation dose corresponded to a matching field of 20 gauss. The radius of an individual vortex is approximately 140 nm, which is close to the penetration depth of this material. Magnetic force microscope (MFM) images show that intrinsic crystalline defects such as stacking fault dislocations are very effective pinning centers for vortices in addition to the pinning centers due to ion bombardment. By counting the number of vortex, we found that the flux trapped at each pinning center is a single flux quantum. At higher magnetic field, the vortex structure showed an Abrikosov lattice disturbed only by immobile vortices located at pinning centers. When increasing or decreasing the external magnetic field, the spatial distribution of vortices showed a Bean model like behavior. 相似文献
4.
本文对Lurgi低压法甲醇工艺中压力的参变效应进行了探讨.通过计算机模拟,给出了合成压力变化的效应情况.计算结果表明煤头小型低压法甲醇装置的合成压力应高于大型装置的合成压力,其值在7.3~8.0MPa之间可取得最佳的节能降耗效果. 相似文献
5.
Wei Fen Zhang Xi Guang Chen Pi Wu Li Cheng Sheng Liu Qiang Zhi He 《Drying Technology》2008,26(1):108-115
Three kinds of carboxymethyl chitosan/β-cyclodextrin microspheres loaded with theophylline were prepared by spray drying intended for pulmonary delivery. Mucociliotoxicity, permeation rate, and drug release characteristics of the product were investigated. The microspheres obtained by spray drying were found to be spherical with smooth or wrinkled surfaces. The mean particle size was between 3.39 and 6.06 µm. The microspheres demonstrated high product yield (43.7-50.2%), high drug loading (13.7-38.1%), and high encapsulation efficiency (86.9-92.8%). FT-IR indicated that there were interactions of theophylline with carboxymethyl chitosan matrix. Further studies on mucociliotoxicity and permeation confirmed that microspheres had better adaptability and high permeation rate. In vitro drug release from the microspheres was not related to the drug/polymer ratios. 相似文献
6.
BACKGROUND: The matrix metalloproteinases (MMPs) MMP2 and MMP9 play a significant role in epidermal detachment, inflammation and re-epithelialization. We have evaluated their activity in toxic epidermal necrolysis (TEN). DESIGN: The level and pattern of activity of MMP2 and MMP9 were investigated by measuring the degradation of 3H-labelled gelatin and by zymography in blister fluid from six TEN patients and compared the results with three other blistering conditions: bullous pemphigoid (n = 6), second-degree burn (n = 13) or suction blister (n = 3). RESULTS: A higher amount of MMP2 was found in TEN blister fluid with the constant presence of a significantly larger proportion of the activated forms of MMP2, a particular feature of TEN, than the other blistering diseases studied. CONCLUSION: This study emphasizes the potential role of MMP2 in the specific inflammatory reaction and reparation process in TEN skin. 相似文献
7.
JC López Pacios L Parra Muntaner MC Pi?eiro Fernández SC Gómez Cisneros E Sánchez Sánchez JA Rivas Escudero FJ Madrid García J García Alonso 《Canadian Metallurgical Quarterly》1998,51(4):331-333
The occurrence of secondary hypogonadism is a common finding in males who seek help with erectile dysfunction, although the relationship to diminished testosterone is unclear. Two possibilities exist regarding both the genesis and maintenance of the hypogonadotropic hypogonadal state. First, a defect in hypothalamic function, resulting in downregulation as well as in alterations of anterior pituitary function; second, estradiol inhibition of gonadotropin release, both of which result in decreased testosterone production. As testosterone levels decrease and estradiol levels increase, the ratio of free testosterone to estradiol reaches a critical point and the estrogenic gonadotropin suppressive effects predominate. This ratio may signal the biological point of no return and could become one of the criteria for defining the separation of the transitional hypogonadal state from the final 'end stage' hypogonadotropic hypogonadal state. As the aging process continues, there is a relative accumulation of fatty tissue, and aromatization accelerates the conversion of testosterone to estradiol. This additional secondary estradiol inhibition results in the maintenance of the testosterone deficient state, and the aging process continues uncontested. 相似文献
8.
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
9.
10.
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