全文获取类型
收费全文 | 183948篇 |
免费 | 16078篇 |
国内免费 | 9193篇 |
专业分类
电工技术 | 11656篇 |
技术理论 | 15篇 |
综合类 | 13065篇 |
化学工业 | 29531篇 |
金属工艺 | 10680篇 |
机械仪表 | 11508篇 |
建筑科学 | 14662篇 |
矿业工程 | 5554篇 |
能源动力 | 4995篇 |
轻工业 | 12784篇 |
水利工程 | 3653篇 |
石油天然气 | 9947篇 |
武器工业 | 1593篇 |
无线电 | 21906篇 |
一般工业技术 | 21295篇 |
冶金工业 | 8662篇 |
原子能技术 | 2039篇 |
自动化技术 | 25674篇 |
出版年
2024年 | 848篇 |
2023年 | 2834篇 |
2022年 | 5457篇 |
2021年 | 7496篇 |
2020年 | 5697篇 |
2019年 | 4631篇 |
2018年 | 5202篇 |
2017年 | 5801篇 |
2016年 | 5333篇 |
2015年 | 7486篇 |
2014年 | 9190篇 |
2013年 | 10896篇 |
2012年 | 12168篇 |
2011年 | 13111篇 |
2010年 | 11626篇 |
2009年 | 11407篇 |
2008年 | 11055篇 |
2007年 | 10648篇 |
2006年 | 9988篇 |
2005年 | 8652篇 |
2004年 | 6015篇 |
2003年 | 5351篇 |
2002年 | 5046篇 |
2001年 | 4438篇 |
2000年 | 4207篇 |
1999年 | 4540篇 |
1998年 | 3576篇 |
1997年 | 3041篇 |
1996年 | 2841篇 |
1995年 | 2342篇 |
1994年 | 2004篇 |
1993年 | 1413篇 |
1992年 | 1094篇 |
1991年 | 845篇 |
1990年 | 678篇 |
1989年 | 611篇 |
1988年 | 436篇 |
1987年 | 293篇 |
1986年 | 217篇 |
1985年 | 139篇 |
1984年 | 116篇 |
1983年 | 68篇 |
1982年 | 87篇 |
1981年 | 61篇 |
1980年 | 62篇 |
1979年 | 24篇 |
1977年 | 14篇 |
1976年 | 21篇 |
1974年 | 17篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
In this paper, a new vectorial boundary element method is introduced and applied to the modal analysis of dielectric waveguides with piecewise homogeneous refractive indexes. The procedure, which is free of spurious modes, determines the full field distribution from the longitudinal fields at the refractive index boundaries. Singular kernels are evaluated through series solutions while the electric field discontinuity at corners is accommodated through either a grid refinement technique or a semianalytic approach. Our formalism generates propagation constants and modal field distributions for several representative refractive index profiles with far higher accuracy than standard finite-difference or finite-element procedures. 相似文献
102.
It is demonstrated for the first time that long nanowires with radii as small as 30 nm can be manufactured with a conventional coupler fabrication rig. The temporal deterioration of nanowire optical properties has been studied and correlated with its mechanical behaviour. The original transmission properties have been restored by a post-fabrication treatment. 相似文献
103.
104.
介绍了平煤集团围绕以人为本的理念开展的提升理念、创新管理、加大投入和提高员工素质等一系列安全活动,为进一步抓好安全生产打下了坚实基础。 相似文献
105.
一种有机化合物名称编码与亚结构检索方法 总被引:1,自引:0,他引:1
本文以 IUPAC 为基础,考虑有机化合物母体和取代基的关联,采用库中已有的化合物名称进行亚结构检索,这种检索方法,由于由化合物名称所劈裂的编码数量较少,所以索引文件小,检索速度较快。另外,这种方法是侧重在化学上有意义的母体和宫能团,它可以和碎片编码亚结构检索方法互相补充。 相似文献
106.
用差热、热重法对原丝的热性能及由不同预处理方法所引起的PVA纤维的热行为变化进行了研究;并通过模拟脱水条件,用不同升温速率,求出了经不同预处理纤维的脱水反应活化能。结果表明,PVA原丝在230℃有一软化点,三种预处理都不同程度地影响了原丝的热效应变化;纤维在180~340℃主要为脱水反应;原丝及经脱水剂、O_3和O_3综合脱水剂处理的纤维,其脱水反应的表观活化能分别为:164.3kJ/mol,92.9kJ/mol,130.5kJ/mol和117.6kJ/mol。 相似文献
107.
通常的数据采集与记录装置不易实现多量程测量。通过对标度方程进行分析得知,要改变量程只须改变两个参数——标度因子和量程下限。我们设计了一个使用单片机的多量程数据采集和记录装置,能处理多达256种量程。本文叙述了算法分析、硬件和软件的设计以及该装置的性能指标。 相似文献
108.
Optical scattering in beef steak to predict tenderness using hyperspectral imaging in the VIS-NIR region 总被引:1,自引:0,他引:1
Kim Cluff Govindarajan Konda Naganathan Jeyamkondan Subbiah Renfu Lu Chris R. Calkins Ashok Samal 《Sensing and Instrumentation for Food Quality and Safety》2008,2(3):189-196
The objective of this research is to develop a non-destructive method for predicting cooked beef tenderness using optical
scattering of light on fresh beef muscle tissue. A hyperspectral imaging system (λ = 496–1,036 nm) that consists of a CCD
camera and an imaging spectrograph, was used to acquire beef steak images. The hyperspectral image consisted of 120 bands
with spectral intervals of 4.54 nm. Sixty-one fresh beef steaks, including 44 strip loin and 17 tenderloin cuts, were collected.
After imaging, the steaks were cooked and Warner-Bratzler shear (WBS) force values were collected as tenderness references.
The optical scattering profiles were derived from the hyperspectral images and fitted to the modified Lorentzian function.
Parameters, such as the peak height, full scattering width at half maximum (FWHM), and the slope around the FWHM were determined
at each wavelength. Stepwise regression was used to identify 7 key wavelengths and parameters. The parameters were then used
to predict the WBS scores. The model was able to predict WBS scores with an R = 0.67. Optical scattering implemented with hyperspectral imaging shows limited success for predicting current status of tenderness
in beef steak. 相似文献
109.
Xinsheng Zhu Hansong Xu Jianmei Lu Juying Wang Shunhua Zhou 《Journal of Polymer Research》2008,15(4):295-300
Poly(ethylene terephthalate) (PET) is of excellent mechanical properties and melt processability and is widely used as raw
material for textile fibers. However, the flame retardant properties of PET were rather poor, and both reactive and additive
phosphorus- and halogen-containing compounds have been employed to enhance the reaction-to-fire properties while the meltdripping
behaviour during burning hasn’t been handled properly with the flame retardants. In this work, fluoropolymer was blended with
both pure PET (pPET) and reactive phosphorus-containing flame retarded copolyester (fPET), and the flame retardance and char
formation and mechanical properties of the resulted pPET and fPET blends were investigated. The tensile strengths of modified
pPET samples were worsen whereas those of modified fPET samples were improved at low concentrations. The initial thermal degradation
in nitrogen was accelerated remarkably for the two polyesters with fluoropolymer. The oxygen indices of the all modified samples
were reduced while char formation and meltdripping suppression were encouraged. The apparent melt viscosity and elasticity
for the two polyesters were gained much with antidripping agent. Therefore, fluoropolymer improved char formation of the two
polyesters based on the gaseous phase mechanism while the partial suppression of meltdripping behavior and the decrease of
mechanical properties mainly originated from the increase of melt viscosity via fibrillation for pPET. 相似文献
110.
Sludge disintegration treatment by using simultaneously ultrasonic irradiation and electrolysis was investigated experimentally. A lab-scale diaphragm cell irradiated with ultrasound at a constant oscillating frequency of 20 kHz was used as a reactor. The batch experiments were carried out under different conditions of electric outputs of the ultrasonic generator, electric current for the electrolysis and different initial SS concentrations. A simultaneous treatment in the cathodic compartment without any chemical doses considerably facilitated the sludge solubilization, compared to the sonication alone. An increase in the electric current up to 400 mA under a constant ultrasonic density decreased the specific energy by 55% within the experimental range. The specific energy consumption was also reduced when the initial SS concentration increased. In addition, before carrying out the simultaneous treatment, a brief electrolysis was effective for further reduction of the specific energy and the acceleration of soluble COD generation. 相似文献