首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5895篇
  免费   120篇
  国内免费   8篇
电工技术   315篇
综合类   11篇
化学工业   1350篇
金属工艺   131篇
机械仪表   111篇
建筑科学   88篇
矿业工程   1篇
能源动力   155篇
轻工业   425篇
水利工程   16篇
石油天然气   4篇
无线电   565篇
一般工业技术   953篇
冶金工业   1401篇
原子能技术   166篇
自动化技术   331篇
  2023年   23篇
  2022年   34篇
  2021年   81篇
  2020年   33篇
  2019年   57篇
  2018年   59篇
  2017年   38篇
  2016年   62篇
  2015年   70篇
  2014年   83篇
  2013年   220篇
  2012年   165篇
  2011年   249篇
  2010年   194篇
  2009年   193篇
  2008年   213篇
  2007年   187篇
  2006年   190篇
  2005年   141篇
  2004年   157篇
  2003年   169篇
  2002年   141篇
  2001年   140篇
  2000年   112篇
  1999年   177篇
  1998年   553篇
  1997年   386篇
  1996年   275篇
  1995年   163篇
  1994年   151篇
  1993年   149篇
  1992年   94篇
  1991年   76篇
  1990年   80篇
  1989年   84篇
  1988年   69篇
  1987年   43篇
  1986年   63篇
  1985年   65篇
  1984年   65篇
  1983年   60篇
  1982年   70篇
  1981年   53篇
  1980年   46篇
  1979年   53篇
  1978年   37篇
  1977年   46篇
  1976年   50篇
  1975年   20篇
  1973年   29篇
排序方式: 共有6023条查询结果,搜索用时 76 毫秒
51.
The N-linked oligosaccharide moieties of sycamore (Acer pseudoplatanus L.) laccase are known to be highly heterogeneous. We confirmed that this oligosaccharide heterogeneity was caused not only during the oligosaccharide biosynthesis in Golgi apparatus, but also after the excretion of laccase protein into a culture medium. The culture medium for the sycamore cells (Acer pseudoplatanus L.) contained beta-galactosidase, alpha-L-fucosidase, beta-N-acetylglucosaminidase, alpha-mannosidase and beta-xylosidase activities. We showed that the largest sugar chain in laccase, oligosaccharide F, [formula: see text] was degraded to [formula: see text] by a crude exoglycosidase mixture in the culture medium.  相似文献   
52.
Carbon fibre/poly (ether-ether-ketone) (PEEK) composites were fabricated from plain weave cloth using the commingled yarn of carbon fibres with PEEK filaments. The undirectional specimen was made from the warp of commingled yarn and the weft of PEEK yarn, while the two-dimensional specimen was made from commingled yarns both of the warp and the weft. During the hot-pressing process, PEEK filaments melt to form the matrix of the composite. The interlaminar fracture toughness of the commingled composite was measured and compared with that of the prepreg composite. The critical strain energy release rates,/'G Ics, obtained for the commingled composites were higher than the prepreg composite. In particular, the two-dimensional composite exhibited higherG Ic than the unidirectional commingled composite. Factors increasing the fracture toughness of commingled composites have also been investigated by SEM observation of the fractured surface.  相似文献   
53.
Ti1−xVxO2 solid solution film photoelectrodes were prepared by the dip-coating sol–gel method. X-ray diffraction and X-ray photoelectron spectroscopy were employed to ensure the formation of the solid solution and their composition. Obvious photoresponses were observed in the visible region for the solid solution film electrodes with x0.05 and the red shift of the photoresponse was enhanced with increasing x. Moreover, the solid solution film electrodes were found to be photoelectrochemically stable. However, the onset potential of photocurrent shifted positively with increasing x. Band model of the solid solution was suggested to explain the effects of the vanadium incorporation on the photoelectrochemical properties.  相似文献   
54.
Under cryogenic operation, a low Vth realizes a high speed performance at a greatly reduced power-supply voltage, which is the most attractive feature of Cryo-CMOS. It is very important in sub-0.25 μm Cryo-CMOS devices to reconcile the miniaturization and the low Vth. Double implanted MOSFET's technology was employed to achieve the low Vth while maintaining the short channel effects immunity. We have investigated both the DC characteristics and the speed performance of 0.25 μm gate length CMOS devices for cryogenic operation. The measured transconductances in the saturation region were 600 mS/mm for 0.2 μm gate length n-MOSFET's and 310 mS/mm for 0.25 μm gate length p-MOSFET's at 80 K. The propagation delay time in the fastest CMOS ring oscillator was 22.8 ps at Vdd=1 V at 80 K. The high speed performance at extremely low power-supply voltages has been experimentally demonstrated. The speed analysis suggests that the sub-l0 ps switching of Cryo-CMOS devices will be realized by reducing the parasitic capacitances and through further miniaturization down to 0.1 μm gate length or below  相似文献   
55.
In the pathogenesis of Parkinson's disease and senile dementia of the Alzheimer type, free radicals might play a role. Fat-soluble vitamins are a kind of anti-oxidative substance. Therefore, fat-soluble vitamins, such as vitamin E, may be useful in treatment of Parkinson's disease and senile dementia of the Alzheimer type. However, it is still unclear whether the concentration of vitamin E in the blood or in the brain tissue, in patients with Parkinson's disease or with of the senile dementia Alzheimer type, is higher than or the same as that in normal subjects. Furthermore, although the effectiveness of vitamin E in the treatment of Parkinson's disease has been reported, the usefulness of vitamin E is still obscure. Further study will be necessary, in order to clarify the role of fat-soluble vitamins in the treatment of Parkinson's disease and senile dementia of the Alzheimer type.  相似文献   
56.
Since the natural estrogens 17 beta-estradiol (E2) and estron (E1), and the synthetic estrogen 17 alpha-ethynyl estradiol (EE2) have strong endocrine disrupting effects and the tendency to persist in effluent from wastewater treatment plants, effective measures are needed to remove them from wastewater. In this research, to gain an understanding of the characteristics of estrogen decomposition by ozonation, experiments were conducted using effluent from an actual wastewater treatment plant. In this experiment, estrogen was added to effluent at a concentration of 200 ng/l and 20 ng/l before the ozonation experiments. The results showed 90% or more of estrogen concentration and estrogenic activity of E2, El and EE2 to be removed at an ozone dose of 1 mg/l. At an ozone dose of 3 mg/l, the estrogen concentration and estrogenic activity of E2, El and EE2 in the treated water fell below the detection limit. The removal rate was not influenced by the kind of estrogen. No generation of byproducts with estrogenic activity was observed. The authors conclude that estrogen in secondary treated wastewater can be almost entirely removed at the practical ozone dose rate applied for the purpose of disinfection, which is up to about 5 mg/l.  相似文献   
57.
This paper describes the implicit integration and consistent tangent modulus of an inelastic constitutive model with transient and steady strain rates, both of which are time‐ and temperature‐dependent; the transient rate is influenced by the evolution of back stress decomposed into parts, while the steady rate depends only on applied stress and temperature. Such a non‐unified model is useful for high‐temperature structural analysis and is practical owing to the ease in determining material constants. The implicit integration is shown to result in two scalar‐valued coupled equations, and the consistent tangent modulus is derived in a quite versatile form by introducing a set of fourth‐rank constitutive parameters into the discretized evolution rule of back stress. The constitutive model is, then, implemented in a finite element program and applied to a lead‐free solder joint analysis. It is demonstrated that the implicit integration is very accurate if the multilinear kinematic hardening model of Ohno and Wang is employed, and that the consistent tangent modulus certainly affords quadratic convergence to the Newton–Raphson iteration in solving nodal force equilibrium equations. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
58.
An improved T-Ω method that can analyze magnetic fields produced not only by eddy currents but also by magnetizing currents is proposed. The method is applied to the analysis of 3-D eddy-current models with holes. The usefulness of the method is investigated by comparing calculated results with measured results and with results obtained by the A-Φ method. The T-Ω method has the advantage that the CPU time can be considerably reduced when most of the analyzed region is current-free and the eddy current flows two-dimensionally. The method is especially effective when the shape of the winding is simple and the distribution of magnetizing current is known beforehand. It is not effective when most of the analyzed region is current-carrying  相似文献   
59.
A series of mixtures of Japanese subbituminous Taiheiyo coal and Athabasca oil sand bitumen (AOB) with various coal concentrations (0–100 wt%) was coprocessed in a 70 ml autoclave at 420°C for 1 h in the presence of H2 (50 kg/cm2 at room temperature) and sulfided Ni---Mo/Al2O2 catalyst. The mixture containing 2 wt% coal produced the largest amount of hexane soluble fraction (HS) and the smallest amount of benzene insoluble fraction (BI). Thus, a synergistic liquid production occurred for this mixture with 2 wt% coal by suppressing the retrogressive reactions which proceeded for pure AOB. The HS obtained from mixtures with 2–30 wt% showed higher H/C ratios and lower heteroatom contents than those obtained from pure AOB and the mixtures with more than 30 wt% coal. The amounts of transferable hydrogen contained in the mixtures were estimated using anthracene as a hydrogen acceptor. The mixtures with 2–10 wt% coal contained higher amounts of donor hydrogen than pure AOB. The HS yield from the various mixtures was correlated with the amount of donor hydrogens contained in the mixtures, except for the mixture with 10 wt% coal. Thus, the important factor which results in synergism is suggested to be the amount of donor hydrogens contained in the feed mixtures.  相似文献   
60.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号