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   1849篇
  免费   54篇
  国内免费   4篇
电工技术   115篇
综合类   1篇
化学工业   427篇
金属工艺   55篇
机械仪表   25篇
建筑科学   54篇
能源动力   54篇
轻工业   134篇
水利工程   2篇
石油天然气   5篇
无线电   180篇
一般工业技术   253篇
冶金工业   403篇
原子能技术   57篇
自动化技术   142篇
  2022年   20篇
  2021年   25篇
  2020年   21篇
  2019年   22篇
  2018年   27篇
  2017年   31篇
  2016年   36篇
  2015年   22篇
  2014年   25篇
  2013年   92篇
  2012年   57篇
  2011年   75篇
  2010年   66篇
  2009年   69篇
  2008年   76篇
  2007年   68篇
  2006年   59篇
  2005年   51篇
  2004年   41篇
  2003年   52篇
  2002年   38篇
  2001年   35篇
  2000年   28篇
  1999年   43篇
  1998年   153篇
  1997年   109篇
  1996年   72篇
  1995年   48篇
  1994年   44篇
  1993年   38篇
  1992年   22篇
  1991年   20篇
  1990年   13篇
  1989年   24篇
  1988年   17篇
  1986年   21篇
  1985年   22篇
  1984年   20篇
  1983年   17篇
  1982年   19篇
  1981年   17篇
  1980年   22篇
  1979年   24篇
  1978年   14篇
  1977年   12篇
  1976年   21篇
  1975年   10篇
  1974年   12篇
  1973年   10篇
  1972年   12篇
排序方式: 共有1907条查询结果,搜索用时 31 毫秒
71.
The prorenin/renin receptor ((P)RR) is a multifunctional protein that is widely distributed in various organs. Despite intensive research for more than 20 years, this receptor has not been fully characterized. In this study, we generated mice overexpressing the tubular epithelial (P)RR gene ((P)RR-TG mice) to test the previously reported functional role of (P)RR by Ramkumar et al. in 2015 using tubular specific (P)RR KO mice. (P)RR-TG mice were maintained and analyzed in individual metabolic cages and were administered angiotensin II blocker (ARB), direct renin inhibitor (DRI), and bafilomycin, that is, vacuolar ATPase (V-ATPase) antagonist. (P)RR-TG mice were hypertensive and had alkalized urine with lower osmolality and Na+ excretion. ARB and DRI, but not bafilomycin, concurrently decreased blood pressure. Bafilomycin acidized urine of (P)RR-TG mice, or equivalently this phenomenon restored the effect of overexpressed transgene, suggesting that (P)RR functioned as a V-ATPase in renal tubules. Afterall, (P)RR-TG mice were mated with alternative renin transgenic mice (ARen2-TG), which we identified as intracellular renin previously, to generate double transgenic mice (DT-TG). Lethal renal tubular damage was observed in DT-TG mice, suggesting that intracellular renin may be a ligand for (P)RR in tubules. In summary, (P)RR did not substantially affect the tissue renin-angiotensin system (RAS) in our model of tubular specific (P)RR gene over-expression, but alternative intracellular renin may be involved in (P)RR signaling in addition to conventional V-ATPase function. Further investigations are warranted.  相似文献   
72.
With the increasing demand of turbochargers with high performance and low turbo lag, high cycle fatigue (HCF) of radial turbine blades has become the most commo...  相似文献   
73.
Carbonization properties of a Ql-free coal-tar pitch (CTP-ASM) prepared by selective precipitation were studied to evaluate it as a source for needle-coke. Its modifying ability for production of needlecoke in co-carbonizations with principal carbonizing substances which gave cokes of mozaic texture in single carbonizations was estimated by changing mixing ratios. The shape and size of the anisotropic optical texture in the co-carbonized coke were measured by point counting. CTP-ASM and Ashland A240, of eight additives, had the highest modifying ability in the co-carbonizations with Khafji vacuum residue. Both contained ca. 6% benzene-insolubles (Bl), and had fa values of ≈0.9. Other additives of either lower or higher Bl or fa showed less modifying ability. The modifying susceptibility of principal carbonizing substances varies with their structure and properties. Based on a systematic investigation of co-carbonizations the compatibility between a principal carbonizing substance and an additive is discussed from a viewpoint of their structural parameters.  相似文献   
74.
Chemiluminescence (CL) analysis was used for determining the oxidation layer formed by the irradiation of polypropylene for medical supplies. The depth of the oxidation layer from the surface depended on dose rate and increased with decreasing dose rate. The oxidation occurred remarkably at a region near the surface area of the film where the diffusion of oxygen is more sufficient. On the contrary, there was very little oxidation in the interior portion. The oxidation layers of polypropylene samples irradiated with electron beam showed U-shaped profiles in the cross-section of film as did as a sample irradiated with γ-rays. However, the degree of oxidation by irradiation with electron beam was very small; CL intensity at the surface area was only one-third that for the γ-irradiated samples.  相似文献   
75.
陈瑶  李任强  田村和弘 《化工学报》2003,54(10):1463-1465
引 言石油是目前最重要的能源 ,除了液体石油外 ,油砂和油岩也能作为石油资源 .油岩分散存在于砂岩层中 ,只能通过物理的方法开采 ,乳化是可利用的提取方式之一 .为了了解乳化的原理及其体系的变化动态 ,作者曾经考察了 2 乙氧基乙醇、癸烷和水的液液三相平衡[1] .作为系统研  相似文献   
76.
Sterol composition of 19 vegetable oils   总被引:6,自引:4,他引:6  
The unsaponifiables from 19 vegetable oils were divided into a sterol and three other fractions by thin-layer chromatography. All except olive and palm kernel oils gave the sterol fraction in a large quantity. Compositions of the sterol fractions were determined by gas liquid chromatography. Identification of each sterol was carried out by gas liquid chromatography and combined gas chromatograph-mass spectrometry. Campesterol, stigmasterol and β-sitosterol were present in all oils, and a minor amount of cholesterol in majority of the oils. Brassicasterol occurrence was widespread but its content was extremely small in oils other than rapeseed oil. Other sterols, presumably δ7-stigmastenol and δ5- and δ7-avenasterol were detected in most of the oils.  相似文献   
77.
The unsaponifiables from threeTheaceae (Camellia japonica L.,Camellia Sasanqua Thunb., andThea sinensis L.) oils and alfalfa, garden balsam, and spinach seed oils and shea fat were separated into four fractions: sterols, 4-methylsterols, triterpene alcohols, and less polar compounds by thin layer chromatography. While the sterol fraction was the major one for the unsaponifiables from alfalfa and spinach seed oils, the triterpene alcohol fraction was predominant for the unsaponifiables from all other oils. The sterol, 4-methylsterol, and triterpene alcohol fractions were analyzed by gas chromatography. All the sterol fractions were alike in their compositions, consisting exclusively of Δ7-sterols, such as α-spinasterol and Δ7-stigmastenol as predominant components together with Δ7-avenasterol and 24-methylcholest-7-enol. Obtusifoliol, gramisterol (occasionally accompanied with cycloeucalenol), and citrostadienol, together with several other unidentified components, were found in the 4-methylsterol fractions from all of the oils except shea fat. The 4-methylsterol fraction from shea fat showed a characteristic composition containing a large proportion of unidentified components which had relative retention time greater than that of citrostadienol, while no citrostadienol was detected. β-Amyrin, lupeol, and butyospermol were major components of the triterpene alcohol fractions from most of the oils, but the fraction from spinach seed oil contained cycloartenol and 24-methylene-cycloartanol as predominant components. There is a close similarity in the compositions of unsaponifiables (sterols, 4-methylsterols, and triterpene alcohols) of the threeTheaceae oils. Two sterols, α-spinasterol and Δ7-stigmastenol, and five triterpene alcohols were isolated from tea seed oil. Moreover, five unidentified components beside parkeol, butyrospermol, α-amyrin, and lupeol were isolated from the triterpene alcohol fraction of shea fat.  相似文献   
78.
To fabricate functionally graded materials, a highly concentrated slurry of SiO2‐Mo system was prepared and centrifugal force was applied in an attempt to achieve a graded composition. Subsequently, we formed a homogeneous green body with compositional gradation by floc‐casting at 80°C, which was then fired at 1750°C for 10 min in Ar. The sintered body had compositional ratios of SiO2 and Mo as well as electrical conductivities that changed gradually along the direction of centrifugal force. The results demonstrate that centrifugation and control of slurry characteristics such as flocculation are effective in fabricating functionally graded SiO2‐Mo materials.  相似文献   
79.
The pseudocapacitance of nanocrystalline RuO2 with BET surface area of 42 m2 g−1 was evaluated using a RuO2 modified Glassy Carbon (RuO2/GC) thin film electrode. The charge storage behavior of the RuO2/GC thin film electrode was studied from fast to slow scan cyclic voltammetry between various potential windows. The utilization of the thin film electrode method for nanocrystalline RuO2 with known specific surface area allowed a semi-quantitative understanding of the electric double-layer capacitance (Cdl), adsorption related charge (Cad), and the irreversible redox related charge (Cirr) per unit mass and surface area of RuO2. Comparison of the cyclic voltammograms between different voltage windows revealed that the contribution from Cirr is especially dominant below 0.4 V (versus RHE) at slow scan rates.  相似文献   
80.
Multilayered thermal barrier coatings (TBC) with different functions were proposed for the hot section components of land-based gas turbines. This article describes a multilayered TBC with an oxidation resistant layer. A conventional duplex TBC and a triplex TBC, in which an aluminized layer was added to the conventional duplex TBC to increase oxidation resistance, were prepared. It was confirmed by a burner rig test that the triplex TBC with the aluminized layer is resistant to oxidation and shows high durability in a thermal cycle test, compared with the conventional duplex TBC. The spalling in the thermal cycle test of each TBC specimen occurred at the same position, when the thickness of the oxidation layer was 11 to 13 μm. The mechanism of spalling of the coating in the thermal cycle test was discussed in terms of stress in the coating. Stress in the direction of spalling occurred by an uneven interface between the bond and top coat and increased with growth of the oxidation layer. It is thought that the high durability of the triplex TBC in the thermal cycle test is derived from suppressing the growth of the oxidation layer and decreasing the stress due to the addition of the aluminized layer.  相似文献   
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