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   690篇
  免费   19篇
  国内免费   1篇
电工技术   15篇
化学工业   169篇
金属工艺   8篇
机械仪表   13篇
建筑科学   15篇
能源动力   16篇
轻工业   176篇
水利工程   1篇
石油天然气   4篇
无线电   38篇
一般工业技术   73篇
冶金工业   122篇
原子能技术   17篇
自动化技术   43篇
  2023年   3篇
  2022年   22篇
  2021年   27篇
  2020年   9篇
  2019年   8篇
  2018年   10篇
  2017年   10篇
  2016年   8篇
  2015年   13篇
  2014年   15篇
  2013年   31篇
  2012年   28篇
  2011年   29篇
  2010年   27篇
  2009年   38篇
  2008年   33篇
  2007年   33篇
  2006年   37篇
  2005年   26篇
  2004年   23篇
  2003年   20篇
  2002年   19篇
  2001年   5篇
  2000年   14篇
  1999年   17篇
  1998年   53篇
  1997年   30篇
  1996年   20篇
  1995年   14篇
  1994年   15篇
  1993年   15篇
  1992年   7篇
  1991年   5篇
  1990年   3篇
  1989年   2篇
  1988年   4篇
  1987年   8篇
  1986年   4篇
  1985年   2篇
  1984年   4篇
  1982年   4篇
  1981年   1篇
  1980年   3篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1975年   1篇
  1974年   2篇
  1971年   1篇
排序方式: 共有710条查询结果,搜索用时 15 毫秒
1.
We studied the in vivo gene transfusion using a gene gun, formerly used in plants and culture cells. The hand-held type gene gun (Helios Gene Gun System) is simple and convenient for effective gene transfection in living animals. This method has some advantages in that there is no need for use of viral vector, independence on the cell cycle and local inducement of plural genes. There is a great possibility for application to local-regional cancer.  相似文献   
2.
XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique. Based on the results for reference compounds, local structures of supported vanadium and niobium species were identified. The composition was estimated from difference spectra for the samples which consisted of two kinds of species.  相似文献   
3.
As the cationic component of natural polymer polyionic complexes, polysaccharide chitosan or polypeptide polylysine, and as the anionic component, polysaccharide carboxymethyl cellulose (=CMC) or polypeptide poly(glutamic acid) (PGA) were used. The degree of chitosan/CMC or polylysine/PGA complex film swelling was minimum, when the amounts of the cationic and anionic groups in these polymers were balanced at 1 : 1 ratio. On the other hand, the degree of chitosan/PGA film swelling was minimum at the ratio with excess of PGA which is a linear flexible chain. Comparing the enthalpies estimated by DSC analysis, it was suggested that the larger quantity of water in the form of nonfreezable bound water was absorbed in the complex films with polysaccharide which is a chain of ring structure. Further, the compressive moduli of swollen complex films were high, when the complex consisted of polysaccharide components.  相似文献   
4.
Copper-ruby glasses were prepared by the sputtering method and the effect of reducing treatment was examined. The reducing was carried out either during sputtering or heat treatment. Optical absorption was related to the growth of copper particles. The results are summarized as follows: (i) the volume fraction of copper particles in the glasses which are heat-treated in air increases with the addition of hydrogen in the sputtering gas. (ii) The copper particles do not grow larger than 8 nm by heat treatment in reducing atmosphere, whereas they grow as large as 12 nm in air. (iii) Reducing during heat treatment gives a pronounced effect only when sputtering was not carried out under reducing conditions. The origin of these phenomena was also discussed, considering the mechanism of nucleation and growth of copper particles.  相似文献   
5.
The demand for energy in Japan is expected to increase steadily into the future, and it seems that the importance of nuclear power generation will be heightened more when the situation of our country which is not rich in energy resources is taken into account.

Furthermore, when we consider the present situation that the light water reactors have become common, recent outlook for the supply and demand for uranium resources, trends in the development of the fast breeder reactor technology, etc., the light water reactors are expected to remain dominant in the nuclear power generation of our country until at least the second half of the 21st century.

Based on such a background five PWR utilities in Japan (Hokkaido, Kansai, Shikoku, Kyushu, and the Japan Atomic Power), and Mitsubishi Heavy Industries, Ltd. have jointly started researching the Next Generation PWR which is expected to be the leading nuclear power plant taking place of APWR.  相似文献   

6.
The bed bath procedure consists of cleansing patients' body, passive position change, changing gown and making a bed. During the procedure, mixed venous desaturation was observed consistently in postoperative cardiac patients. We investigated the cause of the phenomenon in 22 patients undergoing cardiac surgery in their first postoperative day. The patients were breathing oxygen-enriched air via a Venturi mask. Cardiac index (CI), transluminal SvO2, arterial blood gas, Hb, DO2, VO2, FIO2, A-aDO2 and Qp/Qs were measured before and during the bed bath, while the patients were in the supine and left lateral position, respectively. Mean 8.5 +/- 1.5 minutes were required to complete the bed bath. During the bed bath, SvO2 decreased from 71 +/- 7% to 59 +/- 9% (P < 0.001), and returned to the baseline 6.5 +/- 7.4 minutes after the completion of the bed bath. VO2 increased markedly from 128 +/- 27 to 194 +/- 47 ml.min-1.m-2 (P < 0.001), while DO2 increased slightly from 480 +/- 91 to 513 +/- 110 ml.min-1.m-2 (P < 0.05). Among the determinants of DO2, CI increased slightly from 3.3 +/- 0.6 to 3.6 +/- 0.8 l.min-1.m-2, Hb remained unchanged and SaO2 decreased from 98.5 +/- 0.8 to 98.0 +/- 1.1%. FIO2 also decreased, while A-aDO2 and Qp/Qs remained unchanged. There was a negative correlation between VO2 change and SvO2 change, but no correlation between DO2 change and SvO2 change. There was a positive correlation between SaO2 change and SvO2 change, as well as between FIO2 change and SaO2 change. Therefore, the major cause of mixed venous desaturation was not the decreased DO2 or cardiopulmonary decompensation but the increased VO2 due to increased activity of the skeletal muscles. However, the decrease in SaO2 due to markedly increased O2 demand and the limited increase in CI might partially contribute to the marked decline in SvO2 through the limited increase in DO2.  相似文献   
7.
Bioactive glass-ceramics toughened by tetragonal zirconia polycrystal (TZP) were prepared by hot-pressing mixed powders of the MgO-CaO-P2O5-SiO2 glass and TZP containing 20 to 80% alumina. The bending strength and the fracture toughness of the composite materials were improved compared with those of the material without TZP. These composites showed high bending strengths (400 to 500MPa) and high fracture toughness ( 2.8MPa m1/2). The existence of a crack deflection mechanism was observed by scanning electron microscopy. After soaking in simulated physiological solution at 100 °C, no phase transformation from tetragonal to monoclinic of TZP in the composites and no degradation in bending strength occurred.  相似文献   
8.
The enhancement ofT c in Pb-Bi-Sn and Pb-Bi-In system alloy filaments produced by glass-coated melt spinning was investigated as a means of producing a new type of superconducting filament with highT c. Long filaments of Pb-Bi-Sn alloy withT c higher than 10 K and Pb-Bi-In alloy withT c higher than 9 K were obtained from the molten state at a temperature of 1500 K with a winding speed of 2.63 m sec–1. For example, a Pb45Bi35Sn20 filament withT c of 10.1 K was 15 m in diameter and polycrystalline with a grain size of 100 nm. The structure of the filament was a mixture of , tin and bismuth phases and a metastable phase of mixed structure of bismuth and supersaturated solid solution of tin in -phase was detected. TheT c of the filament decreased on heat treatment. A metastable phase of mixed structure of bismuth and -phase was also detected for a Pb45Bi45In10 filament withT c of 9.3 K. As the metastable phase for the Pb-Bi-In filament was more unstable than that for the Pb-Bi-Sn filament, theT c of the filament was drastically decreased by heat treatment. The metastable phase was considered to play an important role in the enhancement ofT c for Pb-Bi-Sn and Pb-Bi-In alloy filaments.  相似文献   
9.
Accumulating evidence has demonstrated that the pathogenesis of epilepsy is linked to neuroinflammation and cerebrovascular dysfunction. Peripheral immune cell invasion into the brain, along with these responses, is implicitly involved in epilepsy. This review explored the current literature on the association between the peripheral and central nervous systems in the pathogenesis of epilepsy, and highlights novel research directions for therapeutic interventions targeting these reactions. Previous experimental and human studies have demonstrated the activation of the innate and adaptive immune responses in the brain. The time required for monocytes (responsible for innate immunity) and T cells (involved in acquired immunity) to invade the central nervous system after a seizure varies. Moreover, the time between the leakage associated with blood–brain barrier (BBB) failure and the infiltration of these cells varies. This suggests that cell infiltration is not merely a secondary disruptive event associated with BBB failure, but also a non-disruptive event facilitated by various mediators produced by the neurovascular unit consisting of neurons, perivascular astrocytes, microglia, pericytes, and endothelial cells. Moreover, genetic manipulation has enabled the differentiation between peripheral monocytes and resident microglia, which was previously considered difficult. Thus, the evidence suggests that peripheral monocytes may contribute to the pathogenesis of seizures.  相似文献   
10.
The processability of polyethylene in sheet-extrusion or calendering may be improved by the addition of plastic flakes. The effects of plastic flake parameters and flow conditions on the viscosity and the die swell of the suspension were determined, and the structure in flow (morphology or dispersion state) and applications were discussed. Flakes of biaxially oriented polystyrene, high-impact polystyrene, polypropylene, polyamide or polypropylene spheres were dry-blended with polyethylene. The viscosity was determined by means of a slit or a capillary rheometer. The quenched extrudate was annealed and its die swell was measured. Flakes of biaxially oriented polystyrene shrunk into rod-like form during heating, but other plastics retained the flake-form. The relative viscosity and the swell ratio of the suspensions depended on the type of plastic and operating conditions. The rheological behavior of suspensions qualitatively suggested that polypropylene flakes deformed or crowded (including stacking), polyamide flakes deformed slightly, and polystyrene flakes were difficult to buckle, but crowded slightly. The thickness of extrudates can be controlled easily by flake addition due to decreased die swell, while the output would be reduced to some extent.  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