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   509篇
  免费   5篇
电工技术   34篇
化学工业   140篇
金属工艺   17篇
机械仪表   11篇
建筑科学   7篇
能源动力   10篇
轻工业   78篇
无线电   22篇
一般工业技术   79篇
冶金工业   52篇
原子能技术   18篇
自动化技术   46篇
  2023年   3篇
  2022年   5篇
  2021年   9篇
  2020年   1篇
  2019年   7篇
  2018年   9篇
  2017年   5篇
  2016年   9篇
  2015年   7篇
  2014年   13篇
  2013年   26篇
  2012年   24篇
  2011年   26篇
  2010年   25篇
  2009年   20篇
  2008年   32篇
  2007年   37篇
  2006年   14篇
  2005年   19篇
  2004年   18篇
  2003年   18篇
  2002年   16篇
  2001年   15篇
  2000年   7篇
  1999年   14篇
  1998年   20篇
  1997年   16篇
  1996年   17篇
  1995年   7篇
  1994年   11篇
  1993年   11篇
  1992年   4篇
  1991年   5篇
  1990年   5篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   6篇
  1985年   2篇
  1984年   5篇
  1983年   4篇
  1982年   3篇
  1979年   4篇
  1978年   4篇
  1976年   4篇
排序方式: 共有514条查询结果,搜索用时 15 毫秒
1.
Glasses with two composition in the CaO---Al2O3---SiO2 system were prepared with different cooling conditions. Glass A has a eutectic composition of wollastonite-gehlenite-rankinite and glass B has that of wollastonite-gehlenite-anorthite. The effects of the thermal history on the structure and hydraulic properties were discussed. Effects of cooling rate on the physical and chemical properties of glasses are found to be different with chemical composition of glass. Cooling rate affects the hydraulic reactivity and crystallization temperature, especially in glass A, but scarcely affects the physical properties such as chemical shift of AlK and surface basicity of the glass.  相似文献   
2.
Ever since 1974, the cadaver has been embalmed by the arterial embalming method, using pre-embalming fluid with blood clot disperser and cell conditioner for the removal of blood clots and drainage of blood, at the Department of Anatomy of the Kawasaki Medical School. According to this method, the cadavers are always very well fixed so that they can be used for not only anatomical dissection but also research for the vascular system by vasography, kinematics of the joint and other histologic examinations. In this report we have described our embalming procedure concretely and its application to research.  相似文献   
3.
4.
A fluorescent converter for fast neutron radiography (FNR) comprising a scintillator and hydrogen-rich resin has been developed and applied to electronic imaging. The rate of the reaction between fast neutrons and the converter is increased by thickening the converter, but its opaqueness attenuates emitted light photons before they reach its surface. To improve the luminosity of a fluorescent converter for FNR, a novel type of converter was designed in which wavelength-shifting fibers were adopted to transport radiated light to the observation end face. The performance of the converter was compared with that of a polypropylene-based fluorescent converter in an experiment conducted at the fast-neutron-source reactor YAYOI in the University of Tokyo.  相似文献   
5.
Power system control equipment needs higher sensitivity and operational reliability. Advanced voltage control equipment is needed for reducing the frequency of tap changes and improving the characteristics (the relationship between the actual voltage and reference voltage) of the voltage to meet today's power system requirements. However, these objectives are in a trade-off relationship. Studies of voltage control derived from a knowledge base suitable for electric power systems can satisfy these objectives using fuzzy inference. Compared with corresponding conventional equipment, the new equipment improved the deviation of 30 min average voltage of 30 percent. This paper describes the design concept of new voltage control equipment using fuzzy inference. In addition, field test results are described along with rules of fuzzy inference, membership functions, and the deviation of 30 min average voltage through detailed simulation.  相似文献   
6.
BACKGROUND: Major depressive disorder is often marked by repeated episodes of depression. We describe recovery from major depression across multiple mood episodes in patients with unipolar major depression at intake and examine the association of sociodemographic and clinical variables with duration of illness. METHODS: A cohort of 258 subjects treated for unipolar major depressive disorder was followed up prospectively for 10 years as part of the Collaborative Depression Study, a multicenter naturalistic study of the mood disorders. Diagnoses were made according to the Research Diagnostic Criteria, and the course of illness was assessed with the Longitudinal Interval Follow-up Evaluation. Survival analyses were used to calculate the duration of illness for the first 5 recurrent mood episodes after recovery from the index episode. RESULTS: Diagnosis remained unipolar major depressive disorder for 235 subjects (91%). The median duration of illness was 22 weeks for the first recurrent mood episode, 20 weeks for the second, 21 weeks for the third, and 19 weeks for the fourth and fifth recurrent mood episodes; the 95% confidence intervals were highly consistent. From one episode to the next, the proportion of subjects who recovered by any one time point was similar. For subjects with 2 or more recoveries, the consistency of duration of illness from one recovery to the next was low to moderate. None of the sociodemographic or clinical variables consistently predicted duration of illness. CONCLUSION: In this sample of patients treated at tertiary care centers for major depressive disorder, the duration of recurrent mood episodes was relatively uniform and averaged approximately 20 weeks.  相似文献   
7.
In order to improve the fracture properties of p, p′-diaminodiphenylmethane-cured epoxy resin, various kinds of aromatic and aliphatic glycidyl compounds were investigated as a modifier at an amount of 30 wt %. Several compounds promoted the fracture toughness. In any glycidyl compounds, however, heat resistance was decreased by the modification. The dynamic mechanical properties of the modified epoxy resins were measured. The crosslinking density ρ was calculated from the theory of rubber elasticity, and the mechanical properties of the resins were discussed in regard to the crosslinking density. Tensile strength was scarcely affected by the crosslinking density. Elongation at break and Izod impact strength increased remarkably with decrease in crosslinking density. The fracture toughness KIc- increased with decrease in crosslinking density except at small ρ.  相似文献   
8.
Thermal cracking of tar-sand bitumens has been carried out using a two-stage pyrolysis reactor with temperature zones of 440°C and 750–800°C, respectively. Feedstocks were pyrolysed in the first stage into cracked oils, which were carried to the second stage for subsequent pyrolysis. Only 12–14 wt% of ethylene was obtained from tar-sand bitumens at the residence time of 1.2 s in the second stage, although 27 and 16 wt% were obtained from Taching and Iranian heavy vacuum residues, respectively. The tar-sand bitumens contain shorter paraffinic straight-chains and have more branched molecules than the vacuum residues of petroleum. A straight-chain paraffin index is proposed, with which a good correlation was obtained between ethylene yield and the fraction of straight-chain paraffin carbons in the heavy oil.  相似文献   
9.
Spin dynamics of3He-4He dilute solution have been studied in the collisionless regime by NMR methods. In cw NMR experiments, we observed spin waves in a magnetic field gradient. The frequency difference between the first mode and the others obeyed a two-thirds power law in the strength of the field gradient. By using a pulsed NMR method, nonlinear spin dynamics were studied. We observed the large amplitude spin waves after an rf pulse. The frequency of each spin-wave mode depended on the tipping angle. By using the parameter determined in the present experiment, the numerical calculated results based on Leggett-Rice theory are in good agreement with the results of the pulsed NMR experiments.  相似文献   
10.
For the effective use of short-lived radioactive beams, soon to be available at the Tokai Radioactive Ion Accelerator Complex, the authors have developed a radiotracer method for diffusion studies in solids. The experimental test was performed by the measurement of the diffusion coefficients of Li in a sample of the compound βLiAl using an α-emitting radiotracer of 8Li (T1/2=0.84 s). It was found that the time-dependent yields of the α particles from the diffusing 8Li that was initially implanted in the sample could be used as a measure of the diffusivity of the tracer in a nondestructive way. The method was applied to measure the self-diffusion coefficients of Li in βLiGa, and for investigating how the Li diffusion in the Li ionic conductors is affected by the concentration of atomic defects (i.e., the existence of the atomic vacancies of Li and the defects in Ga sites that are replaced by Li).  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