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   106299篇
  免费   2943篇
  国内免费   1115篇
电工技术   2051篇
综合类   3334篇
化学工业   15034篇
金属工艺   6243篇
机械仪表   4625篇
建筑科学   3435篇
矿业工程   1192篇
能源动力   1950篇
轻工业   5106篇
水利工程   1586篇
石油天然气   1320篇
武器工业   116篇
无线电   12370篇
一般工业技术   19994篇
冶金工业   3850篇
原子能技术   452篇
自动化技术   27699篇
  2024年   598篇
  2023年   557篇
  2022年   808篇
  2021年   1166篇
  2020年   940篇
  2019年   792篇
  2018年   15133篇
  2017年   14056篇
  2016年   10712篇
  2015年   1531篇
  2014年   1343篇
  2013年   1534篇
  2012年   4539篇
  2011年   10921篇
  2010年   9573篇
  2009年   6832篇
  2008年   7918篇
  2007年   8715篇
  2006年   1080篇
  2005年   2044篇
  2004年   1759篇
  2003年   1791篇
  2002年   1115篇
  2001年   591篇
  2000年   638篇
  1999年   527篇
  1998年   504篇
  1997年   379篇
  1996年   369篇
  1995年   268篇
  1994年   220篇
  1993年   145篇
  1992年   122篇
  1991年   99篇
  1990年   74篇
  1989年   63篇
  1988年   52篇
  1987年   35篇
  1986年   33篇
  1968年   43篇
  1967年   33篇
  1966年   43篇
  1965年   45篇
  1960年   30篇
  1959年   36篇
  1958年   37篇
  1957年   36篇
  1956年   34篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The multiprocessor SoC (MPSoC) revolution is fueled by the need to execute multiple advanced multimedia applications on a single embedded computing platform. At design-time, the applications that will run in parallel and their respective user requirements are unknown. Hence, a run-time manager (RTM) is needed to match all application needs with the available platform resources and services. Creating such a run-time manager requires two decisions. First, one needs to decide what functionality to implement. Second, one has to decide how to implement this functionality in order to meet boundary conditions like e.g. real-time performance. This paper is the first to detail a generic view on MPSoC run-time management functionality and its design space trade-offs. We substantiate the run-time components and the implementation trade-offs with academic state-of-the-art solutions and a brief overview of some industrial multiprocessor run-time management examples. We show a clear trend towards more hardware acceleration, a limited distribution of management functionality over the platform and increasing support for adaptive multimedia applications. In addition, we briefly detail upcoming run-time management research issues.  相似文献   
992.
In the electronic packaging field, the Sn-Zn alloy system has been recommended as a high-temperature Pb-free solder. There is a need for thermodynamic data on the Sn-Ni-Zn ternary system. Such data would serve as a basis for understanding the interfacial reaction between Sn-Zn high-temperature solder and Ni substrates and for thermodynamically evaluating the proper composition level of Ni and Zn in Sn-based solder. This study has investigated the phase equilibria of the Sn-Ni-Zn ternary system at 800°C, 500°C, and 200°C (for Ni composition of less than 60 at.%). Scanning electron microscopy (SEM), x-ray diffraction (XRD), and electron probe microanalysis (EPMA) were used to identify the equilibrium phases. On the basis of the experimental data and thermodynamic parameters, the isothermal sections of the Sn-Ni-Zn ternary system have been described, considering the ternary solubility in the binary phases and newfound ternary phases τ1 (Sn3Ni4Zn3) and τ2 (Sn4Ni4Zn2).  相似文献   
993.
氯化铵溶液中还原浸出海洋锰结核   总被引:4,自引:1,他引:4  
采用亚硫酸钠作还原剂对氯化铵溶液中海洋锰结核的浸出行为进行研究,探讨Na2SO3加入量、NH4Cl浓度及初始pH值、浸出温度和时间等对锰结核中铜、镍、钴、锰、铁浸出率的影响。结果表明5.0mol/LNH4Cl溶液中,初始pH值约5.0及80℃、180min,锰结核与Na2SO3等量加入时,铜、镍、钴、锰的浸出率分别为88.56%、96.14%、78.57%、35.2%,铁几乎未被浸出。而在同样的条件下,控制浸出过程的pH值4.0左右,120min后铜、镍、钴、锰、铁的浸出率分别为90.21%、98.80%、91.43%、98.11%、20.13%。  相似文献   
994.
Chemistry and Technology of Fuels and Oils - Temporary plugging technology is widely used in the volume fracturing of horizontal wells. However, conventional temporary plugging balls and particles...  相似文献   
995.
The optimum solution for maximized radiated energy in a specified time interval from anN-element dipole array at a specified farfield position is presented. The solution is obtained in terms of time-domain dipole terminal voltages which are constrained in bandwidth and total input energy, with the currents on the dipoles satisfying Pocklington's integral equation. The orthogonality of characteristic terminal modes is used in the derivation of the optimum solution, and the far-zone field is expanded as a finite sum of characteristic modal fields with unknown mode coefficients. The optimum mode coefficients are found in terms of prolate spheroidal wave functions. An additional constraint can be used to find the optimum solution with a reduced sidelobe level. The effects of signal bandwidth and time interval specification on the peak field intensity and energy density in the direction of optimization are shown and limiting cases are found to agree with previous results.  相似文献   
996.
The cracks caused by tension are commonly observed on the upper border of loess slope. Most researchers assume that shear failure is the main reason for slope instability. The existing cracks and their development are not fully considered. The finite element method is applied widely in the numerical simulations of slope stability, but it converges and time problems must be considered when a crack occurs. The extended finite element method provides a new way to solve discontinuous media problems. In this paper, a composite model of cracking and shear failure is introduced. The extended finite element method was used to simulate the cracking in loess slope. The model used here had a unified enrichment function and the enriched freedom had a clear physical meaning. Numerical analyses were performed and the simulation results showed that the stress field redistributes. The crack propagated almost vertically at the beginning. The slope stability safety factor was less than that obtained without considering tension failure. Furthermore, the critical sliding surface was determined. This model can be used for analyzing the stability of loess slope and provides a reference for slope safety analyses.  相似文献   
997.
Co-based bulk glassy alloys (BGAs) have become more and more important because of their nearly zero magnetostriction and high giant magneto-impedance effect. Here, we report the improvement of glass-forming ability (GFA), soft-magnetic properties and plasticity by a small addition of Mo atoms in CoFeBSiNbMo BGAs. (Co0.6Fe0.4)69 B 20.8Si5.2Nb5?x Mo x ferromagnetic BGA cylindrical glassy rods were fabricated successfully with a diameter of 5 mm by conventional copper mould casting method. It reveals that the substitution of a small amount of Mo for Nb makes the composition to approach a eutectic point and effectively enhances the GFA of alloy. In addition to high GFA and superhigh strength, the compressive test shows that the Mo addition can improve the plasticity for the obtained BGAs. The combination of high GFA, excellent soft-magnetic properties and good plasticity demonstrated in our alloys is promising for the future applications as functional materials.  相似文献   
998.
Various theoretical and experimental 300 K equations of state of γ-B28, a new ultrahard high pressure orthorhombic phase of boron, have been reviewed. Throughout analyses and critical comparisons, it has been shown that DFT-GGA is capable of describing the EOS of γ-B28 very accurately and that the suggestion, in the literature, of an isostructural phase transformation in γ-B28 at about 40 GPa is inconclusive.  相似文献   
999.
Wf/Cu82Al10Fe4Ni4 composite was fabricated by flow casting method. Dynamic compression tests with strain rate of 1600 s−1 at 20 °C, 200 °C, 400 °C and 600 °C were finished by means of Split Hopkinson Pressure Bar (SHPB). The results showed that the composites possessed obvious high temperature softening behaviors. The damages of Wf/Cu82Al10Fe4Ni4 composites all occurred within the tungsten fibers when compressed at 20 °C, 200 °C and 400 °C, indicating that the interface strength of the composites was high. While the damages of the composites occurred either in the tungsten fibers or in the matrix at 600 °C, in addition, the melt of matrix alloy also occurred. Microstructure of the composites after dynamic compressing at 600 °C was analyzed by transmission electron microscope (TEM), observation revealed that there were a lot of high-density dislocations, stacking faults and twins existing in the matrix. It was also found that the precipitated phase in the matrix played the role of the second phase strengthening.  相似文献   
1000.
Cobalt oxide was prepared from spent lithium ion batteries (LIBs) by reductive leaching, copper sulfide precipitation, cobalt oxalate precipitation and thermal decomposition. The cobalt rich non-magnetic ?16 mesh fraction obtained from spent LIBs by mechanical separation was leached using 2 M H2SO4, 6 vol% H2O2, reaction temperature 60 °C, agitation speed 300 rpm, pulp density 100 g/L, reaction time 1 h. The leaching efficiency of cobalt was more than 99% and its concentration was 27.4 g/L. Copper was removed (99.9%) as CuS by precipitating with Na2S. The crystalline solid CoC2O4·2H2O selectively precipitated by treating the copper-free liquor with oxalic acid was calcined to produce crystalline Co3O4, of which primary average particle size was 340 nm.  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