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   1581篇
  免费   10篇
电工技术   9篇
化学工业   106篇
金属工艺   18篇
机械仪表   8篇
建筑科学   24篇
矿业工程   3篇
能源动力   11篇
轻工业   43篇
水利工程   5篇
石油天然气   2篇
无线电   62篇
一般工业技术   96篇
冶金工业   1155篇
原子能技术   2篇
自动化技术   47篇
  2021年   5篇
  2018年   6篇
  2017年   6篇
  2016年   4篇
  2015年   6篇
  2014年   6篇
  2013年   35篇
  2012年   14篇
  2011年   14篇
  2010年   20篇
  2009年   15篇
  2008年   10篇
  2007年   21篇
  2006年   16篇
  2005年   18篇
  2004年   24篇
  2003年   15篇
  2002年   10篇
  2001年   8篇
  2000年   12篇
  1999年   48篇
  1998年   343篇
  1997年   215篇
  1996年   133篇
  1995年   74篇
  1994年   70篇
  1993年   70篇
  1992年   21篇
  1991年   25篇
  1990年   22篇
  1989年   27篇
  1988年   34篇
  1987年   29篇
  1986年   27篇
  1985年   16篇
  1984年   6篇
  1983年   6篇
  1982年   5篇
  1981年   10篇
  1980年   8篇
  1979年   7篇
  1978年   8篇
  1977年   18篇
  1976年   35篇
  1975年   15篇
  1973年   5篇
  1972年   7篇
  1971年   6篇
  1970年   6篇
  1966年   3篇
排序方式: 共有1591条查询结果,搜索用时 0 毫秒
31.
32.
Artificial illumination is an important factor in the management of layers. In this study, a new monochromatic light system was developed for egg layers. Prelaying pullets (Lohmann) were marked and housed in nine light and temperature control rooms (15 battery cages, 3 hens per cage; n = 45), divided into three light treatments: 0.1 and 0.01 W/m2 light intensity using light emitting diode (LED) lamps and 0.1 W/m2 using mini-fluorescent bulbs (PL) (control). In each of the LED rooms, three wavelengths were tested: 560 (n = 9), 660 (n = 9), 880 (n = 6), and 660 intermitted lighting (15 min light 45 min dark, 660IN) (n = 9). Birds were exposed to 12 h light and 12 h of darkness using PL lamps. At 21 wk of age, the light period was increased to 12.75 h by using 5.5 h of LED lamps and 7.25 of PL light source for Groups 1 and 2, the third group received 12.75 h of PL light. Until 28 wk of age, light hours increased by 0.5 h/w using LED light for Groups 1 and 2 and PL source for the third group, reaching 16 h of light at 28 wk of age. Egg production and feed consumption were recorded daily; egg components were recorded weekly for 10 mo. A significant reduction in egg production was observed in all 880nm groups; no differences in egg production and quality were found in the other groups. Feed consumption was significantly lower by 7% in all 0.01 W/m2 groups. We suggest that an important reduction in rearing costs of laying hens may be obtained by using this system.  相似文献   
33.
This is a study on the loss-grief reaction and coping behavior of a mother whose child died of brain tumor. The researcher used field methods to collect data and analyze observations of mother-nurse interaction. The results showed that this mother had self-blame depression, and guilt feelings and affected the whole family. With the help of nurses and various supportive resources the mother was finally able to go through the grieving process smoothly.  相似文献   
34.
35.
The synthesis and antithrombotic activity of a series of nonpeptide bicyclic thrombin inhibitors is described. We have explored the SAR with modifications to the P1 site. The introduction of arginine mimetics at the P1 site led to potent and selective thrombin inhibitors.  相似文献   
36.
AIM: To examine the association of Epstein-Barr virus (EBV) with carcinoma of the ear. METHODS: Five non-keratinising squamous cell carcinomas and two undifferentiated carcinomas of the ear were examined. In situ hybridisation was used to localised EBV-encoded RNAs (EBER). Immunohistochemical methods to detect LMP-1 and EBNA2 were performed in the EBER positive cases. RESULTS: Two cases were EBER positive, including one non-keratinising and one undifferentiated carcinoma. Both showed identical morphology to those arising from the nasopharynx, with abundant lymphoid stroma. They were both negative for LMP-1 and EBNA2. CONCLUSIONS: EBV associated carcinoma with the morphology of lymphoepithelioma can also arise from the middle ear.  相似文献   
37.
Point-to-point functional movements involve simultaneous shoulder and elbow joint rotations. In able-bodied subjects these movements are fully automatic, and feed-forward control ensures the synergistic activity of many muscles. Synergy between joint rotations was defined and described as a scaling between joint angular velocities [19]. Similarly, subjects who can control their shoulder movements may be assisted in reaching tasks by functional electrical stimulation (FES) of elbow extensor muscles. The synergistic control paradigm can be implemented in real-time by employing a hierarchically structured production-rules method. The use of production-rules necessitates the acquisition of knowledge and the assembly of a rule-base. A nonparametric technique was designed for the identification of the rules. The identification process was divided into two phases: determination of the scaling parameters, and determination of the stimulation parameters. The scaling parameters, needed for the coordination of movements, were determined in able-bodied subjects. Those depend exclusively on the initial and target positions of the hand. The number of scalings could be reduced by dividing the workspace into 12 zones. The stimulation parameters, needed for the execution of movements, were determined in subjects with paralyzed elbow extensor muscles by identifying triplets: elbow angular velocity, elbow angular acceleration (velocity increments), and the corresponding pulse durations for various classes of movements and loads attached to the hand.  相似文献   
38.
Lindsay  R.  Thornton  G. 《Topics in Catalysis》2002,18(1-2):15-19
We review our X-ray absorption spectroscopy studies of adsorbate geometries on the O-terminated (000 ) and Zn-terminated (0001) basel faces, as well as the non-polar (10 0) prism face of ZnO. Studies employing near-edge X-ray absorption fine-structure (NEXAFS) and surface X-ray absorption fine-structure (SEXAFS) are included.  相似文献   
39.
A study of structural determinants in the interleukin-1 fold   总被引:1,自引:0,他引:1  
The structures of interleukin-1ß, basic fibroblastgrowth factor and Erythrina trypsin inhibitor have been analysedin order to determine whether the hydrophobic core remains conserved,even when the structures have extremely low sequence similarities.We find that there are significant differences in the way eachprotein achieves a satisfactory arrangement of core residuesand that positions which contribute to the core of one structureare not guaranteed to contribute to the integrity of another.Furthermore, the side-chain packing arrangements of these coreresidues vary significantly between the three structures. Duringthis analysis the side-chain rotamers for three independentlydetermined interleukin-1ß structures were also compared.It was found that although buried residues are generally inagreement the remaining residues frequently occupy differentrotamers in the three structures. This suggests that althoughmeaningful studies are possible for buried side-chains the resultsobtained from equivalent analyses of accessible residues shouldbe treated with caution. These results are discussed with specificreference to the optimization of side-chain packing in proteinsof known structure.  相似文献   
40.
We investigate vacancy-mediated diffusion in a binary substitutional alloy by explicitly accounting for discrete vacancy sources and sinks. The regions between sources and sinks are treated as binary crystals with a perfect lattice structure containing a dilute concentration of vacancies. The sources and sinks are assumed ideal, maintaining an equilibrium vacancy concentration in their immediate vicinity. Diffusion within the perfect lattice is described with a diffusion-coefficient matrix determined by kinetic Monte Carlo simulations for a binary, thermodynamically ideal alloy in which the components have different vacancy-exchange frequencies. Continuum simulations are performed for diffusion couples with discrete grain boundaries acting as vacancy sources and sinks. Effective grain coarsening due to the Kirkendall effect is observed even in the absence of Gibbs-Thomson driving forces. As in standard ternary systems, uphill diffusion is observed. We also find that the drift of the lattice frame of reference as a result of the Kirkendall effect increases with the source/sink density. Upon increasing the density of vacancy sources and sinks, we recover the conventional treatment of substitutional diffusion, which assumes a dense and uniform distribution of vacancy sources and sinks that maintain an equilibrium vacancy concentration throughout the solid. The inverse Kirkendall effect, where the slower component segregates at grain boundaries acting as vacancy sinks, is also observed in the simulations.  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