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   47084篇
  免费   4367篇
  国内免费   2533篇
电工技术   1090篇
综合类   2904篇
化学工业   11437篇
金属工艺   3066篇
机械仪表   2222篇
建筑科学   2752篇
矿业工程   1280篇
能源动力   2432篇
轻工业   6698篇
水利工程   801篇
石油天然气   3310篇
武器工业   354篇
无线电   4993篇
一般工业技术   5791篇
冶金工业   1544篇
原子能技术   820篇
自动化技术   2490篇
  2024年   242篇
  2023年   816篇
  2022年   1226篇
  2021年   1682篇
  2020年   1739篇
  2019年   1757篇
  2018年   1568篇
  2017年   1843篇
  2016年   1898篇
  2015年   1846篇
  2014年   2706篇
  2013年   3074篇
  2012年   3342篇
  2011年   3473篇
  2010年   2413篇
  2009年   2466篇
  2008年   2243篇
  2007年   2734篇
  2006年   2571篇
  2005年   2143篇
  2004年   1769篇
  2003年   1630篇
  2002年   1385篇
  2001年   1254篇
  2000年   1102篇
  1999年   929篇
  1998年   758篇
  1997年   661篇
  1996年   502篇
  1995年   464篇
  1994年   315篇
  1993年   330篇
  1992年   270篇
  1991年   158篇
  1990年   130篇
  1989年   102篇
  1988年   85篇
  1987年   56篇
  1986年   42篇
  1985年   52篇
  1984年   51篇
  1983年   34篇
  1982年   26篇
  1981年   29篇
  1980年   20篇
  1979年   10篇
  1978年   7篇
  1976年   7篇
  1959年   5篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Cool 3D是一款特效图文制作软件,适用于动画片段、3D文字、图形等制作场合。Cool 3D中制作的特效素材应用于非线性编辑中,可以丰富素材的表现形式,提高节目编辑制作的整体质量。  相似文献   
12.
建立了高放废液中~(147)Pm的测定方法。用HDEHP萃取稀土,再用HDEHP萃淋树脂柱分离AM和稀土。然后用高效液相色谱法将~(147)Pm从Eu、Ce等其它稀土中分离出来,用液体闪烁法测量~(147)Pm的放射性活度。  相似文献   
13.
The extraction of penicillin G from simulated media was performed by water/oil/water (w/o/w) emulsion liquid membranes (ELMs) and studied under various operational conditions in a batch system. The degree of extraction achieved was between 80% and 95% under specific conditions. A concentration of greater than nine times the initial concentration of penicillin G in the external phase was obtained in the internal phase. The pH of the internal aqueous solution, containing a basic salt, was theoretically calculated on the basis of the amount of penicillin G transported into the internal phase. The calculated results agreed with the experimental data well and were used to select a suitable type and concentration of a basic salt in the internal phase to give a pH within the range 5 to 8 where penicillin G was stable after the termination of extraction. The extraction of penicillin G was successfully performed by the ELM process with sodium carbonate in the internal phase.  相似文献   
14.
The understanding of the permeation rate of metal ions through liquid membranes is important for the design of such systems. In this paper, the permeation rates of copper ions through liquid surfactant membranes, including interfacial reaction rates and the diffusion rate of the copper ion, were analyzed using a model based on a mobilized hollow spherical globule configuration. The analysis shows that the extracting reaction is dominant at the external interface of the membrane and the stripping reaction is dominant at the internal interface; this means the reactions at both interfaces are not in equilibrium during the course of extraction. It also shows that the extraction rate, the diffusion rate and the stripping rate are not of equal value, especially at the early stage of the run.  相似文献   
15.
Recombinant cytochrome b5 was extracted into the reversed micelle phase of an anionic surfactant (AOT) in octane and back-extracted to a final aqueous phase. The extraction of the protein was controlled by an electrostatic mechanism, since it was dependent on the global charge of the protein. This was directly demonstrated by experiments with native and mutant cytochromes obtained by site directed mutagenesis. The back-extraction of cytochrome b5 to a fresh aqueous phase was decreased by factors that reduced the size of the water pool of the organic phase, such as high salt concentrations (1–2 mol dm?3 NaCl) and low temperatures (4°C), probably because of an increase in a favourable interaction of this protein with the surfactant at closer distances.  相似文献   
16.
Quenching with gases rather than oil or other liquid media has the advantages of reducing the risks concerning health and environment, while simultaneously homogenizing the quenching results and minimizing distortion due to a wide range of possible process parameter variations and the pure convective heat transfer. In this contribution, a coupled solution for increasing homogenization of quenching results within high pressure gas quenching will be presented. In the first stage, an experimental test facility was set up for flow investigations and in the second stage a numerical simulation model was generated. The numerical and experimental results of the flow through the chamber were compared for several boundary conditions. Finally, after complete verification of the simulation, the model may be used to assist in parameter variation for optimization of homogeneous high pressure gas quenching.  相似文献   
17.
InGaAs(P)分别限制应变单量子阱激光器的优化设计   总被引:1,自引:0,他引:1  
针对较常用的InGaAs(P)分别限制应变单量子阱激光器,给出了为得到最大净增益的优化设计参数。对于激射波长为1.55μm的无应变激光器,最佳的光限制层波长为1.24μm,厚度为100nm。当阱材料引入压缩应变后.由于价带的有效状态密度减小,量子阱激光器的微分增益变大,阱深的增大对增大线性增益的效果更加明显.所以最佳光限制层的波长将变短,为1.20μm  相似文献   
18.
Research has continued in the field sidechain liquid crystal polymers over recent years, but it is becoming clearer that this research is being directed away from the traditional technology areas of electro-optic devices and researchers are developing new and exciting applications for this novel state of matter.  相似文献   
19.
The irreversibly bound interfacial layer deposited by the γ-aminopropysilanetriol adhesion promoter onto a crystalline silicon substrate, which remains even after profuse washing, was found by XPS to have resulted from the fragmentation and rearrangement of the original γ-aminopropylsilanetriol molecule. A mechanism is proposed, involving the homolytic scission of the terminal N-C bond. One of the subsequent reactions is believed to involve hydrogen loss by abstraction and the formation of a terminal vinyl group, which bonds to the substrate. Support for this mechanism is found in IR spectroscopy of this layer.  相似文献   
20.
用反相高效液相色谱法测定卷柏提取物中的穗花杉双黄酮。结果表明:穗花杉双黄酮在质量浓度为41.2mg/L~206mg/L时,峰面积Y与其质量浓度X的线性关系良好,回归方程为Y=547.028X 15.4895(r=0.9999),最低检测限为2.0μg/L;穗花杉双黄酮的平均回收率为99.42%(n=3),相对标准偏差RSD为0.79%;连续进样、日内进样和日间进样所得检测结果的RSD分别为0.12%、0.11%和0.11%。  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