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   13841篇
  免费   1319篇
  国内免费   627篇
电工技术   879篇
技术理论   4篇
综合类   1076篇
化学工业   2372篇
金属工艺   789篇
机械仪表   792篇
建筑科学   1089篇
矿业工程   419篇
能源动力   408篇
轻工业   988篇
水利工程   259篇
石油天然气   719篇
武器工业   99篇
无线电   1707篇
一般工业技术   1627篇
冶金工业   636篇
原子能技术   190篇
自动化技术   1734篇
  2024年   65篇
  2023年   245篇
  2022年   400篇
  2021年   569篇
  2020年   398篇
  2019年   347篇
  2018年   408篇
  2017年   421篇
  2016年   375篇
  2015年   535篇
  2014年   626篇
  2013年   765篇
  2012年   805篇
  2011年   870篇
  2010年   750篇
  2009年   803篇
  2008年   695篇
  2007年   661篇
  2006年   709篇
  2005年   480篇
  2004年   509篇
  2003年   559篇
  2002年   791篇
  2001年   684篇
  2000年   426篇
  1999年   373篇
  1998年   265篇
  1997年   243篇
  1996年   214篇
  1995年   153篇
  1994年   148篇
  1993年   133篇
  1992年   81篇
  1991年   52篇
  1990年   61篇
  1989年   41篇
  1988年   35篇
  1987年   30篇
  1986年   11篇
  1985年   15篇
  1984年   7篇
  1983年   9篇
  1982年   6篇
  1981年   6篇
  1980年   4篇
  1979年   1篇
  1978年   1篇
  1969年   1篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 29 毫秒
941.
以兖州煤为原料 ,在 70 0~ 10 0 0℃下热裂解制备煤基炭材料。氮气物理吸附和X射线衍射分别考察了炭材料的BET比表面积、孔容以及微晶结构的变化 ;并将炭材料制作成电极以考察其嵌锂行为。研究发现随着热处理温度的升高 ,煤基炭材料的微晶结构变得有序 ,而BET比表面积、孔容以及首次充放电可逆容量呈现下降趋势。在 70 0℃下热裂解所制备的炭材料 ,其放电容量高达 470mAh/ g。  相似文献   
942.
The dependence of THMA extraction behaviour for U(VI) and Th(IV) on nitric acid concentration,THMA concentratioin and molecular structure of extracted complex has been studied.For nitric acid solutions of 3.0 mol/L a coordinative mechanism may possibly dominate in the extraction of metal catioins,The complex composition of UO2(NO3)2(THMA)2,Th(NO3)4(THMA)2 and Th(NO3)4(THMA03 are proved.  相似文献   
943.
在深入研究文氏桥电路的基础上研制了EHL-C型润滑状态测试仪。文中阐述了仪器的特点,给出测试所需标定曲线的绘制过程。最终通过高速滚动轴承的测试分析,证明了仪器的可行性,具有推广的价值。  相似文献   
944.
Abstract DNA typing of four tetrameric repeat loci (HUMVWA, HUMTH0I, D21SII and HPRT) was carried out in a Chinese Han population from Shanghai (East China) and one from Guangzhou (South-East China) using a quadruplex PCR amplification and detection of the fluorescent-labeled alleles on the ALF DNA sequencer. All loci were in accordance with Hardy-Weinberg equilibrium except for D21S11 in the Guangzhou population. A test for population differentiation showed no statistical difference in the allele frequency distribution between the two populations. Comparison of the allele frequency data with other Chinese Han populations from North and South-West China for the STR loci HUMVWA and HUMTH01 revealed heterogeneity between Northern Chinese Han and Southern Chinese Han, which is in accordance with previous studies on the basis of protein markers.  相似文献   
945.
开展SPECT影像MonteCarlo模拟和高性能低价格SPECT的研制   总被引:1,自引:1,他引:0  
在SPECT的硬件和软件研制中,MontCarlo模拟是重要的手段,我们正在研制高性能低价格的SPECT,本文介绍这个领域研究工作。  相似文献   
946.
The effects of recombinant human fibroblast growth factor-2 (rhFGF-2) in the presence of eroding 50:50 poly(DL-lactide-co-glycolide) (PDLLG) on acute bone healing were studied in the optical bone chamber (BCI). BCIs were loaded with disks of PDLLG surrounded by one of four rhFGF-2 doses. Fifty-two female rabbit right tibias were implanted. Commencing the third week post implantation (W3) healing in the BCI compartment was observed weekly, using intravital microscopy, until W8. The doses were: unloaded, loaded with polymer only, and polymer plus 0.5, 1.0, and 10 microg rhFGF-2. Videotaped and photographed bone images were measured and analyzed using a frame-grabber digitizing system. Comparison with controls revealed that ossification rates were significantly above normal in rabbits loaded with polymer plus any of the rhFGF-2 doses. Comparison with polymer-only BCIs showed that PDLLG plus any of the three rhFGF-2 doses was linked with ossification rates significantly higher than baseline. The results indicated that FGF-2 in the dose range studied effectively can overcome the retarding effects of eroding polymer on ossification that has been reported by this laboratory. Interpretation of the retarding effects of the polymer disks, although consistent with previously studied washer-shaped devices of the same material, was complicated by a difference in erosion rate. This result supports the notion that erodible device geometry is a major factor in determining biocompatibility and must be considered in the design of carriers. Accordingly, programming of dose specificity for delivering a given polypeptide cytokine to a given host site must allow for the inhibitory effects of an eroding carrier and the influence of device geometry on these effects and erosion.  相似文献   
947.
An earlier analysis of the field structure and energy flow near the axis of any circularly symmetric focusing reflector is applied to the case of a spherical reflector. From the results an estimate is made of the attainable efficiency of corrugated-waveguide aperture-type feeds.  相似文献   
948.
Before 1949, the year the People's Republic of China was founded, there was hardly any rare earth industry in China. Through the efforts made in the past thirty years however, substantial changes have taken place. An attempt is made here to look at the course we have followed and the present situation.  相似文献   
949.
We report on the synthesis of an azobenzene-containing inimer 6-{4-[4-(2-(2-bromoisobutyryloxy)hexyloxy)phenylazo]phenoxy}hexyl methacrylate (I) and used it to prepare hyperbranched homopolymer and copolymers by self-condensing vinyl polymerization (SCVP) and copolymerization (SCVCP) with its precursor 6-{4-[4-(6-hydroxyhexyloxy)phenylazo]phenoxy}hexyl methacrylate (M) using atom transfer radical polymerization (ATRP). Depending on the comonomer ratio, γ=[M]0/[I]0, branched polymethacrylates with number-average weights between 8000 and 20,000 and degree of branching (DB) between 0.08 and 0.49 were obtained by SCVCP, as evidenced by GPC and 1H NMR analysis. In addition, the photochemical properties of the polymers were also studied by UV-vis spectra and found the structure of polymers affect obviously the trans-cis isomerization properties of the branched polymers.  相似文献   
950.
Perchlorate is known to be a minor component of the hyperarid Atacama Desert salts, and its origin has long been a subject of speculation. Here we report the first measurement of the triple-oxygen isotope ratios (18O/16O and 17O/16O) for both man-made perchlorate from commercial sources and natural perchlorate extracted from Atacama soils. We found that the delta 18O values (i.e., normalized 18O/ 16O ratios) of man-made perchlorate were at -18.4+/-1.2%, whereas natural perchlorate has a variable delta 18O value, ranging from -4.5% to -24.8%. The delta 18O and delta 17O values followed the bulk Earth's oxygen isotope fractionation line for man-made perchlorate, but all Atacama perchlorates deviated from this line, with a distinctly large and positive 170 anomaly ranging from +4.2% to +9.6%. These findings provide a tool for the identification and forensics of perchlorate contamination in the environment. Additionally, they confirm an early speculation that the oxidation of volatile chlorine by 03 and the formation of HClO4 can be a sink (albeit a minor one) for atmospheric chlorine.  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