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   1501845篇
  免费   30885篇
  国内免费   8862篇
电工技术   36254篇
技术理论   8篇
综合类   9352篇
化学工业   266218篇
金属工艺   66034篇
机械仪表   43883篇
建筑科学   47805篇
矿业工程   12934篇
能源动力   51369篇
轻工业   107803篇
水利工程   15571篇
石油天然气   39976篇
武器工业   584篇
无线电   199392篇
一般工业技术   282834篇
冶金工业   154965篇
原子能技术   34180篇
自动化技术   172430篇
  2021年   17133篇
  2020年   13212篇
  2019年   15716篇
  2018年   15645篇
  2017年   15081篇
  2016年   21855篇
  2015年   18970篇
  2014年   30770篇
  2013年   90230篇
  2012年   36966篇
  2011年   48792篇
  2010年   43782篇
  2009年   52315篇
  2008年   45639篇
  2007年   42337篇
  2006年   46336篇
  2005年   40299篇
  2004年   42060篇
  2003年   41967篇
  2002年   41001篇
  2001年   37834篇
  2000年   36465篇
  1999年   35615篇
  1998年   42479篇
  1997年   37503篇
  1996年   32522篇
  1995年   30244篇
  1994年   28337篇
  1993年   27926篇
  1992年   25782篇
  1991年   22887篇
  1990年   23320篇
  1989年   22126篇
  1988年   20655篇
  1987年   18946篇
  1986年   18390篇
  1985年   21688篇
  1984年   21944篇
  1983年   19870篇
  1982年   18940篇
  1981年   18963篇
  1980年   17588篇
  1979年   18234篇
  1978年   17493篇
  1977年   17059篇
  1976年   17921篇
  1975年   15720篇
  1974年   15290篇
  1973年   15373篇
  1972年   12929篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
通过对大冶铜绿山矿区周边农田土壤、水稻系统采样分析表明,农田土壤中全量Cd的浓度范围为0.42~1.63 mg/kg,平均值为0.88 mg/kg,土壤中全量Cd含量与易利用态和中等结合态含量有较高的相关系数,相关系数0.8。在水稻籽实(大米)镉积累预测方面,选取土壤中全量Cd、pH、CEC、有机质建立的数学模型能较好地预测大米中Cd的累积。  相似文献   
992.
Proton-detected 100 kHz magic-angle-spinning (MAS) solid-state NMR is an emerging analysis method for proteins with only hundreds of microgram quantities, and thus allows structural investigation of eukaryotic membrane proteins. This is the case for the cell-free synthesized hepatitis C virus (HCV) nonstructural membrane protein 4B (NS4B). We demonstrate NS4B sample optimization using fast reconstitution schemes that enable lipid-environment screening directly by NMR. 2D spectra and relaxation properties guide the choice of the best sample preparation to record 2D 1H-detected 1H,15N and 3D 1H,13C,15N correlation experiments with linewidths and sensitivity suitable to initiate sequential assignments. Amino-acid-selectively labeled NS4B can be readily obtained using cell-free synthesis, opening the door to combinatorial labeling approaches which should enable structural studies.  相似文献   
993.
Metal Science and Heat Treatment - A method for controlling the condition of permanent magnets based on solution of the problem of harmonic balance and full-scale and model tests is suggested. The...  相似文献   
994.
Protection of Metals and Physical Chemistry of Surfaces - Mesoporous titanosilicate structures synthesized by the sol–gel method using the cetylpyridinium template at different Ti/Si ratios...  相似文献   
995.
996.
Russian Engineering Research - On the profilograms obtained for real surfaces machined by different methods, the microprojections resemble elements of sinusoids and cosinusoids. Accordingly, it is...  相似文献   
997.
The present work focuses on the fabrication of βTCP (β-tricalcium phosphate) and HA/βTCP (hydroxyapatite/β-tricalcium phosphate) composite coatings by plasma spraying. The starting powders were produced via solid-state method using 2 wt% MgO to stabilize βTCP phase. The synthesized powders were preliminarily granulated to be used by the plasma spray process. Coatings obtained on titanium substrates are uniform and well adherent but due to the high temperature and cooling rate typical for plasma spraying process, βTCP phase is almost totally transformed into the α allotrope. Thermal treatment at 800 °C allows the reconversion of the phase αTCP→ βTCP. It is therefore possible to produce coatings with tuneable dissolution properties by selecting the proper initial powder mixture and the specific thermal treatment.  相似文献   
998.
Crossover designs are an extremely useful tool to investigators, and group sequential methods have proven highly proficient at improving the efficiency of parallel group trials. Yet, group sequential methods and crossover designs have rarely been paired together. One possible explanation for this could be the absence of a formal proof of how to strongly control the familywise error rate in the case when multiple comparisons will be made. Here, we provide this proof, valid for any number of initial experimental treatments and any number of stages, when results are analyzed using a linear mixed model. We then establish formulae for the expected sample size and expected number of observations of such a trial, given any choice of stopping boundaries. Finally, utilizing the four-treatment, four-period TOMADO trial as an example, we demonstrate that group sequential methods in this setting could have reduced the trials expected number of observations under the global null hypothesis by over 33%.  相似文献   
999.
Carbohydrates and their conjugates play important roles in many biological processes including fertilization, differentiation, development, immune response, and infection. Their activities are largely dependent on the properties of terminal mono‐ or disaccharides. Galactose, mannose, fucose, glucose, sialic acid, etc., are commonly used as powerful scaffolds installed on drug molecules for targeting specific tissues including brain, liver, and cancers, and as epitopes for enhancing the targeting of various vaccines. This review focuses on the influence of their structural variations, including changes in sugar type, substituent groups and their positions, as well as length of linker portion, on the targeting of drugs or their efficacy. Particular attention is paid to the targeting properties of mono‐ and disaccharides applied in drug design and discovery.  相似文献   
1000.
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