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   1408286篇
  免费   35963篇
  国内免费   6806篇
电工技术   34092篇
综合类   6285篇
化学工业   266041篇
金属工艺   62582篇
机械仪表   38872篇
建筑科学   43764篇
矿业工程   11180篇
能源动力   50419篇
轻工业   101437篇
水利工程   13968篇
石油天然气   36392篇
武器工业   128篇
无线电   196866篇
一般工业技术   271662篇
冶金工业   116758篇
原子能技术   33625篇
自动化技术   166984篇
  2021年   15318篇
  2020年   12633篇
  2019年   16616篇
  2018年   15671篇
  2017年   15103篇
  2016年   22585篇
  2015年   19449篇
  2014年   30739篇
  2013年   90474篇
  2012年   34015篇
  2011年   44360篇
  2010年   41526篇
  2009年   50524篇
  2008年   42034篇
  2007年   38419篇
  2006年   43173篇
  2005年   37217篇
  2004年   39959篇
  2003年   39977篇
  2002年   39369篇
  2001年   35491篇
  2000年   34444篇
  1999年   32416篇
  1998年   29875篇
  1997年   29796篇
  1996年   26994篇
  1995年   26724篇
  1994年   25512篇
  1993年   25432篇
  1992年   24751篇
  1991年   21735篇
  1990年   22258篇
  1989年   21182篇
  1988年   19661篇
  1987年   18129篇
  1986年   17494篇
  1985年   20858篇
  1984年   21473篇
  1983年   19436篇
  1982年   18627篇
  1981年   18665篇
  1980年   17266篇
  1979年   17906篇
  1978年   17187篇
  1977年   16278篇
  1976年   16120篇
  1975年   15529篇
  1974年   15103篇
  1973年   15165篇
  1972年   12721篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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   
992.
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   
993.
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   
994.
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   
995.
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   
996.
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   
997.
998.
Targeting the tumor cell mitochondrion could produce novel anticancer agents. We designed an aryl−urea fatty acid ( 1 g ; 16({[4-chloro-3-(trifluoromethyl)phenyl]carbamoyl}amino)hexadecanoic acid) that disrupted the mitochondrion and decreased MDA-MB-231 breast cancer cell viability. To optimize the aryl−ureas the present study evaluated mitochondrial targeting by 1 g analogues containing alkyl chains between 10–17 carbons. Using the dye JC-1, the C12−C17 analogues efficiently disrupted the mitochondrial membrane potential (IC50s 3.5±1.2 to 7.6±1.1 μM) and impaired ATP production; shorter analogues were less active. 7-Aminoactinomycin D/annexin V staining and flow cytometry showed that these agents activated the killing mechanisms of necrosis and apoptosis to varying extents (7-aminoactinomycin D/annexin V staining ratios 4.3–6.0). Indeed, 1 g and its C17 analogue preferentially activated necrosis and apoptosis, respectively (ratios 2.1 and 16). Taken together, alkyl chain length is a determinant of mitochondrial targeting by aryl−ureas and can be varied to develop analogues that activate apoptosis or necrosis in a regulated fashion.  相似文献   
999.
Protection of Metals and Physical Chemistry of Surfaces - The degree of crystallinity of carbon fibers (CFs) of different manufacturers has been determined by means of the Raman scattering method....  相似文献   
1000.
Protection of Metals and Physical Chemistry of Surfaces - The inhibiting effect of benzimidazole derivate (DBI) on corrosion of carbon steel (CS) at temperature range of 303–333 K was...  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