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   1627133篇
  免费   28230篇
  国内免费   7095篇
电工技术   35252篇
综合类   6500篇
化学工业   269676篇
金属工艺   67150篇
机械仪表   47943篇
建筑科学   47943篇
矿业工程   11959篇
能源动力   50613篇
轻工业   124561篇
水利工程   16909篇
石油天然气   37759篇
武器工业   164篇
无线电   201656篇
一般工业技术   308268篇
冶金工业   224684篇
原子能技术   34831篇
自动化技术   176590篇
  2021年   15566篇
  2020年   12074篇
  2019年   14876篇
  2018年   20193篇
  2017年   20081篇
  2016年   23683篇
  2015年   17846篇
  2014年   28993篇
  2013年   88566篇
  2012年   39654篇
  2011年   55878篇
  2010年   47354篇
  2009年   54895篇
  2008年   50758篇
  2007年   49156篇
  2006年   47537篇
  2005年   43886篇
  2004年   44845篇
  2003年   44386篇
  2002年   42787篇
  2001年   39833篇
  2000年   37856篇
  1999年   37923篇
  1998年   64320篇
  1997年   50470篇
  1996年   40363篇
  1995年   34677篇
  1994年   31817篇
  1993年   31627篇
  1992年   26634篇
  1991年   24057篇
  1990年   24424篇
  1989年   23349篇
  1988年   21933篇
  1987年   20146篇
  1986年   19619篇
  1985年   22944篇
  1984年   22569篇
  1983年   20497篇
  1982年   19361篇
  1981年   19486篇
  1980年   18183篇
  1979年   18577篇
  1978年   17843篇
  1977年   18506篇
  1976年   20782篇
  1975年   16051篇
  1974年   15514篇
  1973年   15681篇
  1972年   13154篇
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
991.
Oxidation of Metals - During operation of gas turbine engines, different salts develop that lead to a hot-corrosion attack. While the hot corrosion associated with Na2SO4 and Na3VO4 has received...  相似文献   
992.
993.
994.
995.
Tissue engineered grafts show great potential as regenerative implants for diseased or injured tissues within the human body. However, these grafts suffer from poor nutrient perfusion and waste transport, thus decreasing their viability post-transplantation. Graft vascularization is therefore a major area of focus within tissue engineering because biologically relevant conduits for nutrient and oxygen perfusion can improve viability post-implantation. Many researchers used microphysiological systems as testing platforms for potential grafts owing to an ability to integrate vascular networks as well as biological characteristics such as fluid perfusion, 3D architecture, compartmentalization of tissue-specific materials, and biophysical and biochemical cues. Although many methods of vascularizing these systems exist, microvascular self-assembly has great potential for bench-to-clinic translation as it relies on naturally occurring physiological events. In this review, the past decade of literature is highlighted, and the most important and tunable components yielding a self-assembled vascular network on chip are critically discussed: endothelial cell source, tissue-specific supporting cells, biomaterial scaffolds, biochemical cues, and biophysical forces. This paper discusses the bioengineered systems of angiogenesis, vasculogenesis, and lymphangiogenesis and includes a brief overview of multicellular systems. It concludes with future avenues of research to guide the next generation of vascularized microfluidic models.  相似文献   
996.
997.
We used N-methylpyrrole (Py)-N-methylimidazole-(Im) polyamide as an exogenous agent to modulate the formation of DNA assemblies at specific double-stranded sequences. The concept was demonstrated on the hybridization chain reaction that forms linear DNA. Through a series of melting curve analyses, we demonstrated that the binding of Py−Im polyamide positively influenced both the HCR initiation and elongation steps. In particular, Py−Im polyamide was found to drastically stabilize the DNA duplex such that its thermal stability approached that of an equivalent hairpin structure. Also, the polyamide served as an anchor between hairpin pairs in the HCR assembly, thus improving the originally weak interstrand stability. We hope that these proof-of-concept results can inspire future use of Py−Im polyamide as a molecular tool to modulate the formation of DNA assemblies.  相似文献   
998.
The aim of the study is to investigate the biochemical composition of grapeseed oil and cake from an unexplored Indian grape‐juice cultivar, Manjari Medika (MM). The composition of oil and residual seed cake is evaluated using various chromatographic and spectroscopic techniques. The findings demonstrate that the vitamin E content of MM‐seed oil (1.15–1.35 g kg?1) is distinctively higher than the Codex standard, suggesting its superior quality as an edible oil. The predominant triacylglycerols include trilinolein (LLL, 43%), dilinoleoyl‐stearylglycerol (LSL, 19%), and dilinoleoyl‐palmitoylglycerol (LLP, 11%), which are earlier recognized as natural antioxidants. The seed‐cake is rich in polyphenols including acylated anthocyanins (e.g., pelargonidin‐3‐O‐coumaroyl glucoside) and certain other flavonoids (e.g., catechin). The profile of phytonutrients in MM seed‐oil and cake is significantly superior to its seeded female parent and two other widely cultivated wine‐grape varieties. In brief, the studied by‐products of this new grape‐juice cultivar can be an important source of high‐value ingredients for use in food supplements, nutraceuticals, and functional foods. Practical applications: This study reports the phytochemical profile of the seed‐oil and seed cake derived from a newly developed grape variety, Manjari Medika. High contents of selective antioxidants: lipids, vitamin E, and phenols in the seed‐oil and cake with health benefits suggest their potential for use in nutraceutical and functional foods. These byproducts can be utilised as ingredients of functional foods and nutraceuticals (e.g., grape seed oil capsule) and also as raw materials in food supply chains (e.g., for production of grape cookies or cake). MM can also be utilized as a colorant in the food industry.  相似文献   
999.
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   
1000.
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   
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