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   1482612篇
  免费   27322篇
  国内免费   7027篇
电工技术   34456篇
综合类   6499篇
化学工业   269627篇
金属工艺   64501篇
机械仪表   42065篇
建筑科学   46247篇
矿业工程   11526篇
能源动力   50506篇
轻工业   111197篇
水利工程   14751篇
石油天然气   37788篇
武器工业   153篇
无线电   196398篇
一般工业技术   280430篇
冶金工业   147145篇
原子能技术   34081篇
自动化技术   169591篇
  2021年   15500篇
  2020年   11832篇
  2019年   14640篇
  2018年   15705篇
  2017年   15038篇
  2016年   21250篇
  2015年   17345篇
  2014年   28754篇
  2013年   88209篇
  2012年   35113篇
  2011年   47531篇
  2010年   42603篇
  2009年   51191篇
  2008年   44506篇
  2007年   41783篇
  2006年   44594篇
  2005年   39372篇
  2004年   41454篇
  2003年   41363篇
  2002年   40614篇
  2001年   36728篇
  2000年   35349篇
  1999年   33983篇
  1998年   39205篇
  1997年   35634篇
  1996年   33080篇
  1995年   29494篇
  1994年   27781篇
  1993年   27674篇
  1992年   25950篇
  1991年   22905篇
  1990年   23369篇
  1989年   22427篇
  1988年   20858篇
  1987年   19207篇
  1986年   18558篇
  1985年   21959篇
  1984年   22280篇
  1983年   20245篇
  1982年   19272篇
  1981年   19329篇
  1980年   17958篇
  1979年   18511篇
  1978年   17729篇
  1977年   17362篇
  1976年   17991篇
  1975年   16031篇
  1974年   15539篇
  1973年   15627篇
  1972年   13086篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
The germline carrier of the BRCA1 pathogenic mutation has been well proven to confer an increased risk of breast and ovarian cancer. Despite BRCA1 biallelic pathogenic mutations being extremely rare, they have been reported to be embryonically lethal or to cause Fanconi anemia (FA). Here we describe a patient who was a 48-year-old female identified with biallelic pathogenic mutations of the BRCA1 gene, with no or very subtle FA-features. She was diagnosed with ovarian cancer and breast cancer at the ages of 43 and 44 and had a strong family history of breast and gynecological cancers.  相似文献   
172.
In this communication, the structural, micro-structural, dielectric, electrical, magnetic, and leakage-current characteristics of a double perovskite (Y2CoMnO6) ceramic material have been reported. The material was synthesized via a high-temperature mixed-oxide route. The compound crystallizes in a monoclinic structure which is confirmed from preliminary X-ray structural study. The morphological study by using scanning electron micrograph reveals the almost homogeneous distribution of grains throughout the surface of the sample. The nature of frequency-dependence of dielectric constant has been described by the Maxwell-Wagner model. The occurrence of a dielectric anomaly in the temperature dependence of dielectric permittivity study demonstrates the ferroelectric-paraelectric phase transition in the material. From the Nyquist plots, we found the existence of both grain and grain boundary effects. The frequency dependence of conductivity was studied by the Jonscher’s Power law, and the conduction phenomenon obeys the large overlapping polaron tunneling model. By using the Arrhenius equation, the activation energy has been calculated which is nearly equal to the energy required for the hoping of the electron. Both impedance and conductivity analysis demonstrate that the sample exhibits negative temperature coefficient of resistance (NTCR) properties indicating the semiconducting type of material at high temperatures. The anti-ferromagnetic character of the material is observed from the nature of magnetic hysteresis loop. The leakage current analysis suggests that the conduction process in the material follows the space charge limited conduction phenomenon. Such material will be helpful for modern electronic devices and spintronic applications.  相似文献   
173.
Treating neuroinflammation-related injuries and disorders through manipulation of neuroinflammation functions is being heralded as a new therapeutic strategy. In this study, a novel pectic galactan (PG) polysaccharide based gene therapy approach is developed for targeting reactive gliosis in neuroinflammation. Galectin-3 (Gal-3) is a cell protein with a high affinity to β-galactoside sugars and is highly expressed in reactive gliosis. Since PG carries galactans, it can target reactive gliosis via specific carbohydrate interaction between galactan and Gal-3 on the cell membrane, and therefore can be utilized as a carrier for delivering genes to these cells. The carrier is synthesized by modifying quaternary ammonium groups on the PG. The resulting quaternized PG (QPG) is found to form complexes with plasmid DNA with a mean diameter of 100 nm and have the characteristics required for targeted gene therapy. The complexes efficiently condense large amounts of plasmid per particle and successfully bind to Gal-3. The in vivo study shows that the complexes are biocompatible and safe for administration and can selectively transfect reactive glial cells of an induced cortical lesion. The results confirm that this PG-based delivery system is a promising platform for targeting Gal-3 overexpressing neuroinflammation cells for treating neuroinflammation-related injuries and neurodegenerative diseases.  相似文献   
174.
Jori  Popat K.  Jadhav  Vrushali H. 《Catalysis Letters》2022,152(6):1703-1710
Catalysis Letters - A new zirconium based carbonaceous solid acid catalyst Zr@CC-PA with both Lewis and Bronsted acidic sites was prepared by simultaneous carbonization and phosphonation of glucose...  相似文献   
175.
Russian Engineering Research - Models based on regression analysis for predicting the operational efficiency of high-pressure roller crushers are considered. A systematized and structured...  相似文献   
176.
Journal of Machinery Manufacture and Reliability - A device based on smart alloys has been designed for use in machine building items, in particular, in nuclear engineering, for preventing...  相似文献   
177.
Journal of Machinery Manufacture and Reliability - The problem of calculating the reliability and fatigue life of machine parts by the fatigue failure under random changes in the actual and limit...  相似文献   
178.
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation.  相似文献   
179.
180.
Material encapsulation is a relatively new technique for coating a micro/nanosize particle or droplet with polymeric or inorganic shell. Encapsulation technology has many applications in various fields including drug delivery, cosmetic, agriculture, thermal energy storage, textile, and self-healing polymers. Poly(methyl methacrylate) (PMMA) is widely used as shell material in encapsulation due to its high chemical stability, biocompatibility, nontoxicity, and good mechanical properties. The main approach for micro/nanoencapsulation of materials using PMMA as shell comprises emulsion-based techniques such as emulsion polymerization and solvent evaporation from oil-in-water emulsion. In the present review, we first focus on the encapsulation techniques of liquid materials with PMMA shell by analyzing the effective processing parameters influencing the preparation of PMMA micro/nanocapsules. We then describe the morphology of PMMA capsules in emulsion systems according to thermodynamic relations. The techniques to investigation of mechanical properties of capsule shell and the release mechanisms of core material from PMMA capsules were also investigated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48039.  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