首页 | 官方网站   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   1707155篇
  免费   49505篇
  国内免费   18573篇
工业技术   1775233篇
  2022年   14869篇
  2021年   26782篇
  2020年   20621篇
  2019年   21529篇
  2018年   22071篇
  2017年   22529篇
  2016年   28525篇
  2015年   28541篇
  2014年   43330篇
  2013年   104593篇
  2012年   51842篇
  2011年   64357篇
  2010年   58210篇
  2009年   66199篇
  2008年   57888篇
  2007年   53877篇
  2006年   59502篇
  2005年   51688篇
  2004年   48463篇
  2003年   47498篇
  2002年   45999篇
  2001年   41776篇
  2000年   41257篇
  1999年   41161篇
  1998年   38266篇
  1997年   36790篇
  1996年   35586篇
  1995年   32327篇
  1994年   30161篇
  1993年   28660篇
  1992年   27443篇
  1991年   23916篇
  1990年   23959篇
  1989年   22788篇
  1988年   21068篇
  1987年   19154篇
  1986年   18341篇
  1985年   21492篇
  1984年   21999篇
  1983年   19932篇
  1982年   19079篇
  1981年   19084篇
  1980年   17648篇
  1979年   18220篇
  1978年   17446篇
  1977年   16549篇
  1976年   16164篇
  1975年   15533篇
  1974年   15105篇
  1973年   15166篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
目的:设计一款满足安全、卫生、操作便捷、结构性能稳定等要求的糖霜制品3D打印机.方法:打印机主要包括机械结构和控制系统,机械结构方面采用龙门架结构,并对传统的打印料罐进行改良.控制系统采用“工控机+运动控制卡”的模式.结果:该打印机可快速更换料罐(30s内),打印机成型速度快(≥5000mm/min),速度可调;成型精度控制在1mm 以内;成型件的强度、膨胀率和表面粗糙度指标均较好.自带光源的图像识别及处理系统能够识别产品形状、个数及完整性等.结论:改良后的料罐提高了半流体食品打印的卫生性、生产效率,且便于耗材的更换,能加工出复杂糖画模型以满足造型独特的个性化糖艺制品的需求.  相似文献   
52.
Cell surface proteoglycans are known to be important regulators of many aspects of cell behavior. The principal family of transmembrane proteoglycans is the syndecans, of which there are four in mammals. Syndecan-1 is mostly restricted to epithelia, and bears heparan sulfate chains that are capable of interacting with a large array of polypeptides, including extracellular matrix components and potent mediators of proliferation, adhesion and migration. For this reason, it has been studied extensively with respect to carcinomas and tumor progression. Frequently, but not always, syndecan-1 levels decrease as tumor grade, stage and invasiveness and dedifferentiation increase. This parallels experiments that show depletion of syndecan-1 can be accompanied by loss of cadherin-mediated adhesion. However, in some tumors, levels of syndecan-1 increase, but the characterization of its distribution is relevant. There can be loss of membrane staining, but acquisition of cytoplasmic and/or nuclear staining that is abnormal. Moreover, the appearance of syndecan-1 in the tumor stroma, either associated with its cellular component or the collagenous matrix, is nearly always a sign of poor prognosis. Given its relevance to myeloma progression, syndecan-1-directed antibody—toxin conjugates are being tested in clinical and preclinical trials, and may have future relevance to some carcinomas.  相似文献   
53.
Elevated activation of the autophagy pathway is currently thought to be one of the survival mechanisms allowing therapy-resistant cancer cells to escape elimination, including for cytarabine (AraC)-resistant acute myeloid leukemia (AML) patients. Consequently, the use of autophagy inhibitors such as chloroquine (CQ) is being explored for the re-sensitization of AraC-resistant cells. In our study, no difference in the activity of the autophagy pathway was detected when comparing AraC-Res AML cell lines to parental AraC-sensitive AML cell lines. Furthermore, treatment with autophagy inhibitors CQ, 3-Methyladenine (3-MA), and bafilomycin A1 (BafA1) did not re-sensitize AraC-Res AML cell lines to AraC treatment. However, in parental AraC-sensitive AML cells, treatment with AraC did activate autophagy and, correspondingly, combination of AraC with autophagy inhibitors strongly reduced cell viability. Notably, the combination of these drugs also yielded the highest level of cell death in a panel of patient-derived AML samples even though not being additive. Furthermore, there was no difference in the cytotoxic effect of autophagy inhibition during AraC treatment in matched de novo and relapse samples with differential sensitivity to AraC. Thus, inhibition of autophagy may improve AraC efficacy in AML patients, but does not seem warranted for the treatment of AML patients that have relapsed with AraC-resistant disease.  相似文献   
54.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.  相似文献   
55.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread...  相似文献   
56.
Telecommunication Systems - Energy saving in User Equipment (UE) is one of the important issues for limited sources of power in the device. It is critical for the UE to maximize its energy...  相似文献   
57.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
58.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  相似文献   
59.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  相似文献   
60.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  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-23

京公网安备 11010802026262号