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   565278篇
  免费   7049篇
  国内免费   991篇
电工技术   10502篇
综合类   466篇
化学工业   89458篇
金属工艺   23334篇
机械仪表   18496篇
建筑科学   12527篇
矿业工程   4311篇
能源动力   14429篇
轻工业   45752篇
水利工程   6935篇
石油天然气   14961篇
武器工业   39篇
无线电   60254篇
一般工业技术   116210篇
冶金工业   95547篇
原子能技术   14681篇
自动化技术   45416篇
  2021年   5469篇
  2019年   5264篇
  2018年   9201篇
  2017年   9408篇
  2016年   9829篇
  2015年   6023篇
  2014年   10242篇
  2013年   26099篇
  2012年   15769篇
  2011年   21087篇
  2010年   16967篇
  2009年   18817篇
  2008年   19067篇
  2007年   18764篇
  2006年   16285篇
  2005年   14742篇
  2004年   14006篇
  2003年   13689篇
  2002年   13246篇
  2001年   12850篇
  2000年   12329篇
  1999年   12010篇
  1998年   27649篇
  1997年   20038篇
  1996年   15627篇
  1995年   12006篇
  1994年   10859篇
  1993年   10612篇
  1992年   8331篇
  1991年   8102篇
  1990年   7991篇
  1989年   7762篇
  1988年   7478篇
  1987年   6747篇
  1986年   6534篇
  1985年   7390篇
  1984年   6700篇
  1983年   6436篇
  1982年   5776篇
  1981年   5896篇
  1980年   5630篇
  1979年   5733篇
  1978年   5663篇
  1977年   6178篇
  1976年   7685篇
  1975年   5108篇
  1974年   4903篇
  1973年   4980篇
  1972年   4279篇
  1971年   4038篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
221.
Journal of Computer and Systems Sciences International - The problem of constructing a guaranteeing anticipating control for a shock isolator that protects an object on a movable base from impacts...  相似文献   
222.
Dreissenid mussel veligers compose a substantial component of pelagic biomass in the Great Lakes, yet their dynamics are poorly understood. To evaluate seasonal, spatial, and inter-annual variation in veliger density, we used a 64-μm mesh plankton net (2008, 2013–2016) and a 153-μm mesh plankton net (2007–2016) to collect dreissenid veligers at nearshore (15–25?m depth), transitional (45?m) and offshore (93–110?m) sites in southeast Lake Michigan during March–December. We also evaluated trends in density of recently settled mussels relative to veliger abundance and the density of the standing stock of adult mussels. Veliger density peaked during both summer and fall at all sites, but peak densities in summer were generally higher nearshore, whereas peak densities in the fall were generally higher offshore. The density of veligers in the 153-μm net was overall 28% of that in the 64-μm net, but there was high variability in this comparison among months. Smaller veligers were much more abundant in the 64-μm net, but there was little difference in the size distribution and abundance between nets for the 210–300?μm size classes. Thus, the 153-μm net could still be a useful tool for assessing density trends of larger veligers just prior to their settlement. Newly settled mussels (≤2?mm) were most abundant in summer or fall at the nearshore and offshore sites but were nearly absent at the transitional site despite the high density of veligers there. Factors other than veliger density must play an important role in mussel recruitment.  相似文献   
223.
Breast and prostate cancers are frequently treated with chemotherapy. Several novel chemicals are being reported for this purpose, particularly synthetic and natural benzophenones. This work reports the synthesis of substituted 2-hydroxybenzophenones through 1,4-conjugate addition/intramolecular cycloaddition/dehydration of nitromethane on key intermediate chromones. Structures were extensively studied by means of 2D NMR spectroscopy and single-crystal XRD. Their cytotoxicity was evaluated in vitro in two breast cancer cell lines (MDA-MB-231 and T47-D) and one prostate cancer cell line (PC3). The most potent compound exhibited good cytotoxic effects against the three cancer cell lines (IC50 values ranging from 12.09 to 26.49 μm ) and induced cell-cycle retardation only on prostate cancer cells, which suggested that it might exert cell-type-specific effects.  相似文献   
224.
Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to...  相似文献   
225.
Russian Engineering Research - Improvement in the wear resistance of plunger-pump rods is considered. Hardening by high-frequency current is proposed.  相似文献   
226.
Process analytics is one of the popular research domains that advanced in the recent years. Process analytics encompasses identification, monitoring, and improvement of the processes through knowledge extraction from historical data. The evolution of Artificial Intelligence (AI)-enabled Electronic Health Records (EHRs) revolutionized the medical practice. Type 2 Diabetes Mellitus (T2DM) is a syndrome characterized by the lack of insulin secretion. If not diagnosed and managed at early stages, it may produce severe outcomes and at times, death too. Chronic Kidney Disease (CKD) and Coronary Heart Disease (CHD) are the most common, long-term and life-threatening diseases caused by T2DM. Therefore, it becomes inevitable to predict the risks of CKD and CHD in T2DM patients. The current research article presents automated Deep Learning (DL)-based Deep Neural Network (DNN) with Adagrad Optimization Algorithm i.e., DNN-AGOA model to predict CKD and CHD risks in T2DM patients. The paper proposes a risk prediction model for T2DM patients who may develop CKD or CHD. This model helps in alarming both T2DM patients and clinicians in advance. At first, the proposed DNN-AGOA model performs data preprocessing to improve the quality of data and make it compatible for further processing. Besides, a Deep Neural Network (DNN) is employed for feature extraction, after which sigmoid function is used for classification. Further, Adagrad optimizer is applied to improve the performance of DNN model. For experimental validation, benchmark medical datasets were used and the results were validated under several dimensions. The proposed model achieved a maximum precision of 93.99%, recall of 94.63%, specificity of 73.34%, accuracy of 92.58%, and F-score of 94.22%. The results attained through experimentation established that the proposed DNN-AGOA model has good prediction capability over other methods.  相似文献   
227.
Fedotov  A. A. 《Measurement Techniques》2019,61(12):1238-1243
Measurement Techniques - The article is devoted to the issues of conceptual development of a new generation of electrocardiogram imitators. A mathematical model is proposed for simulating ECG...  相似文献   
228.
Wei  LingNan  Wang  ZhenHua  Zhang  ZhiDong  Liu  Chieh-Wen  Gao  Xuan P. A. 《Nano Research》2020,13(5):1332-1338
Nano Research - We report the composition and back-gate voltage tuned transport properties of ternary compound Bi2(Te1−xSex)3 nanowires synthesized by chemical vapor deposition (CVD). It is...  相似文献   
229.
This Concept article describes the latest developments in the emerging area of late-stage biocatalytic alkylation. Central to these developments is the ability to efficiently prepare S-adenosyl methionine (SAM) cofactor analogues and couple this with enzymatic alkyl transfer. Recent developments in the enzymatic synthesis of SAM cofactor analogues are summarized first, followed by their application as alkyl transfer agents catalyzed by methyltransferases (MTases). Second, innovative methods to regenerate SAM cofactors by enzymatic cascades is reported. Finally, future opportunities towards establishing a generalized platform for late-stage alkylation are described.  相似文献   
230.
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