全文获取类型
收费全文 | 21677篇 |
免费 | 1631篇 |
国内免费 | 801篇 |
专业分类
电工技术 | 889篇 |
技术理论 | 1篇 |
综合类 | 898篇 |
化学工业 | 2630篇 |
金属工艺 | 1023篇 |
机械仪表 | 921篇 |
建筑科学 | 1086篇 |
矿业工程 | 312篇 |
能源动力 | 543篇 |
轻工业 | 1695篇 |
水利工程 | 348篇 |
石油天然气 | 567篇 |
武器工业 | 107篇 |
无线电 | 1824篇 |
一般工业技术 | 2331篇 |
冶金工业 | 6331篇 |
原子能技术 | 190篇 |
自动化技术 | 2413篇 |
出版年
2024年 | 368篇 |
2023年 | 391篇 |
2022年 | 766篇 |
2021年 | 989篇 |
2020年 | 711篇 |
2019年 | 554篇 |
2018年 | 540篇 |
2017年 | 647篇 |
2016年 | 573篇 |
2015年 | 724篇 |
2014年 | 934篇 |
2013年 | 1046篇 |
2012年 | 1141篇 |
2011年 | 1218篇 |
2010年 | 1009篇 |
2009年 | 965篇 |
2008年 | 895篇 |
2007年 | 806篇 |
2006年 | 737篇 |
2005年 | 592篇 |
2004年 | 416篇 |
2003年 | 356篇 |
2002年 | 329篇 |
2001年 | 308篇 |
2000年 | 244篇 |
1999年 | 372篇 |
1998年 | 1885篇 |
1997年 | 1225篇 |
1996年 | 746篇 |
1995年 | 431篇 |
1994年 | 383篇 |
1993年 | 405篇 |
1992年 | 91篇 |
1991年 | 88篇 |
1990年 | 127篇 |
1989年 | 101篇 |
1988年 | 98篇 |
1987年 | 96篇 |
1986年 | 68篇 |
1985年 | 63篇 |
1984年 | 25篇 |
1983年 | 27篇 |
1982年 | 30篇 |
1981年 | 69篇 |
1980年 | 65篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 120篇 |
1976年 | 235篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
1.
2.
Zhu Xiao Di 《Housing Studies》2007,22(4):459-472
Using longitudinal data from the Panel Study of Income Dynamics (PSID) between 1984 and 2001 among only renter households in 1984, this paper looks at the relationship between length of homeownership thereafter during that period and household income in 2001. The study found that the longer the period of homeownership during the studied period, the higher future household income was by 2001. It is estimated that each year of ownership is associated with approximately 2 per cent of increase in household income and doubling the length of ownership increases household income by about 11 per cent. 相似文献
3.
北京远南大厦设计及其成败得失 总被引:2,自引:0,他引:2
介绍了北京南大厦供暖,空调通风,机械排风以及防排烟系统的设计概况,总结了设计中的成功经验,并结合运行情况,提出了一些在设计,生产,施工安装中应注意的问题。 相似文献
4.
Di Zhou Wen‐Bo Li Li‐Xia Pang Jing Guo Ze‐Ming Qi Tao Shao Zhen‐Xing Yue Xi Yao 《Journal of the American Ceramic Society》2014,97(11):3597-3601
Ag2MoO4 ceramic was prepared by using the solid‐state reaction method, which could be sintered at 450°C for 2 h, having a relative permittivity of 8.08, a Qf value of 17 000 GHz, and a temperature coefficient of resonance frequency about ?133 ppm/°C. Ag2MoO4 ceramic was chemically compatible with silver but reacted seriously with aluminum to form (Ag0.5Al0.5)MoO4 during the sintering. The fitting of infrared spectra and the Shannon's additive rule were employed to study intrinsic dielectric behaviors of the ceramics at microwave region. Ionic displacive polarization and the electronic polarization contributed almost equally to the dielectric permittivity of the ceramic at microwave region. The Ag2MoO4 ceramics could be a good candidate for ultra‐low temperature co‐fired microwave devices. 相似文献
5.
压水堆启动前需要进行物理启动试验,其中调临界是相对耗时的一部分。采用次临界条件下的试验,可以省去调临界的步骤,提高物理启动试验的安全性和适用性,加速物理启动试验的进程,提高压水堆的负荷因子。目前,次临界反应性测量受限于测量信号较弱,背景噪声强,误差较大,难以满足商用压水堆的工程应用要求。本文基于源倍增方法,利用空间重要性修正因子和信号线性修正提高次临界反应性测量的精度,成功地在核电厂首循环上实现了次临界反应性测量的蒙特卡罗方法计算,取得了较好的计算精度与效果。 相似文献
6.
7.
为给复合式路面的使用寿命预估提供参考, 采用有限元软件建立了带裂缝的沥青混凝土罩面连续配筋水泥混凝土(AC+CRC)复合式路面结构应力分析模型, 对在正载和偏载作用下沥青面层正应力和剪应力分布进行了分析.计算了沥青层荷载型反射裂缝应力强度因子, 分析出结构层厚度、模量、配筋率、层间结合状态对AC层反射裂缝扩展的影响.分析结果表明, 增加AC层厚度及底基层模量、提高CRC层配筋率、改善层间结合状态等均能较好地抑制复合式路面反射裂缝的发展, 而CRC层厚度及模量、AC层模量对复合式路面反射裂缝的发展基本没有影响.研究结果可为AC+CRC复合式路面结构设计提供一定的理论依据. 相似文献
8.
Ignazio Restivo Alessandro Attanzio Ilenia Concetta Giardina Francesca Di Gaudio Luisa Tesoriere Mario Allegra 《International journal of molecular sciences》2022,23(23)
Eryptosis is a physiological mechanism for the clearance of senescent or damaged erythrocytes by phagocytes. Excessive eryptosis is stimulated under several pathologies and associated with endothelial injury and thrombosis. Cigarette smoke (CS) is an established risk factor for vascular diseases and cigarette smokers have high-levels of eryptotic erythrocytes. This study, for the first time, investigates the mechanism by which CS damages red blood cells (RBCs). CS extract (CSE) from commercial cigarettes was prepared and standardized for nicotine content. Cytofluorimetric analysis demonstrated that treatment of human RBCs with CSE caused dose-dependent, phosphatidylserine externalization and cell shrinkage, hallmarks of apoptotic death. CSE did not affect cellular levels of Ca2+, reactive oxygen species (ROS) or glutathione (GSH). Immununoprecipitation and immunoblotting revealed the assembly of the death-inducing signaling complex (DISC) and oligomerization of Fas receptor as well as cleaved caspase-8 and caspase-3 within 6 h from the treatment. At the same time-interval, CSE elicited neutral sphyngomielinase (nSMase) activity-dependent ceramide formation and phosphorylation of p38 MAPK. Through specific inhibitors’ nSMase, caspase-8 or p38 MAPK activities, we demonstrated that p38 MAPK activation is required for caspase-8-mediated eryptosis and that ceramide generation is initiator caspase-dependent. Finally, ex vivo analysis detected phosphorylated p38 MAPK (p-p38) and Fas-associated signaling complex in erythrocytes from cigarette smokers. In conclusion, our study demonstrates that CSE exposure induces in erythrocytes an extrinsic apoptotic pathway involving p38 MAPK-initiated DISC formation followed by activation of caspase-8/caspase-3 via ceramide formation. 相似文献
9.
Daqian Sun Weizhu Quan Di Wang Jingyan Cui Tianyi Wang Mei Lin Yijin Wang Nan Wang Yuanyuan Dong Xiaowei Li Weican Liu Fawei Wang 《International journal of molecular sciences》2022,23(23)
Camelina sativa (L.) Crantz is an indispensable oilseed crop, and its seeds contain many unsaturated fatty acids. FAD (fatty acid desaturase) regulates the synthesis of unsaturated fatty acids. In this research, we performed CsFAD gene family analysis and identified 24 CsFAD genes in Camelina, which were unevenly distributed on 14 of the 19 total chromosomes. Phylogenetic analysis showed that CsFAD includes four subfamilies, supported by the conserved structures and motifs of CsFAD genes. In addition, we investigated the expression patterns of the FAD family in the different tissues of Camelina. We found that CsFAD family genes were all expressed in the stem, and CsFAD2-2 was highly expressed in the early stage of seed development. Moreover, during low temperature (4 °C) stress, we identified that the expression level of CsFAD2-2 significantly changed. By observing the transient expression of CsFAD2-2 in Arabidopsis protoplasts, we found that CsFAD2-2 was located on the nucleus. Through the detection and analysis of fatty acids, we prove that CsFAD2-2 is involved in the synthesis of linolenic acid (C18:3). In conclusion, we identified CsFAD2-2 through the phylogenetic analysis of the CsFAD gene family and further determined the fatty acid content to find that CsFAD2-2 is involved in fatty acid synthesis in Camelina. 相似文献
10.
Maria Addolorata Bonifacio Riccardo Laterza Angela Vinella Annalisa Schirinzi Mariangela Defilippis Francesca Di Serio Angelo Ostuni Antonio Fasanella Maria Addolorata Mariggi 《International journal of molecular sciences》2022,23(17)
Serological assays are useful in investigating the development of humoral immunity against SARS-CoV-2 in the context of epidemiological studies focusing on the spread of protective immunity. The plaque reduction neutralization test (PRNT) is the gold standard method to assess the titer of protective antibodies in serum samples. However, to provide a result, the PRNT requires several days, skilled operators, and biosafety level 3 laboratories. Therefore, alternative methods are being assessed to establish a relationship between their outcomes and PRNT results. In this work, four different immunoassays (Roche Elecsys® Anti SARS-CoV-2 S, Snibe MAGLUMI® SARS-CoV-2 S-RBD IgG, Snibe MAGLUMI® 2019-nCoV IgG, and EUROIMMUN® SARS-CoV-2 NeutraLISA assays, respectively) have been performed on individuals healed after SARS-CoV-2 infection. The correlation between each assay and the reference method has been explored through linear regression modeling, as well as through the calculation of Pearson’s and Spearman’s coefficients. Furthermore, the ability of serological tests to discriminate samples with high titers of neutralizing antibodies (>160) has been assessed by ROC curve analyses, Cohen’s Kappa coefficient, and positive predictive agreement. The EUROIMMUN® NeutraLISA assay displayed the best correlation with PRNT results (Pearson and Spearman coefficients equal to 0.660 and 0.784, respectively), as well as the ROC curve with the highest accuracy, sensitivity, and specificity (0.857, 0.889, and 0.829, respectively). 相似文献