全文获取类型
收费全文 | 50680篇 |
免费 | 1436篇 |
国内免费 | 186篇 |
专业分类
电工技术 | 633篇 |
综合类 | 650篇 |
化学工业 | 6647篇 |
金属工艺 | 815篇 |
机械仪表 | 1000篇 |
建筑科学 | 1408篇 |
矿业工程 | 478篇 |
能源动力 | 676篇 |
轻工业 | 2612篇 |
水利工程 | 657篇 |
石油天然气 | 68篇 |
武器工业 | 5篇 |
无线电 | 2468篇 |
一般工业技术 | 5032篇 |
冶金工业 | 21826篇 |
原子能技术 | 231篇 |
自动化技术 | 7096篇 |
出版年
2024年 | 70篇 |
2023年 | 304篇 |
2022年 | 319篇 |
2021年 | 427篇 |
2020年 | 210篇 |
2019年 | 254篇 |
2018年 | 673篇 |
2017年 | 930篇 |
2016年 | 1390篇 |
2015年 | 1058篇 |
2014年 | 788篇 |
2013年 | 986篇 |
2012年 | 2628篇 |
2011年 | 3107篇 |
2010年 | 1155篇 |
2009年 | 1214篇 |
2008年 | 1069篇 |
2007年 | 1033篇 |
2006年 | 926篇 |
2005年 | 3613篇 |
2004年 | 2787篇 |
2003年 | 2215篇 |
2002年 | 997篇 |
2001年 | 828篇 |
2000年 | 365篇 |
1999年 | 726篇 |
1998年 | 6262篇 |
1997年 | 3892篇 |
1996年 | 2582篇 |
1995年 | 1496篇 |
1994年 | 1122篇 |
1993年 | 1132篇 |
1992年 | 289篇 |
1991年 | 327篇 |
1990年 | 340篇 |
1989年 | 296篇 |
1988年 | 318篇 |
1987年 | 246篇 |
1986年 | 220篇 |
1985年 | 186篇 |
1984年 | 97篇 |
1983年 | 97篇 |
1982年 | 145篇 |
1981年 | 190篇 |
1980年 | 210篇 |
1979年 | 64篇 |
1978年 | 109篇 |
1977年 | 624篇 |
1976年 | 1345篇 |
1975年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Michael Lommel Vera Froese Moritz Sieber Marvin Jentzsch Tim Bierewirtz Ümit Hasirci Tim Rese Josef Seefeldt Sebastian Schimek Ulrich Kertzscher Christian Oliver Paschereit 《Indoor air》2021,31(6):1860-1873
The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplets that potentially contain infectious viruses. The emission of the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier. 相似文献
3.
Jens Mller Anne Busch Christian Berens Helmut Hotzel Andreas Burkovski 《International journal of molecular sciences》2021,22(7)
Corynebacterium silvaticum is a newly identified animal pathogen of forest animals such as roe deer and wild boars. The species is closely related to the emerging human pathogen Corynebacterium ulcerans and the widely distributed animal pathogen Corynebacterium pseudotuberculosis. In this study, Corynebacterium silvaticum strain W25 was characterized with respect to its interaction with human cell lines. Microscopy, measurement of transepithelial electric resistance and cytotoxicity assays revealed detrimental effects of C. silvaticum to different human epithelial cell lines and to an invertebrate animal model, Galleria mellonella larvae, comparable to diphtheria toxin-secreting C. ulcerans. Furthermore, the results obtained may indicate a considerable zoonotic potential of this newly identified species. 相似文献
4.
Klimis?S.?NtalianisEmail author Anastasios?D.?Doulamis Nikolaos?D.?Doulamis Nikos?E.?Mastorakis Athanasios?S.?Drigas 《Journal of Signal Processing Systems》2015,80(2):153-161
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
5.
Wojciech Jó?wicki Anna A. Bro?yna Jerzy Siekiera Andrzej T. Slominski 《International journal of molecular sciences》2015,16(2):3783-3803
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape. 相似文献
6.
7.
Klaus Reinhardt Hans Georg Breunig Aisada Uchugonova Karsten K?nig 《Journal of the Royal Society Interface》2015,12(110)
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype. 相似文献
8.
Choi Paul Santos Christian Ariane Kim Min-Kun Jung Hyunsook Hong Do-Young Koo Junemo 《Journal of Mechanical Science and Technology》2021,35(11):5007-5022
Journal of Mechanical Science and Technology - This study delivers equations useful for low-height pleated fibrous filter design: two pressure drop equations and one set of optimum design equations... 相似文献
9.
10.
AbstractRecently, a literature has emerged using empirical techniques to study the evolution of international cities over many centuries; however, few studies examine long-run change within cities. Conventional models and concepts are not always appropriate and data issues make long-run neighbourhood analysis particularly problematic. This paper addresses some of these points. First, it discusses why the analysis of long-run urban change is important for modern urban policy and considers the most important concepts. Second, it constructs a novel data set at the micro level, which allows consistent comparisons of London neighbourhoods in 1881 and 2001. Third, the paper models some of the key factors that affected long-run change, including the role of housing. There is evidence that the relative social positions of local urban areas persist over time but, nevertheless, at fine spatial scales, local areas still exhibit change, arising from aggregate population dynamics, from advances in technology, and also from the effects of shocks, such as wars. In general, where small areas are considered, long-run changes are likely to be greater, because individuals are more mobile over short than long distances. Finally, the paper considers the implications for policy. 相似文献