全文获取类型
收费全文 | 5938篇 |
免费 | 362篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 79篇 |
综合类 | 14篇 |
化学工业 | 1466篇 |
金属工艺 | 138篇 |
机械仪表 | 116篇 |
建筑科学 | 405篇 |
矿业工程 | 29篇 |
能源动力 | 147篇 |
轻工业 | 461篇 |
水利工程 | 50篇 |
石油天然气 | 7篇 |
无线电 | 448篇 |
一般工业技术 | 1252篇 |
冶金工业 | 356篇 |
原子能技术 | 40篇 |
自动化技术 | 1297篇 |
出版年
2024年 | 7篇 |
2023年 | 99篇 |
2022年 | 111篇 |
2021年 | 231篇 |
2020年 | 151篇 |
2019年 | 129篇 |
2018年 | 190篇 |
2017年 | 168篇 |
2016年 | 249篇 |
2015年 | 245篇 |
2014年 | 305篇 |
2013年 | 407篇 |
2012年 | 383篇 |
2011年 | 466篇 |
2010年 | 359篇 |
2009年 | 345篇 |
2008年 | 347篇 |
2007年 | 319篇 |
2006年 | 243篇 |
2005年 | 216篇 |
2004年 | 162篇 |
2003年 | 154篇 |
2002年 | 133篇 |
2001年 | 87篇 |
2000年 | 85篇 |
1999年 | 71篇 |
1998年 | 94篇 |
1997年 | 54篇 |
1996年 | 59篇 |
1995年 | 64篇 |
1994年 | 41篇 |
1993年 | 41篇 |
1992年 | 33篇 |
1991年 | 28篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 10篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1974年 | 6篇 |
排序方式: 共有6305条查询结果,搜索用时 31 毫秒
11.
12.
Ugur Gezer Ebru E. Y?rüker Metin Keskin Cemil Burak Kulle Yoganiranjana Dharuman Stefan Holdenrieder 《International journal of molecular sciences》2015,16(12):29654-29662
Circulating nucleic acids (CNAs) are under investigation as a liquid biopsy in cancer as potential non-invasive biomarkers, as stable structure in circulation nucleosomes could be valuable sources for detection of cancer-specific alterations in histone modifications. Our interest is in histone methylation marks with a focus on colorectal cancer, one of the leading cancers respective the incidence and mortality. Our previous work included the analysis of trimethylations of lysine 9 on histone 3 (H3K9me3) and of lysine 20 on histone 4 (H4K20me3) by chromatin immuno- precipitation-related PCR in circulating nucleosomes. Here we asked whether global immunologic measurement of histone marks in circulation could be a suitable approach to show their potential as biomarkers. In addition to H3K9me3 and H4K20me3 we also measured H3K27me3 in plasma samples from CRC patients (n = 63) and cancer free individuals (n = 40) by ELISA-based methylation assays. Our results show that of three marks, the amounts of H3K27me3 (p = 0.04) and H4K20me3 (p < 0.001) were significantly lower in CRC patients than in healthy controls. For H3K9me3 similar amounts were measured in both groups. Areas under the curve (AUC) in receiver operating characteristic (ROC) curves indicating the power of CRC detection were 0.620 for H3K27me3, 0.715 for H4K20me3 and 0.769 for the combination of both markers. In conclusion, findings of this preliminary study reveal the potential of blood-based detection of CRC by quantification of histone methylation marks and the additive effect of the marker combination. 相似文献
13.
14.
Stefan Cenkowski Digvir S. Jayas James K. Daun 《Journal of the science of food and agriculture》1993,63(4):377-383
The presence of green seeds in canola arises primarily from the common practice of swathing the crop prematurely in order to hasten the harvesting process and reduce the shattering losses. The purpose of this study was to determine the effects of plant maturity, swathing and duration of swathing on moisture and chlorophyll contents of canola seeds (Brassica napus L cv Westar), and to determine the effect of canola conditioning with air at 25·C and 90% RH on chlorophyll content. A standing crop of canola with 50% to 10% (w/w) seed moisture content was sampled at regular intervals in two consecutive harvest years (1989 and 1990). Canola was also swathed at three different stages of maturity, and seeds were checked for chlorophyll at 2-3 day intervals and compared with chlorophyll contents of seed from standing crop. Samples were conditioned in a thin layer with air at 25·C and 90% RH for 24 h, and chlorophyll was determined before and after conditioning. The chlorophyll of seeds decreased exponentially with a decrease in moisture content. Conditioning canola seeds decreased chlorophyll content by an average of 16% (SD = ± 12%). 相似文献
15.
Kemper A. Kilger C. Moerkotte G. 《Knowledge and Data Engineering, IEEE Transactions on》1994,6(4):587-608
View materialization is a well-known optimization technique of relational database systems. We present a similar, yet more powerful, optimization concept for object-oriented data models: function materialization. Exploiting the object-oriented paradigm-namely, classification, object identity, and encapsulation-facilitates a rather easy incorporation of function materialization into (existing) object-oriented systems. Only those types (classes) whose instances are involved in some materialization are appropriately modified and recompiled, thus leaving the remainder of the object system invariant. Furthermore, the exploitation of encapsulation (information hiding) and object identity provides for additional performance tuning measures that drastically decrease the invalidation and rematerialization overhead incurred by updates in the object base. First, it allows us to cleanly separate the object instances that are irrelevant for the materialized functions from those that are involved in the materialization of some function result, and this to penalize only those involved objects upon update. Second, the principle of information hiding facilitates fine-grained control over the invalidation of precomputed results. Based on specifications given by the data type implementor, the system can exploit operational semantics to better distinguish between update operations that invalidate a materialized result and those that require no rematerialization. The paper concludes with a quantitative analysis of function materialization based on two sample performance benchmarks obtained from our experimental object base system GOM 相似文献
16.
17.
The natural-convectioe flow of a viscous and heat-conducting fluid in systems of cylinders, arranged vertically in regular patterns, is studied. The aim of the study is to determine the conditions of stability of the fluid when heated from below and cooled from above. In particular, the influence of geometry and thermal properties of the system on the free stationary convection are studied. A new way of calculating the free convection threshold is proposed. The final results are analytical formulas for determining the critical Rayleigh numbers for the studied forms of flow and graphs, showing the dependency of these numbers on the geometrical parameters of arrays. 相似文献
18.
19.
20.