全文获取类型
收费全文 | 3855篇 |
免费 | 263篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 79篇 |
综合类 | 19篇 |
化学工业 | 995篇 |
金属工艺 | 85篇 |
机械仪表 | 63篇 |
建筑科学 | 309篇 |
矿业工程 | 18篇 |
能源动力 | 103篇 |
轻工业 | 264篇 |
水利工程 | 27篇 |
石油天然气 | 2篇 |
无线电 | 320篇 |
一般工业技术 | 805篇 |
冶金工业 | 270篇 |
原子能技术 | 14篇 |
自动化技术 | 749篇 |
出版年
2024年 | 6篇 |
2023年 | 58篇 |
2022年 | 133篇 |
2021年 | 148篇 |
2020年 | 118篇 |
2019年 | 98篇 |
2018年 | 126篇 |
2017年 | 108篇 |
2016年 | 159篇 |
2015年 | 168篇 |
2014年 | 189篇 |
2013年 | 270篇 |
2012年 | 258篇 |
2011年 | 313篇 |
2010年 | 263篇 |
2009年 | 210篇 |
2008年 | 212篇 |
2007年 | 208篇 |
2006年 | 162篇 |
2005年 | 154篇 |
2004年 | 102篇 |
2003年 | 87篇 |
2002年 | 80篇 |
2001年 | 50篇 |
2000年 | 47篇 |
1999年 | 53篇 |
1998年 | 62篇 |
1997年 | 39篇 |
1996年 | 52篇 |
1995年 | 30篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1970年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有4122条查询结果,搜索用时 0 毫秒
991.
Köber R Daus B Ebert M Mattusch J Welter E Dahmke A 《Environmental science & technology》2005,39(19):7650-7655
The bulk of arsenic (As) at contaminated sites is frequently associated with iron (hydr)oxides. Various studies ascribe increasing dissolved As concentrations to the transformation of iron (hydr)oxides into iron sulfides, which is initiated by dissolved sulfide. We investigated whetherthis processes can be utilized as a source treatment approach using compost-based permeable reactive barriers (PRB), which promote microbial sulfate reduction. Arsenic-bearing aquifer sedimentfrom a contaminated industrial site showed a decrease in As content of <10% after 420 days of percolation with sulfide-free artificial groundwater. In contrast, water that had previously passed through organic matter and exhibited sulfide concentrations of 10-30 mg/L decreased As content in the sediment by 87% within 360 days. X-ray diffraction showed no arsenic sulfides, but XANES spectra (X-ray absorption near edge structure) and associated linear combinations revealed that adsorbed arsenate of the original sediment was in part reduced to arsenite and indicated the formation of minor amounts of a substance that contains As and sulfur. The speciation of dissolved As changed from initially As(V)-dominated to As(III)-dominated after sulfide flushing was started, which increases the mobility of As. Because sulfide can be supplied not only by compost-based PRBs but also by direct injection, sulfide flushing has a wide range of application for the source treatment of arsenic. 相似文献
992.
A framework for modeling and analyzing the energy efficiency of road freight transport is presented in this paper. This framework is tested by using the data from the Finnish Goods Transport by Road statistics. The data was enhanced by calculating the fuel consumption for each trip in the data. To calculate this, weight-fuel consumption functions were estimated for each Euro-class vehicles and road type. This is a new method for analyzing the energy efficiency of road freight transport and it could be applied also in other countries gathering freight transport data with continuous company surveys. The analysis show that the energy efficiency of road freight transport in Finland improved during 1995–2002, but has declined since. The major drivers in the development have been the changes in the level of empty running and vehicle fuel efficiency. Extrapolating current statistical trends of factors that influence the energy efficiency show that the target set by the Finnish government for improving energy efficiency by 9% until 2016 will not be achieved. However, the target is possible to be achieved by a combination of small changes to some determinants. 相似文献
993.
In Vitro and In Vivo Inhibition of Intestinal Glucose Transport by Guava (Psidium Guajava) Extracts 下载免费PDF全文
Ulrike Müller Flora Stübl Bettina Schwarzinger Georg Sandner Marcus Iken Markus Himmelsbach Clemens Schwarzinger Nicole Ollinger Verena Stadlbauer Otmar Höglinger Tobias Kühne Peter Lanzerstorfer Julian Weghuber 《Molecular nutrition & food research》2018,62(11)
1 Scope
Known pharmacological activities of guava (Psidium guajava) include modulation of blood glucose levels. However, mechanistic details remain unclear in many cases.2 Methods and results
This study investigated the effects of different guava leaf and fruit extracts on intestinal glucose transport in vitro and on postprandial glucose levels in vivo. Substantial dose‐ and time‐dependent glucose transport inhibition (up to 80%) was observed for both guava fruit and leaf extracts, at conceivable physiological concentrations in Caco‐2 cells. Using sodium‐containing (both glucose transporters, sodium‐dependent glucose transporter 1 [SGLT1] and glucose transporter 2 [GLUT2], are active) and sodium‐free (only GLUT2 is active) conditions, we show that inhibition of GLUT2 was greater than that of SGLT1. Inhibitory properties of guava extracts also remained stable after digestive juice treatment, indicating a good chemical stability of the active substances. Furthermore, we could unequivocally show that guava extracts significantly reduced blood glucose levels (≈fourfold reduction) in a time‐dependent manner in vivo (C57BL/6N mice). Extracts were characterized with respect to their main putative bioactive compounds (polyphenols) using HPLC and LC‐MS.3 Conclusion
The data demonstrated that guava leaf and fruit extracts can potentially contribute to the regulation of blood glucose levels. 相似文献994.
Research on implicit and explicit prejudice has treated implicit prejudices as a unitary construct characterized by automatic access to negative concepts. The present article makes the case that tasks purported to measure implicit prejudice actually assess 2 different processes. Some assess the extent to which prejudice is activated automatically on the perception of a member of the target group. Other implicit tasks assess the extent to which prejudice is automatically applied in judgment. In the reported study, participants completed 4 implicit and 2 explicit measures of prejudice against women. Factor analysis yielded a 3-factor solution. The solution provides support for the distinction between explicit prejudice and 2 types of implicit prejudice corresponding to automatic activation and automatic application of prejudice. Prejudice appears to be a multifaceted construct, different aspects of which are measured by different tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
Uniqueness has positive connotations of freedom and independence in American culture, whereas conformity has positive connotations of connectedness and harmony in East Asian culture. The present research examined how these cultural values and individual preferences for uniqueness and conformity influence each other. In Studies 1 and 2, East Asian and European American preferences for uniqueness were measured using abstract figures. In Study 3, the choice of pens by East Asians and European Americans was examined as a function of whether the pen appeared unique. In Study 4, Korean and American magazine ads were analyzed with a focus on themes of conformity and uniqueness. In all studies, East Asians preferred targets that represented conformity, whereas European Americans preferred targets that represented uniqueness. The results highlight the relationship between individual preference and the adoption and perpetuation of cultural values. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
996.
Bucking the Trends: What the Future May Hold for ERP Packages 总被引:2,自引:0,他引:2
997.
Markus L. Noga 《Informatik-Spektrum》2000,23(3):216-217
Italian LEGO Users Group am 26. M?rz ihre vierte Vollversammlung abhielt. 相似文献
998.
Hausmann Markus; Slabbekoorn Ditte; Van Goozen Stephanie H. M.; Cohen-Kettenis Peggy T.; Güntürkün Onur 《Canadian Metallurgical Quarterly》2000,114(6):1245
The aim of this study was (a) to show that different measures of spatial cognition are modulated by the menstrual cycle and (b) to analyze which steroid is responsible for these cognitive alterations. The authors collected blood samples in 3-day intervals over 6 weeks from 12 young women with a regular menstrual cycle to analyze concentrations of estradiol, progesterone, testosterone, luteinizing hormone, and follicle-stimulating hormone. The performance on 3 spatial tests was measured during the menstrual and the midluteal phases. A significant cycle difference in spatial ability as tested by the Mental Rotation Test was found, with high scores during the menstrual phase and low scores during the midluteal phase. Testosterone had a strong and positive influence on mental rotation performance, whereas estradiol had a negative one. These results clearly indicate that testosterone and estradiol are able to modulate spatial cognition during the menstrual cycle. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
Spatio-Temporal Data Types: An Approach to Modeling and Querying Moving Objects in Databases 总被引:15,自引:2,他引:13
Martin Erwig Ralf Hartmut Gu¨ting Markus Schneider Michalis Vazirgiannis 《GeoInformatica》1999,3(3):269-296
Spatio-temporal databases deal with geometries changing over time. In general, geometries cannot only change in discrete steps, but continuously, and we are talking about moving objects. If only the position in space of an object is relevant, then moving point is a basic abstraction; if also the extent is of interest, then the moving region abstraction captures moving as well as growing or shrinking regions. We propose a new line of research where moving points and moving regions are viewed as 3-D (2-D space+time) or higher-dimensional entities whose structure and behavior is captured by modeling them as abstract data types. Such types can be integrated as base (attribute) data types into relational, object-oriented, or other DBMS data models; they can be implemented as data blades, cartridges, etc. for extensible DBMSs. We expect these spatio-temporal data types to play a similarly fundamental role for spatio-temporal databases as spatial data types have played for spatial databases. The paper explains the approach and discusses several fundamental issues and questions related to it that need to be clarified before delving into specific designs of spatio- temporal algebras. 相似文献
1000.
Migrating Autonomous Objects in a WAN Environment 总被引:2,自引:0,他引:2
Natalija Krivokapić Markus Islinger Alfons Kemper 《Journal of Intelligent Information Systems》2000,15(3):221-251
Along with the fast progress the interconnection of computer systems makes the need for enterprise-wide distributed solutions grows. These systems have to support hundreds or even thousands of sites located all over the world. The distances between the sites will impose high communication costs on distributed activities thus significantly increasing their response times. This problem can be alleviated through migrating objects to the sites where they are needed. However, migration in such systems cannot be managed globally. Therefore, we present a migration protocol for (autonomous) objects which enables them autonomously to decide whether or not and which site to migrate to, thus making the system self-tuning. We also present two migration strategies objects can use to derive their migration decisions. The first one finds the optimal placement for an object while the second strategy in some cases returns a sub-optimal location but induces lower computation costs. The two strategies are evaluated through benchmarks in a distributed system of autonomous objects. The experiments show a significant decrease in communication costs when migration is employed. 相似文献