全文获取类型
收费全文 | 368147篇 |
免费 | 10633篇 |
国内免费 | 6203篇 |
专业分类
电工技术 | 11132篇 |
综合类 | 6456篇 |
化学工业 | 49018篇 |
金属工艺 | 18119篇 |
机械仪表 | 13165篇 |
建筑科学 | 11372篇 |
矿业工程 | 3181篇 |
能源动力 | 9921篇 |
轻工业 | 33895篇 |
水利工程 | 3978篇 |
石油天然气 | 3913篇 |
武器工业 | 982篇 |
无线电 | 47495篇 |
一般工业技术 | 64250篇 |
冶金工业 | 69640篇 |
原子能技术 | 5734篇 |
自动化技术 | 32732篇 |
出版年
2022年 | 3031篇 |
2021年 | 4768篇 |
2020年 | 3411篇 |
2019年 | 3226篇 |
2018年 | 4638篇 |
2017年 | 4667篇 |
2016年 | 4645篇 |
2015年 | 4911篇 |
2014年 | 7247篇 |
2013年 | 17856篇 |
2012年 | 11792篇 |
2011年 | 14953篇 |
2010年 | 12958篇 |
2009年 | 13845篇 |
2008年 | 14681篇 |
2007年 | 14718篇 |
2006年 | 13188篇 |
2005年 | 11872篇 |
2004年 | 10704篇 |
2003年 | 9879篇 |
2002年 | 9440篇 |
2001年 | 9624篇 |
2000年 | 8613篇 |
1999年 | 8965篇 |
1998年 | 22877篇 |
1997年 | 15826篇 |
1996年 | 12376篇 |
1995年 | 9015篇 |
1994年 | 7940篇 |
1993年 | 7718篇 |
1992年 | 5277篇 |
1991年 | 5216篇 |
1990年 | 4766篇 |
1989年 | 4555篇 |
1988年 | 4257篇 |
1987年 | 3474篇 |
1986年 | 3479篇 |
1985年 | 4065篇 |
1984年 | 3594篇 |
1983年 | 3216篇 |
1982年 | 3025篇 |
1981年 | 3027篇 |
1980年 | 2821篇 |
1979年 | 2593篇 |
1978年 | 2478篇 |
1977年 | 3166篇 |
1976年 | 4871篇 |
1975年 | 2080篇 |
1974年 | 1957篇 |
1973年 | 1946篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
从硬件和软件两个角度出发,介绍基于DSP的多元数据同步采集与存储系统的组成、工作模式以及功能的测试。系统主要由上位机和数字采集与存储单元组成,其中数字采集与存储单元的硬件部分包括电源模块,值班电路模块,数据采集模块,数据存储模块,时钟同步模块。系统采用DSP作为中央处理芯片,利用经过同步后的秒脉冲作为触发信号,实现同步数据采集。以CF卡作为存储介质,实现数据自容式存储。软件部分实现自检、同步、数据采集存储功能。经过测试,系统工作稳定,功能正常,同步精度在100ns以内。 相似文献
122.
124.
Multicellular tumor spheroid models (MCTS) are often coined as 3D in vitro models that can mimic the microenvironment of tissues. MCTS have gained increasing interest in the nano‐biotechnology field as they can provide easily accessible information on the performance of nanoparticles without using animal models. Considering that many countries have put restrictions on animals testing, which will only tighten in the future as seen by the recent developments in the Netherlands, 3D models will become an even more valuable tool. Here, an overview on MCTS is provided, focusing on their use in cancer research as most nanoparticles are tested in MCTS for treatment of primary tumors. Thereafter, various types of nanoparticles—from self‐assembled block copolymers to inorganic nanoparticles, are discussed. A range of physicochemical parameters including the size, shape, surface chemistry, ligands attachment, stability, and stiffness are found to influence nanoparticles in MCTS. Some of these studies are complemented by animal studies confirming that lessons from MCTS can in part predict the behaviour in vivo. In summary, MCTS are suitable models to gain additional information on nanoparticles. While not being able to replace in vivo studies, they can bridge the gap between traditional 2D in vitro studies and in vivo models. 相似文献
125.
126.
Wan Huan Wang Hui Scotney Bryan Liu Jun Ng Wing W. Y. 《Multimedia Tools and Applications》2020,79(39-40):29327-29352
Multimedia Tools and Applications - In many real-world classification problems there exist multiple subclasses (or clusters) within a class; in other words, the underlying data distribution is... 相似文献
127.
Y.K. Yang F.L. Liu Y.W. Zhang M.F. Li F. Ling H.T. Wu 《Ceramics International》2018,44(11):12238-12244
In this work, ultra-low loss Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics were successfully prepared via the conventional solid-state method. X-ray photoelectron spectroscopy (XPS), thermally stimulated depolarization current (TSDC) and bond energy were used to determine the distinction between intrinsic and extrinsic dielectric loss in (Mg1/3Nb2/3)4+ ions substituted ceramics. The addition of (Mg1/3Nb2/3)4+ ions enhances the bond energy in unit cell without changing the crystal structure of Li2MgTiO4, which results in high Q·f value as an intrinsic factor. The extrinsic factors such as porosity and grain size influence the dielectric loss at lower sintering temperature, while the oxygen vacancies play dominant role when the ceramics densified at 1400?°C. The Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics sintered at 1400?°C can achieve an excellent combination of microwave dielectric properties: εr =?16.19, Q·f?=?160,000?GHz and τf =??3.14?ppm/°C. In addition, a certain amount of LiF can effectively lower the sintering temperature of the matrix, and the Li2MgTi0.7(Mg1/3Nb2/3)0.3O4-3?wt% LiF ceramics sintered at 1100?°C possess balanced properties with εr?=?16.32, Q·f?=?145,384?GHz and τf =??16.33?ppm/°C. 相似文献
128.
无源光网络(Passive Optical Network,PON)作为当今接入网的主要技术解决方案,具有带宽使用效率高、传输距离远、抗干扰能力强等特点.通过研究PON技术的发展动态,本文首先归纳了各种PON技术的产生背景和应用特点,整理出各技术间的连接关系及主要标准;其次介绍了PON技术的帧结构,并对带宽、波长、传输模式等PON技术的主要参数进行了汇总;然后将国内外研究热点进行划分,围绕媒体访问控制协议、帧结构、动态带宽分配算法、节能机制等关键技术,阐述了其研究现状及在PON中的重要作用;最后对PON技术的发展趋势进行了展望. 相似文献
129.
The reported point centromeres of Scheffersomyces stipitis are retrotransposon long terminal repeats
Point centromeres, found in some ascomycete yeasts such Saccharomyces cerevisiae, are very different in structure from the centromeres of other eukaryotes. They are tiny and nonrepetitive and contain only two short conserved sequence motifs. Until recently, point centromeres were thought to have a single evolutionary origin, in the budding yeast family Saccharomycetaceae. Most yeasts outside this family have centromeres that are many kilobases in size. Some have centromeres consisting of a large inverted repeat sequence, others have centromeric clusters of retrotransposons, and a third group including Candida albicans has centromeres with no conserved sequence features. It was recently reported that Scheffersomyces stipitis has point centromeres with a strongly conserved 125-bp core sequence, which is unexpected because S. stipitis is only distantly related to the known point-centromere species. We show here that the 125-bp core sequence is actually part of the long terminal repeat (LTR) of the Ty5-like retrotransposon Tps5, which forms a cluster in the centromeric region of each S. stipitis chromosome. Thus, the LTR of a centromere-associated retrotransposon confers centromere-like mitotic stability when cloned into a plasmid. The centromeric regions of S. stipitis contain three types of Tps5 element (Tps5a, Tps5b, and Tps5c) and a noncoding nonautonomous large retrotransposon derivative. 相似文献
130.
Antti Voss Niko Hänninen Mohammad Pour-Ghaz Marko Vauhkonen Aku Seppänen 《Materials and Structures》2018,51(3):68
The development of visualizing tools to monitor unsaturated moisture flow in cement-based materials is of great importance, as most degradation processes in cement-based materials are connected to and take place in the presence moisture. This paper investigates the ability of electrical capacitance tomography (ECT) to image two-dimensional (2D) unsaturated moisture flow in cement-based materials. In ECT, the electrical permittivity distribution within an object is reconstructed based on measured capacitances between electrodes attached on the object’s surface. In a series of experiments, mortar specimens with and without discrete cracks were imaged with ECT during a 2D moisture ingress. The results show that ECT is able to monitor the evolution of the moisture flow, and to approximate the shape and position of the moisture front. These findings indicate that ECT is a viable method for monitoring and visualizing 2D unsaturated moisture flow in cement-based materials in the presence and absence of discrete cracks. 相似文献