全文获取类型
收费全文 | 39824篇 |
免费 | 2955篇 |
国内免费 | 1584篇 |
学科分类
工业技术 | 44363篇 |
出版年
2024年 | 61篇 |
2023年 | 607篇 |
2022年 | 767篇 |
2021年 | 1401篇 |
2020年 | 1086篇 |
2019年 | 903篇 |
2018年 | 997篇 |
2017年 | 1179篇 |
2016年 | 1093篇 |
2015年 | 1447篇 |
2014年 | 1853篇 |
2013年 | 2329篇 |
2012年 | 2314篇 |
2011年 | 2659篇 |
2010年 | 2386篇 |
2009年 | 2178篇 |
2008年 | 2220篇 |
2007年 | 2183篇 |
2006年 | 2208篇 |
2005年 | 1895篇 |
2004年 | 1312篇 |
2003年 | 1139篇 |
2002年 | 1099篇 |
2001年 | 936篇 |
2000年 | 967篇 |
1999年 | 1152篇 |
1998年 | 1015篇 |
1997年 | 870篇 |
1996年 | 865篇 |
1995年 | 666篇 |
1994年 | 580篇 |
1993年 | 394篇 |
1992年 | 358篇 |
1991年 | 263篇 |
1990年 | 206篇 |
1989年 | 173篇 |
1988年 | 140篇 |
1987年 | 105篇 |
1986年 | 75篇 |
1985年 | 57篇 |
1984年 | 56篇 |
1983年 | 26篇 |
1982年 | 35篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Scalable Clock Synchronization Analysis: A Symmetric Noncooperative Output Feedback Tubes-MPC Approach 下载免费PDF全文
In the cyber-physical environment, the clock synchronization algorithm is required to have better expansion for network scale. In this paper, a new measurement model of observability under the equivalent transformation of minimum mean square error (MMSE) is constructed based on basic measurement unit (BMU), which can realize the scaled expansion of MMSE measurement. Based on the state updating equation of absolute clock and the decoupled measurement model of MMSE-like equivalence, which is proposed to calculate the positive definite invariant set by using the theoretical-practical Luenberger observer as the synthetical observer, the local noncooperative optimal control problem is built, and the clock synchronization system driven by the ideal state of local clock can reach the exponential convergence for synchronization performance. Different from the problem of general linear system regulators, the state estimation error and state control error are analyzed in the established affine system based on the set-theory-in-control to achieve the quantification of state deviation caused by noise interference. Based on the BMU for isomorphic state map, the synchronization performance of clock states between multiple sets of representative nodes is evaluated, and the scale of evaluated system can be still expanded. After the synchronization is completed, the state of perturbation system remains in the maximum range of measurement accuracy, and the state of nominal system can be stabilized at the ideal state for local clock and realizes the exponential convergence of the clock synchronization system. 相似文献
62.
某含锌锡多金属硫化矿石Zn、Sn、Fe、S含量分别为6.04%、1.05%、29.33%、19.08%,锌主要以铁闪锌矿、闪锌矿的形式存在,锡主要以锡石的形式存在,铁主要以黄铁矿、磁黄铁矿等形式存在,其中的金属矿物共生关系密切,相互包裹现象普遍。为确保不影响后续选锡,对锌浮选流程进行了试验研究。结果表明:矿石在磨矿细度为-0.074 mm占80%的情况下,采用预先脱硫—锌硫混浮再分离流程处理,在选择硫酸铜为锌矿物活化剂、丁基黄药为捕收剂、松醇油为起泡剂、石灰为黄铁矿抑制剂的情况下,经1段脱硫、2粗1扫锌硫混浮、1粗2精锌硫分离,锌硫分离精选尾矿与锌硫混浮扫选精矿2次精选后锌硫分离,最终获得锌精矿Zn品位47.06%、回收率90.76%,试验指标良好。 相似文献
63.
64.
我国是富煤贫油少气的国家,煤炭是我国最重要的一次能源。但从能源激烈的竞争市场环境而言,当前我国煤炭行业发展出现了困境。为了更好地发展六盘水地区的煤炭行业,结合竞争战略理论和六盘水市的煤炭行业发展状况,运用PEST分析法和波特五力模型对六盘水市煤炭行业进行分析,得出整合资源,结合自身优势大力吸引人才,最终达到产业转型的生态化煤炭发展战略模型。分析结果可为提高六盘水煤炭行业竞争力提供理论支持。 相似文献
65.
World Wide Web - To solve the problem that users’ retrieval intentions are seldom considered by personalized websites, we propose an improved incremental collaborative filtering (CF)-based... 相似文献
67.
68.
The hippocampus is crucial in learning, memory and emotion processing, and is involved in the development of different neurological and neuropsychological disorders. Several epigenetic factors, including DNA methylation, histone modifications and non-coding RNAs, have been shown to regulate the development and function of the hippocampus, and the alteration of epigenetic regulation may play important roles in the development of neurocognitive and neurodegenerative diseases. This review summarizes the epigenetic modifications of various cell types and processes within the hippocampus and their resulting effects on cognition, memory and overall hippocampal function. In addition, the effects of exposure to radiation that may induce a myriad of epigenetic changes in the hippocampus are reviewed. By assessing and evaluating the current literature, we hope to prompt a more thorough understanding of the molecular mechanisms that underlie radiation-induced epigenetic changes, an area which can be further explored. 相似文献
70.
In order to improve the utilization rate of avermectin (AVM), a complex was prepared by electrostatic self-assembly using isolated soy protein (ISP) and carboxymethyl chitosan (CMCS) for loading AVM to obtain ISP/CMCS@AVM microspheres. The encapsulation efficiency (EE), sustained release property, ultraviolet (UV) protective ability, and toxicity of the microspheres were evaluated, and the release kinetics of AVM from the microsphere at different pHs were investigated. The results demonstrated that the average particle size of ISP/CMCS@AVM was 283.95 nm, and the EE reached 88.42% for AVM after denaturation. After 70 h of exposure to UV light, the residual rate of AVM in ISP/CMCS@AVM was 78.12%, which was significantly higher than 35.18% in the AVM emulsion. Moreover, the formulation imparted pH sensitivity and sustained-release property to AVM and was consistent with the Korsmeyer–Peppas model, controlled by Fick diffusion. Finally, the insecticidal toxicity of ISP/CMCS@AVM did not differ significantly from that of unmodified AVM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48358. 相似文献