全文获取类型
收费全文 | 43655篇 |
免费 | 4027篇 |
国内免费 | 1976篇 |
专业分类
电工技术 | 2573篇 |
技术理论 | 2篇 |
综合类 | 2507篇 |
化学工业 | 7425篇 |
金属工艺 | 2604篇 |
机械仪表 | 2973篇 |
建筑科学 | 2991篇 |
矿业工程 | 1277篇 |
能源动力 | 1269篇 |
轻工业 | 2845篇 |
水利工程 | 641篇 |
石油天然气 | 2462篇 |
武器工业 | 337篇 |
无线电 | 5346篇 |
一般工业技术 | 5933篇 |
冶金工业 | 2409篇 |
原子能技术 | 490篇 |
自动化技术 | 5574篇 |
出版年
2024年 | 163篇 |
2023年 | 837篇 |
2022年 | 1230篇 |
2021年 | 2110篇 |
2020年 | 1537篇 |
2019年 | 1430篇 |
2018年 | 1498篇 |
2017年 | 1535篇 |
2016年 | 1442篇 |
2015年 | 1888篇 |
2014年 | 2255篇 |
2013年 | 2706篇 |
2012年 | 2796篇 |
2011年 | 3171篇 |
2010年 | 2499篇 |
2009年 | 2465篇 |
2008年 | 2470篇 |
2007年 | 2199篇 |
2006年 | 2299篇 |
2005年 | 1845篇 |
2004年 | 1340篇 |
2003年 | 1200篇 |
2002年 | 1133篇 |
2001年 | 987篇 |
2000年 | 956篇 |
1999年 | 996篇 |
1998年 | 832篇 |
1997年 | 713篇 |
1996年 | 629篇 |
1995年 | 523篇 |
1994年 | 408篇 |
1993年 | 275篇 |
1992年 | 226篇 |
1991年 | 199篇 |
1990年 | 169篇 |
1989年 | 151篇 |
1988年 | 99篇 |
1987年 | 85篇 |
1986年 | 55篇 |
1985年 | 48篇 |
1984年 | 34篇 |
1983年 | 37篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
991.
992.
993.
994.
为平衡混沌映射中结构与性能的关系,保证加密系统安全性,提出一种基于余弦-指数混沌映射的分块图像加密算法。首先,通过非线性指数项对引入了Tent种子映射的余弦映射进行调制,构造新型余弦-指数混沌映射,并利用SHA-256函数产生与明文相关的密钥,生成随机性较强的混沌序列,实现一次一密;然后,基于拉丁方和位级转换,通过两轮拉丁方索引和比特位拼接,分别设计双重拉丁方和扩展比特位算法,并结合二维约瑟夫序列,对块间预置乱后的明文进行块内置乱,实现不同分块的差异化置乱;最后,基于Zig-Zag变换,采用环状仿Zig-Zag变换设计交叉Zig-Zag变换方法,将中间密文与混沌序列进行双向非线性扩散,实现同时改变像素位置与大小,完成图像加密。实验结果表明,该算法密钥空间大,能有效抵御差分分析和统计分析等典型攻击,具有较好的加密效果。 相似文献
995.
水轮机在云南电网中占比很大,为了解决水轮机的水锤效应带来的功率反调现象,提出了一种考虑风电调频特性补偿水锤效应的分析方法。首先,建立了含风、水、网、荷的简单系统数学模型。其次,使用直流潮流法得到水轮机及其调频策略、风机及其调频策略所对应的代数微分方程和系统网络方程。并在此基础上进行线性化处理,推导出负荷扰动时水轮机和风机并网节点频率响应的频域解析式。根据解析式分析调频控制参数等对系统频率的影响。最后,通过以双机系统及实际电网的仿真分析对风机补偿水轮机水锤效应的有效性和可行性进行了验证。 相似文献
996.
Minyoung Jeong Se Gyo Han Woong Sung Seunghyun Kim Jiwoo Min Mi Kyong Kim Wookjin Choi Hansol Lee Dongki Lee Min Kim Kilwon Cho 《Advanced functional materials》2023,33(27):2300695
A photomultiplication (PM)-type organic photodetector (OPD) that exploits the ionic motion in CsPbI3 perovskite quantum dots (QDs) is demonstrated. The device uses a QD monolayer as a PM-inducing interlayer and a donor–acceptor bulk heterojunction (BHJ) layer as a photoactive layer. When the device is illuminated, negative ions in the CsPbI3 QD migrate and accumulate near the interface between the QDs and the electrode; these processes induce hole injection from the electrode and yield the PM phenomenon with an external quantum efficiency (EQE) >2000% at a 3 V applied bias. It is confirmed that the ionic motion of the CsPbI3 QDs can induce a shift in the work function of the QD/electrode interface and that the dynamics of ionic motion determines the response speed of the device. The PM OPD showed a large EQE-bandwidth product >106 Hz with a −3 dB frequency of 125 kHz at 3 V, which is one of the highest response speeds reported for a PM OPD. The PM-inducing strategy that exploits ionic motion of the interlayer is a potential approach to achieving high-efficiency PM OPDs. 相似文献
997.
Jiajia Deng Xin Wang Weihua Zhang Liangyan Sun Xinxin Han Xianqin Tong Liming Yu Jiandong Ding Lin Yu Yuehua Liu 《Advanced functional materials》2023,33(21):2211664
Extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) have emerged as an appealing alternative to cell therapy in regenerative medicine. Unlike bone marrow MSCs (BMSCs) cultured in vitro with normoxia, bone marrow in vivo is exposed to a hypoxic environment. To date, it remains unclear whether hypoxia preconditioning can improve the function of BMSC-derived EVs and be more conducive to bone repair. Herein, it is found that hypoxia preconditioned BMSCs secrete more biglycan (Bgn)-rich EVs via proteomics analysis, and these hypoxic EVs (Hypo-EVs) significantly promote osteoblast proliferation, migration, differentiation, and mineralization by activating the phosphatidylinositide 3-kinase/protein kinase B pathway. Subsequently, an injectable bioactive hydrogel composed of poly(ethylene glycol)/polypeptide copolymers is developed to improve the stability and retention of Hypo-EVs in vivo. The Hypo-EVs-laden hydrogel shows continuous liberation of Hypo-EVs for 3 weeks and substantially accelerates bone regeneration in 5-mm rat cranial defects. Finally, it is confirmed that Bgn in EVs is a pivotal protein regulating osteoblast differentiation and mineralization and exerts its effects through paracrine mechanisms. Therefore, this study shows that hypoxia stimulation is an effective approach to optimize the therapeutic effects of BMSC-derived EVs and that injectable hydrogel-based EVs delivery is a promising strategy for tissue regeneration. 相似文献
998.
Longfei Han Li Wang Zonghai Chen Yongchun Kan Yuan Hu Hao Zhang Xiangming He 《Advanced functional materials》2023,33(32):2300892
Lithium-ion batteries with their portability, high energy density, and reusability are frequently used in today's world. Under extreme conditions, lithium-ion batteries leak, burn, and even explode. Therefore, improving the safety of lithium-ion batteries has become a focus of attention. Researchers believe using a solid electrolyte instead of a liquid one can solve the lithium battery safety issue. Due to the low price, good processability and high safety of the solid polymer electrolytes, increasing attention have been paid to them. However, polymer electrolytes can also decompose and burn under extreme conditions. Moreover, lithium dendrites are formed continuously due to the uneven charge distribution on the surface of the lithium metal anode. A short circuit caused by a lithium dendrite can cause the battery to thermal runaway. As a result, the safety of polymer solid-state batteries remains a challenge. In this review, the thermal runaway mechanism of the batteries is summarized, and the batteries abuse test standard is introduced. In addition, the recent works on the high-safety polymer electrolytes and the solution strategies of lithium anode problems in polymer batteries are reviewed. Finally, the development direction of safe polymer solid lithium batteries is prospected. 相似文献
999.
Xueyan Huang Sheng Huang Tianyi Wang Lei Zhong Dongmei Han Min Xiao Shuanjin Wang Yuezhong Meng 《Advanced functional materials》2023,33(27):2300683
Solid-state lithium metal batteries (SSLMBs) are highly desirable for energy storage because of the urgent need for higher energy density and safer batteries. However, it remains a critical challenge for stable cycling of SSLMBs at low temperature. Here, a highly viscoelastic polyether-b-amide (PEO-b-PA) based composite solid-state electrolyte is proposed through a one-pot melt processing without solvent to address this key process. By adjusting the molar ratio of PEO-b-PA to lithium bis(trifluoromethanesulphonyl)imide (ethylene oxide:Li = 6:1) and adding 20 wt.% succinonitrile, fast Li+ transport channel is conducted within the homogeneous polymer electrolyte, which enables its application at ultra-low temperature (−20 to 25 °C). The composite solid-state electrolyte utilizes dynamic hydrogen-bonding domains and ion-conducting domains to achieve a low interfacial charge transfer resistance (<600 Ω) at −20 °C and high ionic conductivity (25 °C, 3.7 × 10−4 S cm−1). As a result, the LiFePO4|Li battery based on composite electrolyte exhibits outstanding electrochemical performance with 81.5% capacity retention after 1200 cycles at −20 °C and high discharge specific capacities of 141.1 mAh g−1 with high loading (16.1 mg cm−2) at 25 °C. Moreover, the solid-state SNCM811|Li cell achieves excellent safety performance under nail penetration test, showing great promise for practical application. 相似文献
1000.
Chuanming Tian Bin Li Yichuan Rui Hao Xiong Yu Zhao Xuefei Han Xinliang Zhou Yu Qiu Wei An Kerui Li Chengyi Hou Yaogang Li Hongzhi Wang Qinghong Zhang 《Advanced functional materials》2023,33(41):2302270
Despite the outstanding power conversion efficiency (PCE) of perovskite solar cells (PSCs) achieved over the years, unsatisfactory stability and lead toxicity remain obstacles that limit their competitiveness and large-scale practical deployment. In this study, in situ polymerizing internal encapsulation (IPIE) is developed as a holistic approach to overcome these challenges. The uniform polymer internal package layer constructed by thermally triggered cross-linkable monomers not only solidifies the ionic perovskite crystalline by strong electron-withdrawing/donating chemical sites, but also acts as a water penetration and ion migration barrier to prolong shelf life under harsh environments. The optimized MAPbI3 and FAPbI3 devices with IPIE treatment yield impressive efficiencies of 22.29% and 24.12%, respectively, accompanied by remarkably enhanced environmental and mechanical stabilities. In addition, toxic water-soluble lead leakage is minimized by the synergetic effect of the physical encapsulation wall and chemical chelation conferred by the IPIE. Hence, this strategy provides a feasible route for preparing efficient, stable, and eco-friendly PSCs. 相似文献