全文获取类型
收费全文 | 123758篇 |
免费 | 11230篇 |
国内免费 | 6546篇 |
专业分类
电工技术 | 7603篇 |
技术理论 | 9篇 |
综合类 | 10422篇 |
化学工业 | 20016篇 |
金属工艺 | 6735篇 |
机械仪表 | 7678篇 |
建筑科学 | 8764篇 |
矿业工程 | 3073篇 |
能源动力 | 3606篇 |
轻工业 | 9522篇 |
水利工程 | 2520篇 |
石油天然气 | 5463篇 |
武器工业 | 1179篇 |
无线电 | 15145篇 |
一般工业技术 | 13947篇 |
冶金工业 | 5721篇 |
原子能技术 | 1663篇 |
自动化技术 | 18468篇 |
出版年
2024年 | 384篇 |
2023年 | 1542篇 |
2022年 | 3005篇 |
2021年 | 4412篇 |
2020年 | 3302篇 |
2019年 | 2861篇 |
2018年 | 3159篇 |
2017年 | 3427篇 |
2016年 | 3252篇 |
2015年 | 4630篇 |
2014年 | 5931篇 |
2013年 | 7336篇 |
2012年 | 8294篇 |
2011年 | 8880篇 |
2010年 | 8157篇 |
2009年 | 7984篇 |
2008年 | 7876篇 |
2007年 | 7517篇 |
2006年 | 7441篇 |
2005年 | 6228篇 |
2004年 | 4958篇 |
2003年 | 4408篇 |
2002年 | 5009篇 |
2001年 | 4432篇 |
2000年 | 3284篇 |
1999年 | 2734篇 |
1998年 | 2073篇 |
1997年 | 1747篇 |
1996年 | 1489篇 |
1995年 | 1260篇 |
1994年 | 934篇 |
1993年 | 754篇 |
1992年 | 582篇 |
1991年 | 464篇 |
1990年 | 352篇 |
1989年 | 284篇 |
1988年 | 243篇 |
1987年 | 155篇 |
1986年 | 115篇 |
1985年 | 119篇 |
1984年 | 69篇 |
1983年 | 55篇 |
1982年 | 53篇 |
1981年 | 52篇 |
1980年 | 41篇 |
1979年 | 34篇 |
1977年 | 28篇 |
1976年 | 34篇 |
1975年 | 19篇 |
1974年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 186 毫秒
11.
Junjie Li Mei Liang Wanjing Cheng Shuhao Wang 《International Journal of Hydrogen Energy》2021,46(14):9553-9566
Electric vehicles (EVs) are considered a promising alternative to conventional vehicles (CVs) to alleviate the oil crisis and reduce urban air pollution and carbon emissions. Consumers usually focus on the tangible cost when choosing an EV or CV but overlook the time cost for restricting purchase or driving and the environmental cost from gas emissions, falling to have a comprehensive understanding of the economic competitiveness of CVs and EVs. In this study, a life cycle cost model for vehicles is conducted to express traffic and environmental policies in monetary terms, which are called intangible cost and external cost, respectively. Battery electric vehicles (BEVs), fuel cell electric vehicles (FCEVs), and CVs are compared in four first-tier, four new first-tier, and 4 s-tier and below cities in China. The comparison shows that BEVs and FCEVs in most cities are incomparable with CVs in terms of tangible cost. However, the prominent traffic and environmental policies in first-tier cities, especially in Beijing and Shanghai, greatly increase the intangible and external costs of CVs, making consumers more inclined to purchase BEVs and FCEVs. The main policy benefits of BEVs and FCEVs come from three aspects: government subsidies, purchase and driving restrictions, and environmental taxes. With the predictable reduction in government subsidies, traffic and environmental policies present important factors influencing the competitiveness of BEVs and FCEVs. In first-tier cities, BEVs and FCEVs already have a competitive foundation for large-scale promotion. In new first-tier and second-tier and below cities, stricter traffic and environmental policies need to be formulated to offset the negative impact of the reduction in government subsidies on the competitiveness of BEVs and FCEVs. Additionally, a sensitivity analysis reveals that increasing the mileage and reducing fuel prices can significantly improve the competitiveness of BEVs and FCEVs, respectively. 相似文献
12.
As G protein coupled receptors, sphingosine-1-phosphate receptors (S1PRs) have recently gained attention for their role in modulating inflammatory bone loss diseases. Notably, in murine studies inhibiting S1PR2 by its specific inhibitor, JTE013, alleviated osteoporosis induced by RANKL and attenuated periodontal alveolar bone loss induced by oral bacterial inflammation. Treatment with a multiple S1PRs modulator, FTY720, also suppressed ovariectomy-induced osteoporosis, collagen or adjuvant-induced arthritis, and apical periodontitis in mice. However, most previous studies and reviews have focused mainly on how S1PRs manipulate S1P signaling pathways, subsequently affecting various diseases. In this review, we summarize the underlying mechanisms associated with JTE013 and FTY720 in modulating inflammatory cytokine release, cell chemotaxis, and osteoclastogenesis, subsequently influencing inflammatory bone loss diseases. Studies from our group and from other labs indicate that S1PRs not only control S1P signaling, they also regulate signaling pathways induced by other stimuli, including bacteria, lipopolysaccharide (LPS), bile acid, receptor activator of nuclear factor κB ligand (RANKL), IL-6, and vitamin D. JTE013 and FTY720 alleviate inflammatory bone loss by decreasing the production of inflammatory cytokines and chemokines, reducing chemotaxis of inflammatory cells from blood circulation to bone and soft tissues, and suppressing RANKL-induced osteoclast formation. 相似文献
13.
Yu-Hung Lee Ching-Fang Yu Ying-Chieh Yang Ji-Hong Hong Chi-Shiun Chiang 《International journal of molecular sciences》2021,22(4)
The low overall survival rate of patients with pancreatic cancer has driven research to seek a new therapeutic protocol. Radiotherapy (RT) is frequently an option in the neoadjuvant or palliative settings for pancreatic cancer treatment. This study explored the effect of RT protocols on the tumor microenvironment (TME) and their consequent impact on anti-programmed cell death ligand-1 (PD-L1) therapy. Using a murine orthotopic pancreatic tumor model, UN-KC-6141, RT-disturbed TME was examined by immunohistochemical staining. The results showed that ablative RT is more effective than fractionated RT at recruiting T cells. On the other hand, fractionated RT induces more myeloid-derived suppressor cell infiltration than ablative RT. The RT-disturbed TME presents a higher perfusion rate per vessel. The increase in vessel perfusion is associated with a higher amount of anti-PD-L1 antibody being delivered to the tumor. Animal survival is increased by anti-PD-L1 therapy after ablative RT, with 67% of treated animals surviving more than 30 days after tumor inoculation compared to a median survival time of 16.5 days for the control group. Splenocytes isolated from surviving animals were specifically cytotoxic for UN-KC-6141 cells. We conclude that the ablative RT-induced TME is more suited than conventional RT-induced TME to combination therapy with immune checkpoint blockade. 相似文献
14.
Chaozhong Sun Xiaoying Guo Rui Ji Changzheng Hu Laijun Liu Liang Fang Zhenxiang Cheng Nengneng Luo 《Ceramics International》2021,47(4):5038-5043
The triboelectric effect has recently demonstrated its great potential in environmental remediation and even new energy applications for triggering a number of catalytic reactions by utilizing trivial mechanical energy. In this study, Ba4Nd2Fe2Nb8O30 (BNFN) submicron powders were used to degrade organic dyes via the tribocatalytic effect. Under the frictional excitation of three PTFE stirring rods in a 5 mg/L RhB dye solution, BNFN demonstrates a high tribocatalytic degradation efficiency of 97% in 2 h. Hydroxyl radicals (?OH) and superoxide radicals (?O2-) were also detected during the catalysis process, which proves that triboelectric energy stimulates BNFN to generate electron-hole pairs. The tribocatalysis of tungsten bronze BNFN submicron powders provides a novel and efficient method for the degradation of wastewater dye by utilizing trivial mechanical energy. 相似文献
15.
Journal of Signal Processing Systems - With the latest development of automation technology, object detection technology has received more and more research attention. Automated object detection... 相似文献
16.
17.
Yuan-Xia Wang Ying Shi Chen-Chen Wang Jia-Hui Cheng Ying Wang Wen-Jun Shao Li-Zhi Liu 《应用聚合物科学杂志》2021,138(27):50651
Crosslinking of polyolefin elastomer (POE, ENGAGE™ 8480) with Dicumyl Peroxide (DCP) can have effects on its crystallization dynamics, crystal structure, and properties. The POE crosslinked uniformly has significantly lower crystalline ability than the one with only amorphous phase crosslinked, which, in turn, has weaker crystalline ability than neat POE. The crystallinity and melting point depend on how the POE is crosslinked. The neat POE and POE crosslinked in amorphous phase only, are investigated with DSC and in-situ tensile/synchrotron radiation (WAXD/SAXS). In situ tensile/synchrotron X-ray during a uniaxial stretching process indicates that severe crystal fragmentation is observed at a strain around 45%, and with further increase in strain. The stress in the crosslinked POE is significantly larger than neat POE. For both samples, crystal orientation increases sharply within the strain range up to 88% where orientation-induced new crystals aligned in stretching direction are observed. The long period increases more in stretching direction for the crosslinked POE, consistent with larger stress in this sample, and the stress difference is more pronounced at large strains (27.3 vs. 10.9 MPa at a strain 435%). Permanent set of the crosslinked POE is smaller, consistent with less oriented crystals observed after the test for permanent set. 相似文献
18.
19.
20.
介绍了电镀锡机组钝化污染缺陷的宏观形貌;从挤干设备、助熔工艺、钝化工艺、钝化设备等方面分析了钝化污染产生的原因。通过产线实践,发现助熔挤干辊位置,钝化段槽液中重铬酸钠浓度和p H值与钝化污染缺陷的产生无关,钝化极板的清洁程度、钝化液的老化程度以及助熔液的清洁程度才是导致钝化污染的主要原因。通过调整助熔槽液浓度,保证钝化极板清洁性,钝化污染缺陷得到有效控制。 相似文献