全文获取类型
收费全文 | 1732061篇 |
免费 | 48229篇 |
国内免费 | 17601篇 |
专业分类
电工技术 | 50092篇 |
技术理论 | 19篇 |
综合类 | 21985篇 |
化学工业 | 308519篇 |
金属工艺 | 76970篇 |
机械仪表 | 57025篇 |
建筑科学 | 66614篇 |
矿业工程 | 18308篇 |
能源动力 | 57103篇 |
轻工业 | 127914篇 |
水利工程 | 19471篇 |
石油天然气 | 50547篇 |
武器工业 | 2238篇 |
无线电 | 223191篇 |
一般工业技术 | 310005篇 |
冶金工业 | 169121篇 |
原子能技术 | 36638篇 |
自动化技术 | 202131篇 |
出版年
2022年 | 16216篇 |
2021年 | 26032篇 |
2020年 | 19380篇 |
2019年 | 20754篇 |
2018年 | 22024篇 |
2017年 | 22219篇 |
2016年 | 28034篇 |
2015年 | 26937篇 |
2014年 | 40924篇 |
2013年 | 102708篇 |
2012年 | 51217篇 |
2011年 | 64660篇 |
2010年 | 56837篇 |
2009年 | 64788篇 |
2008年 | 57847篇 |
2007年 | 54064篇 |
2006年 | 57556篇 |
2005年 | 50201篇 |
2004年 | 48644篇 |
2003年 | 47422篇 |
2002年 | 45886篇 |
2001年 | 42155篇 |
2000年 | 40877篇 |
1999年 | 40365篇 |
1998年 | 47795篇 |
1997年 | 42096篇 |
1996年 | 38491篇 |
1995年 | 33573篇 |
1994年 | 31200篇 |
1993年 | 30313篇 |
1992年 | 27728篇 |
1991年 | 24425篇 |
1990年 | 24477篇 |
1989年 | 23450篇 |
1988年 | 21872篇 |
1987年 | 19908篇 |
1986年 | 19248篇 |
1985年 | 22528篇 |
1984年 | 22587篇 |
1983年 | 20571篇 |
1982年 | 19424篇 |
1981年 | 19504篇 |
1980年 | 18082篇 |
1979年 | 18678篇 |
1978年 | 17816篇 |
1977年 | 17633篇 |
1976年 | 18672篇 |
1975年 | 16056篇 |
1974年 | 15609篇 |
1973年 | 15663篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
991.
992.
993.
994.
D. A. Kudryashov A. S. Gudovskikh A. M. Mozharov A. D. Bol’shakov I. S. Mukhin Zh. I. Alferov 《Technical Physics Letters》2015,41(12):1120-1123
Design and operation modes of double-junction monolithic lattice-matched solar cells based on the ZnSiP2/Si system of materials have been calculated. The effect of the photoactive region thickness and minority carrier lifetime in ZnSiP2 layers on the efficiency of conversion of the incident solar light energy into electrical power was determined. It is shown that solar cells based on ZnSiP2/Si heterostructures can provide efficiencies of 28.8% at AM1.5D, 100 mW/cm2, and 33.3% at AM1.5D, 200 W/cm2. 相似文献
995.
996.
Tomasz Wasiewicz Paulina Szyszka Miroslawa Cichorek Zorica Janjetovic Robert C. Tuckey Andrzej T. Slominski Michal A. Zmijewski 《International journal of molecular sciences》2015,16(4):6645-6667
Deregulated melanogenesis is involved in melanomagenesis and melanoma progression and resistance to therapy. Vitamin D analogs have anti-melanoma activity. While the hypercalcaemic effect of the active form of Vitamin D (1,25(OH)2D3) limits its therapeutic use, novel Vitamin D analogs with a modified side chain demonstrate low calcaemic activity. We therefore examined the effect of secosteroidal analogs, both classic (1,25(OH)2D3 and 25(OH)D3), and novel relatively non-calcemic ones (20(OH)D3, calcipotriol, 21(OH)pD, pD and 20(OH)pL), on proliferation, colony formation in monolayer and soft-agar, and mRNA and protein expression by melanoma cells. Murine B16-F10 and hamster Bomirski Ab cell lines were shown to be effective models to study how melanogenesis affects anti-melanoma treatment. Novel Vitamin D analogs with a short side-chain and lumisterol-like 20(OH)pL efficiently inhibited rodent melanoma growth. Moderate pigmentation sensitized rodent melanoma cells towards Vitamin D analogs, and altered expression of key genes involved in Vitamin D signaling, which was opposite to the effect on heavily pigmented cells. Interestingly, melanogenesis inhibited ligand-induced Vitamin D receptor translocation and ligand-induced expression of VDR and CYP24A1 genes. These findings indicate that melanogenesis can affect the anti-melanoma activity of Vitamin D analogs in a complex manner. 相似文献
997.
Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk. 相似文献
998.
Semiconductors - The performance of InGaN/GaN multiple quantum well (MQW) solar cells with five different Si-doping concentrations, namely 0, 4 × 1017 cm–3, 1 × 1018 cm–3, 3... 相似文献
999.
Sakizadeh Mohamad Mohamed Mohamed M. A. Klammler Harald 《Water Resources Management》2019,33(4):1425-1437
Water Resources Management - Overexploitation of groundwater in the Malayer Plain has resulted in a continuous decline of groundwater levels over recent years with associated risks to water... 相似文献