全文获取类型
收费全文 | 246723篇 |
免费 | 2653篇 |
国内免费 | 1646篇 |
专业分类
电工技术 | 4291篇 |
综合类 | 2468篇 |
化学工业 | 29405篇 |
金属工艺 | 15572篇 |
机械仪表 | 11779篇 |
建筑科学 | 5299篇 |
矿业工程 | 1439篇 |
能源动力 | 4739篇 |
轻工业 | 10197篇 |
水利工程 | 2700篇 |
石油天然气 | 2503篇 |
武器工业 | 15篇 |
无线电 | 30660篇 |
一般工业技术 | 54049篇 |
冶金工业 | 33287篇 |
原子能技术 | 2733篇 |
自动化技术 | 39886篇 |
出版年
2022年 | 506篇 |
2021年 | 776篇 |
2020年 | 572篇 |
2019年 | 740篇 |
2018年 | 21476篇 |
2017年 | 21140篇 |
2016年 | 14091篇 |
2015年 | 2034篇 |
2014年 | 1880篇 |
2013年 | 5138篇 |
2012年 | 7769篇 |
2011年 | 19744篇 |
2010年 | 17621篇 |
2009年 | 15140篇 |
2008年 | 15810篇 |
2007年 | 18711篇 |
2006年 | 4077篇 |
2005年 | 8092篇 |
2004年 | 6123篇 |
2003年 | 5654篇 |
2002年 | 3845篇 |
2001年 | 3227篇 |
2000年 | 3075篇 |
1999年 | 3220篇 |
1998年 | 9639篇 |
1997年 | 6310篇 |
1996年 | 4916篇 |
1995年 | 3282篇 |
1994年 | 2918篇 |
1993年 | 2839篇 |
1992年 | 1707篇 |
1991年 | 1678篇 |
1990年 | 1567篇 |
1989年 | 1365篇 |
1988年 | 1226篇 |
1987年 | 906篇 |
1986年 | 913篇 |
1985年 | 995篇 |
1984年 | 860篇 |
1983年 | 751篇 |
1982年 | 743篇 |
1981年 | 761篇 |
1980年 | 612篇 |
1979年 | 526篇 |
1978年 | 431篇 |
1977年 | 570篇 |
1976年 | 1002篇 |
1975年 | 340篇 |
1974年 | 306篇 |
1973年 | 281篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
2.
A. Nakano T. Shimazaki M. Sekiya H. Shiozawa K. Ohtsuka A. Aoyagi T. Iwakiri Z. Mikami M. Sato Y. Sugino K. Kinoshita T. Matsuoka T. Imamura Y. Takayama K. Yamamoto 《International Journal of Hydrogen Energy》2021,46(29):15649-15659
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa. 相似文献
3.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic. 相似文献
4.
Kamar M. S. Shalan A. S. Youssef W. M. Hussein A. E. M. Khawassek Y. M. Taha M. H. 《Radiochemistry》2022,64(2):244-256
Radiochemistry - Ferrugination, sericitization, desulfitization, chloritization, and kaolinitization of hydrothermal origin are the main wall rock alterations occurring within the NNW shear zones... 相似文献
5.
The calcium pump (sarco/endoplasmic reticulum Ca2+-ATPase, SERCA) plays a major role in calcium homeostasis in muscle cells by clearing cytosolic Ca2+ during muscle relaxation. Active Ca2+ transport by SERCA involves the structural transition from a low-Ca2+ affinity E2 state toward a high-Ca2+ affinity E1 state of the pump. This structural transition is accompanied by the countertransport of protons to stabilize the negative charge and maintain the structural integrity of the transport sites and partially compensate for the positive charges of the two Ca2+ ions passing through the membrane. X-ray crystallography studies have suggested that a hydrated pore located at the C-terminal domain of SERCA serves as a conduit for proton countertransport, but the existence and function of this pathway have not yet been fully characterized. We used atomistic simulations to demonstrate that in the protonated E2 state and the absence of initially bound water molecules, the C-terminal pore becomes hydrated in the nanosecond timescale. Hydration of the C-terminal pore is accompanied by the formation of water wires that connect the transport sites with the cytosol. Water wires are known as ubiquitous proton-transport devices in biological systems, thus supporting the notion that the C-terminal domain serves as a conduit for proton release. Additional simulations showed that the release of a single proton from the transport sites induces bending of transmembrane helix M5 and the interaction between residues Arg762 and Ser915. These structural changes create a physical barrier against full hydration of the pore and prevent the formation of hydrogen-bonded water wires once proton transport has occurred through this pore. Together, these findings support the notion that the C-terminal proton release pathway is a functional element of SERCA and also provide a mechanistic model for its operation in the catalytic cycle of the pump. 相似文献
6.
Bouaziz Youssef Royer Eric Bresson Guillaume Dhome Michel 《Multimedia Tools and Applications》2022,81(16):22449-22480
Multimedia Tools and Applications - Changes in appearance present a tremendous problem for the visual localization of an autonomous vehicle in outdoor environments. Data association between the... 相似文献
7.
Ava Kwong Cecilia Y. S. Ho Vivian Y. Shin Chun Hang Au Tsun Leung Chan Edmond S. K. Ma 《International journal of molecular sciences》2021,22(2)
The germline carrier of the BRCA1 pathogenic mutation has been well proven to confer an increased risk of breast and ovarian cancer. Despite BRCA1 biallelic pathogenic mutations being extremely rare, they have been reported to be embryonically lethal or to cause Fanconi anemia (FA). Here we describe a patient who was a 48-year-old female identified with biallelic pathogenic mutations of the BRCA1 gene, with no or very subtle FA-features. She was diagnosed with ovarian cancer and breast cancer at the ages of 43 and 44 and had a strong family history of breast and gynecological cancers. 相似文献
8.
9.
10.