全文获取类型
收费全文 | 1488223篇 |
免费 | 27646篇 |
国内免费 | 6931篇 |
专业分类
电工技术 | 33957篇 |
综合类 | 6363篇 |
化学工业 | 255567篇 |
金属工艺 | 64246篇 |
机械仪表 | 42715篇 |
建筑科学 | 43006篇 |
矿业工程 | 11475篇 |
能源动力 | 49964篇 |
轻工业 | 108599篇 |
水利工程 | 15362篇 |
石油天然气 | 36891篇 |
武器工业 | 132篇 |
无线电 | 196425篇 |
一般工业技术 | 283862篇 |
冶金工业 | 170989篇 |
原子能技术 | 34192篇 |
自动化技术 | 169055篇 |
出版年
2021年 | 14638篇 |
2020年 | 11912篇 |
2019年 | 14694篇 |
2018年 | 16980篇 |
2017年 | 16451篇 |
2016年 | 21932篇 |
2015年 | 17484篇 |
2014年 | 28796篇 |
2013年 | 88007篇 |
2012年 | 36089篇 |
2011年 | 49304篇 |
2010年 | 43517篇 |
2009年 | 51832篇 |
2008年 | 45523篇 |
2007年 | 42937篇 |
2006年 | 44725篇 |
2005年 | 39897篇 |
2004年 | 41764篇 |
2003年 | 40990篇 |
2002年 | 38320篇 |
2001年 | 35007篇 |
2000年 | 32825篇 |
1999年 | 32651篇 |
1998年 | 45527篇 |
1997年 | 38614篇 |
1996年 | 33801篇 |
1995年 | 30666篇 |
1994年 | 28647篇 |
1993年 | 28569篇 |
1992年 | 25634篇 |
1991年 | 22836篇 |
1990年 | 23272篇 |
1989年 | 22185篇 |
1988年 | 20719篇 |
1987年 | 19039篇 |
1986年 | 18478篇 |
1985年 | 21800篇 |
1984年 | 21984篇 |
1983年 | 19880篇 |
1982年 | 18932篇 |
1981年 | 19048篇 |
1980年 | 17667篇 |
1979年 | 18169篇 |
1978年 | 17460篇 |
1977年 | 17212篇 |
1976年 | 18125篇 |
1975年 | 15746篇 |
1974年 | 15264篇 |
1973年 | 15376篇 |
1972年 | 12866篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Investigations on the Corrosion Properties of Sn–1Cu–1Ni–xAg Lead Free Solders in 3.5% NaCl Solution
Protection of Metals and Physical Chemistry of Surfaces - Due to the directions and environmental legislations from RoHS (Restrictions of Hazardous Substances), WEEE (World Electrical and... 相似文献
992.
Koji Kamagata Christina Andica Ayumi Kato Yuya Saito Wataru Uchida Taku Hatano Matthew Lukies Takashi Ogawa Haruka Takeshige-Amano Toshiaki Akashi Akifumi Hagiwara Shohei Fujita Shigeki Aoki 《International journal of molecular sciences》2021,22(10)
There has been an increasing prevalence of neurodegenerative diseases with the rapid increase in aging societies worldwide. Biomarkers that can be used to detect pathological changes before the development of severe neuronal loss and consequently facilitate early intervention with disease-modifying therapeutic modalities are therefore urgently needed. Diffusion magnetic resonance imaging (MRI) is a promising tool that can be used to infer microstructural characteristics of the brain, such as microstructural integrity and complexity, as well as axonal density, order, and myelination, through the utilization of water molecules that are diffused within the tissue, with displacement at the micron scale. Diffusion tensor imaging is the most commonly used diffusion MRI technique to assess the pathophysiology of neurodegenerative diseases. However, diffusion tensor imaging has several limitations, and new technologies, including neurite orientation dispersion and density imaging, diffusion kurtosis imaging, and free-water imaging, have been recently developed as approaches to overcome these constraints. This review provides an overview of these technologies and their potential as biomarkers for the early diagnosis and disease progression of major neurodegenerative diseases. 相似文献
993.
Georgina Bezzi Ernesto J. Piga Andrs Binolfi Pablo Armas 《International journal of molecular sciences》2021,22(5)
The Coronavirus Disease 2019 (COVID-19) pandemic has become a global health emergency with no effective medical treatment and with incipient vaccines. It is caused by a new positive-sense RNA virus called severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2). G-quadruplexes (G4s) are nucleic acid secondary structures involved in the control of a variety of biological processes including viral replication. Using several G4 prediction tools, we identified highly putative G4 sequences (PQSs) within the positive-sense (+gRNA) and negative-sense (−gRNA) RNA strands of SARS-CoV-2 conserved in related betacoronaviruses. By using multiple biophysical techniques, we confirmed the formation of two G4s in the +gRNA and provide the first evidence of G4 formation by two PQSs in the −gRNA of SARS-CoV-2. Finally, biophysical and molecular approaches were used to demonstrate for the first time that CNBP, the main human cellular protein bound to SARS-CoV-2 RNA genome, binds and promotes the unfolding of G4s formed by both strands of SARS-CoV-2 RNA genome. Our results suggest that G4s found in SARS-CoV-2 RNA genome and its negative-sense replicative intermediates, as well as the cellular proteins that interact with them, are relevant factors for viral genes expression and replication cycle, and may constitute interesting targets for antiviral drugs development. 相似文献
994.
Prof. Andrea Baier Dr. Anne Kokel Dr. William Horton Ewa Gizińska Dr. Garima Pandey Prof. Ryszard Szyszka Prof. Béla Török Prof. Marianna Török 《ChemMedChem》2021,16(12):1927-1932
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays. 相似文献
995.
Glass and Ceramics - The effect of diopside on the sintering temperature, structure, and properties of low-temperature electrotechnical porcelain was investigated. Diopside concentrate in the... 相似文献
996.
D. Sciti L. Zoli A. Vinci L. Silvestroni S. Mungiguerra P. Galizia 《Journal of the European Ceramic Society》2021,41(5):3045-3050
In this paper the microstructure and mechanical properties of two different Cf/ZrB2-SiC composites reinforced with continuous PyC coated PAN-derived fibres or uncoated pitch-derived fibres were compared.Pitch-derived carbon fibres showed a lower degree of reaction with the matrix phase during sintering compared to PyC/PAN-derived fibres. The reason lies in the different microstructure of the carbon. The presence of a coating for PAN-derived fibres was found to be essential to limit the reaction at the fibre/matrix interface during SPS. However, coated bundles were more difficult to infiltrate, resulting in a less homogeneous microstructure.As far as the mechanical properties are concerned, specimens reinforced with coated PAN-derived fibres provided higher strengths and damage tolerance than uncoated pitch-derived fibres, due to the higher degree of fibre pull-out. On the other hand, the weaker fibre/matrix interface resulted in lower interlaminar shear, off-axis strength and ablation resistance. 相似文献
997.
Jiatong Zhu Xuanyu Meng Ping Zhang Zhuolun Li Jie Xu Michael J. Reece Feng Gao 《Journal of the European Ceramic Society》2021,41(4):2861-2869
A series of rare earth zirconates (RE2Zr2O7) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La2Zr2O7 and Yb2Zr2O7, the smaller “rattling” ions (Yb3+, Er3+, Y3+) have been incorporated into pyrochlore lattice in (La0.2Nd0.2Y0.2Er0.2Yb0.2)2Zr2O7 (LNYEY) while larger ions (La3+, Nd3+, Sm3+, Eu3+) incorporated into fluorite lattice in (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb3+, Er3+, and Y3+, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m-1 K-1, 100-600℃) than LNSGY (1.74-1.75 W m-1 K-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, Hv = 11.47 ± 0.41 GPa; LNSGY, Hv = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10-6 K-1, 1000℃; LNSGY, 11.02 × 10-6 K-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings. 相似文献
998.
999.
Semiconductors - In this work, drain current ID for 5-nm gate length with dual-material (DM) double-surrounding gate (DSG) inversion mode (IM) and junctionless (JL) silicon nanotube (SiNT) MOSFET... 相似文献
1000.
Multidimensional Systems and Signal Processing - Filter banks are the major signal processing blocks that dissipate large amount of power in a portable digital hearing aid device. The power... 相似文献