全文获取类型
收费全文 | 260231篇 |
免费 | 3783篇 |
国内免费 | 869篇 |
专业分类
电工技术 | 5013篇 |
综合类 | 218篇 |
化学工业 | 37846篇 |
金属工艺 | 9684篇 |
机械仪表 | 7712篇 |
建筑科学 | 6472篇 |
矿业工程 | 919篇 |
能源动力 | 7363篇 |
轻工业 | 22141篇 |
水利工程 | 2239篇 |
石油天然气 | 3242篇 |
武器工业 | 15篇 |
无线电 | 34933篇 |
一般工业技术 | 52093篇 |
冶金工业 | 48774篇 |
原子能技术 | 5135篇 |
自动化技术 | 21084篇 |
出版年
2022年 | 1541篇 |
2021年 | 2383篇 |
2020年 | 1745篇 |
2019年 | 2081篇 |
2018年 | 3586篇 |
2017年 | 3612篇 |
2016年 | 3747篇 |
2015年 | 2480篇 |
2014年 | 4304篇 |
2013年 | 12082篇 |
2012年 | 6627篇 |
2011年 | 9031篇 |
2010年 | 7277篇 |
2009年 | 8270篇 |
2008年 | 8843篇 |
2007年 | 8677篇 |
2006年 | 7663篇 |
2005年 | 6738篇 |
2004年 | 6474篇 |
2003年 | 6754篇 |
2002年 | 6213篇 |
2001年 | 6650篇 |
2000年 | 6082篇 |
1999年 | 6497篇 |
1998年 | 16596篇 |
1997年 | 11518篇 |
1996年 | 8870篇 |
1995年 | 6659篇 |
1994年 | 5958篇 |
1993年 | 5901篇 |
1992年 | 4170篇 |
1991年 | 4064篇 |
1990年 | 3885篇 |
1989年 | 3678篇 |
1988年 | 3583篇 |
1987年 | 3042篇 |
1986年 | 2978篇 |
1985年 | 3298篇 |
1984年 | 2980篇 |
1983年 | 2873篇 |
1982年 | 2676篇 |
1981年 | 2573篇 |
1980年 | 2497篇 |
1979年 | 2336篇 |
1978年 | 2142篇 |
1977年 | 2628篇 |
1976年 | 3586篇 |
1975年 | 1780篇 |
1974年 | 1753篇 |
1973年 | 1699篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al2O3)-doped V2O5 ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V2O5 phase formation with increasing strain on the doping of Al2O3 in place of V2O5 in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO5] polyhedra converts into [VO4] polyhedra on the doping of Al2O3 into V2O5. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability. 相似文献
22.
Mohammed Amin Salih Venkatachalam K. Hubálovský S. Trojovský P. Prabu P. 《Mobile Networks and Applications》2022,27(3):1050-1059
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via... 相似文献
23.
Vasanthapriya R. Neelakandeswari N. Uthayarani K. Chitra M. 《Journal of Inorganic and Organometallic Polymers and Materials》2021,31(11):4272-4280
Journal of Inorganic and Organometallic Polymers and Materials - This paper reports the performance of alizarin based SnO2 dye-sensitized solar cells. A novel template assisted method has been... 相似文献
24.
Simon Neumann Pin Hu Felix Bretschneider Holger Schmalz Andreas Greiner 《大分子材料与工程》2021,306(7):2100090
In this study, blends of the bio-based poly(limonene carbonate) (PLimC) with different commodity polymers are investigated in order to explore the potential of PLimC toward generating more sustainable polymer materials by reducing the amount of petro- or food-based polymers. PLimC is employed as minority component in the blends. Next to the morphology and thermal properties of the blends the impact of PLimC on the mechanical properties of the matrix polymers is studied. The interplay of incompatibility and zero-shear melt viscosity contrast determines the blend morphology, leading for all blends to a dispersed droplet morphology for PLimC. Blends with polymers of similar structure to PLimC (i.e., aliphatic/aromatic polyester) show the best performance with respect to mechanical properties, whereas blends with polystyrene or poly(methyl methacrylate) are too brittle and polyamide 12 blends show very low elongations at break. In blends with Ecoflex (poly(butylene adipate-co-terephthalate)) and Arnitel EM400 (copoly(ether ester)) with poly(butylene terephthalate) hard and polytetrahydrofuran soft segments) a threefold increase in E-modulus can be achieved, while keeping the elongation at break at reasonable high values of ≈200%, making these blends highly interesting for applications. 相似文献
25.
Ebrahim A. Mahdy Khadega M. Sahbal Hanan H. Beherei Yasser K. Abdel-Monem 《Ceramics International》2021,47(5):6251-6261
A new TiO2-containing bioactive glass and glass-ceramics based on 50SiO2-(45-X)CaO-(XTiO2)-5P2O5 system was designed using a sol–gel technique (where X = 5, 7.5 and 10 wt %). The roles of the crystallization behavior and physicochemical characteristics of the designed glass and glass-ceramics which were played in the introduction of TiO2 substitutions were investigated. Moreover, cell proliferation and differentiation were evaluated against human osteosarcoma cells (Saos-2). The TiO2/CaO replacements led to the formation of a stronger glass structure and thus increased thermal parameters and the chemical stabilization of the designed materials. The FTIR data confirmed the existence of Ti within the glass and glass-ceramics samples, and no remarkable effect on their chemical integrity was observed. The XRD patterns indicated that calcium-containing minerals, including Ca2SiO4,Ca3(PO4)2, Ca(Ti,Si)O5, CaTiSiO5, and Ca15(PO4)2·(SiO4)6 phases were developed as a role of structure/texture under the applied heat-treatment. The results of the cytotoxicity test proved that a safe sample dose is 12–50 μg/ml, at which cell viability is ≥ 85%. The cell differentiation determined by ALP test proved the superiority of glass-ceramics compared with their native glasses. Therefore, the obtained materials could be safely used as novel biocompatible materials for the regeneration of bone tissue. 相似文献
26.
27.
Katja F. Hellendahl Felix Kaspar Dr. Xinrui Zhou Zhaoyi Yang Prof. Dr. Zhen Huang Prof. Dr. Peter Neubauer Dr. Anke Kurreck 《Chembiochem : a European journal of chemical biology》2021,22(11):2002-2009
Selenium-modified nucleosides are powerful tools to study the structure and function of nucleic acids and their protein interactions. The widespread application of 2-selenopyrimidine nucleosides is currently limited by low yields in established synthetic routes. Herein, we describe the optimization of the synthesis of 2-Se-uridine and 2-Se-thymidine derivatives by thermostable nucleoside phosphorylases in transglycosylation reactions using natural uridine or thymidine as sugar donors. Reactions were performed at 60 or 80 °C and at pH 9 under hypoxic conditions to improve the solubility and stability of the 2-Se-nucleobases in aqueous media. To optimize the conversion, the reaction equilibria in analytical transglycosylation reactions were studied. The equilibrium constants of phosphorolysis of the 2-Se-pyrimidines were between 5 and 10, and therefore differ by an order of magnitude from the equilibrium constants of any other known case. Hence, the thermodynamic properties of the target nucleosides are inherently unfavorable, and this complicates their synthesis significantly. A tenfold excess of sugar donor was needed to achieve 40−48 % conversion to the target nucleoside. Scale-up of the optimized conditions provided four Se-containing nucleosides in 6–40 % isolated yield, which compares favorably to established chemical routes. 相似文献
28.
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
29.
Catalysis Letters - A new zirconium based carbonaceous solid acid catalyst Zr@CC-PA with both Lewis and Bronsted acidic sites was prepared by simultaneous carbonization and phosphonation of glucose... 相似文献
30.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. 相似文献