全文获取类型
收费全文 | 229051篇 |
免费 | 1831篇 |
国内免费 | 871篇 |
专业分类
电工技术 | 3748篇 |
综合类 | 159篇 |
化学工业 | 35600篇 |
金属工艺 | 11970篇 |
机械仪表 | 7743篇 |
建筑科学 | 4448篇 |
矿业工程 | 2256篇 |
能源动力 | 4356篇 |
轻工业 | 14508篇 |
水利工程 | 3425篇 |
石油天然气 | 10177篇 |
武器工业 | 51篇 |
无线电 | 20562篇 |
一般工业技术 | 50948篇 |
冶金工业 | 38242篇 |
原子能技术 | 8801篇 |
自动化技术 | 14759篇 |
出版年
2021年 | 2236篇 |
2019年 | 2132篇 |
2018年 | 4071篇 |
2017年 | 4224篇 |
2016年 | 4562篇 |
2015年 | 2376篇 |
2014年 | 4136篇 |
2013年 | 9243篇 |
2012年 | 6141篇 |
2011年 | 7655篇 |
2010年 | 6313篇 |
2009年 | 7026篇 |
2008年 | 7081篇 |
2007年 | 6955篇 |
2006年 | 5942篇 |
2005年 | 5346篇 |
2004年 | 5156篇 |
2003年 | 4997篇 |
2002年 | 4840篇 |
2001年 | 4863篇 |
2000年 | 4744篇 |
1999年 | 4539篇 |
1998年 | 10295篇 |
1997年 | 7436篇 |
1996年 | 5539篇 |
1995年 | 4260篇 |
1994年 | 3774篇 |
1993年 | 3894篇 |
1992年 | 3095篇 |
1991年 | 3177篇 |
1990年 | 3277篇 |
1989年 | 3152篇 |
1988年 | 3066篇 |
1987年 | 2887篇 |
1986年 | 2948篇 |
1985年 | 3051篇 |
1984年 | 2834篇 |
1983年 | 2743篇 |
1982年 | 2524篇 |
1981年 | 2748篇 |
1980年 | 2584篇 |
1979年 | 2779篇 |
1978年 | 2912篇 |
1977年 | 3060篇 |
1976年 | 3870篇 |
1975年 | 2690篇 |
1974年 | 2721篇 |
1973年 | 2743篇 |
1972年 | 2537篇 |
1971年 | 2275篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The dielectric and pyroelectric properties of Ge-doped (0.1 mol %) TlInS2 crystals are studied. The results demonstrate that TlInS2 is a ferroelectric relaxor. The experimental data are used to evaluate, using the Vogel–Fulcher relation, the activation energy (0.045 eV), preexponential factor (f
0 = 2 × 1013 Hz), and the dipole-freezing temperature (T
F = 142 K) and to determine the temperature range of the stable relaxor (nanodomain) state and the temperature of the transition to the ferroelectric (macrodomain) state, accompanied by an anomaly in the temperature-dependent pyroelectric coefficient. 相似文献
142.
143.
Ellagic acid (2, 3, 7, 8‐tetrahydroxy(1)benzopyrano(5, 4, 3‐cde)(1)benzopyran‐5, 10‐dione) was selected as a model pollutant which is present in the tannic fraction of cork processing wastewater. The ultrafiltration of aqueous ellagic acid solutions through three membranes was studied in tangential UF laboratory equipment. Two of the membranes were polyethersulfone (Biomax10K and Biomax5K, with MWCO of 10000 and 5000 Da, respectively), and the third made of regenerated cellulose (Ultracel5K, with MWCO of 5000 Da). The water hydraulic permeability was evaluated for each membrane. The evolution of the permeate flow rate with processing time was followed, and the influence of the main operating variables (feed flow rate, trans‐membrane pressure and nature of the membranes) on the permeate flux was also established. According to the hypothesis of the film theory, the intrinsic and apparent rejection coefficients, as well as the mass transfer coefficients, were also determined, and the values obtained were discussed as a function of the operating conditions used. 相似文献
144.
145.
O. R. Dornyak 《Journal of Engineering Physics and Thermophysics》2003,76(3):648-654
A rheological equation of state for wood which allows for the running values of its porosity and humidity is considered. 相似文献
146.
Conclusions The chemical mutagenesis method is recommended for use in local purification installations for cleaning up of caprolactam-containing wastewater.Use of this method permits one to carry out a biochemical clean-up of wastewater having a caprolactam content up to 600 mg/liter while increasing the oxidative power of the aeration tank by a factor of two.Translated from Khimicheskie Volokna, No. 6, p. 46, November–December, 1985. 相似文献
147.
148.
Ya. O. Shablovskii 《Inorganic Materials》2007,43(12):1345-1349
The pyroelectric properties of lithium sulfate have been studied theoretically on the hypothesis of a pseudosymmetry of the structure of its polar phase. Analytical expressions are proposed for the temperature dependences of its pyroelectric polarization and pyroelectric coefficient at low temperatures and near the polymorphic transformation. The pyroelectric and piezoelectric coefficients of a polar crystal are shown to be in direct proportion. 相似文献
149.
150.
Networkable Windows-based operating system devices present information security challenges to both vendors and users of such devices. This article highlights some of those threats and offers measures to improve the link between a firm's business strategy, its operational activities, and its information security strategy. 相似文献