全文获取类型
收费全文 | 62343篇 |
免费 | 1778篇 |
国内免费 | 4250篇 |
专业分类
电工技术 | 2787篇 |
综合类 | 1693篇 |
化学工业 | 6381篇 |
金属工艺 | 7280篇 |
机械仪表 | 2954篇 |
建筑科学 | 2767篇 |
矿业工程 | 7058篇 |
能源动力 | 1154篇 |
轻工业 | 6689篇 |
水利工程 | 2966篇 |
石油天然气 | 4382篇 |
武器工业 | 877篇 |
无线电 | 7143篇 |
一般工业技术 | 3725篇 |
冶金工业 | 3371篇 |
原子能技术 | 1967篇 |
自动化技术 | 5177篇 |
出版年
2022年 | 494篇 |
2021年 | 563篇 |
2020年 | 386篇 |
2019年 | 538篇 |
2018年 | 605篇 |
2016年 | 504篇 |
2015年 | 646篇 |
2014年 | 1386篇 |
2013年 | 1075篇 |
2012年 | 1098篇 |
2011年 | 1295篇 |
2010年 | 1194篇 |
2009年 | 1277篇 |
2008年 | 1413篇 |
2007年 | 1598篇 |
2006年 | 1640篇 |
2005年 | 1934篇 |
2004年 | 1993篇 |
2003年 | 1601篇 |
2002年 | 1820篇 |
2001年 | 2082篇 |
2000年 | 1475篇 |
1999年 | 1210篇 |
1998年 | 1011篇 |
1997年 | 867篇 |
1996年 | 1046篇 |
1995年 | 1067篇 |
1994年 | 1026篇 |
1993年 | 1060篇 |
1992年 | 1379篇 |
1991年 | 1322篇 |
1990年 | 1663篇 |
1989年 | 1472篇 |
1988年 | 2243篇 |
1987年 | 2725篇 |
1986年 | 2248篇 |
1985年 | 2589篇 |
1984年 | 2338篇 |
1983年 | 2132篇 |
1982年 | 2355篇 |
1981年 | 2028篇 |
1980年 | 1575篇 |
1979年 | 942篇 |
1978年 | 589篇 |
1975年 | 438篇 |
1974年 | 431篇 |
1966年 | 437篇 |
1965年 | 641篇 |
1964年 | 628篇 |
1956年 | 511篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
正采用随机区组设计,在不添加腐植酸(单独施肥)和添加腐植酸(联合施肥)的条件下,以NPK推荐施肥量100%、80%和60%的3个施肥水平,研究了NPK滴灌对辣椒养分分配和生产率的影响。在较深的土层中,联合施肥能降低土壤速效N和K含量,提高土壤速效P含量。单独施肥的基础上联合施肥,辣椒产量提高了17%~27%。联合施肥的肥 相似文献
42.
采用动态吸湿性能分析法测定高能推进剂的吸湿性,以典型配方NEPE(硝酸酯增塑聚醚)推进剂和低易损性推进剂为研究对象,考察了湿度对其力学性能的影响。结果表明:典型配方NEPE推进剂和低易损性推进剂吸湿性差别很大;高湿环境下,2种高能推进剂的力学性能变化差异明显;经干燥处理,典型配方NEPE推进剂存放3 d后,抗拉强度和伸长率完全恢复,而低易损性推进剂存放10 d,其抗拉强度只恢复至原先的一半。 相似文献
43.
Alireza HEIDARI Ali ESMAEEL NEZHAD Ahmad TAVAKOLI Navid REZAEI Foad H. GANDOMAN Mohammad Reza MIVEH Abdollah AHMADI Majid MALEKPOUR 《Frontiers in Energy》2020,14(3):510
Recently, renewable energy resources and their impacts have sparked a heated debate to resolve the Australian energy crisis. There are many projects launched throughout the country to improve network security and reliability. This paper aims to review the current status of different renewable energy resources along with their impacts on society and the environment. Besides, it provides for the first time the statistics of the documents published in the field of renewable energy in Australia. The statistics include information such as the rate of papers published, possible journals for finding relative paper, types of documents published, top authors, and the most prevalent keywords in the field of renewable energy in Australia. It will focus on solar, wind, biomass, geothermal and hydropower technologies and will investigate the social and environmental impacts of these technologies. 相似文献
44.
Ximei Zhao Matthias Rudolph Abdullah M. Asiri A. Stephen K. Hashmi 《Frontiers of Chemical Science and Engineering》2020,14(3):317
This review summarizes recent advances in the field of gold-catalyzed synthesis of pharmaceutically relevant aza-heterocycles via in situ generated α-imino gold carbene complexes as intermediates. 相似文献
45.
为了平衡体素模型的体素数量与精细度,提出一种实体模型体素加密细化算法。该算法对低分辨率均一体素模型的表面体素进行切分,标记与三角面不相交的体素,并运用边界状态传递判定标记体素的内外位置。通过编码不同八叉树的节点,并进行跨八叉树快速邻居节点搜寻,实现多级加密细分。实验结果表明,该算法可以以低分辨率模型为基础,精确地获得体素单元少的高分辨率模型。 相似文献
46.
选择性去除燃油中的硫化物对环境和人类健康具有重要意义。采用基于密度泛函理论(DFT)和含色散矫正的密度泛函理论(D-DFT)的方法,研究了多孔氮化硼(p-BN)及其空位缺陷对燃油中噻吩类硫化物及非硫化物的吸附行为及吸附选择性。结果表明:B—N极性键与硫化物极性分子之间的分子间力使p-BN能选择性去除燃油中的二苯并噻吩(DBT);引入N、B空位缺陷后,缺陷能级与S原子形成化学相互作用并伴随电荷转移,进一步增强了p-BN对硫化物的吸附。通过对N、B空位缺陷形成能的计算,预测了合成含VN、VB的p-BN所需的化学条件:在富硼条件下,采用B2H4作为B源比采用B、α-B12和BH3等更有利于VN的形成;而在富氮环境下采用N2H4作为N源比采用N2、NH3等更有利于VB形成。为实验上有目的地合成高效吸附脱硫材料提供理论依据。 相似文献
47.
A.A.Boryaev 《火炸药学报》2020,43(2):116-132
A brief review of nitrous oxide decomposition catalysts was presented.The features of catalyst operating conditions in low-thrust engines of space vehicles and requirements to monopropellant(hydrogen peroxide,hydrazine,nitrous oxide)decomposition catalysts were considered.A scientific basis for development of a nitrous oxide decomposition catalyst and general principles for selection of efficient catalysts were formulated.The results of selecting catalyst systems for the development of decomposition catalysts for N2O as a monopropellant were presented.Preliminary selection of catalyst systems for the development of a catalyst designed for low-thrust rocket engines(LTREs)was carried out:supporter—Al2O3 and ZrO2;active substances—Co,Ni,Fe,Pd,Rh,Pt,Ru,Ir,NiO,Fe2O3,RuO2,Rh2O3,PdO,IrO2,PtO2,CoO,Al2O3,La2NiO4,Nd2NiO4,Pr 2NiO4,La2O3,TiO2,NiO,La2O3,TiO2,ZnO.With 71 references. 相似文献
48.
Zirconia graphite refractory is used as a core-nozzle in the thin-strip casting of steel. Post-mortem analysis of used refractory was performed in an effort to establish the failure mechanism. Corrosion behavior was studied against molten steel with Mn O- SiO 2based liquid inclusions. Corrosion of these materials involves dissolution and oxidation of graphite in the matrix followed by penetration of liquid slag leading to degradation of ZrO 2particles. Thermodynamic equilibrium calculations were performed to study this corrosion mechanism. 相似文献
49.
Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a Cd0.8Zn0.2Se/ZnSe quantum dot in the presence of magnetic field strength. The magneto-polaron induced hydrogenic binding energy as a function of dot radius in the wide band gap quantum dot is calculated. The oscillator strength and the spontaneous lifetime are studied taking into account the spatial confinement, magnetic field strength and the phonon contribution. Numerical calculations are carried out using variational formulism within the single band effective mass approximation. The optical properties are computed with the compact density matrix method. The magneto-polaron induced optical gain as a function of photon energy is observed. The results show that the optical telecommunication wavelength in the fiber optic communications can be achieved using CdSe/ZnSe semiconductors and it can be tuned with the proper applications of external perturbations. 相似文献
50.
The critical properties of the mixed manganite La0.67–x Y x Ba0.23Ca0.1Mn O3 with x=0.10 and x=0.15 around the paramagnetic(PM)-ferromagnetic(FM) phase transition were investigated through various techniques. These involved modified Arrott plots, Kouvel-Fisher method and Widom scaling relation. Magnetic data, analyzed in the critical region, using the above methods, yielded the critical exponents for(x=0.10) La0.57Y0.10Ba0.23Ca0.1Mn O3(β=0.312±0.002 and γ=1.147±0.003 at T C=299.23±0.05 K). Moreover, the estimated critical exponents of(x=0.15) La0.52Y0.15Ba0.23Ca0.1Mn O3 were β=0.286±0.004 and γ=0.943±0.002 at T C=289.53±0.06 K. The critical exponents’ values were close to the theoretical values of 3D-Ising model and tricritical mean-field model. These results suggested that the present composition should be close to a tricritical point in the La0.67–x Y x Ba0.23Ca0.1Mn O3 phase diagram. Expressing the field dependence as ΔS M∝H n allowed us to establish a relationship between the exponent n and the critical exponents of the material and to propose a phenomenological universal curve for the field dependence of ΔS M. 相似文献