全文获取类型
收费全文 | 347380篇 |
免费 | 3388篇 |
国内免费 | 1805篇 |
专业分类
电工技术 | 5114篇 |
综合类 | 2568篇 |
化学工业 | 47581篇 |
金属工艺 | 19363篇 |
机械仪表 | 11705篇 |
建筑科学 | 7088篇 |
矿业工程 | 2582篇 |
能源动力 | 6614篇 |
轻工业 | 18032篇 |
水利工程 | 4622篇 |
石油天然气 | 9641篇 |
武器工业 | 27篇 |
无线电 | 38531篇 |
一般工业技术 | 74686篇 |
冶金工业 | 53849篇 |
原子能技术 | 8438篇 |
自动化技术 | 42132篇 |
出版年
2021年 | 2198篇 |
2019年 | 2206篇 |
2018年 | 18254篇 |
2017年 | 17254篇 |
2016年 | 14268篇 |
2015年 | 3156篇 |
2014年 | 4571篇 |
2013年 | 10962篇 |
2012年 | 9760篇 |
2011年 | 18225篇 |
2010年 | 15451篇 |
2009年 | 13867篇 |
2008年 | 15244篇 |
2007年 | 16330篇 |
2006年 | 7717篇 |
2005年 | 8067篇 |
2004年 | 7742篇 |
2003年 | 7517篇 |
2002年 | 6489篇 |
2001年 | 6389篇 |
2000年 | 6082篇 |
1999年 | 6165篇 |
1998年 | 15801篇 |
1997年 | 10919篇 |
1996年 | 8324篇 |
1995年 | 5884篇 |
1994年 | 5240篇 |
1993年 | 5292篇 |
1992年 | 3813篇 |
1991年 | 3853篇 |
1990年 | 3851篇 |
1989年 | 3559篇 |
1988年 | 3438篇 |
1987年 | 3008篇 |
1986年 | 3082篇 |
1985年 | 3176篇 |
1984年 | 2984篇 |
1983年 | 2800篇 |
1982年 | 2648篇 |
1981年 | 2835篇 |
1980年 | 2597篇 |
1979年 | 2718篇 |
1978年 | 2821篇 |
1977年 | 2938篇 |
1976年 | 4009篇 |
1975年 | 2533篇 |
1974年 | 2574篇 |
1973年 | 2587篇 |
1972年 | 2332篇 |
1971年 | 2042篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
91.
92.
93.
The effects of adenosine and sodium nitroprusside (SNP) on central hemodynamics and myocardial blood flow and metabolism were investigated postoperatively after elective coronary artery bypass (CABG) surgery in ten sedated and mechanically ventilated patients in the intensive care unit. During three consecutive 15-min periods, SNP (0.8 +/- 0.1 micrograms.kg-1 x min-1), adenosine (88.9 +/- 13.3 micrograms.kg-1 x min-1), and then again SNP (0.7 +/- 0.1 micrograms.kg-1 x min-1) were infused to control postoperative hypertension at a mean arterial pressure of approximately 80 mm Hg. Systemic and pulmonary hemodynamics and global (coronary sinus flow, CSF) as well as regional (great cardiac vein flow, GCVF) myocardial blood flow and metabolic variables were measured. During adenosine infusion, in comparison to SNP, heart rate was unchanged, stroke volume index and cardiac index increased (24% and 32%, respectively), and the systemic vascular resistance index decreased (-26%). Mean pulmonary arterial pressure (24%) as well as pulmonary capillary wedge pressure (27%) and central venous pressure (18%) were higher with adenosine compared to SNP. Adenosine also increased CSF and GCVF (108% and 103%, respectively) without altering the CSF/GCVF flow ratio compared to SNP. Furthermore, adenosine increased the coronary oxygen content (51%) and decreased the arterio-great cardiac vein oxygen content difference (-48%) without changing regional myocardial oxygen consumption, indicating a more pronounced hyperkinetic myocardial circulation compared to SNP. In addition, adenosine infusion decreased arterial PO2 (-11%) and increased the intrapulmonary shunt fraction (57%). The PR interval time of the electrocardiogram was prolonged (12%) and the ST segment was more depressed during adenosine infusion compared to SNP.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
94.
A multilayer theory has been developed for unidirectional/cross-ply unbalanced laminates subjected to surface shear tractions, using the assumption of plane strain. The analytical solution for the stress field in the laminate is obtained and it is shown that the stresses in each layer are in good agreement with the results of a three-dimensional finite element analysis. Approximate formulae for the analytical stresses are also derived for a laminate subjected to an offset distributed force at one end. The accuracy of this solution is shown by comparison with a three-dimensional finite element analysis. 相似文献
95.
Translated from Izmeritel'naya Tekhnika, No. 3, pp. 40–42, March, 1993. 相似文献
96.
Sh. V. Gedevanishvili V. I. Yukhvid G. Sh. Oniashvili 《Journal of Engineering Physics and Thermophysics》1993,65(5):1134-1137
Use of inexpensive ore concentrates as initial components in SHS metallurgy [1–3] brings about some specific features in the process and the properties of the materials obtained. Ore reagents contain a considerable amount of impurities (Al2O3, SiO2, Fe2O3) that decrease the energetics of SHS systems and the temperature and the rate of combustion and create the limits of combustion and phase separation. In addition, the impurities participate in chemical reactions and enter the desired product. In many cases the presence of silicon, iron, and aluminum in a cast product does not prevent use of this product for practical purposes.Institute of Metallurgy, Academy of Sciences of the Republic of Georgia, Tbilisi. Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 613–616, November, 1993. 相似文献
97.
Y Furuya Y Yoshida T Katayama S Yamamoto A Kawamura 《Canadian Metallurgical Quarterly》1993,31(6):1637-1640
Polymerase chain reaction (PCR) with nested primer pairs was used to diagnose scrub typhus and identify the Rickettsia tsutsugamushi serotype. The primer pairs used for PCR were designed on the basis of the nucleotide sequence of the gene that encodes the 56-kDa antigen. Serotype-specific primers were used in the second PCR amplification. Five serovariants, the Gilliam, Karp, Kato, Kawasaki, and Kuroki strains of R. tsutsugamushi, were identified by nested PCR. In addition, the serotype identified by PCR with DNA from blood clots was the same as that of the strain isolated from five patients with scrub typhus. These findings indicate that this method is useful for diagnosis and identification of the rickettsial serotype in infected patients. 相似文献
98.
The preembedding double immunoreaction method was used to study interrelations of enkephalinergic and GABAergic neuronal elements in the dorsal raphe nucleus of the Wistar albino rat. The enkephalin-like neuronal elements were immunoreacted by the peroxidase-antiperoxidase method and silver-gold intensified, which showed strongly and was specific. The GABA-like immunoreactive neurons were immunoreacted by the peroxidase-antiperoxidase method only. GABA-like neural somata were postsynaptic to both the enkephalin-like immunoreactive and the non-immunoreactive axon terminals. The enkephalin-like immunoreactive axon terminals were also found to synapse GABA-like immunoreactive dendrites. The GABA-like immunoreactive neuronal elements were also found to receive synapses from other non-immunoreactive as well as GABA-like immunoreactive axon terminals. Almost all of the synapses appeared to be asymmetrical. Possible functional activity of interactions among the enkephalinergic, GABAergic, and serotonergic neuronal elements in the dorsal raphe nucleus are discussed. 相似文献
99.
100.
A systematic and straightforward procedure is developed for the synthesis and analysis of transformer-isolated power converters. The procedure can be used to determine the ranges of duty-ratio over which the transformer-isolated power converters of a given class can be operated without transformer saturation. The procedure can also be used to study the dependence of the power converter switch stresses on duty-ratios. This information is useful in the selection of the transformer-isolated power converter most suitable for a given application and in the design of this power converter with minimum switch stresses, high power density, and low cost 相似文献