全文获取类型
收费全文 | 400220篇 |
免费 | 5240篇 |
国内免费 | 1995篇 |
专业分类
电工技术 | 7555篇 |
技术理论 | 5篇 |
综合类 | 1264篇 |
化学工业 | 63680篇 |
金属工艺 | 18546篇 |
机械仪表 | 12569篇 |
建筑科学 | 9215篇 |
矿业工程 | 3252篇 |
能源动力 | 7987篇 |
轻工业 | 32777篇 |
水利工程 | 5121篇 |
石油天然气 | 12842篇 |
武器工业 | 254篇 |
无线电 | 39934篇 |
一般工业技术 | 81102篇 |
冶金工业 | 70415篇 |
原子能技术 | 11033篇 |
自动化技术 | 29904篇 |
出版年
2021年 | 3777篇 |
2019年 | 3409篇 |
2018年 | 5846篇 |
2017年 | 5893篇 |
2016年 | 6410篇 |
2015年 | 4236篇 |
2014年 | 7048篇 |
2013年 | 16782篇 |
2012年 | 11227篇 |
2011年 | 14665篇 |
2010年 | 11749篇 |
2009年 | 12713篇 |
2008年 | 13562篇 |
2007年 | 13593篇 |
2006年 | 11863篇 |
2005年 | 10545篇 |
2004年 | 9688篇 |
2003年 | 9166篇 |
2002年 | 9113篇 |
2001年 | 9180篇 |
2000年 | 8706篇 |
1999年 | 8595篇 |
1998年 | 18949篇 |
1997年 | 13903篇 |
1996年 | 10552篇 |
1995年 | 8041篇 |
1994年 | 7305篇 |
1993年 | 7273篇 |
1992年 | 5772篇 |
1991年 | 5590篇 |
1990年 | 5720篇 |
1989年 | 5616篇 |
1988年 | 5361篇 |
1987年 | 4781篇 |
1986年 | 4868篇 |
1985年 | 5258篇 |
1984年 | 5082篇 |
1983年 | 4800篇 |
1982年 | 4328篇 |
1981年 | 4647篇 |
1980年 | 4282篇 |
1979年 | 4620篇 |
1978年 | 4675篇 |
1977年 | 4818篇 |
1976年 | 6243篇 |
1975年 | 4282篇 |
1974年 | 4154篇 |
1973年 | 4195篇 |
1972年 | 3678篇 |
1971年 | 3298篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed. 相似文献
82.
83.
We consider three types of near-boundary elements: curvilinear quadrangles and families of arcs and points, and their application to a two-dimensional problem of the static theory of elasticity with boundary conditions in displacements. The comparison of the theoretical and numerical aspects of the obtained solutions is performed. It is shown that the accuracy of evaluation of the components of the vector of displacements increases in the following cases: in the case of complete quantization of the near-boundary region (but not in the case of its partial quantization or quantization with overlapping), in the case where the numbers of arcs and points increase, and in the case of simultaneous application of different types of near-boundary elements (specifically, quadrangles and families of arcs). 相似文献
84.
L A Geddes 《IEEE engineering in medicine and biology magazine》2002,21(3):102-103
Poiseuille, known for his law of fluid flow, which is the analog of Ohm's law, introduced the units (mmHg) by which we measure blood pressure by using the mercury manometer, which he described in his medical school thesis in 1828. For 50 years, mean blood pressure was all that could be measured because of the long response time of the mercury manometer. It is true that the height of the mercury column displayed pulsatile oscillations, but their amplitude was much less than that of pulse pressure. It is interesting to note that the slowly responding mercury manometer was made to display first systolic then diastolic pressure by means of an ingenious device that contained two oppositely directed check valves. It took from 1828 to 1903 for high-fidelity graphic recordings of blood pressure to appear in which systolic and diastolic pressures were believable. However, systolic and diastolic pressures were measurable since 1878 when Golz and Gaule created their ingenious valved device that permitted use of the slowly responding mercury manometer to display these pressures accurately 相似文献
85.
Incremental transmission loss analysis has been used for decades, but recent interest in its application to loss allocation calls for new in-depth results. This paper demonstrates that, for incremental methods to be applied correctly in loss allocation, it is first necessary to specify the load distribution and loss supply strategies. Incremental loss allocation among bus power injections is shown to be arbitrary and, therefore, open to challenge as discriminatory. Loss allocation is possible among incremental loads and/or generators, but the proportion of the total losses assigned to either one is arbitrary. Unique, nonarbitrary incremental loss allocations are however possible among the "equivalent" incremental bilateral exchanges between generators and loads. From these basic components it is possible then to calculate the allocation among generators or loads in any specified proportion. The main results, although developed initially for small increments, are extended to large variations. Finally, a general incremental loss allocation algorithm is developed and tested 相似文献
86.
Aluminum and magnesium alloys are the base structural materials in aircraft and spacecraft engineering. The main stages of the development and introduction of light alloys are described. 相似文献
87.
巴西的一个重要电力公司COPEL最近开发了一个水电站高级控制系统,这是在电力部门经受重大变革时期,提高水电竞争力的里程碑。 相似文献
88.
The kinetics of changes in the bound water content in dietetic sucrose-free sponge cakes (DC) during storage was investigated. The effect of edible films of polymyxan, pectin, xanthan, and carboxymethylcellulose upon this kinetics was also investigated. The quantitative changes in both states of water (slightly bound water and strongly bound water) were registered by combined dynamic analysis (thermogravimetry analysis, TGA, and differential thermal analysis, DTA). The moisture changes in DC crumb were analyzed by drying out to constant mass. The rate constants were determined according the equation q = qoe-kt. The values of rate constants 'k', in day-1, concerning the different edible films were as follows: for crumb moisture is (8.00 ≤ k ≤ 12.47) × 10-3, for bound water is (3.07 ≤ kw ≤ 6.26) × 10-2, for slightly bound water is (4.22 ≤ k1 ≤ 8.49) × 10-2 and for strongly bound water is (2.02 ≤ k2 ≤ 5.62) × 10-2 as compared to 18.53 × 10-3, 7.16 × 10-2, 9.04 × 10-2, and 5.36 × 10-2 in the uncovered DC, respectively. The best water-retaining effect in respect to crumb moisture during storage was ascertained in the use of polymyxan and xanthan films. The lowest rate constant values for bound water and its two states were measured for DC covered with pectin. The relation between the kinetics of both bound water states during storage and ageing of the crumb of DC covered with different edible films and the crumb microstructure was represented. By means of scanning electron microscope was read the smallest change in crumb microstructure of pectin-covered DC on the sixth day of storage. 相似文献
89.
90.
N. A. Sivov A. I. Martynenko G. N. Bondarenko M. P. Filatova E. Yu. Kabanova N. I. Popova A. N. Sivov E. B. Kruts’ko 《Petroleum Chemistry》2006,46(1):41-59
Structures and compositions of the monomers guanidine acrylate and guanidine methacrylate, their homopolymers, and copolymers with diallyldimethylammonium chloride enriched in acrylate comonomer units were determined. It was shown that ampholytic copolymers, owing to their ionic nature, contained comonomeric guanidine acrylate or methacrylate units and diallyldimethylammonium chloride units, as well as the acrylate comonomer with the diallyl counterion and polymeric acrylate and diallyl ion pairs. It follows from IR and 1H NMR data that guanidine methacrylate has the same structure (with two hydrogen bonds) in the solid state and in solutions. Guanidine acrylate structures in the solid state and in dimethylsulfoxide are identical and analogous to guanidine methacrylate structure in this solvent. In water, the guanidine acrylate structure has another type of hydrogen bonding (with one hydrogen bond, where the proton is shifted toward the guanidine group). These features of hydrogen bonding of guanidine acrylate and guanidine methacrylate are also retained in their homopolymers and copolymers with diallyldimethylammonium chloride. It was shown that the thermal stability of the copolymers was higher than that of their homopolymers, confirming the formation of intramolecular ion pairs of oppositely charged units of ampholytic copolymers. Moreover, the thermal stability of guanidine methacrylate-diallyldimethylammonium chloride copolymers is higher than that of guanidine acrylate-diallyldimethylammonium chloride copolymers. 相似文献