全文获取类型
收费全文 | 168285篇 |
免费 | 1321篇 |
国内免费 | 191篇 |
专业分类
电工技术 | 2558篇 |
综合类 | 119篇 |
化学工业 | 26475篇 |
金属工艺 | 9476篇 |
机械仪表 | 5718篇 |
建筑科学 | 3013篇 |
矿业工程 | 1887篇 |
能源动力 | 2703篇 |
轻工业 | 8815篇 |
水利工程 | 2730篇 |
石油天然气 | 8693篇 |
武器工业 | 12篇 |
无线电 | 14489篇 |
一般工业技术 | 38259篇 |
冶金工业 | 27812篇 |
原子能技术 | 6936篇 |
自动化技术 | 10102篇 |
出版年
2018年 | 2978篇 |
2017年 | 3092篇 |
2016年 | 3345篇 |
2015年 | 1675篇 |
2014年 | 2958篇 |
2013年 | 6341篇 |
2012年 | 4313篇 |
2011年 | 5397篇 |
2010年 | 4422篇 |
2009年 | 4896篇 |
2008年 | 4942篇 |
2007年 | 4870篇 |
2006年 | 4140篇 |
2005年 | 3821篇 |
2004年 | 3635篇 |
2003年 | 3521篇 |
2002年 | 3453篇 |
2001年 | 3464篇 |
2000年 | 3361篇 |
1999年 | 3212篇 |
1998年 | 7025篇 |
1997年 | 5148篇 |
1996年 | 3822篇 |
1995年 | 2919篇 |
1994年 | 2593篇 |
1993年 | 2721篇 |
1992年 | 2256篇 |
1991年 | 2305篇 |
1990年 | 2410篇 |
1989年 | 2315篇 |
1988年 | 2316篇 |
1987年 | 2191篇 |
1986年 | 2248篇 |
1985年 | 2292篇 |
1984年 | 2206篇 |
1983年 | 2135篇 |
1982年 | 1980篇 |
1981年 | 2193篇 |
1980年 | 2054篇 |
1979年 | 2269篇 |
1978年 | 2434篇 |
1977年 | 2432篇 |
1976年 | 3101篇 |
1975年 | 2244篇 |
1974年 | 2307篇 |
1973年 | 2342篇 |
1972年 | 2155篇 |
1971年 | 1913篇 |
1970年 | 1701篇 |
1969年 | 1634篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
311.
V. Psota I. Boha
enko J. Hartmann M. Budinsk J. Chmelík 《Journal of the Institute of Brewing》2002,108(2):200-203
A newly developed method GFFF (Gravitational Field‐Flow Fractionation) and the well known method LALLS (Low Angle Laser Light Scattering) were used to assess starch granule size distribution of ten varieties of spring barley. As a distribution criterion, the ratio of starch granule content larger than 8 μm (type A) and smaller than 8 μm (type B) was chosen. Both methods divided the observed set in a similar way. Varieties Akcent, Forum and Atribut formed a variety set with the highest ratio of large and small starch granules. Varieties Scarlet and Kompakt had intermediate ratios. The remaining five varieties Amulet, Novum, Olbram, Tolar and Krona had the lowest ratios of large and small starch granules. Statistical analysis showed that there was a highly significant correlation between the GFFF and LALLS methods. 相似文献
312.
Oliveira M. Dart-Mao Cheung C. Al-Zayed A. Chio I.-F.F. Swisher R.R. Lecuyer F. DeLisio M.P. 《Antennas and Propagation, IEEE Transactions on》2002,50(5):698-702
Grid-mixer arrays can achieve high linearity and dynamic range through quasi-optical power combining. We present a 100-element single-ended diode grid mixer operating at 2.45 GHz. Each element incorporates two diodes in series. We measure an input third-order intercept of 11 W (40.5 dBm), and output third-order intercept of 3.4 W (35.4 dBm), and an associated conversion loss of 5.1 dB. The power-handling capability of the array is 100 times larger than that of a microstrip mixer using a single element. The local oscillator (LO) drive requirement for the entire array is 1.4 W (31.6 dBm). The angular dependence of the array's IF power is also presented and is in agreement with theory 相似文献
313.
314.
This report deals with direct observations of microcrack linkage at the crack tip prior to macroscopic crack initiation. It is shown that this process is directly linked to the inclusion distribution in the material and can be considered in terms of an R curve to describe microcrack development. 相似文献
315.
A.K. MANDAGERE J.I. GRAY W.G. IKINS A.M. BOOREN A.M. PEARSON 《Journal of food science》1987,52(5):1147-1148
The possible involvement of glucose in the formation of N-nitrosothiazolidine (NTHZ) in bacon was investigated by pumping pork bellies with brines containing added glucose (2 and 4%). Raw bacon samples processed with glucose had significantly lower levels of N-nitrosothiazolidine-4-carboxylic acid than the smoked control bacons. When the bacon samples with glucose were fried for 6 and 12 min, no NTHZ was detected in the fried products. N-Nitrosopyrrolidine (NPYR) levels in these samples were much lower than those in the fried control samples. Results of this study demonstrate that the contribution of glucose to NTHZ formation in bacon is minimal relative to that of formaldehyde in the wood smoke. 相似文献
316.
317.
On the basis of generalization of the results of investigation of the operation of rodlike elements of composite materials, we make a conclusion that the influence of various factors on the deformability of these elements is studied incompletely. The comparison of the stress-strain states for different models of concrete and reinforced-concrete elements makes it possible to describe the effect of longitudinal reinforcement (coefficient of reinforcement, strength and deformation characteristics) on the critical level of strains in the cross section. According to the results of our investigations, we give recommendations concerning the evaluation of the critical value of the coefficient of reinforcement above which one may observe the effect of reinforcement on the deformability of the analyzed sections. It is shown that the compression strength of the brittle base of the composite with inhomogeneous structure decreases as a result of the fracture processes. It is also demonstrated that the existing procedure used for the evaluation of the indicated decrease in strength requires significant improvement. The problem of evaluation of the ultimate value of the coefficient of reinforcement is also analyzed. 相似文献
318.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献
319.
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
320.
Androstenedione labeled with tritium at positions 1 and 2 was prepared. The molar radioactivity of the sample prepared using homogeneous catalysts was as high as 1.4-1.5 PBq mol-
1. [1,2-3H]Androst-4-ene-3,17-dione can be converted into the [1-3H]steroid with the molar radioactivity of 0.9 PBq mol-
1. 相似文献