全文获取类型
收费全文 | 657237篇 |
免费 | 10211篇 |
国内免费 | 2105篇 |
专业分类
电工技术 | 12392篇 |
综合类 | 597篇 |
化学工业 | 96604篇 |
金属工艺 | 25210篇 |
机械仪表 | 22650篇 |
建筑科学 | 17618篇 |
矿业工程 | 2023篇 |
能源动力 | 17075篇 |
轻工业 | 63432篇 |
水利工程 | 5694篇 |
石油天然气 | 4909篇 |
武器工业 | 16篇 |
无线电 | 83723篇 |
一般工业技术 | 124952篇 |
冶金工业 | 116973篇 |
原子能技术 | 8833篇 |
自动化技术 | 66852篇 |
出版年
2021年 | 4156篇 |
2020年 | 3002篇 |
2019年 | 3793篇 |
2018年 | 13773篇 |
2017年 | 14494篇 |
2016年 | 10658篇 |
2015年 | 5632篇 |
2014年 | 8623篇 |
2013年 | 28127篇 |
2012年 | 17484篇 |
2011年 | 29404篇 |
2010年 | 24024篇 |
2009年 | 25399篇 |
2008年 | 26068篇 |
2007年 | 28060篇 |
2006年 | 18607篇 |
2005年 | 20456篇 |
2004年 | 18151篇 |
2003年 | 17456篇 |
2002年 | 15906篇 |
2001年 | 15753篇 |
2000年 | 14523篇 |
1999年 | 15441篇 |
1998年 | 36356篇 |
1997年 | 26020篇 |
1996年 | 20074篇 |
1995年 | 15565篇 |
1994年 | 13757篇 |
1993年 | 13375篇 |
1992年 | 9752篇 |
1991年 | 9297篇 |
1990年 | 8771篇 |
1989年 | 8394篇 |
1988年 | 8099篇 |
1987年 | 6723篇 |
1986年 | 6570篇 |
1985年 | 8090篇 |
1984年 | 7483篇 |
1983年 | 6635篇 |
1982年 | 6102篇 |
1981年 | 6167篇 |
1980年 | 5744篇 |
1979年 | 5461篇 |
1978年 | 5065篇 |
1977年 | 6156篇 |
1976年 | 8138篇 |
1975年 | 4271篇 |
1974年 | 4045篇 |
1973年 | 3970篇 |
1972年 | 3121篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
91.
Muntasir Hashim Farnoosh Farhad David Smyth‐Boyle Robert Akid Xiang Zhang Philip J. Withers 《工业材料与腐蚀》2019,70(11):2009-2019
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits. 相似文献
92.
The hot corrosion Type II of the alloys FeCr20, FeCr20Ni10, FeCr20Ni20, and FeCr20Co10 is investigated at 700°C in air + 0.5% SO2 with deposits consisting of Na2SO4 and a eutectic mixture of Na2SO4 and MgSO4 for 24, 100, and 300 h. The alloying elements nickel and cobalt have a positive influence when tests are conducted using a MgSO4‐Na2SO4 deposit. In this case, they reduce the metal loss and increase the time to the propagation stage. In contrast, when the alloys are exposed with a Na2SO4 deposit, these alloying elements increase the metal loss and allow for the transition to the propagation stage because they can form molten phases with the Na2SO4. During the incubation stage an oxide scale forms on the FeCr20 alloy, which is thicker than the one formed during exposure without a deposit, and iron oxides are observed, which precipitate in the deposit. The propagation stage occurs by a dissolution and precipitation mechanism forming localized pitting attack. Iron is the main species that dissolves and precipitates, while chromium remains mainly as an oxide beneath the initial surface. The additional elements are found in the pit and in the salt deposit. 相似文献
93.
94.
95.
96.
97.
Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant. 相似文献
98.
Wireless Personal Communications - In this article compact multiple input multiple output (MIMO) antenna with triple notch at the ultra-wideband application having two identical monopole antennas... 相似文献
99.
Madhu H. C. Edachery Vimal Lijesh K. P. Perugu Chandra Shekhar Kailas Satish V. 《Metallurgical and Materials Transactions A》2020,51(8):4086-4099
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result... 相似文献
100.
Sebastian Roth Peter Stockinger Jakob Steff Simon Steimle Dr. Viktor Sautner Prof. Dr. Kai Tittmann Prof. Dr. Jürgen Pleiss Prof. Dr. Michael Müller 《Chembiochem : a European journal of chemical biology》2020,21(18):2615-2619
The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the “classical” SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes. 相似文献