全文获取类型
收费全文 | 10027篇 |
免费 | 568篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 142篇 |
综合类 | 23篇 |
化学工业 | 2613篇 |
金属工艺 | 283篇 |
机械仪表 | 171篇 |
建筑科学 | 635篇 |
矿业工程 | 99篇 |
能源动力 | 306篇 |
轻工业 | 818篇 |
水利工程 | 59篇 |
石油天然气 | 24篇 |
武器工业 | 1篇 |
无线电 | 805篇 |
一般工业技术 | 1979篇 |
冶金工业 | 859篇 |
原子能技术 | 74篇 |
自动化技术 | 1716篇 |
出版年
2023年 | 129篇 |
2022年 | 237篇 |
2021年 | 357篇 |
2020年 | 217篇 |
2019年 | 226篇 |
2018年 | 256篇 |
2017年 | 281篇 |
2016年 | 380篇 |
2015年 | 310篇 |
2014年 | 412篇 |
2013年 | 643篇 |
2012年 | 576篇 |
2011年 | 785篇 |
2010年 | 548篇 |
2009年 | 521篇 |
2008年 | 550篇 |
2007年 | 479篇 |
2006年 | 425篇 |
2005年 | 344篇 |
2004年 | 298篇 |
2003年 | 240篇 |
2002年 | 215篇 |
2001年 | 139篇 |
2000年 | 127篇 |
1999年 | 153篇 |
1998年 | 227篇 |
1997年 | 157篇 |
1996年 | 143篇 |
1995年 | 88篇 |
1994年 | 90篇 |
1993年 | 70篇 |
1992年 | 70篇 |
1991年 | 51篇 |
1990年 | 60篇 |
1989年 | 39篇 |
1988年 | 58篇 |
1987年 | 47篇 |
1986年 | 50篇 |
1985年 | 45篇 |
1984年 | 50篇 |
1983年 | 37篇 |
1982年 | 39篇 |
1981年 | 35篇 |
1980年 | 36篇 |
1978年 | 26篇 |
1977年 | 37篇 |
1976年 | 61篇 |
1975年 | 23篇 |
1974年 | 24篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
The European Space Agency ESA aims at minimizing the safety risks of their space flight projects. Hazard and risk reduction is supported by hazard analysis and probabilistic risk assessment. In hazard analysis hazardous conditions and accident scenarios are identified. Risk assessment is the probabilistic evaluation of accident scenarios and is the basis for risk management. The risk assessment method involves the determination and propagation of event probability. Expert judgement is used in a structured way. In risk management the risk assessment results are used to prioritize and optimize risk reduction efforts and to support risk acceptance evaluations. 相似文献
43.
44.
Nascent high-molecular-weight (UHMW) polyethylene (PE) samples of different origins show a rather high crystallinity of about 70–75% and contain both a major portion of orthorhombic extended chain crystallites and a minor portion of triclinic crystallites. The triclinic content is greater the higher the molecular weight of the sample and the higher the activity of the used catalyser. A melting / recooling treatment results in a reduction of crystallinity by about 15–25% and disappearance of the triclinic phase. Further, an irreversible conversion of nascent orthorhombic extended chain crystallites to orthorhombic folded chain crystallites of increased lateral dimensions and crystalline perfections takes place during the melting / recooling treatment. The results are compared to those obtained for lower-molecular-weight PE samples and for high-strength / modulus PE fibers of different origins. 相似文献
45.
46.
Christian Azar 《Energy》1994,19(12):1255-1261
Haraden's model for estimating the economic cost of global warming is analysed. We change his method of discounting and some of his input parameters in a manner consistent with physical and economic theory as well as empirical data. We then find much higher costs than Haraden found. These costs are compared to the cost of reducing CO2 emissions and we find that deep cuts of the emissions of CO2 are preferable. A check of the sensitivity of our results with respect to some crucial parameter values does not alter that conclusion. 相似文献
47.
MC Dalsing DF Cikrit SG Lalka AP Sawchuk C Schulz 《Canadian Metallurgical Quarterly》1995,21(1):127-134
PURPOSE: This retrospective review of femorodistal vein grafts was analyzed to determine the usefulness of various graft surveillance criteria. METHOD: The surveillance schedule involved evaluations at 1 month, every 3 months the first year, and then every 6 months. Salvage intervention or graft occlusion occurring within the next follow-up interval defined surveillance end points. One hundred two grafts (329 surveillance visits) had an ankle/brachial index (ABI). A duplex scanning-determined midgraft peak systolic flow velocity (PSFV) was available for 81 grafts (262 visits). Forty-eight grafts (137 visits) had both a PSFV and entire graft duplex scanning (EGDS) to determine stenosis greater than 50%, whereas 40 grafts (91 visits) had simultaneous ABI and EGDS. RESULTS: When a greater than 15% decrease in ABI denoted an abnormal surveillance study result, a positive predictive value (PPV) of 24.3% and negative predictive value of 94.5% were noted. Similarly, a PSFV cutoff of less than 35 cm/sec demonstrated values of 26.3% and 94.2%, respectively. When an EGDS of greater than 50% stenosis or a PSFV of less than 35 cm/sec were the cutoff criteria, the PPV was 36.7% and negative predictive value 99.1%, whereas characterizing abnormal results further with ABI (> 15% decreases) increased the PPV to 83.3%. CONCLUSION: The combination of an EGDS, midgraft PSFV, and ABI provides optimal follow-up for our patients with a femorodistal vein graft. 相似文献
48.
49.
50.