全文获取类型
收费全文 | 1506篇 |
免费 | 46篇 |
专业分类
电工技术 | 25篇 |
综合类 | 1篇 |
化学工业 | 176篇 |
金属工艺 | 21篇 |
机械仪表 | 33篇 |
建筑科学 | 49篇 |
矿业工程 | 7篇 |
能源动力 | 31篇 |
轻工业 | 146篇 |
水利工程 | 10篇 |
石油天然气 | 6篇 |
无线电 | 149篇 |
一般工业技术 | 248篇 |
冶金工业 | 441篇 |
原子能技术 | 16篇 |
自动化技术 | 193篇 |
出版年
2022年 | 12篇 |
2021年 | 13篇 |
2018年 | 17篇 |
2017年 | 26篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 84篇 |
2012年 | 40篇 |
2011年 | 52篇 |
2010年 | 57篇 |
2009年 | 37篇 |
2008年 | 51篇 |
2007年 | 35篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 41篇 |
2003年 | 36篇 |
2002年 | 36篇 |
2001年 | 23篇 |
2000年 | 30篇 |
1999年 | 28篇 |
1998年 | 113篇 |
1997年 | 63篇 |
1996年 | 47篇 |
1995年 | 29篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 31篇 |
1984年 | 18篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 9篇 |
1978年 | 20篇 |
1977年 | 36篇 |
1976年 | 36篇 |
1975年 | 23篇 |
1974年 | 21篇 |
1973年 | 23篇 |
1972年 | 18篇 |
1971年 | 9篇 |
排序方式: 共有1552条查询结果,搜索用时 62 毫秒
1.
Quantitative UPLC‐MS/MS analysis of chlorogenic acid derivatives in antioxidant fractionates from dandelion (Taraxacum officinale) root
下载免费PDF全文
![点击此处可从《International Journal of Food Science & Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Owen Kenny Thomas J. Smyth Chandralal M. Hewage Nigel P. Brunton 《International Journal of Food Science & Technology》2015,50(3):766-773
While qualitative studies have identified chlorogenic acids in antioxidant extracts, particularly ethyl acetate‐derived extracts, of Taraxacum officinale, quantitative analysis of these phenolic compounds remains largely unreported for this species. In this study, bioactivity‐guided fractionation of an antioxidant crude ethyl acetate extract (DPPH = 295.481 ± 0.955 mg TE g?1 extract) from T. officinale root resulted in a number of reverse‐phase fractions that demonstrated high antioxidant activity (DPPH = 1058.733–1312.136 mg TE g?1 extract), stronger than that of the synthetic antioxidant Trolox®. UPLC‐MS/MS screening of these fractions for the presence of selected mono‐ and di‐caffeoylquinic acids revealed large quantities of 1,5‐dicaffeoylquinic acid present in several fractions (853.052–907.324 μg mg?1), respectively. Due to the antioxidant potency and high levels of 1,5‐dicaffeoylquinic acid observed in these fractions, it was concluded that specifically this chlorogenic acid derivative is a major contributor to the antioxidant efficacy of dandelion root. 相似文献
2.
IG Sumner A Vaughan R Eisenthal RW Pickersgill AJ Owen PW Goodenough 《Canadian Metallurgical Quarterly》1993,1164(3):243-251
Papaya proteinase omega (pp omega) has been purified from dried latex both by immunoaffinity and traditional methods. Kinetic analysis revealed that (1), the pp omega-catalysed hydrolysis of N-benzoyl-L-arginine p-nitroanilide (BApNA) has a lower specificity (kcat/Km) than the same reaction catalysed by papain; (2), the pp omega-catalysed hydrolysis of a tripeptide substrate having phenylalanine at the second position (S2-site) showed a more similar specificity to that catalysed by papain; (3), the significant difference between the two enzymes is that steady state kinetics with both L-BApNA and a tripeptide enables the identification in pp omega of other ionizations affecting binding. The active sites of papain and pp omega can therefore be distinguished by pH-dependence of kcat/Km. 相似文献
3.
Tipton C.W. Bayne S.B. Griffin T.E. Scozzie C.J. Geil B. Agarwal A.K. Richmond J. 《Electron Device Letters, IEEE》2002,23(4):194-196
This paper reports on the first demonstration of a half-bridge power inverter constructed from silicon carbide gate turn-off thyristors (GTOs) operated in the conventional GTO mode. This circuit was characterized with input bus voltages of up to 600 VDC and 2 A (peak current density of 540 A/cm2) with resistive loads using a pulse-width modulated switching frequency of 2 kHz. We discuss the implications of the thyristor's electrical characteristics and the circuit topology on the overall operation of the half-bridge circuit. This work has determined the conservative critical rate of rise value of the off-state voltage to be 200 V/μs in these devices 相似文献
4.
Art Owen 《Data mining and knowledge discovery》2003,7(1):101-113
Data squashing was introduced by W. DuMouchel, C. Volinsky, T. Johnson, C. Cortes, and D. Pregibon, in Proceedings of the 5th International Conference on KDD (1999). The idea is to scale data sets down to smaller representative samples instead of scaling up algorithms to very large data sets. They report success in learning model coefficients on squashed data. This paper presents a form of data squashing based on empirical likelihood. This method reweights a random sample of data to match certain expected values to the population. The computation required is a relatively easy convex optimization. There is also a theoretical basis to predict when it will and won't produce large gains. In a credit scoring example, empirical likelihood weighting also accelerates the rate at which coefficients are learned. We also investigate the extent to which these benefits translate into improved accuracy, and consider reweighting in conjunction with boosted decision trees. 相似文献
5.
F. Barlat S. Panchanadeeswaran O. Richmond 《Metallurgical and Materials Transactions A》1991,22(7):1525-1534
A simple model of flange behavior during cup drawing was used to predict the earing profile of deep-drawn cups. The relationship
between yield surface shape and earing tendency was established, with plane stress yielding corresponding to no hold-down
pressure on the flange and plane strain corresponding to no thickening. Using the Schmid law, the earing model was applied
to the case of a single crystal in cube position and compared to Tucker’s well-known results.[6] For the plane strain case, good agreement was obtained with the experiment; but for plane stress, the predicted profile did
not agree with the experimental one. Using the Taylor/ Bishop and Hill (TBH) theory[8,9] and measured crystallite orientation distribution functions (CODF), the model was applied to the case of high-purity aluminum
sheet with various cold-rolling reductions (35, 60, 80, and 90 pct). The major experimental trends were again correctly predicted
by the plane strain case. 相似文献
6.
Traffic accidents are a well-known public health problem worldwide. In Mexico research into risk factors for motor involving vehicles accidents and their consequences has recently been taken into account. The relevant literature does not normally describe the methodological aspects involved in the collection of primary data, since most studies have used secondary data the good quality and validity of which are assumed. The paper presented seeks to discuss and share with researchers in this field, some of the methodological aspects to be considered in the attempt to recreate the scene of the accident and obtain information approximating to reality. The measurements in situ of, such traffic accident variables as injury, use of seat belt, speed and alcohol intake are discussed. 相似文献
7.
8.
着重介绍Raychem电路保护部的PolySwitch PPTC(聚合物正温度系数)元件在电源管理中提供电流过载和温度过载的保护过程。另外还介绍了电源适配器、CLA(点烟器)、移动电话设备及电池板的保护装置是如何进一步改善实际使用中的总体可靠性的。 相似文献
9.
Bayne S.B. Tipton C.W. Griffin T. Scozzie C.J. Geil B. Agarwal A.K. Richmond J. 《Electron Device Letters, IEEE》2002,23(6):318-320
The high-temperature operation of a silicon carbide gate turn-off thyristor is evaluated for use in inductively loaded switching circuits. Compared to purely resistive load elements, inductive loads subject the switching device to higher internal power dissipation. The ability of silicon carbide components to operate at elevated temperatures and high power dissipations are important factors for their use in future power conversion/control systems. In this work, a maximum current density of 540 A/cm2 at 600 V was switched at a frequency of 2 kHz and at several case temperatures up to 150°C. The turn-off and turn-on characteristics of the thyristor are discussed 相似文献
10.
Pre-clerking of all patients undergoing elective general surgical operations was introduced at our hospital in an attempt to reduce an unacceptably high operation cancellation rate. A prospective audit has been performed on the effect of this policy on the cancellation rate. Before the introduction of pre-clerking there was a marked seasonal variation in the number of patients who failed to attend for surgery, which could be explained by absence on holiday. This seasonal variation disappeared after the start of pre-clerking clinics, but there has been no reduction in the number of cancellations for medical reasons. 相似文献