全文获取类型
收费全文 | 866篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 6篇 |
综合类 | 1篇 |
化学工业 | 70篇 |
金属工艺 | 3篇 |
机械仪表 | 39篇 |
建筑科学 | 40篇 |
矿业工程 | 12篇 |
能源动力 | 2篇 |
轻工业 | 279篇 |
水利工程 | 22篇 |
石油天然气 | 12篇 |
无线电 | 46篇 |
一般工业技术 | 275篇 |
冶金工业 | 8篇 |
自动化技术 | 53篇 |
出版年
2012年 | 90篇 |
2011年 | 113篇 |
2010年 | 15篇 |
2009年 | 10篇 |
2008年 | 65篇 |
2007年 | 80篇 |
2006年 | 56篇 |
2005年 | 48篇 |
2004年 | 45篇 |
2003年 | 37篇 |
2002年 | 39篇 |
2001年 | 18篇 |
2000年 | 34篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 12篇 |
1996年 | 19篇 |
1995年 | 27篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有868条查询结果,搜索用时 15 毫秒
1.
2.
Dierx AH 《The Annals of Regional Science》1988,22(3):99-110
"The main deficiency of the current literature on the determinants of migration is the large gap between theoretical analyses and empirical applications. If no direct link is established between a theoretical model and its empirical specification, the empirical results cannot validate the model. This paper develops a version of the human capital model of migration which permits empirical specification. The human capital model presented incorporates two important concepts from migration theory: (1) an index of characteristics that uniquely define a specific location; and (2) location-specific human capital. The empirical model is estimated with a data set consisting of a number of cases from the Michigan [United States] Panel Study of Income Dynamics (PSID) survey." 相似文献
3.
4.
5.
Sixty crossbred steers with chronological ages approximating 15 months, carcass weights approximating 270 kg and subcutaneous fat thickness measurements approximating 1·2 cm, were maintained for approximately 210 days on a constantly increasing concentrate ration (13 to 75%, according to NAS nutrient requirements for beef cattle; NAS, 1976). These animals were utilized to evaluate the effects of delayed chilling, hot-boning and electrical stimulation on certain physical, histological, biochemical and sensory properties of three different muscles (Semimembranosus, SM; Longissimus dorsi, LD; and Triceps brachii, TB). Results indicated that neither delayed chilling nor electrical stimulation produced consistent meaningful alterations in any of the physical, cooking or palatability attributes evaluated. However, early post-mortem excision of muscle (hot-boning) consistently produced toughening in all of the muscles evaluated. This was observed to a much greater degree in the TB than in either the SM or LD. Based upon sarcomere length determinations, such toughening could be attributed to cold shortening only in the TB. Electrical stimulation of excised muscle was ineffective in preventing or offsetting this toughening. The delayed chilling treatment imposed (2 h at 12·5°C) was ineffective in enhancing potential effects of electrical stimulation on tenderness. 相似文献
6.
7.
Garrett BC Dixon DA Camaioni DM Chipman DM Johnson MA Jonah CD Kimmel GA Miller JH Rescigno TN Rossky PJ Xantheas SS Colson SD Laufer AH Ray D Barbara PF Bartels DM Becker KH Bowen KH Bradforth SE Carmichael I Coe JV Corrales LR Cowin JP Dupuis M Eisenthal KB Franz JA Gutowski MS Jordan KD Kay BD Laverne JA Lymar SV Madey TE McCurdy CW Meisel D Mukamel S Nilsson AR Orlando TM Petrik NG Pimblott SM Rustad JR Schenter GK Singer SJ Tokmakoff A Wang LS Wettig C Zwier TS 《Chemical reviews》2005,105(1):355-390
8.
A total of 270 pigs from a Yorkshire/Duroc/Landrace 3-way cross, reared under an ad libitum feed regimen, were delivered for slaughter after fasting (with access to water) for 24 and 0 h (Exp. 1), 16 and 0 h (Exp. 2) and 24, 16 and 0 h (Exp. 3). The interval between delivery and slaughter was 4-5 h. Feeding until delivery resulted in a lower pH at 45 min post mortem in the longissimus muscle. Ultimate pH values of longissimus and semimembranosus muscles were higher after feed restriction for 24 h. However, the incidence of dark, firm and dry (DFD) (pH > 6·2) was also increased after fasting in Exp. 1. Assessment of meat quality in samples taken from the longissimus at 20 h post mortem showed that, in comparison with feeding until delivery. Hunter L(?) (Lightness)-values and drip loss decreased and firmness improved by prolonged fasting (24 h). Fasting for 16 h did not reduce drip loss, but colour was improved (lower Hunter L(?)-values) in Exp. 3, although not in Exp. 2. Feeding until delivery resulted in better meat quality in Exp. 2 than in Exp. 1 and 3. A significant reduction in dressing percentage as a result of fasting was only found in Exp. 1. There appears no economic disadvantage in restricting feed for 16 h prior to delivery. Although the incidence of DFD may also increase, a fasting period of 16-24 h is recommended to reduce pale, soft and exudative (PSE) muscle, while losses in carcass yield are minimized. Other advantages of fasting are discussed. 相似文献
9.
We describe the operation of a wire-grid-mirror liquid-crystal light valve and its use for optical pattern recognition. The nonlinear characteristic of the wire-grid-mirror liquid-crystal light valve is used to implement the nonlinear joint transform correlator. Experimental results and computer simulations show that the nonlinear characteristic of the wire-grid-mirror liquid-crystal light valve can produce a well-defined correlation peak and low output background. The performance of the nonlinear joint transform correlator obtained when the wire-grid-mirror liquid-crystal light valve is used is compared with that of the binary joint transform correlator. 相似文献
10.
Thick carbonate-dominated successions in northwestern Siberia document secular variations in the C-isotopic composition of seawater through Mesoproterozoic and early Neoproterozoic (Early to early Late Riphean) time. Mesoproterozoic dolomites of the Billyakh Group, Anabar Massif, have delta 13C values that fall between 0 and -1.9 permil versus PDB, with values in the upper part of the succession (Yusmastakh Formation) consistently higher than those of the lower (Ust'-Il'ya and Kotuikan formations). Consistent with available biostratigraphic and radiometric data, delta 13C values for Billyakh carbonates compare closely with those characterizing early Mesoproterozoic carbonates (about 1600-1200 Ma) worldwide. In contrast, late Mesoproterozoic to early Neoproterozoic limestones and dolomites in the Turukhansk Uplift exhibit moderate levels of secular variation. Only the lowermost carbonates in the Turukhansk succession (Linok Formation) have delta 13C values that approximate Billyakh values. Higher in the Turukhansk succession, delta 13C values vary from -2.7 to +4.6 permil (with outliers as low as -5.0 permil interpreted as diagentically altered). Again, consistent with paleontological and radiometric data, these values compare well with isotopic values from 1200 to 850 Ma successions elsewhere. Five sections measured in different parts of the Turukhansk basin show nearly identical patterns of variation, confirming that carbonate delta 13C correlates primarily with time and not facies. The Siberian sections illustrate the potential of integrated biostratigraphic and chemostratigraphic data in the intra- and interbasinal correlation of Mesoproterozoic and early Neoproterozoic rocks. 相似文献