全文获取类型
收费全文 | 307888篇 |
免费 | 2977篇 |
国内免费 | 480篇 |
专业分类
电工技术 | 5774篇 |
综合类 | 341篇 |
化学工业 | 47452篇 |
金属工艺 | 15285篇 |
机械仪表 | 12355篇 |
建筑科学 | 6703篇 |
矿业工程 | 2041篇 |
能源动力 | 5772篇 |
轻工业 | 25915篇 |
水利工程 | 3477篇 |
石油天然气 | 6152篇 |
武器工业 | 32篇 |
无线电 | 31310篇 |
一般工业技术 | 62554篇 |
冶金工业 | 50438篇 |
原子能技术 | 6787篇 |
自动化技术 | 28957篇 |
出版年
2021年 | 2107篇 |
2019年 | 2017篇 |
2018年 | 11056篇 |
2017年 | 11526篇 |
2016年 | 8023篇 |
2015年 | 2688篇 |
2014年 | 3982篇 |
2013年 | 10235篇 |
2012年 | 8525篇 |
2011年 | 15856篇 |
2010年 | 13872篇 |
2009年 | 13370篇 |
2008年 | 13617篇 |
2007年 | 15661篇 |
2006年 | 6953篇 |
2005年 | 9307篇 |
2004年 | 7673篇 |
2003年 | 7174篇 |
2002年 | 6294篇 |
2001年 | 5625篇 |
2000年 | 5516篇 |
1999年 | 5323篇 |
1998年 | 12575篇 |
1997年 | 8897篇 |
1996年 | 6869篇 |
1995年 | 5340篇 |
1994年 | 4764篇 |
1993年 | 4648篇 |
1992年 | 3681篇 |
1991年 | 3410篇 |
1990年 | 3593篇 |
1989年 | 3472篇 |
1988年 | 3310篇 |
1987年 | 2895篇 |
1986年 | 2932篇 |
1985年 | 3373篇 |
1984年 | 3219篇 |
1983年 | 2892篇 |
1982年 | 2738篇 |
1981年 | 2821篇 |
1980年 | 2719篇 |
1979年 | 2624篇 |
1978年 | 2684篇 |
1977年 | 2948篇 |
1976年 | 3805篇 |
1975年 | 2368篇 |
1974年 | 2242篇 |
1973年 | 2376篇 |
1972年 | 1970篇 |
1971年 | 1858篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
H. E. N. Stone 《Journal of Materials Science》1987,22(5):1749-1752
The ratio of the thermal oxidation parameter to the decomposition point (T
p/T
m) is of the order of 0 85 for Y9Co7, indicating a high degree of chemical binding. The persistence of high values of this ratio has been investigated with respect to (a) other compounds in the Y-Co system, (b) replacement of cobalt in Y9Co7 by other d-e!ements, and (c) replacement of yttrium by other rare-earth elements. High ratios are found for (a) Y-Co compounds where Y/Co > 0.5, (b) Y-3d compounds with cobalt and niche! only, end (c) RE-Co compounds generally. However, there are differences in level of the ratio amongst the rare-earth compounds, from which it is inferred that the highest values coincide with full electron shells, that is, without participation of 4f electrons. Additional work is described on an effect of preparation arc-melting current 0n theT
p value for Y9Co7, and on compounds of the same pattern where both components are changed. 相似文献
992.
Raw and heat processed peanut flours were found to contain higher in vitro trypsin inhibitor activity and lectin content than similarly processed soy flour. When fed to weanling rats at a level of 10% protein, the response pattern in food consumption, growth, liver function, and serum chemistries was not consistent among or between the groups. It is concluded that the levels of antinutritional factors in legumes do not correlate with their overall biological impact in feeding studies with the rat. 相似文献
993.
Hemagglutinins present in Amaranthus leucocarpus seed meal were extracted with saline buffer and nutritive value was estimated by PER, NPR as well as Digestible Energy Consumption Evaluations. Protein digestibility was determined both in vitro and in vivo. Trypsin inhibitor activity was also determined. Saline-extracted Amaranth meal had significantly higher PER and NPR values than whole meal (p<0.05). There were no significant differences in digestible energy (Kcal/day/ animal) and protein consumption (g/day/animal) between diets (p<0.05). A. leucocarpus improves in nutritive value after the saline extraction procedures and has a good potential as a complementary food due to its lysine content. In addition purified agglutinin may be a useful biochemical. 相似文献
994.
995.
Howard Kenneth I.; Krause Merton S.; Orlinsky David E. 《Canadian Metallurgical Quarterly》1986,54(1):106
Presents an analysis of the attrition dilemma in psychotherapy research and reviews the methods used to compensate for data loss. It is argued that attrition is not ultimately a problem of bias but a problem of lack of information. A reformulation is offered that integrates single-case studies with traditional group comparison methodology in an attempt to find optimal causal relations of treatments to outcomes. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
996.
A. Cardador-Martí nez E. Casta o-Tostado G. Loarca-Pi a 《Food Additives & Contaminants》2002,19(1):62-69
Polyphenols with antimutagenic and anticarcinogenic properties are present in fruits, vegetables and legumes. In this study, the Salmonella typhimurium tester strains TA98 and TA100 were used in the microsuspension assay to examine the antimutagenic effect of phenolic compounds extracted from the common bean (Phaseolus vulgaris) against mutagenicity induced by aflatoxin B 1 (AFB 1 ). A dose-response curve was constructed for AFB 1 ; from which a level of 40ng AFB 1 /tube was selected for all antimutagenicity assays. The AFB 1 and phenolic extract (PE) were not toxic to the bacteria at concentrations tested. In the case of PE, results were similar to the number of spontaneous revertants for TA98 and TA100. The inhibitory effect of PE against AFB 1 mutagenicity was dose-dependent at the lower concentrations tested (2.5, 5, 10, 12.5, 15 and 25 μg-equivalent ( + )-catechin/tube for TA98; 0.5, 1, 1.5, 2.5, 5, 10 and 25 μg-equivalent ( + )-catechin/ tube for TA100). Further, a two-stage incubation procedure was used to investigate the potential interaction between PE and AFB 1 . The greatest inhibitory effect of the PE on AFB 1 mutagenicity occurred when PE and AFB 1 were incubated together. When the bacteria were first incubated with PE followed by a second incubation with AFB 1 , lower inhibition was observed. Lower inhibition was also observed when the bacteria were first incubated with AFB 1 followed by a second incubation with PE. The results suggest that the mechanism of inhibition could involve the formation of a chemical complex between of PE and AFB 1 . 相似文献
997.
998.
The dependence of the spectral resolution of a focusing X-ray diffractor on the shape and curvature of the reflecting crystallographic faces in the plane perpendicular to the focusing circle plane is theoretically studied in the point source approximation. The curvature parameters ensuring the best spectral resolution are determined for ellipsoidal and toroidal types of the crystal bending. 相似文献
999.
Narayanaswami C. Kamijoh N. Raghunath M. Inoue T. Cipolla T. Sanford J. Schlig E. Venkiteswaran S. Guniguntala D. Kulkarni V. Yamazaki K. 《Computer》2002,35(1):33-41
Nearly four years in development, the IBM Linux watch contains a complete computer system that runs Linux, displays X11 graphics, and has wireless connectivity. The system fits in a case that could pass as a slightly unusual analog timepiece with a somewhat odd shape and an extraordinarily brilliant face. The developers have created two versions of the watch, one with an organic light-emitting diode display and the other with a liquid crystal display. Still considered a research prototype, the watch already runs some personal information management applications, and it can communicate with PCs, PDAs, and other wireless-enabled devices, viewing condensed e-mail and directly receiving pager-like messages. Eventually, users will be able to access various Internet-based services, such as up-to-the-minute information about weather, traffic conditions, the stock market, and sports 相似文献
1000.