全文获取类型
收费全文 | 338264篇 |
免费 | 3977篇 |
国内免费 | 1426篇 |
专业分类
电工技术 | 5962篇 |
综合类 | 562篇 |
化学工业 | 49364篇 |
金属工艺 | 13832篇 |
机械仪表 | 10489篇 |
建筑科学 | 7761篇 |
矿业工程 | 1969篇 |
能源动力 | 8508篇 |
轻工业 | 27841篇 |
水利工程 | 3735篇 |
石油天然气 | 7514篇 |
武器工业 | 49篇 |
无线电 | 39190篇 |
一般工业技术 | 69420篇 |
冶金工业 | 61195篇 |
原子能技术 | 8962篇 |
自动化技术 | 27314篇 |
出版年
2021年 | 2871篇 |
2020年 | 2171篇 |
2019年 | 2668篇 |
2018年 | 4807篇 |
2017年 | 4897篇 |
2016年 | 5276篇 |
2015年 | 3244篇 |
2014年 | 5577篇 |
2013年 | 14905篇 |
2012年 | 8915篇 |
2011年 | 11940篇 |
2010年 | 9416篇 |
2009年 | 10857篇 |
2008年 | 11189篇 |
2007年 | 11184篇 |
2006年 | 9585篇 |
2005年 | 8793篇 |
2004年 | 8634篇 |
2003年 | 8371篇 |
2002年 | 8076篇 |
2001年 | 8159篇 |
2000年 | 7812篇 |
1999年 | 8034篇 |
1998年 | 19294篇 |
1997年 | 13728篇 |
1996年 | 10525篇 |
1995年 | 8105篇 |
1994年 | 7091篇 |
1993年 | 7081篇 |
1992年 | 5173篇 |
1991年 | 4954篇 |
1990年 | 4900篇 |
1989年 | 4878篇 |
1988年 | 4489篇 |
1987年 | 4031篇 |
1986年 | 4023篇 |
1985年 | 4486篇 |
1984年 | 4083篇 |
1983年 | 3824篇 |
1982年 | 3565篇 |
1981年 | 3596篇 |
1980年 | 3579篇 |
1979年 | 3357篇 |
1978年 | 3360篇 |
1977年 | 3782篇 |
1976年 | 4876篇 |
1975年 | 2906篇 |
1974年 | 2825篇 |
1973年 | 2833篇 |
1972年 | 2420篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Mass media--friend or foe? Radio, television, and/or the printed word regularly enter most of the world's households. With a better understanding between health workers and those who produce what we hear, see and read, positive messages could do much to change the habits the jeopardize health. Clear, accurate information is the first step towards improvement. 相似文献
992.
993.
994.
995.
996.
P Leterme A Théwis E Fran?ois P Van Leeuwen B Wathelet J Huisman 《Canadian Metallurgical Quarterly》1996,126(9):2188-2198
We assessed the use of 15N-labeled dietary proteins as a possible tool for the determination of the true ileal amino acid (AA) digestibility in pigs. The first experiment was designed to study the dietary N excretion pattern at the ileum subsequent to the ingestion of a single 15N-labeled meal. In a second experiment, we compared ileal endogenous AA outputs and true AA digestibility estimates obtained in pigs ingesting 15N-labeled dietary proteins in a single meal vs. intravenous infusion of [15N]leucine for 10 d during the ingestion of a pea-based diet and a protein-free starch diet. The proportion of endogenous N found in the ileal digesta differed when the label was delivered orally (50%) vs. intravenously (72%) and changed with time. As a consequence, the true ileal AA digestibilities measured with labeled diets were lower. A third experiment demonstrated that this was due to the rapid recycling of labeled dietary N in endogenous moieties, because 15N was found in blood within 10 min of consuming the labeled meal, within 50 min of consumption in pancreatic enzymes, 90 min in bile and 4 h in ileal mucins. We conclude that the use of 15N-labeled meals for determination of true ileal AA digestibilities is limited by the fast recycling of dietary N in endogenous secretions following a single 15N-labeled meal. The accuracy of results will depend on meaningful estimates of AA flow during a limited period and accurate estimates of 15N in AA. 相似文献
997.
We studied experimentally the influence of the degree of water emulsification ofM-40 mazut heated to the water boiling point on the self-ignition time with its pulsed high-pressure injection into heated air. It is shown that water addition does not change the chemistry of the reaction and heating the water-fuel emulsion leads to the disappearance of differences in the ignition character of the emulsion and the moisture-free fuel. It is confirmed that the features of selfignition are determined mostly by conditions of mixture formation. Indirect evidence is obtained that the dynamic tensile strength of the fluid strongly influences the primary dispersion of the jet during its outflow from the sprayer nozzle.Institute of Theoretical and Applied Mechanics, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 20–25, July–August, 1995. 相似文献
998.
The compression of a paper web in a calender nip has been simulated using the finite element method. The mechanical properties of the paper were allowed to vary in the thickness and machine directions of the web. This was done in order to model the influence of temperature gradients as well as density variations (due to the presence of fibre floes) on the deformation behaviour in the nip. Paper was assumed to be an elastic-plastic material exhibiting strain hardening. The yielding behaviour was governed by the Drucker-Prager yield condition. Simulations of the deformation behaviour when paper was subjected to a temperature gradient, clearly revealed that the deformation gradually became more concentrated towards the surface layers as the temperature of the surface increased. This is in accordance with experimental results which indicate that temperature-gradient calendering promotes the surface properties, whereas the bulk of the structure is preserved. Modelling the deformation behaviour of a structure containing density variations reveals that the paper may contain an inhomogeneous strain distribution after unloading, i.e. after passage through the nip. 相似文献
999.
1000.
A floating-gate analog memory device for neural networks 总被引:1,自引:0,他引:1
A floating-gate MOSFET device that can be used as a precision analog memory for neural network LSIs is described. This device has two floating gates. One is a charge-injection gate with a Fowler-Nordheim tunnel junction, and the other is a charge-storage gate that operates as a MOSFET floating gate. The gates are connected by high resistance, and the charge-injection gate is small so that its capacitance is much less than that of the charge-storage gate. By applying control pulses to the charge-injection gate, it is possible to charge and discharge the MOSFET floating gate in order to modify the MOSFET current with high resolution over 10 b. The charge injection can be carried out without disturbing the MOSFET output current with high voltage control pulses. This device is useful for on-chip learning in analog neural network LSIs 相似文献