全文获取类型
收费全文 | 25357篇 |
免费 | 2321篇 |
国内免费 | 1323篇 |
学科分类
工业技术 | 29001篇 |
出版年
2024年 | 86篇 |
2023年 | 425篇 |
2022年 | 673篇 |
2021年 | 1013篇 |
2020年 | 836篇 |
2019年 | 690篇 |
2018年 | 768篇 |
2017年 | 864篇 |
2016年 | 781篇 |
2015年 | 1048篇 |
2014年 | 1333篇 |
2013年 | 1570篇 |
2012年 | 1810篇 |
2011年 | 1990篇 |
2010年 | 1475篇 |
2009年 | 1425篇 |
2008年 | 1457篇 |
2007年 | 1436篇 |
2006年 | 1389篇 |
2005年 | 1147篇 |
2004年 | 770篇 |
2003年 | 707篇 |
2002年 | 761篇 |
2001年 | 597篇 |
2000年 | 584篇 |
1999年 | 619篇 |
1998年 | 501篇 |
1997年 | 399篇 |
1996年 | 389篇 |
1995年 | 322篇 |
1994年 | 307篇 |
1993年 | 197篇 |
1992年 | 151篇 |
1991年 | 116篇 |
1990年 | 89篇 |
1989年 | 69篇 |
1988年 | 50篇 |
1987年 | 36篇 |
1986年 | 28篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
Ao Li Man-Tong Zhao Fa-Wen Yin Min Zhang Hui-Lin Liu Da-Yong Zhou Fereidoon Shahidi 《International Journal of Food Science & Technology》2021,56(6):2938-2945
The antioxidant effects of gallic acid (GA) and its alkyl esters including methyl gallate, ethyl gallate, propyl gallate, butyl gallate (GA-C4), octyl gallate, lauryl gallate, hexadecyl gallate and octadecyl gallate in frying oil (soybean oil) and oyster during frying were investigated. Rancimat induction period (RIP) assay indicated GA and its alkyl esters effectively improved the oxidative stability of soybean oil according to the ‘polar paradox’; that is, the antioxidant effects of the polyphenols decreased in lipid system with the increasing of hydrophobicity. Results also indicated that GA and its alkyl esters all effectively retarded lipid oxidation in oyster tissue according to parameters including RIP, peroxide value and electron spin resonance assays. Moreover, the antioxidant efficiency in oyster increased with the alkyl chain length until GA-C4, and thereafter, the antioxidant effects decreased, similar to the ‘cut-off effect’. This study provides basic data for improving the oxidative stability of seafood during frying. 相似文献
992.
随着古镇旅游的迅速发展,物质旅游所造成的拥挤的旅游环境、低层次的旅游内容、残缺的文化气息和过度的商业化氛围、旅游特色同质化等方面的问题逐渐成为专家学者研究的焦点。本文以西塘为例论述人文旅游发展过程中存在的问题,并提出发展人文旅游,以及提供体验式场所来提升旅游质量的对策。 相似文献
993.
By applying a femtosecond electric pump pulse to a polymer, biexcitons are obtained and the relation between its yield and the photoexciting process is also presented. The simulations are performed within the framework of an extended version of one-dimensional Su–Schrieffer–Heeger tight-binding model combined with a nonadiabatic evolution method. In the discussions, effects of both the photoexciting energy and intensity are considered. The main result is that the yield ratio of biexcitons and excitons increases rapidly with the photoexciting intensity, and there exists a critical photoexciting intensity, beyond which the yield efficiency of biexcitons is even higher than that of excitons. The result theoretically verifies that, by increasing the photoexciting intensity, we can obtain biexcitons efficiently, which is consistent with the experimental speculation. 相似文献
994.
995.
996.
Control of finite‐valued networks, including Boolean networks, is currently a hot topic. In this paper the optimization of the networks with time‐discounted performance criterion is discussed. The problem is formulated as a finite strategy game between human and machine. It is first proved that the optimal strategy can be found in the set of essentially periodic strategies, which makes the problem finitely computable, though the computational complexity of exhaustion might be a severe problem. Then an efficient numerical method is develossped to solve the problem. Some interesting examples are presented to demonstrate the efficiency of our results. 相似文献
997.
998.
Optimization algorithms are studied for a class of semi-Markov control processes (SMCPs) with compact action set. Both the long-run average and discounted cost problems are considered. Formulas of performance potentials and optimality equations for SMCPs are derived. A policy iteration algorithm and a value iteration algorithm are proposed, which can lead to an optimal or suboptimal stationary policy in a finite number of iterations. The convergence of these algorithms is established, without the assumption of the corresponding iteration operator being a span-contraction. In addition, an online policy iteration optimization algorithm based on a single sample path is provided to escape ‘curse of dimensionality’. In the end, a numerical example is provided to illustrate the application of the algorithms. 相似文献
999.
G.H. Sun Q.L. Zhang H.J. Yang J.Q. Luo D.L. Sun C.J. Gu S.T. Yin 《Materials Chemistry and Physics》2013
Ho:LuGG single crystal was successfully grown by the Czochralski growth method, and its lattice parameter was found to be 12.2371 Å. Its thermal conductivity was measured to be 5.29 W mK−1 at 300 K. Meanwhile, transmission spectra were recorded at room temperature, and then its absorption spectra were obtained combining with the transmission spectra of LuGG crystal. The transition intensity parameters Ωt (t = 2, 4, 6), the oscillator strengths, fluorescence branching ratios, transition probabilities and the lifetimes of Ho3+ in LuGG crystal were all evaluated by the Judd–Ofelt theory. Furthermore, its emission spectra were also determined and analyzed. 相似文献
1000.