全文获取类型
收费全文 | 36021篇 |
免费 | 4479篇 |
国内免费 | 2349篇 |
专业分类
化学 | 7832篇 |
晶体学 | 126篇 |
力学 | 5338篇 |
综合类 | 544篇 |
数学 | 15236篇 |
物理学 | 13773篇 |
出版年
2024年 | 41篇 |
2023年 | 424篇 |
2022年 | 681篇 |
2021年 | 981篇 |
2020年 | 1268篇 |
2019年 | 1098篇 |
2018年 | 1070篇 |
2017年 | 1385篇 |
2016年 | 1524篇 |
2015年 | 1158篇 |
2014年 | 1975篇 |
2013年 | 3352篇 |
2012年 | 2095篇 |
2011年 | 2341篇 |
2010年 | 1965篇 |
2009年 | 2495篇 |
2008年 | 2359篇 |
2007年 | 2207篇 |
2006年 | 1843篇 |
2005年 | 1676篇 |
2004年 | 1482篇 |
2003年 | 1192篇 |
2002年 | 1101篇 |
2001年 | 830篇 |
2000年 | 756篇 |
1999年 | 700篇 |
1998年 | 616篇 |
1997年 | 483篇 |
1996年 | 439篇 |
1995年 | 428篇 |
1994年 | 384篇 |
1993年 | 322篇 |
1992年 | 290篇 |
1991年 | 210篇 |
1990年 | 184篇 |
1989年 | 147篇 |
1988年 | 140篇 |
1987年 | 150篇 |
1986年 | 124篇 |
1985年 | 170篇 |
1984年 | 179篇 |
1983年 | 93篇 |
1982年 | 120篇 |
1981年 | 87篇 |
1980年 | 45篇 |
1979年 | 53篇 |
1978年 | 41篇 |
1977年 | 36篇 |
1976年 | 21篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
汽配件颜色喷涂顺序问题通常以生产线上相邻汽配件颜色切换次数少为最优目标,以进一步降低生产成本.该类问题具有所有汽配件都必须喷涂一次且只喷涂一次的特点,为此提出了TSP转化与建模的方法.将待喷涂汽配件定义为TSP顶点,任意两个待喷涂汽配件的颜色切换定义为顶点的距离,仿照TSP问题构建0-1规划模型;类似于顶点距离,将某些汽配件的颜色或类别不相邻要求定义为0-1矩阵,巧妙地构造了喷涂生产的约束条件.该建模方法简单快速,通用性高,适用于具有类似特点的各类生产实践问题. 相似文献
24.
The present study optimised the ultrasound-assisted extraction (UAE) of bioactive compounds from Amaranthus hypochondriacus var. Nutrisol. Influence of temperature (25.86–54.14 °C) and ultrasonic power densities (UPD) (76.01–273.99 mW/mL) on total betalains (BT), betacyanins (BC), betaxanthins (BX), total polyphenols (TP), antioxidant activity (AA), colour parameters (L*, a*, and b*), amaranthine (A), and isoamaranthine (IA) were evaluated using response surface methodology. Moreover, betalain extraction kinetics and mass transfer coefficients (KLa) were determined for each experimental condition. BT, BC, BX, TP, AA, b*, KLa, and A were significantly affected (p < 0.05) by temperature extraction and UPD, whereas L*, a*, and IA were only affected (p < 0.05) by temperature. All response models were significantly validated with regression coefficients (R2) ranging from 87.46 to 99.29%. BT, A, IA, and KLa in UAE were 1.38, 1.65, 1.50, and 29.93 times higher than determined using conventional extraction, respectively. Optimal UAE conditions were obtained at 41.80 °C and 188.84 mW/mL using the desired function methodology. Under these conditions, the experimental values for BC, BX, BT, TP, AA, L*, a*, b*, KLa, A, and IA were closely related to the predicted values, indicating the suitability of the developed quadratic models. This study proposes a simple and efficient UAE method to obtain betalains and polyphenols with high antioxidant activity, which can be used in several applications within the food industry. 相似文献
25.
《中国物理 B》2021,30(5):56201-056201
A new three-dimensional(3 D) cellular model based on hinging open-cell Kelvin structure is proposed for its negative compressibility property. It is shown that this model has adjustable compressibility and does exhibit negative compressibility for some certain conformations. And further study shows that the images of compressibility are symmetrical about the certain lines, which indicates that the mechanical properties of the model in the three axial directions are interchangeable and the model itself has a certain geometric symmetry. A comparison of the Kelvin model with its anisotropic form with the dodecahedron model shows that the Kelvin model has stronger negative compressibility property in all three directions.Therefore, a new and potential method to improve negative compressibility property can be derived by selecting the system type with lower symmetry and increasing the number of geometric parameters. 相似文献
26.
27.
28.
An oriented tetrahedron defined on four vertices is a set of four cyclic triples with the property that any ordered pair of vertices is contained in exactly one of the cyclic triples. A tetrahedral quadruple system of order with index , denoted by , is a pair , where is an ‐set and is a set of oriented tetrahedra (blocks) such that every cyclic triple on is contained in exactly members of . A is pure if there do not exist two blocks with the same vertex set. When , the spectrum of a pure TQS has been completely determined by Ji. In this paper, we show that there exists a pure if and only if and . A corollary is that a simple also exists if and only if and . 相似文献
29.
30.
本文基于新的Kronecker型替换,给出两个由黑盒表示的稀疏多项式的新确定性插值算法.令f∈R[x1,……,xn]是一个稀疏黑盒多项式,其次数上界为D.当R是C或者是有限域时,相对于已有算法,新算法具有更好的计算复杂度或者关于D的复杂度更低.特别地,对于一般黑盒模型,D是复杂度中的主要因素,而在所有的确定性算法中,本文的第二个算法的复杂度关于D是最低的. 相似文献