全文获取类型
收费全文 | 9516篇 |
免费 | 1419篇 |
国内免费 | 1077篇 |
专业分类
化学 | 7020篇 |
晶体学 | 105篇 |
力学 | 478篇 |
综合类 | 110篇 |
数学 | 1189篇 |
物理学 | 3110篇 |
出版年
2024年 | 28篇 |
2023年 | 175篇 |
2022年 | 298篇 |
2021年 | 305篇 |
2020年 | 350篇 |
2019年 | 343篇 |
2018年 | 270篇 |
2017年 | 287篇 |
2016年 | 457篇 |
2015年 | 425篇 |
2014年 | 577篇 |
2013年 | 734篇 |
2012年 | 877篇 |
2011年 | 866篇 |
2010年 | 616篇 |
2009年 | 550篇 |
2008年 | 613篇 |
2007年 | 528篇 |
2006年 | 453篇 |
2005年 | 381篇 |
2004年 | 363篇 |
2003年 | 323篇 |
2002年 | 348篇 |
2001年 | 273篇 |
2000年 | 170篇 |
1999年 | 211篇 |
1998年 | 137篇 |
1997年 | 108篇 |
1996年 | 129篇 |
1995年 | 97篇 |
1994年 | 99篇 |
1993年 | 90篇 |
1992年 | 79篇 |
1991年 | 77篇 |
1990年 | 47篇 |
1989年 | 52篇 |
1988年 | 32篇 |
1987年 | 31篇 |
1986年 | 33篇 |
1985年 | 31篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1963年 | 7篇 |
1959年 | 12篇 |
1958年 | 11篇 |
1957年 | 15篇 |
1956年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Wang et al. (J Operat Res Soc 62: 1898–1902, 2011) studied the m identical parallel-machine and unrelated parallel-machine scheduling with a deteriorating maintenance activity to minimize the total completion time. They showed that each problem can be solved in O(n 2m+3) time, where n is the number of jobs. In this note, we discuss the unrelated parallel-machine setting and show that the problem can be optimally solved by a lower order algorithm. 相似文献
992.
We deal with the Galerkin discretization of the boundary integral equations corresponding to problems with the Helmholtz equation in 3D. Our main result is the semi-analytic integration for the bilinear form induced by the hypersingular operator. Such computations have already been proposed for the bilinear forms induced by the single-layer and the double-layer potential operators in the monograph The Fast Solution of Boundary Integral Equations by O. Steinbach and S. Rjasanow and we base our computations on these results. 相似文献
993.
The relative risk/prevalence ratio and odds ratio are very popular in medical research and epidemiological studies. The odds ratio is overused in practice due to its direct relation with the logistic regression. Interpreting the odds ratio in terms of “relative risk” may lead to incorrect inference on the prevalence of certain event. In this paper, we propose to estimate the relative risk using the log-binomial model by maximizing the likelihood with a linear constraint, which can be easily implemented by an existing function, such as “constrOptim” in R. Furthermore, we review other existing methods and compare their performance under a variety of settings using simulated data. We suggest the proposed and COPY methods in practice, based on its performance in the simulations. For illustration, we investigate the vigorous physical activity effects on obesity using data from the National Health and Nutrition Examination Survey, and the treatment effects on lung cancer mortality using data in R. 相似文献
994.
This paper is devoted to constructing an authentication code with arbitration using subspaces of vector spaces over finite fields.Moreover,if we choose the encoding rules of the transmitter and the decoding rules of the receiver according to a uniform probability distribution,then some parameters and the probabilities of successful attacks are computed. 相似文献
995.
996.
Miroslav Vetrík Martin P?ádnýMartin Hrubý Ji?í Michálek 《Polymer Degradation and Stability》2011,96(5):756-759
We describe the synthesis of new crosslinker N′-{3-[2-(4-{2-[3-(methacryloylamino)propanoyl]hydrazono}cyclohexyliden)hydrazino]-3-oxopropyl}-2-methylacrylamide, which is stable at physiological pH, but is hydrolytically cleaved in acidic pH. Study of acid hydrolysis showed that the crosslinker is hydrolyzed into two N′-(3-hydrazino-3-oxopropyl)-2-methylacrylamide molecules and one 1,4-cyclohexanedione molecule. Hydrogels based on poly[N-(2-hydroxypropyl)methacrylamide] crosslinked with this crosslinker were prepared and their degradation rate was studied as a function of pH (in the range of pH 1.5-7.4). The hydrogel is cleaved within 8-27 days at pH between 1.5 and 6 and is stable at pH 7.4 making it promising for the construction of oesophageal stents. 相似文献
997.
Disulfides have been synthesized by oxidation of thiols using air as oxidant catalyzed by Co-Salophen with high yields,mild and neutral conditions,and easy procedures of the catalyst.The products were confirmed by ~1H NMR and IR. 相似文献
998.
Junhan Cho Min Su Park Jin Hyun Choi Byung Chul Ji Sung Soo Han Won Seok Lyoo 《Journal of Polymer Science.Polymer Physics》2001,39(15):1778-1783
A novel blend system was prepared by blending organosoluble nitro‐substituted polybenzimidazole (NO2‐PBI) and polyetherimide (PEI) in a cosolvent at a moderate condition. It was shown that the NO2‐PBI/PEI blends not only possess tractable processability owing to the enhanced solubility of NO2‐PBI but also retain the desirable features of unmodified PBI/PEI blends. Apparent miscibility in the blends was observed and attributed to hydrogen‐bonding interactions between N? H groups in NO2‐PBI and carbonyl groups in PEI. It was revealed that the NO2‐PBI/PEI blends phase‐separate upon heating above the glass‐transition temperatures. The observed mixing of NO2‐PBI and PEI in a molecular level, although sustainable only in the glassy region, was shown to lend synergy effects to the physical properties of the blends. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1778–1783, 2001 相似文献
999.