全文获取类型
收费全文 | 14366篇 |
免费 | 714篇 |
国内免费 | 455篇 |
专业分类
化学 | 834篇 |
力学 | 167篇 |
综合类 | 143篇 |
数学 | 1241篇 |
物理学 | 644篇 |
综合类 | 12506篇 |
出版年
2024年 | 44篇 |
2023年 | 137篇 |
2022年 | 304篇 |
2021年 | 307篇 |
2020年 | 289篇 |
2019年 | 237篇 |
2018年 | 242篇 |
2017年 | 347篇 |
2016年 | 324篇 |
2015年 | 438篇 |
2014年 | 930篇 |
2013年 | 667篇 |
2012年 | 953篇 |
2011年 | 1051篇 |
2010年 | 769篇 |
2009年 | 883篇 |
2008年 | 865篇 |
2007年 | 1055篇 |
2006年 | 996篇 |
2005年 | 834篇 |
2004年 | 759篇 |
2003年 | 566篇 |
2002年 | 416篇 |
2001年 | 398篇 |
2000年 | 282篇 |
1999年 | 266篇 |
1998年 | 190篇 |
1997年 | 173篇 |
1996年 | 125篇 |
1995年 | 114篇 |
1994年 | 95篇 |
1993年 | 118篇 |
1992年 | 83篇 |
1991年 | 80篇 |
1990年 | 45篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 25篇 |
1986年 | 14篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
91.
M. Lacroix M. Gagnon V. Pringsulaka M. Jobin B. Latreille K. Nouchpramool Y. Prachasitthisak S. Charoen P. Adulyatham J. Lettre B. Grad 《Radiation Physics and Chemistry》1993,42(1-3)
Two lots of mangoes of the Nahng Glahng Wahn variety from Thailand were irradiated at the Thai Irradiation Center (TIC) at 0.49 to 0.77 kGy. Following this, one batch was retained in Thailand while the other was shipped to the Canadian Irradiation Center (CIC) for investigation of the same variables during storage. This way, it was hoped to compare the effects of gamma radiation with hot water dip (HWI) or without (I) before and after transportation on the ripening, vitamin C and vitamin A content and sensory qualities of mangoes. The results indicate that the I and HWI treatments delayed the ripening of the mangoes. The irradiated groups appeared to have a slightly higher content of ascorbic acid on the first day after irradiation than their corresponding controls. The sensory evaluation indicates that the panelists mostly favoured the I and HWI irradiated groups for the overall appearance and texture of whole mangoes and pulp and in taste and palatability of the pulp alone. Transportation stress did not appear to have much of an effect on the ascorbic acid and dehydroascorbic acid levels and the sensorial tests. The mangoes stored and studied in Canada appeared to have a lower vitamin A content. 相似文献
92.
93.
Experts were interviewed to identify criteria for evaluation of vocal performance. A scale was then constructed and inter- and intrajudge reliability assessed. Experts listened to 19 different performances, plus 6 presented a second time. Interjudge reliability for one judge was modest, but increased dramatically as the size of the judge panel increased. The most reliable items were overall score and intonation accuracy. Diction was less reliable than other items. Intrajudge reliability was higher for overall score than for any other item. A factor analysis on the test items yielded factors labelled intrinsic quality, execution, and diction. Another factor analysis, using the experts as variables, revealed two underlying evaluative dimensions. It was found that 13 experts were primarily influenced by execution, and that 8 were mainly affected by intrinsic quality. Interjudge and intrajudge reliabilities of these two groups differed. 相似文献
94.
应用马尔科夫状态转移链的作战航空综合体效能评估 总被引:1,自引:0,他引:1
文章阐述了作战航空综合体的相关概念及组成,应用马尔科夫状态转移链建立了作战航空综合体完成典型作战任务时的数学模型,确定了作战效能的评估指标,最后通过具体算例检验了模型的正确性和可行性. 相似文献
95.
The impoverishment of soil nutrients of nine gully head areas in Yuanmou Basin is assessed through an integrated evaluation method established on the basis of Fuzzy mathematics and multivariate mathematical theory. Results show that soil erosion of gully erosion area in Yuanmou basin has resulted in severe impoverishment of soil nutrients. All gully head areas are at high leves of impoverishment except for one at middle. By probing into and analyzing the mechanism of impoverishment of soil nutrients, we find that soil erosion has led to impoverishment of soil nutrients in a way of compacting soil, heightening position of obstacle horizon, and reducing the content of organic matter, as well as the direct loss of nutrient elements. Finally, this paper points out that soil and water conservation arming at the prevention of soil erosion is the most effective way against impoverishment of soil nutrients in Yuanmou basin. 相似文献
96.
In this work we display a numerical comparison, under statistical and computational point of view, between semi-analytical Eulerian and Lagrangian dispersion models to simulate the ground-level concentration values of a passive pollutant released from a low height source. The Eulerian approach is based on the solution of the advection–diffusion equation by the Laplace transform technique. The Lagrangian approach is based on solution of the Langevin equation through the Picard’s Iterative Method. Turbulence inputs are calculated according to a parameterization capable of generating continuous values in all stability conditions and in all heights of the Planetary Boundary Layer (PBL). Numerical simulations and comparisons show a good agreement between predicted and observed concentrations values. The comparison reveals the main advantages and disadvantages between the models. 相似文献
97.
李文斌 《湖北三峡学院学报》2005,27(6):32-35,70
作为生态美学重要的哲学——美学原则的“生态中心主义”,潜藏着颠覆“人本位主义”的危险;而作为对自然进行所谓“生态学的重新审视”而提出的“自然的复魅”,也存在着容易导致另一个极端的不良趋势,并且缺乏可操作性。本文拟对上述观点提出质疑和批评。 相似文献
98.
Liu Xianlong 《数理统计与管理》1998,(6)
本文从理论上讨论了费歇判别与回归模型的等价,指出了利用费歇判别值对企业的综合经济效益进行排序是不合理的,并提出了改进的综合评价方法 相似文献
99.
Polyethers, which are produced by alcoholysis of oxiranes, are often used as solvents in chemical plants. The spectra of the products can be influenced by the choice of the catalyst (acid or base). The results of the base-catalyzed ethanolysis of 1,2-epoxybutane are displayed. The reaction was investigated calorimetrically by varying the molar ratio between ethanol and 1,2-epoxybutane, the starting temperature and the concentration of the catalyst sodium hydroxide. Additionally, the influence of the used alcohol will be shown in one example. To determine the activation parameters, the experiments were evaluated by the nonlinear software package TA-kin v3.3. 相似文献
100.
对城市化途径有关各要素作了综合的叙述,并且指出研究的手段──自人口的聚集至城镇形成发展这一历史的纵剖面及地域、产业结构等横向有关要素作整体系统的分析与比较,并指出应重点研究人口指标分析、产业可比关系、城市化和城市化设施,以及城市体系的研究问题。 相似文献