全文获取类型
收费全文 | 120985篇 |
免费 | 5403篇 |
国内免费 | 3541篇 |
专业分类
化学 | 43788篇 |
晶体学 | 1045篇 |
力学 | 8492篇 |
综合类 | 273篇 |
数学 | 34921篇 |
物理学 | 25309篇 |
综合类 | 16101篇 |
出版年
2024年 | 183篇 |
2023年 | 705篇 |
2022年 | 1108篇 |
2021年 | 1209篇 |
2020年 | 1223篇 |
2019年 | 1126篇 |
2018年 | 11372篇 |
2017年 | 11162篇 |
2016年 | 7508篇 |
2015年 | 2267篇 |
2014年 | 2117篇 |
2013年 | 2605篇 |
2012年 | 6857篇 |
2011年 | 13841篇 |
2010年 | 8072篇 |
2009年 | 8288篇 |
2008年 | 9053篇 |
2007年 | 11243篇 |
2006年 | 2016篇 |
2005年 | 2924篇 |
2004年 | 2873篇 |
2003年 | 3109篇 |
2002年 | 2102篇 |
2001年 | 1206篇 |
2000年 | 1191篇 |
1999年 | 1506篇 |
1998年 | 1439篇 |
1997年 | 1426篇 |
1996年 | 1486篇 |
1995年 | 1149篇 |
1994年 | 1003篇 |
1993年 | 909篇 |
1992年 | 795篇 |
1991年 | 749篇 |
1990年 | 568篇 |
1989年 | 573篇 |
1988年 | 476篇 |
1987年 | 373篇 |
1986年 | 272篇 |
1985年 | 191篇 |
1984年 | 139篇 |
1983年 | 104篇 |
1982年 | 86篇 |
1981年 | 76篇 |
1980年 | 64篇 |
1979年 | 61篇 |
1978年 | 53篇 |
1975年 | 45篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 76 毫秒
71.
新时期,江西提出并实施了要在中部地区快速崛起的发展战略。在这一过程中,江西教育发展面临着极好的机遇,同时,也遭遇到了八个方面的挑战。于是,江西省委省政府提出了江西教育发展的总体要求。江西广大教育行政部门和教育工作者只要不断沿着中央指出的方向,落实省委省政府的部署,埋头苦干、扎实工作,就一定能为建设创新创业江西、绿色生态江西、和谐平安江西,为江西在中部地区的早日崛起提供有力的人才支持、知识基础和文化贡献,就一定能铸造出江西教育事业新的辉煌。 相似文献
72.
The shock structure problem is one of the classical problems of fluid mechanics and at least for non-reacting dilute gases it has been considered essentially solved. Here we present a few recent findings, to show that this is not the case. There are still new physical effects to be discovered provided that the numerical technique is general enough to not rule them out a priori. While the results have been obtained for dense fluids, some of the effects might also be observable for shocks in dilute gases. 相似文献
73.
It is shown that time-dependent temperatures in a transient, conductive system can be approximately modeled by a fractional-order
differential equation, the order of which depends on the Biot number. This approximation is particularly suitable for complex
shapes for which a first-principles approach is too difficult or computationally time-consuming. Analytical solutions of these
equations can be written in terms of the Mittag-Leffler function. The approximation is especially useful if a suitable fractional-order
controller is to be designed for the system. 相似文献
74.
Zhi‐Yong Huang Jin‐Can Shen Zhi‐Xia Zhuang Xiao‐Ru Wang Frank S. C. Lee 《应用有机金属化学》2004,18(6):255-261
Cinnabar, as one of the most widely used mineral drugs in traditional Chinese medicines, has been proven to have prominent curative effects in clinical use for more than 2000 years. But the safety and toxicity of the drug has been under constant debate in clinic usage. Metallothionein (MT) contains about 30% of cysteine in the molecule, and plays an important detoxification role against heavy metals. In this study, it was used as a biomarker to assess mercurial accumulation in rats fed orally with cinnabar. After feeding rats with cinnabar by gastric gavage at different dosages and at different times, the distribution of heavy metals (including mercury, copper and zinc) and MT was investigated among rat tissues, including liver, kidney, heart, brain, testis and blood. Metals and MT determinations were carried out using inductively coupled plasma mass spectrometry (ICP‐MS) and a modified mercury saturation assay technique respectively. The results indicated that mercury was easily accumulated in the tissues of rats exposed to cinnabar, especially in kidney. For example: at a feeding dosage of 5 g kg?1 (bw) for 4 weeks, the mercury concentrations in kidney were 13, 8.7, 21.6 and 26 times those in liver, testis, brain and heart respectively; and at 2.5 g kg?1 (bw) for 2 weeks, the mercury concentrations in kidney were 21, 2.1, 3 and 21 times those in liver, testis, brain and heart respectively. In addition, mercury in kidney and liver of all cinnabar groups was significantly higher than that of the control group (P < 0.01). A high positive correlation observed between MT concentrations and mercury levels in both liver and kidney (R2 = 0.9299, P < 0.02 for liver; R2 = 0.9923, P < 0.0008 for kidney) indicated that MT could be used as a biomarker for mercury in tissues. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
75.
This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of
some granular based composite materials including steelfiber reinforced concrete, sandstone and crystal-polymer composite.
The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation
of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated. The
correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet
transform (WT) coefficients of the transform spectrum. The latter was developed by the authors and showed higher resolution
and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite
materials without any coats of gratings or fringes of optical interferometry, both surface profiles and the deformation fields
of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials.
The project supported by the National Natural Science Foundation of China (10125211 and 10072002), the Scientific Committee
of Yunnan Province for the Program of Steel Fiber Reinforced Concrete, and the Institute of Chemical Materials, CAEP at Mianyang 相似文献
76.
The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
77.
78.
79.
需求特征对供应链中企业资源再利用的影响分析 总被引:1,自引:0,他引:1
为了了解需求因素对供应链中企业资源再利用的影响,选取工业园上下游企业的相互联系为分析背景,建立企业间的供应链模型,研究了需求不确定性σ和需求弹性k对供应链中企业资源再利用的影响.模型仿真结果表明:对存在物料供需关系的2个企业来说,随着主产品需求不确定性σ的不断增大,2个企业的总利润π呈不断下降的趋势,销售损失和库存成本增加,企业资源再利用受到阻碍;随着弹性因子k的不断增大,需求批量与供给批量差距呈现出一种先减小后增大的趋势,总利润π减小,对企业资源再利用起到了负面的影响,阻碍其发展. 相似文献
80.