全文获取类型
收费全文 | 46861篇 |
免费 | 2603篇 |
国内免费 | 3027篇 |
专业分类
化学 | 26117篇 |
晶体学 | 275篇 |
力学 | 4260篇 |
综合类 | 538篇 |
数学 | 8289篇 |
物理学 | 13012篇 |
出版年
2024年 | 77篇 |
2023年 | 476篇 |
2022年 | 1189篇 |
2021年 | 1186篇 |
2020年 | 1158篇 |
2019年 | 1104篇 |
2018年 | 987篇 |
2017年 | 1288篇 |
2016年 | 1697篇 |
2015年 | 1319篇 |
2014年 | 1897篇 |
2013年 | 3122篇 |
2012年 | 2556篇 |
2011年 | 2632篇 |
2010年 | 2240篇 |
2009年 | 2881篇 |
2008年 | 2698篇 |
2007年 | 3227篇 |
2006年 | 2714篇 |
2005年 | 2239篇 |
2004年 | 2193篇 |
2003年 | 1858篇 |
2002年 | 1359篇 |
2001年 | 1163篇 |
2000年 | 1082篇 |
1999年 | 998篇 |
1998年 | 924篇 |
1997年 | 835篇 |
1996年 | 780篇 |
1995年 | 715篇 |
1994年 | 615篇 |
1993年 | 510篇 |
1992年 | 466篇 |
1991年 | 401篇 |
1990年 | 365篇 |
1989年 | 236篇 |
1988年 | 241篇 |
1987年 | 151篇 |
1986年 | 130篇 |
1985年 | 155篇 |
1984年 | 121篇 |
1983年 | 63篇 |
1982年 | 107篇 |
1981年 | 63篇 |
1980年 | 50篇 |
1979年 | 81篇 |
1978年 | 36篇 |
1977年 | 16篇 |
1976年 | 25篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 322 毫秒
31.
The γcmc values of CTAB-SDS decrease from 63.67 mN/m at 10‡C to 36.38 mN/m at 90‡C, slightly lower than those of either CTAB or SDS.
Correspondingly, the CMC of CTAB-SDS decreases almost by half. The increase of surface activity of CTAB-SDS can be attributed
to the relatively weak electrostatic interaction at high temperature, which is supported by the increase of solubility of
CTAB-SDS with rise in temperature. Catalytic effect on oxidation of toluene derivatives with potassium permanganate follows
the order CTAB-SDS > SDS > CTAB. This is not caused by the dissociative effect of CTAB-SDS with low surface activity at low
temperature, as seen from the fact that almost all oxidative products can be retrieved for different toluene derivatives and
surfactants by mimicking the conditions of reaction. In the emulsifications of toluene derivatives at 90‡C, the time that
turbid water layers of surfactant solutions take to become clear is the same as that of the catalytic effect on oxidation
of toluene derivatives. Thus, it can be inferred that surfactants can improve the oxidation yields of toluene derivatives
by increasing the contact between two reacting phases. 相似文献
32.
Sensitivity analysis is a mathematical tool, first developed for optimization methods, which aim is to characterize a system response through the variations of its output parameters following modifications imposed on the input parameters of the system. Such an analysis may quickly become laborious when the thermal model under consideration is complex or the number of input parameters is high. In this paper, we develop a mathematical model to analyse the heat exchanges in four different types of solar air collectors. When building this thermal model we show that for each collector, at quasi-steady state, the energy balance equations of the components of the collector cascade into a single first-order non-linear differential equation that is able to predict the thermal behaviour of the collector. Our heat transfer model clearly demonstrates the existence of an important dimensionless parameter, referred to as the thermal performance factor of the collector, that compares the useful thermal energy which can be extracted from the heater to the overall thermal losses of that collector for a given set of input parameters. A sensitivity analysis of our thermal model has been performed for the most significant input parameters such as the incident solar irradiation, the inlet fluid temperature, the air mass flow rate, the depth of the fluid channel, the number and nature of the transparent covers in order to measure the impact of each of these parameters on our model. An important result which can be drawn from this study is that the heat transfer model developed is robust enough to be used for thermal design studies of most known flat plate solar air heaters, but also of flat plate solar water collectors and linear solar concentrators. 相似文献
33.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
34.
35.
36.
本文给出了C^n中子空间之间最大和最小主角在矩阵逼近,投影算子的扰动分析,群逆以及Oraxin逆的扰动估计,条件数理论,Bott-Duffin系统扰动分析中一些应用。 相似文献
37.
本文研究了胆绿素的表面增强拉曼光谱。结果表明,在溶液酸度不同时,拉曼光谱特征频率的变化表现出胆绿素的质子化。铜离子与胆绿素的相互作用实验结果说明金属铜离子可与胆绿素生成金属配合物。 相似文献
38.
39.
固体力学有限元体系的结构拓扑变化理论 总被引:2,自引:1,他引:1
本文是文[1]的继续.文[1]提出了杆件系统的结构拓扑变化理论和拓扑变化法本文将这一理论和方法推进到连续体有限元体系;且在此基础上揭示出有限元体系的一个新性质,称为基本位移之梯度的正交性定理,从而给出一套设计敏度的显式表达式,可直接用于计算. 相似文献
40.