全文获取类型
收费全文 | 115262篇 |
免费 | 22675篇 |
国内免费 | 10073篇 |
专业分类
化学 | 94543篇 |
晶体学 | 1076篇 |
力学 | 6049篇 |
综合类 | 458篇 |
数学 | 11738篇 |
物理学 | 34146篇 |
出版年
2024年 | 192篇 |
2023年 | 1700篇 |
2022年 | 2477篇 |
2021年 | 3038篇 |
2020年 | 4386篇 |
2019年 | 5340篇 |
2018年 | 3626篇 |
2017年 | 3162篇 |
2016年 | 6866篇 |
2015年 | 6864篇 |
2014年 | 7581篇 |
2013年 | 9620篇 |
2012年 | 10084篇 |
2011年 | 9561篇 |
2010年 | 7708篇 |
2009年 | 7504篇 |
2008年 | 7472篇 |
2007年 | 6372篇 |
2006年 | 5741篇 |
2005年 | 5184篇 |
2004年 | 4226篇 |
2003年 | 3534篇 |
2002年 | 4133篇 |
2001年 | 3181篇 |
2000年 | 2913篇 |
1999年 | 2238篇 |
1998年 | 1688篇 |
1997年 | 1584篇 |
1996年 | 1551篇 |
1995年 | 1294篇 |
1994年 | 1181篇 |
1993年 | 921篇 |
1992年 | 830篇 |
1991年 | 726篇 |
1990年 | 654篇 |
1989年 | 479篇 |
1988年 | 420篇 |
1987年 | 366篇 |
1986年 | 336篇 |
1985年 | 284篇 |
1984年 | 196篇 |
1983年 | 134篇 |
1982年 | 113篇 |
1981年 | 98篇 |
1980年 | 90篇 |
1979年 | 50篇 |
1978年 | 44篇 |
1977年 | 51篇 |
1976年 | 37篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
211.
212.
213.
214.
凯尔文电桥是国内大学基础物理实验所开设的实验内容之一,且多为自组式.关于自组凯尔文电桥的测量精度与桥路参数精度之间的关系,有些实验教材已有推导,但尚未涉及与两低阻相邻电压接头间跨桥电阻的定量关系,不注意这一点,会给测量结果带来一定的误差.本文就实际中常用的等双臂凯尔文电桥从理论上定量地推出了这一关系,进而给出了跨桥电阻可忽略时的适当阻值. 相似文献
215.
Liyue Liu Yingge Yang Yafei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2004,24(3-4):343-348
The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution. 相似文献
216.
By using the quasi-Lyapunov function, some sufficient conditions of global exponential stability for impulsive systems are established, which is the basis for the following discussion. Then, by employing Riccati inequality and Hamilton-Jacobi inequality approach, some sufficient conditions of robust exponential stability for uncertain linear/nonlinear impulsive systems are derived, respectively. Finally, some examples are given to illustrate the applications of the theory. 相似文献
217.
差分吸收光谱法测量大气痕量气体浓度误差分析及改善方法 总被引:8,自引:2,他引:6
差分吸收光谱技术(DOAS)中采用线性最小二乘拟合方法,用痕量气体标准差分吸收截面对测量得到的差分吸收光谱进行拟合,得出大气中痕量气体的浓度.计算结果的准确性不仅取决于光谱的测量精度,而且受标准差分吸收截面以及仪器函数和温度等诸多因素的影响.详细地分析了计算误差的产生原因,提出了用高浓度样品池得到标准吸收截面的方法,针对光谱固有结构,以及温度对标准吸收截面的影响,改进了浓度反演算法.大量的实验表明,综合运用上述方法,即便对低浓度的样气,相对测量误差也能降低到10%以下. 相似文献
218.
219.
Yang Mujie Zhao Jian Li Aibing Shen Zhiquan Zhang Mingjian Lin Senhao 《Journal of polymer science. Part A, Polymer chemistry》1989,27(11):3829-3835
This paper reports that 60Co γ-ray irradiation can convert cis-polyphenylacetylene (cis-PPA) films prepared with rare-earth coordination catalysts to highly photosensitive materials. The dependence of the photosensitivity on irradiation dose, preparation methods, and microstructure of the PPA films has been investigated by means of a potential discharge technique. The photosensitivity was enhanced with increasing irradiation dose. The critical dose to produce a light response was 5 × 103 Gy. The maximum surface potential discharge rate was 618 V/s, and the dark decay was approximately 2 V/s for cis-PPA films irradiated with 60Co γ-ray (dose: 2 × 105 Gy). The cis-transoidal-PPA and an electrophotographic photoreceptor device incorporating cis-PPA showed a higher irradiation effect. The structure and properties of 60Co γ-ray irradiated rare-earth PPA films are similar to the unirradiated films. 相似文献
220.
X Y Liu C J Li 《Science in China. Series B, Chemistry, life sciences & earth sciences》1989,32(10):1215-1223
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP. 相似文献