全文获取类型
收费全文 | 61717篇 |
免费 | 14765篇 |
国内免费 | 6645篇 |
专业分类
化学 | 60303篇 |
晶体学 | 742篇 |
力学 | 2096篇 |
综合类 | 400篇 |
数学 | 5566篇 |
物理学 | 14020篇 |
出版年
2024年 | 33篇 |
2023年 | 609篇 |
2022年 | 837篇 |
2021年 | 1238篇 |
2020年 | 2494篇 |
2019年 | 3792篇 |
2018年 | 2137篇 |
2017年 | 1864篇 |
2016年 | 4785篇 |
2015年 | 4992篇 |
2014年 | 5275篇 |
2013年 | 6366篇 |
2012年 | 5850篇 |
2011年 | 5150篇 |
2010年 | 5017篇 |
2009年 | 4917篇 |
2008年 | 4525篇 |
2007年 | 3782篇 |
2006年 | 3361篇 |
2005年 | 3138篇 |
2004年 | 2603篇 |
2003年 | 2029篇 |
2002年 | 1706篇 |
2001年 | 1491篇 |
2000年 | 1142篇 |
1999年 | 664篇 |
1998年 | 511篇 |
1997年 | 409篇 |
1996年 | 346篇 |
1995年 | 329篇 |
1994年 | 313篇 |
1993年 | 226篇 |
1992年 | 221篇 |
1991年 | 189篇 |
1990年 | 183篇 |
1989年 | 126篇 |
1988年 | 98篇 |
1987年 | 82篇 |
1986年 | 90篇 |
1985年 | 65篇 |
1984年 | 30篇 |
1983年 | 30篇 |
1982年 | 22篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1971年 | 5篇 |
1959年 | 3篇 |
1957年 | 5篇 |
1936年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 223 毫秒
1.
2.
Science China Mathematics - This paper studies exact synchronization and asymptotic synchronization problems for a controlled linear system of ordinary differential equations. In this paper, we... 相似文献
3.
Hu Duo-Duo Gao Qian Dai Jing-Cheng Cui Ru Li Yuan-Bo Li Yuan-Ming Zhou Xiao-Guo Bian Kang-Jie Wu Bing-Bing Zhang Kai-Fan Wang Xi-Sheng Li Yan 《中国科学:化学(英文版)》2022,65(4):753-761
Science China Chemistry - A light-induced, nickel-catalyzed three-component arylsulfonation of 1,3-enynes in the absence of photocatalyst is reported. This methodology exhibited mild conditions,... 相似文献
5.
Zhi Sun Mengfan Zhao Lihua Zuo Shengnan Zhou Feng Fan Qingquan Jia Lianping Xue Hanbing Li Jian Kang Xiaojian Zhang 《Journal of separation science》2022,45(2):518-528
Juglandis Mandshuricae Cortex is the bark of Juglans mandshurica Maxim., which has been used as a folk medicine plant in China and India. In this study, an ultra-high performance liquid chromatography–quadrupole/orbitrap high-resolution mass spectrometry method was developed to clarify and quantify the chemical profiling of Juglandis Mandshuricae Cortex rapidly. A total of 113 compounds were characterized. Among them, seven flavonoids were simultaneously quantified in 15 min, including myricetin, myricetrin, taxifolin, kaempferol, quercetin, quercitrin, and naringenin. The method was validated for accuracy, precision, and the limits of detection and quantification. All calibration curves showed a good linear relationship (r > 0.9990) within test ranges. The intra- and inter-day relative standard deviations were less than 2.16%. Accuracy validation showed that the recovery was between 95.6 and 101.3% with relative standard deviation values below 2.85%. The validated method was successfully applied to determine the contents of seven flavones in Juglandis Mandshuricae Cortex from seven sources and the contents of these places were calculated respectively. This method provides a theoretical basis for further developing the medicinal value of Juglandis Mandshuricae Cortex. 相似文献
6.
Given a graph sequence denote by T3(Gn) the number of monochromatic triangles in a uniformly random coloring of the vertices of Gn with colors. In this paper we prove a central limit theorem (CLT) for T3(Gn) with explicit error rates, using a quantitative version of the martingale CLT. We then relate this error term to the well-known fourth-moment phenomenon, which, interestingly, holds only when the number of colors satisfies . We also show that the convergence of the fourth moment is necessary to obtain a Gaussian limit for any , which, together with the above result, implies that the fourth-moment condition characterizes the limiting normal distribution of T3(Gn), whenever . Finally, to illustrate the promise of our approach, we include an alternative proof of the CLT for the number of monochromatic edges, which provides quantitative rates for the results obtained in [7]. 相似文献
7.
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0. 相似文献
8.
Journal of Fluorescence - Carbon nanodots (CDs) have exhibited excellent sensing capability for various metal ions. However, it is difficult to determine the selectivity of CDs to metal ions. In... 相似文献
9.
Applied Mathematics and Mechanics - A consequence of nonlinearities is a multi-harmonic response via a mono-harmonic excitation. A similar phenomenon also exists in random vibration. The power... 相似文献
10.
低维硅锗材料是制备纳米电子器件的重要候选材料,是研发高效率、低能耗和超高速新一代纳米电子器件的基础材料之一,有着潜在的应用价值。采用密度泛函紧束缚方法分别对厚度相同、宽度在0.272 nm~0.554 nm之间的硅纳米线和宽度在0.283 nm~0.567 nm之间的锗纳米线的原子排布和电荷分布进行了计算研究。硅、锗纳米线宽度的改变使原子排布,纳米线的原子间键长和键角发生明显改变。纳米线表层结构的改变对各层内的电荷分布产生重要影响。纳米线中各原子的电荷转移量与该原子在表层内的位置相关。纳米线的尺寸和表层内原子排列结构对体系的稳定性产生重要影响。 相似文献