全文获取类型
收费全文 | 183800篇 |
免费 | 17195篇 |
国内免费 | 12519篇 |
专业分类
化学 | 57162篇 |
晶体学 | 2926篇 |
力学 | 18464篇 |
综合类 | 2100篇 |
数学 | 60084篇 |
物理学 | 72778篇 |
出版年
2023年 | 1180篇 |
2022年 | 3267篇 |
2021年 | 3250篇 |
2020年 | 3210篇 |
2019年 | 3434篇 |
2018年 | 3275篇 |
2017年 | 3627篇 |
2016年 | 3961篇 |
2015年 | 3425篇 |
2014年 | 5892篇 |
2013年 | 9517篇 |
2012年 | 6421篇 |
2011年 | 7988篇 |
2010年 | 7648篇 |
2009年 | 13250篇 |
2008年 | 14201篇 |
2007年 | 12819篇 |
2006年 | 11328篇 |
2005年 | 8669篇 |
2004年 | 7999篇 |
2003年 | 7735篇 |
2002年 | 10489篇 |
2001年 | 6701篇 |
2000年 | 6209篇 |
1999年 | 5667篇 |
1998年 | 4912篇 |
1997年 | 3864篇 |
1996年 | 3401篇 |
1995年 | 3510篇 |
1994年 | 3341篇 |
1993年 | 2721篇 |
1992年 | 2277篇 |
1991年 | 1648篇 |
1990年 | 1366篇 |
1989年 | 1157篇 |
1988年 | 1097篇 |
1987年 | 798篇 |
1986年 | 566篇 |
1985年 | 1457篇 |
1984年 | 1071篇 |
1983年 | 734篇 |
1982年 | 1065篇 |
1981年 | 1184篇 |
1980年 | 1051篇 |
1979年 | 943篇 |
1978年 | 858篇 |
1977年 | 724篇 |
1976年 | 680篇 |
1974年 | 424篇 |
1973年 | 565篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
1.
2.
Dan Chen Kaixin Du Xiaochen Niu Hongwei Zhang Xue Zhang Yu Tang Jianchun Zhao 《Biomedical chromatography : BMC》2022,36(3):e5288
Amlexanox, an anti-inflammatory and anti-allergic agent, has been widely used clinically for the treatment of canker sores, asthma, and allergic rhinitis. Recently, amlexanox has received considerable attention in curing nonalcoholic fatty liver diseases and hepatitis virus infection. Herein, we first established a sensitive high-performance liquid chromatography-tandem mass spectrum (LC–MS/MS) method for the determination of amlexanox in rat plasma. Propranolol was used as the internal standard (IS). Using a simple protein precipitation method, the amlexanox and IS were separated with Capcell Pak C18 column (2.0 × 50 mm, 5 μm) and eluted with water and acetonitrile each containing 0.1% formic acid using gradient elution condition at a flow rate of 0.4 mL·min−1. Amlexanox and IS were detected by a triple quadrupole mass in multiple reactive monitoring (MRM) under the transitions of m/z 299.2 → 281.2 and m/z 259.9 → 116.1 with positive electrospray ionization, respectively. The calibration curves of amlexanox were established with the range of 50 to 2000 ng·mL−1 (r2 > 0.99). The validation method consisted of selectivity, accuracy, precision, carryover effect, matrix effect, recovery, dilution effect, and stability. The fully validated method was successfully applied to the pharmacokinetic study of amlexanox in Wistar rats. 相似文献
3.
This paper is concerned with the Cauchy problem on the Boltzmann equation without angular cutoff assumption for hard potential in the whole space. When the initial data is a small perturbation of a global Maxwellian, the global existence of solution to this problem is proved in unweighted Sobolev spaces with . But if we want to obtain the optimal temporal decay estimates, we need to add the velocity weight function, in this case the global existence and the optimal temporal decay estimate of the Boltzmann equation are all established. Meanwhile, we further gain a more accurate energy estimate, which can guarantee the validity of the assumption in Chen et al. (0000). 相似文献
4.
《Indagationes Mathematicae》2021,32(1):55-85
We show that the differential structure of the orbit space of a proper action of a Lie group on a smooth manifold is weakly reflexive. This implies that the orbit space is a differentiable space in the sense of Smith, which ensures that the orbit space has an exterior algebra of differential forms, that satisfies Smith’s version of de Rham’s theorem. Because the orbit space is a locally closed subcartesian space, it has vector fields and their flows. 相似文献
5.
M. Amar D. Andreucci R. Gianni C. Timofte 《Journal of Mathematical Analysis and Applications》2021,493(2):124533
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation. 相似文献
6.
7.
科学评价大学生科研创新能力对我国科研水平的提高具有重要意义.采用机器学习模型来预测大学生科研能力可以起到良好的效果,提出一种GAXGBoost模型来实现对大学生的科研能力预测.此模型是以Xgboost算法为基础,然后充分利用遗传算法的全局搜索能力自动搜索Xgboost最优超参数,避免了人为经验调参不准确的缺陷,最后采用精英选择策略以此确保每一轮都是最佳的进化结果.通过分析表明,所采用的GAXGBoost模型在大学生科研能力预测的结果中具有很高的精度,将此模型与Logistic Regression、Random Forest、SVM等模型进行对比,GAXGBoost模型的预测精度最高. 相似文献
8.
9.
Bifurcation analysis of visual angle model with anticipated time and stabilizing driving behavior
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xueyi Guan 《中国物理 B》2022,31(7):70507-070507
In the light of the visual angle model (VAM), an improved car-following model considering driver's visual angle, anticipated time and stabilizing driving behavior is proposed so as to investigate how the driver's behavior factors affect the stability of the traffic flow. Based on the model, linear stability analysis is performed together with bifurcation analysis, whose corresponding stability condition is highly fit to the results of the linear analysis. Furthermore, the time-dependent Ginzburg-Landau (TDGL) equation and the modified Korteweg-de Vries (mKdV) equation are derived by nonlinear analysis, and we obtain the relationship of the two equations through the comparison. Finally, parameter calibration and numerical simulation are conducted to verify the validity of the theoretical analysis, whose results are highly consistent with the theoretical analysis. 相似文献
10.