全文获取类型
收费全文 | 78636篇 |
免费 | 6479篇 |
国内免费 | 4986篇 |
专业分类
化学 | 23342篇 |
晶体学 | 1807篇 |
力学 | 3500篇 |
综合类 | 338篇 |
数学 | 17982篇 |
物理学 | 43132篇 |
出版年
2023年 | 152篇 |
2021年 | 305篇 |
2020年 | 619篇 |
2019年 | 923篇 |
2018年 | 882篇 |
2017年 | 579篇 |
2016年 | 421篇 |
2015年 | 394篇 |
2014年 | 1037篇 |
2013年 | 1607篇 |
2012年 | 1136篇 |
2011年 | 1676篇 |
2010年 | 2277篇 |
2009年 | 6796篇 |
2008年 | 7852篇 |
2007年 | 6323篇 |
2006年 | 5770篇 |
2005年 | 3931篇 |
2004年 | 3751篇 |
2003年 | 3971篇 |
2002年 | 4717篇 |
2001年 | 3678篇 |
2000年 | 3495篇 |
1999年 | 3317篇 |
1998年 | 2729篇 |
1997年 | 1901篇 |
1996年 | 1718篇 |
1995年 | 2193篇 |
1994年 | 2136篇 |
1993年 | 1590篇 |
1992年 | 1098篇 |
1991年 | 827篇 |
1990年 | 677篇 |
1989年 | 602篇 |
1988年 | 562篇 |
1987年 | 401篇 |
1986年 | 190篇 |
1985年 | 943篇 |
1984年 | 618篇 |
1983年 | 487篇 |
1982年 | 639篇 |
1981年 | 792篇 |
1980年 | 719篇 |
1979年 | 558篇 |
1978年 | 581篇 |
1977年 | 538篇 |
1976年 | 540篇 |
1975年 | 317篇 |
1974年 | 354篇 |
1973年 | 462篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
51.
52.
ABSTRACTNumerical approximations of the solution of a boundary value problem when an exact solution is not available can be constructed by means of a variety of methods. In this paper, we present a technique that is based on the integral representation of the solution of an elliptic problem and the properties of the associated layer potentials. The procedure is illustrated in application to the mathematical model of bending of plates with transverse shear deformation in a finite domain, in the presence of Dirichlet, Neumann, and Robin conditions prescribed on the boundary. 相似文献
53.
An Ensemble Kalman Filter Approach Based on Level Set Parameterization for Acoustic Source Identification Using Multiple Frequency Information 下载免费PDF全文
In this paper, a reconstruction problem of the spatial dependent acoustic source from multiple frequency data is discussed. Suppose that the source function is supported on a bounded domain and the piecewise constant intensities of the source are known on the support. We characterize unknown domain by the level set technique. And the level set function can be modeled by a Hamilton-Jacobi system. We use the ensemble Kalman filter approach to analyze the system state. This method can avoid to deal with the nonlinearity directly and reduce the computation complexity. In addition, the algorithm can achieve the stable state quickly with the Hamilton-Jacobi system. From some numerical examples, we show these advantages and verify the feasibility and effectiveness. 相似文献
54.
55.
56.
57.
《Arabian Journal of Chemistry》2022,15(11):104297
This study aimed to investigate the chemical composition of Tribulus terrestris L. fruit (TT) extract named TT15 and its protective effect against ischemic stroke (IS) as well as corresponding mechanisms. The chemical composition of TT15 was analyzed by liquid chromatography-mass spectrometry (LC-MS), and the compound identification was conducted via searching the in-house database. The LC-MS-based multi-omics approach was applied to search the differential metabolites and differential proteins in rat brain tissue and to explore the biomarker and molecular mechanism of TT15 against middle cerebral artery occlusion (MCAO). A total of 20 compounds were identified from TT15, mainly including alkaloids, flavonoids, phenols, quinones, and esters. These 20 compounds significantly affected the metabolism of 44 metabolites and the expression of 51 proteins. Joint pathway analysis showed that these metabolites and proteins were mainly involved in the response to elevated platelet cytosolic Ca2+ and platelet activation, which inferred that TT15 may exert a protective effect against cerebral ischemic injury via regulating platelet function. This study provides useful information for further exploration of the mechanisms of TT extract against IS. 相似文献
58.
59.
60.