全文获取类型
收费全文 | 54486篇 |
免费 | 3797篇 |
国内免费 | 4169篇 |
专业分类
化学 | 20363篇 |
晶体学 | 149篇 |
力学 | 2227篇 |
综合类 | 1095篇 |
数学 | 26831篇 |
物理学 | 11787篇 |
出版年
2023年 | 425篇 |
2022年 | 540篇 |
2021年 | 1647篇 |
2020年 | 1049篇 |
2019年 | 1256篇 |
2018年 | 1007篇 |
2017年 | 1125篇 |
2016年 | 1297篇 |
2015年 | 1233篇 |
2014年 | 1991篇 |
2013年 | 3512篇 |
2012年 | 2029篇 |
2011年 | 2730篇 |
2010年 | 2503篇 |
2009年 | 3278篇 |
2008年 | 3514篇 |
2007年 | 3664篇 |
2006年 | 2873篇 |
2005年 | 2189篇 |
2004年 | 1881篇 |
2003年 | 2028篇 |
2002年 | 4419篇 |
2001年 | 1890篇 |
2000年 | 1534篇 |
1999年 | 1337篇 |
1998年 | 1307篇 |
1997年 | 1034篇 |
1996年 | 902篇 |
1995年 | 622篇 |
1994年 | 651篇 |
1993年 | 595篇 |
1992年 | 550篇 |
1991年 | 381篇 |
1990年 | 319篇 |
1989年 | 251篇 |
1988年 | 282篇 |
1987年 | 236篇 |
1986年 | 236篇 |
1985年 | 375篇 |
1984年 | 304篇 |
1983年 | 168篇 |
1982年 | 353篇 |
1981年 | 510篇 |
1980年 | 472篇 |
1979年 | 496篇 |
1978年 | 399篇 |
1977年 | 301篇 |
1976年 | 253篇 |
1974年 | 84篇 |
1973年 | 160篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
在完备的度量空间中,讨论了一类新型的非线性压缩映射ρ(Tx,Ty)≤a(ρ(x,y))ρ(x,Tx)+b(ρ(x,y))ρ(y,Ty)+c(ρ(x,y))ρ(x,y)通过构造迭代序列,指出该映射的不动点的存在性和唯一性,并给出相应的误差估计式,拓展和改进了有关文献的范围. 相似文献
2.
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
3.
Clemens G. Raab Georg Regensburger Jamal Hossein Poor 《Journal of Pure and Applied Algebra》2021,225(5):106564
A formal computation proving a new operator identity from known ones is, in principle, restricted by domains and codomains of linear operators involved, since not any two operators can be added or composed. Algebraically, identities can be modelled by noncommutative polynomials and such a formal computation proves that the polynomial corresponding to the new identity lies in the ideal generated by the polynomials corresponding to the known identities. In order to prove an operator identity, however, just proving membership of the polynomial in the ideal is not enough, since the ring of noncommutative polynomials ignores domains and codomains. We show that it suffices to additionally verify compatibility of this polynomial and of the generators of the ideal with the labelled quiver that encodes which polynomials can be realized as linear operators. Then, for every consistent representation of such a quiver in a linear category, there exists a computation in the category that proves the corresponding instance of the identity. Moreover, by assigning the same label to several edges of the quiver, the algebraic framework developed allows to model different versions of an operator by the same indeterminate in the noncommutative polynomials. 相似文献
4.
5.
We propose a conjecture on the relative twist formula of l-adic sheaves, which can be viewed as a generalization of Kato—Saito's conjecture. We verify this conjecture under some transversal assumptions. We also define a relative cohomological characteristic class and prove that its formation is compatible with proper push-forward. A conjectural relation is also given between the relative twist formula and the relative cohomological characteristic class. 相似文献
7.
8.
In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance. 相似文献
9.
10.