全文获取类型
收费全文 | 421436篇 |
免费 | 6993篇 |
国内免费 | 3417篇 |
专业分类
化学 | 230485篇 |
晶体学 | 5951篇 |
力学 | 19297篇 |
综合类 | 203篇 |
数学 | 47322篇 |
物理学 | 128588篇 |
出版年
2021年 | 3027篇 |
2020年 | 3603篇 |
2019年 | 3897篇 |
2018年 | 4553篇 |
2017年 | 4572篇 |
2016年 | 7199篇 |
2015年 | 5022篇 |
2014年 | 7259篇 |
2013年 | 18392篇 |
2012年 | 14686篇 |
2011年 | 17851篇 |
2010年 | 12222篇 |
2009年 | 11976篇 |
2008年 | 16302篇 |
2007年 | 16375篇 |
2006年 | 15497篇 |
2005年 | 14225篇 |
2004年 | 12842篇 |
2003年 | 11487篇 |
2002年 | 11441篇 |
2001年 | 12516篇 |
2000年 | 9741篇 |
1999年 | 7502篇 |
1998年 | 6225篇 |
1997年 | 6173篇 |
1996年 | 5906篇 |
1995年 | 5405篇 |
1994年 | 5420篇 |
1993年 | 4993篇 |
1992年 | 5685篇 |
1991年 | 5678篇 |
1990年 | 5344篇 |
1989年 | 5201篇 |
1988年 | 5268篇 |
1987年 | 5105篇 |
1986年 | 4828篇 |
1985年 | 6637篇 |
1984年 | 6869篇 |
1983年 | 5691篇 |
1982年 | 5928篇 |
1981年 | 5672篇 |
1980年 | 5576篇 |
1979年 | 5566篇 |
1978年 | 5917篇 |
1977年 | 5847篇 |
1976年 | 5871篇 |
1975年 | 5524篇 |
1974年 | 5479篇 |
1973年 | 5698篇 |
1972年 | 3839篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
21.
Zhengcheng Wang Shangyan Zhou Wei Liao Qian Zhou Meida Chen Jin Long Prof. Qingmei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(66):e202201987
The designs of efficient and inexpensive Pt-based catalysts for methanol oxidation reaction (MOR) are essential to boost the commercialization of direct methanol fuel cells. Here, the highly catalytic performance PtFe alloys supported on multiwalled carbon nanotubes (MWCNTs) decorating nitrogen-doped carbon (NC) have been successfully prepared via co-engineering of the surface composition and electronic structure. The Pt1Fe3@NC/MWCNTs catalyst with moderate Fe3+ feeding content (0.86 mA/mgPt) exhibits 2.26-fold enhancement in MOR mass activity compared to pristine Pt/C catalyst (0.38 mA/mgPt). Furthermore, the CO oxidation initial potential of Pt1Fe3@NC/MWCNTs catalyst is lower relative to Pt/C catalyst (0.71 V and 0.80 V). Benefited from the optimal surface compositions, the anti-corrosion ability of MWCNT, strong electron interaction between PtFe alloys and MWCNTs and the N-doped carbon (NC) layer, the Pt1Fe3@NC/MWCNTs catalyst presents an improved MOR performance and anti-CO poisoning ability. This study would open up new perspective for designing efficient electrocatalysts for the DMFCs field. 相似文献
22.
Siberian Mathematical Journal - Let $ \{(A_{i},B_{i})\}_{i=1}^{m} $ be a set pair system. Füredi, Gyárfás, and Király called it $ 1 $ -cross intersecting if $... 相似文献
23.
Let p ∈ [1, ∞), q ∈ [1, ∞), α∈ R, and s be a non-negative integer. Inspired by the space JNp introduced by John and Nirenberg(1961) and the space B introduced by Bourgain et al.(2015), we introduce a special John-Nirenberg-Campanato space JNcon(p,q,s) over Rn or a given cube of R;with finite side length via congruent subcubes, which are of some amalgam features. The limit space of such spaces as p →∞ is just the Campanato space which coincides with the space BMO(the space of functions with bounded mean oscillations)when α = 0. Moreover, a vanishing subspace of this new space is introduced, and its equivalent characterization is established as well, which is a counterpart of the known characterization for the classical space VMO(the space of functions with vanishing mean oscillations) over Rn or a given cube of Rn with finite side length.Furthermore, some VMO-H1-BMO-type results for this new space are also obtained, which are based on the aforementioned vanishing subspaces and the Hardy-type space defined via congruent cubes in this article. The geometrical properties of both the Euclidean space via its dyadic system and congruent cubes play a key role in the proofs of all these results. 相似文献
24.
Edward G. Sheetz Zhao Zhang Alyssa Marogil Minwei Che Dr. Maren Pink Dr. Veronica Carta Prof. Dr. Krishnan Raghavachari Prof. Dr. Amar H. Flood 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201584
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3−). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3−, by cyanostar macrocycles that are size-complementary to the inorganic BF4− progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3− anions. 相似文献
25.
26.
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
27.
28.
Kopytov G. F. Malyshko V. V. Goryachko A. I. Sharafan M. V. Churkina A. V. Moiseev A. V. Shashkov D. I. Lyasota O. M. 《Russian Physics Journal》2021,64(2):255-260
Russian Physics Journal - The specific features of the sorption activity of silver nanoparticles (AgNPs) on biodegradable polymers of natural (collagen) and artificial (polyamide 6.6) origin have... 相似文献
29.
30.
本文首先对双层规划的一个特殊例子即道德风险模型中使用的一阶条件方法(FOA)做简要的梳理,然后提出一种更为一般的使FOA有效的原则与方法。新方法主要依赖于代理人对委托人设置的目标的最优反应映射是否存在不动点,这个性质不要求原问题与用一阶条件放松以后的问题之间的约束集等价,从而也不要求代理人的期望效用对行动具有全局凹性。在新方法下,可以用较为简单的方法证明FOA在以下两种情形之一有效,即如果分布函数是概率分布的凸组合或者分布函数来自某些特殊的指数族分布。 相似文献