全文获取类型
收费全文 | 49962篇 |
免费 | 7518篇 |
国内免费 | 4760篇 |
专业分类
化学 | 13937篇 |
晶体学 | 218篇 |
力学 | 5822篇 |
综合类 | 550篇 |
数学 | 26164篇 |
物理学 | 15549篇 |
出版年
2024年 | 130篇 |
2023年 | 537篇 |
2022年 | 883篇 |
2021年 | 1061篇 |
2020年 | 1690篇 |
2019年 | 1631篇 |
2018年 | 1419篇 |
2017年 | 1535篇 |
2016年 | 1976篇 |
2015年 | 1718篇 |
2014年 | 2566篇 |
2013年 | 4507篇 |
2012年 | 2779篇 |
2011年 | 3170篇 |
2010年 | 2919篇 |
2009年 | 3252篇 |
2008年 | 3360篇 |
2007年 | 3441篇 |
2006年 | 2987篇 |
2005年 | 2818篇 |
2004年 | 2335篇 |
2003年 | 2296篇 |
2002年 | 1819篇 |
2001年 | 1523篇 |
2000年 | 1421篇 |
1999年 | 1318篇 |
1998年 | 1134篇 |
1997年 | 1001篇 |
1996年 | 746篇 |
1995年 | 611篇 |
1994年 | 513篇 |
1993年 | 393篇 |
1992年 | 346篇 |
1991年 | 343篇 |
1990年 | 280篇 |
1989年 | 166篇 |
1988年 | 176篇 |
1987年 | 162篇 |
1986年 | 149篇 |
1985年 | 171篇 |
1984年 | 147篇 |
1983年 | 75篇 |
1982年 | 129篇 |
1981年 | 122篇 |
1980年 | 83篇 |
1979年 | 91篇 |
1978年 | 85篇 |
1977年 | 64篇 |
1976年 | 49篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
1.
2.
Dr. Jordan Donat Mr. Patrick Dubourdeaux Dr. Martin Clémancey Dr. Julia Rendon Clara Gervasoni Mr. Morgan Barbier Jessica Barilone Dr. Jacques Pécaut Prof. Dr. Serge Gambarelli Prof. Dr. Pascale Maldivi Prof. Dr. Jean-Marc Latour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202201875
Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two-electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor. 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.
5.
Tomoyuki Nakatsuka 《Mathematische Nachrichten》2021,294(1):98-117
We study the existence of a time‐periodic solution with pointwise decay properties to the Navier–Stokes equation in the whole space. We show that if the time‐periodic external force is sufficiently small in an appropriate sense, then there exists a time‐periodic solution of the Navier–Stokes equation such that and uniformly in as . Our solution decays faster than the time‐periodic Stokes fundamental solution and the faster decay of its spatial derivatives of higher order is also described. 相似文献
6.
《Mendeleev Communications》2022,32(4):507-509
We report on the synthesis of new Ru(bpy)2(phen) catalyst for the oscillatory Belousov–Zhabotinsky chemical reaction and on the preparation of novel Ru(bpy)2(phen)-based self-oscillating gels. The synthesized gels exhibit high-amplitude autonomous mechanical oscillations when the Belousov–Zhabotinsky reaction proceeds inside these gels 相似文献
7.
Dr. Manussada Ratanasak Takumi Murata Taishin Adachi Prof. Jun-ya Hasegawa Prof. Tadashi Ema 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(58):e202202210
BPh3 catalyzes the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO2 and PhSiH3; these reactions proceed at 30–40 °C under solvent-free conditions. In contrast, B(C6F5)3 shows little or no activity. 11B NMR spectra suggested the generation of [HBPh3]−. The detailed mechanism of the BPh3-catalyzed N-methylation of N-methylaniline ( 1 ) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N-methylaniline and CO2) into a zwitterionic carbamate to give three-component species [Ph(Me)(H)N+CO2−⋅⋅⋅BPh3]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3]−, which is used to produce key CO2-derived species, such as silyl formate and bis(silyl)acetal, essential for the N-methylation of 1 . DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3]− species. 相似文献
8.
9.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
10.