全文获取类型
收费全文 | 44804篇 |
免费 | 4532篇 |
国内免费 | 2769篇 |
专业分类
化学 | 14381篇 |
晶体学 | 51篇 |
力学 | 3868篇 |
综合类 | 374篇 |
数学 | 21699篇 |
物理学 | 11732篇 |
出版年
2024年 | 89篇 |
2023年 | 502篇 |
2022年 | 771篇 |
2021年 | 822篇 |
2020年 | 1396篇 |
2019年 | 1376篇 |
2018年 | 1283篇 |
2017年 | 1337篇 |
2016年 | 1509篇 |
2015年 | 1367篇 |
2014年 | 1975篇 |
2013年 | 3616篇 |
2012年 | 2378篇 |
2011年 | 2875篇 |
2010年 | 2536篇 |
2009年 | 2983篇 |
2008年 | 2970篇 |
2007年 | 2881篇 |
2006年 | 2539篇 |
2005年 | 2379篇 |
2004年 | 1961篇 |
2003年 | 1797篇 |
2002年 | 1641篇 |
2001年 | 1219篇 |
2000年 | 1131篇 |
1999年 | 1012篇 |
1998年 | 946篇 |
1997年 | 733篇 |
1996年 | 642篇 |
1995年 | 533篇 |
1994年 | 453篇 |
1993年 | 292篇 |
1992年 | 273篇 |
1991年 | 273篇 |
1990年 | 230篇 |
1989年 | 153篇 |
1988年 | 145篇 |
1987年 | 136篇 |
1986年 | 121篇 |
1985年 | 118篇 |
1984年 | 110篇 |
1983年 | 63篇 |
1982年 | 105篇 |
1981年 | 94篇 |
1980年 | 65篇 |
1979年 | 72篇 |
1978年 | 48篇 |
1977年 | 34篇 |
1976年 | 29篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
1.
Dr. Zaifa Shi Dr. Yihuang Jiang Dr. Jingxiong Yu Prof. Shanjun Chen Prof. Jun Chen Prof. Zichao Tang Prof. Lansun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(8):e202103546
At present, the reactivity of cyclic alkanes is estimated by comparison with acyclic hydrocarbons. Due to the difference in the structure of cycloalkanes and acycloalkanes, the thermodynamic data obtained by analogy are not applicable. In this study, a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer (MB-VUV-PI-TOFMS) was applied to study the low-temperature oxidation of cyclopentane (CPT) at a total pressure range from 1–3 atm and low-temperature range between 500 and 800 K. Low-temperature reaction products including cyclic olefins, cyclic ethers, and highly oxygenated intermediates (e. g., ketohydroperoxide KHP, keto-dihydroperoxide KDHP, olefinic hydroperoxides OHP and ketone structure products) were observed. Further investigation of the oxidation of CPT – electronic structure calculations – were carried out at the UCCSD(T)-F12a/aug-cc-pVDZ//B3LYP/6-31+ G(d,p) level to explore the reactivity of O2 molecules adding sequentially to cyclopentyl radicals. Experimental and theoretical observations showed that the dominant product channel in the reaction of CPT radicals with O2 is HO2 elimination yielding cyclopentene. The pathways of second and third O2 addition – the dissociation of hydroperoxide – were further confirmed. The results of this study will develop the low-temperature oxidation mechanism of CPT, which can be used for future research on accurately simulating the combustion process of CPT. 相似文献
2.
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
3.
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.
7.
8.
9.
10.
Florence Drui Emmanuel Franck Philippe Helluy Laurent Navoret 《Comptes Rendus Mecanique》2019,347(3):259-269
The over-relaxation approach is an alternative to the Jin–Xin relaxation method in order to apply the equilibrium source term in a more precise way. This is also a key ingredient of the lattice Boltzmann method for achieving second-order accuracy. In this work, we provide an analysis of the over-relaxation kinetic scheme. We compute its equivalent equation, which is particularly useful for devising stable boundary conditions for the hidden kinetic variables. 相似文献