全文获取类型
收费全文 | 4087篇 |
免费 | 187篇 |
国内免费 | 24篇 |
专业分类
化学 | 2602篇 |
晶体学 | 63篇 |
力学 | 105篇 |
综合类 | 5篇 |
数学 | 717篇 |
物理学 | 806篇 |
出版年
2023年 | 21篇 |
2022年 | 24篇 |
2021年 | 94篇 |
2020年 | 65篇 |
2019年 | 83篇 |
2018年 | 94篇 |
2017年 | 74篇 |
2016年 | 180篇 |
2015年 | 144篇 |
2014年 | 200篇 |
2013年 | 356篇 |
2012年 | 243篇 |
2011年 | 254篇 |
2010年 | 145篇 |
2009年 | 181篇 |
2008年 | 211篇 |
2007年 | 190篇 |
2006年 | 167篇 |
2005年 | 116篇 |
2004年 | 121篇 |
2003年 | 117篇 |
2002年 | 82篇 |
2001年 | 64篇 |
2000年 | 54篇 |
1999年 | 48篇 |
1998年 | 41篇 |
1997年 | 37篇 |
1996年 | 45篇 |
1995年 | 55篇 |
1994年 | 42篇 |
1993年 | 24篇 |
1992年 | 38篇 |
1991年 | 36篇 |
1990年 | 37篇 |
1989年 | 40篇 |
1988年 | 27篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 48篇 |
1984年 | 53篇 |
1983年 | 26篇 |
1982年 | 44篇 |
1981年 | 29篇 |
1980年 | 40篇 |
1979年 | 37篇 |
1978年 | 27篇 |
1977年 | 33篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1923年 | 14篇 |
排序方式: 共有4298条查询结果,搜索用时 703 毫秒
1.
Bucataru Ioan Constantinescu Oana Creţu Georgeta 《Annals of Global Analysis and Geometry》2022,62(4):815-827
Annals of Global Analysis and Geometry - We prove that in a Finsler manifold with vanishing $$\chi $$ -curvature (in particular with constant flag curvature) some non-Riemannian geometric... 相似文献
2.
3.
Mariusz Marć Marek Tobiszewski Bożena Zabiegała Miguel de la Guardia Jacek Namieśnik 《Analytica chimica acta》2015
This review summarizes the different tools and concepts that are commonly applied in air quality monitoring. The monitoring of atmosphere is extremely important as the air quality is an important problem for large communities. Main requirements for analytical devices used for monitoring include a long period of autonomic operation and portability. These instruments, however, are often characterized by poor analytical performance. Monitoring networks are the most common tools used for monitoring, so large-scale monitoring programmes are summarized here. Biomonitoring, as a cheap and convenient alternative to traditional sample collection, is becoming more and more popular, although its main drawback is the lack of standard procedures. Telemonitoring is another approach to air monitoring, which offers some interesting opportunities, such as ease of coverage of large or remote areas, constituting a complementary approach to traditional strategies; however, it requires huge costs. 相似文献
4.
Prof. Piotr Bałczewski Dr. Emilia Kowalska Dr. Ewa Różycka-Sokołowska Dr. Joanna Skalik Dr. Krzysztof Owsianik Dr. Marek Koprowski Dr. Bernard Marciniak Dr. Dariusz Guziejewski Prof. Witold Ciesielski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14148-14161
The highly substituted mono-aryl/alkylthio-(hetero)acenes prepared in this study have been found to be thermally more stable (Tdecomp.=331–354 °C) than the known di-aryl/alkylthio-substituted acenes by an average of 25 °C. They are also much more photostable at 254 and 365 nm (in both argon and air) than the parent anthracene and other reported anthracenes. The most photostable aryl/alkylthio-anthracenes at 254 nm were found to be 60–70 (in air) and 130 (in argon) times more stable in solution than the unsubstituted anthracene, and much more stable than known EDG/EWG-substituted anthracenes (EDG=electron-donating group, EWG=electron-withdrawing group) with an extended aromatic core. Furthermore, the acenes showed significantly higher photostability at 365 nm in both air and argon. The anthracenes were obtained by the novel thio-Friedel–Crafts/Bradsher cyclization reaction of hitherto unknown [o-(1,3-dithian-2-yl)aryl](aryl)methyl thioethers. The developed approach provides a general access to mono-aryl/alkylthio-substituted (hetero)acene frameworks containing at least three fused (hetero)aromatic rings. The characteristic feature of this approach, which leads to highly substituted acenes, is that the substituents, unlike in other methods, may be introduced at an early stage of the synthesis. DFT and TD-DFT calculations confirmed the stabilizing role of the aryl/alkylthio substituent in the mono-aryl/alkylthio-substituted anthracenes, which are the most stable anthracenes prepared to date. Their high photostability is mainly due to the quenching of singlet oxygen by the acene and the quenching of the acene S1 state by molecular oxygen. 相似文献
5.
M. A. Augustyniak-Jabłokow K. Łukaszewicz A. Pietraszko V. E. Petrashen Yu. V. Yablokov 《Physics of the Solid State》2002,44(8):1480-1483
The EPR spectra evolution of Cs2Zn1?x Cux(ZrF6)2 · 6H2O (x=0.01, 0.6, 0.8, and 1.0) in the temperature range 4.2–330 K and the x-ray structure analysis of the compound with x=1.0 in the range 150–327 K show that the Jahn-Teller (JT) complex Cu(H2O)6 coordination sphere undergoes a plastic deformation. The observed effect is due to the combined influence of small lattice strains existing in the paraphase and a new one appearing as a result of a ferroelastic phase transition and increasing with decreasing temperature below T c . It is proved that both cooperative interactions between JT complexes and ferroelastic strain stabilize a certain JT configuration. The problem of instability of a JT configuration compressed at T ~ 265 K is discussed. 相似文献
6.
Jacek Doskocz Jadwiga Sołoducho Joanna Cabaj Mieczysław Łapkowski Sylwia Golba Krystyna Palewska 《Electroanalysis》2007,19(13):1394-1401
A convenient and higher yielding synthetic route to N‐alkyl‐bis(thiophene)phenothiazine derivatives is reported and their aggregation, electrochemical properties and polymerization are characterized. The key step in the synthesis of this group of compounds has been the Stille type coupling reaction between the N‐alkyldibromophenothiazine and tin derivatives of thiophene as the best way for preparation of conjugated N‐alkylphenothiazine derivatives. For this group of compounds we also present an electrochemical polymerization effect and widely adopted approach to prepare structurally ordered thin, electroconducting films by Langmuir–Blodgett technique. 相似文献
7.
Oleg Palumbíny 《Czechoslovak Mathematical Journal》2003,53(2):467-477
The paper deals with oscillation criteria of fourth order linear differential equations with quasi-derivatives. 相似文献
8.
J. Łukasik G. Auger M. L. Begemann-Blaich N. Bellaize R. Bittiger F. Bocage B. Borderie R. Bougault B. Bouriquet J. L. Charvet A. Chbihi R. Dayras D. Durand J. D. Frankland E. Galichet D. Gourio D. Guinet S. Hudan P. Lautesse F. Lavaud A. Le Fèvre R. Legrain O. Lopez U. Lynen W. F. J. Müller L. Nalpas H. Orth E. Plagnol E. Rosato A. Saija C. Schwarz C. Sfienti B. Tamain W. Trautmann A. Trzciński K. Turzó E. Vient M. Vigilante C. Volant B. Zwiegliński 《Acta Physica Hungarica A》2006,25(2-4):229-239
Directed and elliptic flow for the 197Au+197Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4π multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the σ NN and demonstrate the importance of angular momentum conservation in transport codes at low energies. 相似文献
9.
We study the asymptotic distribution of the fill‐up level in a binary trie built over n independent strings generated by a biased memoryless source. The fill‐up level is the number of full levels in a tree. A level is full if it contains the maximum allowable number of nodes (e.g., in a binary tree level k can have up to 2k nodes). The fill‐up level finds many interesting applications, e.g., in the internet IP lookup problem and in the analysis of level compressed tries (LC tries). In this paper, we present a complete asymptotic characterization of the fill‐up distribution. In particular, we prove that this distribution concentrates on one or two points around the most probably value k = ?log1/qn ? log log log n + 1 + log log(p/q)?, where p > q = 1 ? p is the probability of generating the more likely symbol (while q = 1 ? p is the probability of the less likely symbol). We derive our results by analytic methods such as generating functions, Mellin transform, the saddle point method, and analytic depoissonization. We also present some numerical verification of our results. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004 相似文献
10.
We consider noncommutative line bundles associated with the Hopf fibrations of SUq(2) over all Podle? spheres and with a locally trivial Hopf fibration of S3pq. These bundles are given as finitely generated projective modules associated via 1-dimensional representations of U(1) with Galois-type extensions encoding the principal fibrations of SUq(2) and S3pq. We show that the Chern numbers of these modules coincide with the winding numbers of representations defining them. To cite this article: P.M. Hajac et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003). 相似文献