全文获取类型
收费全文 | 70714篇 |
免费 | 14217篇 |
国内免费 | 6604篇 |
专业分类
化学 | 64742篇 |
晶体学 | 762篇 |
力学 | 2926篇 |
综合类 | 406篇 |
数学 | 5738篇 |
物理学 | 16961篇 |
出版年
2024年 | 141篇 |
2023年 | 769篇 |
2022年 | 1408篇 |
2021年 | 1549篇 |
2020年 | 2656篇 |
2019年 | 3878篇 |
2018年 | 2231篇 |
2017年 | 1864篇 |
2016年 | 4916篇 |
2015年 | 5165篇 |
2014年 | 5397篇 |
2013年 | 6501篇 |
2012年 | 6093篇 |
2011年 | 5305篇 |
2010年 | 4996篇 |
2009年 | 4908篇 |
2008年 | 4687篇 |
2007年 | 3817篇 |
2006年 | 3454篇 |
2005年 | 3266篇 |
2004年 | 2729篇 |
2003年 | 2388篇 |
2002年 | 3205篇 |
2001年 | 2423篇 |
2000年 | 2090篇 |
1999年 | 1184篇 |
1998年 | 628篇 |
1997年 | 556篇 |
1996年 | 545篇 |
1995年 | 457篇 |
1994年 | 404篇 |
1993年 | 329篇 |
1992年 | 299篇 |
1991年 | 261篇 |
1990年 | 212篇 |
1989年 | 161篇 |
1988年 | 164篇 |
1987年 | 106篇 |
1986年 | 94篇 |
1985年 | 78篇 |
1984年 | 54篇 |
1983年 | 51篇 |
1982年 | 21篇 |
1981年 | 28篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1975年 | 6篇 |
1965年 | 4篇 |
1957年 | 8篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
Jensen and Toft 8 conjectured that every 2‐edge‐connected graph without a K5‐minor has a nowhere zero 4‐flow. Walton and Welsh 19 proved that if a coloopless regular matroid M does not have a minor in {M(K3,3), M*(K5)}, then M admits a nowhere zero 4‐flow. In this note, we prove that if a coloopless regular matroid M does not have a minor in {M(K5), M*(K5)}, then M admits a nowhere zero 4‐flow. Our result implies the Jensen and Toft conjecture. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
64.
Zhao Zheng Zhang Jian-hua Jiang Ya-ling 《International Journal of Theoretical Physics》1997,36(6):1359-1368
The Hawking effect of a nonuniformly rectilinearly accelerating Kinnersley black hole is studied. Its horizons are rotationally
symmetric. Its Hawking temperature depends not only on the time, but also on the polar angle. When a Kinnersley black hole
touches its Rindler horizon, the Hawking temperature at the contact point is reduced to zero. But at the opposite pole of
the black hole, the Hawking temperature increases rapidly. A jet appears as a tail of the accelerating black hole. 相似文献
65.
We present a variational treatment for the E × e pseudo Jahn-Teller system. Through canonical transformation the electron and phonon states are decoupled. An analytical form is obtained for the ground state energy by scaling transformation. Including both the dynamical displacement of phonon modes and the softening of phonon frequency, this approach yields fairly accurate results for the ground state energy. The energy splitting and Ham's reduction factor are calculated, which also generates fairly good results compared with other perturbation results. We argue that our variational wave function is valid for the weak and intermediate coupling range. 相似文献
66.
67.
To incorporate an acceptor type polythiophene segment onto a supramolecular block copolymer for potential light harvesting applications, effective synthetic routes for the end‐functionalized and acceptor‐substituted polythiophenes are critical. The Ullmann coupling reaction can be utilized to obtain electron‐deficient polythiophenes and to attach terminal thiophene units that carry functional groups. In this article, the reactions involving a 2,5‐dibromothiophene monomer containing an electron‐withdrawing fluorinated ester and 5‐bromo‐2‐thiophenecarboxaldehyde (the end‐capper) were studied in detail. It was found that the Ullmann coupling reaction of the dibromide is very fast (completed in a few minutes) and the terminal bromine group does not survive long under the reaction condition. These findings lead to the development of an effective procedure for aldehyde end‐capping of electron‐deficient polythiophenes. Polymers with molecular weights around 4000 Da are routinely obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 41–47, 2007 相似文献
68.
Sang Kyu Lee Min Ju Cho Jung‐Il Jin Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2007,45(3):531-542
New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene‐based chromophore. The 2‐(3‐cyano‐4‐(2‐{4‐[hexyl‐(6‐hydroxy‐hexyl)‐amino]‐phenyl}‐vinyl)‐5‐oxo‐1‐{4‐[4‐(3‐oxo‐3‐phenyl‐propenyl)‐ phenoxy]‐butyl}‐1,5‐dihydro‐pyrrol‐2‐ylidene)‐malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (λ = 330–360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531–542, 2007 相似文献
69.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
70.
J‐F. Masson Slaana Bundalo‐Perc Ana Delgado 《Journal of Polymer Science.Polymer Physics》2005,43(3):276-279
Differential scanning calorimetry (DSC) does not allow for easy determination of the glass‐transition temperature (Tg) of the polystyrene (PS) block in styrene–butadiene–styrene (SBS) block copolymers. Modulated DSC (MDSC), which deconvolutes the standard DSC signal into reversing and nonreversing signals, was used to determine the (Tg) of both the polybutadiene (PB) and PS blocks in SBS. The Tg of the PB block was sharp, at ?92 °C, but that for the PS blocks was extremely broad, from ?60 to 125 °C with a maximum at 68 °C because of blending with PB. PS blocks were found only to exist in a mixed PS–PB phase. This concurred with the results from dynamic mechanical analysis. Annealing did not allow for a segregation of the PS blocks into a pure phase, but allowed for the segregation of the mixed phase into two mixed phases, one that was PB‐rich and the other that was PS‐rich. It is concluded that three phases coexist in SBS: PB, PB‐rich, and PS‐rich phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 276–279, 2005 相似文献