全文获取类型
收费全文 | 5872篇 |
免费 | 132篇 |
国内免费 | 14篇 |
专业分类
化学 | 4067篇 |
晶体学 | 65篇 |
力学 | 117篇 |
数学 | 537篇 |
物理学 | 1232篇 |
出版年
2021年 | 41篇 |
2020年 | 45篇 |
2019年 | 63篇 |
2016年 | 91篇 |
2015年 | 85篇 |
2014年 | 116篇 |
2013年 | 223篇 |
2012年 | 133篇 |
2011年 | 199篇 |
2010年 | 144篇 |
2009年 | 128篇 |
2008年 | 224篇 |
2007年 | 183篇 |
2006年 | 203篇 |
2005年 | 183篇 |
2004年 | 159篇 |
2003年 | 158篇 |
2002年 | 149篇 |
2001年 | 119篇 |
2000年 | 107篇 |
1999年 | 102篇 |
1998年 | 80篇 |
1997年 | 93篇 |
1996年 | 106篇 |
1995年 | 111篇 |
1994年 | 118篇 |
1993年 | 135篇 |
1992年 | 113篇 |
1991年 | 78篇 |
1990年 | 67篇 |
1989年 | 76篇 |
1988年 | 59篇 |
1987年 | 90篇 |
1986年 | 80篇 |
1985年 | 77篇 |
1984年 | 77篇 |
1983年 | 73篇 |
1982年 | 70篇 |
1981年 | 76篇 |
1980年 | 86篇 |
1979年 | 69篇 |
1978年 | 89篇 |
1977年 | 55篇 |
1976年 | 77篇 |
1975年 | 79篇 |
1974年 | 77篇 |
1973年 | 83篇 |
1972年 | 49篇 |
1971年 | 48篇 |
1967年 | 48篇 |
排序方式: 共有6018条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
A. Breakstone G. Claesson H. B. Crawley G. M. Dallavalle K. Doroba D. Drijard F. Fabbri A. Firestone M. A. Faessler H. G. Fischer S. Y. Fung S. Garpman W. Geist G. Giacomelli R. Gokieli M. Gorbics C. R. Gruhn P. Hanke M. Heiden W. Herr T. J. Ketel E. E. Kluge J. W. Lamsa T. Lohse I. Lund R. Mankel W. T. Meyer G. Mornacchi T. Nakada I. Otterlund M. Panter H. Pugh A. Putzer K. Rauschnabel B. Rensch F. Rimondi M. Schmelling G. P. Siroli R. Sosnowski E. Stenlund M. Szczekowski R. Szwed O. Ullaland R. Walczak D. Wegener M. Wunsch 《Zeitschrift fur Physik C Particles and Fields》1986,30(4):507-512
The relative yields of kaons and protons compared with the yield of pions at highp T and polar angles θ away from 90° (in the range from 10° to 45°) are presented forpp, dd, and αα interactions at a centre-of-mass energy \(\sqrt {s_{NN} } = 31\) GeV per nucleon-nucleon collision. The measured particle ratios depend on the atomic mass numberA of the beam particles and on θ. TheA dependence of the ratios becomes stronger for largerp T and is more pronounced at smaller polar angles. 相似文献
55.
W. Bell K. Braune G. Claesson D. Drijard M. A. Faessler H. G. Fischer H. Frehse R. W. Frey S. Garpman W. Geist C. Gruhn P. Hanke M. Heiden W. Herr P. G. Innocenti T. J. Ketel E. E. Kluge I. Lund G. Mornacchi T. Nakada I. Otterlund M. Panter B. Povh A. Putzer E. Stenlund T. J. M. Symons R. Szwed O. Ullaland 《Zeitschrift fur Physik C Particles and Fields》1986,30(4):513-520
Properties of secondaries associated with a high-p T charged trigger particle (3<p T <5 GeV/c) were studied for αp and αα interactions at c.m. energies \(\sqrt s = 88\) GeV and 125 GeV, respectively. Thep T distributions of secondaries in the away-jet and trigger-jet regions were compared with those for high-p T pp interactions. No statistically significant differences were seen, except at lowp T . Momentum and angular distributions of spectator and leading protons were studied as a function of charge and rapidity of the trigger hadron. The observed correlations between trigger charge and number of spectator protons provide evidence of valence quark contributions to the trigger jet. 相似文献
56.
Synthetic erythropoietic proteins: tuning biological performance by site-specific polymer attachment
Chen SY Cressman S Mao F Shao H Low DW Beilan HS Cagle EN Carnevali M Gueriguian V Keogh PJ Porter H Stratton SM Wiedeke MC Savatski L Adamson JW Bozzini CE Kung A Kent SB Bradburne JA Kochendoerfer GG 《Chemistry & biology》2005,12(3):371-383
Chemical synthesis in combination with precision polymer modification allows the systematic exploration of the effect of protein properties, such as charge and hydrodynamic radius, on potency using defined, homogeneous conjugates. A series of polymer-modified synthetic erythropoiesis proteins were constructed that had a polypeptide chain similar to the amino acid sequence of human erythropoietin but differed significantly in the number and type of attached polymers. The analogs differed in charge from +5 to -26 at neutral pH and varied in molecular weight from 30 to 54 kDa. All were active in an in vitro cell proliferation assay. However, in vivo potency was found to be strongly dependent on overall charge and size. The trends observed in this study may serve as starting points for the construction of more potent synthetic EPO analogs in the future. 相似文献
57.
The excitation energy in the multiphoton ionization spectrum of the trans-1-naphthol/N(2) cluster shows only a small red shift with respect to isolated naphthol, indicating a van der Waals pi-bound structure rather than a hydrogen-bonded one. To confirm this interpretation, high-level electronic structure calculations were performed for several pi- and hydrogen-bonded isomers of this cluster. The calculations were carried out at the second order M?ller-Plesset (MP2) level of perturbation theory with the family of correlation consistent basis sets up to quintuple-zeta quality including corrections for the basis set superposition error and extrapolation to the MP2 complete basis set (CBS) limit. We report the optimal geometries, vibrational frequencies, and binding energies (D(e)), also corrected for harmonic zero-point energies (D(0)), for three energetically low-lying isomers. In all calculations the lowest energy structure was found to be an isomer with the N(2) molecule bound to the pi-system of the naphthol ring carrying the OH group. In the CBS limit its dissociation energy was computed to be D(0) = 2.67 kcal/mol (934 cm(-1)) as compared to D(0) = 1.28 kcal/mol (448 cm(-1)) for the H-bound structure. The electronic structure calculations therefore confirm the assignment of the experimental electronic spectrum corresponding to a van der Waals pi-bound structure. The energetic stabilization of the pi-bound isomer with respect to the hydrogen-bonded one is rather unexpected when compared with previous findings in related systems, in particular phenol/N(2). 相似文献
58.
The first basic mercurous tetrafluoroborate, Hg2(OH)[BF4], was obtained through a synproportionation reaction of red mercuric oxide, HgO, and elemental mercury in a 35% solution of HBF4 in water as colourless single crystals. The crystal structure (orthorhombic, Pbca, Z = 8, a = 985.0(1), b = 991.0(1), c = 1141.0(2) pm) contains [(HO)1/2—Hg—Hg—(OH)1/2]+ zig‐zag chains that are further connected via weak Hg—OH interchain interactions to layers between which the [BF4]— are located in an up and down fashion. 相似文献
59.
Cushman M Yang D Gerhardt S Huber R Fischer M Kis K Bacher A 《The Journal of organic chemistry》2002,67(16):5807-5816
A series of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-D-ribityllumazine were synthesized as inhibitors of both Escherichia coli riboflavin synthase and Bacillus subtilis lumazine synthase. The compounds were designed to bind to both the ribitylpurine binding site and the phosphate binding site of lumazine synthase. In the carboxyalkyl series, maximum activity against both enzymes was observed with the 3'-carboxypropyl compound 22. Lengthening or shortening the chain linking the carboxyl group to the lumazine by one carbon resulted in decreased activity. In the phosphonoxyalkyl series, the 3'-phosphonoxypropyl compound 33 was more potent than the 4'-phosphonoxybutyl derivative 39 against lumazine synthase, but it was less potent against riboflavin synthase. Molecular modeling suggested that the terminal carboxyl group of 6-(3'-carboxypropyl)-7-oxo-8-D-ribityllumazine (22) may bind to the side chains of Arg127 and Lys135 of the enzyme. A hypothetical molecular model was also constructed for the binding of 6-(2'-carboxyethyl)-7-oxolumazine (15) in the active site of E. coli riboflavin synthase, which demonstrated that the active site could readily accommodate two molecules of the inhibitor. 相似文献
60.
Structures of New SeII and TeII Complexes Containing 2,2-Dicyanethylene-1,1-dithiolate, 2,2-Dicyanethylene-1,1-thioselenolate, and 2,2-Dicyanethylene-1,1-diselenolate (NBu4)2{Se[S2C?C(CN)2]2} ( I ), (AsPh4)2 · {Te[SSeC?C(CN)2]2} ( II ), and (NBu4)2{Te[Se2C?C(CN)2]2} ( III ) containing the bidentate chelate ligands 2,2-dicyanethylene-1,1-dithiolate i-mnt , 2,2-dicyanethylene-1,1-thioselenolate i-mnts , and 2,2-dicyanethylene-1,1-diselenolate i-mns have been prepared and characterized by X-ray structure analysis. The central units consist of [M(X? X)2E2]2? (M = Se, Te; X? X = ligand; E = lone-pair) with fourfold coordinated SeII and TeII, respectively. The complex anions [Se(i-mnt)2E2]2? as well as [Te(i-mnts)2E2]2? show a trapezoide distortion with d(Se? S) = 2.276(5); 2.287(5); 2.803(5); 2.789(5) Å and d(Te? Se) = 2.611(2); 2.617(3); d(Te? S) = 2.889(5); 2.935(4) Å. In III there are centrosymmetric complex anions [Te(i-mns)2E2]2? with nearly identical Te? Se-bond-lengths: 2.674(3) and 2.692(2) Å. These Te? Se bonds are elongated compared to usual Te? Se bonds. 相似文献