全文获取类型
收费全文 | 1203篇 |
免费 | 98篇 |
国内免费 | 5篇 |
专业分类
化学 | 1010篇 |
晶体学 | 12篇 |
力学 | 8篇 |
数学 | 100篇 |
物理学 | 176篇 |
出版年
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 28篇 |
2020年 | 37篇 |
2019年 | 52篇 |
2018年 | 37篇 |
2017年 | 24篇 |
2016年 | 51篇 |
2015年 | 42篇 |
2014年 | 67篇 |
2013年 | 67篇 |
2012年 | 96篇 |
2011年 | 104篇 |
2010年 | 44篇 |
2009年 | 36篇 |
2008年 | 78篇 |
2007年 | 66篇 |
2006年 | 70篇 |
2005年 | 76篇 |
2004年 | 63篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 19篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1969年 | 3篇 |
排序方式: 共有1306条查询结果,搜索用时 0 毫秒
1.
2.
Seiichi Nishizawa Tomoyuki Kamaishi Tomoyuki Yokobori Ryo Kato Ying-Yu Cui Takeshi Shioya Norio Teramae 《Analytical sciences》2004,20(11):1559-1565
Facilitated SO4(2-) transfers by hydrogen bond-forming ionophores are investigated across the nitrobenzene (NB)-water interface by using polarography with a dropping electrolyte electrode. Bis-thiourea 1, alpha,alpha'-bis(N'-p-nitrophenylthioureylene)-m-xylene, is found to significantly facilitate the transfer of the highly hydrophilic SO4(2-) whereas its counterpart, N-(p-nitrophenyl)-N'-propylthiourea (ionophore 2), cannot. In contrast to the predominant formation of a 1:1 complex with SO4(2-) in the bulk NB phase, the SO4(2-) transfer assisted by 1 is indeed based on the formation of a 1:2 complex between SO4(2-) and ionophore, even under the condition of [SO4(2-)]aq > [1]org. Such an exclusive formation of the 1:2 (SO4(2-) to ionophore) complex at the NB-water interface is not observed with structurally similar bis-thiourea 3, alpha,alpha'-bis(N'-phenylthioureylene)-m-xylene, where p-nitrophenyl moietes of bis-thiourea 1 are simply replaced by phenyl groups. The facilitated transfer of SO4(2-) with bis-thiourea 1 is further compared to that of HPO4(2-) and H2PO4- across the NB-water interface, which was previously shown to be assisted by 1 through the formation of the 1:1 and 2:1 (anion to ionophore) complexes, respectively. On the basis of these examinations, unique binding behaviors of hydrogen bond-forming ionophores at the NB-water interface are discussed, with a view towards development of ionophore-based anion-selective chemical sensors. 相似文献
3.
Yumi ShimadaMakoto Nakamura Toshimasa SuzukaJunji Matsui Ryo TatsumiKen Tsutsumi Tsumoru MorimotoHideo Kurosawa Kiyomi Kakiuchi 《Tetrahedron letters》2003,44(7):1401-1403
A new method for the construction of the AB-ring core of Taxol was developed utilizing a new skeletal transformation protocol as a pivotal step. The acid-catalyzed rearrangement of the cyclopentenone-allene photoadduct gave a bridged seven-membered ketone, which was easily transformed, using the intramolecular Suzuki reaction and the oxidative cleavage of the vicinal diol, to the bicyclic diketone. 相似文献
4.
5.
Kazuhiko Hashimoto Hiroshi Saito Ryo Ohsawa 《Journal of polymer science. Part A, Polymer chemistry》2006,44(16):4895-4903
Two kinds of new glycopolymers, (P(VB‐1‐GlcaH‐co‐AAm), 9 ) and (P(VB‐1‐Glco‐co‐AAm), 10 ), were synthesized through the radical copolymerization of styrene derivatives bearing pendant D ‐glucaric and D ‐gluconic moieties, N‐(p‐vinylbenzyl)‐1‐D ‐glucaramide (VB‐1‐GlcaH, 7 ), and N‐(p‐vinylbenzyl)‐D ‐gluconamide (VB‐1‐Glco, 8 ), with acrylamide (AAm). Glycopolymer 9 bearing the pendant glucaric moiety at the first position inhibited the hydrolysis of a model compound for xenobiotics‐β‐glucuronide conjugates, p‐nitrophenyl β‐D ‐glucuronide, uncompetitively, in contrast to the competitive inhibition in the presence of the corresponding isomeric glycopolymer bearing the pendant D ‐glucaric unit at the sixth position (P(VB‐6‐GlcaH‐co‐AAm), 3 ) reported in our previous article. On the other hand, another copolymer 10 bearing the gluconic moiety was found not to inhibit the hydrolysis as well as the corresponding copolymer bearing pendant gulonic unit (P(VB‐6‐Glco‐co‐AAm), 4 ). These results indicate that the hydrolysis is influenced not only by existence of pendant carboxyl units but also by the direction on the linkage of the glyco‐units to the polymer frame. Therefore the configurational position of hydroxy groups in pendant glyco‐units in macromolecular inhibitors may be essential for the interaction with β‐glucuronidase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4895–4903, 2006 相似文献
6.
Merchant KA Noid WG Akiyama R Finkelstein IJ Goun A McClain BL Loring RF Fayer MD 《Journal of the American Chemical Society》2003,125(45):13804-13818
Spectrally resolved infrared stimulated vibrational echo data were obtained for sperm whale carbonmonoxymyoglobin (MbCO) at 300 K. The measured dephasing dynamics of the CO ligand are in agreement with dephasing dynamics calculated with molecular dynamics (MD) simulations for MbCO with the residue histidine-64 (His64) having its imidazole epsilon nitrogen protonated (N(epsilon)-H). The two conformational substate structures B(epsilon) and R(epsilon) observed in the MD simulations are assigned to the spectroscopic A(1) and A(3) conformational substates of MbCO, respectively, based on the agreement between the experimentally measured and calculated dephasing dynamics for these substates. In the A(1) substate, the N(epsilon)-H proton and N(delta) of His64 are approximately equidistant from the CO ligand, while in the A(3) substate, the N(epsilon)-H of His64 is oriented toward the CO, and the N(delta) is on the surface of the protein. The MD simulations show that dynamics of His64 represent the major source of vibrational dephasing of the CO ligand in the A(3) state on both femtosecond and picosecond time scales. Dephasing in the A(1) state is controlled by His64 on femtosecond time scales, and by the rest of the protein and the water solvent on longer time scales. 相似文献
7.
(+)-Steganacin was synthesized in a new and highly specific asymmetric pathway based on the novel application of chiral γ-lactone as a chiral synthon. By this synthesis the absolute stereochemistry of natural (?)-steganacin could be determined in unequivocal way. 相似文献
8.
Matsuda R Kitaura R Kitagawa S Kubota Y Kobayashi TC Horike S Takata M 《Journal of the American Chemical Society》2004,126(43):14063-14070
In situ synchrotron X-ray powder diffraction patterns of porous coordination polymers [[Cu(2)(pzdc)(2)(bpy)].G] have been measured (pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4'-bipyridine) (where G = H(2)O for CPL-2 superset H(2)()O, G = benzene for CPL-2 superset benzene, and G = void for the apohost). The structures of apohost and CPL-2 superset benzene were determined from Rietveld analysis. Adsorption of benzene in the channels induced a remarkable contraction in the crystal (b axis; 6.8%, volume; 4.9%), although the channels were occupied by the benzene molecules. This crystal transformation provides a new pore structure that is well suited for benzene molecules, and we denote it as a "shape-responsive fitting" transformation. This type of pore gives rise to a new guideline: frameworks can be composed of flexible motifs that are linked via strong bond and/or stiff motifs that are connected via weaker bonds. 相似文献
9.
1,1-Difluoroethysilanes (R3SiCF2CH3, R = Me or Et) were synthesized from 1,1-difluoroethyl phenyl sulfone and chlorosilanes using magnesium metal via reductive 1,1-difluoroethylation. It was confirmed that 1,1-difluoroethylsilanes were effective 1,1-difluoroethylating reagents for carbonyl compounds. 相似文献
10.
The intercalation of 4-phenylazoaniline (PAA) in supercritical carbon dioxide (SC-CO(2)) into montmorillonite (TMA-Mnt) pillared with tetramethylammonium ions at 313 K and 15 MPa was investigated. The adsorption rate and equilibrium PAA uptake were compared with those in n-hexane, CCl(4) and benzene solutions at 313 K. The XRD and N(2) adsorption/desorption analyses showed that TMA-Mnt after adsorption of PAA in SC-CO(2) had the same pore structure as after adsorption of PAA in normal solvents. SC-CO(2) was found to be a good medium for PAA adsorption owing to its having a relatively high adsorption rate and the highest adsorptivity at the same PAA concentration. The properties of PAA adsorption on TMA-Mnt could be well elucidated by the difference in solubility parameters between liquid and solid phases. 相似文献