全文获取类型
收费全文 | 5612篇 |
免费 | 160篇 |
国内免费 | 30篇 |
专业分类
化学 | 4401篇 |
晶体学 | 49篇 |
力学 | 76篇 |
数学 | 347篇 |
物理学 | 929篇 |
出版年
2023年 | 24篇 |
2022年 | 48篇 |
2021年 | 56篇 |
2020年 | 65篇 |
2019年 | 94篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 110篇 |
2015年 | 97篇 |
2014年 | 134篇 |
2013年 | 285篇 |
2012年 | 315篇 |
2011年 | 387篇 |
2010年 | 207篇 |
2009年 | 238篇 |
2008年 | 381篇 |
2007年 | 376篇 |
2006年 | 416篇 |
2005年 | 363篇 |
2004年 | 336篇 |
2003年 | 277篇 |
2002年 | 274篇 |
2001年 | 84篇 |
2000年 | 67篇 |
1999年 | 58篇 |
1998年 | 72篇 |
1997年 | 70篇 |
1996年 | 66篇 |
1995年 | 54篇 |
1994年 | 35篇 |
1993年 | 42篇 |
1992年 | 29篇 |
1991年 | 37篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 45篇 |
1985年 | 58篇 |
1984年 | 47篇 |
1983年 | 23篇 |
1982年 | 52篇 |
1981年 | 53篇 |
1980年 | 44篇 |
1979年 | 38篇 |
1978年 | 29篇 |
1977年 | 27篇 |
1976年 | 23篇 |
1975年 | 15篇 |
1973年 | 18篇 |
排序方式: 共有5802条查询结果,搜索用时 15 毫秒
31.
Ginting Suka IrwanShin-ichi Kuroda Hitoshi Kubota Takashi Kondo 《European Polymer Journal》2002,38(6):1145-1150
The effect of monomer concentration on photografting of methacrylic acid (MAA) onto linear low-density polyethylene (PE) film (thickness=30 μm) was investigated at 60 °C in water solvent together with the location of MAA-grafted chains. Xanthone was used as a photoinitiator which was coated on the film sample earlier. The higher percentage of grafting and graft efficiency were afforded for the system with the higher monomer concentration. The resultant MAA-grafted films were subjected to measurements of pH-responsive character and ability to adsorb cupric ion in order to understand the characteristics of function introduced. The grafted samples exhibited the pH-responsive character, where they shrank and swelled in acidic and alkaline media, respectively. The pH-responsive character of the grafted films was higher for the samples prepared in the system with a higher monomer concentration. Moreover, the grafted samples exhibited the ability to adsorb cupric ion, and the ability was reduced when the sample was prepared in the system with a higher monomer concentration. The different extents of the pH-responsive character and ability to adsorb cupric ion of the resulting grafted PE films were discussed in terms of location of grafted chains in the film substrate, which was determined by a scanning electron microscope and an attenuated total reflection infrared spectroscopy. 相似文献
32.
The complete structure of palytoxin (1) was elucidated by us in 1982.1 Our continuous interests in palytoxin led us to examine minor constituents of Okinawan Palythoa tuberculosa. In this paper, we describe successful isolation and structural elucidation of four minor toxins, which were named homopalytoxin (2), bishomopalytoxin (3), neopalytoxin (4) and deoxypalytoxin (5). 相似文献
33.
[reaction: see text] A formal total synthesis of the sex attractant of male dried bean beetle, methyl (R,E)-(-)-tetradeca-2,4,5-trienoate, was achieved by a new efficient route utilizing the Pd-catalyzed asymmetric allene synthesis reaction. It was found that the atropisomeric biaryl bisphosphine (R)-segphos showed better enantioselectivity than (R)-binap in the Pd-catalyzed reaction for preparing alkyl-substituted axially chiral allenes. 相似文献
34.
Tadatomi Nishikubo Takashi Iizawa Seiji Saita 《Journal of polymer science. Part A, Polymer chemistry》1986,24(7):1685-1695
Addition reactions of pendant epoxide groups in poly(glycidyl methacrylate) (PGMA) with various active esters such as 1-benzotriazolyl benzoate, S-(2-benzoxazolyl) thiobenzoate, S-(2-benzothiazolyl) thiobenzoate, 4-nitrophenyl benzoate (4NPB), and S-phenyl thiobenzoate (PTB) were carried out using quaternary salts as catalysts. The reactions of PGMA with those active esters proceeded in diglyme at 100°C for 24 h quantitatively without the formation of 2-hydroxyl pendant groups in the polymer when 10 mol % of tetraethylammonium bromide was used as a catalyst. Furthermore, it was found that the respective quaternary salts have higher catalytic activity than tertiary amines in the reaction of PGMA with the active esters, and the reaction of PGMA with 4NPB gave the corresponding polymer with the highest conversion by addition of tetrabutylammonium bromide as a catalyst, while tetraethylammonium chloride showed the highest activity for the reaction of PGMA with PTB. In addition, the rate of reaction of PGMA with 4NPB was proportional to third order kinetics of the epoxide concentration, the ester concentration and the catalyst concentration as follows: ?d[Epoxide]/dt = ?[Ester]/dt = k3[Epoxide] [Ester] [Catalyst]. 相似文献
35.
Yoshinori Kadoma Takashi Toida Kenji Takeda Keikichi Uno Yoshio Iwakura 《Journal of polymer science. Part A, Polymer chemistry》1975,13(3):707-716
The polymerization of picryl (PMA), 2,4-dinitrophenyl (2,4-DNMA),2,6-dinitrophenyl (2,6-DNMA), 2-methyl-4,6-dinitrophenyl (MDNMA), and 2,6-dimethylphenyl methacrylates (DMMA) was carried out in benzene at 60°C. PMA, 2,6-DNMA, and MDNMA did not undergo radical homopolymerization, while 2,4-DNMA and DMMA did. The results suggest that the growing radical readily attacks the oxygen atom of the nitro group at the 2 position of the terminal phenyl group due to the steric effect of the substituent at the 6 position, resulting in chain termination. PMA formed a charge-transfer complex with 2-naphthyl methacrylate (NMA). The stoichiometric composition of this complex was shown to be 1:1 molar complex. PMA was readily copolymerized with NMA. The amount of solvent affected the composition of the copolymer obtained at a given same mole fraction in feed. The results suggest that charge-transfer interaction between the ester groups affects the copolymerization mechanism. 相似文献
36.
Tabushi Iwao Kuroda Yasuhisa Yamada Masahiko Sera Takashi 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(6):599-603
Deuterium relaxation times ofd- andl--d-tryptophan included in -cyclodextrin derivatives were directly measured by deuterium NMR spectroscopy. The results showed that the molecular motion of the tryptophan molecule was strongly restricted even in the cavity of unmodified -cyclodextrin and the additional recognition groupings — ammonium and carboxylate — on -cyclodextrin did not affect the molecular motion of tryptophan, though the association constants were significantly enhanced.Deceased on March 22, 1987. 相似文献
37.
Makoto Minato Takefumi Kaneko Shogo Masauji Takashi Ito 《Journal of organometallic chemistry》2006,691(11):2483-2488
We describe the synthesis of a new asymmetric P,N,N′-tridentate ligand (bis(pyrid-2-ylethyl) menthylphosphine, BPEMP), containing two pyridyl rings and (1S,2R,5S)-menthylphosphino group. The ligand is obtained in five steps from natural abundant l-menthol. The coordination behavior of the ligand toward cationic (allylic)Pd(II) moiety and its first application in palladium-catalyzed asymmetric allylic alkylation are presented. Crystallographic and spectroscopic analyses reveal that [(η3-allylic)Pd(BPEMP)]+ complex forms only one isomer in the solid state as well as in solution. 相似文献
38.
Hirokazu Morisawa Takashi Utagawa Takeshi Miyoshi Fumihiro Yoshinaga Akihiro Yamazaki Koji Mitsugi 《Tetrahedron letters》1980,21(5):479-482
An enzymatic transarabinosylation between 2-chlorohypoxanthine and 1-β--arabinofuranosyluracil gave 9-β--arabinofuranosyl-2-chlorohypoxanthine which was chemically converted to 9-β--arabinofuranosylguanine and its derivatives. 相似文献
39.
Electron-phonon interactions in the photoinduced excited electronic states in molecular systems such as phenanthrene-edge-type hydrocarbons are discussed and compared with those in the monoanions and cations. The complete phase patterns difference between the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) (the atomic orbitals between two neighboring carbon atoms combined in phase (out of phase) in the HOMO are combined out of phase (in phase) in the LUMO) are the main reason that the C-C stretching modes around 1500 cm(-1) afford much larger electron-phonon coupling constants in the excited electronic states than in the charged electronic states. The frequencies of the vibrational modes that play an essential role in the electron-phonon interactions for the excited electronic states are similar to those for the monoanions and cations in phenanthrene-edge-type hydrocarbons. Possible electron pairing and Bose-Einstein condensation in the photoinduced excited electronic states as well as those in the monoanions and cations in molecular systems such as phenanthrene-edge-type hydrocarbons are also discussed. 相似文献
40.
Kazuhiro Watanabe Noboru Akino Tetsuo Aoyagi Noboru Ebisawa Yukio Fujiwara Atsusi Honda Takashi Inoue Takao Itoh Mikito Kawai Minoru Kazawa Junichi Koizumi Masaaki Kuriyama Kenji Miyamoto Naoki Miyamoto Kazuhiko Mogaki Yoshihiro Ohara Tokumichi Ohga Yoshikazu Okumura Hiroshi Oohara Katsumi Ohshima Fujio Satoh Kazuhiko Shimizu Syunji Takahashi Hirotsugu Usami Katsutomi Usui Masahiro Yamamoto Takeshi Yamazaki 《Radiation Physics and Chemistry》1997,49(6):631-639
A negative-ion-based neutral beam injector (N-NBI) has been constructed for JT-60U. The N-NBI is designed to inject 500 keV, 10 MW neutral beams using two ion sources, each producing a 500 keV, 22 A D− ion beam. In the preliminary experiment using one ion source, a D− ion beam of 13.5 A has been successfully accelerated with an energy of 400 keV (5.4 MW) for 0.12 s at an operating pressure of 0.22 Pa. This is the highest D− beam current and power in the world. Co-extracted electron current was effectively suppressed to the ratio of Ie/ID− < 1. The highest energy beam of 460 keV, 2.4 A, 0.44 s has also been obtained. To realize 1 MeV class NBI system for ITER (International Thermonuclear Experimental Reactor), demonstration of ampere class negative ion beam acceleration up to 1 MeV is an important mile stone. To achieve the mile stone, a prototype accelerator and a 1 MV, 1 A test facility called MeV Test Facility (MTF) were constructed. Up to now, an H− ion beam was accelerated up to the energy of 805 keV with an acceleration drain current of 150 mA for 1 s in a five stage electrostatic multi-aperture accelerator. 相似文献