全文获取类型
收费全文 | 4071篇 |
免费 | 98篇 |
国内免费 | 13篇 |
专业分类
化学 | 3059篇 |
晶体学 | 30篇 |
力学 | 68篇 |
数学 | 162篇 |
物理学 | 863篇 |
出版年
2022年 | 30篇 |
2021年 | 37篇 |
2020年 | 39篇 |
2019年 | 49篇 |
2018年 | 31篇 |
2017年 | 34篇 |
2016年 | 63篇 |
2015年 | 78篇 |
2014年 | 73篇 |
2013年 | 188篇 |
2012年 | 170篇 |
2011年 | 184篇 |
2010年 | 97篇 |
2009年 | 98篇 |
2008年 | 181篇 |
2007年 | 175篇 |
2006年 | 207篇 |
2005年 | 228篇 |
2004年 | 208篇 |
2003年 | 168篇 |
2002年 | 209篇 |
2001年 | 136篇 |
2000年 | 103篇 |
1999年 | 73篇 |
1998年 | 48篇 |
1997年 | 42篇 |
1996年 | 62篇 |
1995年 | 55篇 |
1994年 | 59篇 |
1993年 | 55篇 |
1992年 | 77篇 |
1991年 | 63篇 |
1990年 | 54篇 |
1989年 | 49篇 |
1988年 | 44篇 |
1987年 | 37篇 |
1986年 | 48篇 |
1985年 | 70篇 |
1984年 | 62篇 |
1983年 | 24篇 |
1982年 | 48篇 |
1981年 | 29篇 |
1980年 | 30篇 |
1979年 | 46篇 |
1978年 | 38篇 |
1977年 | 44篇 |
1976年 | 31篇 |
1975年 | 29篇 |
1974年 | 30篇 |
1973年 | 34篇 |
排序方式: 共有4182条查询结果,搜索用时 15 毫秒
111.
A ternary complex reagent of lithium ester enolate-chiral diether-lithium diisopropylamide was formed in an equimolar mixture of these reagents in toluene based on low-temperature NMR spectroscopy. The use of [6Li,15N]-lithium diisopropylamide as a lithiodeprotonation and complexing reagent produced two sets of doublet peaks in 6Li NMR of a 1:1:1 mixture of lithium enolate-chiral diether-lithium diisopropylamide, indicating the formation of a ternary complex reagent. 相似文献
112.
T.M. Nakatani Y.K. Takahashi M. Yamamoto 《Journal of magnetism and magnetic materials》2010,322(3):357-361
We have investigated the structure of Co2MnSi/MgO/Co2MnSi magnetic tunneling junctions with different tunnel magnetoresistance values depending on the in situ annealing temperatures just after the deposition of the upper Co2MnSi electrodes. The nano-beam diffraction patterns indicated that the degree of order of the upper Co2MnSi electrode annealed at 550 °C was higher than that of an electrode annealed at 400 °C. Moreover, the degree of the L21 order of the upper Co2MnSi electrode annealed at 550 °C was even lower than that of the lower Co2MnSi electrode annealed at an almost equal temperature of 600 °C. Atomic-scale observation using a high-angle annular dark-field (HAADF) method distinctly showed the existence of the L21-ordered regions in the B2-ordered matrix in the upper Co2MnSi electrode annealed at 400 °C. 相似文献
113.
Yu Suzuki Takanori Higashi Takahiro Yamamoto Hideyasu Okamura Takehiro K. Sato Tetsuo Asakura 《Molecules (Basel, Switzerland)》2022,27(2)
Spider dragline silk is a biopolymer with excellent mechanical properties. The development of recombinant spider silk protein (RSP)-based materials with these properties is desirable. Formic acid (FA) is a spinning solvent for regenerated Bombyx mori silk fiber with excellent mechanical properties. To use FA as a spinning solvent for RSP with the sequence of major ampullate spider silk protein from Araneus diadematus, we determined the conformation of RSP in FA using solution NMR to determine the role of FA as a spinning solvent. We assigned 1H, 13C, and 15N chemical shifts to 32-residue repetitive sequences, including polyAla and Gly-rich regions of RSP. Chemical shift evaluation revealed that RSP is in mainly random coil conformation with partially type II β-turn structure in the Gly-Pro-Gly-X motifs of the Gly-rich region in FA, which was confirmed by the 15N NOE data. In addition, formylation at the Ser OH groups occurred in FA. Furthermore, we evaluated the conformation of the as-cast film of RSP dissolved in FA using solid-state NMR and found that β-sheet structure was predominantly formed. 相似文献
114.
H Yamabayashi M Izumo R Motoki T Yamamoto H Nishida S Shin K Sato Y Suzuki 《Radioisotopes》1985,34(3):144-150
A technique for the blood volume measurement of newborns was established in which nonradioactive 50Cr was used in patients for whom radioactive labels were not advisable. The red blood cells (RBC) in the newborn's blood withdrawn from umbilical cord after birth were tagged with enriched stable isotope 50Cr (96%, normal abundance 4.3%) and reinjected into the newborn. Blood samples (0.5 ml) were withdrawn at 30 min and thereafter at 6, 12, 24, 48, 72 and 120 hours old. Samples were centrifugalized and portion of RBC was then freeze-dried, weighed and sealed into polyethylene sheet bag together with 50Cr standard. Neutron irradiation was performed in the reactors of the JAERI with thermal neutron flux 5 X 10(13), 2 X 10(13), 8 X 10(13) cm-2s-1 at JRR-2, -3 and -4 respectively for 20 min and samples were left for about two weeks after irradiation. Induced radioactivity (51Cr, 59Fe) of the sample was measured with a Ge(Li) gamma-ray detector system and 4096 channels pulse height analyzer. Analysis of activity data was carried out by BOB-76 code. The RBC and total blood volume of the newborn was calculated using an isotopic dilution technique. We have investigated on tagging efficiency of 50Cr to RBC, washing effect and dilution rate by 50Cr content or 51Cr/59Fe ratio. Significant difference was observed in the total blood volume of newborns depending on the delivery style and in addition, it changed dynamically along the time elapsed after birth. 相似文献
115.
Yasunori Inoue Hiro-o Hamaguchi Kotaro T. Yamamoto Mitsuo Tasumi Masaki Furuya 《Photochemistry and photobiology》1985,42(4):423-427
Abstract— Fluorescence spectra of native rye phytochrome were determined under different light conditions at liquid nitrogen temperature. Fluorescence spectrum of the red-light-absorbing form (Pr) had a major peak at about 685 nm (14 600 cm−1 ) and a broad sub-peak at about 515 nm (19 400 cm−1 ). The peak height at 685 nm was reduced by irradiation with monochromatic light of 640 nm, and a new peak became obvious at about 702 nm (14250 cm−1 ). This spectral change was almost completely reversed by subsequent irradiation with 700-nm light. Fluorescence spectrum of the photoequilibrium mixture of Pr and far-red-light absorbing form under continuous red light showed a sharp peak at about 685 nm having a peak height ca. 12% of Pr, and a broad sub-peak at about 508 nm (19 700 cm−1 ). Light of 730 nm did not reduce the peak height at about 685 nm but induced a new shoulder at about 699 nm (14300 cm−1 ). Monochromatic light of 640 and 700 nm given following the light of 730 nm could not reverse the spectral change at 699 nm induced by the irradiation with 730-nm light. Fluorescence spectrum of Pr in partially degraded phytochrome was similar to that in native phytochrome but the peak position in the red region was shifted by about 5 nm (100 cm−1 ) to the blue. 相似文献
116.
Isao Saito Shigeru Muramatsu Hiroshi Sugiyama Akihiro Yamamoto Teruo Matsuura 《Tetrahedron letters》1985,26(48):5891-5894
Photochemical hydrogen-deuterium exchange reaction of biologically important indoles is reported. The regioselectivity of the photodeuteration was found to be controlled by the ammonium group of the side chain. 相似文献
117.
I. Yamamoto M. Nishii E. Tokuoka T. Handa K. Miyajima 《Colloid and polymer science》1997,275(7):627-633
We evaluated the hydrolysis of egg yolk phosphatidylcholine (PC) by phospholipase D from Streptomyces chromofuscus (PLD) in small unilamellar vesicles (SUV) in presence of 50 μM Ca2+. After initial choline production (hydrolysis of 1.5% of the PC at the outer leaflets of the vesicle bilayers), the hydrolysis
was reduced to 5% of the initial velocity. The kinetic behavior in SUV of premixed PC and a low percentage of the hydrolysis
product, phosphatidic acid (PA), was similar to that of PC SUV. The reduced velocity disappeared when the membrane structure
was disintegrated by means of a nonionic surfactant. In the retardation phase, the partially hydrolyzed vesicles (postsubstrates)
had much higher affinity for PLD than fresh PC SUV. These results indicated that small clusters of the product, PA, at the
vesicle surface were responsible for the reduced velocity of hydrolysis.
The initial velocity increased in a biphasic manner with the substrate concentration. At a PC concentration range up to 4 mM,
the experimental data fit Michaelis–Menten kinetics. At concentrations above 6 mM, the velocity again markedly increased.
Negatively charged mixed vesicles of PC and PA did not have such kinetics. Furthermore, adding PC SUV to the postsubstrates,
where the fraction of free PLD was less than 0.05, induced steep choline production. These results showed that PLD bound to
vesicles had higher activity than free PLD. We speculated that PLD bound to vesicles collided with and was directly transferred
to PC SUV when the fraction of free PLD in aqueous medium was very small.
Received: 5 November 1996 Accepted: 26 February 1997 相似文献
118.
The interaction of AlR2(BHT)(OEt2) and AlMe(BHT)2 with methylmethacrylate (MMA) leads to the formation of the Lewis acid-base complexes AlR2(BHT)(MMA) [R = Me (1), Et (2)] and AlMe-(BHT)2(MMA) (3), respectively. The molecular structure of 1 has been determined by X-ray crystallography. The decrease in the C=O and C=C stretching frequencies in the IR spectrum, and downfield shift in the 13C NMR spectrum of the - and γ-carbons of the MMA, when compared to free MMA, is presented with respect to the activator ability of sterically crowded aryloxide compounds of aluminum to aluminum-porphyrin catalyzed (Inoue) polymerization of MMA. 相似文献
119.
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
120.
Yuta Yamamoto Shogo Nakano Fumio Seki Yasuteru Shigeta Sohei Ito Hiroaki Tokiwa Makoto Takeda 《Molecules (Basel, Switzerland)》2021,26(5)
Infection of hosts by morbilliviruses is facilitated by the interaction between viral hemagglutinin (H-protein) and the signaling lymphocytic activation molecule (SLAM). Recently, the functional importance of the n-terminal region of human SLAM as a measles virus receptor was demonstrated. However, the functional roles of this region in the infection process by other morbilliviruses and host range determination remain unknown, partly because this region is highly flexible, which has hampered accurate structure determination of this region by X-ray crystallography. In this study, we analyzed the interaction between the H-protein from canine distemper virus (CDV-H) and SLAMs by a computational chemistry approach. Molecular dynamics simulations and fragment molecular orbital analysis demonstrated that the unique His28 in the N-terminal region of SLAM from Macaca is a key determinant that enables the formation of a stable interaction with CDV-H, providing a basis for CDV infection in Macaca. The computational chemistry approach presented should enable the determination of molecular interactions involving regions of proteins that are difficult to predict from crystal structures because of their high flexibility. 相似文献