全文获取类型
收费全文 | 2809篇 |
免费 | 150篇 |
国内免费 | 1篇 |
专业分类
化学 | 1774篇 |
晶体学 | 13篇 |
力学 | 68篇 |
数学 | 361篇 |
物理学 | 744篇 |
出版年
2023年 | 19篇 |
2022年 | 34篇 |
2021年 | 97篇 |
2020年 | 89篇 |
2019年 | 116篇 |
2018年 | 135篇 |
2017年 | 113篇 |
2016年 | 167篇 |
2015年 | 106篇 |
2014年 | 130篇 |
2013年 | 178篇 |
2012年 | 175篇 |
2011年 | 201篇 |
2010年 | 128篇 |
2009年 | 99篇 |
2008年 | 144篇 |
2007年 | 126篇 |
2006年 | 128篇 |
2005年 | 101篇 |
2004年 | 77篇 |
2003年 | 62篇 |
2002年 | 64篇 |
2001年 | 37篇 |
2000年 | 27篇 |
1999年 | 20篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1983年 | 9篇 |
1981年 | 17篇 |
1979年 | 15篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 14篇 |
1974年 | 15篇 |
1973年 | 21篇 |
1972年 | 8篇 |
1971年 | 13篇 |
1970年 | 12篇 |
1966年 | 7篇 |
1965年 | 8篇 |
排序方式: 共有2960条查询结果,搜索用时 375 毫秒
181.
A review of the history and present state of the use of palladium complexes in the synthesis of alternating CO copolymers with different monomers (mainly ethylene, propylene, and styrene) is presented. The effect of mono- and bidentate phosphine ligands, the nature of reaction medium and acid on the rate of the CO copolymerization with ethylene, and the effect of different bidentate PP, PN, and NN ligands on the structure and properties of chiral CO–propylene and CO-styrene copolymers are considered. 相似文献
182.
French SA Sokol AA Bromley ST Catlow CR Rogers SC King F Sherwood P 《Angewandte Chemie (International ed. in English)》2001,40(23):4437-4440
183.
de Meijere A von Seebach M Zöllner S Kozhushkov SI Belov VN Boese R Haumann T Benet-Buchholz J Yufit DS Howard JA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(18):4021-4034
Perspirocyclopropanated bicyclopropylidene (6) was prepared in three steps from 7-cyclopropylidenedispiro[2.0.2.1]heptane (4) (24% overall) or, more efficiently, through dehalogenative coupling of 7,7-dibromo[3]triangulane (15) (82%). This type of reductive dimerization turned out to be successful for the synthesis of (E)- and (Z)-bis(spiropentylidene) 14 (67%) and even of the "third-generation" spirocyclopropanated bicyclopropylidene 17 (17% overall from 15). Whereas the parent bicyclopropylidene 1 dimerized at 180 degrees C to yield [4]rotane, dimerization of 6 at 130 degrees C under 10 kbar pressure occured only with opening of one three-membered ring to yield the polyspirocyclopropanated (cyclopropylidene)cyclopentane derivative 19 (34% yield), and at the elevated temperature the polyspirocyclopropanated 2-cyclopropylidene[3.2.2]propellane derivative 20 (25 % yield). Perspirocyclopropanated bicyclopropylidene 6 and the "third-generation" bicyclopropylidene 17 gave addition of bromine, hydrogen bromide, and various dihalocarbenes without rearrangement. The functionally substituted branched [7]triangulane 28 and branched dichloro-C2v-[15]triangulane 32 were used to prepare the perspirocyclopropanated [3]rotane (D3h-[10]triangulane) 49 (six steps from 6, 1.4% overall yield) and the C2v-[15]triangulane 51 (two steps from 17, 41% overall). Upon catalytic hydrogenation, the perspirocyclopropanated bicyclopropylidene 6 yielded 7,7'-bis(dispiro[2.0.2.]-heptyl) (52) and, under more forcing conditions, 1,1'-bis(2,2,3,3-tetramethylcyclopropyl) (53). The bromofluorocarbene adduct 33 of 17 reacted with butyllithium to give the unexpected polyspirocyclopropanated 1,4-di-n-butyl-2-cyclopropylidenebicyclo[2.2.0]hexane derivative 37 as the main product (55% yield) along with the expected "third-generation" perspirocyclopropanated dicyclopropylidenemethane 38 (21% yield). Mechanistic aspects of this and the other unusual reactions are discussed. The structures of all new unusual hydrocarbons were proven by X-ray crystal structure analyses, and the most interesting structural and crystal packing features are presented. 相似文献
184.
Spatiotemporal magnetization reversal dynamics in a Ni(80)Fe(20) microstructure is studied using ps time scale scanning Kerr microscopy. Time domain images reveal a striking change in the reversal associated with the reduction in switching time when a transverse bias field is applied. Magnetization oscillations subsequent to reversal are observed at two resonance frequencies, which sensitively depend on the bias field strength. The oscillation at f = 2 GHz is caused by the damped precession of M, while the lower frequency approximately 0.8 GHz mode is interpreted in terms of domain wall oscillation. 相似文献
185.
Abu-Zayyad T Belov K Bird DJ Boyer J Cao Z Catanese M Chen GF Clay RW Covault CE Cronin JW Dai HY Dawson BR Elbert JW Fick BE Fortson LF Fowler JW Gibbs KG Glasmacher MA Green KD Ho Y Huang A Jui CC Kidd MJ Kieda DB Knapp BC Ko S 《Physical review letters》2000,84(19):4276-4279
The average mass composition of cosmic rays with primary energies between 10(17) and 10(18) eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases. 相似文献
186.
Tran Duc Thiep Truong Thi An Nguyen The Vinh Phan Viet Cuong A. G. Belov O. D. Maslov Trinh Thi Thu My 《Physics of Particles and Nuclei Letters》2007,4(5):397-402
We have carried out the study on the isomeric ratios in (γ,p) photonuclear reactions with isotopes
40
92
Zr and
74
183
W in the giant dipole resonance (GDR) region. The targets were irradiated with bremsstrahlungs produced by electron accelerator
Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Russia. Spectra
of the irradiated samples were measured with a spectroscopic system consisting of 8192-channel analyzer CANBERRA and high-energy
resolution semiconductor detector CANBERRA. The results were discussed and compared with those of other authors.
The text was submitted by the authors in English. 相似文献
187.
188.
O. V. Belov 《Physics of Particles and Nuclei Letters》2007,4(6):519-523
On the basis of the analysis of experimental data for relative concentration of the LexA protein, relative concentrations of single stranded DNA are calculated for active and inactive conformation of the RecA protein. Opportunities of further theoretical and experimental investigations are discussed 相似文献
189.
Alexey A. Morozov 《Applied Physics A: Materials Science & Processing》2013,111(4):1107-1112
A theoretical study of the time-of-flight (TOF) distributions under pulsed laser ablation has been performed. 2D simulations of pulsed evaporation of atoms into vacuum on the base of the direct simulation Monte Carlo (DSMC) method have been carried out. It is found that for large evaporating spots (when the spot radius exceeds the initial plume length by a factor of five) the TOF distributions practically do not change with the spot radius variation. Moreover, it is shown that such distributions can be obtained from 1D calculations. Thus, in the frames of 1D approach, the TOF distribution is a function only of the number of the evaporated monolayers, but not of the spot radius. The shape of the TOF distribution is shown to strongly depend on the amount of the evaporated matter. Based on the calculated TOF distributions, dependence of the particle kinetic energy on the number of the evaporated monolayers has been obtained. To verify the theoretical results, experimental data on laser ablation of niobium and mercury have been used, which confirm the obtained dependences. The obtained results allow estimating the irradiated surface temperature from the TOF distributions for monatomic neutral gas. 相似文献
190.
Alexey N. Egorochkin Nadiya M. Khamaletdinova 《Journal of organometallic chemistry》2011,696(10):2199-2205
The literature data on substituent influence on the CS, CN, NC, NN, and NO stretching frequencies (ν) in the IR spectra and in specific cases on their respective stretching force constants (k) have been analyzed for 28 series of the transition metal complexes. The ν and k values were first established to depend not only on the inductive and resonance effects but on the polarizability of substituents as well. The contribution of the polarizability effect varies from 0 to 57% with the type of series. 相似文献