全文获取类型
收费全文 | 6154篇 |
免费 | 794篇 |
国内免费 | 763篇 |
专业分类
化学 | 4560篇 |
晶体学 | 114篇 |
力学 | 217篇 |
综合类 | 51篇 |
数学 | 749篇 |
物理学 | 2020篇 |
出版年
2024年 | 13篇 |
2023年 | 89篇 |
2022年 | 192篇 |
2021年 | 156篇 |
2020年 | 197篇 |
2019年 | 210篇 |
2018年 | 186篇 |
2017年 | 176篇 |
2016年 | 242篇 |
2015年 | 227篇 |
2014年 | 310篇 |
2013年 | 398篇 |
2012年 | 480篇 |
2011年 | 527篇 |
2010年 | 365篇 |
2009年 | 393篇 |
2008年 | 412篇 |
2007年 | 400篇 |
2006年 | 346篇 |
2005年 | 291篇 |
2004年 | 220篇 |
2003年 | 186篇 |
2002年 | 194篇 |
2001年 | 153篇 |
2000年 | 165篇 |
1999年 | 121篇 |
1998年 | 74篇 |
1997年 | 79篇 |
1996年 | 90篇 |
1995年 | 69篇 |
1994年 | 83篇 |
1993年 | 63篇 |
1992年 | 68篇 |
1991年 | 39篇 |
1990年 | 38篇 |
1989年 | 27篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 30篇 |
1985年 | 21篇 |
1983年 | 21篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 25篇 |
1976年 | 15篇 |
1975年 | 19篇 |
1971年 | 10篇 |
排序方式: 共有7711条查询结果,搜索用时 15 毫秒
181.
ClnOPodiumpoIycePhalum(VantjCYWhetHsuancalled'DuanXielin'inChineseisusedinfolkmedicineforthetreatInentofhaemorrhagiadisease.lInordertofmdtheactivecomPounds,studiesonthechedricalconstituentsofthewholeplan,collectedatHuoShanofAnhuiprovince,werecarriedout.Fromthealcoholicextracts,wehaveisolatedanewanthraquinone,Glyceroyl-l,6,8-trihydroxy-3-methyl-9)lO-dioxo-2-anthrcenecarboxylateI(Figurel).Iwasobtainedasredneedles,mP:ll9-l2l"C.TheHR-MSdareaffordedthefor-mulaasCl9Hl6O9(Found388.O791;… 相似文献
182.
183.
184.
185.
D. M. Moltz J. C. Batchelder T. F. Lang T. J. Ognibene Joseph Cerny P. E. Haustein P. L. Reeder 《Zeitschrift für Physik A Hadrons and Nuclei》1992,342(3):273-276
The beta-delayed two-proton decay of theT
z
=–5/2 nuclide39Ti has been observed. The39Sc isobaric analog state has been calculated to lie at 8.82 MeV using the measured two-proton sum energy of 4750±40 keV for its decay to the37K ground state. Combining this excitation energy with a Coulomb displacement energy calculation has lowered the energy available for ground state two-proton emission of39Ti from 760 to 530 keV.This work was supported by Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U.S. Depeartment of Energy under Contracts DE-AC03-76SF00098 with Lawrence Berkeley Laboratory, DE-AC02-76CH00016 with Brookhaven National Laboratory and DE-AC06-76RL0 1830 with Pacific Northwest Laboratories. 相似文献
186.
A. Lang B. Blättel W. Cassing V. Koch U. Mosel K. Weber 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(3):287-295
Within a covariant BUU-approach we simulate heavyion collisions at various bombarding energies from 400 MeV/u to 1 GeV/u. We evaluate locally the energymomentum tensorT
v
(x), and extract pressures, energydensities and temperatures. The connection of these thermodynamical quantities to experimental observables and their sensitivity to the equation of state is discussed. Furthermore, we investigate the question of local equilibration and evaluate the entropy produced in these reactions.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday. Work supported by BMFT and GSI Darmstadt 相似文献
187.
In order to study the kinetic mechanism of the e-beam pumped Ar/Xe laser, the temporal profiles of individual laser lines during multiline oscillation have been measured as a function of power deposition (1–12MW/cm3) and gas laser pressure (2–14 bar) using a short pulse (30 ns) coaxial electron beam as excitation source. It was found that the optimum output energy at each pressure was obtained at the same specific power deposition.Strong line competition has been observed between the 2.65 and 1.73 m transitions. In order to explain our results we suggest that besides electron collision mixing (ECM) between the 5d and 6p levels of Xe, there is also a redistribution between all 6p levels which strongly favours the lower levels at higher pumping densities. 相似文献
188.
189.
Giuseppe Mascolo Mauro Giustini Pier Luigi Luisi Jacques Lang 《Journal of colloid and interface science》1990,140(2)
The coupling reaction between cetylbromide (CB) and trimethylamine (TMA) to yield the surfactant cetyltrimethylammonium bromide (CTAB) is studied in the system chloroform/isooctane (2/1,v/v)/water in which CTAB forms reverse micelles. This system affords an endogenous micelle population growth, i.e., an increase of the concentration of the micelles due to appearance of the surfactant in situ. The reaction is studied in the presence of preexisting CTAB reverse micelles. The rate of CTAB formation is measured by NMR spectroscopy, and the endogenous micelle population growth is directly monitored by time-resolved fluorescence quenching analysis. Under our experimental conditions, a 100% yield of the chemical reaction brings about a fourfold increase in the population of the reverse micelles. Since the water concentration is constant during chemical reaction, the newly formed water pools are formed at the expense of the initial ones, which brings about a decrease of the average water pool radius during micellar growth. The implication of the endogenous micelle population growth as a model for biological systems is briefly discussed. 相似文献
190.
Lophenol, cholest-4α-methyl-7-en-3β-ol (1), obtained from Dracaena cochinchinensis (Lour.) S. C. Chen, was structurally modified. It was acetylated to protect 3β-hydroxyl group, and then oxidised by selenium dioxide in acetic acid to give cholest-4a-methyl-8-en-3β, Ta-diol diacetate (3). This compound 3 is unstable in chloroform solution or when heated and easily converted to a diene compound, cholest-4a-methyl-7,14-dien-3β-ol acetate (4). The structures of 3 and 4 were elucidated by means of IR, ^1H NMR, ^13C NMR and MS, and the absolute configuration of 3 was established by X-ray crystallography. The property of 3 was also discussed in this paper. Both 3 and 4 are new compounds and were reported for the first time. 相似文献