全文获取类型
收费全文 | 6745篇 |
免费 | 156篇 |
国内免费 | 21篇 |
专业分类
化学 | 4408篇 |
晶体学 | 81篇 |
力学 | 252篇 |
数学 | 667篇 |
物理学 | 1514篇 |
出版年
2021年 | 43篇 |
2020年 | 56篇 |
2019年 | 59篇 |
2018年 | 67篇 |
2017年 | 38篇 |
2016年 | 115篇 |
2015年 | 117篇 |
2014年 | 100篇 |
2013年 | 318篇 |
2012年 | 285篇 |
2011年 | 323篇 |
2010年 | 186篇 |
2009年 | 161篇 |
2008年 | 274篇 |
2007年 | 279篇 |
2006年 | 307篇 |
2005年 | 278篇 |
2004年 | 227篇 |
2003年 | 220篇 |
2002年 | 228篇 |
2001年 | 143篇 |
2000年 | 133篇 |
1999年 | 103篇 |
1998年 | 94篇 |
1997年 | 135篇 |
1996年 | 138篇 |
1995年 | 100篇 |
1994年 | 121篇 |
1993年 | 149篇 |
1992年 | 128篇 |
1991年 | 79篇 |
1990年 | 74篇 |
1989年 | 101篇 |
1988年 | 90篇 |
1987年 | 87篇 |
1986年 | 81篇 |
1985年 | 100篇 |
1984年 | 112篇 |
1983年 | 80篇 |
1982年 | 85篇 |
1981年 | 83篇 |
1980年 | 86篇 |
1979年 | 78篇 |
1978年 | 76篇 |
1977年 | 80篇 |
1976年 | 68篇 |
1975年 | 85篇 |
1974年 | 77篇 |
1973年 | 64篇 |
1972年 | 37篇 |
排序方式: 共有6922条查询结果,搜索用时 601 毫秒
151.
Photolysis of complexes of the type M(2)(CO)(6)(RC(5)H(4))(2) (where M = W, Mo, Cr and R = H (Cp) or CH(3) (Cp')) leads to the production of short lived 17-electron radicals. Direct electrochemical characterization of these intermediates has been achieved using a technique known as photomodulated voltammetry (PMV). The results from PMV analysis are in excellent agreement with literature estimates for CpMo(CO)(3)(*) and CpCr(CO)(3)(*). However, CpW(CO)(3)(*) is found to be shifted oxidatively 115 mV relative to previous literature estimates. The change in the value for the tungsten complex changes previous estimates to the bond dissociation energy for tungsten metal hydrides by 3.0 +/- 0.9 kcal/mol. Lifetime information on the radicals is also reported based on the phase shift of the electrochemical signal observed by PMV under limiting current conditions. 相似文献
152.
G. T. Jones R. W. L. Jones B. W. Kennedy D. R. O. Morrison D. B. Miller M. M. Mobayyen S. Wainstein M. Aderholz D. Hantke U. F. Katz J. Kern N. Schmitz W. Wittek H. P. Borner G. Myatt F. W. Bullock S. Burke 《Zeitschrift fur Physik C Particles and Fields》1993,58(3):375-386
Evidence is presented for diffractive production of -mesons and of -systems invp and
chargedcurrent interactions. In the (anti-)neutrino energy range 10 GeVE
v
<60 gev=" the=" cross=" sections=" for=" diffractive=">60> and diffractive production are found to be (0.64±0.14 (stat.)±0.08 (syst.))% and (0.28±0.08 (stat.)±0.04 (syst.))% of the charged-current cross section. The diffractive signal is consistent with being entirely due to diffractivea
1 production. However, the data cannot distinguish between diffractivea
1 and diffractive nonresonant production. The experimental distributions ofW, Q
2,x
Bj
andy
Bj
for diffractive and events are consistent with model predictions. 相似文献
153.
A. E. Asratyan M. Aderholz V. V. Ammosov W. Burkot E. F. Clayton T. Coghen O. Erriquez G. S. Gapienko V. A. Gapienko J. Guy D. Hantke G. T. Jones V. S. Kaftanov U. F. Katz J. Kern V. A. Korotkov S. P. Krutchinin M. A. Kubantsev P. Marage D. B. Miller M. M. Mobayyen D. R. O. Morrison M. Neveu J. Sacton N. Schmitz K. Varvell W. Venus W. Wittek V. G. Zaetz 《Zeitschrift fur Physik C Particles and Fields》1993,58(1):55-60
The diffractive production of charmed strangeD s * and possiblyD s mesons by neutrinos and antineutrinos on nucleons in hydrogen, deuterium and neon targets is observed. The slope parameter of thet distribution is 3.3±0.8 (GeV)?2. The production rate per charged current neutrino interaction with an isoscalar target times the D s + →φτ+ branching fraction is (1.03±0.27)×10?4. 相似文献
154.
155.
156.
Bean A Gronberg J Kutschke R Menary S Morrison RJ Nelson H Richman J Tajima H Schmidt D Sperka D Witherell M Procario M Yang S Daoudi M Ford WT Johnson DR Lingel K Lohner M Rankin P Smith JG Alexander JP Bebek C Berkelman K Besson D Browder TE Cassel DG Coffman DM Drell PS Ehrlich R Galik RS Garcia-Sciveres M Geiser B Gittelman B Gray SW Hartill DL Heltsley BK Honscheid K Jones C Kandaswamy J Katayama N Kim PC Kreinick DL Ludwig GS Masui J Mevissen J Mistry NB Ng CR Nordberg E O'Grady C 《Physical review letters》1993,70(2):138-142
157.
158.
159.
Addition of terpyridine to (TMEDA)Ni(CH3)2 results in the high-yield formation of (terpyridyl)NiMe (3). This NiI organometallic complex was found to be capable of transferring its methyl group to iodocyclohexane to produce methylcyclohexane in high yield. Compound 3 can also serve as an initiator for the catalytic cross-coupling of alkyl electrophiles performed under Negishi-like conditions. 相似文献
160.
Frank Seela Karin Mersmann Jane A. Grasby Michael J. Gait 《Helvetica chimica acta》1993,76(5):1809-1820
A 7-deazaadenosine ( = tubercidin; c7A; 1 ) building block for solid-phase oligoribonucleotide synthesis was prepared. The amino group of 1 was protected with the (dimethylamino)methylidene residue (→ 3 ), and the monomethoxytrityl group was introduced at OH? C(5′) (→ 4 ). Protection of OH? C(2′) was carried out by silylation, showing that use of the (i-Pr)3Si group resulted in high 2′-O-selectivity (→ 5b , 80%). Reaction of 5b with PCl3 afforded the phosphonate 7 which was used in solid-phase oligoribonucleotide synthesis. The autocatalytic hydrolysis of hammerhead ribozymes using pG-G-G-A-G-U-C-A-G-U-C-C-C-U-U-C-G-G-G-G-A-C-U-C-U-G-A-A-G-A-G-G-C-G-C as substrate strand (S) and modified G-C-G-C-C-G-A-A-A-C-U-C-C-C as enzyme strand (E) was studied. When c7A replaced A13 or A14, a small decrease of catalytic activity was observed, while modification in position A15 enhanced the autocatalytic hydrolysis. The results demonstrate, that the atom N(7) of adenosine in any of these positions is not crucial for ribozyme action. 相似文献