全文获取类型
收费全文 | 3586篇 |
免费 | 118篇 |
国内免费 | 9篇 |
专业分类
化学 | 2506篇 |
晶体学 | 25篇 |
力学 | 104篇 |
数学 | 563篇 |
物理学 | 515篇 |
出版年
2023年 | 43篇 |
2022年 | 75篇 |
2021年 | 100篇 |
2020年 | 92篇 |
2019年 | 84篇 |
2018年 | 53篇 |
2017年 | 49篇 |
2016年 | 119篇 |
2015年 | 100篇 |
2014年 | 110篇 |
2013年 | 230篇 |
2012年 | 240篇 |
2011年 | 281篇 |
2010年 | 140篇 |
2009年 | 131篇 |
2008年 | 180篇 |
2007年 | 180篇 |
2006年 | 192篇 |
2005年 | 156篇 |
2004年 | 98篇 |
2003年 | 122篇 |
2002年 | 96篇 |
2001年 | 33篇 |
2000年 | 30篇 |
1999年 | 15篇 |
1998年 | 25篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 26篇 |
1994年 | 30篇 |
1993年 | 18篇 |
1992年 | 24篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1985年 | 21篇 |
1984年 | 29篇 |
1983年 | 24篇 |
1982年 | 35篇 |
1981年 | 33篇 |
1980年 | 29篇 |
1979年 | 26篇 |
1978年 | 21篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1975年 | 21篇 |
1973年 | 23篇 |
1972年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有3713条查询结果,搜索用时 15 毫秒
11.
The recently proposed Harbola–Sahni local potential in its exchange-only version [Phys. Rev. Lett. 62 , 689 (1989)] is found to give the static dipole and quadrupole polarizabilities for the Neisoelectronic series in excellent agreement with the corresponding Hartree–Fock estimates. © 1992 John Wiley & Sons, Inc. 相似文献
12.
By means of exponential laws we show a Bianchi Type I model of the universe where we define overall deceleration and Hubble's parameters that have constant values. We employ a convenient relation for defining the radius of the universe. Pressure and density have constant values, too. 相似文献
13.
S. R. Grace 《Mathematische Nachrichten》1989,142(1):297-305
New theorems on the oscillatory and asymptotic behavior of solutions of the damped differential equations with deviating arguments of the form are established. 相似文献
14.
15.
16.
Appleby I Boulton LT Cobley CJ Hill C Hughes ML de Koning PD Lennon IC Praquin C Ramsden JA Samuel HJ Willis N 《Organic letters》2005,7(10):1931-1934
Two methods to produce (2S)-5-amino-2-(1-n-propyl-1H-imidazol-4-ylmethyl)-pentanoic acid were investigated. Diastereoisomeric salt resolution, using the quinidine salt, gave the desired intermediate in 98% ee and 33% yield. Asymmetric hydrogenation of various substrates gave high conversions, with up to 83% ee. Integration of these two approaches via asymmetric hydrogenation of a quinidine salt substrate followed by crystallization provided the desired intermediate in 94% ee and 76% yield. 相似文献
17.
Loomis S. Chen Grace J. Chen Chirst Tamborski 《Journal of organometallic chemistry》1980,193(3):283-292
Experimental conditions have now been developed whereby o-bromophenyllithium(II) may be prepared in excellent yields and used as an organometallic intermediate for the synthesis of a variety of ortho bromo substituted phenyl compounds (o-BrC6H4X). THe thermal stability, decomposition products and reactions of II wre studied. REactions between II and a variety of substrates, e.g., CO2, dimethylformamide, fluorinated esters, hexafluorobenzene, and organosilicon chlorides were examined. 相似文献
18.
Samuel Natelson 《Microchemical Journal》1991,44(3)
When glutamic acid is amidinated, guanidinoglutaric acid is formed. This is readily converted by boiling in water to its lactam [2-imino-4-oxo-5-(3′-propane acid) imidazolidine; GGAL]. In the present study GGAL is dehydrated to form a second lactam, anhydro-GGAL (AGGAL), with trifluoroacetic anhydride. The molecular weight of this compound was ascertained gravimetrically by precipitation with flavianic acid and by mass spectrography to be 153.14. UV and infrared spectra and hydrogen and 13C NMR studies determined its structure as an imidazolidine ring fused to a pyrrol ring, 2-imino-4-oxo-imidazolidine-1,5-pyrrolidone-8. On paper electrophoresis, GGAL traveled to the anode, while AGGAL traveled to the cathode. On TLC plates (butanol 60, H2O 25, acetic 15), the Rf value of GGAL was 0.42 and that of AGGAL was 0.38, confirming that AGGAL was more basic than GGAL. The preparation of 1,3-di-(phenylcarbamoyl)-GGAL is also described. 相似文献
19.
R. R. Mendel Kimball A. Milton James H. Reid Mark A. Samuel 《Zeitschrift fur Physik C Particles and Fields》1986,32(4):517-520
Several methods to determine (or set an upper bound on) the mass of the tau neutrino are described. The decay spectrum of \(\tau \to e\bar \nu _e \nu _\tau \) near the high center-of-mass electron-energy end is particularly sensitive to the tau-neutrino mass. It is shown that an upper bound of 20 MeV or lower may be feasible. In addition, improved limits on the mass and mixing angle of a heavy component of the tau-neutrino may be readily obtained. We also discuss the purely leptonic decays of theD andF mesons, and show how measurements of the ratiosB(D→τντ/B(D→μνμ,B(F→τντ/B(D→μνμ can be sensitive to tau-neutrino masses of 30 MeV or greater. 相似文献
20.
Treatment of [Ti(O-i-Pr)(2)Cl(2)] with NaL(OEt) (L(OEt)(-) = [CpCo[P(O)(OEt)(2)](3)](-), Cp = eta(5)-C(5)H(5)) afforded [L(OEt)Ti(O-i-Pr)(2)Cl] that reacted with HCl in ether to give [L(OEt)TiCl(3)] (1). The average Ti-O and Ti-Cl distances in 1 are 1.975 and 2.293 A, respectively. Reaction of titanyl sulfate with NaL(OEt) in water followed by addition of HBF(4) afforded [L(OEt)TiF(3)] (2), the Ti-O and Ti-F distances of which are 2.020(2) and 1.792(2) A, respectively. The Zr(IV) analogue [L(OEt)ZrF(3)] (3) was prepared similarly from zirconyl nitrate, NaL(Oet), and HBF(4) in water. The Zr-O and average Zr-F distances in 3 are 2.139(2) and 1.938(2) A, respectively. Treatment of 1 with tetrachlorocatechol (H(2)Cl(4)cat) afforded [L(OEt)Ti(Cl(4)cat)Cl] (4). The average Ti-O(P), Ti-O(C), and Ti-Cl distances in 4 are 1.972, 1.926, and 2.334 A, respectively. Hydrolysis of 4 in the presence of Et(3)N yielded the mu-oxo dimer [(L(OEt))(2)Ti(2)(Cl(4)cat)(2)(mu-O)] (5). The average Ti-O(P), Ti-O(C), and Ti-O(Ti) distances in 5 are 2.027, 1.926, and 1.7977(9) A. Treatment of 1 with 1,1'-binaphthol (BINOLH(2)) in the presence of Et(3)N afforded [(L(OEt))(2)Ti(2)(mu-O)(2)(mu-BINOL)] x 2BINOLH(2) (6.2BINOLH(2)). Complex 1 is capable of catalyzing ring opening of epoxides with Me(3)SiN(3) under solvent-free conditions presumably via a Ti-azide intermediate. 相似文献