全文获取类型
收费全文 | 3733篇 |
免费 | 71篇 |
国内免费 | 17篇 |
专业分类
化学 | 2299篇 |
晶体学 | 26篇 |
力学 | 76篇 |
数学 | 600篇 |
物理学 | 820篇 |
出版年
2022年 | 29篇 |
2021年 | 36篇 |
2020年 | 58篇 |
2019年 | 41篇 |
2018年 | 25篇 |
2017年 | 22篇 |
2016年 | 46篇 |
2015年 | 51篇 |
2014年 | 47篇 |
2013年 | 164篇 |
2012年 | 162篇 |
2011年 | 178篇 |
2010年 | 100篇 |
2009年 | 87篇 |
2008年 | 153篇 |
2007年 | 189篇 |
2006年 | 178篇 |
2005年 | 173篇 |
2004年 | 168篇 |
2003年 | 139篇 |
2002年 | 125篇 |
2001年 | 84篇 |
2000年 | 96篇 |
1999年 | 53篇 |
1998年 | 65篇 |
1997年 | 54篇 |
1996年 | 62篇 |
1995年 | 62篇 |
1994年 | 50篇 |
1993年 | 71篇 |
1992年 | 43篇 |
1991年 | 40篇 |
1990年 | 44篇 |
1989年 | 45篇 |
1988年 | 37篇 |
1987年 | 42篇 |
1986年 | 41篇 |
1985年 | 58篇 |
1984年 | 47篇 |
1983年 | 38篇 |
1982年 | 34篇 |
1981年 | 37篇 |
1980年 | 37篇 |
1979年 | 26篇 |
1978年 | 30篇 |
1977年 | 39篇 |
1976年 | 45篇 |
1975年 | 49篇 |
1974年 | 42篇 |
1973年 | 45篇 |
排序方式: 共有3821条查询结果,搜索用时 15 毫秒
991.
T D Wilson 《Journal of chromatography. A》1987,391(2):409-418
A reversed-phase high-performance liquid chromatographic method has been applied utilizing ion-pairing to measure Tornalate in solution dosage forms. Specificity of the method was demonstrated by selectivity for Tornalate analysis, analysis of stressed samples and by peak homogeneity tests. These included the diode-array derived spectral overlay test and fraction collection with rechromatography in an alternate normal phase system. Linearity was also demonstrated in terms of recovery from synthetic samples and detector response. 相似文献
992.
David W. Gaibler Willie E. Rochefort James B. Wilson Stephen S. Kelley 《Cellulose (London, England)》2004,11(2):225-237
A series of miscible cellulose ester/poly (vinyl phenol) (CE/PVP) blends containing a latent formaldehyde source were prepared. Due to the low molecular weight of the PVP, the maximum PVP content ID the films was 50 wt %. The blends were then thermally cross-linked ID an attempt to create semi-interpenetrating polymer networks (semi-IPN). The blends were characterized with differential scanning calorimetry, swelling experiments, pyrolysis molecular beam mass spectrometry (py-MBMS), and Fourier transform infrared (FTIR) spectroscopy. The results from the swelling experiments, py-MBMS and FTIR showed that the PVP component did react with the formation of methylene bridges. Blends that contained 50% PVP and high levels of formaldehyde formed semi-IPN structures. 相似文献
993.
The mass spectra of benzophenone oxime O-methyl and O-methylthiomethyl ethers, α,α-diphenyl-N-methyl and methylthiomethyl nitrones, and some deuterated analogues, are reported. Fragmentation pathways are discussed, with particular reference to the structures of ion m/e 211 found in all the spectra. Some evidence suggests nitrone → O-ether rearrangement at either neutral molecule or molecular ion level. 相似文献
994.
Gordon AG Smith RI Wilson C Stoeva Z Gregory DH 《Chemical communications (Cambridge, England)》2004,(24):2812-2813
New nitridocobaltates Li(3-x-y)Co(x)N are revealed to contain significant Li(+) vacancies (y approximately 0.45) disordered within lithium-nitrogen planes and to exist as partially delocalised spin systems as a result of increased covalency through infinite -N-(Li,Co)-N- chains. 相似文献
995.
Michael addition-electrophilic quench reactions of N-alkyl maleimides are possible using dialkylzincs in combination with a copper catalyst and a phosphoramidite ligand. Up to 55% ee has been achieved for one example (E = H) using a chiral ligand. 相似文献
996.
We show that the inverse correlation lengthm(z) of the truncated spin-spin correlation function of theZ
d
Ising model with + or — boundary conditions admits the representationm(z) = –(4d–4)ln z(1–d1) + r(z) for smallz=e
–, i.e., large inverse temperatures
is ad-dependent analytic function atz = 0, already known in closed form ford = 1 and 2; ford = 3 bn can be computed explicitly from a finite number of the Zd limits of z = 0 Taylor series coefficients of the finite lattice correlation function at a finite number of points ofZ
d. 相似文献
997.
Baker CF Barker MG Wilson C Gregory DH 《Dalton transactions (Cambridge, England : 2003)》2004,(9):1298-1303
New molybdenum(VI) nitride oxides were synthesised by the reaction of strontium nitride and calcium nitride with molybdenum foil at high temperature in sealed stainless steel crucibles. The reactions yielded single crystalline products determined by X-ray diffraction to form complex structures in the triclinic space group P1(no. 2). The mixed alkaline earth compounds with composition Ca38Sr13[MoN4]12N8O3 and Ca36Sr15[MoN4]12N8O3 are isostructural with the quaternary nitride oxides Sr51[WN4]12N8O3 and Ca51[WN4]12N8O3. The structures contain isolated [MoN4](6-) tetrahedra, partially disordered alkaline earth cations and an ordered sublattice of N(3-) and O(2-) anions. Oxide anions are coordinated only to the alkaline earth metals. The title compounds are the first mixed alkaline earth metal nitride oxides. 相似文献
998.
999.
Clarke PA Arnold PL Smith MA Natrajan LS Wilson C Chan C 《Chemical communications (Cambridge, England)》2003,(20):2588-2589
Model studies are presented that suggest the mechanism of the lanthanide(III) salt catalysed mono acylation of symmetrical diols proceeds via chelation of the diol and the anhydride to the lanthanide salt, followed by an 'intramolecular' acyl transfer. 相似文献
1000.
Bursten BE Chisholm MH Clark RJ Firth S Hadad CM MacIntosh AM Wilson PJ Woodward PM Zaleski JM 《Journal of the American Chemical Society》2002,124(12):3050-3063
The compounds ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3) (M(4)OXA), where M = Mo or W, are shown by analysis of powder X-ray diffraction data to have extended lattice structures wherein oxygen atoms from the oxalate and pivalate ligands of one M(4)OXA molecule are linked to metal atoms of neighboring molecules. Raman, resonance Raman, electronic absorption (2-325 K in 2-MeTHF), and emission spectra are reported, together with corresponding spectra of the mu-O(2)(13)C(13)CO(2) isotopomers. To aid in the assignment, the Raman spectra of K(2)C(2)O(4).H(2)O and K(2)(13)C(2)O(4).H(2)O have also been recorded. The visible region of the electronic spectra is dominated by intense, fully allowed MLCT transitions, M(2) delta to oxalate pi*, which show pronounced thermochromism and extensive vibronic progressions associated with the oxalate ligand at low temperatures. With excitation into these charge-transfer bands, strong resonance enhancement is seen for Raman bands assigned to the oxalate nu(1)(a(g)) and, to a lesser extent, nu(2)(a(g)) modes. Electronic structure calculations for the model compounds (HCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)CH)(3), employing density functional theory (gradient corrected and time-dependent) with the Gaussian 98 and ADF 2000 packages, predict the planar oxalate D(2h) configuration to be favored, which maximizes M(2) delta to oxalate pi* back-bonding, and indicate low barriers (<8 kcal mol(-1)) to rotation about the oxalate C-C bonds. 相似文献