全文获取类型
收费全文 | 1227篇 |
免费 | 76篇 |
国内免费 | 35篇 |
专业分类
化学 | 1217篇 |
晶体学 | 4篇 |
力学 | 2篇 |
综合类 | 1篇 |
物理学 | 114篇 |
出版年
2023年 | 35篇 |
2022年 | 15篇 |
2021年 | 27篇 |
2020年 | 27篇 |
2019年 | 34篇 |
2018年 | 28篇 |
2017年 | 27篇 |
2016年 | 42篇 |
2015年 | 30篇 |
2014年 | 44篇 |
2013年 | 147篇 |
2012年 | 43篇 |
2011年 | 59篇 |
2010年 | 54篇 |
2009年 | 53篇 |
2008年 | 62篇 |
2007年 | 69篇 |
2006年 | 52篇 |
2005年 | 68篇 |
2004年 | 58篇 |
2003年 | 51篇 |
2002年 | 42篇 |
2001年 | 45篇 |
2000年 | 34篇 |
1999年 | 43篇 |
1998年 | 27篇 |
1997年 | 19篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有1338条查询结果,搜索用时 296 毫秒
61.
An inexpensive flow-injection instrument for determining low concentrations of dissolved reactive phosphorus in natural waters is reported. The unique feature is the use of an inexpensive detector consisting of a flow cell and a simple photometer that incorporates a super-bright light-emitting diode as the source and a photodiode as the detector. The tin(II) chloride-molybdate method was optimized using a modified simplex optimization method. Silicate interference up to 5 mg Si l?1 was removed by addition of 0.10% (w/v) tartaric acid. Using the tartaric acid-modified optimized reagents, a detection limit of 0.6 μg P l?1 was achieved. The method was linear over the range 0–100 μg P l?1 with an excellent precision (r.s.d. 2.9% at 2.0 and 0.5% at 50 μg P l?1). An in-line pre-concentration anion-exchange column was used to obtain an even lower detection limit of 0.1 μg P l?1 and applied to the analysis of real samples. 相似文献
62.
Pierre Braunstein 《Journal of organometallic chemistry》2004,689(24):3953-3967
In this account, we focus on results from our laboratory to illustrate recent developments in various fields of organometallic chemistry. Studies on hemilabile P,N donor ligands and on the ion-pair behaviour of cationic Pd(II) complexes have led to the full characterization of complexes with η1-allyl ligands. This still rare bonding mode for the allyl ligand in palladium chemistry allows facile insertion of CO into the Pd-C σ-bond, in contrast to the situation in related η3-allyl Pd(II) complexes. In order to develop new homogeneous catalysts for the selective dimerization and oligomerization of ethylene, a range of Ni(II) complexes have been prepared with new chelating P,N ligands where P represents a phosphine, phosphinite or phosphonite donor group and N a pyridine or oxazoline moiety. Finally, we shall examine bottom-up approaches to the formation of new nanomaterials of magnetic or catalytic interest by covalent anchoring of metal complexes and clusters into mesoporous materials using functional phosphine or alkyne ligands containing an alkoxysilyl group. 相似文献
63.
Daniel Carmona Joaquina Ferrer María Pilar Lamata Luis A. OroHans-Heinrich Limbach Gerd SchererJos Elguero María Luisa Jimeno 《Journal of organometallic chemistry》1994,470(1-2):271-274
The Arrhenius equation corresponding to the process P---Ag+P*---Ag*→---P---Ag*+P*---Ag has been determined for [(η6-p-cymene)Ru(μ-pz)3Ag(PPh3)] (1) by complete line-shape analysis of the 31P NMR spectra between −40°C and +30°C. It has the form K = 1011.8± e(−46±5 kJ mol−1/RT). The preexponential term, log A = 11.8 corresponds to a small activation entropy, whereas the activation energy, 46 kJ mol−1 is comparable to those determined for other phosphorus—metal compounds. 相似文献
64.
The New Data for the Reaction of Arylenedioxy Trihalogenophosphoranes with Alkyl- and Arylacetylenes
Vladimir F. Mironov Alfiya A. Shtyrlina Ravil R. Petrov Tamara A. Baronova Fedor F. Alekseev Elena N. Varaksina 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1381-1385
The new data concerning the reaction between substituted arylenedioxy trihalogenophosphoranes and monoalkyl- or arylacetylenes are summarized. The reaction leads to formation of six-membered heterocycles-2-oxo-4-R-benzo[ e ]-1,2-oxaphosphorin-3-enes. The substituent effects in the phosphorane and acetylene molecules on the ipso -substitution and halogenation regiochemistry are discussed. The ipso -substitution of tert -butyl group on chlorine and the exchange of bromine on chlorine and iodine on hydrogen have been observed, along with formation of benzophosphorines. The interaction of tetrachloro- ortho -benzoquinone with phosphorus trichloride and arylacetylenes is proposed as a new modification of the reaction leading to the formation of benzo[ e ]-1,2-oxaphosphorines. The structures of some benzo[ e ]-1,2-oxaphosphorines are determined by the single crystal X-ray diffraction. 相似文献
65.
Mohammad Reza Islami Zahra Hassani Hassan Sheibani 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2547-2554
Phthalimide or succinimide undergo a reaction with dialkyl acetylenedicarboxylates and triphenylphosphine to produce highly-functionalized stable heterocyclic phosphorus ylides in good yields in water-tetrahydrofuran (6:1). This methodology is of interest because of the use of water as solvent, thus minimizing the cost, operational hazards, and environmental pollution. 相似文献
66.
67.
68.
Malek Taher Maghsoodlou Sayyed Mostafa Habibi Khorasani Nourollah Hazeri Mahmoud Nassiri Reza KaKaei Ghasem Marandi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):553-560
Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of strong NH-acids, such as imidazole, 2-methylimidazole, 4-methylimidazole, 2-ethylimidazole, benzimidazole, and 5,6-dimethylbezimidazole. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond resulting from the conjugation of the ylide moiety with the adjacent carbonyl group. 相似文献
69.
Dr. Damián Padín Prof. Jesús A. Varela Prof. Carlos Saá 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(33):7470-7478
Ruthenium vinyl carbenes derived from Cp/Cp*RuCl-based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5-pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs-type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α-unsubstituted and α-substituted alkynals showcases the peculiarities of these intermediates. Although Z-vinyl dihydrooxazines are preferentially obtained with the former, Z-vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η3-coordination mode of the ruthenium vinyl carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species. 相似文献
70.