全文获取类型
收费全文 | 3726篇 |
免费 | 177篇 |
国内免费 | 36篇 |
专业分类
化学 | 2462篇 |
晶体学 | 27篇 |
力学 | 111篇 |
数学 | 689篇 |
物理学 | 650篇 |
出版年
2023年 | 22篇 |
2022年 | 38篇 |
2021年 | 70篇 |
2020年 | 70篇 |
2019年 | 91篇 |
2018年 | 83篇 |
2017年 | 56篇 |
2016年 | 132篇 |
2015年 | 126篇 |
2014年 | 167篇 |
2013年 | 233篇 |
2012年 | 288篇 |
2011年 | 336篇 |
2010年 | 183篇 |
2009年 | 168篇 |
2008年 | 250篇 |
2007年 | 230篇 |
2006年 | 211篇 |
2005年 | 195篇 |
2004年 | 167篇 |
2003年 | 155篇 |
2002年 | 120篇 |
2001年 | 71篇 |
2000年 | 56篇 |
1999年 | 34篇 |
1998年 | 36篇 |
1997年 | 30篇 |
1996年 | 36篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 33篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1961年 | 3篇 |
1942年 | 6篇 |
1940年 | 3篇 |
排序方式: 共有3939条查询结果,搜索用时 250 毫秒
101.
Fondo M García-Deibe AM Corbella M Ruiz E Tercero J Sanmartín J Bermejo MR 《Inorganic chemistry》2005,44(14):5011-5020
The new tetranuclear carbonate complex [Cu2L)2(CO3)] x 8H2O (1 x 8H2O) (H3L = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) has been obtained by two different synthetic routes and fully characterized. Recrystallization of 1 x 8H2O in methanol yields single crystals of {[(Cu2L)2(CO3)]}2 x 12H2O (1 x 6H2O), suitable for X-ray diffraction studies. The crystal structure of 1 x 6H2O shows two crystallographically different tetranuclear molecules in the asymmetric unit, 1a and 1b. Both molecules can be understood as self-assembled from two dinuclear [Cu2L]+ cations, joined by a mu4-eta(2):eta(1):eta(1) carbonate ligand. The copper atoms of each crystallographically different [(Cu2L)2(CO3)] molecule present miscellaneous coordination polyhedra: in both 1a and 1b, two metal centers are in square pyramidal environments, one displays a square planar chromophore and the other one has a geometry that can be considered as an intermediate between square pyramid and trigonal bipyramid. Magnetic studies reveal net intramolecular ferromagnetic coupling between the metal atoms. Density functional calculations allow the assignment of the different magnetic coupling constants and explain the unexpected ferromagnetic behavior, because of the presence of an unusual NCN bridging moiety and countercomplementarity of the phenoxo (or carbonate) and NCN bridges. 相似文献
102.
Fandos R Hernández C Otero A Rodríguez A Ruiz MJ Terreros P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(3):671-677
Titanium complexes with chelating alkoxide ligands [TiCp*(O(2)Bz)(OBzOH)] (1) and [TiCp*(Me)((OCH(2))(2)Py)] (2) were synthesised by reaction of [TiCp*Me(3)] (Cp*=eta(5)-C(5)Me(5)) with 2-hydroxybenzyl alcohol ((HO)(2)Bz) and 2,6-pyridinedimethanol ((HOCH(2))(2)Py), respectively. Complex 1 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) to yield the early-late heterobimetallic complexes [TiCp*(O(2)Bz)(2)M(cod)] [M=Rh (3), Ir (4)]. Carbon monoxide readily replaces the COD ligand in 3 to give the rhodium dicarbonyl derivative [TiCp*(O(2)Bz)(2)Rh(CO)(2)] (5). Compound 2 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) with protonolysis of a Tibond;Me bond to give [TiCp*((OCH(2))(2)Py)(mu-O)M(cod)] [M=Rh (6), Ir (7)]. The molecular structures of complexes 3, 5 and 7 were established by single-crystal X-ray diffraction studies. 相似文献
103.
Julio Belmar Claudio Jimnez C. Ruiz‐Prez F. S. Delgado Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):o599-o601
In the title compound, C15H20N2O, the bond distances and angles are consistent with the presence of the hydroxy tautomer. This tautomer was unambiguously determined by the clear presence of a H atom bonded to oxygen, as well as the total absence of any residual electron density around the N atom in the heterocycle, thus precluding any possibility of desmotropism. 相似文献
104.
Rodrigues e Silva AA da Silva Góes AJ de Lima WT de Souza Maia MB 《Chemical & pharmaceutical bulletin》2003,51(12):1351-1355
The search for new anti-inflammatory drugs has been constant in several research centers. The use of the Bioisostery concept allows the elaboration of new bioactive compounds with different properties through the introduction of substitute groups in one or more positions of a main molecule with known biological activity. Preliminary works accomplished at our laboratory with 2,4-thiazolidinedione isosters demonstrated inhibitory activity on edema formation for N-tryptophyl-5-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2,4-thiazolidinedione (GS28) and N-tryptophyl-5-(3,5-di-tert-butyl-4-hydroxybenzylidene) rhodanine (GS26). We verified the antiedematogenic and ulcerogenic activity of these two compounds in Wistar rats. The carrageenan induced paw edema suffered significant (p<0.05) inhibition (28.36% on average) for GS28 (100 mg/kg; v.o.) during the entire time of the experiment. GS26 (50 and 100 mg/kg; v.o.) significantly inhibited (p<0.05) the paw edema dextran induced (22.1 and 27.8%, for the respective doses) after 180 min. The compounds GS26 and GS28 did not show ulcerogenic activity on gastric mucous. The results suggest antiedematogenic action for both compounds without the appearance of gastric lesions. 相似文献
105.
Arantzazu Zabala?Ruiz Dominik?Brühwiler Takayuki?Ban Gion?CalzaferriEmail author 《Monatshefte für Chemie / Chemical Monthly》2005,136(1):77-89
Summary. A convenient synthesis of zeolite L is presented. The size of the crystals can be tuned between 30 and 6000nm, spanning a volume range of seven orders of magnitude. The zeolite L crystals, which typically feature a cylindrical morphology, are synthesized with various aspect ratios ranging from elongated to disc-shaped. The importance of obtaining zeolite crystals with well-defined size and morphology is discussed in view of potential applications of zeolite L containing organic dye molecules as guests.This revised version was published online in February 2005. In the previous version the issue was not marked as a special issue, and the issue title and the editor was missing 相似文献
106.
The stability and electronic properties of highly packed 1-hexyl-naphthalene (HNap) molecular wire on Si(0 0 1) have been studied with first principles DFT method. HNap assembles into a 1D arrangement on the Si(0 0 1)[2 × 1] surface on which molcules adopt a commensurate structure along a dimer row with an intermolecular distance of 3.8 Å. HNap is attached to the surface through the hexyl chain, and stands normal to the surface. This highly packed structure leads to the formation of delocalized π-orbitals over the entire wire but essentially localized on the naphthalene counterpart, and well separated from the Si surface states. Cohesion energy within the wire arises from a significant attraction between hexyl chains, and to a weaker stabilizing π–π interaction between naphthalenes. 相似文献
107.
108.
Alvarez CM Alvarez MA García-Vivó D García ME Ruiz MA Saáez D Falvello LR Soler T Herson P 《Dalton transactions (Cambridge, England : 2003)》2004,(24):4168-4179
The new hydride complexes [Mo2Cp2(mu-H)(mu-PHR)(CO)4] having bulky substituents (R = 2,4,6-C(6)H2tBu3= Mes*, R = 2,4,6-C6H2Me3= Mes) have been prepared in good yield by addition of Li[PHR] to the triply bonded [Mo2Cp2(CO)4] and further protonation of the resulting anionic phosphide complex [Mo2Cp2(mu-PHR)(CO)4]-. Protonation of the Mes* compound with either [H(OEt2)2][B{3,5-C6H3(CF3)2}4] or HBF4.OEt2 gives the cationic phosphinidene complex [Mo2Cp2(mu-H)(mu-PMes*)(CO)4]+ in high yield. In contrast, protonation of the analogous hydride compounds with Mes or Cy substituents on phosphorus give the corresponding unsaturated tetracarbonyls [Mo2Cp2(mu-PHR)(CO)4]+, which are unstable at room temperature and display a cis geometry. Decomposition of the latter give the electron-precise pentacarbonyls [Mo2Cp2(mu-PHR)(mu-CO)(CO)4]+, also displaying a cis arrangement of the metal fragments. In the presence of BF4- as external anion, fluoride abstraction competes with carbonylation to yield the neutral fluorophosphide hydrides [Mo2Cp2(mu-H)(mu-PFR)(CO)4]. Similar results were obtained in the protonation reactions of the hydride compounds having a Ph substituent on phosphorus. In that case, using HCl as protonation reagent gave the chloro-complex [Mo2ClCp2(mu-PHPh)(CO)4] in good yield. The structures and dynamic behaviour of the new compounds are analyzed on the basis of solution IR and 1H, 31P, 19F and 13C NMR data as well as the X-ray studies carried out on [Mo2Cp2(mu-H)(mu-PHMes)(CO)4](cis isomer), [Mo2Cp2(mu-H)(mu-PFMes)(CO)4](trans isomer), [Mo2Cp2(mu-PHCy)(mu-CO)(CO)4](BF4) and [Mo2ClCp2(mu-PHPh)(CO)4]. 相似文献
109.
Cuccia LA Ruiz E Lehn JM Homo JC Schmutz M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(15):3448-3457
The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers). Strong intermolecular interactions of the highly ordered lock-washer subunits of compound 3 results in hierarchical supramolecular self-assembly into protofibrils and fibrils. Compound 3 also forms mechanically stable two-dimensional Langmuir-Blodgett and cast thin films. 相似文献
110.
Oliveira SC Paiva TC Visconti AE Giudici R 《Applied biochemistry and biotechnology》1998,74(3):161-172
Discrimination between different rival models for describing the inhibitory effect of ethanol both on yeast growth and on
fermentation was studied for a continuous process of alcoholic fermentation in a tower reactor with recycling of flocculating
cells. Models tested include linear, parabolic, hyperbolic, exponential, and generalized nonlinear power-law types. The best
expressions were identified under the criteria that all the kinetic parameters should assume acceptable values in a feasible
range and should result in the best fit of the experimental data. The kinetic parameters were estimated from steady-state
data of several sugar concentrations in feeding stream (S0 = 160, 170, 180, 190, 200 g/L), constant dilution rate (D = 0.2 h-1), recycle ratio (α = 13.6), and temperature (T = 30°C). The best model for the yeast growth was of power-law type, whereas
for the product formation the best model was of linear type. These models were able to reproduce the trends of the process
variables satisfactorily. 相似文献