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991.
Huang HC Lee JF Chao HP Yeh PW Yang YF Liao WL 《Journal of colloid and interface science》2005,286(1):127-133
The influence of natural organic matter (NOM) constituents on contaminant distribution coefficients was evaluated by determining the Koc values of aromatic and aliphatic organic compounds (solutes) with clays modified with both aromatic- and aliphatic-rich organic constituents. The studied compounds consisted of naphthalene, phenanthrene, n-pentane, and 2,3,4-trimethylmethane; the solid samples comprised two clays with little organic content, kaolinite and Ca-montmorillonite. Two aliphatic surfactants and three aromatic dyes, sorbed to the clays, served as reference NOM constituents. For solutes of comparable water solubilities, the organic-carbon normalized distribution coefficients (Koc) of the aliphatic solutes between sorbed aliphatic organic matter and aqueous solution slightly exceed those of the aromatic solutes. By contrast, the aromatic solutes exhibited higher Koc values than did the aliphatic compounds with sorbed aromatic-rich organic matter. The difference in Koc values could be attributed to either comparable solubility parameters or the difference in the chemical structure between nonionic organic solutes and specific components of the simulated NOM. The much higher Koc values observed for the aromatic solutes indicate that the NOM composition is a major factor determining the NOC environmental distribution. 相似文献
992.
Han Nim Choi Jee Hoon Han Ji Ae Park Joong Min Lee Won‐Yong Lee 《Electroanalysis》2007,19(17):1757-1763
A highly sensitive and selective glucose biosensor has been developed based on immobilization of glucose oxidase within mesoporous carbon nanotube–titania–Nafion composite film coated on a platinized glassy carbon electrode. Synergistic electrocatalytic activity of carbon nanotubes and electrodeposited platinum nanoparticles on electrode surface resulted in an efficient reduction of hydrogen peroxide, allowing the sensitive and selective quantitation of glucose by the direct reduction of enzymatically‐liberated hydrogen peroxide at ?0.1 V versus Ag/AgCl (3 M NaCl) without a mediator. The present biosensor responded linearly to glucose in the wide concentration range from 5.0×10?5 to 5.0×10?3 M with a good sensitivity of 154 mA M?1cm?2. Due to the mesoporous nature of CNT–titania–Nafion composite film, the present biosensor exhibited very fast response time within 2 s. In addition, the present biosensor did not show any interference from large excess of ascorbic acid and uric acid. 相似文献
993.
994.
Si-Geun Lee Young-Whan Park Dae-Woo Nam Hyosun Lee Kwang Ho Song 《Journal of organometallic chemistry》2004,689(16):2586-2592
Methylene-bridged ansa-metallocene complexes bearing substituents on the cyclopentadienyl (Cp) and fluorenyl (Flu) moieties, namely methylene[9-(2,7-di-tert-butyl)fluorenyl(2-(1,3-dimethylcyclopentadienyl))]zirconium dichloride (1a) and its analogue, methylene[(9-(2,7-di-tert-butyl)fluorenyl(2-(1-methyl-3-phenyl)cyclopentadienyl))]zirconium dichloride (2a), have been prepared from (2,7-di-tert-butyl)-9-prop-2-ynyl-9H-fluorene (2). This procedure includes the use of 3-bromo-1-propyne which affords the methylene bridging unit by way of an intermolecular Pauson-Khand reaction in which norbornadiene and a pendant alkyne cyclize to form a ring that later becomes a substituted cyclopentadienyl group. Ethylene-norbornene (E-N) copolymerization was then carried out using these new complexes (1a and 1b) in the presence of methylaluminoxane (MAO) as a cocatalyst; these activities can be compared to that of isopropylene[9-fluorenyl-cyclopentadienyl]zirconium dichloride (3a). The activity of catalyst 1a was comparable to that of 3a but much higher than that of 2a. In addition, 1a shows higher norbornene insertion performance, and gives an E-N copolymer with a higher glass transition temperature (Tg) than 2a under identical conditions; both 1a and 2a give a lower Tg polymer than 3a does. 相似文献
995.
Four new triphenylgermylruthenium carbonyl compounds HRu(CO)4GePh3, 14; Ru(CO)4(GePh3)2, 15; Ru2(CO)8(GePh3)2, 16; and Ru3(CO)9(GePh3)3(μ-H)3, 17 were obtained from the reaction of Ru(CO)5 with Ph3GeH in hexane solvent at reflux, 68 °C. The major product 14 was formed by loss of CO from the Ru(CO)5 and an oxidative addition of the GeH bond of the Ph3GeH to the metal atom. This six coordinate complex contains one terminal hydrido ligand. Compound 15 is formed from 14 and contains two trans-positioned GePh3 ligands in the six coordinate complex. Compound 16 contains two Ru(CO)4(GePh3) fragments joined by an Ru–Ru single bond. Compound 17 contains a triangular cluster of three ruthenium atoms with three bridging hydrido ligands and one terminal GePh3 ligand on each metal atom. When heated to 125 °C, 14 was converted to the new triruthenium compound Ru3(CO)10(μ-GePh2)2, 18. Compound 18 consists of a triangular tri-ruthenium cluster with two GePh2 ligands bridging two different edges of the cluster and one bridging CO ligand. Ru3(CO)12 was found to react with Ph3GeH at 97 °C to yield three products: 15, and two new compounds Ru3(CO)9(μ-GePh2)3, 19 and Ru2(CO)6(μ-GePh2)2(GePh3)2, 20 were obtained. Compound 19 is similar to 18 having a triangular tri-ruthenium cluster but has three bridging GePh2 ligands, one on each Ru–Ru bond. Compound 20 contains only two ruthenium atoms joined by a single Ru–Ru bond that has two bridging GePh2 ligands and a terminal GePh3 ligand on each metal atom. All compounds were characterized by a combination of IR, 1H NMR, single-crystal X-ray diffraction analyses.
This report is dedicated to Professor Dieter Fenske on the occasion of his 65th birthday for his many pioneering contributions
to the chemistry of metal chalcogenide cluster complexes. 相似文献
996.
We report the details of the first total synthesis of erythromycin B using two different strategies for the end game. The first of these follows a classical approach in which the desosamine and cladinose residues are sequentially appended to a macrocyclic lactone, which was formed by cyclization of a seco acid derivative, to give a bis-glycosylated macrolide intermediate that is converted into erythromycin B. The second strategy features an abiotic approach in which a seco acid bearing a desosamine residue is cyclized to give a monoglycosylated macrocyclic lactone that is then transformed into erythromycin B via a sequence of steps involving refunctionalizations and a glycosylation to introduce the cladinose moiety. Attempts to prepare a bis-glycosylated seco acid by de novo synthesis were unsuccessful. The syntheses of the key seco acid intermediates feature the oxidative transformation of a furan containing C(3)-C(10) to provide a dioxabicyclo[3.3.1]nonenone that served as a template on which to create the stereocenters at C(6) and C(8). A stereoselective aldol reaction was used to establish the C(11)-C(15) segment, and a stereoselective crotylation was implemented to introduce the propionate subunit comprising C(1)-C(2). 相似文献
997.
Carina Hey Pui Cheung Jianchao Xu Chi Lung Lee Yanfeng Zhang Ruohan Wei Donald Bierer Xuhui Huang Xuechen Li 《Chemical science》2021,12(20):7091
Herein, we report the development of a facile synthetic strategy for constructing diverse peptide structural architectures via chemoselective peptide ligation. The key advancement involved is to utilize the benzofuran moiety as the peptide salicylaldehyde ester surrogate, and Dap–Ser/Lys–Ser dipeptide as the hydroxyl amino functionality, which could be successfully introduced at the side chain of peptides enabling peptide ligation. With this method, the side chain-to-side chain cyclic peptide, branched/bridged peptides, tailed cyclic peptides and multi-cyclic peptides have been designed and successfully synthesized with native peptidic linkages at the ligation sites. This strategy has provided an alternative strategic opportunity for synthetic peptide development. It also serves as an inspiration for the structural design of PPI inhibitors with new modalities.Methods of introducing peptide salicylaldehyde esters and hydroxyl amine functionality into the peptide side chain have been developed. Diverse peptide structural motifs were constructed via ligation with native amide linkages at the ligation sites. 相似文献
998.
999.
Phosphoinositide-based signaling processes are crucially important in intracellular signal transduction events. Inositol phosphate analogues have been useful in probing the structure-activity relationships between inositol phosphates and biomacromolecules, and in studying biological functions of newly found inositol phosphates. Thus, a systematic and ready access to inositol stereoisomers is highly desirable. And practical and convenient syntheses of conduritols and related compounds are also important because of their biological activities and their synthetic utilities in the preparation of other bioactive molecules. We herein report the first syntheses of all possible diastereomers of conduritol and various derivatives of eight inositol stereoisomers in high enantiopurity from myo-inositol, which involve efficient enzymatic resolution of the intermediates conduritol B and C derivatives, followed by oxidation-reduction or the Mitsunobu reaction, and cis-dihydroxylation in stereo- and regioselective manners. 相似文献
1000.
The reaction of Mn(2)(CO)(7)(mu-S(2)), 1, with Pt(PPh(3))(2)(PhC(2)Ph) yielded the new complex, Mn(2)(CO)(6)Pt(PPh(3))(2)(mu(3)-S)(2), 3, by loss of CO and insertion of a Pt(PPh(3))(2) group into the S-S bond of 1. Complex 3 was characterized crystallographically and was found to consist of an open Mn(2)Pt cluster with one Mn-Mn bond, 2.8154(14) A, one Mn-Pt bond, 2.9109(10) A, and two triply bridging sulfido ligands. Compound 3 reacts with CO to form adduct Mn(2)(CO)(6)(mu-CO)Pt(PPh(3))(2)(mu(3)-S)(2), 4. Compound 4 also contains an open Mn(2)Pt cluster with two triply bridging sulfido ligands but has only one metal-metal bond, Mn-Mn = 2.638(2) A. Under nitrogen, compound 4 readily loses CO and reverts back to 3. 相似文献