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991.
992.
H Han L Lu Q Wang M Zhu C Yuan S Xing X Fu 《Dalton transactions (Cambridge, England : 2003)》2012,41(36):11116-11124
Five oxovanadium(iv) complexes, which were divided into two groups, [V(IV)O(bhbb, nhbb)(H(2)O)(2)] (tridentate ligands: H(2)bhbb = 2-(5-bromo-2-hydroxylbenzylideneamino)benzoic acid, ; H(2)nhbb = 2-(5-nitro-2-hydroxylbenzylideneamino)benzoic acid, ) and [V(IV)O(cpmp, bpmp, npmp)(2)] (bidentate ligands: Hcpmp = 4-chloro-2-((phenylimino)methyl)phenol, ; Hbpmp = 4-bromo-2-((phenylimino)methyl)phenol, ; Hnpmp = 4-nitro-2-((phenylimino)methyl) phenol, ) have been prepared and characterized by elemental analysis, infrared, UV-visible and electrospray ionization mass spectrometry. The coordination in [V(IV)O(bhbb)(H(2)O)(2)] () was confirmed by X-ray crystal structure analysis. The oxidation state of V(iv) with d(1) configuration in was confirmed by EPR. The speciation of VO/H(2)bhbb in methanol-aqueous solution was investigated by potentiometric pH titrations. The result indicated that the main species were [V(IV)O(bhbb)(OH)](-) and [V(IV)O(bhbb)(OH)(2)](2-) at the pH range 7.0-7.4. The structure-activity relationship of the vanadium complexes in inhibiting protein tyrosine phosphatases (protein tyrosine phosphatase 1B, PTP1B; T-cell protein tyrosine phosphatase, TCPTP; megakaryocyte protein-tyrosine phosphatase, PTP-MEG2; Src homology phosphatase 1, SHP-1 and Src homology phosphatase 2, SHP-2) was investigated. The oxovanadium(iv) complexes were potent inhibitors of PTP1B, TCPTP, PTP-MEG2, SHP-1 and SHP-2, but exhibited different inhibitory abilities over different PTPs. Complexes and displayed better selectivity to PTP1B over the other four PTPs. Kinetic data showed that complex inhibited PTP1B, TCPTP and SHP-1 with a noncompetitive inhibition mode, but a classical competitive inhibition mode for PTP-MEG2 and SHP-2. The results demonstrated that both the structures of vanadium complexes and the conformations of PTPs influenced PTP inhibition activity. The proper modification of the organic ligand moieties may result in screening potent and selective vanadium-based PTP1B inhibitors. 相似文献
993.
Manual shaking-enhanced, ultrasound-assisted emulsification microextraction (MS-USAEME) combined with ultraperformance liquid chromatography (UPLC) with UV detection has been developed for the determination of five endocrine-disrupting phenols (EDPs) in seawater samples and detergent samples: 4-tert-butylphenol (4-t-BP), 4-cumylphenol (4-CP), 4-tert-octylphenol (4-t-OP), 2,4-di-tert-butylphenol (2,4-di-t-BP) and 4-nonylphenol (4-NP). Optimum conditions were found to be: 25 μL 1-bromohexadecane as extraction solvent, 5 mL of aqueous sample and 1 g of NaCl to control the ionic strength; manual shaking for 10 s; ultrasonication for 1 min; centrifugation for 3 min at 5000 rpm (speed). For MS-USAEME, manual shaking for 10 s is essential for effective extraction when the ultrasonic extraction time is as brief as 1 min. The small volume of aqueous sample enhances the effect of manual shaking significantly. For seawater samples, the limit of detection (LOD) was 0.5-2.8 ng mL(-1), the limit of quantification (LOQ) was 1.8-9.3 ng mL(-1) with the relative standard deviation (RSD) in the range 4.2-10.3%. For detergent samples, the LOD was 0.4-2.4 ng mL(-1), LOQ was 1.6-8.2 ng mL(-1) and RSD 4.7-10.0%. The relative recovery was 96-109% for seawater samples and 81-106% for the detergent samples. 相似文献
994.
Dr. Min‐Rui Gao Zhao‐Yang Lin Dr. Jun Jiang Dr. Chun‐Hua Cui Ya‐Rong Zheng Prof. Dr. Shu‐Hong Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(27):8423-8429
We report a first solution strategy for controlled synthesis of Adams’ catalyst (i.e., α‐PtO2) by a facile and totally green approach using H2PtCl6 and water as reactants. The prepared α‐PtO2 nanocrystals (NCs) are ultrasmall in size and have very “clean” surfaces, which can be reduced to Pt NCs easily in ethanol under ambient conditions. Such Adams’ catalysts have been applied as electrocatalysts beyond the field of heterogeneous catalysis. Noticeably, the water‐only synthesized α‐PtO2 NCs and their derivative Pt NCs all exhibit much higher oxygen reduction reaction (ORR) activities and stabilities than that of the state‐of‐art Pt/C electrocatalysts. This study provides an example on the organics‐free synthesis of α‐PtO2 and Pt NCs as promising cathode catalysts for fuel cell applications and, particularly, this simple, straightforward method may open a new way for the synthesis of other “clean” functional nanomaterials. 相似文献
995.
Dr. Sheng‐Liang Zhong Dr. Yang Lu Dr. Min‐Rui Gao Dr. Shu‐Juan Liu Jun Peng Le‐Cheng Zhang Prof. Dr. Shu‐Hong Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5222-5231
A family of monodisperse YF3, YF3:Ce3+ and YF3:Ce3+/Ln3+ (Ln=Tb, Eu) mesocrystals with a morphology of a hollow spindle can be synthesized by a solvothermal process using yttrium nitrate and NH4F as precursors. The effects of reaction time, fluorine source, solvents, and reaction temperature on the synthesis of these mesocrystals have been studied in detail. The results demonstrate that the formation of a hollow spindle‐like YF3 can be ascribed to a nonclassical crystallization process by means of a particle‐based reaction route in ethanol. It has been shown that the fluorine sources selected have a remarkable effect on the morphologies and crystalline phases of the final products. Moreover, the luminescent properties of Ln3+‐doped and Ce3+/Ln3+‐co‐doped spindle‐like YF3 mesocrystals were also investigated. It turns out that Ce3+ is an efficient sensitizer for Ln3+ in the spindle‐like YF3 mesocrystals. Remarkable fluorescence enhancement was observed in Ce3+/Ln3+‐co‐doped YF3 mesocrystals. The mechanism of the energy transfer and electronic transition between Ce3+ and Ln3+ in the host material of YF3 mesocrystals was also explored. The cytotoxicity study revealed that these YF3‐based nanocrystals are biocompatible for applications, such as cellular imaging. 相似文献
996.
通过Stille反应合成了一系列含有均苯四甲酸二酰亚胺受体单元的共轭聚合物P1~P7.该系列聚合物在常见有机溶剂中溶解性良好,在370~600 nm范围内有较强吸收.通过循环伏安法测量其LUMO能级范围在-3.66~-3.90 eV之间,HOMO能级在-5.25~-6.17 eV之间,在同类分子中接近最低值.通过改变主链中噻吩单元的数量和给电子单元,可以调节分子的能隙,使其电化学能隙在2.45~1.55 eV范围内变化.将含均苯四甲酸二酰亚胺受体单元的P1~P7应用于有机太阳能电池中,作为给体材料与PC61BM共混制成本体异质结聚合物电池,器件开路电压普遍较高.其中基于均苯四甲酸二酰亚胺与二噻吩并噻咯的聚合物P7的器件,在AM 1.5 G,86 mW/cm2光照条件下,开路电压为0.72 V,短路电流为1.22 mA/cm2,能量转换效率为0.27%. 相似文献
997.
998.
The neck linker is widely believed to play a critical role in the hand-over-hand walking of conventional kinesin 1. Experiments have shown that change of the neck linker length will significantly change the stepping velocity of the motor. In this paper, we studied this length effect based on a highly simplified chemically powered ratchet model. In this model, we assume that the chemical steps (ATP hydrolysis, ADP and P(i) release, ATP binding, neck linker docking) are fast enough under conditions far from equilibrium and the mechanical steps (detachment, diffusional search and re-attachment of the free head) are rate-limiting in kinesin walking. According to this model, and regarding the neck linker as a worm-like-chain polypeptide, we can calculate the steady state stepping velocity of the motor for different neck linker lengths. Our results show, under the actual values of binding energy between kinesin head and microtubule (~15k(B)T) and the persistence length of neck linker (~0.5 nm), that there is an optimal neck linker length (~14-16 a.a.) corresponding to the maximal velocity, which implies that the length of the wild-type neck linker (~15 a.a.) might be optimally designed for kinesin 1 to approach the largest stepping velocity. 相似文献
999.
An L(2,1)-labelling of a graph G is a function from the vertex set V (G) to the set of all nonnegative integers such that |f(u) f(v)| ≥ 2 if d G (u,v)=1 and |f(u) f(v)| ≥ 1 if d G (u,v)=2.The L(2,1)-labelling problem is to find the smallest number,denoted by λ(G),such that there exists an L(2,1)-labelling function with no label greater than it.In this paper,we study this problem for trees.Our results improve the result of Wang [The L(2,1)-labelling of trees,Discrete Appl.Math.154 (2006) 598-603]. 相似文献
1000.
D Jiang I Rauda S Han S Chen F Zhou 《Langmuir : the ACS journal of surfaces and colloids》2012,28(35):12711-12721
Amyloid β (Aβ) fibrils are present as a major component in senile plaques, the hallmark of Alzheimer's disease (AD). Diffuse plaques (nonfibrous, loosely packed Aβ aggregates) containing amorphous Aβ aggregates are also formed in brain. This work examines the influence of Cu(2+) complexation by Aβ on the aggregation process in the context of charge and structural variations. Changes in the surface charges of Aβ molecules due to Cu(2+) binding, measured with a ζ-potential measurement device, were correlated with the aggregate morphologies examined by atomic force microscopy. As a result of the charge variation, the "colloid-like" stability of the aggregation intermediates, which is essential to the fibrillation process, is affected. Consequently, Cu(2+) enhances the amorphous aggregate formation. By monitoring variations in the secondary structures with circular dichroism spectroscopy, a direct transformation from the unstructured conformation to the β-sheet structure was observed for all types of aggregates observed (oligomers, fibrils, and/or amorphous aggregates). Compared to the Aβ aggregation pathway in the absence of Cu(2+) and taking other factors affecting Aβ aggregation (i.e., pH and temperature) into account, our investigation indicates that formations of amorphous and fibrous aggregates diverge from the same β-sheet-containing partially folded intermediate. This study suggests that the hydrophilic domain of Aβ also plays a role in the Aβ aggregation process. A kinetic model was proposed to account for the effects of the Cu(2+) binding on these two aggregation pathways in terms of charge and structural variations. 相似文献