全文获取类型
收费全文 | 447篇 |
免费 | 13篇 |
国内免费 | 13篇 |
专业分类
化学 | 296篇 |
晶体学 | 5篇 |
力学 | 4篇 |
数学 | 120篇 |
物理学 | 48篇 |
出版年
2021年 | 5篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 3篇 |
2013年 | 24篇 |
2012年 | 20篇 |
2011年 | 15篇 |
2010年 | 23篇 |
2009年 | 9篇 |
2008年 | 37篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 14篇 |
2004年 | 32篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 12篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 10篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有473条查询结果,搜索用时 234 毫秒
81.
Henares TG Funano S Terabe S Mizutani F Sekizawa R Hisamoto H 《Analytica chimica acta》2007,590(2):173-179
Gastrodin is a bioactive constituent of rhizome in Gastrodia elata Blume (Orchidaceae) The aim of this study is to develop a rapid and sensitive liquid chromatographic method coupled to microdialysis sampling system to measure the unbound of gastrodin in rat blood, brain and bile. Microdialysis probes were simultaneously inserted into the jugular vein, brain striatum and bile duct of each anesthetized rat for sampling after the administration of gastrodin (100 or 300 mg kg−1) through the femoral vein. Separation of unbound gastrodin from various biological fluids was applied to an RP-select B column (250 mm × 4.6 mm i.d., 5 μm). The mobile phase consisted of acetonitrile–50 mM potassium dihydrogen phosphate buffer–triethylamine (5:95:0.1, v/v/v, adjusted to pH 2.5 with orthophosphoric acid) with a flow rate of 1 mL min−1. The UV detector wavelength was set at 221 nm. Fifteen minutes after the administration, the gastrodin reached the peak concentration in brain and bile. In addition, the results indicate that gastrodin penetrates the blood-brain barrier (BBB) and goes through hepatobiliary excretion. 相似文献
82.
This paper describes a high throughput LC-MS-MS method for the screening of 75 basic drugs in equine plasma at sub-ppb levels. The test scope covers diversified classes of drugs including some alpha- and beta-blockers, alpha- and beta-agonists, antihypotensives, antihypertensives, analgesics, antiarrhythmics, antidepressants, antidiabetics, antipsychotics, antiulcers, anxiolytics, bronchodilators, CNS stimulants, decongestants, sedatives, tranquilizers and vasodilators. A plasma sample was first deproteinated by addition of trichloroacetic acid. Basic drugs were then extracted by solid-phase extraction (SPE) using a Bond Elut Certify cartridge, and analysed by LC-MS-MS in positive electrospray ionization (+ESI) and multiple reaction monitoring (MRM) mode. Liquid chromatography was performed using a short C(8) column (3.3 cm L x 2.1mm ID with 3 microm particles) to provide fast analysis time. The overall instrument turnaround time was 8 min, inclusive of post-run and equilibration time. No interference from the matrices at the expected retention times of the targeted masses was observed. Over 60% of the drugs studied gave limits of detection (LoD) at or below 25 pg/mL, with some LoDs reaching down to 0.5 pg/mL. The inter-day precision for the relative retention times ranged from 0.01 to 0.54%, and that for the relative peak area ratios (relative to the internal standard) ranged from 4 to 37%. The results indicated that the method has acceptable precision to be used on a day-to-day basis for qualitative identification. 相似文献
83.
Kuznetsova LA Bazou D Coakley WT 《Langmuir : the ACS journal of surfaces and colloids》2007,23(6):3009-3016
The formation of a two-dimensional aggregate of 25 microm latex particles in a 1.5 MHz ultrasound standing wave (USW) field and its disintegration in a flow were studied. The aggregate was held in the pressure node plane, which allowed continuous microscope observation and video recording of the processes. The trajectories and velocities of the particles approaching the formation site were analyzed by particle image velocimetry (PIV). Since the direct radiation force on the particles dominated the drag due to acoustic streaming, the acoustic pressure profile in the vicinity of the aggregate was quantifiable. The drag coefficients D(coef) for 2- to 485-particle aggregates were estimated from the balance of the drag force FD and the buoyancy-corrected gravitational force during sedimentation on termination of the ultrasound when the long axis of the aggregate was in the vertical plane. D(coef) were calculated from FD as proportional to the aggregate velocity. Experiments on particle detachment by flow (in-plane velocity measured by PIV) from horizontal aggregates suspended in deionized water and CaCl2 solution of different concentrations showed that the mechanical strength of the aggregates depended on the acoustic pressure amplitude P0 and ionic strength of the solution. In deionized water the flow velocity required to detach the first single particle from an aggregate increased from 1 mm s-1 at P0 = 0.6 MPa to 4.2 mm s-1 at P0 = 1.4 MPa. The balance of forces acting on particles in a USW trap is discussed. The magnitude of the shear stress employed ( approximately 0.05 Pa) and separation forces suggests that this technique can be applied to studying the mechanical responses of cell aggregates to hydrodynamic flow, where cell-cell interaction can be separated from the effects of solid substrata. 相似文献
84.
Flood C Cosgrove T Qiu D Espidel Y Howell I Revell P 《Langmuir : the ACS journal of surfaces and colloids》2007,23(5):2408-2413
Solvent relaxation NMR and small-angle neutron scattering have been used to characterize adsorbed poly(ethylene oxide) (PEO) layers on silica at a range of surfactant and electrolyte concentrations. Below the critical aggregation concentration (cac), the results suggest that sodium dodecyl sulfate (SDS) interacts relatively weakly, perhaps analogously to a simple salt reducing the solvency of PEO. This is evidenced by a decrease in the adsorbed layer thickness combined with an increase in the bound fraction, although the total adsorbed amount is not greatly affected. The layer thickness goes through a minimum at the cac, after which further SDS addition results in the formation of PEO/SDS aggregates that repel each other and, hence, tend to desorb. The adsorbed amount therefore decreases, from 0.7 mg m(-2) initially to 0.2 mg m(-2) with 32 mM SDS. The aggregates that remain adsorbed also repel, and hence, there is an increase in the layer thickness and the persistence length, while the bound fraction is reduced. In comparison, the effects of electrolyte at the ionic strength studied are relatively minimal. There is, however, evidence that the repulsions between adsorbed PEO/SDS aggregates are partially screened, allowing them to approach each other more readily. This leads to a contraction of the adsorbed layer when the SDS concentration is sufficiently high. 相似文献
85.
86.
Qiu D Cosgrove T Howe AM Dreiss CA 《Langmuir : the ACS journal of surfaces and colloids》2006,22(2):546-552
The structure factors of colloidal silica dispersions at rather high volume fractions (from 0.055 to 0.22) were measured by small-angle X-ray scattering and fitted with both the equivalent hard-sphere potential model (EHS) and the Hayter-Penfold/Yukawa potential model (HPY). Both of these models described the interactions in these dispersions successfully, and the results were in reasonable agreement. The strength and range of the interaction potentials decreased with increasing particle volume fractions, which suggests shrinkage of the electrical double layer arising from an increase in the counterion concentration in the bulk solution. However, the interactions at the average interparticle separation increased as the volume fraction increased. The interaction ranges (delta) determined by the two models were very similar. Structure factors were also used to determine the size and volume fraction of the particles. The values of the size obtained from the structure factors were slightly larger than those obtained from the form factors; this difference is ascribed to the nonspherical shape and polydispersity of the colloidal particles. The volume fractions measured by these two methods were very similar and are both in good agreement with the independently measured results. 相似文献
87.
Dynamic shim updating on the human brain 总被引:1,自引:0,他引:1
Koch KM McIntyre S Nixon TW Rothman DL de Graaf RA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,180(2):286-296
Dynamic alteration of shim settings during a multi-slice imaging experiment can improve static magnetic-field homogeneity over extended volumes. In this report, a pre-emphasized dynamic shim updating (DSU) system capable of rapidly updating all non-degenerate zeroth through second-order shims is presented and applied to high-field multi-slice imaging studies on the human brain. DSU is utilized in both non-oblique and oblique slicing geometries while updating in-plane and through-slice shims. Image-based magnetic-field maps are used to quantify homogeneity improvements and comparisons are made on a slice-specific basis between static global shimming and increasing orders of shim inclusion utilized DSU. The influence of oblique slicing geometry on DSU-utilized global homogeneity is also quantified computationally. Finally, the effect of DSU on susceptibility artifact reduction in single-shot axial-sliced EPI is analyzed using experimental acquisitions. 相似文献
88.
Ryan T 《Micron (Oxford, England : 1993)》2004,35(3):161-171
The anatomy and functions of the blood and lymph vessels of human skin are described. Variation in these due to site, ageing and events during life consequent to exposure to a threatening environment are emphasised. Gradual atrophy and greater heterogeneity are features of ageing. Responses to injury and repair are complex and the interaction of mechanical signals distorting skin cells with numerous chemical signals are referred to. The lymphatics are part of an immunosurveillance system to monitor skin barrier penetration. The review attempts to draw attention to key recent advances in our understanding of the cytokine and growth factor production of the skin in the context of previous mainly physiological reviews especially influenced by 50 years of clinical practice as a dermatologist with an eye on both the skin and the fields of microcirculation and lymphology. 相似文献
89.
Directed evolution of high-affinity antibody mimics using mRNA display 总被引:11,自引:0,他引:11
Xu L Aha P Gu K Kuimelis RG Kurz M Lam T Lim AC Liu H Lohse PA Sun L Weng S Wagner RW Lipovsek D 《Chemistry & biology》2002,9(8):933-942
We constructed a library of >10(12) unique, covalently coupled mRNA-protein molecules by randomizing three exposed loops of an immunoglobulin-like protein, the tenth fibronectin type III domain (10Fn3). The antibody mimics that bound TNF-alpha were isolated from the library using mRNA display. Ten rounds of selection produced 10Fn3 variants that bound TNF-alpha with dissociation constants (K(d)) between 1 and 24 nM. After affinity maturation, the lowest K(d) measured was 20 pM. Selected antibody mimics were shown to capture TNF-alpha when immobilized in a protein microarray. 10Fn3-based scaffold libraries and mRNA-display allow the isolation of high-affinity, specific antigen binding proteins; potential applications of such binding proteins include diagnostic protein microarrays and protein therapeutics. 相似文献
90.
Bhargava S Kitadai K Masashi T Drumm DW Russo SP Yam VW Lee TK Wagler J Mirzadeh N 《Dalton transactions (Cambridge, England : 2003)》2012,41(16):4789-4798
A mixture of cyclic gold(I) complexes [Au(2)(μ-cis-dppen)(2)]X(2) (X = OTf 1, PF(6)3) and [Au(cis-dppen)(2)]X (X = OTf 2, PF(6)4) is obtained from the reaction of [Au(tht)(2)]X (tht = tetrahydrothiophene) with one equivalent of cis-dppen [dppen = 1,2-bis(diphenylphosphino)ethylene]. The analogous reaction with trans-dppen or dppa [dppa = bis(diphenylphosphino)acetylene] affords the cyclic trinuclear [Au(3)(μ-trans-dppen)(3)]X(3) (X = OTf 11, PF(6)12) and tetranuclear [Au(4)(μ-dppa)(4)]X(4) (X = OTf 13, PF(6)14, ClO(4)15) gold complexes, respectively. Recrystallization of 15 from CH(2)Cl(2)/MeOH yielded a crystal of the octanuclear gold cluster [Au(8)Cl(2)(μ-dppa)(4)](ClO(4))(2)16. Attempts to prepare dicationic binuclear gold(II) species from the reaction of a mixture of 3 and 4 with halogens gave a mixture of products, the components of which confirmed to be acyclic binuclear gold(I) [Au(2)X(2)(cis-dppen)] (X = I 5, Br 7) and cyclic mononuclear gold(III) [AuX(2)(cis-dppen)]PF(6) (X = I 6, Br 8) complexes. Complexes 11-14 reveal weak emission in butyronitrile glass at 77 K, but they are non-emissive at room temperature. Ab initio modelling was performed to determine the charge state of the gold atoms involved. Extensive structural comparisons were made to experimental data to benchmark these calculations and rationalize the conformations. 相似文献