全文获取类型
收费全文 | 830篇 |
免费 | 19篇 |
国内免费 | 12篇 |
专业分类
化学 | 471篇 |
力学 | 12篇 |
数学 | 258篇 |
物理学 | 120篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 23篇 |
2014年 | 14篇 |
2013年 | 49篇 |
2012年 | 44篇 |
2011年 | 41篇 |
2010年 | 31篇 |
2009年 | 22篇 |
2008年 | 56篇 |
2007年 | 42篇 |
2006年 | 48篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 33篇 |
2002年 | 28篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 21篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有861条查询结果,搜索用时 125 毫秒
691.
692.
Dr. Martin R. L. Paine Dr. Berwyck L. J. Poad Gert B. Eijkel Dr. David L. Marshall Prof. Stephen J. Blanksby Prof. Dr. Ron M. A. Heeren Dr. Shane R. Ellis 《Angewandte Chemie (International ed. in English)》2018,57(33):10530-10534
Mass spectrometry imaging (MSI) enables the spatial distributions of molecules possessing different mass‐to‐charge ratios to be mapped within complex environments revealing regional changes at the molecular level. Even at high mass resolving power, however, these images often reflect the summed distribution of multiple isomeric molecules, each potentially possessing a unique distribution coinciding with distinct biological function(s) and metabolic origin. Herein, this chemical ambiguity is addressed through an innovative combination of ozone‐induced dissociation reactions with MSI, enabling the differential imaging of isomeric lipid molecules directly from biological tissues. For the first time, we demonstrate both double bond‐ and sn‐positional isomeric lipids exhibit distinct spatial locations within tissue. This MSI approach enables researchers to unravel local lipid molecular complexity based on both exact elemental composition and isomeric structure directly from tissues. 相似文献
693.
694.
Kate McLeod Roger St.C. Smart Nicolas H. Voelcker Ron Sekel 《Applied Surface Science》2006,253(5):2644-2651
This paper reports the use of X-ray photoelectron spectroscopy (XPS) to investigate bisphosphonate (BP) adsorption onto plasma sprayed hydroxyapatite (HA) coatings commonly used for orthopaedic implants. BPs exhibit high binding affinity for the calcium present in HA and hence can be adsorbed onto HA-coated implants to exploit their beneficial properties for improved bone growth at the implant interface. A rigorous XPS analysis of pamidronate, a commonly used nitrogenous BP, adsorbed onto plasma sprayed HA-coated cobalt-chromium substrates has been carried out, aimed at: (a) confirming the adsorption of this BP onto HA; (b) studying the BP diffusion profile in the HA coating by employing the technique of XPS depth profiling; (c) confirming the bioactivity of the adsorbed BP. XPS spectra of plasma sprayed HA-coated discs exposed to a 10 mM aqueous BP solution (pamidronate) for periods of 1, 2 and 24 h showed nitrogen and phosphorous photoelectron signals corresponding to the BP, confirming its adsorption onto the HA substrate. XPS depth profiling of the 2 h BP-exposed HA discs showed penetration of the BP into the HA matrix to depths of at least 260 nm. The bioactivity of the adsorbed BP was confirmed by the observed inhibition of osteoclast (bone resorbing) cell activity. In comparison to the HA sample, the HA sample with adsorbed BP exhibited a 25-fold decrease in primary osteoclast cells. 相似文献
695.
Ron Buckmire 《Numerical Methods for Partial Differential Equations》2003,19(3):380-398
It is well known that standard finite‐difference schemes for singular boundary value problems involving the Laplacian have difficulty capturing the singular (??(1/r) or ??(log r)) behavior of the solution near the origin (r = 0). New nonstandard finite‐difference schemes that can capture this behavior exactly for certain singular boundary value problems encountered in theoretical aerodynamics are presented here. These schemes are special cases of nonstandard finite differences which have been extensively researched by Professor Ronald E. Mickens of Clark Atlanta University in their most general form. Several examples of these “Mickens‐type” finite differences that illustrate both their accuracy and utility for singular boundary value problems in both cylindrical and spherical co‐ordinates are investigated. The numerical results generated by the Mickens‐type schemes are compared favorably with solutions obtained from standard finite‐difference schemes. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 380–398, 2003. 相似文献
696.
The least concave majorant, \(\hat F\), of a continuous function F on a closed interval, I, is defined by We present an algorithm, in the spirit of the Jarvis March, to approximate the least concave majorant of a differentiable piecewise polynomial function of degree at most three on I. Given any function F ∈ C4(I), it can be well-approximated on I by a clamped cubic spline S. We show that \(\hat S\) is then a good approximation to \(\hat F\).
We give two examples, one to illustrate, the other to apply our algorithm. 相似文献
$$\hat F\left( x \right) = \inf \left\{ {G\left( x \right):G \geqslant F,Gconcave} \right\},x \in I.$$
697.
Bryn Flinders Emma Beasley Ricky M. Verlaan Eva Cuypers Simona Francese Tom Bassindale Malcolm R. Clench Ron M. A. Heeren 《Journal of the American Society for Mass Spectrometry》2017,28(11):2462-2468
Matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) has been employed to rapidly screen longitudinally sectioned drug user hair samples for cocaine and its metabolites using continuous raster imaging. Optimization of the spatial resolution and raster speed were performed on intact cocaine contaminated hair samples. The optimized settings (100 × 150 μm at 0.24 mm/s) were subsequently used to examine longitudinally sectioned drug user hair samples. The MALDI-MS/MS images showed the distribution of the most abundant cocaine product ion at m/z 182. Using the optimized settings, multiple hair samples obtained from two users were analyzed in approximately 3 h: six times faster than the standard spot-to-spot acquisition method. Quantitation was achieved using longitudinally sectioned control hair samples sprayed with a cocaine dilution series. A multiple reaction monitoring (MRM) experiment was also performed using the ‘dynamic pixel’ imaging method to screen for cocaine and a range of its metabolites, in order to differentiate between contaminated hairs and drug users. Cocaine, benzoylecgonine, and cocaethylene were detectable, in agreement with analyses carried out using the standard LC-MS/MS method. 相似文献
698.
Anjusha Mathew Gert B. Eijkel Ian G. M. Anthony Shane R. Ellis Ron M. A. Heeren 《Journal of mass spectrometry : JMS》2022,57(4):e4820
Time-of-flight (TOF) systems are one of the most widely used mass analyzers in native mass spectrometry (nMS) for the analysis of non-covalent multiply charged bio-macromolecular assemblies (MMAs). Typically, microchannel plates (MCPs) are employed for high mass native ion detection in TOF MS. MCPs are well known for their reduced detection efficiency when impinged by large slow moving ions. Here, a position- and time-sensitive Timepix (TPX) detector has been added to the back of a dual MCP stack to study the key factors that affect MCP performance for MMA ions generated by nMS. The footprint size of the secondary electron cloud generated by the MCP on the TPX for each individual ion event is analyzed as a measure of MCP performance at each mass-to-charge (m/z) value and resulted in a Poisson distribution. This allowed us to investigate the dependency of ion mass, ion charge, ion velocity, acceleration voltage, and MCP bias voltage on MCP response in the high mass low velocity regime. The study of measurement ranges; ion mass = 195 to 802,000 Da, ion velocity = 8.4 to 67.4 km/s, and ion charge = 1+ to 72+, extended the previously examined mass range and characterized MCP performance for multiply charged species. We derived a MCP performance equation based on two independent ion properties, ion mass and charge, from these results, which enables rapid MCP tuning for single MMA ion detection. 相似文献
699.
正交各向异性板壳的弹塑性分析 总被引:1,自引:0,他引:1
用最小二乘配点法对正交各项异性薄板和双曲扁壳的弹性问题进行了分析.文中采用Huber—Mises屈服函数在各向异性问题中的推广形式,把材料的塑性变形作为等效塑性荷载处理,并取双五次样条函数为位移试函数,推出了迭代公式.算例证明,该法精度高、收敛快,所需计算机内存少,是简单、精确、高效的. 相似文献
700.
Donald?F.?SmithEmail author Carl?Schulz Marco?Konijnenburg Mehmet?Kilic Ron?M.?A.?HeerenEmail author 《Analytical and bioanalytical chemistry》2015,407(8):2321-2327
High-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry imaging enables the spatial mapping and identification of biomolecules from complex surfaces. The need for long time-domain transients, and thus large raw file sizes, results in a large amount of raw data (“big data”) that must be processed efficiently and rapidly. This can be compounded by large-area imaging and/or high spatial resolution imaging. For FT-ICR, data processing and data reduction must not compromise the high mass resolution afforded by the mass spectrometer. The continuous mode “Mosaic Datacube” approach allows high mass resolution visualization (0.001 Da) of mass spectrometry imaging data, but requires additional processing as compared to feature-based processing. We describe the use of distributed computing for processing of FT-ICR MS imaging datasets with generation of continuous mode Mosaic Datacubes for high mass resolution visualization. An eight-fold improvement in processing time is demonstrated using a Dutch nationally available cloud service. 相似文献