全文获取类型
收费全文 | 10604篇 |
免费 | 1969篇 |
国内免费 | 831篇 |
专业分类
化学 | 3487篇 |
晶体学 | 79篇 |
力学 | 1106篇 |
综合类 | 89篇 |
数学 | 506篇 |
物理学 | 8137篇 |
出版年
2024年 | 7篇 |
2023年 | 57篇 |
2022年 | 202篇 |
2021年 | 225篇 |
2020年 | 248篇 |
2019年 | 182篇 |
2018年 | 217篇 |
2017年 | 361篇 |
2016年 | 453篇 |
2015年 | 397篇 |
2014年 | 739篇 |
2013年 | 861篇 |
2012年 | 649篇 |
2011年 | 755篇 |
2010年 | 533篇 |
2009年 | 687篇 |
2008年 | 780篇 |
2007年 | 727篇 |
2006年 | 624篇 |
2005年 | 608篇 |
2004年 | 615篇 |
2003年 | 512篇 |
2002年 | 425篇 |
2001年 | 390篇 |
2000年 | 345篇 |
1999年 | 306篇 |
1998年 | 276篇 |
1997年 | 245篇 |
1996年 | 191篇 |
1995年 | 183篇 |
1994年 | 124篇 |
1993年 | 103篇 |
1992年 | 86篇 |
1991年 | 69篇 |
1990年 | 35篇 |
1989年 | 30篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1968年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
In the development of therapeutic proteins, analytical assessment of structural stability and integrity constitutes an important activity, as protein stability and integrity influence drug efficacy, and ultimately patient safety. Existing analytical methodologies solely rely on relative changes in optical properties such as fluorescence or scattering upon thermal or chemical perturbation. Here, we present an absolute analytical method for assessing protein stability, structure, and unfolding utilizing Taylor dispersion analysis (TDA) and LED-UV fluorescence detection. The developed TDA method measures the change in size (hydrodynamic radius) and intrinsic fluorescence of a protein during in-line denaturation with guanidinium hydrochloride (GuHCl). The conformational stability of the therapeutic antibody adalimumab and human serum albumin were characterized as a function of pH. The simple workflow and low sample consumption (40 ng protein per data point) of the methodology make it ideal for assessing protein characteristics related to stability in early drug development or when having a scarce amount of sample available. 相似文献
52.
I. M. J. J. van de Ven-Lucassen M. F. Kemmere P. J. A. M. Kerkhof 《Journal of solution chemistry》1997,26(12):1145-1167
The Taylor dispersion technique is used to measure the ternary mutual diffusion coefficients of aqueous nonelectrolyte solutions at 25°C. The dispersion of the injected solutes is recorded by a differential refractometer and an ultraviolet-visible detector. The diffusion coefficients are calculated directly by fitting the theoretical dispersion equations to about six experimental curves simultaneously. If the ternary diffusion effects in the measured dispersion profiles are not confused by the inaccuracy of the experimental method or an unfavorable relative detector sensitivity, the diffusion coefficients are precise. For the system methanol + acetone + water, it is shown that the Taylor dispersion method is unsuitable for the determination of all the diffusion coefficients if the methanol mole fraction is less than 0.45 or the acetone mole fraction if more than 0.001. 相似文献
53.
54.
Verheyen S. Blaton N. Kinget R. Van den Mooter G. 《Journal of Thermal Analysis and Calorimetry》2003,73(2):563-576
The effect of grinding on the physical properties and pharmaceutical performance of solid dispersions made of poly(ethylene)
glycol 6000 (PEG6000) and temazepam or diazepam was studied using differential scanning calorimetry (DSC), X-ray powder diffraction
and dissolution experiments. DSC-analysis of flash-cooled dispersions revealed that amorphous PEG present immediately after
grinding crystallised upon aging mainly into the twice folded modification and to a small extent into the extended form. DSC-analysis
of dispersions kept in the slab form for 1 month and subsequently ground, revealed that in the abscence of the grinding impulse
crystallisation of PEG6000 takes place in the same way as in dispersions ground immediately after preparation and then aged
for 1 month. Grinding solid dispersions immediately after preparation resulted in superior dissolution properties compared
with solid dispersions kept in the monolith-slab form and subsequently ground. This difference in dissolution properties was
found to be attributed to the drug and not to the polymer, more precisely, it was suggested that the drug particle size in
ground dispersions was smaller than in dispersions kept in the slab form and subsequently ground. These findings suggest that
grinding of solid dispersions immediately after preparation is the preparation method of choice instead of liquid filling
of hard gelatin capsules resulting in monoliths.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
55.
Quantitative analysis of MWCNT agglomeration in polymeric‐based membranes using atomic force microscope 下载免费PDF全文
Hatijah Basri Masooma Irfan Muhammad Irfan Woei‐Jye Lau Sutrasno Kartohardjono 《Surface and interface analysis : SIA》2017,49(1):55-62
In this work, we performed an analysis on the surface properties of polyethersulfone (PES)‐based ultrafiltration membranes that were prepared by incorporating acid functionalized multiwalled carbon nanotube (f‐MWCNT) and polyvinylpyrrolidone into membrane matrix via simple blending method. The bonding‐chemistry of the nanocomposites implanted within the PES membrane was investigated by Fourier transform infrared spectrometer while atomic force microscope was employed to observe the distribution of f‐MWCNT in the membrane matrix and further measured its agglomeration quantitatively. The resultant 3D atomic force microscope images provided the most satisfactory way to examine the distribution of nanomaterials in the membranes, and with the help of ‘point profile data’ the maximum height and width of the agglomerated cluster could be quantitatively calculated. Moreover, the surface profile studies of the membrane surface provided the information about the length, volume, area, perimeter, radius and diameter of grains. It was observed that PES/nanocomposite blended membranes were held together via strong hydrogen bonding, but poor dispersion of MWCNT in the membrane matrix reduced the membrane performance in terms of protein (pepsin and bovine albumin serum) rejection and increased the surface roughness. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
56.
57.
A time domain dispersion measurement apparatus was successfully built and tested at the Indian Institute of Technology, Madras. This instrument can measure directly the pulse broadening in a multimode optical fibre. The basic dispersion mechanisms in optical fibres and the design details of the system are discussed. 相似文献
58.
DING Ya-mei YUAN Xiao-yan ZHAO Jin GUO Wan-chun WANG Xiu-kui 《高等学校化学研究》2007,23(3):366-369
Ultrafine apatite fibers were prepared by electrospinning of sol-gel precursor/poly( vinyl pyrrolidone) (PVP) solutions followed by subsequent calcination. The as-electrospun and calcinated fibers were observed under a scanning electron microscope and an optical polarizing microscope. Results show that the morphology and the diameter of as-electrospun fibers strongly depend on the viscosity and the surface tension of sol-gel precursor/PVP solutions. After calcination, the smooth as-electrospun fibers shrink and the fiber diameter decreases because of the removal of the polymer. The chemical evolution upon the transformation of the precursor from a gel to the final apatite fibers was investigated by thermogravimetric-differenfial thermal analysis, X-ray diffraction, and Fourier transform infrared spectroscopy. It is thus suggested that the crystalline structure of the calcined fibers is largely influenced by the calcination temperature. After being calcined at 600 ℃, the apatite fibers with a diameter of about 280 nm containing β-tricalcium phosphate were obtained. 相似文献
59.
报道了一种由纤芯直径分别为15 μm和25 μm的大模场光纤组成的全光纤脉冲放大器模块。当注入脉冲宽度为10 ns,重复频率为1 Hz,光谱宽度为0.3 nm,脉冲能量为80 nJ的激光脉冲时,经过两级放大输出的激光脉冲峰值功率为30 kW,单脉冲能量为300 μJ。此外,实验研究了该放大器模块输出的时间特性。研究发现:由于受激布里渊散射(SBS)效应,限制了单纵模光纤激光在光纤中的高能量放大,采用宽带激光脉冲可以有效地抑制SBS效应,提高光纤放大器的SBS阈值。 相似文献
60.
仿真和实验研究了一种控制Nd:YAG脉冲激光能量通断的光纤直接连接型光开关。建立光纤耦合模型,分析了光纤对准误差中对耦合效率的影响,其中横向偏移的影响最显著。采用微机电系统V型槽固定光纤,微小型凸轮作为制动器,步进电机驱动凸轮旋转,微小型凸轮与移动光纤相切,带动光纤移动,实现两光纤的错开和对准。制造了这种高功率直接连接型光纤光开关原理样机,并进行了主要性能测试。测试结果表明,这种光开关能够满足激光点火系统的大容量、高隔离度的要求。 相似文献