全文获取类型
收费全文 | 9259篇 |
免费 | 1764篇 |
国内免费 | 1321篇 |
专业分类
化学 | 5326篇 |
晶体学 | 379篇 |
力学 | 895篇 |
综合类 | 135篇 |
数学 | 177篇 |
物理学 | 5432篇 |
出版年
2024年 | 14篇 |
2023年 | 58篇 |
2022年 | 199篇 |
2021年 | 280篇 |
2020年 | 248篇 |
2019年 | 240篇 |
2018年 | 276篇 |
2017年 | 385篇 |
2016年 | 446篇 |
2015年 | 347篇 |
2014年 | 470篇 |
2013年 | 860篇 |
2012年 | 658篇 |
2011年 | 603篇 |
2010年 | 558篇 |
2009年 | 592篇 |
2008年 | 542篇 |
2007年 | 622篇 |
2006年 | 553篇 |
2005年 | 500篇 |
2004年 | 473篇 |
2003年 | 418篇 |
2002年 | 354篇 |
2001年 | 306篇 |
2000年 | 309篇 |
1999年 | 302篇 |
1998年 | 232篇 |
1997年 | 196篇 |
1996年 | 181篇 |
1995年 | 152篇 |
1994年 | 132篇 |
1993年 | 152篇 |
1992年 | 124篇 |
1991年 | 71篇 |
1990年 | 70篇 |
1989年 | 64篇 |
1988年 | 84篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 28篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
971.
内螺纹挤压加工温度及其变化规律的实验研究 总被引:2,自引:0,他引:2
采用自制的温度传感器,使用不同规格、不同结构的挤压丝锥,在不同的工件材料、不同预制孔径、不同挤压速度、不同切削液的实验条件下,对内螺纹挤压加工温度及其变化规律进行了实验研究.从降低挤压加工温度出发,提出延长挤压丝锥寿命、提高内螺纹质量的优化措施. 相似文献
972.
用电子束蒸发方法制备了HfO2薄膜,根据镀膜前后基片曲率半径的变化,用Stoney公式计算了薄膜应力,讨论了沉积温度对薄膜残余应力的影响。结果发现,HfO2薄膜的残余应力均为张应力,应力值随沉积温度的升高先增大后减小,在280 ℃左右出现极大值。对样品进行了XRD测试,从微观结构上对实验结果进行了分析,发现微结构演变引起的内应力变化是引起薄膜残余应力改变的主要因素,HfO2薄膜在所选沉积温度60~350 ℃内出现了晶态转变,堆积密度随温度升高而增大。 相似文献
973.
A new kind of the thermo-sensitive and fluorescent complex of poly(N-isopropylacrylamide) (PNIPAM) and Tb(III) was synthesized by free radical polymerization, in which PNIPAM was used as a polymer ligand. The complex was characterized by using X-ray photoelectron spectroscopy (XPS), ultraviolet-visual (UV), Fourier transform infrared (FT-IR) and fluorescence spectroscopy. The results from the experiments indicated that there is a strong interaction between PNIPAM and Tb(III), leading to a decrease in the electron density of nitrogen and oxygen atoms and an increase in the electron density of Tb(III) in the PNIPAM containing Tb(III) by contrast with PNIPAM and Tb(III), respectively, meanwhile, exhibiting that the Tb(III) is mainly bonded to oxygen atoms in the polymer chain of PNIPAM and formed the complex of PNIPAM-Tb(III). After forming the PNIPAM-Tb(III) complex, the emission fluorescence intensity of Tb(III) in the PNIPAM-Tb(III) complex is significantly enhanced because the effective intramolecular energy transfer from PNIPAM to Tb(III). Especially, the emission intensity of the fluorescence peak at 547 nm can be increased as high as 145 times comparing with that of the pure Tb(III). The intramolecular energy transfer efficiency for fluorescence peak at 547 nm can reach as high as 68%. The fluorescence intensity is related the weight ratio of Tb(III) and PNIPAM in the PNIPAM-Tb(III) complex. When the weight ratio is 1.4%, the maximum fluorescence enhancement can be obtained. Nevertheless, the lower critical solution temperature of PNIPAM containing a low content of Tb(III) has not obviously changed after the formation of the complex of PNIPAM-Tb(III) by the interaction between PNIPAM and Tb(III). This novel thermosensitive and fluorescence characterization of the PNIPAM-Tb(III) complex may be useful in the fluorescence systems and the biomedical field. 相似文献
974.
Chi Wang Yong‐Wen Cheng Yao‐Chung Hsu Tsang‐Lang Lin 《Journal of Polymer Science.Polymer Physics》2002,40(15):1626-1636
Lamellar morphology and thickness of syndiotactic polystyrene (sPS) samples melt‐crystallized at various temperatures were probed using transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS). In addition, the melting temperature and enthalpy of the crystallized samples were characterized with differential scanning calorimetry. Under appropriate thermal treatments, all the samples investigated in this study were crystallized into β′ crystal modification, as revealed by wide‐angle X‐ray diffraction. From the SAXS intensity profiles, a scattering peak (or shoulder) associated with lamellar features as well as the presence of anomalous scattering at the zero‐scattering vector were evidently observed. The peculiar zero‐angle scattering was successfully described by the Debye–Bueche model, and subtraction of its contribution from the raw intensity profiles was carried out to deduce the intensity profile merely associated with the lamellar feature. The lamellar thickness obtained from Lorentz‐corrected intensity profiles in this manner agrees with that measured from the TEM images, provided that the two‐phase model is applied. On the basis of the Gibbs–Thomson equation, the modest estimations of equilibrium melting temperature and the surface free energy of the fold lamellar surface are 292.7 ± 2.7 °C and 20.2 ± 2.6 erg/cm2, respectively, when lamellar thicknesses measured by TEM are applied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1626–1636, 2002 相似文献
975.
The construction of a three-terminal capacitance cell and a bath type cryostat to measure thermal expansion of solids in the temperature range 77 K to 350 K is described. Calculation of the thermal expansion coefficients by using spline approximation is discussed along with the various errors involved in the measurement. The capacitance cell is calibrated by using aluminium and germanium as standard reference materials. The cell has an accuracy of 4% in the measurement of thermal expansion coefficient and a resolution of 1 Å change in length of sample of length 1 cm. 相似文献
976.
温度变化导致航天相机光学系统像面位移的研究 总被引:3,自引:0,他引:3
温度变化导致的像面位移会影响航天相机光学系统的成像质量。根据高斯光学理论,推导出了温度变化时的相机光学系统的像面位移公式,确定了温度敏感性最低的主、次反射镜的材料及与之相匹配的镜筒材料。最后计算和比较了在不同温度变化时的光学系统的传递函数。 相似文献
977.
We review two methods discussed in the literature to determine the effective parameters of strongly interacting particles
as they move through a heat bath. The first one is the general method of chiral perturbation theory, which may be readily
applied to this problem. The other is the method of thermal QCD sum rules. We show that, when the spectral sides of the sum
rules are calculated correctly, they do not lead to any new results, but reproduce those of the vacuum sum rules. 相似文献
978.
一种实用化实时测温系统的优化设计 总被引:11,自引:1,他引:10
基于基尔霍夫定律,利用半导体激光器及钽酸锂热释电探测器设计了一种实用化的实时测温系统。依照测温系统各主要技术指标(温度分辨力、温度的标准偏差及测温范围)与各主要技术参量(激光光源的能量、波长、放大器的带宽及光学系统的相对孔径等)之间的关系,对实时测温系统的各主要参量(激光光源的能量、光学系统的相对孔径及放大器的带宽)进行了优化设计。实验表明,在测温范围673~1473K内,温度测量的不确定度优于0.3%,分辨力优于0.4K,均符合设计要求。 相似文献
979.
Steven Swier Kurt Van Durme Bruno Van Mele 《Journal of Polymer Science.Polymer Physics》2003,41(15):1824-1836
The heat capacity or reversing heat flow signal from modulated‐temperature differential scanning calorimetry can be used to measure the onset of phase separation in a poly(vinylmethylether)/water mixture, clearly showing the special type III lower critical solution temperature demixing behavior. Characteristic of this demixing behavior is a three‐phase region, which is detected in the nonreversing heat flow signal. Stepwise quasi‐isothermal measurements through the phase transition show large excess contributions in the (apparent) heat capacity signal, caused by demixing/remixing heat effects on the timescale of the modulation (fast process). These excess contributions and their time‐dependent evolutions (slow process) are useful in understanding the kinetics of phase separation and the morphology (interphase) development. Care has to be taken, however, in interpreting the heat capacity signal derived from the amplitude of the modulated heat flow because nonlinear effects lead to the occurrence of higher harmonics. Therefore, the raw heat flow signal for quasi‐isothermal demixing and remixing measurements is also examined in the time domain. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1824–1836, 2003 相似文献
980.