全文获取类型
收费全文 | 3165篇 |
免费 | 481篇 |
国内免费 | 431篇 |
专业分类
化学 | 2306篇 |
晶体学 | 30篇 |
力学 | 225篇 |
综合类 | 45篇 |
数学 | 313篇 |
物理学 | 1158篇 |
出版年
2024年 | 8篇 |
2023年 | 55篇 |
2022年 | 110篇 |
2021年 | 118篇 |
2020年 | 135篇 |
2019年 | 104篇 |
2018年 | 116篇 |
2017年 | 116篇 |
2016年 | 145篇 |
2015年 | 129篇 |
2014年 | 177篇 |
2013年 | 218篇 |
2012年 | 213篇 |
2011年 | 288篇 |
2010年 | 200篇 |
2009年 | 196篇 |
2008年 | 210篇 |
2007年 | 194篇 |
2006年 | 158篇 |
2005年 | 121篇 |
2004年 | 95篇 |
2003年 | 75篇 |
2002年 | 75篇 |
2001年 | 69篇 |
2000年 | 60篇 |
1999年 | 72篇 |
1998年 | 60篇 |
1997年 | 50篇 |
1996年 | 48篇 |
1995年 | 51篇 |
1994年 | 51篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有4077条查询结果,搜索用时 0 毫秒
101.
利用脉宽约为50ps的类镍银139nm软X射线激光作为探针,探测由脉宽80ps的驱动激光打C8H8靶产生的等离子体在1ns后的电子密度分布信息,获得了清晰的莫尔条纹图像.对结果的处理,给出了峰值电子密度为11×1021cm-3,并对在靶面附近莫尔条纹的消失现象作了初步解释
关键词:
软X射线激光探针 莫尔条纹 等离子体电子密度 相似文献
102.
In this paper, we prove the existence of Hermitian-Einstein metrics for holomorphic vector bundles on a class of complete Kähler manifolds which include Hermitian symmetric spaces of noncompact type without Euclidean factor, strictly pseudoconvex domains with Bergman metrics and the universal cover of Gromov hyperbolic manifolds etc. We also solve the Dirichlet problem at infinity for the Hermitian-Einstein equations on holomorphic vector bundles over strictly pseudoconvex domains.
103.
针对玻璃缺陷在线无损检测的迫切需求,本文报道了一种基于线照明并行谱域光学相干层析成像系统的大视场检测系统.该系统采用快速面阵CMOS相机,单次拍摄即可获取完整的横截面(B-scan)图像.基于线照明面阵探测器的并行谱域光学相干层析成像系统,可以同时获取沿线照明方向各位置处的深度分辨信息,避免了横向扫描机构的应用.研制系统的轴向分辨率为17.9μm,并行方向上的横向分辨率55.7μm,扫描方向上的横向分辨率为24.8μm,轴向扫描速率为128 000 A-scan/s,横向视场为32 mm,空气中成像深度大于6 mm,成像灵敏度达到62 dB以上.利用研制的线照明并行谱域光学相干层析成像系统,开展了不同类型玻璃表面及其内部缺陷的检测应用研究. 相似文献
104.
倪仁兴 《数学物理学报(A辑)》2006,26(2):297-305
证明了广义最速下降逼近强收敛于定义在一致光滑实Banach空间的真子集上的有界拟增生算子的零点的一充要条件,几个相关的结果处理含-强拟增生算子方程解或拟伪压缩映射不动点的强收敛性.所得的这些结果推广和统一了许多前人的近期相应结果. 相似文献
105.
106.
The doctor-blade method is investigated for the preparation of Cu2ZnSnS4 films for low-cost solar cell application.Cu2ZnSnS4 precursor powder,the main raw material for the doctor-blade paste,is synthesized by a simple ball-milling process.The doctor-bladed Cu2ZnSnS4 films are annealed in N2 ambient under various conditions and characterized by X-ray diffraction,ultraviolent/vis spectrophotometry,scanning electron microscopy,and current-voltage(J-V) meansurement.Our experimental results indicate that(i) the X-ray diffraction peaks of the Cu2ZnSnS4 precursor powder each show a red shift of about 0.4°;(ii) the high-temperature annealing process can effectively improve the crystallinity of the doctor-bladed Cu 2 ZnSnS 4,whereas an overlong annealing introduces defects;(iii) the band gap value of the doctor-bladed Cu 2 ZnSnS 4 is around 1.41 eV;(iv) the short-circuit current density,the open-circuit voltage,the fill factor,and the efficiency of the best Cu2ZnSnS4 solar cell obtained with the superstrate structure of fluorine-doped tin oxide glass/TiO2/In2S3/Cu2ZnSnS4/Mo are 7.82 mA/cm2,240 mV,0.29,and 0.55%,respectively. 相似文献
107.
??Recurrent event data usually occur in long-term studies which concern
recurrence rates of the disease. In studies of medical sciences, patients who have infected
with the disease, like cancer, were conventionally regarded as impossible to be cured. However,
with the development of medical sciences, recently those patients were found to be possibly
recovered from the disease. The recurrence rate of the events, which is of primary interest,
may be affected by the cure rate that may exist. Therefore, we proposed semiparametric
statistical analysis for recurrent event data with subjects possibly being cured. In our
approach, we present a proportional rate model for recurrence rate with the cure rate adjusted
through a Logistic regression model, and develop some estimating equations for estimation of
the regression parameters, with their large sample properties, including consistency and
asymptotic normality established. Numerical studies under different settings were conducted
for assessing the proposed methodology and the results suggest that they work well for
practical situations. The approach is applied to a bladder cancer dataset which motivated our
study. 相似文献
recurrence rates of the disease. In studies of medical sciences, patients who have infected
with the disease, like cancer, were conventionally regarded as impossible to be cured. However,
with the development of medical sciences, recently those patients were found to be possibly
recovered from the disease. The recurrence rate of the events, which is of primary interest,
may be affected by the cure rate that may exist. Therefore, we proposed semiparametric
statistical analysis for recurrent event data with subjects possibly being cured. In our
approach, we present a proportional rate model for recurrence rate with the cure rate adjusted
through a Logistic regression model, and develop some estimating equations for estimation of
the regression parameters, with their large sample properties, including consistency and
asymptotic normality established. Numerical studies under different settings were conducted
for assessing the proposed methodology and the results suggest that they work well for
practical situations. The approach is applied to a bladder cancer dataset which motivated our
study. 相似文献
108.
Using the technique of block-operators, in this note, we prove that if P and Q are idempotents and (P - Q)^2n+1 is in the trace class, then (P - Q)^2m+1 is also in the trace class and tr(P - Q)^2m+1 = dim(k(P) ∩ k(Q)^⊥) -dim(k(P)^⊥ N k(Q)), for all m ≥ n. Moreover, we prove that dim(k(P)∩ k(Q)^⊥) = dim(k(P)^⊥ ∩k(Q)) if and only if there exists a unitary U such that UP = QU and PU = UQ, where k(T) denotes the range of T. Keywords Fredholm, orthogonal projection, positive operator 相似文献
109.
S. H. Li C. Wang J. S. Liu X. X. Wang R. X. Li G. Q. Ni Z. Z. Xu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,34(1-3):215-218
Using time-of-flight spectrometry, the interaction of intense femtosecond
laser pulses with argon clusters has been studied by measuring the energy
and yield of emitted ions. With two different supersonic nozzles, the
dependence of average ion energy
on cluster size
in a large range of
has been measured. The experimental results indicate that
when the cluster size
, the average ion
energy
Coulomb explosion is the
dominant expansion mechanism. Beyond this size, the average ion energy gets
saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic
expansion behavior. We also find that with the increasing gas backing
pressure, there is a maximum ion yield, the ion yield decreases as the gas
backing pressure is further increased. 相似文献
110.
A numerical model is established to investigate the influence of transparent coating thickness on the laser-generated thermoelastic force source and ultrasound waves in the coating-substrate system by using the finite element method (FEM). Taking into account the effects of thermal diffusion, the finite width and duration of the laser source, as well as the temperature dependence of material properties, the transient temperature distributions are obtained firstly. Applying this temperature field to structure analyses as thermal loading, the thermoelastic stress field and laser-generated ultrasound wave in the specimen are obtained. The generation and propagation of the laser thermoelastically induced stress field and ultrasonic waves in coating-substrate system are presented in detail. The influence of transparent coating thickness on the transient temperature distribution, thermoelastic force source and the laser-generated ultrasound waveforms is investigated. The numerical results indicate that the thermoelastic force source and laser-generated ultrasound waveform are strongly affected by the coating thickness due to the constraint of coating. This method can provide insight into the generation and propagation of the laser-generated stress field in coating-substrate system consisting of a transparent coating and an opaque metallic substrate. It provides theoretical basics to optimize ultrasonic signal generation in particular applications and invert the physical and geometrical parameter of the coating-substrate system more accurately in the experiment. 相似文献