全文获取类型
收费全文 | 31843篇 |
免费 | 5812篇 |
国内免费 | 7663篇 |
专业分类
化学 | 24464篇 |
晶体学 | 854篇 |
力学 | 1922篇 |
综合类 | 934篇 |
数学 | 4078篇 |
物理学 | 13066篇 |
出版年
2024年 | 77篇 |
2023年 | 452篇 |
2022年 | 909篇 |
2021年 | 987篇 |
2020年 | 1081篇 |
2019年 | 1248篇 |
2018年 | 1037篇 |
2017年 | 1201篇 |
2016年 | 1299篇 |
2015年 | 1510篇 |
2014年 | 1854篇 |
2013年 | 2630篇 |
2012年 | 2680篇 |
2011年 | 3004篇 |
2010年 | 2422篇 |
2009年 | 2432篇 |
2008年 | 2653篇 |
2007年 | 2523篇 |
2006年 | 2190篇 |
2005年 | 1916篇 |
2004年 | 1603篇 |
2003年 | 1279篇 |
2002年 | 1444篇 |
2001年 | 1353篇 |
2000年 | 1176篇 |
1999年 | 802篇 |
1998年 | 506篇 |
1997年 | 346篇 |
1996年 | 361篇 |
1995年 | 290篇 |
1994年 | 295篇 |
1993年 | 257篇 |
1992年 | 244篇 |
1991年 | 193篇 |
1990年 | 176篇 |
1989年 | 159篇 |
1988年 | 121篇 |
1987年 | 101篇 |
1986年 | 92篇 |
1985年 | 84篇 |
1984年 | 73篇 |
1983年 | 54篇 |
1982年 | 32篇 |
1981年 | 34篇 |
1980年 | 15篇 |
1979年 | 32篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
191.
A new formulation derived from thermal characters of inclusions and host films for estimating laser induced damage threshold has been deduced. This formulation is applicable for dielectric films when they are irradiated by laser beam with pulse width longer than tens picoseconds. This formulation can interpret the relationship between pulse-width and damage threshold energy density of laser pulse obtained experimentally. Using this formulation, we can analyze which kind of inclusion is the most harmful inclusion. Combining it with fractal distribution of inclusions, we have obtained an equation which describes relationship between number density of inclusions and damage probability. Using this equation, according to damage probability and corresponding laser energy density, we can evaluate the number density and distribution in size dimension of the most harmful inclusions. 相似文献
192.
腺嘌呤及其β-环糊精包结物的光谱研究 总被引:4,自引:0,他引:4
通过紫外光谱的摩尔比法确定了腺嘌呤与β-环糊精(β-CD)包结物的包结比为1:1,通过紫外光谱和荧光光谱研究了腺嘌呤在酸性,中性,及碱性条件下的光谱变化及与β-CD包结物的光谱变化,分别求得了它们与β-CD包结的平衡常数。 相似文献
193.
S—R分解定理的唯一性,存在性和客观性 总被引:3,自引:0,他引:3
对于连续体的一切物理可能的变形场,其变形梯度张量F可被分解为一个对称张量S和一个正交张量R的直和,这便是S-R分解定理.本文通过矩阵方法和张量方法证明了S-R分解定理的唯一性、存在性和客观性. 相似文献
194.
Using a scanning tunneling microscope, quantum dots with diameters of order 25 Å have been fabricated on the cleaved InSb (110) surface in UHV. Both In and Sb atoms were clearly resolved on the cleaved surface. 相似文献
195.
Nd:YAG激光器中的自锁模 总被引:5,自引:2,他引:3
本文报道在Nd:YAG激光器中首次获得的自锁模脉冲序列.自锁模是由于Nd:YAG棒中的自相位调制引起的.在主被动对撞锁模运转情况下,自锁模对脉冲波形有较大的影响. 相似文献
196.
Liang Ruixi Peng Jun Shen Jianhua 《Annals of Differential Equations》2006,22(4):502-510
The boundedness of the every solution and the asymptotic behavior of all solutions of the nonlinear neutral delay differential equation [x(t) - P(t)x(t - t)]' Q1 (t)f(x{t-σ1))-Q2(t)f(x(t -σ2))=0,t≥t0 are investigated, whereτ,σ1,σ2∈(0,∞), P∈C([t0,∞),R), and Q1,Q2∈C([t0,∞),R), f∈C(R,R). The sufficient conditions obtained improve the existing results in the literatures. 相似文献
197.
In this paper, based on the Pauli matrices, a notion of augmented spinor space is introduced, and a uniqueness of such augmented spinor space of rank n is proved. It may be expected that this new notion of spaces can be used in mathematical physics and geometry. 相似文献
198.
Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs. 相似文献
199.
We evaluate the practical relevance of two measures of conic convex problem complexity as applied to second-order cone problems solved using the homogeneous self-dual (HSD) embedding model in the software SeDuMi. The first measure we evaluate is Renegar's data-based condition measure C(d), and the second measure is a combined measure of the optimal solution size and the initial infeasibility/optimality residuals denoted by S (where the solution size is measured in a norm that is naturally associated with the HSD model). We constructed a set of 144 second-order cone test problems with widely distributed values of C(d) and S and solved these problems using SeDuMi. For each problem instance in the test set, we also computed estimates of C(d) (using Peña’s method) and computed S directly. Our computational experience indicates that SeDuMi iteration counts and log (C(d)) are fairly highly correlated (sample correlation R = 0.675), whereas SeDuMi iteration counts are not quite as highly correlated with S (R = 0.600). Furthermore, the experimental evidence indicates that the average rate of convergence of SeDuMi iterations is affected by the condition number C(d) of the problem instance, a phenomenon that makes some intuitive sense yet is not directly implied by existing theory. 相似文献
200.
An economical magnetocardiogram (MCG) system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device (SQUID) magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements. 相似文献