全文获取类型
收费全文 | 13288篇 |
免费 | 2412篇 |
国内免费 | 869篇 |
专业分类
化学 | 1900篇 |
晶体学 | 179篇 |
力学 | 2992篇 |
综合类 | 265篇 |
数学 | 5381篇 |
物理学 | 5852篇 |
出版年
2024年 | 30篇 |
2023年 | 122篇 |
2022年 | 277篇 |
2021年 | 304篇 |
2020年 | 387篇 |
2019年 | 308篇 |
2018年 | 288篇 |
2017年 | 432篇 |
2016年 | 478篇 |
2015年 | 348篇 |
2014年 | 632篇 |
2013年 | 927篇 |
2012年 | 711篇 |
2011年 | 708篇 |
2010年 | 609篇 |
2009年 | 704篇 |
2008年 | 777篇 |
2007年 | 885篇 |
2006年 | 786篇 |
2005年 | 796篇 |
2004年 | 685篇 |
2003年 | 718篇 |
2002年 | 631篇 |
2001年 | 541篇 |
2000年 | 491篇 |
1999年 | 477篇 |
1998年 | 351篇 |
1997年 | 352篇 |
1996年 | 247篇 |
1995年 | 209篇 |
1994年 | 157篇 |
1993年 | 167篇 |
1992年 | 144篇 |
1991年 | 111篇 |
1990年 | 102篇 |
1989年 | 57篇 |
1988年 | 69篇 |
1987年 | 59篇 |
1986年 | 48篇 |
1985年 | 70篇 |
1984年 | 54篇 |
1983年 | 31篇 |
1982年 | 38篇 |
1981年 | 47篇 |
1980年 | 27篇 |
1979年 | 40篇 |
1978年 | 44篇 |
1977年 | 33篇 |
1976年 | 22篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
41.
本文提供了预条件不精确牛顿型方法结合非单调技术解光滑的非线性方程组.在合理的条件下证明了算法的整体收敛性.进一步,基于预条件收敛的性质,获得了算法的局部收敛速率,并指出如何选择势序列保证预条件不精确牛顿型的算法局部超线性收敛速率. 相似文献
42.
近年来,决定椭圆型方程系数反问题在地磁、地球物理、冶金和生物等实际问题上有着广泛的应用.本文讨论了二维的决定椭圆型方程系数反问题的数值求解方法.由误差平方和最小原则,这个反问题可化为一个变分问题,并进一步离散化为一个最优化问题,其目标函数依赖于要决定的方程系数.本文着重考察非线性共轭梯度法在此最优化问题数值计算中的表现,并与拟牛顿法作为对比.为了提高算法的效率我们适当选择加快收敛速度的预处理矩阵.同时还考察了线搜索方法的不同对优化算法的影响.数值实验的结果表明,非线性共轭梯度法在这类大规模优化问题中相对于拟牛顿法更有效. 相似文献
43.
A new approach to the robust handling of non‐linear constraints for GAs (genetic algorithms) optimization is proposed. A specific feature of the approach consists of the change in the conventional search strategy by employing search paths which pass through both feasible and infeasible points (contrary to the traditional approach where only feasible points may be included in a path). The method (driven by full Navier–Stokes computations) was applied to the problem of multiobjective optimization of aerodynamic shapes subject to various geometrical and aerodynamic constraints. The results demonstrated that the method retains high robustness of conventional GAs while keeping CFD computational volume to an acceptable level, which allowed the algorithm to be used in a demanding engineering environment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
44.
45.
Yu. Satov B. Sharkov H. Haseroth Yu. Smakovski K. Makarov S. Kondrashev V. Roerich A. Stepanov H. Kugler R. Scrivens O. Camut A. Shumshurov A. Balabaev A. Charushin 《Journal of Russian Laser Research》2004,25(3):205-216
Experimental and numerical calculation results devoted to development of an optical system for an ion source based on a repetition rate CO2 laser are described. The laser chain consists of a master oscillator, gas absorber cells, and a four-pass amplifier. The optical system provides smooth laser pulses with variable duration and high spatial quality that ensures efficiency for plasma heating and ion generation. The parameters of the plasma ion component measured in the CERN laboratory are applied for a lead target illumination. 相似文献
46.
The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004 相似文献
47.
V.B. Fainerman V.N. Kazakov S.V. Lylyk A.V. Makievski R. Miller 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):97-102
One of the essential differences in the design of bubble pressure tensiometers consists in the geometry of the measuring capillaries. To reach extremely short adsorption times of milliseconds and below, the so-called deadtime of the capillaries must be of the order of some 10 ms. In particular, for concentrated surfactant solutions, such as micellar solutions, short deadtimes are needed to minimize the initial surfactant load of the generated bubbles. A theoretical model is derived and confirmed by experiments performed for a wide range of experimental conditions, mainly in respect to variations in deadtime and bubble volume. 相似文献
48.
49.
Sufficient conditions are established for the asymptotic behavior of solutionsof nonlinear delay differential equations x′(t)+sum from i=1 to m(pi(t)x(t-т_i))=F(t,x_t),t≥0where 0<т_1<т_2<…<т_m≤r,pi∈C([0,∞)),i=1,2,…,m,F∈C([0,∞)×C_0,R).C_0=C([-r,0],R)equipped with the sup norm ||·|| forsome r>0. A new result is established, some known results are improved. 相似文献
50.
Zhu Yongliang; Pagilla Prabhakar R. 《IMA Journal of Mathematical Control and Information》2005,22(2):181-186
We derive some useful and easily computable necessary conditionsfor the existence of a positive semi-definite solution to thealgebraic Ricatti equation (ARE). A motivating example is givento highlight the usefulness of the conditions for controllerand observer designs for nonlinear systems. Further, an upperbound on the trace of the solution to the ARE is also derived. 相似文献