全文获取类型
收费全文 | 8676篇 |
免费 | 636篇 |
国内免费 | 176篇 |
专业分类
化学 | 6018篇 |
晶体学 | 42篇 |
力学 | 328篇 |
综合类 | 12篇 |
数学 | 1222篇 |
物理学 | 1866篇 |
出版年
2023年 | 116篇 |
2022年 | 142篇 |
2021年 | 197篇 |
2020年 | 211篇 |
2019年 | 190篇 |
2018年 | 176篇 |
2017年 | 163篇 |
2016年 | 398篇 |
2015年 | 351篇 |
2014年 | 362篇 |
2013年 | 540篇 |
2012年 | 590篇 |
2011年 | 611篇 |
2010年 | 396篇 |
2009年 | 377篇 |
2008年 | 478篇 |
2007年 | 443篇 |
2006年 | 423篇 |
2005年 | 377篇 |
2004年 | 297篇 |
2003年 | 229篇 |
2002年 | 250篇 |
2001年 | 150篇 |
2000年 | 138篇 |
1999年 | 133篇 |
1998年 | 110篇 |
1997年 | 130篇 |
1996年 | 126篇 |
1995年 | 108篇 |
1994年 | 79篇 |
1993年 | 79篇 |
1992年 | 50篇 |
1991年 | 63篇 |
1990年 | 64篇 |
1989年 | 51篇 |
1988年 | 38篇 |
1987年 | 44篇 |
1986年 | 40篇 |
1985年 | 32篇 |
1983年 | 23篇 |
1982年 | 27篇 |
1981年 | 34篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 30篇 |
1977年 | 35篇 |
1976年 | 24篇 |
1975年 | 22篇 |
1974年 | 26篇 |
1973年 | 28篇 |
排序方式: 共有9488条查询结果,搜索用时 15 毫秒
81.
Pu-yanNie 《计算数学(英文版)》2003,21(5):613-624
In a composite-step approach, a step sk is computed as the sum of two components vk and hk. The normal component vk, which is called the vertical step, aims to improve the linearized feasibility, while the tangential component hk, which is also called horizontal step, concentrates on reducing a model of the merit functions. As a filter method, it reduces both the infeasibility and the objective function. This is the same property of these two methods. In this paper, one concerns the composite-step like filter approach. That is, a step is tangential component hk if the infeasibility is reduced. Or else, sk is a compositestep composed of normal component Vk and tangential component hk. 相似文献
82.
Kurt Leichtweiß 《Journal of Geometry》2003,78(1-2):92-121
Analogue to the definition $K + L := \bigcup_{x\in K}(x + L)$ of the
Minkowski addition in the euclidean geometry it is proposed to define the
(noncommutative) addition $K \vdash L := \bigcup_{0\, \leqsl\, \rho\,\leqsl\,
a(\varphi),0\,\leqsl\,\varphi\,<\, 2\pi}T_{\rho}^{(\varphi)}(L)$ for compact,
convex and smoothly bounded sets K and
L in the hyperbolic plane $\Omega$
(Kleins model). Here $\rho = a(\varphi)$ is the representation of the boundary
$\partial$ K in geodesic polar coordinates
and $T_{\rho}^{(\varphi)}$ is the hyperbolic translation of $\Omega$ of length
$\rho$ along the line through the origin o of
direction $\varphi$. In general this addition does not preserve
convexity but nevertheless we may prove as main results: (1) $o \in$ int
$K, o \in$ int L and K,L horocyclic convex imply the strict
convexity of $K \vdash L$, and (2) in this case there exists a hyperbolic mixed
volume $V_h(K,L)$ of K and L which has a representation by a suitable
integral over the unit circle. 相似文献
83.
本文研究了T型管状接头在面内和面外弯曲循环载荷作用下的疲劳强度问题,通过将材料常数和初始裂纹尺寸作为随机变量,采用MonCarlo模拟方法对疲劳寿命进行了统计分析.同时,对计算结果进行了线性回归,并与实验结果作了比较。 相似文献
84.
S. A. Goncharov A. M. Mukhamedzhanov E. A. Romanovskii G. E. Valiev I. R. Gulamov Yu. I. Denisov T. Iskhakov A. Karakhodzhaev G. K. Nie R. Yarmuchamedov V. A. Stepanenko V. Kroha 《Czechoslovak Journal of Physics》1988,38(1):12-18
The differential cross sections of tritons from the (d, t) reaction on9Be,10B and13C targets have been measured in the angular range of 5°
LAB110° with relatively small errors, 5%. The experimental data were analysed in terms of the standard DWBA using both zero-range and exact finite-range approaches. 相似文献
85.
A. Türler H. W. Gäggeler D. T. Jost P. Armbruster W. Brüchle H. Folger F. P. Heßberger S. Hofmann G. Münzenberg V. Ninov M. Schädel K. Sümmerer J. V. Kratz U. Scherer 《Zeitschrift für Physik A Hadrons and Nuclei》1988,331(3):363-364
The isotope254No was produced in the fusion reaction48Ca +208Pb. Using the velocity filter SHIP and radiochemical techniques it was found that the nuclide254No with a half-life of 55 s decays byα, EC, and spontaneous-fission. Deduced partial half-lives are (61±2) s forα-decay, (550 ?160 +370 ) s for EC and [2.2 ?1.0 +2.0 ]×104 s for spontaneous fission. 相似文献
86.
G. Großkopf R. Ludwig R. Molt H. G. Weber S. B. Zhang 《Applied physics. B, Lasers and optics》1988,45(3):171-174
The application of a semiconductor-laser amplifier with reduced facet reflectivity as all-optical switch is described. An optical data signal is switched on and off with an extinction ratio of 10 dB when an optical control signal is turned on and off. The two optical signals are polarized perpendicularly to each other. The device was operated up to 100 MHz.Nanjing Institute of Posts and Telecommunication Nanjing, PR China 相似文献
87.
G. Rauprich H. J. Hähn M. Karus P. Nießen K. R. Nyga H. Oswald L. Sydow H. Paetz gen Schieck Y. Koike 《Few-Body Systems》1988,5(2):67-77
The
elastic scattering was investigated especially in the Coulomb sensitive scattering regions. Angular distributions of the differential cross section and of the analyzing powerA
y, with emphasis on small scattering angles, were measured at 10.0 and 14.1 MeV. For extreme backward angles up toJ
c.m.=179° the differential cross section was measured at 12.0, 14.1 and 16.5 MeV. The data have been compared with recent Faddeev calculations based on the realistic meson-exchange Paris potential and including an approximate Coulomb correction. There are discrepancies between the data and the calculations especially for the analyzing power. This indicates that the approximate treatment of Coulomb effects and possibly also the purely nuclear part of the calculations need to be improved. 相似文献
88.
An inhomogeneous steady state pattern of nonlinear reaction-diffusion equations with no-flux boundary conditions is usually computed by solving the corresponding time-dependent reaction-diffusion equations using temporal schemes. Nonlinear solvers (e.g., Newton's method) take less CPU time in direct computation for the steady state; however, their convergence is sensitive to the initial guess, often leading to divergence or convergence to spatially homogeneous solution. Systematically numerical exploration of spatial patterns of reaction-diffusion equations under different parameter regimes requires that the numerical method be efficient and robust to initial condition or initial guess, with better likelihood of convergence to an inhomogeneous pattern. Here, a new approach that combines the advantages of temporal schemes in robustness and Newton's method in fast convergence in solving steady states of reaction-diffusion equations is proposed. In particular, an adaptive implicit Euler with inexact solver (AIIE) method is found to be much more efficient than temporal schemes and more robust in convergence than typical nonlinear solvers (e.g., Newton's method) in finding the inhomogeneous pattern. Application of this new approach to two reaction-diffusion equations in one, two, and three spatial dimensions, along with direct comparisons to several other existing methods, demonstrates that AIIE is a more desirable method for searching inhomogeneous spatial patterns of reaction-diffusion equations in a large parameter space. 相似文献
89.
90.
Halmer D von Basum G Horstjann M Hering P Mürtz M 《Isotopes in environmental and health studies》2005,41(4):303-311
We present a ring-down absorption spectrometer based on a continuous-wave CO laser in the mid-infrared spectral region near lambda = 5 microm. Using a linear ring-down cavity (length: 0.5 m) with high reflective mirrors (R = 99.988 %), we observed a noise-equivalent absorption coefficient of 3 x 10(-10) cm(-1)Hz(-1/2). This corresponds to a noise-equivalent concentration of 800 parts per trillion (ppt) for (14)NO and 40 ppt for (15)NO in 1 s averaging time. We achieve a time resolution of 1 s which allows time resolved simultaneous detection of the two N isotopes. The delta(15)N value was obtained with a precision of +/-1.2 per thousand in a sample with a NO fraction of 11 ppm. The simultaneous detection enables the use of (15)NO as a tracer molecule for endogenous biomedical processes. 相似文献