全文获取类型
收费全文 | 19239篇 |
免费 | 3415篇 |
国内免费 | 3268篇 |
专业分类
化学 | 14864篇 |
晶体学 | 287篇 |
力学 | 1098篇 |
综合类 | 264篇 |
数学 | 2128篇 |
物理学 | 7281篇 |
出版年
2024年 | 38篇 |
2023年 | 366篇 |
2022年 | 551篇 |
2021年 | 762篇 |
2020年 | 840篇 |
2019年 | 847篇 |
2018年 | 663篇 |
2017年 | 703篇 |
2016年 | 939篇 |
2015年 | 1003篇 |
2014年 | 1183篇 |
2013年 | 1513篇 |
2012年 | 1731篇 |
2011年 | 1837篇 |
2010年 | 1354篇 |
2009年 | 1315篇 |
2008年 | 1456篇 |
2007年 | 1257篇 |
2006年 | 1206篇 |
2005年 | 1030篇 |
2004年 | 760篇 |
2003年 | 623篇 |
2002年 | 601篇 |
2001年 | 517篇 |
2000年 | 387篇 |
1999年 | 343篇 |
1998年 | 318篇 |
1997年 | 249篇 |
1996年 | 238篇 |
1995年 | 238篇 |
1994年 | 188篇 |
1993年 | 163篇 |
1992年 | 122篇 |
1991年 | 141篇 |
1990年 | 100篇 |
1989年 | 93篇 |
1988年 | 66篇 |
1987年 | 42篇 |
1986年 | 39篇 |
1985年 | 30篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Cai Kairen 《数学年刊B辑(英文版)》1991,12(3):267-271
The author gives an optimum estimate of the first eigenvalue of a compact Riemannian manifold. It is shown that let M be a compact Riemannian manifold, then the first eigenvalue λ_1 of the Laplace operator of M satisfies α_1+max{0,-(n-1)K}≥π~2/d~2 where d is the diameter of M and (n-1)K is the negative lower bound of the Ricci curvature of M. 相似文献
92.
Zi‐Cai Li Tzon‐Tzer Lu Hung‐Tsai Huang Alexander H.‐D. Cheng 《Numerical Methods for Partial Differential Equations》2007,23(1):93-144
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
93.
关于可达矩阵的求法探讨 总被引:6,自引:0,他引:6
在《离散数学》、《图论》课程中 ,用矩阵表示图时 ,涉及到一类重要的矩阵——可达矩阵 ,它是判别图中任意两点是否有通路的重要手段 ,也是求强分图的重要方法 ,但是可达矩阵的求法比较复杂 .本文针对这一问题 ,对可达矩阵的求法进行了改进 ,提出了一种简单可行的算法 . 相似文献
94.
热等离子体裂解天然气制备C2烃 总被引:1,自引:0,他引:1
采用氮气热等离子体来裂解天然气制备乙炔乙烯,着重研究了天然气转化率和乙炔、乙烯收率随氮气流量和天然气流量的变化.结果表明,天然气流量与氮气流量之比为11时,可得到较好的结果.当等离子体功率为15kW、天然气流量为3Nm3*h-1、氮气流量为3Nm3*h-1时得到最好的结果.这时天然气转化率为57%,乙炔、乙烯的收率分别为34%和9%;乙炔在反应气中的体积浓度为7.5%,与部分氧化法相似;扣除不参加反应的氮气,乙炔在气相产品中的体积浓度为13.2%,与热力学平衡计算结果基本符合. 相似文献
95.
The following results are proved in this paper. Let G be a 2k-edge-connected eulerian graph. (i) For every set {e1, e2, ?, e2k+1} ? E(G) there is an eulerian trail T of the form e1, e2, ?, e2k+1, ?. (ii) For every set E* = {e1, e2, ?, ek} ? E(G) there is an eulerian trail T = e1, ?, e2, ?, ek, ? in which the elements of E* are traversed in accordance with a prescribed orientation. © 1995 John Wiley & Sons, Inc. 相似文献
96.
97.
Zhengqian Luo Guoyong Sun Zhiping Cai Miaoling Si Qibo Li 《Optics Communications》2007,277(1):118-124
In this paper, continuous wave Yb3+-doped double-clad fiber lasers (DCFLs) with linear-cavity are investigated theoretically and numerically using the rate equations. Under the steady state conditions, the simplified analytic solutions of Yb3+-doped DCFLs under considering the scattering loss are deduced in the strongly pump condition. Compared with the known analytic solutions in published literatures, our analytic solutions are more accurate, especially, at higher reflectivity of output mirror. In addition, a fast and stable algorithm based on the Newton-Raphson method is proposed to simulate numerically Yb3+-doped DCFLs. The results by simplified analytic solutions are in good agreement with those by the numerical simulation. Moreover, we have performed the optimization of an Yb3+-doped DCFL using the simplified analytic solutions and the numerical simulations, respectively. 相似文献
98.
The fission barrier for ^240pu is investigated beyond the second saddle point in the potentiM energy surface by the constrained relativistic mean field method with the newly proposed parameter set PK1. The microscopic correction for the centre-of-mass motion is essentiM to provide the correct potential energy surface. The shell effects that stabilize the nuclei against the fission is also investigated by the Strutinsky method. The shapes for the ground state, fission isomer and saddle-points, etc, are studied in detail. 相似文献
99.
In this note we study constant mean curvature surfaces in asymptotically flat 3-manifolds. We prove that, outside a given compact subset in an asymptotically flat 3-manifold with positive mass, stable spheres of given constant mean curvature are unique. Therefore we are able to conclude that the foliation of stable spheres of constant mean curvature in an asymptotically flat 3-manifold with positive mass outside a given compact subset is unique.
100.