全文获取类型
收费全文 | 90958篇 |
免费 | 758篇 |
国内免费 | 846篇 |
专业分类
化学 | 63627篇 |
晶体学 | 21篇 |
力学 | 635篇 |
综合类 | 277篇 |
数学 | 977篇 |
物理学 | 27025篇 |
出版年
2023年 | 90篇 |
2022年 | 105篇 |
2021年 | 98篇 |
2020年 | 88篇 |
2019年 | 82篇 |
2018年 | 105篇 |
2017年 | 61篇 |
2016年 | 153篇 |
2015年 | 130篇 |
2014年 | 252篇 |
2013年 | 183篇 |
2012年 | 8080篇 |
2011年 | 11351篇 |
2010年 | 1953篇 |
2009年 | 492篇 |
2008年 | 8731篇 |
2007年 | 8872篇 |
2006年 | 8979篇 |
2005年 | 8601篇 |
2004年 | 6664篇 |
2003年 | 4956篇 |
2002年 | 4403篇 |
2001年 | 2699篇 |
2000年 | 3443篇 |
1999年 | 806篇 |
1998年 | 293篇 |
1997年 | 248篇 |
1996年 | 1427篇 |
1995年 | 904篇 |
1994年 | 1203篇 |
1993年 | 1649篇 |
1992年 | 1387篇 |
1991年 | 595篇 |
1990年 | 553篇 |
1989年 | 473篇 |
1988年 | 407篇 |
1987年 | 372篇 |
1986年 | 429篇 |
1985年 | 348篇 |
1984年 | 64篇 |
1983年 | 54篇 |
1982年 | 56篇 |
1981年 | 49篇 |
1979年 | 38篇 |
1977年 | 35篇 |
1976年 | 51篇 |
1975年 | 56篇 |
1974年 | 40篇 |
1958年 | 36篇 |
1948年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
方德清 Yamaguchi T. 郑涛 Ozawa A. Chiba M. Kanungo R. Kato T. Morimoto K. Ohnishi T. Suda T. Yamaguchi Y. Yoshida A. Yoshida K. Tanihata I.< 《中国物理 C》2004,28(Z1)
实验测量了83A MeV 14,15C的核反应总截面(σR)及15C产生14,15C和14C产生13C的动量分布(P//). 分析得到了15C产生14C和13C的动量分布半高宽(FWHM)分别为71±9MeV/c和223±28MeV/c, 而14C产生13C的FWHM为195±21MeV/c. 从15C和14C产生13C的FWHM与Goldhaber模型的预言基本一致. 而15C产生14C的FWHM却要比该模型计算小得多. 同时观测到15C的σR比相邻核有反常增加. 在Glauber模型框架中, 对实验测得的P//和σR进行了探讨. P//和σR的分析结果同时显示15C的最后一个中主要处于s1/2态, 具有中子晕结构. 相似文献
12.
本文从极冠模型出发导出辐射束的强度分布和新的光度公式.新的光度公式无需对磁倾角和视线扫过辐射束的部位作出假定,采用新的射电光度值来研究光度的演化规律,发现在周期和周期变率的整个取值范围内射电光度可以用关系式L∝(B/P2)1.1和L∝Q’-1.4来描写.这和近几年流行的光度规律不同. 相似文献
13.
We report a non-destructive characterization of planar two-dimensional(2D)photonic crystals(PhCs) made in silicon on insulator(SOI)wafers using ellipsometric or Fourier transformed infrared(FTIR) spectroscope.At large wavelengths,devices behave as homogeneous isotropic materials defined by an effective filling factor.The experimental results related to the PhC limited dimensions confirm this characterization. 相似文献
14.
在Linux操作平台下应用FAST_wmg有限元前后处理软件对机械密封焊接金属波纹管膜片建立了有限元模型并进行了非线性有限元分析.在同等条件下对焊接金属波纹管采用了S型膜片和V型膜片,并分别进行了有限元强度评价和对比分析.结果表明,两种膜片最大应力集中都在膜片两端周围发生.这与文献所叙述的波纹管的主要失效发生在膜片两端与焊谷接近的部位非常吻合,但是,在同样边界条件下,在同样位移量时S型膜片最大应力值比V型膜片最大应力值小,压缩量大. 相似文献
15.
Jindun Liu A. J. B. Kemperman G. H. Koops M. Wessling 《中国颗粒学报》2006,4(2):98-102
A novel method of fabricating composite mosaic membranes was studied on the basis of interracial polymerization (IP) by coating a thin selective layer onto the surface of a micro-porous hollow-fiber membrane, in which, 2,5-diaminobenzene sulfonic acid was used as one monomer of the IP reaction, and a mixture of trimesoyl chloride (TMCI) and 4-(chloromethyl) benzoyl chloride as the other monomer. Through the IP reaction a thin selective layer with negatively charged groups could be first formed on the polyethersulfone (PES) support membrane. Then trimethylamine solution was introduced to modify the IP layer through a quaternization reaction. Thus the selective layer of this composite membrane contained both negatively charged and positively charged groups to perform the mosaic functionality. Characterization of the composite mosaic membranes was carried out through permeation experiments using different inorganic salts and dyes. The experimental results showed that the membranes could permeate both mono- and bi-valent inorganic salts, but reject larger organic molecules. Such a mosaic membrane is potentially useful for the separation of salts from water-soluble organics, especially in dye and textile industries. 相似文献
16.
本文讨论圆形区域内芽虫分布模型,特别研究了芽虫与天敌接触时产生与避免outbreak状态的可能性。 相似文献
17.
LIUXiang XUZengyu S.Tamura N.Yoshida 《核工业西南物理研究院年报(英文版)》2002,(1):66-69
Since tungsten was chose as the divertor tiles of 1TER, the investigation of tungsten and its coating as plasma facing material (PFM) have been paid more attentions by fusion scientists all over the world. Recent years, tungsten coatings have been successfully 相似文献
18.
V. A. KHATSKEVICH V.A. SENDEROV 《数学学报(英文版)》2006,22(6):1687-1694
The operator sets, which are the subject of this paper, have been studied in many papers where, under different restrictions on the generating operators, convexity, compactness in the weak operator topology, and nonemptiness were proved for sets of different classes under study. Then the results obtained were used in these papers to solve several applied problems. Namely, they played the key role in establishing the dichotomy of nonautonomous dynamical systems, with either continuous or discrete time. In the present paper, we generalize and sharpen the already known criteria and obtain several new criteria for convexity, compactness, and nonemptiness of several special operator sets. Then, using the assertions obtained, we construct examples of sets of the form under study which are nonconvex, noncompact in the weak operator topology, as well as empty, and are generated by "smooth" operators of a special class. The existence problem for such sets remained open until the authors of this paper announced some of its results. 相似文献
19.
A sufficient condition for the order of approximation of a continuous 2π periodic function with a givenmajorant for the modulus of continuity by the [F, d_n] means of its Fourier serier to be of Jackson order isobtained. This sufficient condition is shown to be not enough for the order of approximation by partial sums oftheir Fourier series to be of Jackson order. The error estimate is shown to be the best possible. 相似文献
20.
The present paper establishes sufficient conditions for the uniformly bounded of any solution of (1.1) and which tend to zero as t → ∞. 相似文献