全文获取类型
收费全文 | 24775篇 |
免费 | 2714篇 |
国内免费 | 1406篇 |
专业分类
化学 | 17595篇 |
晶体学 | 289篇 |
力学 | 1079篇 |
综合类 | 68篇 |
数学 | 2637篇 |
物理学 | 7227篇 |
出版年
2024年 | 56篇 |
2023年 | 379篇 |
2022年 | 712篇 |
2021年 | 773篇 |
2020年 | 836篇 |
2019年 | 765篇 |
2018年 | 655篇 |
2017年 | 590篇 |
2016年 | 971篇 |
2015年 | 1004篇 |
2014年 | 1114篇 |
2013年 | 1713篇 |
2012年 | 1956篇 |
2011年 | 2033篇 |
2010年 | 1317篇 |
2009年 | 1257篇 |
2008年 | 1640篇 |
2007年 | 1407篇 |
2006年 | 1344篇 |
2005年 | 1235篇 |
2004年 | 994篇 |
2003年 | 831篇 |
2002年 | 789篇 |
2001年 | 593篇 |
2000年 | 498篇 |
1999年 | 440篇 |
1998年 | 288篇 |
1997年 | 233篇 |
1996年 | 305篇 |
1995年 | 263篇 |
1994年 | 212篇 |
1993年 | 218篇 |
1992年 | 176篇 |
1991年 | 140篇 |
1990年 | 158篇 |
1989年 | 145篇 |
1988年 | 104篇 |
1987年 | 88篇 |
1986年 | 72篇 |
1985年 | 90篇 |
1984年 | 66篇 |
1983年 | 41篇 |
1982年 | 46篇 |
1981年 | 59篇 |
1980年 | 36篇 |
1979年 | 29篇 |
1977年 | 28篇 |
1976年 | 29篇 |
1975年 | 25篇 |
1974年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Zhong Hong YAN Chun Hao YANG Xi Han WU Yu Yuan XIEDivision of Chemistry Shanghai Second Medical University Shanghai Sate Key Laboratory of Drug Research Shanghai Institute of Materia Medica Shanghai Institutesfor Biological Sciences Shanghai 《中国化学快报》2004,(4)
The first and facile synthesis of (±)syringaresinol was described. 相似文献
63.
HANXI'AN HUANGXILI 《高校应用数学学报(英文版)》1998,13(4):445-450
For two rational quadratic B-spline curves with same control vertexes, the cross ratio of four eollinear points are represented; which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the twocurves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Beeier curves, the value is generally related with the loeation of the ray, and the necessary and sufficient condition o5 the ratio being independent of the ray‘s loeation is showed. Alsn another cross ratio o5 the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initlal vertex intersects respectivdy with the curve segmentt the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only whh the ray‘s location, butnot with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments. 相似文献
64.
时滞种群模型的正周期解对所有正解的吸引性 总被引:5,自引:0,他引:5
李永昆 《高校应用数学学报(A辑)》1997,(3)
建立了对数种群模型N′(t)=N(t){r(t)-a1(t)ln[N(t)]-a2(t)ln[N(t-τ(t))]}的周期正解的存在性,并得到了正周期解对所有正解的吸引性. 相似文献
65.
66.
L.-Q. Han S.-Y. Zhao Y.-D. Zhou P.-L. Zhang 《Applied physics. B, Lasers and optics》1997,65(3):399-402
Received: 18 June 1996/Revised version: 3 January 1997 相似文献
67.
Benjamin S. Hsiao Rong-Ming Ho Stephen Z. D. Cheng 《Journal of Polymer Science.Polymer Physics》1995,33(17):2439-2447
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc. 相似文献
68.
69.
采用MSDI严格角动量投影46Ti、48Cr形变HF谱 总被引:1,自引:1,他引:0
采用修正的表面δ相互作用(MSDI),以球形壳模型单粒子态作基矢,对fp壳层区偶偶核46Ti、48Cr进行形变Hartree–Fock(HF)计算,并用形变HF单粒子态构造Slater行列式波函数,即形变HF内禀态,然后对其实施严格角动量投影程序,得到比较合理的结果. 相似文献
70.