全文获取类型
收费全文 | 40617篇 |
免费 | 4000篇 |
国内免费 | 10068篇 |
专业分类
化学 | 45104篇 |
晶体学 | 643篇 |
力学 | 891篇 |
综合类 | 309篇 |
数学 | 2415篇 |
物理学 | 5323篇 |
出版年
2024年 | 76篇 |
2023年 | 526篇 |
2022年 | 954篇 |
2021年 | 1249篇 |
2020年 | 1759篇 |
2019年 | 1484篇 |
2018年 | 1539篇 |
2017年 | 1516篇 |
2016年 | 1699篇 |
2015年 | 1535篇 |
2014年 | 2270篇 |
2013年 | 3759篇 |
2012年 | 3149篇 |
2011年 | 2580篇 |
2010年 | 2040篇 |
2009年 | 2415篇 |
2008年 | 2701篇 |
2007年 | 2874篇 |
2006年 | 2679篇 |
2005年 | 2518篇 |
2004年 | 2431篇 |
2003年 | 1894篇 |
2002年 | 1354篇 |
2001年 | 1085篇 |
2000年 | 1118篇 |
1999年 | 989篇 |
1998年 | 862篇 |
1997年 | 788篇 |
1996年 | 707篇 |
1995年 | 683篇 |
1994年 | 582篇 |
1993年 | 432篇 |
1992年 | 491篇 |
1991年 | 371篇 |
1990年 | 288篇 |
1989年 | 231篇 |
1988年 | 183篇 |
1987年 | 120篇 |
1986年 | 123篇 |
1985年 | 99篇 |
1984年 | 89篇 |
1983年 | 49篇 |
1982年 | 54篇 |
1981年 | 50篇 |
1980年 | 37篇 |
1979年 | 31篇 |
1978年 | 36篇 |
1977年 | 34篇 |
1976年 | 37篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Govindarajan Sankar A. Sultan Nasar 《Journal of polymer science. Part A, Polymer chemistry》2007,45(8):1557-1570
A series of substituted N‐methylaniline‐blocked polyisocyanates based on 4,4′‐methylenebis(phenyl isocyanate) and poly(tetrahydrofuran) were prepared and characterized thoroughly with FTIR, 1H NMR, and 13C NMR spectroscopy methods. Compared with unsubstituted N‐methylaniline, a blocking agent with an electron‐releasing substituent at the para position took a shorter time, whereas those with an electron‐releasing substituent at the ortho position or an electron‐withdrawing substituent at the ortho and para positions took longer times for the blocking reaction. The thermal dissociation reactions of blocked polyisocyanates were carried out with an FTIR spectrophotometer attached to hot‐stage accessories under dynamic and isothermal conditions. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate the deblocking kinetics and activation parameters. The cure times of blocked polyisocyanates with hydroxyl‐terminated polybutadiene were also determined. The deblocking temperatures, the results of cure‐time studies, and the kinetic parameters revealed that the thermal dissociation of the N‐methylaniline‐blocked polyisocyanates was retarded by electron‐donating substituents and facilitated by electron‐withdrawing substituents. The action of N‐methylanilines as blocking agents for isocyanate was explained by the formation of a four‐center, intramolecularly hydrogen‐bonded ring structure during the thermal dissociation of the blocked polyisocyanates. The formation of such a hydrogen‐bonded ring structure was confirmed and supported by variable‐temperature 1H NMR studies and entropy parameters, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1557–1570, 2007 相似文献
142.
Gheorghe Munteanu 《Periodica Mathematica Hungarica》2007,55(1):97-112
In [Mu1] we underlined the motifs of holomorphic subspaces in a complex Finsler space: induced nonlinear connection, coupling
connections, and the induced tangent and normal connections. In the present paper we investigate the equations of Gauss, H-and A-Codazzi, and Ricci equations of a holomorphic subspace. We deduce the link between the holomorphic curvatures of the Chern-Finsler
connection and its induced tangent connection. Conditions for totally geodesic holomorphic subspaces are obtained.
Communicated by János Szenthe 相似文献
143.
复Finsler流形上的Koppelman-Leray-Norguet公式 总被引:1,自引:1,他引:0
利用不变积分核(Berndtsson核),复Finsler度量和联系于Chern-Finsler联络的非线性联络,研究复Finsler流形上具有逐块光滑C~((1))边界的有界域上(p,q)型微分形式的积分表示,得到了(p,q)型微分形式的Koppelman-Leray-Norguet公式和■-方程的解.作为应用,利用复Finsler度量和联系于Chern-Finsler联络的非线性联络,给出了Stein流形上具有逐块光滑C~((1))边界的有界域上(p,q)型微分形式的Koppelman- Leray-Norguet公式以及■-方程的解,并且得到了Stein流形上实非退化强拟凸多面体上(p,q)型微分形式的积分表示式和■-方程的解. 相似文献
144.
Florence Newberger 《Geometriae Dedicata》2003,97(1):215-249
The goal of this paper is to provide a tool, the Global Measure Formula, that will facilitate the study of the limit set of discrete geometrically finite groups of isometries of the rank one symmetric spaces. We consider the shadow of a ball from a fixed reference point onto the boundary, and prove a formula that describes the measure of the shadow in terms of the center of the shadowed ball, generalizing a result from real hyperbolic geometry. 相似文献
145.
146.
析氢反应动力学的交流阻抗法研究 总被引:1,自引:0,他引:1
利用交流阻抗法测定析氢电化学动力学参数,得到与极化曲线法一致的结果,为确定复杂析氢过程速率的决定步骤提供了判据。 相似文献
147.
Gabor Schmera Adi Bulsara David Pierson Frank Moss Enrico Di Cera 《Journal of statistical physics》1993,71(5-6):1179-1190
We consider the class of experiments which can be characterized by a Fokker-PIanck dynamics corresponding to the overdamped motion of a state point in a suitable stochastic potential. We assume that the general form of the potential is known (or can be guessed with reasonable accuracy), but that its parameters are to be determined experimentally by measurements made with a noisy instrument. This possible method for determining the potential parameters, which exploits the system's own internal stochastic motion in order to explore rapidly its available parameter space, is substantially more efficient than traditional methods involving time averages of single point measurements, and yet does not appear to have been previously considered. The method could be important when, for example, the experiment must be completed in a limited time owing either to the expense of the experimental materials or to the temporary stationarity of the preparation, situations which are commonly encountered in experimental biochemistry and biology. 相似文献
148.
149.
150.
测定了室温下烃类(乙炔、乙烷)烟粒的红外复折射率,并讨论了所获数据在测量烟浓度与烟粒大小分类、计算光谱吸收系数及在特定浓度与温度下评估烟雾辐射率方面的应用。 相似文献