全文获取类型
收费全文 | 36800篇 |
免费 | 4786篇 |
国内免费 | 7052篇 |
专业分类
化学 | 34860篇 |
晶体学 | 289篇 |
力学 | 1750篇 |
综合类 | 268篇 |
数学 | 1709篇 |
物理学 | 9762篇 |
出版年
2024年 | 75篇 |
2023年 | 468篇 |
2022年 | 900篇 |
2021年 | 1156篇 |
2020年 | 1713篇 |
2019年 | 1411篇 |
2018年 | 1452篇 |
2017年 | 1440篇 |
2016年 | 1592篇 |
2015年 | 1571篇 |
2014年 | 2160篇 |
2013年 | 3393篇 |
2012年 | 2111篇 |
2011年 | 2529篇 |
2010年 | 1999篇 |
2009年 | 2272篇 |
2008年 | 2377篇 |
2007年 | 2588篇 |
2006年 | 2368篇 |
2005年 | 2183篇 |
2004年 | 1998篇 |
2003年 | 1735篇 |
2002年 | 1251篇 |
2001年 | 992篇 |
2000年 | 1014篇 |
1999年 | 859篇 |
1998年 | 706篇 |
1997年 | 630篇 |
1996年 | 544篇 |
1995年 | 483篇 |
1994年 | 429篇 |
1993年 | 330篇 |
1992年 | 319篇 |
1991年 | 245篇 |
1990年 | 176篇 |
1989年 | 183篇 |
1988年 | 133篇 |
1987年 | 99篇 |
1986年 | 72篇 |
1985年 | 109篇 |
1984年 | 79篇 |
1983年 | 44篇 |
1982年 | 71篇 |
1981年 | 53篇 |
1980年 | 39篇 |
1979年 | 39篇 |
1977年 | 35篇 |
1976年 | 48篇 |
1974年 | 42篇 |
1973年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
141.
本文用准平衡模型分析讨论了线性电压扫描下MIS器件的I/V瞬态.文中除了给出一般的处理方法以外,还给出了几种不同电压扫描率下I/Y特性的计算结果,并与已往的模型作了比较. 相似文献
142.
In the present paper, a new two-parameter inverted equation of state (EOS) is developed which is found to be working very
well in the high-pressure region. To check its success and validity, this EOS has been applied in a number of solids. The
computed volume compression is found to be in very good agreement with the experimental data in the whole range of pressure
in all the solids. The minimum and the maximum pressure range used in the present study is 0–320 kbar and 0–3000 kbar, respectively. 相似文献
143.
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
144.
Ekatherina A. Karatsuba 《Numerical Algorithms》2007,45(1-4):127-137
A new approach to the study of the Jaynes–Cummings sum, which determines the atomic inversion in quantum model of a single
two-level atom interacting with a single mode of the quantized radiation field, based on the number theory theorems on approximation
of trigonometric sums is presented.
相似文献
145.
Yen-Shung TSAI 《中国科学A辑(英文版)》2007,50(7):1026-1034
By means of further investigation of solid codes,the problem“Is every fd-domain uni- formly dense”proposed by Yuqi Guo,C.M.Reis and G.Thierrin in 1988 is solved in this paper. 相似文献
146.
PURE STATE APPROACH TO C(x)_αZ_nLIBINGREN;LINQING(InstituteofMathematics,AcademiaSinica,Beijing100080,China.Projectsupportedbyth?.. 相似文献
147.
148.
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
149.
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
150.
The solid transitions of C21, C23 and C25
n-paraffins are examined from a piezothermal point of view. The paper is divided into two parts. The first is a report of the main features of a piezothermal analyzer when pressure scanning allows the continuous record of the expansivity as a function of pressure up to 5 Kilobars. Small samples are required and the scanning speeds vary from 0.3 to 16 Kilobars per hour. The second part describes the experimental procedure appropriate for solid state determinations. The resulting piezothermograms are presented and entropies of transformation are determined. A model allows a crude statistical approach giving the entropies of transformation with the correct order of magnitude. Problems related with phase transformations under a shearing stress are considered.
Zusammenfassung Feststoffumwandlungen bei C21, C23 und C25 n-Paraffinen wurden unter dem Gesichtspunkt der Piezowärme untersucht. Im ersten Teil vorliegender Arbeit werden die Haupteigenschaften eines piezothermischen Analysators beschrieben, bei dem durch Druck-Scanning die kontinuierliche Aufzeichnung des Ausdehnungsvermögens als Punktion des Druckes bis zu 5 kbar ermöglicht wird. Es werden nur kleine Proben benötigt, die Scanning-Geschwindigkeit variiert zwischen 0,3 und 16 kbar/h. Der zweite Teil beschreibt das geeignete experimentelle Verfahren zur Feststoffzustandsbestimmung. Die erhaltenen Piezothermogramme werden dargestellt und die Entropien der Umwandlung bestimmt. Ein Modell liefert eine grobe statistische Näherung, die die Entropien der Umwandlung in der richtigen Grö\enordnung liefert. Probleme in Zusammenhang mit Phasenumwandlungen bei Scherbeanspruchungen werden betrachtet.相似文献