全文获取类型
收费全文 | 48570篇 |
免费 | 6123篇 |
国内免费 | 3563篇 |
专业分类
化学 | 25169篇 |
晶体学 | 719篇 |
力学 | 8636篇 |
综合类 | 485篇 |
数学 | 5707篇 |
物理学 | 17540篇 |
出版年
2024年 | 54篇 |
2023年 | 381篇 |
2022年 | 760篇 |
2021年 | 1065篇 |
2020年 | 1385篇 |
2019年 | 1233篇 |
2018年 | 1284篇 |
2017年 | 1561篇 |
2016年 | 1876篇 |
2015年 | 1745篇 |
2014年 | 2091篇 |
2013年 | 4217篇 |
2012年 | 2808篇 |
2011年 | 2940篇 |
2010年 | 2339篇 |
2009年 | 2679篇 |
2008年 | 2730篇 |
2007年 | 2763篇 |
2006年 | 2623篇 |
2005年 | 2250篇 |
2004年 | 2227篇 |
2003年 | 1982篇 |
2002年 | 1922篇 |
2001年 | 1438篇 |
2000年 | 1466篇 |
1999年 | 1292篇 |
1998年 | 1159篇 |
1997年 | 1077篇 |
1996年 | 954篇 |
1995年 | 926篇 |
1994年 | 725篇 |
1993年 | 640篇 |
1992年 | 611篇 |
1991年 | 448篇 |
1990年 | 434篇 |
1989年 | 346篇 |
1988年 | 339篇 |
1987年 | 248篇 |
1986年 | 225篇 |
1985年 | 216篇 |
1984年 | 209篇 |
1983年 | 95篇 |
1982年 | 166篇 |
1981年 | 76篇 |
1980年 | 58篇 |
1979年 | 60篇 |
1978年 | 28篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
随机化交通灯的二维元胞自动机交通模型 总被引:8,自引:0,他引:8
元胞自动机交通模型以简单的规则反映交通系统中的多种因素,可以分析各种交通现象,且可在计算机上方便、高效地运作·Biham-Middleton-Levine模型(BML模型)实现了二维交通问题的元胞自动机模型的模拟研究·本文对BML模型作了改进,解除了该模型中关于交通灯同步变化的限制·在新模型中,每个路口的交通灯可以自由选定起始工作时间和变化节奏,于是可以更全面、准确地反映交通灯对交通系统性能的影响·本文还对新模型中出现的若干新效应作了解释· 相似文献
142.
Two Convergence Problems for Monotone Sequences 总被引:1,自引:0,他引:1
Eight measures of rate of convergence of monotone sequences of real numbers have been proposed and discussed in a paper by Beyer, Ebanks, and Qualls (Acta Appl. Math. 20 (1990), 267–284). These rates arose in discussions of dynamical systems. In the comparisons of these rates, two problems remained. A complete answer is given to one of the problems and a partial answer is given to the other problem. 相似文献
143.
We establish the optimal asymptotic decay rate of per-session queue length tail distributions for a two-queue system where
a single constant rate server serves the two queues using the Generalized Processor Sharing (GPS) scheduling discipline. The
result is obtained using the sample-path large deviation principle and has implications in call admission control for high-speed
communication networks.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
144.
A highly selective solid phase extraction sorbent for pre-concentration of sameridine made by molecular imprinting 总被引:5,自引:0,他引:5
Summary A novel approach to solid phase extraction, based on the use of a highly selective molecularly imprinted polymer, is presented.
The versatility of this type of sorbent for solid phase extraction was demonstrated in a model batch-wise pre-concentration
of sameridine prior to gas chromatography. Problems associated with leakage of remaining imprint molecules during the desorption
phase could be eliminated by the use of a close structural analogue of sameridine as the imprint species. It was found that
a major benefit of the imprinted polymer was its specificity, which lead to distinctly cleaner chromatographic traces and
ability to improve sensitivity by extracting sameridine from larger sample volumes. 相似文献
145.
A free-piston driver that employs entropy-raising shock processes with diaphragm rupture has been constructed, which promises
significant theoretical advantages over isentropic compression. Results from a range of conditions with helium and argon driver
gases are reported. Significant performance gains were achieved in some test cases. Heat losses are shown to have a strong
effect on driver processes. Measurements compare well with predictions from a quasi-one-dimensional numerical code.
Received 7 September 1996 / Accepted 5 October 1996 相似文献
146.
Peptides containing azaglycine located terminally or within the backbone have been prepared in the solid phase by means of an automatic synthesizer. 相似文献
147.
148.
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
149.
D. V. Kazakov A. I. Voloshin N. N. Kabal'nova V. V. Shereshovets V. P. Kazakov 《Russian Chemical Bulletin》1996,45(10):2452-2453
Chemiluminescence (CL) was found upon the isomerization of dimethyldioxirane in the gas phase under argon atmosphere. The intensity of CL increases as temperature increases and decreases with time at constant temperature. If Silipor is placed in a cell containing the dimethyldioxirane vapor in argon, the intensity of CL sharply increases (more than 10 times) and then decreases following the exponential law. In all cases tripletly excited methyl acetate is the emitter of chemiluminescence.[/ p]Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2582–2583, October 1996. 相似文献
150.
A method employing a wide pore polymeric reversed phase column has been developed for the separation of most of the chlorophylls and related compounds previously described as occurring in marine microalgae. The high selectivity toward molecular shape of this kind of stationary phase has enabled compounds of very similar structure, such as chlorophylls c1, c2 and Mg-divinylpheoporphyrin a5 monomethyl ester, and chlorophyll a and the phytol-substituted chlorophyll c-like pigments, which commonly coelute on monomeric bonded phases, to be resolved in a single run. Some of these pigments, formerly thought to be a single compound, have, in fact, been demonstrated to be groups of two or more. The method has been successfully applied to both algal cultures and natural sea water samples. When visible light absorbance detection was used, the method proved suitable for separation of various carotenoids. 相似文献