全文获取类型
收费全文 | 80146篇 |
免费 | 8201篇 |
国内免费 | 7700篇 |
专业分类
化学 | 41619篇 |
晶体学 | 2836篇 |
力学 | 6749篇 |
综合类 | 1167篇 |
数学 | 17213篇 |
物理学 | 26463篇 |
出版年
2023年 | 596篇 |
2022年 | 1178篇 |
2021年 | 2497篇 |
2020年 | 2089篇 |
2019年 | 2090篇 |
2018年 | 1814篇 |
2017年 | 2265篇 |
2016年 | 2846篇 |
2015年 | 2395篇 |
2014年 | 3535篇 |
2013年 | 6205篇 |
2012年 | 3972篇 |
2011年 | 4412篇 |
2010年 | 3974篇 |
2009年 | 4824篇 |
2008年 | 4863篇 |
2007年 | 5090篇 |
2006年 | 4383篇 |
2005年 | 3549篇 |
2004年 | 3425篇 |
2003年 | 2989篇 |
2002年 | 5262篇 |
2001年 | 2512篇 |
2000年 | 2004篇 |
1999年 | 1830篇 |
1998年 | 1674篇 |
1997年 | 1254篇 |
1996年 | 1233篇 |
1995年 | 1141篇 |
1994年 | 1073篇 |
1993年 | 1001篇 |
1992年 | 933篇 |
1991年 | 668篇 |
1990年 | 495篇 |
1989年 | 395篇 |
1988年 | 405篇 |
1987年 | 361篇 |
1986年 | 335篇 |
1985年 | 477篇 |
1984年 | 383篇 |
1983年 | 224篇 |
1982年 | 393篇 |
1981年 | 534篇 |
1980年 | 455篇 |
1979年 | 504篇 |
1978年 | 399篇 |
1977年 | 311篇 |
1976年 | 260篇 |
1974年 | 80篇 |
1973年 | 174篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
This paper reports that the m-plane GaN layer is grown on (200)-plane LiAlO2 substrate by metal-organic chemical wpour deposition (MOCVD) method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer's thickness. The high transmittance (80%), sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate. 相似文献
122.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
123.
Bajdik J. Pintye-Hódi K. Novák Cs. Kelemen A. Regdon G. Erős I. 《Journal of Thermal Analysis and Calorimetry》2002,68(2):613-627
The extents of the protective effects of coating films on the surface of crystals were determined. Three different samples
were made with different quantities of coating fluid (Sepifilm LP 010 in 10% aqueous solution). Since the atomizing rate was
constant, the coating time increased in parallel with the volume of coating fluid applied. The direct measurement of film
thickness and smoothness is very difficult, and therefore indirect methods were used. Dimenhydrinate was chosen as model drug;
this is a heat-sensitive antihistamine with a low melting point. This temperature can be reached during the tableting process.
The behaviour of samples on exposure to heat was examined by differential scanning calorimetry. The water uptakes of the samples
were determined with an Enslin apparatus. Plasticity was studied with an instrumented tablet machine. These indirect methods
(thermal conductivity, water uptake and plasticity measurements) revealed connections between the results of the various experiments.
An overlong coating time decreased the protective effect of the coating film.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
124.
125.
中国证券市场股指波动的条件异方差特性分析 总被引:6,自引:0,他引:6
股指的波动具有持续性、集聚性 ,如何进行判别 ?本文用 Garch模型理论探讨沪深股指的这种条件异方差特征 ,进一步分析波动是否影响股指未来变化 ,以及股市对利好、利空的消息是否存在不对称的反映。同时 ,比较不同类型的股指的共性及差异 ,并对上述现象作了解释和说明。 相似文献
126.
沈有根 《中国科学A辑(英文版)》2002,45(3):400-408
Using the membrane model which is based on brick wall model, we calculated the free energy and entropy of Garfinkle-Horne dilatonic black hole due to arbitrary spin fields. The result shows that the entropy of scalar field and the entropy of Fermionic field have similar formulas. There is only a coefficient between them. 相似文献
127.
Cosmic dust and our origins 总被引:1,自引:0,他引:1
J Mayo Greenberg 《Surface science》2002,500(1-3):793-822
The small solid particles in the space between the stars provide the surfaces for the production of many simple and complex molecules. Processes involving the effects of ultraviolet irradiation of the thin (hundredth micron) mantles are shown to produce a wide range of molecules and ions also seen in comets. Some of the more complex ones inferred from laboratory experiments are expected to play an important role in the origin of life. An outline of the chemical evolution of interstellar dust as observed and as studied in the laboratory is presented. Observations of comets are shown to provide substantial evidence for their being fluffy aggregates of interstellar dust as it was in the protosolar nebula, i.e. the interstellar cloud which collapsed to form the solar system. The theory that comets may have brought the progenitors of life to the earth is summarized. 相似文献
128.
Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles. 相似文献
129.
F. Balibrea 《Topology and its Applications》2006,153(12):2092-2095
Recently, Forti, Paganoni and Smítal constructed an example of a triangular map of the unite square, F(x,y)=(f(x),g(x,y)), possessing periodic orbits of all periods and such that no infinite ω-limit set of F contains a periodic point. In this note we show that the above quoted map F has a homoclinic orbit. As a consequence, we answer in the negative the problem presented by A.N. Sharkovsky in the eighties whether, for a triangular map of the square, existence of a homoclinic orbit implies the existence of an infinite ω-limit set containing a periodic point. It is well known that, for a continuous map of the interval, the answer is positive. 相似文献
130.