全文获取类型
收费全文 | 15226篇 |
免费 | 1163篇 |
国内免费 | 1007篇 |
专业分类
化学 | 12676篇 |
晶体学 | 80篇 |
力学 | 823篇 |
综合类 | 128篇 |
数学 | 429篇 |
物理学 | 3260篇 |
出版年
2024年 | 19篇 |
2023年 | 111篇 |
2022年 | 329篇 |
2021年 | 292篇 |
2020年 | 408篇 |
2019年 | 343篇 |
2018年 | 359篇 |
2017年 | 439篇 |
2016年 | 503篇 |
2015年 | 496篇 |
2014年 | 526篇 |
2013年 | 914篇 |
2012年 | 1202篇 |
2011年 | 751篇 |
2010年 | 643篇 |
2009年 | 680篇 |
2008年 | 669篇 |
2007年 | 871篇 |
2006年 | 782篇 |
2005年 | 649篇 |
2004年 | 667篇 |
2003年 | 603篇 |
2002年 | 502篇 |
2001年 | 381篇 |
2000年 | 419篇 |
1999年 | 428篇 |
1998年 | 379篇 |
1997年 | 398篇 |
1996年 | 332篇 |
1995年 | 349篇 |
1994年 | 291篇 |
1993年 | 257篇 |
1992年 | 294篇 |
1991年 | 192篇 |
1990年 | 159篇 |
1989年 | 160篇 |
1988年 | 129篇 |
1987年 | 90篇 |
1986年 | 70篇 |
1985年 | 52篇 |
1984年 | 68篇 |
1983年 | 29篇 |
1982年 | 36篇 |
1981年 | 22篇 |
1980年 | 33篇 |
1979年 | 23篇 |
1978年 | 16篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Summary The gas chromatographic behaviour of crosslinked macroporous 2-hydroxyethyl methacrylate grafted with 2-methyloxazoline was
investigated and the range of applicability of the copolymer was assessed. Retention index values were measured on this copolymer
and compared with those obtained on the terpolymer 2-hydroxyethyl methacrylate-ethylene dimethacrylate-acrylonitrile. Rohrschneider
constants and efficiency data for selected sorbates are given. The use of this type of polymer in the separation of various
types of compounds is documented by various examples. 相似文献
22.
Summary The solubility parameters of cationic surfactants were obtained using the inverse gas chromatographic technique. The surfactants
didodecyl dimethyl ammonium bromide, dioctadecyl dimethyl ammonium bromide and dodecyl pyridinium chloride were used as stationary
phase and retention data of different probe solutes were measured at different temperatures. The results were analysed by
the combination of Flory-Huggins and Hildebrand theories, and the solubility parameters of the surfactants were obtained in
a range of temperatures between 80–120°C. 相似文献
23.
燃煤烟气中AsSePb的形态分布及SCl元素对其形态分布的影响 《燃料化学学报》2003,48(11):1298-1309
基于化学热力学平衡分析方法,计算分析了燃煤烟气中重金属As、Se、Pb的形态分布规律,研究了S、Cl等元素对As、Se、Pb的形态分布规律的影响。结果表明,氧化性气氛下,As以As2O5、As4O6、AsO等氧化物的形式存在;Se主要以SeO2形式存在;Pb在1000 K以下主要是固态PbSO4,1200 K以上为气态PbO。还原性气氛下,As在较低温度时为固态As2S2,900-1400 K以As2、AsS、AsN气体共存,2000 K以上全部转化为气态AsO。Se在1100 K以下主要以气态H2Se存在,1100 K开始生成SeS和Se2气体,1800 K时主要是气态Se和少量气态SeO;Pb在中低温时主要是PbS,1800 K以上气态Pb为主要存在形态。S在还原性气氛下增大了AsS(g)、PbS(g)、SeS(g)的比例,氧化性气氛下对As、Se、Pb形态分布基本无影响;Cl无论在氧化还是还原气氛下对As、Se影响均较小,但对Pb的形态分布影响较大。 相似文献
24.
25.
I. El-Kady R. Biswas Y. Ye M. F. Su I. Puscasu Martin Pralle E. A. Johnson J. Daly A. Greenwald 《Photonics and Nanostructures》2003,1(1):69-77
In this work, we present both the theoretical basis as well as supporting experimental measurements for development of a novel mid-infrared thermally stimulated narrow band emitter with a spectral bandwidth of less than 10%. To achieve this, we utilize a metallized-surface 2D photonic crystal of air voids in a silicon background with hexagonal structure symmetry. Our results are based on the generation of discrete surface plasmon (SP) modes in the thin metallized layer residing on the top surface. This yields a series of adequately spaced discrete peaks in the reflection spectrum, dominated by a single sharp feature corresponding to the lowest plasmon order, in an otherwise uniform highly reflective spectrum (>90%) over most of the IR spectrum. This, in turn, gives rise to a sharp absorption feature with a correspondingly narrow thermal emission peak in the emission spectrum. Transfer matrix calculations simulate well both the position and strengths of the absorption peaks. By altering the period of the surface photonic lattice, the SP peak and emissive band can be tuned to the desired wavelength. These devices promise a new class of tunable infrared emitters with high power in a narrow spectral bandwidth. Such narrow band sources are critical to achieving high efficiency gas sensors. 相似文献
26.
27.
The hydrocarbon discovery prediction problem is important to firms having to make decisions about the deployment of scarce exploration resources. Traditional methods for estimating the discovery rate rely on the completion of time consuming simulation experiments. A rapid approximation that does not require the completion of simulation exists and has been shown to have some promise as a prediction tool. This paper investigates the accuracy of the approximation method under a wide variety of distributional and drilling efficiency assumptions. The results indicate that the approximation produces predictions close to those of simulation under most of the tested conditions. This suggests that resource exploration firms could conveniently use the method for a wide variety of planning purposes without incurring the same costs in time and personnel required for simulation. 相似文献
28.
This contribution discusses the phenomena of retrograde condensation of one or two liquids. It w1 be shown that both phenomena can be well understood. Also the relation of retrograde condensation of one liquid phase with the condensation behavior of natural gas will be discussed. Similarly that of two liquid phases with multiple phase behavior occurring in low temperature reservoir fluids will be pointed out. 相似文献
29.
G. N. Merrill 《Journal of Physical Organic Chemistry》2007,20(1):19-29
Ab initio molecular orbital calculations were carried out on epibromohydrin (EBH) and epichlorohydrin (ECH) in an attempt to elucidate their reactivity with respect to a hard nucleophile, hydroxide. These systems were modeled in both the gas phase and a polar solvent under basic conditions. In the gas phase, it was determined that a direct displacement mechanism (nucleophilic attack at the C1 position) was operative for EBH, while an indirect pathway (nucleophilic attack at the C3 position and subsequent intramolecular displacement) was followed for ECH. In an acetone solution, only the indirect displacement mechanism was found to occur. An electrostatic argument is advanced to account for this behavior in polar solution. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
30.