全文获取类型
收费全文 | 4841篇 |
免费 | 658篇 |
国内免费 | 1646篇 |
专业分类
化学 | 5027篇 |
晶体学 | 406篇 |
力学 | 183篇 |
综合类 | 59篇 |
数学 | 117篇 |
物理学 | 1353篇 |
出版年
2024年 | 11篇 |
2023年 | 76篇 |
2022年 | 246篇 |
2021年 | 264篇 |
2020年 | 249篇 |
2019年 | 157篇 |
2018年 | 153篇 |
2017年 | 216篇 |
2016年 | 241篇 |
2015年 | 213篇 |
2014年 | 251篇 |
2013年 | 502篇 |
2012年 | 348篇 |
2011年 | 418篇 |
2010年 | 331篇 |
2009年 | 354篇 |
2008年 | 381篇 |
2007年 | 418篇 |
2006年 | 395篇 |
2005年 | 352篇 |
2004年 | 281篇 |
2003年 | 252篇 |
2002年 | 215篇 |
2001年 | 137篇 |
2000年 | 128篇 |
1999年 | 88篇 |
1998年 | 89篇 |
1997年 | 70篇 |
1996年 | 57篇 |
1995年 | 42篇 |
1994年 | 51篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1959年 | 1篇 |
排序方式: 共有7145条查询结果,搜索用时 62 毫秒
991.
在150℃下对聚酰胺6(PA6)纤维进行了水热处理,通过二维广角X射线衍射(2D-WAXD)、二维小角X射线散射(2D-SAXS)、示差扫描量热法(DSC)、场发射扫描电子显微镜(FE-SEM)和单丝强力测试等表征方法,研究了水热处理对纤维结构、热学和力学性能的影响.水热条件下,随温度的增加,水分子渗透作用增强,分子链的运动加剧,纤维的内部结构发生变化.纤维晶区结构由原来的γ晶型转变成为α晶型,结晶度和晶区完善程度提高,微晶尺寸增加,从而使纤维的热稳定性提高,熔融温度和熔融焓增加.水热处理使得纤维形成了折叠链片晶结构.在拉伸过程中,纤维的长周期不断增加,片晶有序性排列程度提高.水热处理后PA6纤维非晶区体积分数降低,并伴随有微孔和大的孔洞的形成,纤维的断裂强度和断裂伸长率都有所降低. 相似文献
992.
Dr. Jing Guo Dr. Hanzheng Guo Amanda L. Baker Prof. Michael T. Lanagan Dr. Elizabeth R. Kupp Prof. Gary L. Messing Prof. Clive A. Randall 《Angewandte Chemie (International ed. in English)》2016,55(38):11457-11461
This paper describes a sintering technique for ceramics and ceramic‐based composites, using water as a transient solvent to effect densification (i.e. sintering) at temperatures between room temperature and 200 °C. To emphasize the incredible reduction in sintering temperature relative to conventional thermal sintering this new approach is named the “Cold Sintering Process” (CSP). Basically CSP uses a transient aqueous environment to effect densification by a mediated dissolution–precipitation process. CSP of NaCl, alkali molybdates and V2O5 with small concentrations of water are described in detail, but the process is extended and demonstrated for a diverse range of chemistries (oxides, carbonates, bromides, fluorides, chlorides and phosphates), multiple crystal structures, and multimaterial applications. Furthermore, the properties of selected CSP samples are demonstrated to be essentially equivalent as samples made by conventional thermal sintering. 相似文献
993.
Cover Picture: Fast‐Geomimicking using Chemistry in Supercritical Water (Angew. Chem. Int. Ed. 34/2016)
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
994.
995.
996.
997.
Agibert SA Moreira MB Ratusznei SM Rodrigues JA Zaiat M Foresti E 《Applied biochemistry and biotechnology》2007,136(2):193-206
The effect of temperature on the performance of an anaerobic sequencing biofilm batch reactor (ASBBR) with liquid-phase recirculation
was assessed. Assays were performed using a recirculation velocity of 0.20 cm/s, 8-h cycles, and an average treated synthetic
wastewater volume of 2 L/cycle with a concentration of 500 mg of Chemical Oxygen Demand (COD)/L. Operation temperatures were
15, 20, 25, 30, and 35°C. At 25, 30, and 35°C, organic matter removal efficiencies for filtered samples ranged from 81 to
83%. At lower temperatures, namely 15 and 20°C, removal efficiency decreased significantly to 61 and 65%, respectively. A
first-order model could be fitted to the experimental concentration profile values. The first-order kinetic parameter value
of this model varied from 0.46 to 0.81 h1 considering the lowest and highest temperature studied. Moreover, analysis of the removal profile values allowed fitting
of an Arrhenius-type equation with an activation energy of 5715 cal/mol. 相似文献
998.
Alginate polysaccharide is a promising biosorbent for metal uptake. Dry protonated calcium alginate beads for biosorption
applications were prepared, briefly characterized and tested for lead uptake. Several advantages of this biosorbent are reported
and discussed in comparison with other alginate-based sorbents. The alginate beads contained 4.7 mmol/g of COOH groups, which
suffered hydrolysis near pH 4. The Weber and Morris model, applied to kinetic results of lead uptake, showed that intraparticle
diffusion was the rate-controlling step in lead sorption by dry alginate beads. Equilibrium experiments were performed and
the data were fitted with different isotherm models. The Langmuir equation was the most adequate to model lead sorption. The
maximum uptake capacity (q
max) was estimated as 339 mg/g and the Langmuir constant (b) as 0.84 l/mg. These values were compared with that of other sorbents found in the literature, indicating that dry protonated
calcium alginate beads are among the best biosorbents for the treatment and recovery of heavy metals from aqueous streams. 相似文献
999.
Concern is growing over the contamination of the environment with pharmaceutical residues, among which non-steroidal anti-inflammatory
drugs (NSAIDs) are one of the most abundant groups. Their widespread appearance in the aquatic environment is because of their
high consumption and their incomplete removal during wastewater treatment. Because effective operation of wastewater-treatment
plants is important for minimising the release of xenobiotic compounds, for example pharmaceutical products, into the aquatic
environment, our study focuses on removal of commonly used NSAIDs (ibuprofen, naproxen, ketoprofen, diclofenac) and clofibric
acid in a specially designed small-scale pilot wastewater treatment plant (PWWTP). This study shows that, except for diclofenac,
steady-rate removal of NSAIDs over a two-year monitoring period has been achieved. Elimination of the compounds in the PWWTP
was ≥87% for ibuprofen, naproxen and ketoprofen but only 49–59% for diclofenac. We also studied clofibric acid. Results after
one month of operation revealed 30% elimination with no sign of adaptation by the biomass. Also described are degradation
products of diclofenac, which we were able to identify because of the similarity of their mass spectra with those in the NIST
library and by comparing the retention times of different compounds. Although the structures of these compounds were confirmed
with a high probability (99%), we still need to compare the fragmentation of authentic compounds with degradation products
formed under our experimental conditions. Degradation products of ibuprofen, naproxen, ketoprofen, and clofibric acid were
found but these must be identified by use of high-resolution mass spectrometry and analysis of authentic compounds. 相似文献
1000.
The interaction of a Pt6 nanoparticle with different oxide supports, viz., γ-Al2O3, FAU and MFI zeolites, was investigated using the density functional theory. The interaction with the basic oxygen anions of the lattice and with hydroxyl groups of the support affects the electronic structure of the metal particles. The transfer of H atoms of the hydroxyl groups to the metal particle suppresses the Brönsted acidity of the support, and the activation energy of proton transfer decreases with an increase in the acidity of the support. The potential energy profiles were calculated for the transfer processes, and changes in the electronic structures and charge distribution of the supported particles were outlined. The H atom transfer results in positive charging by the metal particles, whereas the interaction with basic sites leads to the appearance of electron-enriched metal clusters. 相似文献