全文获取类型
收费全文 | 2476篇 |
免费 | 148篇 |
国内免费 | 16篇 |
专业分类
化学 | 1943篇 |
晶体学 | 23篇 |
力学 | 82篇 |
数学 | 114篇 |
物理学 | 478篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 29篇 |
2021年 | 69篇 |
2020年 | 43篇 |
2019年 | 61篇 |
2018年 | 41篇 |
2017年 | 42篇 |
2016年 | 95篇 |
2015年 | 96篇 |
2014年 | 118篇 |
2013年 | 159篇 |
2012年 | 272篇 |
2011年 | 256篇 |
2010年 | 152篇 |
2009年 | 136篇 |
2008年 | 189篇 |
2007年 | 157篇 |
2006年 | 146篇 |
2005年 | 125篇 |
2004年 | 101篇 |
2003年 | 93篇 |
2002年 | 87篇 |
2001年 | 36篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有2640条查询结果,搜索用时 312 毫秒
941.
An efficient and regioselective introduction method of 2-methylpyridines to the secondary position of Baylis-Hillman adducts has been developed. A base treatment of 2-methylpyridinium salt of Baylis-Hillman bromide generated N-allylenamine intermediate which underwent a facile 3-aza-Cope rearrangement under mild conditions to produce the product. 相似文献
942.
943.
We have developed a microfluidic gradient device for controlling mucin gene expression of NCI-H292 epithelial cells derived from lung tissues. We hypothesized that gradient profiles would control mucin gene expression of lung epithelial cells. However, it was not possible to generate various stable gradient profiles using conventional culture methods. To address this limitation, we used a microfluidic gradient device to create various gradient profiles (i.e. non-linear, linear, and flat) in a temporal and spatial manner. NCI-H292 lung epithelial cells were exposed to concentration gradients of epidermal growth factor in a microfluidic gradient device with continuous medium perfusion. We demonstrated an effect of gradient profiles on mucin expression of lung epithelial cells cultured in the microfluidic gradient device. It was revealed that NCI-H292 lung epithelial cells exposed to the flat gradient profile of the epidermal growth factor exhibited high expression of mucin as compared with cells exposed to non-linear and linear gradient profiles. Therefore, this microfluidic gradient device could be a potentially useful tool for regulating the mucin expression of lung epithelial cells exposed to chemokine gradient profiles. 相似文献
944.
Myung Ho Lee Euo Chang Jung Kyuseok Song Yun Hee Han Hyun Sang Shin 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(2):639-645
This work investigates the sorption of americium [Am(III)] onto kaolinite and the influence of humic acid (HA) as a function
of pH (3–11). It has been studied by batch experiments (V/m = 250:1 mL/g, C
Am(III) = 1 × 10−5 mol/L, C
HA = 50 mg/L). Results showed that the Am(III) sorption onto the kaolinite in the absence of HA was typical, showing increases
with pH and a distinct adsorption edge at pH 3–5. However in the presence of HA, Am sorption to kaolinite was significantly
affected. HA was shown to enhance Am sorption in the acidic pH range (pH 3–4) due to the formation of additional binding sites
for Am coming from HA adsorbed onto kaolinite surface, but reduce Am sorption in the intermediate and high pH above 6 due
to the formation of aqueous Am-humate complexes. The results on the ternary interaction of kaolinite–Am–HA are compared with
those on the binary system of kaolinite–HA and kaolinite–Am and adsorption mechanism with pH are discussed. Effect of different
molecular weight of HA, with three HA fractions separated by ultrafiltration techniques, on the Am sorption to kaolinite were
also studied. The results showed that the enhancement of the sorption of Am onto kaolinite at the acidic pH conditions (pH
3–4) was higher with HA fractions of higher molecular weight. Also, the Am sorption over a pH range from 6 to 10 decreased
with decreasing molecular weight of HA. 相似文献
945.
Hui-Jun Won Byambatseren Baigalmaa Jei-Kwon Moon Chong-Hun Jung Kune-Woo Lee Jae-Hyuk Hyun 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(2):525-531
Type 304 stainless steel specimens artificially contaminated with CsCl solution were treated with KOH solution and KNO3 solution, respectively. Cs+ ion removal tests by a Q-switched Nd:YAG laser at 1064 nm at a given fluence of 57.3 J/cm2 were performed. The surface morphology and the relative atomic mole ratio of the specimen surface were investigated by SEM
and EPMA. The order of Cs+ ion removal efficiency of laser was no-treatment < KOH < KNO3 during the 42 shots. From the investigation of XPS peaks around 532.7 and 292.9 eV, KNO3 on a surface of specimen was found to be fully decomposed during the laser irradiation. It was suggested that Cs2O particulates formed by the reaction between the reactive oxygen generated from the nitrate ion and Cs+ ion on the metal surface could be easily suspended. For the KOH system, FeOOH was formed during the laser irradiation and
it changed into Fe2O3. It was also suggested that Cs2O particulates were formed by the reaction between the reactive oxygen generated from the decomposition of K2O and Cs+ ion on the metal surface.. 相似文献
946.
947.
948.
949.
The standard centrifuge is a laboratory instrument widely used by biologists and medical technicians for preparing cell samples. Efforts to automate the operations of concentration, cell separation, and solution exchange that a centrifuge performs in a simpler and smaller platform have had limited success. Here, we present a microfluidic chip that replicates the functions of a centrifuge without moving parts or external forces. The device operates using a purely fluid dynamic phenomenon in which cells selectively enter and are maintained in microscale vortices. Continuous and sequential operation allows enrichment of cancer cells from spiked blood samples at the mL min(-1) scale, followed by fluorescent labeling of intra- and extra-cellular antigens on the cells without the need for manual pipetting and washing steps. A versatile centrifuge-analogue may open opportunities in automated, low-cost and high-throughput sample preparation as an alternative to the standard benchtop centrifuge in standardized clinical diagnostics or resource poor settings. 相似文献
950.
A portable sensor platform for the detection of small molecular species is crucial for the on-site monitoring of environmental pollutants, food toxicants, and disease-related metabolites. However, it is still extremely difficult to find highly selective and sensitive sensor platforms for general small molecular detection. Herein, we report aptamer sandwich-based carbon nanotube sensor strategy for small molecular detection, where aptamers were utilized to capture target molecules as well as to enhance the sensor signals. We successfully demonstrated the detection of non-polar bisphenol A molecules with a 1 pM sensitivity. Significantly, our sensors were able to distinguish between similar small molecular species with single-carbon-atomic resolution. Furthermore, using the additional biotin modification on labeling aptamer, we enhanced the detection limit of our sensors down to 10 fM. This strategy allowed us to detect non-polar small molecular species using carbon nanotube transistors, thus overcoming the fundamental limitation of field effect transistor-based sensors. Considering the extensive applications of sandwich assay for the detection of rather large biomolecules, our results should open up completely new dimension in small molecular detection technology and should enable a broad range of applications such as environmental protection and food safety. 相似文献