全文获取类型
收费全文 | 12169篇 |
免费 | 1270篇 |
国内免费 | 1279篇 |
专业分类
化学 | 10205篇 |
晶体学 | 95篇 |
力学 | 1058篇 |
综合类 | 184篇 |
数学 | 569篇 |
物理学 | 2607篇 |
出版年
2024年 | 28篇 |
2023年 | 185篇 |
2022年 | 413篇 |
2021年 | 511篇 |
2020年 | 596篇 |
2019年 | 422篇 |
2018年 | 439篇 |
2017年 | 458篇 |
2016年 | 596篇 |
2015年 | 530篇 |
2014年 | 582篇 |
2013年 | 1249篇 |
2012年 | 696篇 |
2011年 | 697篇 |
2010年 | 530篇 |
2009年 | 606篇 |
2008年 | 587篇 |
2007年 | 699篇 |
2006年 | 614篇 |
2005年 | 547篇 |
2004年 | 484篇 |
2003年 | 410篇 |
2002年 | 412篇 |
2001年 | 274篇 |
2000年 | 303篇 |
1999年 | 249篇 |
1998年 | 243篇 |
1997年 | 200篇 |
1996年 | 169篇 |
1995年 | 153篇 |
1994年 | 114篇 |
1993年 | 125篇 |
1992年 | 110篇 |
1991年 | 79篇 |
1990年 | 63篇 |
1989年 | 36篇 |
1988年 | 44篇 |
1987年 | 36篇 |
1986年 | 30篇 |
1985年 | 33篇 |
1984年 | 32篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
The water behavior on (001) and (100) crystal faces of hydroxyapatite (HAP) were studied using molecular dynamics (MD) simulations.
The study showed that the water molecules between the HAP faces were under conditions of strong electrical field and high
pressure, and hence formed 2–3 well-organized water layers on the crystal surfaces. These structured water layers had ice-like
features. Compared with the crystallographic [100] direction of HAP, the polarity along the [001] direction was stronger,
which resulted in more structured water layers on the surface. The interaction of water molecules with the calcium and phosphate
sites at the HAP-water interface was also studied. The results indicated the multiple pathways of water adsorption onto the
HAP surfaces. This study revealed the formation and the detailed structure of water layers on HAP surfaces and suggested that
the interfacial water played an important role in stabilizing the HAP particles in aqueous solutions.
Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(8): 1392–1400 (in Chinese) 相似文献
982.
983.
A review of heat treatment on polyacrylonitrile fiber 总被引:3,自引:0,他引:3
Developing carbon fiber from polyacrylonitrile (PAN) based fiber is generally subjected to three processes namely stabilization, carbonization, and graphitization under controlled conditions. The PAN fiber is first stretched and simultaneously oxidized in a temperature range of 200-300 °C. This treatment converts thermoplastic PAN to a non-plastic cyclic or a ladder compound. After oxidation, the fibers are carbonized at about 1000 °C in inert atmosphere which is usually nitrogen. Then, in order to improve the ordering and orientation of the crystallites in the direction of the fiber axis, the fiber must be heated at about 1500-3000 °C until the polymer contains 92-100%. High temperature process generally leads to higher modulus fibers which expel impurities in the chain as volatile by-products. During heating treatment, the fiber shrinks in diameter, builds the structure into a large structure and upgrades the strength by removing the initial nitrogen content of PAN precursor and the timing of nitrogen. With better-controlled condition, the strength of the fiber can achieve up to 400 GPa after this pyrolysis process. 相似文献
984.
A one-dimensional chain coordination polymer [Co(Ⅱ)(C6H5CH=CHCOOH)2(4,4'-bipy)(H2O)5]n has been synthesized with cinnamylic acid, 4,4'-bipy and cobaltous chloride as raw materials. Crystal data for this complex: monoclinic, space group P21/c, a - 1.1481(3), b =1.1230(2), c = 1.1759(3) nm, β = 97.054(4)°, V = 1.5046(6) nm3, Mr= 617.50, Dc = 1.363 g/cm3, Z= 2, μ(MoKα) = 0.627 mm-1, F(000) = 646, S = 1.062, R 0.0443 and wR = 0.1178. The crystal structure shows that two neighboring cobalt(Ⅱ) ions are linked together by one 4,4'-bipy, and the whole complex molecule adopts a one-dimensional chain structure. Each cobalt(Ⅱ) ion is coordinated with two nitrogen atoms from two 4,4'-bipy molecules and four oxygen atoms from four water molecules, giving a distorted octahedral coordination geometry. The electrochemical properties were analyzed by combining with the crystal structure. 相似文献
985.
固相萃取-液质联用法同时测定饮用水中双酚A和邻苯二甲酸二丁酯 总被引:8,自引:0,他引:8
建立了饮用水中痕量双酚A和邻苯二甲酸二丁酯同时测定的LC/MS-MS快速分析方法.水样中双酚A和邻苯二甲酸二丁酯经HLB固相萃取小柱富集,以V(乙腈)∶V(水)=90∶10为流动相,选择双酚A m/z 227/212、邻苯二甲酸二丁酯m/z 301/228为检测离子对,利用多反应监测(MRM)和扫描时间分段检测技术实现正、负离子不同扫描模式一次完成.该方法对水样体积为250 mL时双酚A和邻苯二甲酸二丁酯的线性范围为0.4~40 ng/L,检出限分别为0.16和0.10 ng/L,低中高3个不同水平的加标平均回收率均在90%以上.应用于5种不同来源的饮用水及原水中双酚A和邻苯二甲酸二丁酯的测定. 相似文献
986.
环境水样中百菌清残留的单滴微萃取-反相液相色谱测定 总被引:6,自引:1,他引:6
应用单滴微萃取(SDME)-反相液相色谱(RPLC)检测了环境水样中的百菌清残留.优化了单滴微萃取条件:环己烷萃取剂6 μL、单滴体积2 μL、搅拌速率350 r/min、萃取时间40 min、水溶液温度35 ℃、无盐度.水样经单滴微萃取后,使用Hypersil C18柱反相液相色谱分离测定百菌清.反相液相色谱条件:100%甲醇流动相、流速1.0 mL/min、柱温25 ℃、224 nm检测.方法的线性范围、检出限、相对标准偏差和富集倍数分别为1.0 ~50 μg/L、0.02 μg/L、6.1%和427倍.采用该法对环境水样中的百菌清残留进行了测定,环境水样的加标回收率为98% ~106%. 相似文献
987.
988.
在对某研究区进行环境调查的基础之上,质予以评价,查明研究区内地下水环境质量现状。源合理利用和规划需要提供一定的依据。对区内地下水进行了取样分析,并对地下水水为该区域地下水资源利用、环境保护、土地资 相似文献
989.
An overview of analytical methodologies for the determination of antibiotics in environmental waters 总被引:3,自引:0,他引:3
The widespread occurrence of antibiotics as contaminants in the aquatic environment has increased attention in the last years. The concern over the release of antibiotics into the environment is related primarily to the potential for the development of antimicrobial resistance among microorganisms. This article presents an overview of analytical methodologies for the determination of quinolone (Qs) and fluoroquinolone (FQs), macrolide (MLs), tetracycline (TCs), sulfonamide (SAs) antibiotics and trimethoprim (TMP) in different environmental waters. The analysis of these antibiotics has usually been carried out by high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS/MS) and to a lesser extent by ultraviolet (UV) or fluorescence detection (FD). A very important step before LC analysis is sample preparation and extraction leading to elimination of interferences and prevention of matrix effect and preconcentration of target analytes. 相似文献
990.
Hydroxyl (OH) is identified and characterized on the Ni(111) surface by high‐resolution electron energy loss spectroscopy. We find clear evidence of stretching, bending, and translational modes that differ significantly from modes observed for H2O and O on Ni(111). Hydroxyl may be produced from water by two different methods. Annealing of water co‐adsorbed with atomic oxygen at 85 K to above 170 K leads to the formation of OH with simultaneous desorption of excess water. Pure water layers treated in the same fashion show no dissociation. However, the exposure of pure water to 20 eV electrons at temperatures below 120 K produces OH in the presence of adsorbed H2O. In combination with temperature‐programmed desorption studies, we show that the OH groups recombine between 180 and 240 K to form O and immediately desorbing H2O. The lack of influence of co‐adsorbed H2O at 85 K on the O? H stretching mode indicates that OH does not participate in a hydrogen‐bonding network. 相似文献