全文获取类型
收费全文 | 9995篇 |
免费 | 1984篇 |
国内免费 | 1315篇 |
专业分类
化学 | 7211篇 |
晶体学 | 165篇 |
力学 | 540篇 |
综合类 | 118篇 |
数学 | 1187篇 |
物理学 | 4073篇 |
出版年
2024年 | 43篇 |
2023年 | 308篇 |
2022年 | 491篇 |
2021年 | 485篇 |
2020年 | 569篇 |
2019年 | 573篇 |
2018年 | 487篇 |
2017年 | 414篇 |
2016年 | 571篇 |
2015年 | 591篇 |
2014年 | 635篇 |
2013年 | 849篇 |
2012年 | 938篇 |
2011年 | 874篇 |
2010年 | 653篇 |
2009年 | 618篇 |
2008年 | 601篇 |
2007年 | 520篇 |
2006年 | 435篇 |
2005年 | 382篇 |
2004年 | 319篇 |
2003年 | 270篇 |
2002年 | 253篇 |
2001年 | 206篇 |
2000年 | 158篇 |
1999年 | 162篇 |
1998年 | 122篇 |
1997年 | 99篇 |
1996年 | 105篇 |
1995年 | 86篇 |
1994年 | 71篇 |
1993年 | 54篇 |
1992年 | 45篇 |
1991年 | 53篇 |
1990年 | 48篇 |
1989年 | 33篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
941.
隔膜式电解槽生物膜阴极降解苯酚的过程及其条件的优化 总被引:2,自引:0,他引:2
以炼油废水中的主要污染物苯酚为目标污染物, 采用不同生物膜电极反应器对苯酚进行降解, 从而寻找出降解苯酚的最佳反应途径. 研究结果表明, 运用隔膜式电解槽生物膜阴极区域对苯酚废水进行处理, 其苯酚的去除效果虽然没有在生物膜阴极与阳极相混合的混合式反应器中处理效果好, 但在18 h内苯酚浓度降解到0, 并且其化学需氧量(COD)去除率最高, 在16 h内COD去除率达到80%. 对于隔膜式电解槽生物膜阴极区域的降解条件优化后发现, 电流设定为5 mA, 初始苯酚质量浓度低于200 mg/L, 温度为35 ℃时, 苯酚降解效果最佳. 相似文献
942.
南北五味子镇静催眠活性部位共有成分的分析 总被引:1,自引:0,他引:1
对南北五味子药材进行系统化学部位分离,用镇静催眠药理实验探讨各化学部位的活性作用;同时采用高效液相色谱-电喷雾飞行时间质谱HPLC-DAD-ESI-TOF/MS联用技术分析两种五味子镇静催眠活性部位的组成成分,本方法可对7个联苯环辛烯类成分进行定量分析,并对异构体进行了分离鉴定.结果显示,它们的活性部位分别由约20个联苯环辛烯类化合物组成,这类化合物在活性部位含量均大于80%,检测到10个共有成分,但是成分组成完全不同.对南北五味子各3个产地9批的活性部位进行了检测,均验证了活性部位中联苯环辛烯类总量相近而共有成分组成完全不同的结果. 相似文献
943.
三相中空纤维液相微萃取在羟基苯甲酸类化合物分析中的应用 总被引:1,自引:1,他引:1
在优化的三相中空纤维液相微萃取(3p-HFLPME)条件下,研究了6种羟基苯甲酸类化合物(HBAs)的3p-HFLPME行为;揭示了HBAs的富集因子(EF)与其正庚醇/水条件分配系数(log Pn-heptanol/5 mmol/L HCl)、pKa和羟基数目(N)的相关性,初步阐明了聚偏氟乙烯中空纤维对HBAs的电荷转移传递机理以及有机溶剂对HBAs的选择性萃取机理。优化的3p-HFLPME条件: 以MOF 503聚偏氟乙烯中空纤维为有机溶剂支持体,正庚醇为有机相,5 mmol/L HCl体系为给体,80 mmol/L NH3·H2O为接受相,搅拌速度为1200 r/min,萃取35 min。该方法的精密度(以相对标准偏差计)小于3%,检出限为0.09~30.00 μg/L,加标回收率为93.3%~107.1%,HBAs质量浓度为5 mg/L时的富集因子最高达107.6倍。 相似文献
944.
在含有邻苯二胺和三乙醇胺(TEA)的酸性溶液中,用循环伏安法(CV)在铂电极上制备聚邻苯二胺(PoPD)薄膜.通过对该薄膜进行深入的电化学分析,并将结果与无三乙醇胺参与的聚邻苯二胺的性能进行比较,发现在三乙醇胺参与下得到的聚邻苯二胺薄膜在铂电极表现出更好的粘附性,同时在氢离子选择性电极方面表现出优良的性能.在pH 2~13范围内具有良好的Nernst响应,直线斜率为59.62 mV/pH,相关系数达0.99以上,碱性条件下响应时间可缩短至30 s左右.该电极对大多数普通干扰物具有较好的选择性,可用于实际样品的测试. 相似文献
945.
LingShu Wan BeiBei Ke XiaoKai Li XiangLin Meng LuYao Zhang ZhiKang Xu 《中国科学B辑(英文版)》2009,52(7):969-974
Highly ordered honeycomb-patterned polystyrene (PS)/poly(ethylene glycol) (PEG) films were prepared by a water-assisted method
using an improved setup, which facilitated the formation of films with higher regularity, better reproducibility, and larger
area of honeycomb structures. Surface aggregation of hydrophilic PEG and adsorption of bovine serum albumin (BSA) on the honeycomb-patterned
films were investigated. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were used to
observe the surface morphologies of the films before and after being rinsed with water. As confirmed by the FESEM images and
the AFM phase images, PEG was enriched in the pores and could be gradually removed by water. The adsorption of fluorescence-labeled
BSA on the films was studied in visual form using laser scanning confocal microscopy. Results clearly demonstrated that the
protein-resistant PEG was selectively enriched in the pores. This water-assisted method may be a latent tool to prepare honeycomb-patterned
biofunctional surfaces.
Supported by the National Natural Science Foundation of China (Grant No. 50803053), the National Natural Science Foundation
of China for Distinguished Young Scholars (Grant No. 50625309), the National Postdoctoral Science Foundation of China (Grant
Nos. 20070421172 & 20081466) and the National Undergraduate Innovative Test Program 相似文献
946.
A rapid and simple as well as sensitive inductively coupled plasma mass spectrometry (ICP-MS) method for the determination
of cobalamin is described. Cobalamin in human urine and medicine tablet solutions was converted on-line into free cobalt ions
in acid medium, the cobalt ions were then detected by ICP-MS. Cobalamin was determined by measuring the increase of integral
counts per second intensity, which was linear over the cobalamin concentration range of 1.0 × 10−10 g mL−1 to 8.0 × 10−5 g mL−1, and the limit of detection was 0.05 ng mL−1 (3σ). At the pump rate of 30 rotations per minute, one analysis cycle of cobalamin, including sampling and washing, could be
accomplished in 0.5 min with the relative standard deviations of less than 5 %. The proposed procedure was applied successfully
in monitoring cobalamin in human urine without any pretreatment process and in rapid determination of cobalamin in multivitamin
tablets. 相似文献
947.
Meng Xue RongRong Zhu LiLi Qin FaJie Li ZhiXue Liu XiaoYu Sun ShiLong Wang 《中国科学B辑(英文版)》2009,52(8):1253-1257
To evaluate the antitumor activity and pharmacokinetics of podophyllotoxin (PPT) incorporated into solid lipid nanoparticles
(SLN), Kunming mice inoculated with flesh tumor were used as animal model. The mice received a single daily intraperitoneal
injection of PPT in 20% ethanol (5 mg/kg) and PPT-SLN (5 mg/kg in PPT) for 3 weeks. Gross tumor volumes, body weight and clinical
observations were recorded daily. The mice were sacrificed for 24 h after the last administration, and the tumor inhibition
rate was calculated with the tumor weight. For the pharmacokinetics research, the mice were treated with intraperitoneal injection
of PPT (10 mg/kg) and PPT-SLN (10 mg/kg in PPT). Blood samples were collected at different time to determine the PPT concentration
in plasma by HPLC. Blood drug level-time curve was made and pharmacokinetic parameters were calculated. As a result of drug
administration, the tumor volume and weight of the mice injected with PPT-SLN were significantly restrained compared with
mice treated with PPT or negative control. The tumor inhibition rate of 58.13% showed a significant antitumor activity of
PPT-SLN. At the same time, the increased weight gain of the mice injected with PPT-SLN suggested a reduced toxicity of PPT
in SLN. Pharmacokinetics study displayed a higher blood concentration, a prolonged circulation time, and an increased bioavailability
of PPT-SLN compared with those of PPT. Our results demonstrated that PPT-SLN could optimize pharmacokinetics, enhance antitumor
activity and attenuate toxicity, so it has a promising prospect for the application in anti-tumor treatment.
Supported by the National Natural Science Foundation of China (Grant No. 50673078), the Innovation Program of Shanghai Municipal
Education Commission (Grant No. 08ZZ21) and the Shanghai Key Fundamental Project (Grant No. 07DZ19603) 相似文献
948.
N-取代马来酰亚胺由于刚性内酰亚胺五元环的存在,在聚合时一般按反式加成进行,得到苏式双全同和苏式双间同两种构型的聚合物.其中苏式双间同结构由于具有等量的(R,R)和(S,S)结构而不产生光学活性,而苏式双全同结构中含有过量的(R,R)或(S,S)结构时聚合物呈现光学活性.而且,高度连续的(R,R)或(S,S)结构能使主链形成螺旋构象.N-取代马来酰亚胺单体上不同的取代基、不同的聚合方法以及聚合时选用的不同配体都对得到的聚合物主链中苏式双全同构象的量有显著影响.本文综述了各种N-取代马来酰亚胺光学活性聚合物的研究进展. 相似文献
949.
作为一种新型的免疫检测方法, 表面增强拉曼光谱(SERS)技术被应用于标记免疫多组分检测. 以多种不同的标记分子(苯硫酚, 联吡啶类分子, 氰基吡啶类分子)分别标记多种不同免疫金溶胶, 通过抗体抗原之间所具有的特异吸附性, 进一步组装“固相抗体-待测抗原-标记免疫金溶胶”多组分三明治复合体系. 利用表面增强拉曼光谱谱峰较窄, 具有较强的分辨率及高灵敏度的特点, 对多种标记分子特征谱峰进行分析判断, 从而识别所加入的多种抗原, 实现SERS标记免疫多组分同时检测的目的, 并对其中氰基吡啶类分子的吸附进行了探讨. 相似文献
950.
The hydrogen donation kinetics of four 3-aryl-benzofuranones with different chemical structures toward tert-butoxyl radicals were studied using laser flash photolysis (LFP) technique. The rate constants of hydrogen reactions, which can be used to evaluate the hydrogen donating abilities of 3-aryl-benzofuranones toward radicals, were obtained. The results showed that the position of substituted methyl group has a very important effect on the hydrogen donating ability of benzofuranone toward tert-butoxyl radicals, i.e. if the methyl group is on 2′-position, the hydrogen donation of 3-aryl-benzofuranone toward tert-butoxyl radicals will be prevented and the hydrogen donating ability will be weakened. 相似文献