全文获取类型
收费全文 | 3121篇 |
免费 | 474篇 |
国内免费 | 372篇 |
专业分类
化学 | 2413篇 |
晶体学 | 30篇 |
力学 | 176篇 |
综合类 | 40篇 |
数学 | 319篇 |
物理学 | 989篇 |
出版年
2024年 | 16篇 |
2023年 | 64篇 |
2022年 | 113篇 |
2021年 | 121篇 |
2020年 | 139篇 |
2019年 | 127篇 |
2018年 | 99篇 |
2017年 | 103篇 |
2016年 | 148篇 |
2015年 | 135篇 |
2014年 | 193篇 |
2013年 | 231篇 |
2012年 | 244篇 |
2011年 | 288篇 |
2010年 | 191篇 |
2009年 | 160篇 |
2008年 | 168篇 |
2007年 | 164篇 |
2006年 | 144篇 |
2005年 | 134篇 |
2004年 | 115篇 |
2003年 | 92篇 |
2002年 | 95篇 |
2001年 | 83篇 |
2000年 | 76篇 |
1999年 | 79篇 |
1998年 | 73篇 |
1997年 | 52篇 |
1996年 | 55篇 |
1995年 | 41篇 |
1994年 | 43篇 |
1993年 | 29篇 |
1992年 | 37篇 |
1991年 | 15篇 |
1990年 | 23篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3967条查询结果,搜索用时 265 毫秒
991.
992.
Zhang K.Feng X.Dong J.G.Guan C.Yu Y. 《数学学报》2015,(1):125-130
Multiplication operator is an important class of operators in function space. We mainly research the properties of the multiplication operator on the weighted Bergman space of the unit ball. ©, 2015, Chinese Academy of Sciences. All right reserved. 相似文献
993.
994.
The aim of this study was to evaluate the clinical utility of an image-guided Raman endoscopy technique for in vivo differential diagnosis of benign and malignant ulcerous lesions in the stomach. A rapid-acquisition image-guided Raman endoscopy system with 785 nm laser excitation has been developed to acquire in vivo gastric tissue Raman spectra within 0.5 s during clinical gastroscopic examinations. A total of 1102 in vivo Raman spectra were acquired from 71 gastric patients, in which 924 Raman spectra were from normal tissue, 111 Raman spectra were from benign ulcers whereas 67 Raman spectra were from ulcerated adenocarcinoma. There were distinctive spectral differences in Raman spectra among normal mucosa, benign ulcers and malignant ulcers, particularly in the spectral ranges of 800-900, 1000-1100, 1245-1335, 1440-1450 and 1500-1800 cm(-1), which primarily contain signals related to proteins, DNA, lipids and blood. The malignant ulcerous lesions showed Raman signals to be mainly associated with abnormal nuclear activity and decrease in lipids as compared to benign ulcers. Partial least squares-discriminant analysis (PLS-DA) was employed to generate multi-class diagnostic algorithms for classification of Raman spectra of different gastric tissue types. The PLS-DA algorithms together with leave-one tissue site-out, cross validation technique yielded diagnostic sensitivities of 90.8%, 84.7%, 82.1%, and specificities of 93.8%, 94.5%, 95.3%, respectively, for classification of normal mucosa, benign and malignant ulcerous lesions in the stomach. This work demonstrates that image-guided Raman endoscopy technique associated with PLS-DA diagnostic algorithms has for the first time promising clinical potential for rapid, in vivo diagnosis and detection of malignant ulcerous gastric lesions at the molecular level. 相似文献
995.
A series of parent poly(aryl ether ketone)s bearing different content of unsaturated pendant propenyl groups were synthesized via nucleophilic substitution polymerization from 3,3′-diallyl-4,4′-dihydroxybiphenyl, 9,9′-bis(4-hydroxyphenyl) fluorene and 4,4′-difluorobenzophenone. The polymers with pendant aliphatic sulfonic acid groups were further synthesized by free radical thiol-ene coupling reactions between 3-mercapto-1-propanesulfonic sodium and the parent propenyl functional copolymers. The resulting sulfonated polymers with high inherent viscosity (1.83-4.69 dL/g) were soluble in polar organic solvents and can form flexible and transparent membranes by casting from their solutions. The copolymers with different ion exchange capacity could be conveniently synthesized by varying the monomers ratios. Transmission electron microscopy (TEM) was used to examine the microstructures of the membrane and the results revealed that significant hydrophilic/hydrophobic microphase separation with spherical, uniform-sized (5-10 nm) and well-dispersed hydrophilic domains was afforded. The proton conductivities of the as-prepared membranes and the state-of-the-art Nafion 117 membrane in fully hydrated state were investigated. The results revealed that the proton conductivity of the synthesized membranes increased more remarkably than that of Nafion 117 membrane with increasing temperature. The membrane with 1.69 mequiv/g of IEC had a conductivity of 2.5 × 10−2 Scm−1 at 100 °C. The membranes also possessed excellent mechanical properties, good thermal, oxidative, hydrolytic and dimensional stabilities. 相似文献
996.
Yali Yuan Yaqin Chai Ying Zhuo Zhongyuan Liu Li Mao Shu Guan Xiaoqing Qian 《Analytica chimica acta》2010,668(2):171-127
Herein, a novel label-free electrochemical aptasensor based on direct immobilization of the redox probes on an electrode surface was reported. Gold electrode coated Nafion was firstly modified with redox probe-thionine (Thi) through ion exchange adsorption. Then, with the help of chemisorption and electrostatic adsorption, negatively charged nano-Au and positively charged Thi were layer-by-layer (LBL) self-assembled onto the modified electrode surface, which formed {nano-Au/Thi+}n multilayer films for improving the amount of redox probes and immobilizing thiolated thrombin aptamers (TBA). In the presence of target thrombin (TB), the TBA on the multilayer film could catch the TB onto the electrode surface, which resulted in a barrier for electro-transfer, leading to decrease of the current. The proposed method avoided the cubsome redox probe labeling process, increased the amount of redox probe and reduced the distance between the redox probe and electrode surface. Thus, the approach showed a high sensitivity and a wider linearity to TB in the range from 0.12 nM to 46 nM with a detection limit of 40 pM. 相似文献
997.
Juan Han Cuilan Yu Yun Wang Xueqiao Xie Yongsheng Yan Guowu Yin Weixing Guan 《Fluid Phase Equilibria》2010
Binodal curves of the aqueous 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) + sodium citrate (Na3C6H5O7), [Bmim]BF4 + sodium tartrate (Na2C4H4O6) and [Bmim]BF4 + sodium acetate (NaC2H3O2) systems have been determined experimentally at 298.15 K. The Merchuk equation was used to correlate the binodal data. The effective excluded volume (EEV) values obtained from the binodal model for these three systems were determined. The binodal curves and EEV both indicate that the salting-out abilities of the three salts follow the order: Na3C6H5O7 > Na2C4H4O6 > NaC2H3O2. The liquid–liquid equilibrium (LLE) data were obtained by density determination and binodal curves correlation of these systems. Othmer–Tobias and Bancraft, and Setschenow equations were used for the correlation of the tie-line data. Good agreement was obtained with the experimental tie-line data with both models. 相似文献
998.
Youwen You Cornelius E. Uboh Lawrence R. Soma Fuyu Guan Xiaoqing Li Ying Liu Jinwen Chen Deborah Tsang 《Chromatographia》2010,72(11-12):1097-1106
Testosterone and testosterone enanthate are performance-enhancing substances that are banned in racehorses competing in the State of Pennsylvania (PA). A tolerance concentration of 2,000 pg mL?1 plasma has been established for testosterone in intact colts and stallions at the time they are competing in PA. Testosterone enanthate is a precursor of testosterone and can be used to boost plasma testosterone concentration above natural, age and seasonally variable plasma concentration. To control abuse, a verifiable method for rapid determination of both substances in equine plasma was needed. For this reason, an ultra high performance liquid chromatography-tandem mass spectrometry method for high-throughput analysis of both analytes in equine plasma was developed. Analytes were recovered from plasma by liquid–liquid extraction using mixture of methyl tert-butyl ether and ethyl acetate (50:50, v/v), separated on a C18 sub-2 μm column and detected on a triple quadrupole mass spectrometer using positive electrospray ionization mode with selected reaction monitoring scan. SRM ion transitions of m/z 289 → m/z 97, m/z 289 → m/z 109, m/z 289 → m/z 79 were used for testosterone identification while m/z 401 → m/z 253, m/z 401 → m/z 271, m/z 401 → m/z 97 were employed for testosterone enanthate. Retention time and product ion intensity ratio were used as confirmation criteria to ascertain the presence of both analytes in equine plasma. The limits of detection, quantification and confirmation were 50 pg 0.5 mL?1, 100 pg 0.5 mL?1 and 250 pg 0.5 mL?1, respectively for both analytes. The method was validated for recovery efficiency, sensitivity, matrix effect, linearity, precision and accuracy. This method is routinely used in the PA program for androgenic anabolic steroids doping control in racehorses and in the on-going testosterone enanthate pharmacokinetics study. The method is defensible, fast, selective, specific and reproducibly reliable. 相似文献
999.
1000.
W. Tang L.L. Liu S. Tian L. Li Y.B. Yue Y.P. Wu S.Y. Guan K. Zhu 《Electrochemistry communications》2010,12(11):1524-1526
Crystalline nanoparticles of LiCoO2 are prepared by a sol–gel method at 550 °C and characterized by X-ray diffraction. Their electrochemical behaviors were characterized by cyclic voltammograms, capacity measurement and cycling performance. Results show that the reversible capacity of the nano-LiCoO2 can be up to 143 mAh/g at 1000 mA/g and still be 133 mAh/g at 10,000 mA/g (about 70C) in 0.5 mol/l Li2SO4 aqueous electrolyte. In addition, their cycling behavior is also very satisfactory, no evident capacity fading during the initial 40 cycles. These data present great promise for the application of aqueous rechargeable lithium batteries. 相似文献