全文获取类型
收费全文 | 2016篇 |
免费 | 70篇 |
国内免费 | 17篇 |
专业分类
化学 | 1316篇 |
晶体学 | 80篇 |
力学 | 46篇 |
数学 | 273篇 |
物理学 | 388篇 |
出版年
2023年 | 16篇 |
2022年 | 44篇 |
2021年 | 47篇 |
2020年 | 61篇 |
2019年 | 45篇 |
2018年 | 51篇 |
2017年 | 44篇 |
2016年 | 76篇 |
2015年 | 52篇 |
2014年 | 67篇 |
2013年 | 134篇 |
2012年 | 117篇 |
2011年 | 140篇 |
2010年 | 79篇 |
2009年 | 62篇 |
2008年 | 84篇 |
2007年 | 93篇 |
2006年 | 86篇 |
2005年 | 67篇 |
2004年 | 57篇 |
2003年 | 54篇 |
2002年 | 46篇 |
2001年 | 18篇 |
2000年 | 22篇 |
1999年 | 23篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 37篇 |
1983年 | 28篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 32篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1974年 | 9篇 |
1957年 | 11篇 |
排序方式: 共有2103条查询结果,搜索用时 0 毫秒
71.
Venkatapuram Padmavathi Annaji Venkata Nagendra Mohan Konda Mahesh 《Journal of heterocyclic chemistry》2008,45(4):1131-1138
Novel bisheterocycles, 1,2,3‐selenadiazoles, thiadiazoles and 2H‐diazaphospholes in combination with oxadiazoles, thiadiazoles and triazoles were prepared from phenacylsulfonylacetic acid methyl ester. 相似文献
72.
Bellm SM Builth-Williams JD Jones DB Chaluvadi H Madison DH Ning CG Wang F Ma XG Lohmann B Brunger MJ 《The Journal of chemical physics》2012,136(24):244301
Cross section data for electron scattering from DNA are important for modelling radiation damage in biological systems. Triply differential cross sections for the electron impact ionization of the highest occupied outer valence orbital of tetrahydrofurfuryl alcohol, which can be considered as an analogue to the deoxyribose backbone molecule in DNA, have been measured using the (e,2e) technique. The measurements have been performed with coplanar asymmetric kinematics at an incident electron energy of 250 eV, an ejected electron energy of 20 eV, and at scattered electron angles of -5°, -10°, and -15°. Experimental results are compared with corresponding theoretical calculations performed using the molecular 3-body distorted wave model. Some important differences are observed between the experiment and calculations. 相似文献
73.
Subhash Banerjee Hari KhatriVagulejan Balasanthiran Ranjit T. Koodali Grigoriy Sereda 《Tetrahedron》2011,67(32):5717-5724
Pd-MCM-48 has been employed as a heterogeneous catalyst for the synthesis of substituted acetylenes via Sonogashira reactions under copper and amine-free reaction conditions. In addition, the catalyst exhibited excellent regioselectivity for primary alcohols towards C-O coupling leading to formation of alkyl-aryl ethers in high yields. A green procedure for the stereoselective synthesis of 2-alkene-4-ynoates and nitriles from the reactions of vic-(E)-diiodoalkenes with activated alkenes has also been demonstrated using Pd-MCM-48 catalyst. The catalyst was easily recovered from the reaction mixture by filtration and reused for at least six times with minimal loss of activity. 相似文献
74.
E. Dadapeer K. Reddi Mohan Naidu C. Naga Raju 《Journal of the Iranian Chemical Society》2012,9(4):513-519
A facile iterative synthesis of a phosphorus dendron with bisphenol A at the focal point by following the divergent procedure is described. The phosphorus dendron peripherally functionalized with phenolic OH group has been accomplished in a very versatile simple fashion, using the Schiff condensation and nucleophilic substitution reactions using P(S)Cl3, P(O)Cl3, 3-hydroxybenzaldehyde and 3-aminopheno. The structures of intermediate dendrons were confirmed by IR, NMR (1H, 13C and 31P), LC-Mass and C, H, N analysis. The structure of the final dendron (5) was confirmed by IR, NMR (1H, 13C and 31P), MALDI-TOF-MS, and C, H, N analysis. The thermal stability of the resulting functionalized dendron has been checked by TGA/DTA analysis. The surface topography observed by scanning electronic microscopic study (SEM) gives the reminiscent of the dendritic structure. 相似文献
75.
Anand Mohan Yadav Nikkam Suresh Abhishek Sundaram Pravesh Painkra Ashish Kumar Raja Md Arshad 《Journal of Dispersion Science and Technology》2018,39(5):754-764
The high cost of the bridging liquid subdues the implementation and commercialization of oil agglomeration process. To overcome this problem, waste oils from different sectors were used in this present study. The performance of the process was assessed based on the responses like ash rejection and organic matter recovery. The aim of the present study was to investigate the usage of waste oils from different sectors and to optimize and analyze the behavioral pattern showcased by different variables (pulp density, oil dosage, agglomeration time and oil type) using response surface methodology (Box-Behnken design). Experimental investigation shows that the optimum pulp density, oil dosage, agglomeration time and oil type condition obtained as 3%, 15%, 15?min and waste engine oil, respectively. At optimum condition, the % ash rejection and % organic matter recovery obtained as 63.94% and 81.8%, respectively. 相似文献
76.
A microdialysis junction is employed as the interface for on-line coupling of capillary isoelectric focusing with transient isotachophoresis-zone electrophoresis in a two-dimensional separation system. Capillary isoelectric focusing not only provides high-resolution separation of tryptic peptides based on their differences in isoelectric point, but also potentially allows the analysis of low-abundance proteins with a typical concentration factor of 50-100 times. Carrier ampholytes, employed for the creation of a pH gradient during focusing, are further utilized as the leading electrolyte in the second separation dimension, transient isotachophoresis-zone electrophoresis. Many peptides which have the same isoelectric point would most likely have different charge-to-mass ratios, and thus different electrophoretic mobilities in zone electrophoresis. Two-dimensional separation of proteolytic peptides is demonstrated using standard proteins, including cytochrome c, ribonuclease A, and carbonic anhydrase II. The maximum peak capacity is estimated to be around approximately 1600 and can be significantly increased by simply increasing the capillary column length and manipulating the range of pH gradient in isoelectric focusing. In addition to enhanced separation efficiency and resolution, this two-dimensional electrokinetic separation system permits sensitive and comprehensive analysis of peptide fragments, especially when integrated with electrospray ionization mass spectrometry for peptide/protein identification. 相似文献
77.
Mohan-Kumari H. Puttananjaiah Mohan Appasaheb Dhale Vaishali Gaonkar Shradha Keni 《Applied biochemistry and biotechnology》2011,163(2):215-222
Atherosclerosis is a chronic inflammatory disease of multiple etiologies. It is associated with the accumulation of oxidized
lipids in arterial lesions leading to coronary heart disease. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors
(commonly known as statins) are widely used in cardiovascular disease prevention to lower the cholesterol. The antioxidant
activity of HMG-CoA reductase inhibitors was studied by lipid peroxidation inhibition assay, DPPH, and hydroxyl radical scavenging-activity
methods. The lovastatin (93%) and simvastatin (96%) showed significant action of lipid peroxidation inhibition compared to
other HMG-CoA reductase inhibitors. The DPPH radical and hydroxyl radical scavenging activity of simvastatin was 38% and 33%,
respectively. The oxidative modification of serum lipid due to reactive oxygen species causes atherosclerosis. This study
revealed the importance of lovastatin and simvastatin to prevent oxidative stress-related cardiovascular diseases. 相似文献
78.
79.
Gowravaram Sabitha B. V. Subba Reddy J. S. Yadav Nishant Jain B. Jagan Mohan Reddy 《Journal of heterocyclic chemistry》2018,55(4):863-870
A series of new 1,3,4‐oxadiazole‐linked 1,2,3‐triazole/isoxazole derivatives were designed and synthesized. All the synthesized compounds were screened for in vitro anticancer activity against four human cancer cells: HeLa (cervical), MDA‐MB‐231 (breast), DU‐145 (prostate), and HEPG2 (liver). Among 17 compounds tested, 7a , 7c , and 7d showed potent activity toward four cell lines. 相似文献
80.
MONITORING LIGHT-INDUCED CHANGES IN ISOLATED, INTACT EYE LENSES 总被引:1,自引:0,他引:1
Fluorescence spectral changes occurring upon irradiation with 300 nm light have been monitored in situ in isolated, intact, whole lenses from the eyes of several species. The findings corroborate observations on other individual constituent protein molecules in the solution state, and also reveal features attributable to the supramolecular protein assembly that exists in the whole lens. Irradiation of the lens with 300 nm light causes red shifts in the tryptophan emission spectrum, suggesting alterations in the protein packing in the lens. Intermolecular energy transfer from tryptophan to one of the photoproducts, presumably N-formylkynurenine (N-FK), occurs in the condensed-phase sample. The N-FK formed is photodegraded efficiently in the lens, indicating that the photodynamic effects of endogenous N-FK might not be as severe as has been thought. Species variation in the photoevents are evident, particularly in avian lenses that contain the variant δ-crystallin as the core protein. The photoinduced changes in the near-UV circular dichroism of δ-crystallin (which is α-helical, as opposed to the β-sheet structure of α-, β-, and -γ-crystallins), isolated from chicken lenses, are remarkably different from other crystallins. Irradiation of δ-crystallin leads to a drastic reduction of circular dichroism intensity in the 250–300 nm region, whereas no changes are seen in the peptide absorption band. 相似文献