全文获取类型
收费全文 | 3229篇 |
免费 | 138篇 |
国内免费 | 6篇 |
专业分类
化学 | 2597篇 |
晶体学 | 19篇 |
力学 | 43篇 |
数学 | 296篇 |
物理学 | 418篇 |
出版年
2023年 | 21篇 |
2022年 | 96篇 |
2021年 | 138篇 |
2020年 | 69篇 |
2019年 | 79篇 |
2018年 | 59篇 |
2017年 | 43篇 |
2016年 | 133篇 |
2015年 | 101篇 |
2014年 | 124篇 |
2013年 | 187篇 |
2012年 | 177篇 |
2011年 | 255篇 |
2010年 | 145篇 |
2009年 | 162篇 |
2008年 | 238篇 |
2007年 | 197篇 |
2006年 | 166篇 |
2005年 | 168篇 |
2004年 | 130篇 |
2003年 | 101篇 |
2002年 | 89篇 |
2001年 | 50篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 25篇 |
1997年 | 18篇 |
1996年 | 25篇 |
1995年 | 23篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有3373条查询结果,搜索用时 31 毫秒
941.
Sonja Fuchs Arumugam Jayaraman Ivo Krummenacher Laura Haley Marta Batovanovi Maximilian Fest Krzysztof Radacki Holger Helten Holger Braunschweig 《Chemical science》2022,13(10):2932
We report that the outcome of the tin–boron exchange reaction of a mixed thiophene-benzo-fused stannole with aryldibromoboranes is associated with the steric bulk of the aryl substituent of the borane reagent, leading to either boroles or large diboracycles as products. NMR spectroscopic studies indicate that the two products can reversibly interconvert in solution, and mechanistic density functional theory (DFT) calculations reveal boroles to be intermediates in the formation of the diboracyclic products. The addition of Lewis bases to the diboracycles leads to the corresponding borole adducts, demonstrating that they react as “masked” boroles. Additionally, the reaction of the title compounds with a series of organic azides affords complex heteropropellanes, formally 2 : 1 borole-azide adducts, that deviate from the usual BN aromatic compounds formed via nitrogen atom insertion into the boroles.Diboramacrocycles are a new form of borole dimers, participating in various addition reactions as “masked” boroles. The reaction of a less crowded diboramacrocycle with organic azides affords unprecedented complex heteropropellanes. 相似文献
942.
Two tridentate N,N,O donor Schiff bases, HL1 (4-(2-ethylamino-ethylimino)-pentan-2-one) and HL2 (3-(2-amino-propylimino)-1-phenyl-butan-1-one) on reaction with CuII acetate in presence of triethyl amine yielded two basal-apical, mono-atomic acetate oxygen-bridging dimeric copper(II) complexes, [Cu2L12(OAc)2] (1), [Cu2L22(OAc)2] (2). Whereas two other similar tridentate ligands HL3 (4-(2-amino-propylimino)-pentane-2-one) and HL4 (3-(2-amino-ethylimino)-1-phenyl-butan-1-one) under the same conditions produced a mixture of the corresponding dimers and a one-dimensional alternating chain of the dimer and copper acetate moiety, [Cu4L32(OAc)6]n (3) and [Cu4L42(OAc)6]n (4), formed by a very rare μ3 bridging mode of the acetate ion. All four complexes (1–4) have been characterized by X-ray crystallography. The isotropic Hamiltonian, H = −JS1S2 has been used to interpret the magnetic data. Magnetic measurements of 1 and 2 in the temperature range 2–300 K reveal a very weak antiferromagnetic coupling for both complexes (J = −0.56 and −1.19 cm−1 for 1 and 2, respectively). 相似文献
943.
Stuart Ibsen Yongxuan Su John Norton Eran Zahavy Tomoko Hayashi Stephen Adams Wolf Wrasidlo Sadik Esener 《Journal of mass spectrometry : JMS》2013,48(7):768-773
The localized conversion of inactive doxorubicin prodrug chemotherapeutics to pharmacalogically active forms is difficult to quantify in mouse tumor models because it occurs only in small regions of tissue. The tumor tissue extraction protocol and LC–MS/MS analysis method described here were optimized to obtain a detection limit of 7.8 pg for the activated doxorubicin and 0.36 ng for the doxorubicin prodrug. This method can be useful for determining the biodistribution and activation efficiency for many different doxorubicin prodrugs. It can also be used for quantification of doxorubicin from tumor models that have poor vascularization resulting in low tissue accumulation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
944.
Marta Kus Klaudia Gorniak Piotr Czaklosz Anna Olejnik Paulina Skupin-Mrugalska Izabela Ibragimow Hanna Piotrowska-Kempisty 《Molecules (Basel, Switzerland)》2022,27(7)
Perindopril arginine (PA) as an angiotensin-converting enzyme (ACE) inhibitor is widely used in cardiovascular diseases, especially in systemic hypertension and heart failure. Although the pharmacokinetics of PA are well documented, there is no available detailed data on its permeation in in vitro conditions. The present study aimed to assess the transport of PA across both biological membranes and artificial biomimetic ones. For the determination of PA transport, the Caco-2 cell line was selected as a reliable in vitro model of gastrointestinal biological barriers. Additionally, a novel 96-well plate with phospholipid membrane PermeaPad was used to evaluate the transport of PA by passive diffusion. We confirmed that PA is relatively poorly permeable across the Caco-2 monolayer. The permeability results obtained from the non-cell-based model demonstrated higher transport of PA as compared to that of Caco-2. Thus, PA transport across the biological membranes might be suggested to be regulated by the membrane transporters. 相似文献
945.
Aleksandra Felczak Katarzyna Zawadzka Przemysaw Bernat Marta Nowak-Lange Katarzyna Lisowska 《Molecules (Basel, Switzerland)》2022,27(7)
Quinoline is an N-heterocyclic compound commonly found in wastewater, especially that derived from coal processing, chemical, and pharmaceutical industries. In the present study, the microscopic fungus Curvularia lunata IM 4417, which is known to degrade various xenobiotics, was used. The aim of the research was to study the elimination of quinoline and its influence on fungal phospholipids, which are considered to be excellent indicators of environmental monitoring. Quinoline biodegradation products and phospholipid contents were analyzed using gas chromatography–mass spectrometry and liquid chromatography–tandem mass spectrometry. C. lunata IM 4417 degraded quinoline, which led to the formation of conjugates of glucose with hydroxylated derivatives of the compound. Toxicity tests (Artoxkit M and Microtox assay) indicated that the elimination of lower concentrations of quinoline was efficient and led to a reduction in sample toxicity. The presence of quinoline also significantly affected the profile of fatty acids and phospholipids. The addition of quinoline to a culture of C. lunata IM 4417 caused an increase in the content of phosphatidylcholine (PC) and a decrease in the amount of phosphatidylethanolamine (PE), two major structural lipids. Additionally, decreases in the contents of phosphatidylinositol (PI) and phosphatidylserine (PS), which are responsible for tolerance to toxic substances, cell viability, and signal transduction, were noted. Thus, it can be concluded that the presence of quinoline modifies the membrane composition, and this change may be an important indicator of the presence of N-heterocyclic compounds or other toxins in the environment. 相似文献
946.
947.
948.
Marta Filizola Silvina M. Tasso Gilda H. Loew Hugo O. Villar 《Journal of computational chemistry》2001,22(16):2018-2027
Metabotropic glutamate receptors (mGluRs) are important as candidate therapeutic targets for many neurological disorders. In the present work, the focus has been on the mGluR1 subtype, where agonists have a proconvulsant profile while antagonists exert anticonvulsant activity. Identification of molecular determinants for the inhibition of mGluR1 provides a new avenue for the discovery and development of novel anticonvulsant drugs. Spatial configuration of key groups alone cannot explain activation selectivity at this specific receptor subtype. In fact, all known agonists and antagonists acting at mGluR1 can accommodate the same critical moieties in a similar geometric arrangement that corresponds to the extended conformation of glutamate. Therefore, other factors must account for the differences in activation. This study presents the results of an analysis of a large suite of steric, topological, electrostatic, and thermodynamic molecular properties calculated for a representative set of potent mGluR1 agonists and antagonists. Global steric parameters and the total nonpolar area provide discrimination between the mGluR1 agonists and antagonists considered in the present work. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 2018–2027, 2001 相似文献
949.
950.