全文获取类型
收费全文 | 4157篇 |
免费 | 132篇 |
国内免费 | 10篇 |
专业分类
化学 | 2241篇 |
晶体学 | 27篇 |
力学 | 126篇 |
数学 | 470篇 |
物理学 | 1435篇 |
出版年
2022年 | 37篇 |
2021年 | 64篇 |
2020年 | 76篇 |
2019年 | 75篇 |
2018年 | 86篇 |
2017年 | 60篇 |
2016年 | 112篇 |
2015年 | 80篇 |
2014年 | 104篇 |
2013年 | 265篇 |
2012年 | 227篇 |
2011年 | 263篇 |
2010年 | 162篇 |
2009年 | 150篇 |
2008年 | 211篇 |
2007年 | 208篇 |
2006年 | 217篇 |
2005年 | 183篇 |
2004年 | 127篇 |
2003年 | 115篇 |
2002年 | 98篇 |
2001年 | 73篇 |
2000年 | 70篇 |
1999年 | 43篇 |
1998年 | 40篇 |
1997年 | 38篇 |
1996年 | 42篇 |
1995年 | 49篇 |
1994年 | 45篇 |
1993年 | 55篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 50篇 |
1989年 | 41篇 |
1988年 | 38篇 |
1987年 | 38篇 |
1986年 | 29篇 |
1985年 | 44篇 |
1984年 | 38篇 |
1983年 | 39篇 |
1982年 | 36篇 |
1981年 | 37篇 |
1980年 | 38篇 |
1979年 | 32篇 |
1978年 | 37篇 |
1977年 | 33篇 |
1976年 | 38篇 |
1975年 | 33篇 |
1974年 | 34篇 |
1973年 | 37篇 |
排序方式: 共有4299条查询结果,搜索用时 46 毫秒
51.
Structure‐cytotoxicity relationship of di?/tri‐organotin(IV) derivatives of mandelic acid ( 1 – 4 ), L‐proline ( 5 – 7, 15, 16 ), and mixed ligand complexes of latter with 1,10‐phenanthroline ( 8 – 14 ) investigated on the basis of MTT assay against human cancer cell lines, viz. MCF‐7 (mammary cancer), HepG2 (liver cancer) and PC‐3 (prostate cancer) in vitro indicated that all complexes except methyl‐ and octyl‐ analogues displayed potential cytotoxicity. The most active one is dibutyltin(IV) mandelate ( 2 ) exhibiting IC50 2.03 ± 0.40, 0.98 ± 0.23 and 3.86 ± 1.68 μM against MCF‐7, HepG2 and PC‐3, respectively, which is ≈ 15 and 2.5 times against MCF‐7, 20 and 5 times against HepG2 and 5 and ≈ 3 times against PC‐3 more cytotoxic than cis‐platin and 5‐fluorouracil, respectively. Diorganotin(IV) derivatives of mandelic acid are more cytotoxic than triorganotin analogues. Organotin(IV) derivatives of L‐proline (except Bu3Sn(Pro) 16 ) are less cytotoxic than those of mandelic acid but their cytotoxicity is enhanced by complexion with 1,10‐phenanthroline. This may be due to the structural planarity and extended π system of 1,10‐phenanthroline which facilitates their transportation across the cell membrane and enhances the possibility of DNA intercalation over the planar L‐proline ring, and eventually, their DNA binding affinity so as to interfere with the cellular functions of DNA leading to apoptosis. Various biophysical experiments such as DNA fragmentation, acridine orange and comet assays, and flow cytometry assay using annexin V–fluorescein isothiocyanate (FITC) and propidium iodide (PI) have been carried out in order to ascertain their mode of action. The observed results indicated that the major cause of cancer cell death is apoptosis, but a minor role played by necrosis cannot be excluded. It is concluded on the basis of the observed results that the nature and number of organic groups bonded to tin as well as the nature of counter anions play an important role in determining the cytotoxicity of organotin(IV) compounds. 相似文献
52.
Prof. Dr. Steven Stevenson Amanda J. Rothgeb Katelyn R. Tepper Prof. Dr. James Duchamp Prof. Dr. Harry C. Dorn Xian B. Powers Mrittika Roy Prof. Dr. Marilyn M. Olmstead Prof. Dr. Alan L. Balch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12545-12551
Purified samples of Ho3N@C2(22010)-C78 and Tb3N@C2(22010)-C78 have been isolated by two distinct processes from the rich array of fullerenes and endohedral fullerenes present in carbon soot from graphite rods doped with Ho2O3 or Tb4O7. Crystallographic analysis of the endohedral fullerenes as cocrystals with Ni(OEP) (in which OEP is the dianion of octaethylporphyrin) shows that both molecules contain the chiral C2(22010)-C78 cage. This cage does not obey the isolated pentagon rule (IPR) but has two sites where two pentagons share a common C−C bond. These pentalene units bind two of the metal ions, whereas the third metal resides near a hexagon of the cage. Inside the cages, the Ho3N or Tb3N unit is planar. Ho3N@C2(22010)-C78 and Tb3N@C2(22010)-C78 use the same cage previously found for Gd3N@C2(22010)-C78 rather than the IPR-obeying cage found in Sc3N@D3h-C78. 相似文献
53.
54.
Roy Hodgkinson Václav Jurčík Hans Nedden Andrew Blackaby Martin Wills 《Tetrahedron letters》2018,59(10):930-933
A new route towards a series of tethered η6-arene/Ru(II) catalysts for use in the transfer and pressure hydrogenation of ketones and aldehydes to alcohols is reported. The route proceeds through the formation of an amide from the diamine precursor, followed by reduction, rather than the direct alkylation of the diamine. This has the advantage that dialkylation of the amine is avoided during the synthesis. Through this new route, both racemic and enantiomerically-pure η6-arene/Ru(II) tethered catalysts can be prepared in high yield. 相似文献
55.
The compound 4 propyl paraethoxy phenyl cyclohexyl carboxylate (code name D302) is a member of a homologous series and exhibits liquid crystalline (nematic) behavior in the temperature range 48°C to 78°C. An experiment has been set up for conducting X-ray studies of liquid crystal samples at various temperatures. From X-ray studies conducted at different temperatures on D302, the apparent molecular length and inter-molecular distance and their temperature dependence have been determined. The variation of the orientational-order parameter <P2>xray has been determined from the intensities of the scanned X-ray photographs taken at different temperatures. The results have been compared with the<P2>opt values obtained by us from birefringence studies. 相似文献
56.
Multidrug‐Containing,Salt‐Based,Injectable Supramolecular Gels for Self‐Delivery,Cell Imaging and Other Materials Applications 下载免费PDF全文
Rajdip Roy Prof. Parthasarathi Dastidar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):14929-14939
Both molecular and crystal‐engineering approaches were exploited to synthesize a new class of multidrug‐containing supramolecular gelators. A well‐known nonsteroidal anti‐inflammatory drug, namely, indomethacin, was conjugated with six different l ‐amino acids to generate the corresponding peptides having free carboxylic acid functionality, which reacted further with an antiviral drug, namely, amantadine, a primary amine, in 1:1 ratio to yield six primary ammonium monocarboxylate salts. Half of the synthesized salts showed gelation ability that included hydrogelation, organogelation and ambidextrous gelation. The gels were characterized by table‐top and dynamic rheology and different microscopic techniques. Further insights into the gelation mechanism were obtained by temperature‐dependent 1H NMR spectroscopy, FTIR spectroscopy, photoluminescence and dynamic light scattering. Single‐crystal X‐ray diffraction studies on two gelator salts revealed the presence of 2D hydrogen‐bonded networks. One such ambidextrous gelator (capable of gelling both pure water and methyl salicylate, which are important solvents for biological applications) was promising in both mechanical (rheoreversible and injectable) and biological (self‐delivery) applications for future multidrug‐containing injectable delivery vehicles. 相似文献
57.
58.
59.
60.
Hydrogen peroxide activated by boric acid in the presence of sulfuric acid has been shown to be an efficient oxidizing system for direct conversion of aromatic aldehydes and ketones to phenols. 相似文献