全文获取类型
收费全文 | 783篇 |
免费 | 69篇 |
国内免费 | 2篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 22篇 |
2021年 | 31篇 |
2020年 | 26篇 |
2019年 | 34篇 |
2018年 | 41篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 33篇 |
2014年 | 53篇 |
2013年 | 45篇 |
2012年 | 55篇 |
2011年 | 71篇 |
2010年 | 34篇 |
2009年 | 32篇 |
2008年 | 29篇 |
2007年 | 21篇 |
2006年 | 20篇 |
2005年 | 20篇 |
2004年 | 24篇 |
2003年 | 18篇 |
2002年 | 21篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1969年 | 4篇 |
1967年 | 4篇 |
1965年 | 4篇 |
1964年 | 2篇 |
排序方式: 共有854条查询结果,搜索用时 156 毫秒
31.
Abdel Galil A. Hewaidy Gamal M. El Qot El Sayed M. Moneer 《Annales de Paléontologie》2019,105(1):45-61
The Campanian–lower Eocene sedimentary succession in the Kharga Oasis yields rare cephalopods that have so far received little attention. Eight cephalopod species; six nautiloids and two ammonites, are identified in the study area. The nautiloids are referred to five genera in three families. All nautiloid species are recorded from the Paleocene and Eocene rocks, two of which are described as new, as follows: Cimomia kurkurensis nov. sp. and Deltoidonautilus hassani nov. sp. The two ammonite species are Libycoceras ismaelis (von Zittel, 1884) and Baculites ovatus Say, 1820, representing the families Sphenodiscidae and Baculitidae, respectively. Baculites anceps of Quaas (1902, non Lamarck, 1822) from the Maastrichtian of the Western Desert of Egypt is here assigned to Baculites ovatus. The palaeobiogeography of these species is studied in detail. 相似文献
32.
33.
Jacques D Abdel Malak NA Sader S Perreault C 《Canadian journal of physiology and pharmacology》2003,81(3):259-266
The aims of the present study are to investigate the presence and distribution of angiotensin II (Ang II), as well as AT1 and AT2 receptors, in endocardial endothelial cells (EECs) and to determine if the effect of Ang II on intracellular calcium in these cells is mediated via the AT1 or the AT2 receptor. Immunofluorescence and 3D confocal microscopy techniques were used on 20-week-old fetal human EECs. Our results showed that Ang II and its receptors, the AT1 and the AT2 types, are present and exhibit a different distribution in human EECs. Ang II labelling is found throughout the cell with a fluorescence signal higher in the cytosol when compared with the nucleus. Like Ang II, the AT1 receptor fluorescence signal is also homogeneously distributed in human EECs but with a preferential labelling at the level of the nucleus, while the AT2 receptor labelling is solely present in the nucleus. Using fluo-3 and 3D confocal microscopy technique, superfusion of human EECs with increasing concentration of Ang II induced a dose-dependent sustained increase in free cytosolic and nuclear Ca2+ levels. This effect of Ang II on human EEC's intracellular Ca2+ ([Ca2+]) was completely prevented by losartan, an AT1 receptor antagonist. Our results suggest that Ang II, as well as AT1 and AT2 receptors, is present but differentially distributed in EECs of 20-week-old fetal human hearts, and that the AT1 receptor mediates the effects of Ang II on [Ca2+]i in these cells. 相似文献
34.
El-hamid Ismail A Abdel Aleem AA Abdel Bary H El-Assaly S 《Nucleosides, nucleotides & nucleic acids》2002,21(6-7):469-475
2-Naphthylsulfonylhydrazine was reacted with aromatic aldehydes or aldehydo sugars to give the corresponding hydrazones which undergo Michael addition reactions with malononitrile or ethyl cyanoacetate to form pyrazole derivatives. 相似文献
35.
Red blood cells (RBCs) are probably the most common target through the damaging action of reactive oxygen species on the cells. The photohemolysis activity of m-chloroperbenzoic acid (CPBA) was concentration- and exposure time-dependent. Twenty minutes photo exposure time and 200 μm of CPBA concentration were optimum to study the effect of generated superoxide (O2-) and hydroxyl (&bull•OH) radicals on RBCs. RBCs lysis photosensitized by CPBA was investigated in the presence of [(VL2O)(VL2H2O)]Cl6, [MnL2O]2Cl42H2O, [FeL2Cl2]Cl H2O, [CoL2Cl2]4H2O or [ZnL2Cl2]H2O respectively, where L is 2-methylaminopyridine, with SOD-mimetic activities with the aim of ascertaining their protective activity towards the photo induced cell damage. The decrease of photolytic activity caused by these complexes was concentration-dependent and the maximum percentage of protective activity was 75, 70, 68, 57 or 24% for [(VL2O)(VL2H2O)]Cl6, [MnL2O]2Cl4 2H2O, [FeL2Cl2]Cl H2O, [CoL2Cl2]4H2O or [ZnL2Cl2]H2O complex respectively, against the cell irradiated without addition of metal complexes. The comparison between the decrease of photolytic activity caused by these complexes and their SOD-mimetic activity of these metal complexes showed an appreciable correlation. 相似文献
36.
The 1-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-3-aryl-5-benzyl (or substituted benzyl)-1,2,4-triazin-6(1H)-/ones or thiones were prepared via galactosidation of 3-aryl-5-benzyl (or substituted benzyl)-1,2,4-triazin-6(1H)-/ones or thiones with 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide. The structure of the new galactosyl derivatives was based on both spectroscopic and chemical evidences. 相似文献
37.
Synthetic routes towards different 2-alpha-L-arabinopyranosyl-3-thioxo-2,3-dihydro-1,2,4-triazin-5(4H)-/ones or thiones were investigated. Primary human anticancer screening of two selected compounds resulted in an active compound against SF-268 (CNS) cell line. 相似文献
38.
Four new triterpenoid saponins were isolated and identified from the aerial parts of Fagonia cretica. They were characterized as 3-O-[beta-D-glucopyranosyl (1-->2)-alpha-L-arabinopyranosyl] hederagenin 28-O-beta-D-glucopyranosyl ester, 3-O-[beta-D-glucopyranosyl (1-->2)-alpha-L-arabinopyranosyl] oleanolic acid 28-O-[beta-D-glucopyranosyl (1-->6)-beta-D-glucopyranosyl] ester, 3-O-[beta-D-glucopyranosyl (1-->2)-alpha-L-arabinopyranosyl] 27-hydroxy oleanolic acid 28-O-[beta-D-glucopyranosyl (1-->6)-beta-D-glucopyranosyl] ester and 3beta-O-[beta-D-glucopyranosyl (1-->2)-alpha-L-arabinopyranosyl] olean-12-en-27-al-28-oic acid 28-O-[beta-D-glucopyranosyl (1-->6)-beta-D-glucopyranosyl] ester. The structures of the saponins were assigned by spectral analyses (FABMS, 1H, 13C NMR, 1H-1H COSY, TOCSY, HMQC and HMBC spectra) and NOE experiments. To the best of our knowledge the genin 3beta hydroxy olean-12-en-27-al-28-oic acid is new. 相似文献
39.
It is believed that some wastes play an important role on the pollution prevention. In this paper, three different natural biomasses were investigated as biosorbent. Salsola green plant which grown at Jubail (industrial area) in KSA, it is phyto remediation plant. Salsola is metal hyper accumulation plant, it adsorbed (23.5, 25.7 mg lead per gram stem or leaf) from soil. Also it can be reused as ion exchanger for pb2+ from solution. Shrimp shell’s used for extraction of chitosan in laboratory with degree of substitution 81%. Chitosan and crosslinked carboxymethyl chitosan were investigated for pb2+ adsorption and compared with crosslinked carboxymethyl corn cob. The adsorption experiments demonstrated that the three biomasses have high adsorption capacity for pb2+, good reusability and stability for three cycles. 相似文献
40.
Megan A. Perry Drew S. Coleman David L. Dettman Abdel Halim al‐Shiyab 《American journal of physical anthropology》2009,140(3):429-441
The Byzantine Empire managed a complex administrative network that controlled the mining and processing of natural resources from within its boundaries. Scholars relying upon archeological and textual evidence debate the level of imperial involvement in these ventures, particularly in the provinces. Ancient sources note that many mining camps, for instance, purportedly contained criminal laborers and elite administrators transported from distant locales, indicating significant organization and expenditures by the imperial administration to run the mines. This analysis explores the presence of these nonlocal individuals in a cemetery associated with the third to seventh century A.D. mining camp of Phaeno (Faynan), located in modern Jordan. Strontium isotope analysis of 31 burials indicates that most spent their childhood in a similar geological region as Phaeno, implying that they were locally born. The δ18O results mirror the homogeneous 87Sr/86Sr values, confirming a local origin for most of the sample. Isotopic evidence therefore suggests that the Phaeno mining camp was largely a local operation, contrary to the picture presented in textual sources, although the profits surely padded imperial coffers. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc. 相似文献