全文获取类型
收费全文 | 4634篇 |
免费 | 369篇 |
出版年
2024年 | 5篇 |
2023年 | 30篇 |
2022年 | 37篇 |
2021年 | 93篇 |
2020年 | 73篇 |
2019年 | 74篇 |
2018年 | 133篇 |
2017年 | 110篇 |
2016年 | 195篇 |
2015年 | 272篇 |
2014年 | 314篇 |
2013年 | 358篇 |
2012年 | 427篇 |
2011年 | 366篇 |
2010年 | 254篇 |
2009年 | 227篇 |
2008年 | 312篇 |
2007年 | 273篇 |
2006年 | 281篇 |
2005年 | 224篇 |
2004年 | 215篇 |
2003年 | 166篇 |
2002年 | 167篇 |
2001年 | 47篇 |
2000年 | 30篇 |
1999年 | 28篇 |
1998年 | 20篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 23篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1986年 | 7篇 |
1984年 | 10篇 |
1983年 | 15篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 7篇 |
1971年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有5003条查询结果,搜索用时 15 毫秒
41.
The distribution ofPapio hamadryas in Saudi Arabia: Ecological correlates and human influence 总被引:1,自引:0,他引:1
Sylvain Biquand Véronique Biquand-Guyot Ahmed Boug Jean-Pierre Gautier 《International journal of primatology》1992,13(3):223-243
We describe the distribution ofPapio hamadryas in Saudi Arabia in relation to ecological constraints and recent changes in human activities and land use. Baboons are present
only in the Sarawat and southern Hijaz mountains, which border the Red Sea in the southwestern region of the country. Our
distribution data confirms that their range, described as of 1981, should be extended 200 km northward, from 21°40N (Taif)
to 23°20N (Al Akhal). This new limit of range is not due to recent deployment of the baboons, but instead corrects inaccurate
surveys by previous reporters. Ecological factors that affect baboon distribution include low annual rainfall (less than 100
mm per yr), which limits baboon range in the north and east, and the absence of suitable sleeping cliffs in the coastal plain,
which limits their range in the west. Relative abundance is discussed in relation to vegetation and predator distribution.
Human influence is also significant: commensal troops persist near urban centers, while agricultural development reduces baboon
numbers in some regions. Habitat characteristics are discussed in comparison with similar data on the range of hamadryas in
Ethiopia. 相似文献
42.
Over ten years, the individuals of an orthoclone of Notommata copeus gradually lost their sensitivity to photoperiod. This loss is transmissible but reversible in three generations. It is endogenous but not chromosomal. The hypothesis is forwarded that it is induced by external factors, and quite possibly crowding. 相似文献
43.
Besides ethanol, other aliphatic alcohols such as n-propanol and isopropanol induce a triacylglycerol (TAG) accumulation in the liver. To determine whether a common mechanism is responsible for the effects of these three alcohols on hepatic lipid metabolism, each was administered by gastric tube to female Wistar rats at the dose of 50 mmol/kg body wt. Whichever alcohol was administered, the hepatic triacylglycerol accumulation was found to be related to the duration of elevated blood alcohol concentration. After administration of n-propanol or isopropanol, the liver [14C]palmitate uptake was increased whereas hepatic palmitate oxidation to 14CO2 was impaired and palmitate esterification into TAG enhanced; these perturbations were however more discrete than after ethanol administration. In contrast to ethanol and n-propanol which, at the dose presently used, increase precursor incorporation into blood TAG, isopropanol inhibits this incorporation. Interference with the process of very low density lipoprotein (VLDL) synthesis and/or secretion, which appears only at a late stage of isopropanol intoxication, is probably responsible for the intensity and duration of the fatty liver observed after administration of this alcohol. 相似文献
44.
Sylvain P. Terver Ronald M. Constine John Csongradi Richard Kleinman Eugene E. Bleck 《The Western journal of medicine》1979,131(2):98-103
A retrospective analysis of 62 patients with 78 congenital dislocations of the hip (CDH) referred to Children''s Hospital at Stanford was done to ascertain whether CDH was being diagnosed as early as had been thought possible and whether various treatments were effective. In this series there were a substantial number of cases of CDH that were not diagnosed within the first 48 hours of life. At Children''s Hospital the Pavlik harness was the most effective form of treatment of congenital dislocations of the hip in the perinatal period. 相似文献
45.
Biochemical research on oogenesis. RNA accumulation during oogenesis of the dogfish Scyliorhinus caniculus 总被引:2,自引:0,他引:2
Four biochemical mechanisms have been shown to operate in the oocytes of amphibians and teleosts: (1) amplification of the 28 S and 18 S genes, (2) noncoordinate accumulation of 5 S RNA and 28 S + 18 S RNA, (3) storage of 5 S and transfer RNA made in excess by small oocytes within nucleoprotein particles, (4) expression of different 5 S genes in oocytes and somatic cells. We have tried to extend these observations to another group of vertebrates, i.e., selacians (Chondrichthya). Our data suggest that ribosomal gene amplification is low or absent in the oocytes of the dogfish Scyliorhinus caniculus. However, previtellogenic oocytes of this species accumulate more 5 S RNA than needed for ribosome assembly. Transfer and 5 S RNA present in small oocytes are probably not free in the cell sap. A substantial fraction of these RNAs sediments at 10 S when homogenates of immature ovaries are centrifuged in sucrose density gradients. In contrast to what we observed in amphibians and teleosts, 5 S RNA from ovaries of S. caniculus is identical in sequence to 5 S RNA from liver. Among the four mechanisms mentioned above, the second and probably the third one are used by the oocytes of S. caniculus. Mechanism (4) is absent in this species. No definitive conclusion can be drawn concerning mechanism (1), i.e., ribosomal gene amplification. 相似文献
46.
A Chaibi J Clément-Champougny 《Archives internationales de physiologie et de biochimie》1975,83(3):535-552
The purpose of this work was to study the quantitative modifications of the hepatic lipids in adult thyroidectomized rats after administration of tetracycline or ethanol (acute dose or prolonged ingestion). 1. - Thyroidectomy did not inhibit the accumulation of fat in the liver of fed euthyroid or hypothyroid rats after intraperitoneal infusion of tetracycline (320 mg/body weight in 2 injections at an interval of 16 h, the diet containing 6% of lipids). 2. - Sixteen hours after the oral administration of a single large dose of ethanol (5 g/kg body weight), there were only found some small modifications of the lipid composition of the liver in fasting euthyroid or thyroidectomized rats, receiving a diet with 6% of lipids before the experiment; on the contrary, when the diet contained 19% of lipids, a fatty liver occurred in the intact rat, but not in the thyroidectomized rat. 3. - The prolonged ethanol intake (in a 20% solution in water) for 5 months with a diet containing 19% of lipids did not induce a fatty liver in intact rats but produced a decrease of hepatic non-phosphorus lipid and an increase of the cholesterol amounts. After the administration of L-thyroxin (10 mug/100 g body weight per day) to these alcoholic thyroidectomized rats during 2 weeks, it was found an increase of the hepatic non phosphorus lipids till an higher amount than in the euthyroid rats. 4. - The hepatic phospholipid amounts were relatively constant in the different experiments. These results accounting for this differential effects were discussed. 相似文献
47.
48.
49.
Katy Jeannot Laure Diancourt Sophie Vaux Michelle Thouverez Amandina Ribeiro Bruno Coignard Patrice Courvalin Sylvain Brisse 《PloS one》2014,9(12)
Carbapenem-resistant Acinetobacter baumannii have emerged globally. The objective of this study was to investigate the epidemiology, clonal diversity and resistance mechanisms of imipenem non-susceptible A. baumannii isolates in France. Between December 2010 and August 2011, 132 notifications were collected, including 37 outbreaks corresponding to 242 cases (2 to 55 per cluster). Multilocus sequence typing, pulsed-field gel electrophoresis (PFGE) and characterisation of carbapenemase-encoding genes were performed on 110 non-repetitive isolates. Gene bla
OXA-23 was the most frequently detected (82%), followed by bla
OXA-24 (11%) and bla
OXA-58 (7%). Eleven sequence types (ST) were distinguished, among which sequence types ST1, ST2 (64%), ST20, ST25, ST85 and ST107. Isolates from epidemiological clusters had the same ST and resistance genes, indicating probable transmission within centres. In contrast, PFGE types of isolates differed among centres, arguing against transmission among centers. This study provides the first epidemiological snapshot of the population of A. baumannii with reduced susceptibility to carbapenems from France, and further underlines the predominance of international clones. 相似文献
50.
Alice Kunzler Eduardo Antônio Kolling Jeferson Delgado da Silva-Jr Juciano Gasparotto Matheus Augusto de Bittencourt Pasquali José Cláudio Fonseca Moreira Daniel Pens Gelain 《Neurochemical research》2017,42(10):2788-2797
Retinoids (vitamin A and derivatives) are recognized as essential factors for central nervous system (CNS) development. Retinol (vitamin A) also was postulated to be a major antioxidant component of diet as it modulates reactive species (RS) production and oxidative stress in biological systems. Oxidative stress plays a major role either in pathogenesis or development of neurodegenerative diseases, or even in both. Here we investigate the role of retinol supplementation to human neuron-derived SH-SY5Y cells over RS production and biochemical markers associated to neurodegenerative diseases expressed at neuronal level in Parkinson’s disease and Alzheimer’s disease: α-synuclein, β-amyloid peptide, tau phosphorylation and RAGE. Retinol treatment (24 h) impaired cell viability and increased intracellular RS production at the highest concentrations (7 up to 20 µM). Antioxidant co-treatment (Trolox 100 µM) rescued cell viability and inhibited RS production. Furthermore, retinol (10 µM) increased the levels of α-synuclein, tau phosphorylation at Ser396, β-amyloid peptide and RAGE. Co-treatment with antioxidant Trolox inhibited the increased in RAGE, but not the effect of retinol on α-synuclein, tau phosphorylation and β-amyloid peptide accumulation. These data indicate that increased availability of retinol to neurons at levels above the cellular physiological concentrations may induce deleterious effects through diverse mechanisms, which include oxidative stress but also include RS-independent modulation of proteins associated to progression of neuronal cell death during the course of neurodegenerative diseases. 相似文献