全文获取类型
收费全文 | 1274篇 |
免费 | 104篇 |
出版年
2023年 | 14篇 |
2022年 | 14篇 |
2021年 | 41篇 |
2020年 | 29篇 |
2019年 | 40篇 |
2018年 | 47篇 |
2017年 | 38篇 |
2016年 | 43篇 |
2015年 | 104篇 |
2014年 | 68篇 |
2013年 | 107篇 |
2012年 | 132篇 |
2011年 | 112篇 |
2010年 | 74篇 |
2009年 | 54篇 |
2008年 | 66篇 |
2007年 | 64篇 |
2006年 | 51篇 |
2005年 | 46篇 |
2004年 | 37篇 |
2003年 | 29篇 |
2002年 | 36篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1985年 | 2篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1968年 | 2篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1378条查询结果,搜索用时 15 毫秒
1.
Background
Evolution of parasite traits is inextricably linked to their hosts. For instance one common definition of parasite virulence is the reduction in host fitness due to infection. Thus, traits of infection must be viewed in both protagonists and may be under shared genetic and physiological control. We investigated these questions on the oomycete Hyaloperonospora arabidopsis (= parasitica), a natural pathogen of the Brassicaceae Arabidopsis thaliana. 相似文献2.
3.
Drahomíra Kenov Lucie oltysov Michal Pravenec Marie-Pierre Moisan W. Theodore Kurtz Vladimír Ken 《Journal of Experimental Animal Science》2000,41(1-2)
The SHR-Lx congenic strain carrying a differential segment of chromosome 8 of BN and PD origin was recently shown to exhibit a significant decrease in blood pressure as compared to the SHR strain. There were two positional candidate genes for blood pressure control mapped to the differential segment: the rat kidney epithelial potassium channel gene (Kcnj1) and brain dopamine receptor 2 gene (Drd2). Bot these genes were separated into SHR.BN-RNO8 congenic substrains. In this communication, we are presenting the assignment of two further putative candidate genes, which might be involved in blood pressure control to the BN/PD differential segment of the SHR-Lx congenic strain. These are: the gene coding for smooth muscle cell specific protein 22 (Sm22) defined by the D8Mcw1 marker and neuronal nicotinic acetylcholine receptor gene cluster, defined by the D8Bord1 marker. Moreover, the glutamate receptor gene Grik4 which also maps to the differential segment of the SHR-Lx should be taken into account. The genetic separation of all these putative candidate genes of blood pressure control is being performed by recombinations and subsequent selection using (SHR×SHR-Lx) intercross population. 相似文献
4.
P H Chanh B Lasserre R Kaiser J Couquelet P Coudert C Rubat 《Prostaglandins, leukotrienes, and essential fatty acids》1990,40(2):143-148
Experiments carried out under the conditions adopted showed the strong affinity of aminopyridazine derivatives for the eicosanoids TXA2 and PGI2. But this affinity depended on the chemical structure of the molecule: a small change in the radical grafted onto the pyridazine ring could completely modify the pharmacological activity of the molecule. Consequently it should be possible to control the properties of pyridazine derivatives according to pharmacological needs. Thus: --pyridazin-3-one derivatives were mainly active on TXA2 biosynthesis: 2-aminoalkyl 5-arylidene 6-methyl (4H) pyridazin-3-ones inhibited the TXA2-synthesizing activity of cardiac tissue whereas 3-amino 4,6-diaryl pyridazin-3-ones were specific inhibitors of the TXA2 synthetase in vitro, but these effects were weak. --pyridazine derivatives were devoid of any effect on the TXA2-synthesizing activity of cardiac tissue: they acted on either TXA2 synthetase or PGI2 synthetase according to the radicals grafted onto the pyridazine ring. --none of the compounds under study was active on the PGI2-synthesizing activity of cardiac tissue. 相似文献
5.
H C Pham V Dossou-Gbete R Kaiser B Lasserre R Chahine J Couquelet P Coudert C Rubat 《Prostaglandins, leukotrienes, and essential fatty acids》1990,39(1):19-25
Some 3-amino 4,6-diarylpyridazine derivatives were tested for their effects on TXA2 and PGI2 biosyntheses in vitro and on the TXA2- and PGI2-synthesizing activities of cardiac tissue. Horse platelet and aorta microsomes were used as sources of thromboxane and prostacyclin synthetases respectively. The TXA2- and PGI2-synthesizing activities of cardiac tissue were studied on isolated perfused rabbit hearts (the heart microsomes being used both as TXA2 synthetase and PGI2 synthetase sources). TXB2 and 6-keto PGF1 alpha were determined by RIA. Among the compounds under study, 3-morpholino 4,6-diphenylpyridazine (III) was shown to inhibit specifically the TXA2 synthetase. Substitution of the morpholino group by a dimethylamino one (I) reinforced the inhibiting effects on TXA2 synthetase but it also revealed a slight anti-prostacyclin synthetase action of the molecule. Replacement of 3-morpholino moieties by either a 3-hydrazino (IV), or a 2-dimethylaminoethylamino (V), or a 2-morpholinoethylamino group (VI) abolished completely the effects of the molecule on TXA2 and PGI2 synthetases. Likewise the addition of chlorine on the para-position on the phenyl ring of I neutralized all its inhibitory effects both on TXA2 and PGI2 synthetases in vitro. None of the 3-amino 4,6-diarylpyridazine derivatives was active on either the TXA2- or PGI2-synthesizing activities of cardiac tissue. 相似文献
6.
B Graf F Coudert O Mazzella L Cauchy 《Archives d'anatomie microscopique et de morphologie expérimentale》1985,74(2):151-166
Diaphyseal tibial bones of 11-14-17 th day-old hatched chicks infected with retrovirus myeloblastic MAV 2-0 were examined by conventional optical microscopy. The characteristic lesion is osteoblastic hyperplasia with the development of spongious bone. The new formed bone contains abnormal chondroid tissue. The relation between osseous and cartilaginous tissues in this experimental model is discussed. As connective tissue took part in the constitution of this hyperostosis, this osteopathy may be considered as an hyperplastic, monodermic mesenchymatous, pluritissular tumour. The numerous works concerning the "avian hyperostosis osteopetrosis" are commented. 相似文献
7.
8.
Eastmond Peter; Kolc Lucie; Rawsthorne Stephen 《Journal of experimental botany》1996,47(11):1763-1769
The aim of this study was to assess the photosynthetic potentialof developing seeds of oilseed rape (Brassica napus L.) andto compare photosynthetic properties of embryo plastids withthose of leaf chloroplasts from the same species. Measurementsof CO2-dependent O2 evolution show that developing seeds ofB. napus are photosynthetically active in vitro. Essentially,all of the photosynthetic activity of the developing seed isaccounted for by the embryo. The rate of photosynthesis by developingembryos increased until the onset of desiccation, after whichit declined, so that by maturity embryos were no longer photosyntheticallyactive. Photosynthetic activity was positively correlated withchlorophyll content throughout development. Comparison of thephotosynthetic characteristics of leaf and embryo chloroplastsrevealed that rates of uncoupled electron transport were 2.5-foldgreater in those from the embryo. Light-saturated rates of CO2-dependentO2 evolution, per unit chlorophyll, and CO2 saturation pointswere similar for chloroplasts from both tissues. However, light-saturationpoints and chlorophyll a/b ratios were lower for embryo thanfor leaf choroplasts. Embryos and embryo chloroplasts also containedconsiderably less ribulose 1,5-bisphosphate carboxylase/oxygenaseprotein per unit total protein, than leaves. Although excisedembryos were capable of high rates of CO2-dependent O2 evolution(90100 mol mg1 chlorophyll h1) under asaturating photosynthetic photon flux density (PPFD), low transmittanceof light through the silique wall (30%), together with the highPPFD required to achieve light compensation points in developingseeds (500 mol m2 s1), suggests that photosynthesisin vivo is unlikely to make a net contribution to carbon economyunder normal environmental conditions. Key words: Embryo, development, photosynthesis, chloroplast, Brassica napus L. 相似文献
9.
Robert de Jonge Mario Bedu Nicole Fellmann Stephen Blonc Hilde Spielvogel Jean Coudert 《European journal of applied physiology and occupational physiology》1996,74(4):367-374
We have previously observed that 11-year-old children of low socio-economic status (LSES) showed a delayed physical growth of approximately 2 years and developed lower normalized short-term power output than children of high socio-economic status (HSES) of the same age. In contrast, maximal oxygen uptake
per unit of fat free mass was no different in either group. The aim of this study was to evaluate the effect of anthropometric characteristics between HSES and LSES prepubertal children in aerobic and anaerobic performance. To compare children of the same body dimensions, 11-year-old boys (n = 30) and girls (n = 31) of LSES and 9-year-old boys (n = 21) and girls (n = 27) of HSES were studied. Anthropometric measurements,
(direct test), maximal anaerobic power (P
max, force-velocity test) and mean anaerobic power (
, Wingate test) were determined. In these children having the same body dimensions: mean
were the same in LSES and HSES children [1.2 (SD 0.2)1-min–1];P
max and
were lower in LSES subjects [154.0 (SD 33.2) vs 174.6 (SD 38.4) W and 116.3 (SD 23.3) vs 128.2 (SD 28.0) W, respectively]; the linear relationships between
and fat free mass were the same in LSES and HSES boys but, in the girls, the LSES group had lower values. For anaerobic performance, the relationships were significantly different: the slopes were the same but LSES values for the both sexes were lower. These results would suggest that factors other than differences in body dimensions alone were responsible for the lower performance of LSES girls and boys. Cultural factors and motor learning, structural and functional alterations of muscle induced by marginal malnutrition have been discussed. 相似文献
10.
G. Falgairette M. Bedu N. Fellmann H. Spielvogel E. Van Praagh P. Obert J. Coudert 《European journal of applied physiology and occupational physiology》1994,69(1):36-43
Field tests of running and laboratory tests were performed in La Paz [high altitude (HA), 3700 m] and in Clermont-Ferrand [low altitude (LA), 300 m] to investigate their validity at HA. Prepubertal boys of mean ages 10.6 years (HA1,n = 16; LA1,n = 28) and pubertal boys of 13.7 years (HA2,n = 12; LA2,n = 41) took part in the study. All the boys performed a 30-m sprint (v
30m), a 30-s shuttle run (v
3os) and a progressive shuttle run test until their maximal aerobic velocity (v
maxsRT). Maximal oxygen consumption was extrapolated from the last test.
. In the laboratory, the boys performed a force-velocity test (P
max), a Wingate test (P
Wing) and a graded test to measure maximal oxygen consumption
; direct method) on a cycle ergometer. At similar ages, there was no significant difference between HA and LA boys forv
30m andP
max. Thev
30s of HA boys was 3%–4% lower than those of LA boys (P<0.05); there was no significant difference forP
Wing. Significant relationships were observed at both altitudes betweenP
max (watts per kilogram) andv
30m (HA:r=0.76; LA:r=0.84) and betweenP
Wing andv
30s (HA:r=0.67; LA:r = 0.77); the slopes and the origins were the same at HA and LA. The
,v
maxSRT and
were lower by 9%, 12% and 20%, respectively, at HA than at LA (P<0.05). However, the relationships between
and
(litres per minute) at HA (r=0.88) and at LA (r=0.93) were identical. In conclusion, chronic hypoxia did not modify performance in very short dash exercises. The influence of HA appeared when the exercise duration increased and, during a maximal shuttle run test, performance was reduced by 10% at HA. Moreover, it was possible to assessP
max,P
Wing and
at HA as well as at LA from field tests. 相似文献