全文获取类型
收费全文 | 4417篇 |
免费 | 328篇 |
国内免费 | 1篇 |
出版年
2023年 | 24篇 |
2022年 | 40篇 |
2021年 | 103篇 |
2020年 | 82篇 |
2019年 | 81篇 |
2018年 | 120篇 |
2017年 | 62篇 |
2016年 | 144篇 |
2015年 | 229篇 |
2014年 | 263篇 |
2013年 | 314篇 |
2012年 | 424篇 |
2011年 | 328篇 |
2010年 | 217篇 |
2009年 | 224篇 |
2008年 | 247篇 |
2007年 | 224篇 |
2006年 | 248篇 |
2005年 | 216篇 |
2004年 | 216篇 |
2003年 | 194篇 |
2002年 | 193篇 |
2001年 | 59篇 |
2000年 | 46篇 |
1999年 | 39篇 |
1998年 | 58篇 |
1997年 | 48篇 |
1996年 | 42篇 |
1995年 | 37篇 |
1994年 | 24篇 |
1993年 | 25篇 |
1992年 | 26篇 |
1991年 | 26篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 2篇 |
排序方式: 共有4746条查询结果,搜索用时 15 毫秒
11.
The photosynthetic behaviour ofDunaliella viridis has been studied under a combination of three variables: irradiance (0–900 mol m–2 s–1), temperature (15, 23, 31, 38, 42 °C) and nitrogen concentration (0.05, 0.5, 1.5, 5, 10 mM NO
3
-
) at a salinity of 2 M NaCl.The highest rates of photosynthesis have been found at 31 °C and a nitrate concentration of 10 mM. There exists a synergistic effect between temperature and nitrogen availability on the photosynthesis ofD. viridis; under nitrogen deficiency oxygen evolution is low, even null at high temperature. The interaction between these two variables of control occurs in a multiplicative way. There is also a general increase in photosynthetic pigments following the increase in nitrogen concentration in the culture medium. The normalization of net photosynthesis data in relation to chlorophylla shows that nitrogen concentration makes an indirect control of the photosynthetic rate ofD. viridis through the variation of pigment concentration. 相似文献
12.
C Dauphin-Villemant F Leboulenger F Xavier H Vaudry 《Journal of steroid biochemistry》1988,30(1-6):457-460
A perifusion system technique was developed in order to determine in vitro the respective roles of ACTH and ANG II in the regulation of adrenal steroidogenesis in the lizard Lacerta vivipara. Synthetic human ACTH 1-39, administered as 20-min pulses, stimulated corticosterone (B) and aldosterone (A) release in a dose-dependent manner. The increase in corticosterone output was higher than that in aldosterone output, leading to an enhancement of the B/A ratio. Iterative stimulations with 1 nM ACTH (20-min pulses every 120 min) led to reproducible increases in corticosterone and aldosterone release. Prolonged stimulation with 1 nM ACTH (up to 240 min) caused a sustained increase in corticosteroid release, suggesting that, in the lizard, ACTH does not induce any desensitization phenomenon. The angiotensin II analogue [Sar1, Val5] ANG II also stimulated corticosterone and aldosterone release in a dose-dependent manner; the stimulatory effects of ANG II on both steroids were very similar. These results indicate that, in lizards, ACTH plays a major role in the regulation of adrenal steroidogenesis. Since ANG II stimulates the production of gluco- and mineralocorticoids, our data raise the question of the existence of two cell types synthesizing corticosterone and aldosterone, respectively, in reptiles. 相似文献
13.
Xavier Jeunemaitre Brigitte Rigat Anne Charru Anne-Marie Houot Florent Soubrier Pierre Corvol 《Human genetics》1992,88(3):301-306
Summary Although essential arterial hypertension is believed to have a strong genetic predisposition, the gene(s) responsible are unknown. The mechanisms underlying the regulation of blood pressure and experimental studies place the renin gene among the main candidate genes that need to be tested in humans. We tested the hypothesis of a linkage between the renin gene and essential hypertension using the affected sib pair method. Siblings (133 subjects, 52.1±10.9 years) from 57 families were selected for sustained hypertension (160.7 ± 22.9/99.5 ± 12.8 mmHg with 80% of patients under antihypertensive treatment), of early onset (40.7 ± 12.0 years), in the absence of obesity, diabetes mellitus, and secondary hypertension. Eight renin haplotypes were generated from three diallelic renin restriction fragment length polymorphisms (RFLPs) (TaqI, Hinfi, HindIII) located throughout the renin gene. The allelic concordance between the sib pairs was analyzed by identity by state relationships for 98 sib pairs (41 for 41 couples, 39 for 13 trios, 18 for 3 quartets). Allelic frequencies in the 57 hypertensive probands were similar to those observed among 102 hypertensive subjects studied previously. Six of eight possible haplotypes were observed, the informativity of the marker corresponded to 70% of heterozygosity. Allelic concordance for all sib pairs according to sibship size was not significantly different from that expected under the hypothesis of no linkage (t = 0.52, P = 0.15) reflecting only a small excess of renin alleles shared by the hypertensive sibs (1.44 ± 0.6 vs 1.36 ± 0.6). Likewise the linkage hypothesis was unsupported by weighted estimates to correct for possible bias due to large sibship size. Thus, the sib pair analysis suggests that the renin gene does not have a frequent role in the pathogenesis of essential hypertension; further more powerful linkage studies or other approaches will be needed to detect contributions at the renin locus to the heritability of essential hypertension. 相似文献
14.
Christian Bry Edgar Basset Xavier Rognon François Bonamy 《Environmental Biology of Fishes》1992,35(1):75-84
Synopsis Sibling cannibalism in pike, Esox lucius, larvae and juveniles living in outdoor rearing ponds was studied using stomach contents analysis. For the two initial densities tested (6 and 18 larvae m–2, equivalent to 12 and 36 larvae m–3), cannibalism was non-existent during the larval period (13 to 35 mm total length) and was observed only during the juvenile stages. Initial density of larvae influenced both the date of first detection of cannibalistic individuals and the rate of development of cannibalism in the population. At initial stocking densities of 18 larvae m–2 (36 larvae m–3), cannibalism was observed from 21 days after the start of exogenous feeding (mean total length: 60 mm) onwards. At a mean total length of 100 mm and for initial stocking densities of 6 and 18 larvae m–2, (12 and 36 larvae m–3), the average proportions of cannibals in the populations of juveniles were 7.8% and 41.3% and the cannibals accounted for 15.5% and 65.9% of the total pike biomass, respectively. In stomachs of cannibals, young pike were the dominant prey in terms of weight. Dry weights of invertebrate-prey were lower in cannibals than in non-cannibals of similar size. Cannibalism among pike juveniles was characterized by the prey being swallowed whole and head first in the vast majority of cases. There was a strong positive correlation between predator and prey size and the mouth size of a cannibal was found to be an important constraint determining maximum victim size. The overall mean ratio of pike prey length to pike cannibal length was 66.2% and the average ratio of prey head depth to predator mouth width amounted to 87.6%. Prey size selection could be demonstrated for several length-groups of cannibals. These results are compared with the characteristics of early cannibalism in other fish species. 相似文献
15.
Distribution pattern of decapod larvae off the north-western Iberian Peninsula coast (NE Atlantic) 总被引:3,自引:0,他引:3
In October 1977 the model of general circulation of the watermasses off the coast of Galicia, and the presence of a coastalupwelling, led to a high primary productivity. This high productivityin turn favoured the development of a rich population of decapodlarvae. The abundance and distribution pattern of these organismswere closely linked (i) to the abundant presence of the correspondingadult species in the area, (ii) with the spatial distributionof phytoplanktonic populations concurrently studied by Estrada[J. Plankton Res ., 6, 417434 (1984)] and (iii) withthe hydrodynamic pattern in the area. Fifty-two decapod larvaetaxa were identified and Solenocera membranacea, Pisidia longicornis,Pilumnushirtellus and Goneplax rhomboides were the most representativespecies It was observed that the greatest concentrations oflarvae (3387 larvae 102 m3) were to be found nearthe mouth of the Rfas Baixas (situated in the south-west ofthe coastal area) and in some zones further out to sea (863larvae 102 m3) (due to a process of hydrodynamictransport) 相似文献
16.
17.
18.
F Xavier M Guillomot M Charlier J Martal P Gaye 《Biology of the cell / under the auspices of the European Cell Biology Organization》1991,73(1):27-33
Expression of the c-fos proto-oncogene by ovine conceptuses was analyzed by Northern and slot blots and indirect immunohistofluorescence in relation to the expression of the embryonic interferon-alpha (oTP) during implantation. c-fos was expressed initially in the trophoblast, and then in the allantois, when this tissue began to develop (day 17). In the embryonic tissues, the c-fos proto-oncogene was weakly expressed up to day 22 and increased thereafter. In the trophoblast, the expression of c-fos proto-oncogene was transient, occurring when the oTP gene was transcribed at a maximal level at the beginning of implantation (days 14-15), and decreased thereafter, following the pattern of oTP gene expression. This decline is due essentially to the arrest of c-fos and oTP gene expression by the trophoblastic cells which established cellular contacts with the uterine epithelium during the implantation process. 相似文献
19.
Use of a monoclonal antibody to measure the surface expression of thrombospondin following platelet activation 总被引:3,自引:0,他引:3
The radiolabelled monoclonal antibody, 5G11, directed against native thrombospondin, has been used to assess the surface expression of secreted thrombospondin on human blood platelets. Emphasis has been placed on studying the role of fibrinogen in this process. Unstimulated platelets bound low amounts of 5G11 (about 2000 molecules/platelet). Binding increased 2-fold and 5-7-fold after stimulation of platelets with ADP or thrombin (or ionophore A23187) respectively. Unstimulated platelets from patients deficient in alpha-granule proteins (gray platelet syndrome) bound baseline levels of 5G11. However, binding was not increased after activation. Thrombospondin expression on thrombin-stimulated normal platelets was for a large part divalent-cation-dependent and was not affected by AP-2, a monoclonal antibody to GPIIb-IIIa complexes. However, binding of 5G11 was some 50% lower when platelets were stimulated in the presence of Fab fragments of a polyclonal rabbit antibody to fibrinogen. This suggested either a direct binding of thrombospondin to surface-bound fibrinogen or a steric inhibition due to a close proximity of the two proteins. The fact that binding of 5G11 was at the lower limit of the normal range to the stimulated platelets of an afibrinogenaemic patient specifically lacking detectable fibrinogen favoured the latter explanation. Thus, a major fibrinogen-independent pathway for thrombospondin expression must exist. 相似文献