全文获取类型
收费全文 | 6259篇 |
免费 | 329篇 |
国内免费 | 10篇 |
专业分类
6598篇 |
出版年
2024年 | 19篇 |
2023年 | 92篇 |
2022年 | 224篇 |
2021年 | 334篇 |
2020年 | 158篇 |
2019年 | 178篇 |
2018年 | 192篇 |
2017年 | 160篇 |
2016年 | 288篇 |
2015年 | 315篇 |
2014年 | 338篇 |
2013年 | 501篇 |
2012年 | 448篇 |
2011年 | 491篇 |
2010年 | 275篇 |
2009年 | 253篇 |
2008年 | 329篇 |
2007年 | 308篇 |
2006年 | 279篇 |
2005年 | 231篇 |
2004年 | 211篇 |
2003年 | 178篇 |
2002年 | 174篇 |
2001年 | 50篇 |
2000年 | 41篇 |
1999年 | 40篇 |
1998年 | 32篇 |
1997年 | 32篇 |
1996年 | 18篇 |
1995年 | 27篇 |
1994年 | 29篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 8篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1974年 | 8篇 |
1966年 | 7篇 |
排序方式: 共有6598条查询结果,搜索用时 15 毫秒
11.
C. Kirda A. R. A. G. Mohamed K. S. Kumarasinghe A. Montenegro F. Zapata 《Plant and Soil》1992,147(2):217-223
A field experiment was conducted to investigate if carbon isotope (13C) discrimination () measured at the vegetative stage of spring wheat (Triticum turgidum L. var. durum) is related with the yield and water use efficiency (WUE) at ripening. A line source sprinkler irrigation system exposed the wheat genotypes to different watering regimes, from rainfed to full irrigation and thereby increased the range in yield and WUE attainable in the four genotypes studied. The results indicated that values measured at the late stem elongation stage 60 days after planting (DAP), showed strong positive correlation with total dry matter yield (r=0.732***), and a highly significant negative correlation with WUE (r=–0.755***) measured at ripening 105 DAP. The data suggest that the imprints of measured at vegetative growth stage persists throughout the entire growth period, until maturity. Subject to confirmation from additional studies in other crops and locations, early measurements of may prove a useful tool for rapid and early screening of cultivars, for high yield and high WUE. 相似文献
12.
Mohammed S. Taghour Hazem Elkady Wagdy M. Eldehna Nehal M. El-Deeb Ahmed M. Kenawy Eslam B. Elkaeed Aisha A. Alsfouk Mohamed S. Alesawy Ahmed M. Metwaly Ibrahim. H. Eissa 《Journal of enzyme inhibition and medicinal chemistry》2022,37(1):1903
A thiazolidine-2,4-dione nucleus was molecularly hybridised with the effective antitumor moieties; 2-oxo-1,2-dihydroquinoline and 2-oxoindoline to obtain new hybrids with potential activity against VEGFR-2. The cytotoxic effects of the synthesised derivatives against Caco-2, HepG-2, and MDA-MB-231 cell lines were investigated. Compound 12a was found to be the most potent candidate against the investigated cell lines with IC50 values of 2, 10, and 40 µM, respectively. Furthermore, the synthesised derivatives were tested in vitro for their VEGFR-2 inhibitory activity showing strong inhibition. Moreover, an in vitro viability study against Vero non-cancerous cell line was investigated and the results reflected a high safety profile of all tested compounds. Compound 12a was further investigated for its apoptotic behaviour by assessing the gene expression of four genes (Bcl2, Bcl-xl, TGF, and Survivin). Molecular dynamic simulations authenticated the high affinity, accurate binding, and perfect dynamics of compound 12a against VEGFR-2. 相似文献
13.
Shamsudeen Varisai Mohamed Jih-Min Sung Toong-Long Jeng Chang-Sheng Wang 《Plant Cell, Tissue and Organ Culture》2006,86(2):187-199
A step-wise procedure for the regeneration of fertile plants by organogenesis from cultures of the economically important Phaseolus angularis L., cultivars: KS-6, KS-7 and KS-8 using etiolated seedlings was established. Pre-culture of 5-day old seedling explants with MS (Murashige and Skoog (1962) Physiol Plant 15:473–493) + B5-vitamins (Gamborg et al. (1968) Exp Cell Res 50:151–158) liquid medium containing either 5.0 μM TDZ or 5.0 μM BAP under dark condition was essential for organogenesis. Bud growth and shoot multiplication were stimulated by reducing the BAP concentrations from 5.0 to 2.5 μM after 3 weeks. The maximum frequency of shoot induction was 65.2% (33.8 ± 2.54 shoots/explant) in cultivar KS-8 followed by KS-7 34.6% (23.4 ± 1.91 shoots/explant) and KS-6 30.6% (21.2 ± 2.28 shoots/explant). The multiplied buds elongated after transferring to solid MSB5 medium supplemented with 4.0 μM GA3, 12.5 μM AgNO3 and 0.4 μM IBA. Up to 98% rooting efficiency of was obtained when the shoots were pulse-treated with liquid medium containing 4.5 μM IBA for 10 min. The rooted plantlets were transferred to pots in the greenhouse, where they grew, mature, flowered and bared pod normally. The efficient shoot bud induction capability was found to be cultivar dependent. All the three cultivars tested formed multiple shoots. This efficient and rapid regeneration system may also be helpful for Agrobacterium- or particle gun-mediated transformation for this important legume crop. 相似文献
14.
Nabiel A. M. Saleh Salwa A. Maksoud Mohamed N. El-hadidi Wafaa M. M. Amer 《Biochemical Systematics and Ecology》1987,15(6):673-675
The leaf flavonoids of the family Papaveraceae were studied. 相似文献
15.
Pribat A Noiriel A Morse AM Davis JM Fouquet R Loizeau K Ravanel S Frank W Haas R Reski R Bedair M Sumner LW Hanson AD 《The Plant cell》2010,22(10):3410-3422
Tetrahydropterin-dependent aromatic amino acid hydroxylases (AAHs) are known from animals and microbes but not plants. A survey of genomes and ESTs revealed AAH-like sequences in gymnosperms, mosses, and algae. Analysis of full-length AAH cDNAs from Pinus taeda, Physcomitrella patens, and Chlamydomonas reinhardtii indicated that the encoded proteins form a distinct clade within the AAH family. These proteins were shown to have Phe hydroxylase activity by functional complementation of an Escherichia coli Tyr auxotroph and by enzyme assays. The P. taeda and P. patens AAHs were specific for Phe, required iron, showed Michaelian kinetics, and were active as monomers. Uniquely, they preferred 10-formyltetrahydrofolate to any physiological tetrahydropterin as cofactor and, consistent with preferring a folate cofactor, retained activity in complementation tests with tetrahydropterin-depleted E. coli host strains. Targeting assays in Arabidopsis thaliana mesophyll protoplasts using green fluorescent protein fusions, and import assays with purified Pisum sativum chloroplasts, indicated chloroplastic localization. Targeting assays further indicated that pterin-4a-carbinolamine dehydratase, which regenerates the AAH cofactor, is also chloroplastic. Ablating the single AAH gene in P. patens caused accumulation of Phe and caffeic acid esters. These data show that nonflowering plants have functional plastidial AAHs, establish an unprecedented electron donor role for a folate, and uncover a novel link between folate and aromatic metabolism. 相似文献
16.
Ana Gorostidi Alberto Bergareche Javier Ruiz-Martínez José F. Martí-Massó María Cruz Shiji Varghese Mohamed M. Qureshi Fatimah Alzahmi Abdulmonem Al-Hayani Adolfo López de Munáin Omar M.A. El-Agnaf 《PloS one》2012,7(12)
The diagnosis of Parkinson’s disease (PD) remains primarily a clinical issue, based mainly on phenotypic patterns. The identification of biomarkers capable of permitting the preclinical detection of PD is critically needed. α-Synuclein is a key protein in PD, with missense and multiplication mutations in the gene encoding α-synuclein (SNCA) having been reported in familial cases of PD, and accumulation of the protein identified in Lewy bodies (LBs) and Lewy neurites (LNs) in affected brain regions. With the objective of validating the use of α-synuclein as a clinical or progressive biomarker in an accessible tissue, we used an enzyme-linked immunosorbent assay (ELISA) to measure α-synuclein levels in the peripheral blood plasma of idiopathic PD and LRRK2 mutation carrier patients and compared our findings with healthy control subjects. Compared to healthy controls, we found a significant decrease in plasma total α-synuclein levels in idiopathic PD (iPD) patients (n = 134, p = 0.010). However, the reduction was less significant in patients who were LRRK2 mutation carriers (n = 32, p = 0.133). This lack of significance could be due to the small number of individuals employed in this group. No predictive value of total α-synuclein in the diagnosis of PD was found in a receiver operating characteristic (ROC) curve analysis. Although this is a pilot study requiring corroboration on a larger cohort of patients, our results highlight the possible use of plasma α-synuclein as a biomarker for PD. 相似文献
17.
18.
Hydrological conditions prevailing before, during and after the Messinian salinity crisis in Sicily have been approached using dinoflagellate cyst records. The synthetic sequence considered is based on five classical sections from the Caltanissetta Basin. Our interpretations are based on the recognition of autochthonous, allochthonous and reworked population among the dinocyst assemblages. For the first time, sea-surface temperatures and seasonal salinity contrasts were tentatively reconstructed using a “Mutual Climatic Range Method”. Sicilian late Tortonian deposits correspond to marine environment with significant terrestrial inputs favourable to eutrophic dinocyst species. Immediately after the beginning of the Messinian Stage, euryhaline assemblages took place, followed by meso-hyperhaline taxa, within a general trend to shallowing. At the end of the Tripoli diatomitic Formation, environment appears confined, with regular oceanic inflows. Such marine inflows remain persistent during the deposition of the salt Member, witnessing the probable persistence of nearby normal marine sea-surface water conditions in the Mediterranean Sea but with possible reduced hydrological circulation and/or low nutrient component. Such inflows are slightly decreasing up to the top of the Sicilian Upper Evaporites. At the same time, river inputs appear weak during the salt deposition, as the consequence of a rather dry climatic context. As shown by reworking activity, terrestrial inputs increase progressively from the base of the Upper Evaporites. During the Lago Mare period, while climate remains rather dry (absence of freshwater algae inputs, very low amount in trees requiring humid conditions), local deposition environment is confined with mesohaline to hypohaline sea-surface waters, in a context with relatively high seasonal sea-surface salinity contrast (up to 6‰). The very high reworking observed in the Arenazzolo silts, in addition to slightly increasing water depth, led us to consider the presence of a discontinuity between the Lago Mare and the Arenazzolo Fms. We consider the Arenazzolo Formation as a transgressive facies following a deep downcutting period. The Arenazzolo Formation presents a two-step development. The first one, correlative with the presence of a G. etrusca (a species with Paratethyan affinities), corresponds to a relative high-stand sea-level with oceanic influxes, low seasonal sea-surface salinity contrast and probable more humid context, as revealed by the important freshwater algal inputs. During the second step, salinity becomes much more variable, with a clear increase of seasonal sea-surface salinity contrast, a possible slight mean sea-surface temperature increase (only few degrees) and a clear weakening of the river inputs. Taking the proposed Zanclean position of the Arenazzolo Fm. into consideration, we state that mean sea-surface temperature did not change significantly from the base of the Messinian to the earliest Zanclean. At 5.33 Ma, the suddenly achieved flooding restored a fair, deep oceanic environment characterized, at the beginning, by a clear mean sea-surface temperature cooling (up to 6-7 °C) and a nutrient depletion, associated with the basins starvation. Sea-surface salinities were normal, with very low seasonal contrast. Hydrodynamics then nutrient supply became then quite normal from c.a. 5.08 Ma. The status of the Sicilian Caltanissetta Basin as a marginal basin although fastly deepening and the stratigraphical location of the Messinian discontinuity at the base of the Arenazzolo is the scenario that best matches our dinocyst record. 相似文献
19.
Effect of vegetation on density thresholds of adult desert locust gregarization from survey data in Mauritania 总被引:1,自引:0,他引:1
Sory Cisse Saïd Ghaout Ahmed Mazih Mohamed Abdallahi Ould Babah Ebbe Ahmed Salem Benahi Cyril Piou 《Entomologia Experimentalis et Applicata》2013,149(2):159-165
In the desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae), the threshold density inducing the gregarization phenomenon has never been determined under natural conditions. The influence of environmental factors on this phenomenon has been studied mostly in controlled environments. Based on data collected during several years by the survey teams of the National Center for Locust Control in Mauritania, we analyzed the influence of locust density, vegetation cover, and vegetation status on the probability of observing gregarious locusts. We assumed that a probability to observe gregarious locusts of 0.5 corresponded to the density threshold of gregarization. The results showed in detail the change in the threshold of gregarization according to the cover and status of the vegetation. Low cover and dry vegetation led to a low density threshold of gregarization probably due to high probability of individuals to touch each other. Dense and green vegetation favored a high threshold of gregarization probably due to a dispersion of the individuals and a low probability of individual encounters. These findings should help the management of locusts and decision making during control operations. 相似文献
20.
A Neuro-Comparative Study between Single/Successive Thorium Dose Intoxication and Alginate Treatment
Mohamed M. Rezk 《Biological trace element research》2018,185(2):414-423
The adult male albino rats were grouped into five groups (control group and four variably treated groups with thorium (Th) in single or successive with or without alginate treatment). The IP administration of thorium nitrate (13.6 mg/kg b.wt.) induced a regional distribution and accumulation ordered as cerebellum > cerebral cortex > brain stem > hippocampus > hypothalamus > striatum. Also, it induces a significant increase in Na+, Ca2+, and Fe3+ ion content and malondialdehyde (MDA) level while K+ ions and glutathione (GSH) level were significantly decreased. On the other hand, the daily oral administration of 5% alginate showed a significant decreasing in the accumulation of thorium in the different brain areas and mitigated its hazardous effects. By the alginate treatment, Na+, Ca2+, Fe3+, and level of MDA were declined while K+ ions and GSH level showed a significant increase. The improvement of the investigated parameters was attributed to the specific chelating, regeneration, and antioxidant properties of the alginate. So, alginate administration could ameliorate the hazardous effects of thorium nitrate. 相似文献