全文获取类型
收费全文 | 1278篇 |
免费 | 122篇 |
专业分类
1400篇 |
出版年
2023年 | 12篇 |
2022年 | 22篇 |
2021年 | 32篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 28篇 |
2017年 | 14篇 |
2016年 | 25篇 |
2015年 | 60篇 |
2014年 | 72篇 |
2013年 | 79篇 |
2012年 | 95篇 |
2011年 | 65篇 |
2010年 | 47篇 |
2009年 | 51篇 |
2008年 | 46篇 |
2007年 | 72篇 |
2006年 | 46篇 |
2005年 | 47篇 |
2004年 | 42篇 |
2003年 | 54篇 |
2002年 | 38篇 |
2001年 | 16篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 9篇 |
排序方式: 共有1400条查询结果,搜索用时 15 毫秒
911.
Avishek Datta Brian M. Sindel Paul Kristiansen Robin S. Jessop Warwick L. Felton 《Plant and Soil》2008,303(1-2):49-54
A glasshouse experiment was conducted to investigate the effect of soil pH on chickpea (Cicer arietinum) tolerance to isoxaflutole applied pre-emergence at 0, 75 (recommended rate) and 300 g a.i. ha−1. For this study, the variables examined were two desi chickpea genotypes (97039-1275 as a tolerant line and 91025-3021 as
a sensitive line) and four pH levels (5.1, 6.9, 8.1, and 8.9). The results demonstrated differential tolerances among chickpea
genotypes to isoxaflutole at different rates and soil pH levels. Isoxaflutole applied pre-emergence resulted in increased
phytotoxicity with increases in soil pH and herbicide rate. Even the most tolerant chickpea genotype was damaged when exposed
to higher pH and herbicide rates, as indicated by increased leaf chlorosis and significant reductions in plant height, and
shoot and root dry weight. The effects were more severe with the sensitive genotype. The susceptibility of chickpea to this
herbicide depends on genotype and soil pH which should be taken into account in breeding new lines, and in the agronomy of
chickpea production. 相似文献
912.
Bellis C Cox HC Dyer TD Charlesworth JC Begley KN Quinlan S Lea RA Heath SC Blangero J Griffiths LR 《Human genetics》2008,124(5):543-552
To understand the underlying genetic architecture of cardiovascular disease (CVD) risk traits, we undertook a genome-wide
linkage scan to identify CVD quantitative trait loci (QTLs) in 377 individuals from the Norfolk Island population. The central
aim of this research focused on the utilization of a genetically and geographically isolated population of individuals from
Norfolk Island for the purposes of variance component linkage analysis to identify QTLs involved in CVD risk traits. Substantial
evidence supports the involvement of traits such as systolic and diastolic blood pressures, high-density lipoprotein-cholesterol,
low-density lipoprotein-cholesterol, body mass index and triglycerides as important risk factors for CVD pathogenesis. In
addition to the environmental influences of poor diet, reduced physical activity, increasing age, cigarette smoking and alcohol
consumption, many studies have illustrated a strong involvement of genetic components in the CVD phenotype through family
and twin studies. We undertook a genome scan using 400 markers spaced approximately 10 cM in 600 individuals from Norfolk
Island. Genotype data was analyzed using the variance components methods of SOLAR. Our results gave a peak LOD score of 2.01
localizing to chromosome 1p36 for systolic blood pressure and replicated previously implicated loci for other CVD relevant
QTLs. 相似文献
913.
A general hypothesis on mating patterns in alpine plants states that self-fertilization should increase with increasing altitude as a result of pollinator limitation at higher altitudes. However, realized selfing rates under natural conditions, as based on genetic progeny analysis, have not yet been determined for any alpine species across altitude. We therefore assessed the realized selfing rates in about 100 open-pollinated families of the high-alpine cushion plant Eritrichium nanum, sampled along an altitudinal gradient in the Swiss Alps, by using progeny analysis based on six microsatellites. In marked contrast to the general hypothesis, realized selfing rates in E. nanum significantly decreased with increasing altitude, and only progenies from low altitudes were predominantly selfed. However, the higher selfing rates of individuals at lower altitudes could have been caused by unfavorable weather conditions during early growing season when low-elevation plants flowered. In summary, our results on selfing rates in an alpine plant across altitude as well as the results of other studies using experimental hand-pollinations and/or population genetic methods generally do not support the expectation of higher selfing rates at higher altitudes. We therefore ask for further critical examination of realized mating systems in alpine plants. 相似文献
914.
Zonadhesin is a multiple-domain transmembrane protein that is believed to function as a sperm-zona pellucida binding protein. In this study we sequenced zonadhesin from rabbit testis and analyzed its processing, expression, localization, and zona pellucida binding. We show that the precursor protein occurs exclusively in the testis and that proteolytic processing results in the formation of three fragments: p43 (D1 domain), p97 (D2-D4 domains), and p58 (D4 domain-C-terminal). In mature spermatozoa the p43 and p97 fragments exist as disulfide-bonded dimers. During spermatogenesis, synthesis of zonadhesin mRNA chiefly occurs in primary spermatocytes, whereas the protein is abundant in both Sertoli cells and spermatids. In spermatozoa the protein is localized exclusively to the anterior acrosome but is not available for binding antibody on live spermatozoa. Once the acrosome reaction is induced, zonadhesin is lost from the spermatozoon, but remains with the acrosomal shroud. We show that recombinant D4 domain can bind zona pellucida, and we propose that zonadhesin functions after the acrosome reaction has been initiated to bind the acrosomal shroud to the zona pellucida. 相似文献
915.
Lysine metabolism in higher plants 总被引:4,自引:0,他引:4
Summary. The essential amino acid lysine is synthesised in higher plants via a pathway starting with aspartate, that also leads to
the formation of threonine, methionine and isoleucine. Enzyme kinetic studies and the analysis of mutants and transgenic plants
that overaccumulate lysine, have indicated that the major site of the regulation of lysine synthesis is at the enzyme dihydrodipicolinate
synthase. Despite this tight regulation, there is strong evidence that lysine is also subject to catabolism in plants, specifically
in the seed. The two enzymes involved in lysine breakdown, lysine 2-oxoglutarate reductase (also known as lysine α-ketoglutarate reductase) and saccharopine dehydrogenase exist as a single bifunctional protein, with the former activity
being regulated by lysine availability, calcium and phosphorylation/dephosphorylation.
Received December 21, 1999 Accepted February 7, 2000 相似文献
916.
Nutrient (P and N) enrichment experiments in small enclosures (20 l) were carried out to determine P and/or N limitation of bacterioplankton in Lake Võrtsjärv. The specific interest of the study was to test if it is possible to detect nutrient `physiological' or growth (rate) limitation of bacterioplankton and competition for nutrients (N and P) with phytoplankton in generally nutrient rich lake. Thymidine and leucine incorporation; leucine aminopeptidase, -D-glucosidase and alkaline phosphatase activity, total count of bacteria, chlorophyll a concentration and primary production as well as the concentrations of different chemical forms of N and P were followed during 4–5 days of the experiment. To address the question of the interactions between nutrients, bacterio- and phytoplankton, experimental and seasonal data sets were included in the analyses. Phosphorus (P) had a positive effect on bacterioplankton in enclosure experiments in June 1997; no effects of nutrients were found in September 1996, while in May 1996, P affected mainly the phytoplankton. On the seasonal scale, the development of bacterioplankton was connected to primary production, total phosphorus and temperature. In enrichment experiments, bacterioplankton was mainly related with primary productivity but the possible importance of bacterial grazers could be presumed. Thus, no evidence was found for nutrient growth limitation and/or competition for N and/or P, rather bacterioplankton depended on organic food supply originating from phytoplankton. 相似文献
917.
Bayesian semiparametric inference on long-range dependence 总被引:1,自引:0,他引:1
918.
Antioxidant enzymes responses to cadmium in radish tissues 总被引:28,自引:0,他引:28
To investigate the antioxidant responses of radish (Raphanus sativus L.) to cadmium (Cd) treatment, seedlings of a tolerant variety were grown in increasing concentrations of CdCl(2), ranging from 0.25-1 mM, for up to 72 h in a hydroponic system. Analysis of Cd uptake indicated that most of the Cd accumulated in the roots, but some was also translocated and accumulated in the leaves, especially at the higher concentrations of Cd used in the experiments. Roots and leaves were analysed for catalase, glutathione reductase and superoxide dismutase activities. Catalase and glutathione reductase activities increased considerably in the roots and leaves after 24 h exposure to the metal, indicating a direct correlation with Cd accumulation. The analysis of native PAGE enzyme activity staining, revealed several superoxide dismutase isoenzymes in leaves, with the two predominant isoenzymes exhibiting increases in activity in response to Cd treatment. The results suggest that in radish, the activity of antioxidant enzymes responds to Cd treatment. The main response may be via the activation of the ascorbate-glutathione cycle for the removal of hydrogen peroxide, or to ensure the availability of glutathione for the synthesis of Cd-binding proteins. 相似文献
919.
Protoplasts and mitochondria were isolated from leaves of homozygous barley ( Hordeum vulgare L.) mutant deficient in glycine decarboxylase complex (GDC, EC 2.1.2.10) and wild-type plants. The photosynthetic rates of isolated protoplasts from the mutant and wild-type plants under saturating CO2 were similar, but the respiratory rate of the mutant was two-fold higher. Respiration in the mutant plants was much more strongly inhibited by antimycin A than in wild-type plants and a low level of the alternative oxidase protein was found in mitochondria. The activities of NADP- and NAD-dependent malate dehydrogenases were also increased in mutant plants, suggesting an activation of the malate-oxaloacetate exchange for redox transfer between organelles. Mutant plants had elevated activities of NADH- and NADPH-dependent glyoxylate/hydroxypyruvate reductases, which may be involved in oxidizing excess NAD(P)H and the scavenging of glyoxylate. We estimated distribution of pools of adenylates, NAD(H) and NADP(H) between chloroplasts, cytosol and mitochondria. Under photorespiratory conditions, ATP/ADP and NADPH/NADP ratios in the mutant were higher in chloroplasts as compared to wild-type plants. The cytosolic NADH/NAD ratio was increased, whereas the ratio in mitochondria decreased. It is concluded that photorespiration serves as an effective redox transfer mechanism from the chloroplast. Plants with a lowered GDC content are deficient in this mechanism, which leads to over-reduction and over-energization of the chloroplasts. 相似文献
920.
The first reaction of mitochondrial beta-oxidation, which is catalyzed by acyl-CoA dehydrogenases, was studied with unsaturated fatty acids that have a double bond either at the 4,5 or 5,6 position. The CoA thioesters of docosahexaenoic acid, arachidonic acid, 4,7,10-cis-hexadecatrienoic acid, 5-cis-tetradecenoic acid, and 4-cis-decenoic acid were effectively dehydrogenated by both rat and human long-chain acyl-CoA dehydrogenases (LCAD), whereas they were poor substrates of very long-chain acyl-CoA dehydrogenases (VLCAD). VLCAD, however, was active with CoA derivatives of long-chain saturated fatty acids or unsaturated fatty acids that have double bonds further removed from the thioester function. Although bovine LCAD effectively dehydrogenated 5-cis-tetradecenoyl-CoA (14:1) and 4,7,10-cis-hexadecatrienoyl-CoA, it was nearly inactive toward the other unsaturated substrates. The catalytic efficiency of rat VLCAD with 14:1 as substrate was only 4% of the efficiency determined with tetradecanoyl-CoA, whereas LCAD acted equally well on both substrates. The conclusion of this study is that LCAD serves an important, if not essential function in the beta-oxidation of unsaturated fatty acids. 相似文献