全文获取类型
收费全文 | 742篇 |
免费 | 26篇 |
国内免费 | 3篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 33篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 29篇 |
2015年 | 16篇 |
2014年 | 33篇 |
2013年 | 74篇 |
2012年 | 42篇 |
2011年 | 50篇 |
2010年 | 35篇 |
2009年 | 29篇 |
2008年 | 39篇 |
2007年 | 32篇 |
2006年 | 49篇 |
2005年 | 29篇 |
2004年 | 25篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1978年 | 5篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1962年 | 2篇 |
1960年 | 1篇 |
1955年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有771条查询结果,搜索用时 15 毫秒
1.
A new species of Hirschmanniella was found in bulrush roots; LM and SEM morphological studies revealed that it is distinct from other species in the genus. Therefore, it is designated Hirschmanniella pomponiensis n. sp. Six lips are fused to form a hexagonal labial plate, six inner sensilla encircle the stoma opening, and four cephalic sensilla open in the corners of subdorsal and subventral lips. Cephalic lip region consists of six or seven annuli. The female has incomplete areolation in the lateral field, the intestine overlaps the rectum, the tail tip is pointed and without annulation. 相似文献
2.
Meloidogyne californiensis n. sp. is described and illustrated from bulrush Scirpus robustus in California. LM and SEM studies revealed that this species differs from other known species in the genus Meloidogyne especially by the prominent posterior cuticular protuberances in the female, the distinct shape of the perineal pattern which is marked by one prominent stria in the perineum, indistinct lateral lines, many broken discontinuous striae on both sides of the arch, and the excretory pore being located posterior to stylet base. Second-stage juveniles 448-628 μm long, stylet length 11-13 μm, styler delicate, with small knobs sloping posteriorly, cephalic region with 2 or 3 annuli, and inflated rectum. Males vary greatly in size (712-1,952 μm), stylet length 18-28 μm (mean 22 μm), cephalic region slightly set off the body with two or three annuli, spear heavy with massive rounded knobs, lateral field marked by four areolated incisures as seen by SEM. 相似文献
3.
A. M. Abdel-Rahman 《Biologia Plantarum》1987,29(5):365-373
Salinity had generally little influence on the water content of different parts of cowpea(Vigna sinensis L.), calabrese(Brassica oleracea L. var.botrylis) and red radish(Raphanus salivus L.) plants. Salinity showed a promotive effect on the growth of cowpea, while in calabrese the effect was either promotive
or depressive depending upon the concentration of the NaCl, and in red radish plants salinity progressively suppressed growth.
Total nitrogen, phosphorus, potassium and sodium contents of cowpea leaves were not affected by salinity treatments, while
in calabrese and red radish leaves the contents of N, P and K were generally decreased as the salinity level increased. Gibberellin
(GA3) applied to salt-treated plants had either a stimulatory or inhibitory effect on the growth, water content and contents of
N, P, K and Na in the leaves depending upon the plant type, the concentration of GA3 and level of salinity. 相似文献
4.
R D Russ A A Abdel-Rahman W R Wooles 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1989,190(1):1-6
The ability of ethanol to reduce alpha-adrenergic receptor-mediated pressor responsiveness in vivo was investigated in chloralose-anesthetized male Sprague-Dawley rats. Catheters were inserted in the jugular vein and the femoral artery of rats for the injection of drugs and the measurement of blood pressure, respectively. Dose-response curves for phenylephrine and norepinephrine were constructed by plotting the change in mean arterial pressure following a bolus dose of the agent against the dose of the pressor agent used. Following construction of an initial dose-response curve, animals were challenged with either a 1 g/kg dose of ethanol or an equivalent volume of saline (iv) and the dose-response curves were repeated. Using a similar protocol, pressor responsiveness was evaluated in animals pretreated with either yohimbine (1 mg/kg) or prazosin (3.9 micrograms/kg), a dose sufficient to produce partial blockade of alpha receptor-mediated pressor responsiveness, and then treated with ethanol. Ethanol produced a partial blockade of alpha receptors when the animals were challenged with either phenylephrine or norepinephrine. This blockade produced by ethanol was shown to be similar to that produced by the receptor blocking agents used in this study. To rule out any nonspecific effects of ethanol in reducing vascular reactivity, some animals were challenged with angiotensin II both before and after treatment with ethanol, yohimbine, or prazosin and after both drugs were administered together. Ethanol, as well as the alpha 1- and alpha 2-adrenergic blocking agents tested failed to have any significant effect on angiotensin II-pressor responsiveness, ruling out any nonspecific effect of ethanol on the vasculature. It is concluded, therefore, that ethanol has alpha receptor blocking-like activity in vivo. 相似文献
5.
Suitability of different mite prey for the development of the predatory mite,Phytoseiulus persimilis
Development of the phytoseiid mitePhytoseiulus persimilis Athias-Henriot was studied when fed on three mite species as prey. The tenuipalpid mite,Brevipalpus pulcher (Canestrini & Fanzago), is an unsuitable prey forP. persimilis as predatory larvae reared on any stages developed to the protonymphal stage only. WhenP. persimilis larvae were reared on the eriophyid mite,Eriophyes dioscoridis Soliman & Abou-Awad, only a few developed to adulthood, but failed to oviposit. On the contrary, predatory larvae fed on the tetranychid mite,Tetranychus urticae Koch, matured in a significantly shorter period and resulting females exhibited a high rate of reproduction. 相似文献
6.
Summary The N-metabolism ofArthrocnemum fruticosum (L.) Moq., growing in a saline area north-east of the Dead Sea in Jordan, was studied over its vegetative growth period from
March to September 1981. Plant and soil samples were taken at monthly intervals. Water content, Na+, K+, Cl−, NH
4
+
, NO
2
−
and NO
3
−
concentrations were determined in the soil extracts, and the same determinations plus ash weight, soluble carbohydrates,
proline, proteins andin vivo nitrate reductase in the plant roots and shoots.
Soil humidity decreased and salinity increased from March to August, with re-wetting occurring in late July. K+ and Cl− were much lower in the soils than Na+. Plant relative dry weight increased during summer due to the absorption of Na+ in addition to increased organic dry weight. The uptake of Na+ was not balanced by a similar uptake of Cl−.
Ammonium and nitrate decreased in soil and plants in parallel with increasing salinity. Nitrite was only found in the roots
and always in very low quantities. Proline was found only in March. The total soluble carbohydrates in the roots showed a
short increase in June when the sodium in the plants also increased. It was concluded that carbohydrates may be used to balance
osmotic shocks, but that another compatible compounds is necessary to maintatin long-term osmotic equilibrium.
The nitrate reductase activity, measuredin vivo, and the soluble protein changed roughly in parallel with the internal nitrate from May to August, suggesting that nitrogen
uptake and reduction in the plant is inhibited during summer when the soil is dry and very saline. This could be a direct
effect of drought and/or salinity on the plants, or an indirect onevia an inhibition of nitrifying bacteria. 相似文献
7.
Salinity caused a consistent reduction in the growth of cowpea plants and water content in their leaves. The total as well
as the pigment fractions, except carotenoids, exhibited lower values than those of control plants at almost all salinity levels.
With the rise of salinization, the total nitrogen and potassium contents in the leaves were decreased but the sodium content
was increased and phosphorus content was not significantly affected as compared with the controls.
The application of IAA to salt-treated plants increased the water content in the leaves but it had no effect on the number
of leaves and the stem length. The pigment contents in the leaves were either promoted or inhibited with the application of
IAA, depending upon the level of salinization. The application of IAA to plants irrigated with water of the highest salinity
level was effective in increasing the potassium content in the leaves as compared with the control, but it had no effect on
the other mineral elements. 相似文献
8.
The interactive effect of salinity and presoaking in ascorbic acid or phyridoxine on germination, seedling growth, and some
relevant metabolic changes ofLupinus termis andVicia faba seeds were studied. Germination studies indicated that broad bean tolerated NaCl salinity up to 240mM NaCl and lupin to 200mM NaCl. The lengths of roots and shoots and their water content, as well as dry matter yield, remained more or less unchanged
up to the level of 80mM NaCl.
Salinity induced marked progressive increases of carbohydrates and proline in broad bean and soluble protein in lupin seedlings,
irrespective of the salinity level used.
The other organic solutes (soluble protein in broad bean and carbohydrates in lupin seedlings) remained more or less unchanged
at low and moderate levels of NaCl. However, under the higher salinity levels, in lupin the losses in carbohydrates were accompanied
by increases in soluble protein, whereas in broad bean an opposite effect was obtained. The level of 40mM NaCl had a pronounced stimulatory effect on the all the variables studied.
Presoaking seeds in either ascorbic acid or pyridoxine counteracted the adverse effects of salinity on germination and seedling
growth as well as on some metabolic mechanisms of lupin and broad bean plants.
The importance of these processes to the salinity tolerance of broad bean and lupin have been discussed. 相似文献
9.
Aly H. Rasmy H. A. Abdel-Rahman M. M. Abdek-Kader H. E. Hussein 《Experimental & applied acarology》1990,10(2):151-155
The effects of attack by the three predaceous mite speciesPhytoseiulus persimilis Athias-Henriot,Phytoseius finitimus Ribaga andAmblyseius gossipi Elbadry on the development, reproduction and mortality of the two-spotted spider miteTetranyschus urticae Koch were evaluated after the prey larvae being exposed to attack by these predators for limited periods. Development of the surviving prey immatures was significantly prolonged; this influence was more distinctive when prey larvae were exposed to the predators for a longer period. The number of prey adults which died early was positively correlated with the length of the feeding period allowed to the predators. A substantial reduction in the number of eggs deposited by the prey females was noted, although the oviposition by the prey females was noted, although the oviposition period and adult longivity were not significantly affected. 相似文献
10.
Citrus Tristeza Virus (CTV), usually occurs in nature as a mixture of genotypes. Six naturally infected citrus
(Citrus sinensis) trees grafted on sour orange rootstock were collected from three citrus growing governorates
in Egypt (Sharqia, Qalyubia and Garbia). In this study, RT-PCR, Single-Strand Conformation Polymorphism
(SSCP) and nucleotide sequence analysis were used for four independent CTV genomic regions (p65, p18,
p20, and p23) to detect and assess the sequence and genetic variabilities among CTV Egyptian isolates. RTPCR products (650 bp) for the CTV p23 gene obtained from the selected isolates were used for the SSCP analysis
and DNA sequencing. SSCP patterns of p23 gene for individual isolates yielded different complex haplotype patterns. Nucleotide sequence analysis of p23 region amplified from six isolates under study revealed that p23 shared
high nucleotide identity 98.7% with T36 isolate from USA, Florida. Phylogenetic analysis of p23 gene indicated a
close evolutionary relationship between all examined isolates and Qaha isolate (T36 isolate group), suggesting that
they may have originated from closely related ancestors. Nucleotide sequence analysis of the three genes located
on CTV 3′-coterminal overhang, p18, p20 and p65, amplified from isolate A3, Sharqia governorate, revealed that
the p18, p65, and p20 genes were related to the T3-KB isolate from South Africa with 99%–100% sequence
homology. Phylogenetic relationship analysis for p65, p18 and p20 ORFs clustered the current A3 isolate with
T3 genotype group. The recombination analysis identified three of six isolates from Sharqia, and Garbia as potential recombinant for p23 gene. The isolates T36 and T3 were identified as major donors for recombination events
in isolate A3. Our results concluded that p23 ORF likely to be as a hotspot region for recombination and originated through recombination event. The current study indicated that recombination is an important factor for the
origin of CTV strains in Egypt. 相似文献