全文获取类型
收费全文 | 1031篇 |
免费 | 61篇 |
出版年
2022年 | 9篇 |
2021年 | 31篇 |
2019年 | 21篇 |
2018年 | 29篇 |
2017年 | 20篇 |
2016年 | 17篇 |
2015年 | 37篇 |
2014年 | 41篇 |
2013年 | 56篇 |
2012年 | 67篇 |
2011年 | 58篇 |
2010年 | 41篇 |
2009年 | 35篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 40篇 |
2005年 | 34篇 |
2004年 | 45篇 |
2003年 | 30篇 |
2002年 | 25篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1995年 | 6篇 |
1992年 | 9篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1985年 | 12篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1970年 | 8篇 |
1969年 | 9篇 |
1968年 | 13篇 |
1967年 | 7篇 |
排序方式: 共有1092条查询结果,搜索用时 15 毫秒
801.
Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), commonly called gram pod borer, is a serious pest of pulse crops in India and damages
chickpea (Cicer arietinum L). On average a 30% crop loss is reported. One of the potential natural enemies reported for its biological control is Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae), an idiobiont parasitic wasp that attacks second instar larvae of the pod borer. Male-biased
sex ratios hinder efforts to mass release parasitic Hymenoptera for biological control by making the production of females
costly. Parental age at time of mating is known to affect the progeny sex ratio in some Braconidae. In this view, we examined
the reproduction and survival of the parasitoid C. chlorideae in the laboratory [22 ± 4°C, 70 ± 10% R.H. and 10:14 h light:dark photoperiod]. All the nine (i.e. 3 × 3) combinations of
possible mating were made for males and females, being each of different age groups (0–12, 48–60 and 96–108 h old). Second
instar larvae of the pod borer were reared on chickpea and exposed to mated females of different mating age group combinations.
Results revealed that (a) newly emerged females (0–12 h old) mated to aged males yielded more progeny contrasted to the older
females inseminated by newly emerged males (0–12 h old). This implies that increased maternal age at mating caused greater
reduction in the progeny yield than that of paternal age; (b) the progeny sex ratio was lowest (0.344 ± 0.057) (mean ± SD)
when parents mated just after emergence (0–12 h old). It became more and more male biased as parents were deprived of mate
and was highest (0.666 ± 0.701) for 96–108 h old parents. The analysis of variance of the data shows that mate deprived males
caused greater contribution in the production of sons, resulting a male-biased progeny sex ratio. Our conclusion indicate
that newly emerged parasitoids (0–12 h old) are most fecund and should be used in rearing practices in order to enhance the
progeny yield, particularly with respect to daughters.
Handling Editor: Torsten Meiners 相似文献
802.
Mathur R Choi WS Eldstrom J Wang Z Kim J Steele DF Fedida D 《Biochemical and biophysical research communications》2006,342(1):1-8
We have previously reported that SAP97 enhancement of hKv1.5 currents requires an intact Kv1.5 N-terminus and is independent of the PDZ-binding motif at the C-terminus of the channel [J. Eldstrom, W.S. Choi, D.F. Steele, D. Fedida, SAP97 increases Kv1.5 currents through an indirect N-terminal mechanism, FEBS Lett. 547 (2003) 205-211]. Here, we report that an interaction between the two proteins can be detected under certain conditions but their interaction is irrelevant to the enhancement of channel expression. Instead, a threonine residue at position 15 in the hKv1.5 N-terminus is critically important. Mutation of this residue, which lies within a consensus site for phosphorylation by protein kinase C, to an alanine, completely abrogated the effect of SAP97 on channel expression. Although we were unable to detect phosphorylation of this residue, specific inhibition of kinase C by Calphostin C eliminated the increase in wild-type hKv1.5 currents associated with SAP97 overexpression suggesting a role for this kinase in the response. 相似文献
803.
The structures of two dehydropentapeptides, Boc-Pro-DeltaPhe-Val-DeltaPhe-Ala-OMe (I) and Boc-Pro-DeltaPhe-Gly-DeltaPhe-Ala-OMe (II) (Boc: t-butoxycarbonyl), have been determined by nuclear magnetic resonance (NMR), circular dichroism (CD), and X-ray crystallographic studies. The peptide I assumes a S-shaped flat beta-bend structure, characterized by two partially overlapping type II beta-bends and absence of a second 1 <-- 4 (N4--H . . . O1') intramolecular hydrogen bond. This is in contrast to the generally observed 3(10)-helical conformation in peptides with DeltaPhe at alternate positions. This report describes the novel conformation assumed by peptide I and compares it with that of the conserved tip of the V3 loop of the HIV-1 envelope glycoprotein gp120 (sequence, G:P319 to F:P324, PDB code 1ACY). The tip of the V3 loop also assumes a S-shaped conformation with Arg:P322, making an intramolecular side-chain-backbone interaction with the carbonyl oxygen of Gly:P319. Interestingly, in peptide I, C(gamma)HVal(3) makes a similar side-chain-backbone C--H . . . O hydrogen bond with the carbonyl oxygen of the Boc group. The observed overall similarity indicates the possible use of the peptide as a viral antagonist or synthetic antigen. Peptide II adopts a unique turn followed by a 3(10)-helix. Both peptides I and II are classical examples of stabilization of unusual structures in oligopeptides. 相似文献
804.
Selection and characterization of replicon variants dually resistant to thumb- and palm-binding nonnucleoside polymerase inhibitors of the hepatitis C virus
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Le Pogam S Kang H Harris SF Leveque V Giannetti AM Ali S Jiang WR Rajyaguru S Tavares G Oshiro C Hendricks T Klumpp K Symons J Browner MF Cammack N Nájera I 《Journal of virology》2006,80(12):6146-6154
Multiple nonnucleoside inhibitor binding sites have been identified within the hepatitis C virus (HCV) polymerase, including in the palm and thumb domains. After a single treatment with a thumb site inhibitor (thiophene-2-carboxylic acid NNI-1), resistant HCV replicon variants emerged that contained mutations at residues Leu419, Met423, and Ile482 in the polymerase thumb domain. Binding studies using wild-type (WT) and mutant enzymes and structure-based modeling showed that the mechanism of resistance is through the reduced binding of the inhibitor to the mutant enzymes. Combined treatment with a thumb- and a palm-binding polymerase inhibitor had a dramatic impact on the number of replicon colonies able to replicate in the presence of both inhibitors. A more exact characterization through molecular cloning showed that 97.7% of replicons contained amino acid substitutions that conferred resistance to either of the inhibitors. Of those, 65% contained simultaneously multiple amino acid substitutions that conferred resistance to both inhibitors. Double-mutant replicons Met414Leu and Met423Thr were predominantly selected, which showed reduced replication capacity compared to the WT replicon. These findings demonstrate the selection of replicon variants dually resistant to two NS5B polymerase inhibitors binding to different sites of the enzyme. Additionally, these findings provide initial insights into the in vitro mutational threshold of the HCV NS5B polymerase and the potential impact of viral fitness on the selection of multiple-resistant mutants. 相似文献
805.
Sonal Dubey Amit K. Sharma D.P. Jindal Alan Harvey Randhir Singh S.L. Bodhankar 《Steroids》2010,75(4-5):323-329
The interonium distance plays a major role in neuromuscular blocking activity of bis-quaternary ammonium compounds. In this study we tried to alter the distance between two quaternary nitrogens in some of the steroidal derivatives synthesized and evaluated them for neuromuscular blocking activity using in vivo (in chicks) and in vitro models (rectus abdominus and chick biventer cervis muscle) for their mechanism of action. All the synthesized compounds have shown to possess good depolarizing, competitive neuromuscular blocking activity, particularly the 17-acetoxy derivative and the increase in the distance between two quaternary nitrogens decreased the activity. 相似文献
806.
Pneumadin: a new lung peptide which triggers antidiuresis 总被引:1,自引:0,他引:1
Normal mammalian lungs, including human fetal lungs, contain significant amounts of a decapeptide which releases arginine-vasopressin from the neurophypophysis and therefore has antidiuretic activity. The rat peptide is: Tyr-Gly-Glu-Pro-Lys-Leu-Asp-Ala-Gly-Val-NH2. The peptide from human fetal lungs has Ala instead of Tyr. It may be a normal regulatory substance and its role in the pathogenesis of the syndrome of inappropriate antidiuresis associated with lung diseases merits investigation. In view of its source and action, the antidiuretic lung peptide may be called Pneumadin. 相似文献
807.
808.
Root nodules ofPhaseolus mungo were extracted for their cytokinin content. Four cytokininsviz. zeatin, zeatin riboside, N6(‡2-isopentenyl) aminopurine and its riboside were identified on the basis of Rf values obtained by co-chromatography with authentic
samples of cytokinins on thin layer of a mixture of polyvinylpyrrolidone/CaSO4. 相似文献
809.
810.
Histochemical study of the innervation of the heart of the Indian flying fox Pteropus giganteus has been made using Coupland and Holmes' technique for cholinesterase. Distribution of nerve plexuses in the heart wall has been described. Nerve cells, nerve endings and various types of synapses have been reported. Specialized muscle fibres are found to contain less nerve fibres and conduction of the impulse of contraction is reported to take place through muscle fibres. 相似文献