全文获取类型
收费全文 | 6298篇 |
免费 | 510篇 |
国内免费 | 2篇 |
出版年
2022年 | 46篇 |
2021年 | 71篇 |
2020年 | 35篇 |
2019年 | 69篇 |
2018年 | 62篇 |
2017年 | 85篇 |
2016年 | 145篇 |
2015年 | 200篇 |
2014年 | 247篇 |
2013年 | 370篇 |
2012年 | 394篇 |
2011年 | 402篇 |
2010年 | 283篇 |
2009年 | 299篇 |
2008年 | 397篇 |
2007年 | 411篇 |
2006年 | 396篇 |
2005年 | 387篇 |
2004年 | 390篇 |
2003年 | 412篇 |
2002年 | 384篇 |
2001年 | 70篇 |
2000年 | 52篇 |
1999年 | 86篇 |
1998年 | 130篇 |
1997年 | 86篇 |
1996年 | 72篇 |
1995年 | 84篇 |
1994年 | 64篇 |
1993年 | 57篇 |
1992年 | 64篇 |
1991年 | 50篇 |
1990年 | 38篇 |
1989年 | 34篇 |
1988年 | 33篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 37篇 |
1983年 | 16篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 33篇 |
1979年 | 30篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1972年 | 15篇 |
排序方式: 共有6810条查询结果,搜索用时 15 毫秒
991.
Alain Hamon Nicolas Gilles Pierre Sautière Arlette Martinage Charles Kopeyan Chris Ulens Jan Tytgat Jean-Marc Lancelin Dalia Gordon 《European journal of biochemistry》2002,269(16):3920-3933
Two novel toxins, Lqh6 and Lqh7, isolated from the venom of the scorpion Leiurus quinquestriatus hebraeus, have in their sequence a molecular signature (8Q/KPE10) associated with a recently defined group of alpha-toxins that target Na channels, namely the alpha-like toxins [reviewed in Gordon, D., Savarin, P., Gurevitz, M. & Zinn-Justin, S. (1998) J. Toxicol. Toxin Rev. 17, 131-159]. Lqh6 and Lqh7 are highly toxic to insects and mice, and inhibit the binding of alpha-toxins to cockroach neuronal membranes. Although they kill rodents by intracerebroventricular injection, they do not inhibit the binding of antimammal alpha-toxins (e.g. Lqh2) to rat brain synaptosomes, not even at high concentrations. Furthermore, in voltage-clamp experiments, rat brain Na channels IIA (rNav1.2A) expressed in Xenopus oocytes are not affected by Lqh6 nor by Lqh7 below 3 micro m. In contrast, muscular Na channels (rNav1.4 and hNav1.5) expressed in the same cells respond to nanomolar concentrations of Lqh6 and Lqh7 by slowing of Na current inactivation and a leftward shift of the peak conductance-voltage curve. The structural and pharmacological properties of the new toxins are compared to those of other scorpion alpha-toxins in order to re-examine the hallmarks previously set for the alpha-like toxin group. 相似文献
992.
Claire Berkaloff Bernard Rousseau Alain Cout Eliette Casadevall Pierre Metzger Christian Chirac 《Journal of phycology》1984,20(3):377-389
Different samples of Botryococcus braunii Kütz., freshly collected from nature or laboratory-grown from culture collection strains, were studied by electron microscopy and their hydrocarbon content analyzed. Although the general internal structure of the cells was rather constant, the organization of the outer walls forming the hydrocarbon-rich matrix of the colonies differed greatly from one sample to another. In the majority of cultivated strains, the colonies were rather small, the different successive external walls remained distinct and all strains contained dienic or trienic hydrocarbons. In contrast, most of the collected samples possessed large colonies with a rather compact matrix formed by the hydrocarbon-rich part of the successive closely appressed external wall layers. These samples contained polyunsaturated hydrocarbons, i.e. botryococcenes. Well defined cell caps which sheared off the cells were observed only in those strains with a compact matrix. The Austin strain and some collected samples, however, were intermediate with rather small colonies, dense matrix, definite cell caps and dienic hydrocarbons. Thus, the hydrocarbon composition did not correlate directly with the variations in wall structure; however, the occurence of dienic and botryococcene-like hydrocarbons together in one strain was never observed, although analyzed at various stages of growth. Thus, the existence of distinct strains of Botryococcus braunii, some synthesizing dienes, others botryococcenes, appears highly probable. 相似文献
993.
A complete, unambiguous assignment of all the 13C signals of cellobiose and maltose has been achieved using methods such as selective proton decoupling, 13C selective spin labeling, and isotopic chemical shift induced by deuterium. The chemical-shift variation of the 13C signals with the degree of polymerization in each α or β (1 → 4) series is discussed. The chemical-shift dependence on temperature and solvent in these two series is shown and interpreted in terms of modifications of the solvation and of the conformation. 相似文献
994.
995.
Population cycles of many forest-defoliating insects often show synchronous fluctuations at both intra-specific (spatial synchrony) and inter-specific levels. However, population dynamics of different host-associated biotypes of the same species, such as those of the larch budmoth (LBM), Zeiraphera diniana (Lepidoptera: Tortricidae), have never been compared. This species causes extensive defoliation of larch forests every 8 to 9 years in the Alps, but it consists of two genetically-differentiated host races, the first one developing on European larch, Larix decidua , and the other one developing on Swiss stone pine, Pinus cembra . The dynamics of Zeiraphera populations have been extensively studied on larch, whereas little is known about larval density and possible population fluctuations on sympatric pines. A larval census on Swiss stone pine was conducted in the Swiss Alps intermittently between 1958 to 2004 and in the French Alps from 1992 to 2004. Population density of Zeiraphera on pine varied up to 5000-fold and showed periodic oscillations, with five peaks in Switzerland and one in France. Because the feeding activity of the pine race is restricted to the elongating shoot of the current year, no conspicuous defoliation of pine trees was noted during years of high larval densities. Zeiraphera populations on pine oscillated in significant synchrony with larch-associated populations, and peak densities were observed either the same year or shifted by±one year. Our results did not allow any explanation for cyclic fluctuations of LBM on pine, but the synchrony with the larch race's cycle suggests that studies on genetics as well as on parasitism should be intensified. 相似文献
996.
Alain Jacot† Hannes Scheuber & Martin W. G. Brinkhof‡ 《Ethology : formerly Zeitschrift fur Tierpsychologie》2007,113(6):615-620
Models of sexual selection suggest that females should prefer to mate with older males because old age is evidence of heritable high viability. In a longitudinal analysis, we demonstrate that male field crickets (Gryllus campestris) alter their calling song with age. Carrier frequency, a calling song character related to growing condition and the main song component under female preference, changed towards higher sexual attractiveness with age. Body mass decreased slightly with age, while chirp rate, an indicator of current condition, remained stable. By choosing males singing at a low frequency, female field crickets would base their mate choice decision on a sexual trait that indicates superior growing conditions as juvenile and on viability, i.e. enhanced current condition as adult. 相似文献
997.
Nicolas Place Alain Martin Yves Ballay Romuald Lepers 《Journal of electromyography and kinesiology》2007,17(3):253-263
The aim of the study was to examine alterations in contractile and neural processes in response to an isometric fatiguing contraction performed with EMG feedback (constant-EMG task) when exerting 40% of maximal voluntary contraction (MVC) torque with the knee extensor muscles. A task with a torque feedback (constant-torque task) set at a similar intensity served as a reference task. Thirteen men (26+/-5 yr) attended two experimental sessions that were randomized across days. Endurance time was greater for the constant-EMG task compared with the constant-torque task (230+/-156 s vs. 101+/-32s, P<0.01). Average EMG activity for the knee extensor muscles increased from 33.5+/-4.5% to 54.7+/-21.7% MVC EMG during the constant-torque task (P<0.001), whereas the torque exerted during the constant-EMG task decreased from 42.8+/-3.0% to 17.9+/-5.6% MVC torque (P<0.001). Comparable reductions in knee extensors MVC (-15.7+/-8.7% for the constant-torque task vs. -17.5+/-9.8% for the constant-EMG task, P>0.05) and voluntary activation level were observed at exhaustion. In contrast, excitation-contraction coupling process, assessed with an electrically evoked twitch and doublet, was altered significantly more at the end of the constant-EMG task despite the absence of M-wave changes for both tasks. Present results suggest that prolonged contractions using EMG biofeedback should be used cautiously in rehabilitation programs. 相似文献
998.
Geraldine Monchanin Laura D Serpero Philippe Connes Julien Tripette Dieudonné Wouassi Laurent Bezin Alain Francina Jeanne Ngongang Monica de la Pe?a Raphael Massarelli David Gozal Patrice Thiriet Cyril Martin 《Journal of applied physiology》2007,102(1):169-173
The aim of the study was to examine the effects of exercise on soluble vascular cell adhesion molecule-1 (sVCAM-1) and intercellular adhesion molecule-1 (sICAM-1) in sickle cell trait (SCT) athletes with or without alpha-thalassemia. Six athletes with SCT, seven athletes with both SCT and alpha-thalassemia (SCTAT), and seven control athletes (Cont) performed an incremental and maximal test on cycloergometer. Levels of sICAM-1 and sVCAM-1 were assessed at rest, immediately after the end of exercise, and 1, 2, and 24 h after exercise. Although Cont and SCTAT groups exhibited similar basal plasma levels of inflammatory and adhesion molecules, the SCT group had higher sVCAM-1 basal concentrations. Incremental exercise resulted in a significant increase of sVCAM-1 in all subjects, which remained elevated only in the SCT group during the recovery period. In conclusion, as sVCAM-1 increased with exercise and during the recovery period, our findings support the concept that SCT athletes might be at risk for microcirculatory disturbances and adhesive phenomena developing at rest and several hours after exercise. alpha-Thalassemia might be considered protective among exercising SCT subjects. 相似文献
999.
Alain Beck Christine Klinguer-Hamour Marie-Claire Bussat Thierry Champion Jean-Fran?ois Haeuw Liliane Goetsch Thierry Wurch Masae Sugawara Alain Milon Alain Van Dorsselaer Thien Nguyen Nathalie Corva?a 《Journal of peptide science》2007,13(9):588-602
Peptides are essential tools for discovery and pre-clinical and pharmaceutical development of viral and cancer vaccines ('active immunotherapies') as well as for therapeutic antibodies ('passive immunotherapies'). They help to trigger and analyze immune responses at a molecular level (B-cell, T-helper and CTL epitopes). They contribute largely to the design of new vaccine candidates and to the generation of monoclonal antibodies. They are also valuable analytical reference compounds for the structural characterisation by liquid chromatography and mass spectrometry of recombinant proteins used as biopharmaceuticals. As for other therapeutic applications, formulation, solubilisation, batch consistency and stability, issues have to be addressed to allow the pre-clinical and clinical development of this class of compounds as immunotherapeutic drugs. In the present review, three case studies dealing with (i) the design and the characterisation of Respiratory Syntycial Virus subunit vaccines, (ii) peptide-based melanoma vaccines, and (iii) therapeutic monoclonal antibodies, all investigated in clinical trials, are reported and discussed. 相似文献
1000.
Rotavirus Infection Reduces Sucrase-Isomaltase Expression in Human Intestinal Epithelial Cells by Perturbing Protein Targeting and Organization of Microvillar Cytoskeleton 总被引:10,自引:5,他引:5 下载免费PDF全文
Nathalie Jourdan Jean Philippe Brunet Catherine Sapin Anne Blais Jacqueline Cotte-Laffitte Franoise Forestier Anne-Marie Quero Germain Trugnan Alain L. Servin 《Journal of virology》1998,72(9):7228-7236
Rotavirus infection is the most common cause of severe infantile gastroenteritis worldwide. These viruses infect mature enterocytes of the small intestine and cause structural and functional damage, including a reduction in disaccharidase activity. It was previously hypothesized that reduced disaccharidase activity resulted from the destruction of rotavirus-infected enterocytes at the villus tips. However, this pathophysiological model cannot explain situations in which low disaccharidase activity is observed when rotavirus-infected intestine exhibits few, if any, histopathologic changes. In a previous study, we demonstrated that the simian rotavirus strain RRV replicated in and was released from human enterocyte-like Caco-2 cells without cell destruction (N. Jourdan, M. Maurice, D. Delautier, A. M. Quero, A. L. Servin, and G. Trugnan, J. Virol. 71:8268–8278, 1997). In the present study, to reinvestigate disaccharidase expression during rotavirus infection, we studied sucrase-isomaltase (SI) in RRV-infected Caco-2 cells. We showed that SI activity and apical expression were specifically and selectively decreased by RRV infection without apparent cell destruction. Using pulse-chase experiments and cell surface biotinylation, we demonstrated that RRV infection did not affect SI biosynthesis, maturation, or stability but induced the blockade of SI transport to the brush border. Using confocal laser scanning microscopy, we showed that RRV infection induces important alterations of the cytoskeleton that correlate with decreased SI apical surface expression. These results lead us to propose an alternate model to explain the pathophysiology associated with rotavirus infection. 相似文献