全文获取类型
收费全文 | 1281篇 |
免费 | 92篇 |
出版年
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 13篇 |
2020年 | 23篇 |
2019年 | 16篇 |
2018年 | 19篇 |
2017年 | 24篇 |
2016年 | 35篇 |
2015年 | 48篇 |
2014年 | 64篇 |
2013年 | 72篇 |
2012年 | 98篇 |
2011年 | 100篇 |
2010年 | 66篇 |
2009年 | 43篇 |
2008年 | 67篇 |
2007年 | 73篇 |
2006年 | 84篇 |
2005年 | 70篇 |
2004年 | 60篇 |
2003年 | 48篇 |
2002年 | 51篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1972年 | 5篇 |
1969年 | 5篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1881年 | 8篇 |
排序方式: 共有1373条查询结果,搜索用时 156 毫秒
161.
Armin J. Hinterwirth Billie Medina Jacob Lockey David Otten Joel Voldman Jeffrey H. Lang John G. Hildebrand Thomas L. Daniel 《PloS one》2012,7(12)
Insect antennae are sensory organs involved in a variety of behaviors, sensing many different stimulus modalities. As mechanosensors, they are crucial for flight control in the hawkmoth Manduca sexta. One of their roles is to mediate compensatory reflexes of the abdomen in response to rotations of the body in the pitch axis. Abdominal motions, in turn, are a component of the steering mechanism for flying insects. Using a radio controlled, programmable, miniature stimulator, we show that ultra-low-current electrical stimulation of antennal muscles in freely-flying hawkmoths leads to repeatable, transient changes in the animals'' pitch angle, as well as less predictable changes in flight speed and flight altitude. We postulate that by deflecting the antennae we indirectly stimulate mechanoreceptors at the base, which drive compensatory reflexes leading to changes in pitch attitude. 相似文献
162.
Crémieux L Bischoff A Smilauerová M Lawson CS Mortimer SR Dolezal J Lanta V Edwards AR Brook AJ Tscheulin T Macel M Leps J Müller-Schärer H Steinger T 《The New phytologist》2008,180(2):524-533
Genetic differentiation among plant populations and adaptation to local environmental conditions are well documented. However, few studies have examined the potential contribution of plant antagonists, such as insect herbivores and pathogens, to the pattern of local adaptation. Here, a reciprocal transplant experiment was set up at three sites across Europe using two common plant species, Holcus lanatus and Plantago lanceolata. The amount of damage by the main above-ground plant antagonists was measured: a rust fungus infecting Holcus and a specialist beetle feeding on Plantago, both in low-density monoculture plots and in competition with interspecific neighbours. Strong genetic differentiation among provenances in the amount of damage by antagonists in both species was found. Local provenances of Holcus had significantly higher amounts of rust infection than foreign provenances, whereas local provenances of Plantago were significantly less damaged by the specialist beetle than the foreign provenances. The presence of surrounding vegetation affected the amount of damage but had little influence on the ranking of plant provenances. The opposite pattern of population differentiation in resistance to local antagonists in the two species suggests that it will be difficult to predict the consequences of plant translocations for interactions with organisms of higher trophic levels. 相似文献
163.
The presence of vascular calcification (VC) is a predictor of poor survival in the general population. The development of VC is an active process that requires a pre-existing injury as an inducer and promoting factors such as hyperphosphatemia and hypercalcemia, as well as a deficiency in calcification repressor factors. Vascular smooth muscle cells possess an endogenous enzyme system for the biosynthesis of the vitamin D hormone calcitriol from its precursor 25-hydroxyvitamin D and also a cytosolic calcitriol receptor, indicating that the vasculature is an important target tissue for vitamin D. The toxic effects of supra-physiological vitamin D dosages on the vasculature have been known for several decades. Recent experimental data also demonstrate important physiological effects of vitamin D on factors that are protective for vascular health. This review article summarises the molecular basis of protective and toxic vitamin D actions on the vasculature. Chronic kidney disease can be considered as a human model of severe VC and poor survival. The disease is associated with calcitriol deficiency, hyperparathyroidism, and hyperphosphatemia. Evidence is increasing that phosphate overload plays a key role in the process of VC in chronic kidney disease. The first clinical studies indicate that vitamin D receptor activation can improve survival in these patients. Although less severe than in chronic kidney disease, vitamin D deficiency and secondary hyperparathyroidism are also frequent in the general population, especially in elderly and obese subjects. Future studies should focus on the impact of vitamin D deficiency on VC and clinical outcome in these groups. 相似文献
164.
Giessmann D Heidler P Haemers T Van Calenbergh S Reichenberg A Jomaa H Weidemeyer C Sanderbrand S Wiesner J Link A 《化学与生物多样性》2008,5(4):643-656
The conversion of 1-deoxy-D-xylulose-5-phosphate (DOXP) to 2-C-methyl-D-erythritol-4-phosphate (MEP) is effectively blocked by 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Dxr) inhibitors such as the natural antibiotic fosmidomycin. Prediction of binding affinities for closely related Dxr ligands as well as estimation of the affinities of structurally more distinct inhibitors within this class of non-hydrolyzable phosphate mimics relies on the synthesis of fosmidomycin derivatives with a broad range of target affinity. Maintaining the phosphonic acid moiety, linear modifications of the lead structure were carried out in an effort to expand the SAR of this physicochemically challenging class of compounds. Synthetic access to a set of phosphonic acids with inhibitory activity (IC(50)) in the range from 1 to >30 microM vs. E. coli Dxr and 0.4 to 20 microM against P. falciparum Dxr is reported. 相似文献
165.
Egbert Strauß Andreas Grauer Martina Bartel Roland Klein Ludger Wenzelides Grit Greiser Alexander Muchin Heike Nösel Armin Winter 《European Journal of Wildlife Research》2008,54(1):142-147
The German Wildlife Information System, founded in 2001, is a long-term monitoring program documenting occurrence, number,
and development of game populations throughout Germany. Population numbers are recorded by standardized counting methods in
so-called reference areas. The population densities of the European hare are calculated by spotlight strip censuses in the
reference areas each spring and autumn all across Germany. From 2002 to 2005, the censuses were carried out by local hunters
in 510 to 676 reference areas each year. During these years, the calculated spring densities increased significantly from
11.0 (2002) to 14.5 hares/km2 (2005) nationwide. The overall increase in spring densities was primarily caused by the population rise from spring 2003
to 2004, which correlates with the high net growth rate in 2003. In 2005, the number of counted hares varied between less
than 1 and more than 107 hares/km2 in spring and between 0 and more than 170 hares/km2 in autumn. Because of differing landscapes in Germany, three regions were differentiated. In spring 2005, the average population
densities (median) in East Germany (5.4 hares/km2) and Southwest Germany (14.6 hares/km2) were significantly lower than in Northwest Germany (23.9 hares/km2). These regional differences had been similarly distinct in former years. 相似文献
166.
Monaci P Luzzago A Santini C De Pra A Arcuri M Magistri F Bellini A Ansuini H Ambrosio M Ammendola V Bigotti MG Cirillo A Nuzzo M Nasti AA Neuner P Orsatti L Pezzanera M Sbardellati A Silvestre G Uva P Viti V Barbato G Colloca S Demartis A De Rinaldis E Giampaoli S Lahm A Palombo F Talamo F Vitelli A Nicosia A Cortese R 《PloS one》2008,3(1):e1508
A novel and efficient tagArray technology was developed that allows rapid identification of antibodies which bind to receptors with a specific expression profile, in the absence of biological information. This method is based on the cloning of a specific, short nucleotide sequence (tag) in the phagemid coding for each phage-displayed antibody fragment (phage-Ab) present in a library. In order to set up and validate the method we identified about 10,000 different phage-Abs binding to receptors expressed in their native form on the cell surface (10 k Membranome collection) and tagged each individual phage-Ab. The frequency of each phage-Ab in a given population can at this point be inferred by measuring the frequency of its associated tag sequence through standard DNA hybridization methods. Using tiny amounts of biological samples we identified phage-Abs binding to receptors preferentially expressed on primary tumor cells rather than on cells obtained from matched normal tissues. These antibodies inhibited cell proliferation in vitro and tumor development in vivo, thus representing therapeutic lead candidates. 相似文献
167.
Notari S Strammiello R Capellari S Giese A Cescatti M Grassi J Ghetti B Langeveld JP Zou WQ Gambetti P Kretzschmar HA Parchi P 《The Journal of biological chemistry》2008,283(45):30557-30565
In prion disease, the abnormal conformer of the cellular prion protein, PrP(Sc), deposits in fibrillar protein aggregates in brain and other organs. Limited exposure of PrP(Sc) to proteolytic digestion in vitro generates a core fragment of 19-21 kDa, named PrP27-30, which is also found in vivo. Recent evidence indicates that abnormal truncated fragments other than PrP27-30 may form in prion disease either in vivo or in vitro. We characterized a novel protease-resistant PrP fragment migrating 2-3 kDa faster than PrP27-30 in Creutzfeldt-Jakob disease (CJD) brains. The fragment has a size of about 18.5 kDa when associated with PrP27-30 type 1 (21 kDa) and of 17 kDa when associated with type 2 (19 kDa). Molecular mass and epitope mapping showed that the two fragments share the primary N-terminal sequence with PrP27-30 types 1 and 2, respectively, but lack a few amino acids at the very end of C terminus together with the glycosylphosphatidylinositol anchor. The amounts of the 18.5- or 17-kDa fragments and the previously described 13-kDa PrP(Sc) C-terminal fragment relatively to the PrP27-30 signal significantly differed among CJD subtypes. Furthermore, protease digestion of PrP(Sc) or PrP27-30 in partially denaturing conditions generated an additional truncated fragment of about 16 kDa only in typical sporadic CJD (i.e. MM1). These results show that the physicochemical heterogeneity of PrP(Sc) in CJD extends to abnormal truncated forms of the protein. The findings support the notion of distinct structural "conformers" of PrP(Sc) and indicate that the characterization of truncated PrP(Sc) forms may further improve molecular typing in CJD. 相似文献
168.
Salman Can Adam Fiolka Dirk Wilhelm Maria Burian Stefan von Delius Alexander Meining Armin Schneider Hubertus Feussner 《Biomedizinische Technik》2008,53(4):185-189
Abstract One of the current main challenges in transluminal surgery is in obtaining sterile and secure access to the peritoneal cavity. Since the transgastric approach has not fulfilled these requirements up to now, a new transcolonic surgical approach was developed to achieve these objectives and enhance the potential of transluminal surgery. A new set of instruments comprising an endoscopic trocar, a flexible obturator and a modified transanal endoscopic microsurgery device was designed to permit sterile sigmoid access for transcolonic surgery. The set of instruments has already been successfully tested in an experimental in vivo survival study that confirmed safety and sterility as objectives during surgical intervention. The suitability of the instruments for use in the human anatomy was confirmed by a cadaveric study. 相似文献
169.
The central protein of the sulfur-oxidizing enzyme system of Paracoccus pantotrophus, SoxYZ, reacts with three different Sox proteins. Its active site Cys110(Y) is on the carboxy-terminus of the SoxY subunit. SoxYZ "as isolated" consisted mainly of the catalytically inactive SoxY-Y(Z)(2) heterotetramer linked by a Cys110(Y)-Cys110(Y) interprotein disulfide. Sulfide activated SoxYZ "as isolated" 456-fold, reduced the disulfide, and yielded an active SoxYZ heterodimer. The reductant tris(2-carboxyethyl)phosphine (TCEP) inactivated SoxYZ. This form was not re-activated by sulfide, which identified it as a different inactive form. In analytical gel filtration, the elution of "TCEP-treated" SoxYZ was retarded compared to active SoxYZ, indicating a conformational change. The possible enzymes involved in the re-activation of each inactive form of SoxYZ are discussed. 相似文献
170.