全文获取类型
收费全文 | 2154篇 |
免费 | 119篇 |
国内免费 | 8篇 |
出版年
2023年 | 42篇 |
2022年 | 62篇 |
2021年 | 94篇 |
2020年 | 53篇 |
2019年 | 60篇 |
2018年 | 80篇 |
2017年 | 76篇 |
2016年 | 85篇 |
2015年 | 112篇 |
2014年 | 108篇 |
2013年 | 162篇 |
2012年 | 183篇 |
2011年 | 188篇 |
2010年 | 95篇 |
2009年 | 106篇 |
2008年 | 98篇 |
2007年 | 110篇 |
2006年 | 91篇 |
2005年 | 76篇 |
2004年 | 50篇 |
2003年 | 53篇 |
2002年 | 58篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 23篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 18篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有2281条查询结果,搜索用时 31 毫秒
1.
Igor Loncaric Gabrielle L. Stalder Kemal Mehinagic Renate Rosengarten Franz Hoelzl Felix Knauer Chris Walzer 《PloS one》2013,8(12)
In order to test whether rooks (Corvus frugilegus) represent good indicators for the potential circulation of antibiotics in their native habitat, two populations with different migratory behavior were tested for the presence of beta-lactamase producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus (MRSA). In all, 54 and 102 samples of fresh feces of a migratory and a resident population were investigated. A total of 24 and 3 cefotaxime-resistant enterobacterial isolates were obtained from the migratory and resident population, respectively. In these isolates CTX-M-1 (n = 15), CTX-M-3 (n = 3), and CTX-M-15 (n = 3) genes were detected. TEM-1 and OXA-1 were associated with CTX-M in 3 and 2 isolates, respectively. In two E. coli isolates CMY-2 could be detected, where from one isolate displayed an overexpression of chromosomal AmpC as well. Among E. coli isolates the most common phylogenetic group was A (n = 11) and ST1683 (n = 5). In one E. coli of B2-ST131 the rfbO25b locus was detected. Three Enterobacter isolates were stably derepressed AmpC-producers. In five samples of the migratory population, PVL positive MRSA could be isolated. Two isolates were typed SCCmec IVa, spa type t127, and ST1. Three isolates carried a SCCmec type IVc, with spa type t852 and ST22. The highly significant difference of the occurrence of antibiotic resistance between the migratory population from eastern Europe compared to resident population in our study indicates that rooks may be good indicator species for the evaluation of environmental contamination with antibiotic resistant bacteria, especially due to their ecology, foraging behavior and differing migratory behavior. 相似文献
2.
Minh Thac Nguyen Ryan Denniston Hien Thi Thu Nguyen Tuan Anh Hoang Hana Ross Anthony D. So 《PloS one》2014,9(1)
Illicit trade carries the potential to magnify existing tobacco-related health care costs through increased availability of untaxed and inexpensive cigarettes. What is known with respect to the magnitude of illicit trade for Vietnam is produced primarily by the industry, and methodologies are typically opaque. Independent assessment of the illicit cigarette trade in Vietnam is vital to tobacco control policy. This paper measures the magnitude of illicit cigarette trade for Vietnam between 1998 and 2010 using two methods, discrepancies between legitimate domestic cigarette sales and domestic tobacco consumption estimated from surveys, and trade discrepancies as recorded by Vietnam and trade partners. The results indicate that Vietnam likely experienced net smuggling in during the period studied. With the inclusion of adjustments for survey respondent under-reporting, inward illicit trade likely occurred in three of the four years for which surveys were available. Discrepancies in trade records indicate that the value of smuggled cigarettes into Vietnam ranges from $100 million to $300 million between 2000 and 2010 and that these cigarettes primarily originate in Singapore, Hong Kong, Macao, Malaysia, and Australia. Notable differences in trends over time exist between the two methods, but by comparison, the industry estimates consistently place the magnitude of illicit trade at the upper bounds of what this study shows. The unavailability of annual, survey-based estimates of consumption may obscure the true, annual trend over time. Second, as surveys changed over time, estimates relying on them may be inconsistent with one another. Finally, these two methods measure different components of illicit trade, specifically consumption of illicit cigarettes regardless of origin and smuggling of cigarettes into a particular market. However, absent a gold standard, comparisons of different approaches to illicit trade measurement serve efforts to refine and improve measurement approaches and estimates. 相似文献
3.
B Alexandre F Thiébaut M Allary E Boschetti C Séné J Saint-Blancard 《Revue fran?aise de transfusion et immuno-hématologie》1987,30(1):57-66
In this work the human plasma fibronectin was purified by affinity chromatography using a tandem column system. The first affinity column was filled with gelatin-Trisacryl whereas the second one contained heparin-Trisacryl. This double affinity chromatography demonstrated its high efficiency in term of purity and yield. Several analytical methods (electrophoresis, immunoelectrophoresis, F.P.L.C. and adhesion assay on cultured eucaryotic cells) evidenced in fact the high purity of the preparation as well as its biological behaviour in term of cell adhesion and spreading. The performances of the sorbents used facilitate the scaling up when large quantities of FNP are needed. 相似文献
4.
TNF inhibitors are currently considered both effective and cost-effective in patients with active rheumatoid arthritis (RA),
particularly in patients who have not responded fully to methotrexate. There is substantial doubt about the cost-effectiveness
of TNF inhibitors as initial treatment for active RA. New data from the National Data Bank for Rheumatic Diseases now question
the current consensus in methotrexate failures. The data suggest that in routine clinical practice TNF inhibitors provide
only modest incremental benefits over best conventional therapy. If confirmed, these observational studies suggest that the
economic argument underpinning the widespread use of TNF inhibitors in established RA is unsustainable. 相似文献
5.
Gabrielle C. Winters Gianluca Polese Anna Di Cosmo Leonid L. Moroz 《Journal of morphology》2020,281(7):790-801
Neuropeptide Y (NPY) is an evolutionarily conserved neurosecretory molecule implicated in a diverse complement of functions across taxa and in regulating feeding behavior and reproductive maturation in Octopus. However, little is known about the precise molecular circuitry of NPY-mediated behaviors and physiological processes, which likely involve a complex interaction of multiple signal molecules in specific brain regions. Here, we examined the expression of NPY throughout the Octopus central nervous system. The sequence analysis of Octopus NPY precursor confirmed the presence of both, signal peptide and putative active peptides, which are highly conserved across bilaterians. In situ hybridization revealed distinct expression of NPY in specialized compartments, including potential “integration centers,” where visual, tactile, and other behavioral circuitries converge. These centers integrating separate circuits may maintain and modulate learning and memory or other behaviors not yet attributed to NPY-dependent modulation in Octopus. Extrasomatic localization of NPY mRNA in the neurites of specific neuron populations in the brain suggests a potential demand for immediate translation at synapses and a crucial temporal role for NPY in these cell populations. We also documented the presence of NPY mRNA in a small cell population in the olfactory lobe, which is a component of the Octopus feeding and reproductive control centers. However, the molecular mapping of NPY expression only partially overlapped with that produced by immunohistochemistry in previous studies. Our study provides a precise molecular map of NPY mRNA expression that can be used to design and test future hypotheses about molecular signaling in various Octopus behaviors. 相似文献
6.
Kinga Michno David Knight Jorge M. Campussano Diana van de Hoef Gabrielle L. Boulianne 《PloS one》2009,4(9)
Much of our current understanding about neurodegenerative diseases can be attributed to the study of inherited forms of these disorders. For example, mutations in the presenilin 1 and 2 genes have been linked to early onset familial forms of Alzheimer''s disease (FAD). Using the Drosophila central nervous system as a model we have investigated the role of presenilin in one of the earliest cellular defects associated with Alzheimer''s disease, intracellular calcium deregulation. We show that expression of either wild type or FAD-mutant presenilin in Drosophila CNS neurons has no impact on resting calcium levels but does give rise to deficits in intracellular calcium stores. Furthermore, we show that a loss-of-function mutation in calmodulin, a key regulator of intracellular calcium, can suppress presenilin-induced deficits in calcium stores. Our data support a model whereby presenilin plays a role in regulating intracellular calcium stores and demonstrate that Drosophila can be used to study the link between presenilin and calcium deregulation. 相似文献
7.
Cutting edge: precursor frequency affects the helper dependence of cytotoxic T cells. 总被引:3,自引:0,他引:3
Justine D Mintern Gayle M Davey Gabrielle T Belz Francis R Carbone William R Heath 《Journal of immunology (Baltimore, Md. : 1950)》2002,168(3):977-980
Generation of CTL immunity often depends on the availability of CD4 T cell help. In this report, we show that CTL responses induced by cross-priming can be converted from CD4-dependent to CD4-independent by increasing the frequency of CTL precursors. In the absence of CD4 T cells, high numbers of CTL precursors were able to expand in number and become effector CTL. The ability of high frequencies of CD8 T cells to override help was not due to their ability to signal CD40 via expression of CD154. These findings suggest that when precursor frequencies are high, priming of CD8 T cell responses may not require CD4 T cell help. 相似文献
8.
9.
Neural crest development in the Xenopus laevis embryo, studied by interspecific transplantation and scanning electron microscopy 总被引:3,自引:0,他引:3
The Xenopus borealis quinacrine marker and scanning electron microscopy have been used to study the appearance, migration, and homing of neural crest cells in the embryo of Xenopus. The analysis shows that the primordium of the neural crest develops from the nervous layer of the ectoderm and consists of three segments at early neurula stages. This primordium is located in the lateral halves of the neural folds behind the prospective eye vesicles. The histological and experimental evidence shows that the neural crest cells also originate from the medial portion of the neural folds. The neural crest segments in the cephalic region start to migrate just before the closure of the neural tube. Isotopic and isochronic unilateral grafts of X. borealis neural crest into X. laevis embryos were performed in order to map the fate of the cranial crest segments and the vagal-truncal neural crest. The analysis of the X. laevis host embryos shows that the mandibular crest segment contributes to the lower jaw (Meckel's cartilage), quadrate, and ethmoid-trabecular cartilages, as well as to the ganglionic and Schwann cells of the trigeminus nerve, the connective tissues, the mesenchymal and choroid layers of the eye, and the cornea. The hyoid crest segment is located in the ceratohyal cartilage and in ganglia VII and VIII. The branchial crest segment migrates from the caudal part of the otic vesicle and divides into two portions which contribute to the cartilages of the gills. The vagal-truncal neural crest starts to migrate later at stage 25. It migrates by means of the vagus complex in a ventral direction and penetrates into the splanchnic layer of the digestive tract. The trunk neural crest cells disperse into three different pathways which differ from those of the avian embryo at this level. 相似文献
10.
Boudreau James C.; Do Ly Thi; Sivakumar Latha; Oravec Joseph; Rodriguez Carlos A. 《Chemical senses》1987,12(3):437-458
Single unit recordings were taken from sensory ganglion cellsin the petrosal ganglion (PG) of the glossopharyngeal nerveof the rat. These taste units were examined with respect tospontaneous and evoked discharge patterns and responsivenessto a wide variety of chemical compounds, most of natural occurrence.Spontaneous activity patterns, with few exceptions, tended tobe extremely irregular with both bursting (clusters of 23spikes) and grouping (large groups of spikes as in evoked discharges).Most interspike interval histograms of spontaneous activitywere multimodal, similar to rat geniculate ganglion (GG) units.Evoked discharges usually displayed grouping of spikes, andlong latencies of onset and persistence of discharge after rinsewere sometimes seen. Little response was shown to nucleotidesor salts. Units responsive to amino acids tended to show largedischarge to only one or two amino acids; and the most responsiveamino acid usually varied from cell to cell. Units responsiveto alkaloids only responded to a few alkaloids with atropineand quinine being the most stimulatory. Units responsive toacids only discharged to a few of the acids tested and oftenacids of low pH elicited no discharge. Saccharin activated unitsresponsive to both sugar and alkaloids. A few units highly responsiveto both sugar and alkaloids were seen. The units were placedinto four clusters on the basis of chemicals activating themand certain neurophysiological characteristics: PG salt units,PG acid units and, tentatively, amino acid (sugar) units andX (alkaloid and alkaloid plus) units. The PG salt units didnot show the exclusive sensitivity to sodium and lithium compoundsas did the GG salt units. The PG acid units could also be differentiatedfrom the GG acid units. The petrosal amino acid and X units,on the other hand, could not be differentiated from similarunits in the rat GG. 相似文献