全文获取类型
收费全文 | 6256篇 |
免费 | 528篇 |
国内免费 | 5篇 |
专业分类
6789篇 |
出版年
2023年 | 39篇 |
2022年 | 95篇 |
2021年 | 175篇 |
2020年 | 90篇 |
2019年 | 96篇 |
2018年 | 138篇 |
2017年 | 129篇 |
2016年 | 220篇 |
2015年 | 400篇 |
2014年 | 439篇 |
2013年 | 428篇 |
2012年 | 622篇 |
2011年 | 566篇 |
2010年 | 334篇 |
2009年 | 292篇 |
2008年 | 403篇 |
2007年 | 398篇 |
2006年 | 385篇 |
2005年 | 292篇 |
2004年 | 312篇 |
2003年 | 211篇 |
2002年 | 217篇 |
2001年 | 42篇 |
2000年 | 27篇 |
1999年 | 46篇 |
1998年 | 42篇 |
1997年 | 46篇 |
1996年 | 29篇 |
1995年 | 20篇 |
1994年 | 35篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1978年 | 6篇 |
1977年 | 13篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1970年 | 4篇 |
1960年 | 3篇 |
排序方式: 共有6789条查询结果,搜索用时 15 毫秒
211.
Carbohydrate uptake in Advenella mimigardefordensis strain DPN7T is mediated by periplasmic sugar oxidation and a TRAP‐transport system 下载免费PDF全文
Christina Meinert Jana Senger Marco Witthohn Jan Hendrik Wübbeler Alexander Steinbüchel 《Molecular microbiology》2017,104(6):916-930
In this study, we investigated an SBP (DctPAm) of a tripartite ATP‐independent periplasmic transport system (TRAP) in Advenella mimigardefordensis strain DPN7T. Deletion of dctPAm as well as of the two transmembrane compounds of the tripartite transporter, dctQ and dctM, impaired growth of A. mimigardefordensis strain DPN7T, if cultivated on mineral salt medium supplemented with d ‐glucose, d ‐galactose, l ‐arabinose, d ‐fucose, d ‐xylose or d ‐gluconic acid, respectively. The wild type phenotype was restored during complementation studies of A. mimigardefordensis ΔdctPAm using the broad host vector pBBR1MCS‐5::dctPAm. Furthermore, an uptake assay with radiolabeled [14C(U)]‐d ‐glucose clearly showed that the deletion of dctPAm, dctQ and dctM, respectively, disabled the uptake of this aldoses in cells of either mutant strain. Determination of KD performing thermal shift assays showed a shift in the melting temperature of DctPAm in the presence of d ‐gluconic acid (KD 11.76 ± 1.3 µM) and the corresponding aldonic acids to the above‐mentioned carbohydrates d ‐galactonate (KD 10.72 ± 1.4 µM), d ‐fuconic acid (KD 13.50 ± 1.6 µM) and d ‐xylonic acid (KD 8.44 ± 1.0 µM). The sugar (glucose) dehydrogenase activity (E.C.1.1.5.2) in the membrane fraction was shown for all relevant sugars, proving oxidation of the molecules in the periplasm, prior to transport. 相似文献
212.
Elise Huchard Christina Albrecht Susanne Schliehe-Diecks Alice Baniel Christian Roos Peter M. Kappeler Peter Markus Brameier 《Immunogenetics》2012,64(12):895-913
The critical role of major histocompatibility complex (MHC) genes in disease resistance, along with their putative function in sexual selection, reproduction and chemical ecology, make them an important genetic system in evolutionary ecology. Studying selective pressures acting on MHC genes in the wild nevertheless requires population-wide genotyping, which has long been challenging because of their extensive polymorphism. Here, we report on large-scale genotyping of the MHC class II loci of the grey mouse lemur (Microcebus murinus) from a wild population in western Madagascar. The second exons from MHC-DRB and -DQB of 772 and 672 individuals were sequenced, respectively, using a 454 sequencing platform, generating more than 800,000 reads. Sequence analysis, through a stepwise variant validation procedure, allowed reliable typing of more than 600 individuals. The quality of our genotyping was evaluated through three independent methods, namely genotyping the same individuals by both cloning and 454 sequencing, running duplicates, and comparing parent–offspring dyads; each displaying very high accuracy. A total of 61 (including 20 new) and 60 (including 53 new) alleles were detected at DRB and DQB genes, respectively. Both loci were non-duplicated, in tight linkage disequilibrium and in Hardy–Weinberg equilibrium, despite the fact that sequence analysis revealed clear evidence of historical selection. Our results highlight the potential of 454 sequencing technology in attempts to investigate patterns of selection shaping MHC variation in contemporary populations. The power of this approach will nevertheless be conditional upon strict quality control of the genotyping data. 相似文献
213.
Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m?2 · s?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m?2 · s?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m?2 · s?1 and 200 μmol photon · m?2 · s?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m?2 · s?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues. 相似文献
214.
Birthe Tegtmeyer Gabrielle Vieyres Daniel Todt Chris Lauber Corinne Ginkel Michael Engelmann Maike Herrmann Christian K. Pfaller Florian W. R. Vondran Ruth Broering Ehsan Vafadarnejad Antoine-Emmanuel Saliba Christina Puff Wolfgang Baumgrtner Csaba Miskey Zoltn Ivics Eike Steinmann Thomas Pietschmann Richard J. P. Brown 《Journal of virology》2021,95(10)
215.
216.
Marion C. Hoepflinger Anja Geretschlaeger Aniela Sommer Margit Hoeftberger Christina Hametner Takashi Ueda Ilse Foissner 《Traffic (Copenhagen, Denmark)》2015,16(5):534-554
RAB5 GTPases are important regulators of endosomal membrane traffic. Among them Arabidopsis thaliana ARA7/RABF2b is highly conserved and homologues are present in fungal, animal and plant kingdoms. In land plants ARA7 and its homologues are involved in endocytosis and transport towards the vacuole. Here we report on the isolation of an ARA7 homologue (CaARA7/CaRABF2) in the highly evolved characean green alga Chara australis. It encodes a polypeptide of 202 amino acids with a calculated molecular mass of 22.2 kDa and intrinsic GTPase activity. Immunolabelling of internodal cells with a specific antibody reveals CaARA7 epitopes at multivesicular endosomes (MVEs) and at MVE‐containing wortmannin (WM) compartments. When transiently expressed in epidermal cells of Nicotiana benthamiana leaves, fluorescently tagged CaARA7 localizes to small organelles (putative MVEs) and WM compartments, and partially colocalizes with AtARA7 and CaARA6, a plant specific RABF1 GTPase. Mutations in membrane anchoring and GTP binding sites alter localization of CaARA7 and affect GTPase activity, respectively. This first detailed study of a conventional RAB5 GTPase in green algae demonstrates that CaARA7 is similar to RAB5 GTPases from land plants and other organisms and shows conserved structure and localization. 相似文献
217.
Christina Hvilsom Frands Carlsen Rasmus Heller Nina Jaffré Hans R. Siegismund 《Primates; journal of primatology》2014,55(1):101-112
The Pleistocene epoch was a period of dramatic climate change that had profound impacts on the population sizes of many animal species. How these species were shaped by past events is often unclear, hindering our understanding of the population dynamics resulting in present day populations. We analyzed complete mitochondrial genomes representing all four recognized chimpanzee subspecies and the bonobo to infer the recent demographic history and used simulations to exclude a confounding effect of population structure. Our genus-wide Bayesian coalescent-based analysis revealed surprisingly dissimilar demographic histories of the chimpanzee subspecies and the bonobo, despite their overlapping habitat requirements. Whereas the central and eastern chimpanzee subspecies were inferred to have expanded tenfold between around 50,000 and 80,000 years ago and today, the population size of the neighboring bonobo remained constant. The changes in population size are likely linked to changes in habitat area due to climate oscillations during the late Pleistocene. Furthermore, the timing of population expansion for the rainforest-adapted chimpanzee is concurrent with the expansion of the savanna-adapted human, which could suggest a common response to changed climate conditions around 50,000–80,000 years ago. 相似文献
218.
Christina Nagel Regina Erber Natascha Ille Mareike von Lewinski Jörg Aurich Erich Möstl Christine Aurich 《Theriogenology》2014
External and internal stressors prolong parturition in different species. At parturition, sympathoadrenal activation should be avoided because an increased sympathetic tone may cause uterine atonia via β2-receptors. We hypothesized that at physiological parturition, horses are under parasympathetic dominance, and stress-response mechanisms are not activated during delivery of the foal. To evaluate stress responses, heart rate, heart rate variability, catecholamines, and cortisol were analyzed in mares (n = 17) throughout foaling. Heart rate decreased from 2 hours before (51 ± 1 beats/minute) to 2 hours after delivery (41 ± 2 beats/minute; P < 0.05). Heart rate variability variables, standard deviation of the beat-to-beat interval, and root mean square of successive beat-to-beat differences, changed over time (P < 0.05) with the highest values within 15 minutes after delivery. The number of mares with atrioventricular blocks and the number of atrioventricular blocks per mare increased over time (P < 0.01) and were significantly elevated from 15 minutes before to 45 minutes after birth of the foal. Salivary cortisol concentrations increased to a maximum at 30 minutes after delivery (25.0 ± 3.4 ng/mL; P < 0.01). Plasma epinephrine and norepinephrine concentrations showed significant fluctuations from rupture of the allantochorion to expulsion of the fetal membranes (P < 0.01) but were not markedly elevated at any time. In conclusion, mares give birth under high parasympathetic tone. Cortisol release during and after foaling is most likely part of the endocrine pathways regulating parturition and not a labor-associated stress response. 相似文献
219.
Dirk S Paul Paul Guilhamon Anna Karpathakis Lee M Butcher Christina Thirlwell Andrew Feber Stephan Beck 《Epigenetics》2014,9(5):678-684
We present a systematic assessment of RainDrop BS-seq, a novel method for large-scale, targeted bisulfite sequencing using microdroplet-based PCR amplification coupled with next-generation sequencing. We compared DNA methylation levels at 498 target loci (1001 PCR amplicons) in human whole blood, osteosarcoma cells and an archived tumor tissue sample. We assessed the ability of RainDrop BS-seq to accurately measure DNA methylation over a range of DNA quantities (from 10 to 1500 ng), both with and without whole-genome amplification (WGA) following bisulfite conversion. DNA methylation profiles generated using at least 100 ng correlated well (median R = 0.92) with those generated on Illumina Infinium HumanMethylation450 BeadChips, currently the platform of choice for epigenome-wide association studies (EWAS). WGA allowed for testing of samples with a starting DNA amount of 10 and 50 ng, although a reduced correlation was observed (median R = 0.79). We conclude that RainDrop BS-seq is suitable for measuring DNA methylation levels using nanogram quantities of DNA, and can be used to study candidate epigenetic biomarker loci in an accurate and high-throughput manner, paving the way for its application to routine clinical diagnostics. 相似文献
220.