全文获取类型
收费全文 | 4086篇 |
免费 | 345篇 |
国内免费 | 1篇 |
专业分类
4432篇 |
出版年
2023年 | 40篇 |
2022年 | 81篇 |
2021年 | 140篇 |
2020年 | 106篇 |
2019年 | 111篇 |
2018年 | 116篇 |
2017年 | 111篇 |
2016年 | 132篇 |
2015年 | 217篇 |
2014年 | 211篇 |
2013年 | 286篇 |
2012年 | 300篇 |
2011年 | 293篇 |
2010年 | 234篇 |
2009年 | 181篇 |
2008年 | 169篇 |
2007年 | 159篇 |
2006年 | 139篇 |
2005年 | 123篇 |
2004年 | 108篇 |
2003年 | 101篇 |
2002年 | 81篇 |
2001年 | 59篇 |
2000年 | 75篇 |
1999年 | 39篇 |
1998年 | 22篇 |
1997年 | 34篇 |
1996年 | 33篇 |
1995年 | 24篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 43篇 |
1991年 | 26篇 |
1990年 | 36篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 25篇 |
1975年 | 17篇 |
1972年 | 16篇 |
1968年 | 14篇 |
排序方式: 共有4432条查询结果,搜索用时 15 毫秒
51.
Sancho-Alonso María Taoro-Gonzalez Lucas Cabrera-Pastor Andrea Felipo Vicente Teruel-Martí Vicent 《Neurochemical research》2022,47(7):2016-2031
Neurochemical Research - Chronic hyperammonemia alters membrane expression of AMPA and NMDA receptors subunits in hippocampus leading to impaired memory and learning. Increasing extracellular cGMP... 相似文献
52.
The adaptation to extrauterine nutrition involves complex physiological changes at birth which may be regulated by genetic endowment; enteral nutrients, secretions, and bacteria; and endogenous hormones and exogenous hormones in breast milk. The hypothesis is explored that enteral feeding after birth may trigger key adaptations in the gut and in metabolism partly through the mediation of gastrointestinal hormone secretion. Gut peptides are found in the early human fetal gut and by the second trimester some are found in high concentrations in the fetal circulation and amniotic fluid. Major plasma hormonal surges occur during the neonatal period in term and preterm infants: notably in enteroglucagon, gastrin, motilin, neurotensin, gastrointestinal peptide, and pancreatic polypeptide. These events do not occur in neonates deprived of enteral feeding. A progressive development of dynamic gut hormonal responses to feeding is observed. The pattern of gut endocrine changes after birth is influenced by the type and route of feeding. Potential pathophysiological effects of depriving high risk neonates of enteral feeding are considered. It is speculated that infants committed to prolonged total parenteral nutrition from birth may benefit from the biological effects of intraluminal nutrients used in subnutritional quantities. 相似文献
53.
54.
Lanzarotti E Pellizza L Bercovich A Foti M Coria SH Vazquez SC Ruberto L Hernández EA Dias RL Mac Cormack WP Cicero DO Smal C Nicolas MF Vasconcelos AT Marti MA Turjanski AG 《Journal of bacteriology》2011,193(23):6797-6798
A psychrotolerant marine bacterial strain, designated JUB59(T), was isolated from Antarctic surface seawater and classified as a new species of the genus Bizionia. Here, we present the first draft genome sequence for this genus, which suggests interesting features such as UV resistance, hydrolytic exoenzymes, and nitrogen metabolism. 相似文献
55.
Hasegawa M Fujimoto Y Lucas PC Nakano H Fukase K Núñez G Inohara N 《The EMBO journal》2008,27(2):373-383
Nod1 and Nod2 are intracellular proteins that are involved in host recognition of specific bacterial molecules and are genetically associated with several inflammatory diseases. Nod1 and Nod2 stimulation activates NF-kappaB through RICK, a caspase-recruitment domain-containing kinase. However, the mechanism by which RICK activates NF-kappaB in response to Nod1 and Nod2 stimulation is unknown. Here we show that RICK is conjugated with lysine-63-linked polyubiquitin chains at lysine 209 (K209) located in its kinase domain upon Nod1 or Nod2 stimulation and by induced oligomerization of RICK. Polyubiquitination of RICK at K209 was essential for RICK-mediated IKK activation and cytokine/chemokine secretion. However, RICK polyubiquitination did not require the kinase activity of RICK or alter the interaction of RICK with NEMO, a regulatory subunit of IkappaB kinase (IKK). Instead, polyubiquitination of RICK was found to mediate the recruitment of TAK1, a kinase that was found to be essential for Nod1-induced signaling. Thus, RICK polyubiquitination links TAK1 to IKK complexes, a critical step in Nod1/Nod2-mediated NF-kappaB activation. 相似文献
56.
Lucas JW 《Plant physiology》1954,29(3):245-251
57.
Jean Armengaud Agnès Delaunay-Moisan Jean-Yves Thuret Eelco van Anken Diego Acosta-Alvear Tomás Aragón Carolina Arias Marc Blondel Ineke Braakman Jean-François Collet René Courcol Antoine Danchin Jean-François Deleuze Jean-Philippe Lavigne Sophie Lucas Thomas Michiels Edward R. B. Moore Jonathon Nixon-Abell Ramon Rossello-Mora Zheng-Li Shi Antonio G. Siccardi Roberto Sitia Daniel Tillett Kenneth N. Timmis Michel B. Toledano Peter van der Sluijs Elisa Vicenzi 《Environmental microbiology》2020,22(6):1997-2000
The current SARS-CoV-2 pandemic is wreaking havoc throughout the world and has rapidly become a global health emergency. A central question concerning COVID-19 is why some individuals become sick and others not. Many have pointed already at variation in risk factors between individuals. However, the variable outcome of SARS-CoV-2 infections may, at least in part, be due also to differences between the viral subspecies with which individuals are infected. A more pertinent question is how we are to overcome the current pandemic. A vaccine against SARS-CoV-2 would offer significant relief, although vaccine developers have warned that design, testing and production of vaccines may take a year if not longer. Vaccines are based on a handful of different designs (i), but the earliest vaccines were based on the live, attenuated virus. As has been the case for other viruses during earlier pandemics, SARS-CoV-2 will mutate and may naturally attenuate over time (ii). What makes the current pandemic unique is that, thanks to state-of-the-art nucleic acid sequencing technologies, we can follow in detail how SARS-CoV-2 evolves while it spreads. We argue that knowledge of naturally emerging attenuated SARS-CoV-2 variants across the globe should be of key interest in our fight against the pandemic. 相似文献
58.
Comparison of Models Describing Light Dependence of N2 Fixation in Heterocystous Cyanobacteria 总被引:1,自引:0,他引:1 下载免费PDF全文
Marc Staal Sacco te Lintel Hekkert Peter Herman Lucas J. Stal 《Applied microbiology》2002,68(9):4679-4683
The abilities of four models to describe nitrogenase light-response curves were compared, using the heterocystous cyanobacterium Nodularia spumigena and a cyanobacterial bloom from the Baltic Sea as examples. All tested models gave a good fit of the data, and the rectangular hyperbola model is recommended for fitting nitrogenase-light response curves. This model describes an enzymatic process, while the others are empirical. It was possible to convert the process parameters between the four models and compare N2 fixation with photosynthesis. The physiological meanings of the process parameters are discussed and compared to those of photosynthesis. 相似文献
59.
Brassinosteroids promote development of rice pollen grains and seeds by triggering expression of Carbon Starved Anther,a MYB domain protein 总被引:2,自引:0,他引:2 下载免费PDF全文
Xiaolei Zhu Wanqi Liang Xiao Cui Mingjiao Chen Changsong Yin Zhijing Luo Jiaying Zhu William J. Lucas Zhiyong Wang Dabing Zhang 《The Plant journal : for cell and molecular biology》2015,82(4):570-581
Transport of photoassimilates from leaf tissues (source regions) to the sink organs is essential for plant development. Here, we show that a phytohormone, the brassinosteroids (BRs) promotes pollen and seed development in rice by directly promoting expression of Carbon Starved Anther (CSA) which encodes a MYB domain protein. Over‐expression of the BR‐synthesis gene D11 or a BR‐signaling factor OsBZR1 results in higher sugar accumulation in developing anthers and seeds, as well as higher grain yield compared with control non‐transgenic plants. Conversely, knockdown of D11 or OsBZR1 expression causes defective pollen maturation and reduced seed size and weight, with less accumulation of starch in comparison with the control. Mechanically, OsBZR1 directly promotes CSA expression and CSA directly triggers expression of sugar partitioning and metabolic genes during pollen and seed development. These findings provide insight into how BRs enhance plant reproduction and grain yield in an important agricultural crop. 相似文献
60.
Dominique Martinez Lotfi Arhidi Elodie Demondion Jean-Baptiste Masson Philippe Lucas 《Journal of visualized experiments : JoVE》2014,(90)
Robots designed to track chemical leaks in hazardous industrial facilities1 or explosive traces in landmine fields2 face the same problem as insects foraging for food or searching for mates3: the olfactory search is constrained by the physics of turbulent transport4. The concentration landscape of wind borne odors is discontinuous and consists of sporadically located patches. A pre-requisite to olfactory search is that intermittent odor patches are detected. Because of its high speed and sensitivity5-6, the olfactory organ of insects provides a unique opportunity for detection. Insect antennae have been used in the past to detect not only sex pheromones7 but also chemicals that are relevant to humans, e.g., volatile compounds emanating from cancer cells8 or toxic and illicit substances9-11. We describe here a protocol for using insect antennae on autonomous robots and present a proof of concept for tracking odor plumes to their source. The global response of olfactory neurons is recorded in situ in the form of electroantennograms (EAGs). Our experimental design, based on a whole insect preparation, allows stable recordings within a working day. In comparison, EAGs on excised antennae have a lifetime of 2 hr. A custom hardware/software interface was developed between the EAG electrodes and a robot. The measurement system resolves individual odor patches up to 10 Hz, which exceeds the time scale of artificial chemical sensors12. The efficiency of EAG sensors for olfactory searches is further demonstrated in driving the robot toward a source of pheromone. By using identical olfactory stimuli and sensors as in real animals, our robotic platform provides a direct means for testing biological hypotheses about olfactory coding and search strategies13. It may also prove beneficial for detecting other odorants of interests by combining EAGs from different insect species in a bioelectronic nose configuration14 or using nanostructured gas sensors that mimic insect antennae15. 相似文献