全文获取类型
收费全文 | 8715篇 |
免费 | 574篇 |
国内免费 | 1篇 |
出版年
2023年 | 45篇 |
2022年 | 92篇 |
2021年 | 177篇 |
2020年 | 98篇 |
2019年 | 159篇 |
2018年 | 218篇 |
2017年 | 160篇 |
2016年 | 275篇 |
2015年 | 409篇 |
2014年 | 478篇 |
2013年 | 584篇 |
2012年 | 749篇 |
2011年 | 660篇 |
2010年 | 429篇 |
2009年 | 425篇 |
2008年 | 568篇 |
2007年 | 524篇 |
2006年 | 462篇 |
2005年 | 477篇 |
2004年 | 423篇 |
2003年 | 397篇 |
2002年 | 370篇 |
2001年 | 84篇 |
2000年 | 73篇 |
1999年 | 83篇 |
1998年 | 95篇 |
1997年 | 68篇 |
1996年 | 70篇 |
1995年 | 48篇 |
1994年 | 67篇 |
1993年 | 50篇 |
1992年 | 48篇 |
1991年 | 42篇 |
1990年 | 31篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 11篇 |
1968年 | 10篇 |
排序方式: 共有9290条查询结果,搜索用时 15 毫秒
121.
Roberto A. Saenz Paula Medone Natalia di Clemente Anthony Tongen Jorge Rabinovich 《Physiological Entomology》2017,42(4):336-345
The molting process and body growth in Rhodnius prolixus (Hemiptera: Reduviidae) (Ståhl, 1859) are significantly influenced by the availability and quality of food. Based on the body weight of each stage, the present study provides estimates of a potential critical weight threshold required for molt initiation in R. prolixus. In addition, a new measure given by the area under the weight curve is proposed, which encapsulates both body weight and time. It is shown that this measure is consistent with the data, and allows the estimation of a pre‐refractory period (i.e. the time interval between the moment at which the critical weight threshold is reached and the moment when no further meals are accepted). The present analysis estimates the critical weight threshold as 1.6, 5.3, 12.9, 42.0 and 97.0 mg for stages 1–5, respectively, whereas the values of the area under the curve threshold as 5, 16, 31.2, 159.7 and 329.9 mg days for stages 1–5, respectively. The results of the present study confirm the existence of a weight‐dependent mechanism for the initiation of molting in R. prolixus. 相似文献
122.
Riccardo Danielli Roberto Patuzzo Anna Maria Di Giacomo Gianfranco Gallino Andrea Maurichi Annabella Di Florio Ornella Cutaia Andrea Lazzeri Carolina Fazio Clelia Miracco Leonardo Giovannoni Giuliano Elia Dario Neri Michele Maio Mario Santinami 《Cancer immunology, immunotherapy : CII》2015,64(8):999-1009
123.
Tomas Majtan Angel L. Pey Roberto Fernández José A. Fernández Luis A. Martínez-Cruz Jan P. Kraus 《PloS one》2014,9(8)
Cystathionine beta-synthase (CBS) is a key regulator of sulfur amino acid metabolism diverting homocysteine, a toxic intermediate of the methionine cycle, via the transsulfuration pathway to the biosynthesis of cysteine. Although the pathway itself is well conserved among eukaryotes, properties of eukaryotic CBS enzymes vary greatly. Here we present a side-by-side biochemical and biophysical comparison of human (hCBS), fruit fly (dCBS) and yeast (yCBS) enzymes. Preparation and characterization of the full-length and truncated enzymes, lacking the regulatory domains, suggested that eukaryotic CBS exists in one of at least two significantly different conformations impacting the enzyme’s catalytic activity, oligomeric status and regulation. Truncation of hCBS and yCBS, but not dCBS, resulted in enzyme activation and formation of dimers compared to native tetramers. The dCBS and yCBS are not regulated by the allosteric activator of hCBS, S-adenosylmethionine (AdoMet); however, they have significantly higher specific activities in the canonical as well as alternative reactions compared to hCBS. Unlike yCBS, the heme-containing dCBS and hCBS showed increased thermal stability and retention of the enzyme’s catalytic activity. The mass-spectrometry analysis and isothermal titration calorimetry showed clear presence and binding of AdoMet to yCBS and hCBS, but not dCBS. However, the role of AdoMet binding to yCBS remains unclear, unlike its role in hCBS. This study provides valuable information for understanding the complexity of the domain organization, catalytic specificity and regulation among eukaryotic CBS enzymes. 相似文献
124.
125.
126.
Robert P. Wagensommer Giancarlo Bistocchi Andrea Arcangeli Andrea Rubini Claudia Perini Roberto Venanzoni 《Plant biosystems》2013,147(6):1329-1337
AbstractA Red List of all 108 Pezizomycotina (Ascomycota) species recorded in Umbria Region (central Italy) is provided. According to the IUCN categories and criteria, 60.18% of the assessed species are classified as threatened, whereas 12.96% are Near Threatened (NT), 1.86% are Least Concerned (LC) and a noteworthy amount of 25% are Data Deficient (DD). As a consequence of the downlisting applied to the majority of the assessed taxa, according to the guidelines for application of IUCN red list criteria at Regional level, only 1.54% of the threatened species is Critically Endangered (CR), while 46.15% are Endangered (EN) and 52.31% are Vulnerable (VU). Given that the present work represents the first complete regional red list of Pezizomycotina in Italy, and that a national, as well as a European red list do not exist to date, it could be considered as a case study for other Italian Regions as well as for other European countries, aiming at the compilation of a national and European red list of this fungal group mostly overlooked in conservation strategies. 相似文献
127.
Susanne Siebentritt Enrico Avancini Marcus Br Jakob Bombsch Emilie Bourgeois Stephan Buecheler Romain Carron Celia Castro Sebastien Duguay Roberto Flix Evelyn Handick Dimitrios Hariskos Ville Havu Philip Jackson Hannu‐Pekka Komsa Thomas Kunze Maria Malitckaya Roberto Menozzi Milos Nesladek Nicoleta Nicoara Martti Puska Mohit Raghuwanshi Philippe Pareige Sascha Sadewasser Giovanna Sozzi Ayodhya Nath Tiwari Shigenori Ueda Arantxa Vilalta‐Clemente Thomas Paul Weiss Florian Werner Regan G. Wilks Wolfram Witte Max Hilaire Wolter 《Liver Transplantation》2020,10(8)
128.
Andrs García María Cecilia Scarf Alejandro Loydi Roberto Alejandro Distel 《Austral ecology》2020,45(1):70-78
In this study, we made an attempt to reveal how competition intensity from established plants impacts on palatable and unpalatable grass seedlings recruitment, in a natural mesic grassland of central Argentina. Our objective was to assess the seedling recruitment of a palatable species (Chascolytrum subaristatum) and an unpalatable species (Nassella trichotoma) in microsites differing in competition intensity from established plants. Identity (C. subaristatum and N. trichotoma) and defoliation severity were used as surrogate for competition intensity. In March 2017, we permanently marked established individuals of N. trichotoma and C. subaristatum and placed two circular plots adjacent to each individual. In one plot we added seeds of N. trichotoma and in the other seeds of C. subaristatum. After seeding, established plants were randomly assigned to one of three level of defoliation: without defoliation, low defoliation severity and high defoliation severity. From April to November 2017 (i.e. over a complete annual growing cycle), we measured seedling density, recruitment and growth. Our results supported the hypothesis that seedlings of palatable grasses are more competitive than seedlings of unpalatable grasses. Seedling of the palatable grass C. subaristatum recruited successfully regardless the intensity of competition from established plants, whereas seedlings of the unpalatable grass N. trichotoma recruited better under low competitive pressure from established plants. Our results suggest that the availability of microsites with low competitive pressure from the established vegetation, created by selective grazing of palatable grasses, promotes the recruitment of unpalatable grass seedlings. This mechanism may contribute to the species replacement process commonly observed in heavy grazed grasslands. 相似文献
129.
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
130.
Romain Minebois Roberto Pérez-Torrado Amparo Querol 《Environmental microbiology》2020,22(9):3700-3721
The monitoring of fermentation at low temperatures (12–15°C) is a current practice in the winery for retention and enhancement of the flavour volatile content of wines. Among Saccharomyces species, Saccharomyces uvarum and Saccharomyces kudriavzevii have revealed interesting industrial properties, including better adaptation at low temperatures. To gather deeper knowledge of the fermentative metabolism at a low temperature of these species together with S. cerevisiae, we performed a comparative metabolomic analysis using four representative strains. We used batch cultures to obtain an exhaustive and dynamic image of the metabolome of strains passing through the sequential stresses related to the winemaking environment. A great variety of intra- and extracellular metabolites (>500 compounds) were quantified across fermentation using distinct chromatographic methods. Besides a global decrease in the lipid composition of the four strains when they entered into the stationary phase, we reported some strain-specific high magnitude changes. Examples of these differences included divergent patterns of production of short-chain fatty acids and erythritol in the S. uvarum strain. Strains also differed in expression for aromatic amino acid biosynthesis and sulphur metabolism, including the glutathione pathway. These data will allow us to refine and obtain the most value of fermentations with this alternative Saccharomyces species. 相似文献