全文获取类型
收费全文 | 4222篇 |
免费 | 305篇 |
国内免费 | 1篇 |
出版年
2022年 | 23篇 |
2021年 | 58篇 |
2020年 | 43篇 |
2019年 | 38篇 |
2018年 | 93篇 |
2017年 | 78篇 |
2016年 | 119篇 |
2015年 | 198篇 |
2014年 | 218篇 |
2013年 | 250篇 |
2012年 | 341篇 |
2011年 | 288篇 |
2010年 | 175篇 |
2009年 | 110篇 |
2008年 | 220篇 |
2007年 | 180篇 |
2006年 | 165篇 |
2005年 | 157篇 |
2004年 | 159篇 |
2003年 | 145篇 |
2002年 | 151篇 |
2001年 | 123篇 |
2000年 | 108篇 |
1999年 | 79篇 |
1998年 | 24篇 |
1996年 | 31篇 |
1995年 | 25篇 |
1992年 | 58篇 |
1991年 | 69篇 |
1990年 | 45篇 |
1989年 | 36篇 |
1988年 | 37篇 |
1987年 | 34篇 |
1986年 | 48篇 |
1985年 | 25篇 |
1984年 | 26篇 |
1983年 | 18篇 |
1981年 | 24篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1977年 | 24篇 |
1976年 | 19篇 |
1975年 | 28篇 |
1974年 | 18篇 |
1973年 | 27篇 |
1972年 | 18篇 |
1971年 | 29篇 |
1969年 | 19篇 |
1968年 | 18篇 |
1966年 | 18篇 |
排序方式: 共有4528条查询结果,搜索用时 671 毫秒
121.
A new cyanogenic glycoside isolated from pods of Acacia sieberiana var. woodii has been shown by chemical and spectroscopic methods to be (2S)-2-[(6-O-α-l-arabinopyranosyl-β-d-glucopyranosyl)oxy]-3-methylbut-3-enenitrileo. Acid-catalysed hydrolysis of the glycoside afforded arabinose and proacacipetalin, and base-catalysed double-bond migration gave 2- [(6-O-α-l-arabinopyranosyl-β- d-glucopyranosyl)oxy ]-3-methylbut-2-enenitrile. 相似文献
122.
Carolin Schott Juliane Steingroewer Thomas Bley Ulana Cikalova Beatrice Bendjus 《Engineering in Life Science》2020,20(7):287-295
Monitoring is indispensable for the optimization and simulation of biotechnological processes. Hairy roots (hr, plant tissue cultures) are producers of valuable relevant secondary metabolites. The genetically stable cultures are characterized by a rapid filamentous growth, making monitoring difficult with standard methods. This article focuses on the application of laser speckle photometry (LSP) as an innovative, non‐invasive method to characterize Beta vulgaris (hr). LSP is based on the analysis of time‐resolved interference patterns. Speckle interference patterns of a biological object, known as biospeckles, are characterized by a dynamic behavior that is induced by physical and biological phenomena related to the object. Speckle contrast, a means of measuring the dynamic behavior of biospeckles, was used to assess the biospeckle activity. The biospeckle activity corresponds to processes modifying the object and correlates with the biomass growth. Furthermore, the stage of the cultures’ physiological development was assessed by speckle contrast due to the differentiation between active and low active behavior. This method is a new means of monitoring and evaluating the biomass growth of filamentous cultures in real time. As a potential tool to characterize hairy roots, LSP is non‐invasive, time‐saving, can be used online and stands out for its simple, low‐cost setup. 相似文献
123.
Hansen Joan H. Skov Christian Baktoft Henrik Brönmark Christer Chapman Ben B. Hulthén Kaj Hansson Lars-Anders Nilsson P. Anders Brodersen Jakob 《Ecosystems》2020,23(2):292-306
Ecosystems - Patterns of animal migration and the ecological forces that shape them have been studied for centuries. Yet ecological impacts caused by the migration, such as altered... 相似文献
124.
125.
126.
Kimia Ekramzadeh Chantal Brämer Thore Frister Jörg Fohrer Andreas Kirschning Thomas Scheper Sascha Beutel 《Biotechnology progress》2020,36(2):e2935
The patchoulol synthase (PTS) from Pogostemon cablin is a versatile sesquiterpene synthase and produces more than 20 valuable sesquiterpenes by conversion of the natural substrate farnesyl pyrophosphate (FPP). PTS has the potential to be used as a biocatalyst for the production of valuable sesquiterpenes such as (−)-patchoulol. The objective of the present study is to develop an efficient biotransformation and to characterize the biocatalytic mechanism of the PTS in detail. For this purpose, soluble PTS was prepared using an optimized cultivation protocol and continuous downstream process with a purity of 98%. The PTS biotransformation was then optimized regarding buffer composition, pH-value, and temperature for biotransformation as well as functional and kinetic properties to improve productivity. For the bioconversion of FPP, the highest enzyme activity was reached with the 2-(N-morphlino)ethanesulfonic acid (MES) buffer containing 10% (v/v) glycerol and 10 mM MgCl2 at pH 6.4 and 34°C. The PTS showed an unusual substrate inhibition for sesquiterpene synthases indicating an intermediate sesquiterpene formed in the active center. Deuteration experiments were used to gain further insights into the biocatalytic mechanism described in literature. Thus it could be shown that a second substrate binding site must be responsible for substrate inhibition and that further protonation and deprotonation steps are involved in the reaction mechanism. 相似文献
127.
Leen Depauw Michael P. Perring Dries Landuyt Sybryn L. Maes Haben Blondeel Emiel De Lombaerde Guntis Brūmelis Jörg Brunet Déborah Closset-Kopp Guillaume Decocq Jan Den Ouden Werner Härdtle Radim Hédl Thilo Heinken Steffi Heinrichs Bogdan Jaroszewicz Martin Kopecký Ilze Liepiņa Martin Macek František Máliš Wolfgang Schmidt Simon M. Smart Karol Ujházy Monika Wulf Kris Verheyen 《应用植被学》2021,24(1):e12532
128.
Patrick Gérardin Adrian Fianu Alain Michault Corinne Mussard Karim Boussa?d Olivier Rollot Philippe Grivard Somar Kassab Eric Bouquillard Gianandrea Borgherini Bernard-Alex Gaüzère Denis Malvy Gérard Bréart Fran?ois Favier 《Arthritis research & therapy》2013,15(1):R9
Introduction
Long-lasting relapsing or lingering rheumatic musculoskeletal pain (RMSP) is the hallmark of Chikungunya virus (CHIKV) rheumatism (CHIK-R). Little is known on their prognostic factors. The aim of this prognostic study was to search the determinants of lingering or relapsing RMSP indicative of CHIK-R.Methods
Three hundred and forty-six infected adults (age ≥ 15 years) having declared RMSP at disease onset were extracted from the TELECHIK cohort study, Reunion island, and analyzed using a multinomial logistic regression model. We also searched for the predictors of CHIKV-specific IgG titres, assessed at the time of a serosurvey, using multiple linear regression analysis.Results
Of these, 111 (32.1%) reported relapsing RMSP, 150 (43.3%) lingering RMSP, and 85 (24.6%) had fully recovered (reference group) on average two years after acute infection. In the final model controlling for gender, the determinants of relapsing RMSP were the age 45-59 years (adjusted OR: 2.9, 95% CI: 1.0, 8.6) or greater or equal than 60 years (adjusted OR: 10.4, 95% CI: 3.5, 31.1), severe rheumatic involvement (fever, at least six joints plus four other symptoms) at presentation (adjusted OR: 3.6, 95% CI: 1.5, 8.2), and CHIKV-specific IgG titres (adjusted OR: 3.2, 95% CI: 1.8, 5.5, per one unit increase). Prognostic factors for lingering RMSP were age 45-59 years (adjusted OR: 6.4, 95% CI: 1.8, 22.1) or greater or equal than 60 years (adjusted OR: 22.3, 95% CI: 6.3, 78.1), severe initial rheumatic involvement (adjusted OR: 5.5, 95% CI: 2.2, 13.8) and CHIKV-specific IgG titres (adjusted OR: 6.2, 95% CI: 2.8, 13.2, per one unit increase). CHIKV specific IgG titres were positively correlated with age, female gender and the severity of initial rheumatic symptoms.Conclusions
Our data support the roles of age, severity at presentation and CHIKV specific IgG titres for predicting CHIK-R. By identifying the prognostic value of the humoral immune response of the host, this work also suggest a significant contribution of the adaptive immune response to the physiopathology of CHIK-R and should help to reconsider the paradigm of this chronic infection primarily shifted towards the involvement of the innate immune response. 相似文献129.
Anjana Singh Narendiran Rajasekaran Bettina Hartenstein Sibylle Szabowski Mieczyslaw Gajda Peter Angel Rolf Br?uer Harald Illges 《Arthritis research & therapy》2013,15(6):R222
Introduction
Matrix metalloproteinases (MMPs) are important in tissue remodelling. Here we investigate the role of collagenase-3 (MMP-13) in antibody-induced arthritis.Methods
For this study we employed the K/BxN serum-induced arthritis model. Arthritis was induced in C57BL/6 wild type (WT) and MMP-13-deficient (MMP-13–/–) mice by intraperitoneal injection of 200 μl of K/BxN serum. Arthritis was assessed by measuring the ankle swelling. During the course of the experiments, mice were sacrificed every second day for histological examination of the ankle joints. Ankle sections were evaluated histologically for infiltration of inflammatory cells, pannus tissue formation and bone/cartilage destruction. Semi-quantitative PCR was used to determine MMP-13 expression levels in ankle joints of untreated and K/BxN serum-injected mice.Results
This study shows that MMP-13 is a regulator of inflammation. We observed increased expression of MMP-13 in ankle joints of WT mice during K/BxN serum-induced arthritis and both K/BxN serum-treated WT and MMP-13–/– mice developed progressive arthritis with a similar onset. However, MMP-13–/– mice showed significantly reduced disease over the whole arthritic period. Ankle joints of WT mice showed severe joint destruction with extensive inflammation and erosion of cartilage and bone. In contrast, MMP-13–/– mice displayed significantly decreased severity of arthritis (50% to 60%) as analyzed by clinical and histological scoring methods.Conclusions
MMP-13 deficiency acts to suppress the local inflammatory responses. Therefore, MMP-13 has a role in the pathogenesis of arthritis, suggesting MMP-13 is a potential therapeutic target. 相似文献130.
Local temperatures inferred from plant communities suggest strong spatial buffering of climate warming across Northern Europe 总被引:1,自引:0,他引:1
Jonathan Lenoir Bente Jessen Graae Per Arild Aarrestad Inger Greve Alsos W. Scott Armbruster Gunnar Austrheim Claes Bergendorff H. John B. Birks Kari Anne Bråthen Jörg Brunet Hans Henrik Bruun Carl Johan Dahlberg Guillaume Decocq Martin Diekmann Mats Dynesius Rasmus Ejrnæs John‐Arvid Grytnes Kristoffer Hylander Kari Klanderud Miska Luoto Ann Milbau Mari Moora Bettina Nygaard Arvid Odland Virve Tuulia Ravolainen Stefanie Reinhardt Sylvi Marlen Sandvik Fride Høistad Schei James David Mervyn Speed Liv Unn Tveraabak Vigdis Vandvik Liv Guri Velle Risto Virtanen Martin Zobel Jens‐Christian Svenning 《Global Change Biology》2013,19(5):1470-1481
Recent studies from mountainous areas of small spatial extent (<2500 km2) suggest that fine‐grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate‐change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine‐grained thermal variability across a 2500‐km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000‐m2 units (community‐inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1‐km2 units; (2) the relationship between CiT range and topographically and geographically derived predictors at 1‐km resolution; and (3) whether spatial turnover in CiT is greater than spatial turnover in GiT within 100‐km2 units. Ellenberg temperature indicator values in combination with plant assemblages explained 46–72% of variation in LmT and 92–96% of variation in GiT during the growing season (June, July, August). Growing‐season CiT range within 1‐km2 units peaked at 60–65°N and increased with terrain roughness, averaging 1.97 °C (SD = 0.84 °C) and 2.68 °C (SD = 1.26 °C) within the flattest and roughest units respectively. Complex interactions between topography‐related variables and latitude explained 35% of variation in growing‐season CiT range when accounting for sampling effort and residual spatial autocorrelation. Spatial turnover in growing‐season CiT within 100‐km2 units was, on average, 1.8 times greater (0.32 °C km?1) than spatial turnover in growing‐season GiT (0.18 °C km?1). We conclude that thermal variability within 1‐km2 units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains. 相似文献