全文获取类型
收费全文 | 818篇 |
免费 | 33篇 |
国内免费 | 17篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 23篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 27篇 |
2014年 | 41篇 |
2013年 | 73篇 |
2012年 | 27篇 |
2011年 | 42篇 |
2010年 | 37篇 |
2009年 | 45篇 |
2008年 | 54篇 |
2007年 | 50篇 |
2006年 | 47篇 |
2005年 | 39篇 |
2004年 | 36篇 |
2003年 | 37篇 |
2002年 | 21篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有868条查询结果,搜索用时 359 毫秒
51.
Chamorovsky SK Chamorovsky CS Knox PP Chizhov IV Zubov BV 《European biophysics journal : EBJ》2007,36(6):601-608
Laser-induced temperature jump experiments were used for testing the rates of thermoinduced conformational transitions of
reaction center (RC) complexes in chromatophores of Chromatium minutissimum. The thermoinduced transition of the macromolecular RC complex to a state providing effective electron transport from the
multiheme cytochrome c to the photoactive bacteriochlorophyll dimer within the temperature range 220–280 K accounts for tens of seconds with activation
energy 0.166 eV/molecule. The rate of the thermoinduced transition in the cytochrome–RC complex was found to be three orders
of magnitude slower than the rate of similar thermoinduced transition of the electron transfer reaction from the primary to
secondary quinone acceptors studied in the preceding work (Chamorovsky et al. in Eur Biophys J 32:537–543, 2003). Parameters of thermoinduced activation of the electron transfer from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer are discussed in terms of cytochrome c docking onto the RC. 相似文献
52.
Krishna Mohan PM 《Biochimie》2007,89(11):1409-1415
To understand the rules governing the protein folding process it is essential to study the stability and unfolding of small monomeric proteins. Here, I present the pH dependent thermal unfolding energetics and conformational stability analysis of monomeric Dynein light chain protein (DLC8) in the pH range 3.5-2.0. DLC8 is the smallest and the most conserved light chain among the light chains of the dynein motor assembly. Thermal unfolding of DLC8 monomer is much complex with the presence of transient intermediates, which is in contrast to the notion that small proteins unfold via simple two-state process. The unfolding seems to be more cooperative at lower pH and the temperature of highest conformational stability (T(s)) is found to be maximum (295.7 K) at pH 2.76. Stability curves have been simulated to understand the thermodynamic parameters that govern the shapes of the experimentally obtained curves. Further, an effort has been made to correlate the observed differences in the denaturation energetics with the protein sequence in order to throw light on the structure-folding paradigm of the DLC8 monomer. 相似文献
53.
54.
C.E. Kawalilak J.D. Johnston W.P. Olszynski S.A. Kontulainen 《Journal of musculoskeletal & neuronal interactions》2015,15(2):190-196
Background:
Least Significant Change (LSC) assists in determining whether observed bone change is beyond measurement precision. Monitoring Time Interval (MTI) estimates time required to reliably detect skeletal changes. MTIs have not been defined for bone outcomes provided by high resolution peripheral quantitative computed tomography (HR-pQCT). The purpose of this study was to determine the LSCs and MTIs for HR-pQCT derived bone area, density and micro-architecture with postmenopausal women.Methods:
Distal radius and tibia of 33 postmenopausal women (mean age: 77, SD: ±7 years), from the Saskatoon cohort of the Canadian Multicentre Osteoporosis Study (CaMos), were measured using HR-pQCT at baseline and 1-year later. We determined LSC from precision errors and divided them by the median annual percent changes to define MTIs for bone area, density, and micro-architecture.Results:
Distal radius: HR-pQCT LSCs indicated a 1-8% observed change was needed for reliable monitoring of bone area and density while a 3-18% change was needed for micro-architectural measures. The longest MTIs (>3 years) pertained to cortical and trabecular area and density measures, cortical thickness and bone volume fraction; the shortest MTIs (~2 years) pertained to bone micro-architectural measures (trabecular number, thickness, separation and heterogeneity). Distal tibia: LSCs indicated a <1-5% observed change was needed for reliable monitoring of bone area and density, while a 3-19% change was needed for micro-architectural measures. The longest MTIs (>3 years) pertained to trabecular density, bone volume fraction, number, separation and heterogeneity; the shortest MTIs (~1 year) pertained to cortical and trabecular area, cortical density and thickness.Conclusion:
MTIs suggest that performing HR-pQCT follow-up measures in postmenopausal women every 2 years at the distal radius and every 1 year at the distal tibia to monitor true skeletal changes as indicated by the LSCs. 相似文献55.
The Contribution of Agriculture,Forestry and other Land Use activities to Global Warming, 1990–2012
下载免费PDF全文
![点击此处可从《Global Change Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Francesco N. Tubiello Mirella Salvatore Alessandro F. Ferrara Jo House Sandro Federici Simone Rossi Riccardo Biancalani Rocio D. Condor Golec Heather Jacobs Alessandro Flammini Paolo Prosperi Paola Cardenas‐Galindo Josef Schmidhuber Maria J. Sanz Sanchez Nalin Srivastava Pete Smith 《Global Change Biology》2015,21(7):2655-2660
We refine the information available through the IPCC AR5 with regard to recent trends in global GHG emissions from agriculture, forestry and other land uses (AFOLU), including global emission updates to 2012. Using all three available AFOLU datasets employed for analysis in the IPCC AR5, rather than just one as done in the IPCC AR5 WGIII Summary for Policy Makers, our analyses point to a down‐revision of global AFOLU shares of total anthropogenic emissions, while providing important additional information on subsectoral trends. Our findings confirm that the share of AFOLU emissions to the anthropogenic total declined over time. They indicate a decadal average of 28.7 ± 1.5% in the 1990s and 23.6 ± 2.1% in the 2000s and an annual value of 21.2 ± 1.5% in 2010. The IPCC AR5 had indicated a 24% share in 2010. In contrast to previous decades, when emissions from land use (land use, land use change and forestry, including deforestation) were significantly larger than those from agriculture (crop and livestock production), in 2010 agriculture was the larger component, contributing 11.2 ± 0.4% of total GHG emissions, compared to 10.0 ± 1.2% of the land use sector. Deforestation was responsible for only 8% of total anthropogenic emissions in 2010, compared to 12% in the 1990s. Since 2010, the last year assessed by the IPCC AR5, new FAO estimates indicate that land use emissions have remained stable, at about 4.8 Gt CO2 eq yr?1 in 2012. Emissions minus removals have also remained stable, at 3.2 Gt CO2 eq yr?1 in 2012. By contrast, agriculture emissions have continued to grow, at roughly 1% annually, and remained larger than the land use sector, reaching 5.4 Gt CO2 eq yr?1 in 2012. These results are useful to further inform the current climate policy debate on land use, suggesting that more efforts and resources should be directed to further explore options for mitigation in agriculture, much in line with the large efforts devoted to REDD+ in the past decade. 相似文献
56.
This paper considers inference for the break point in the segmented regression or piece‐wise regression model. Standard likelihood theory does not apply because the break point is absent under the null hypothesis. We use results by Davies for this type of non‐standard set‐up [Biometrika 64 (1977), 247–254 and 74 (1987), 33–43] to obtain a test for the null hypothesis of no break point. A confidence interval can be constructed provided replicate data are available. The methods are exemplified using two longitudinal datasets, the one from ecology, the other from pharmacology. 相似文献
57.
Xing-Qiang Lü Li Zhang Chun-Long Chen Cheng-Yong Su Bei-Sheng Kang 《Inorganica chimica acta》2005,358(6):1771-1776
Two 1D organic-inorganic coordination polymers, [Cd(3-pmpmd)(CH3CN)2(H2O)2]n · 2n(ClO4)2 (1) and [Zn(3-pmpmd)1.5(H2O)2]n · 2n(ClO4)2 · nCH3CN (2), were obtained from M(ClO4)2 (M = Cd, Zn) and the semi-flexible 3,3′-N-donor bis-pyridyl ligand 3-pmpmd: 1 has an 1D zigzag framework with 3-pmpmd in the ZT-mode (anti, trans-) conformation, while 2 has an 1D rod and loop network with 3-pmpmd in both ZT- and ZC-mode (anti, cis-) conformations. Results showed that the metal ions could influence the coordination mode of a semi-flexible bis-pyridyl ligand. 相似文献
58.
Defined mutant alleles with resident transposons display characteristic patterns of germinal and somatic reversion, and heritable
changes in the timing and frequency of reversions, which have been termed “change of state” by McClintock, constantly arise.
Several mechanisms were proposed to account for these changes. They may be ascribed to the structure and composition of the
elements themselves (composition hypothesis) or to their location (position hypothesis). In the current study, insertion positions
were determined for three autonomous En-controlled mutable alleles of the A2 locus in maize that show different somatic reversion patterns. A relationship was observed between En insertion positions in the single coding region of the intronless A2 gene and anthocyanin variegation patterns in the aleurone. An insertion in the 5′ region of the coding sequence produced
a very late somatic variegation pattern, whereas two early variegation patterns were caused by En insertions in the 3′ region of the coding sequence. 相似文献
59.
3,4-Di-O-benzyl-6-deoxy-6-diethoxyphosphinyl-1,2-O-isopropylidene-beta-D-fructofuranose (13) was prepared from the known 1,2-O-isopropylidene-6-O-tosyl-beta-D-fructofuranose in five steps. Reduction of 13 with sodium dihydrobis(2-methoxyethoxy)aluminate, followed by the action of hydrochloric acid and then hydrogen peroxide, afforded the 6-deoxy-6-hydroxyphosphinyl-D-fructopyranose derivative. This was converted into the 1,2,3,4,5-penta-O-acetyl-6-deoxy-6-methoxyphosphinyl-D-fructopyranoses, whose structure and conformation were established by 1H NMR spectroscopy. 相似文献
60.
A flexible approach for understanding protein stability 总被引:1,自引:0,他引:1
A distance constraint model (DCM) is presented that identifies flexible regions within protein structure consistent with specified thermodynamic condition. The DCM is based on a rigorous free energy decomposition scheme representing structure as fluctuating constraint topologies. Entropy non-additivity is problematic for naive decompositions, limiting the success of heat capacity predictions. The DCM resolves non-additivity by summing over independent entropic components determined by an efficient network-rigidity algorithm. A minimal 3-parameter DCM is demonstrated to accurately reproduce experimental heat capacity curves. Free energy landscapes and quantitative stability-flexibility relationships are obtained in terms of global flexibility. Several connections to experiment are made. 相似文献