全文获取类型
收费全文 | 6317篇 |
免费 | 512篇 |
国内免费 | 3篇 |
出版年
2023年 | 56篇 |
2022年 | 54篇 |
2021年 | 101篇 |
2020年 | 83篇 |
2019年 | 119篇 |
2018年 | 131篇 |
2017年 | 136篇 |
2016年 | 234篇 |
2015年 | 298篇 |
2014年 | 350篇 |
2013年 | 530篇 |
2012年 | 466篇 |
2011年 | 473篇 |
2010年 | 388篇 |
2009年 | 267篇 |
2008年 | 319篇 |
2007年 | 256篇 |
2006年 | 278篇 |
2005年 | 237篇 |
2004年 | 276篇 |
2003年 | 237篇 |
2002年 | 222篇 |
2001年 | 73篇 |
2000年 | 51篇 |
1999年 | 70篇 |
1998年 | 64篇 |
1997年 | 62篇 |
1996年 | 73篇 |
1995年 | 52篇 |
1994年 | 38篇 |
1993年 | 63篇 |
1992年 | 55篇 |
1991年 | 44篇 |
1990年 | 29篇 |
1989年 | 32篇 |
1988年 | 48篇 |
1987年 | 27篇 |
1986年 | 41篇 |
1985年 | 41篇 |
1984年 | 34篇 |
1983年 | 39篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1979年 | 25篇 |
1978年 | 28篇 |
1977年 | 31篇 |
1976年 | 25篇 |
1974年 | 19篇 |
1973年 | 25篇 |
1972年 | 21篇 |
排序方式: 共有6832条查询结果,搜索用时 15 毫秒
91.
Production and properties of inulinase from Aspergillus niger 总被引:5,自引:0,他引:5
Summary A thermostable inulinase was identified in a strain of A. niger. The highest activity was observed at 50 °C (50 Lml–1) and 77% and 34% of this was retained at 60° and 65°C, respectively. pH stability, the effect of thermal stabilizers such as Propylene glycol (10%) and Sorbitol (10%) and effects of different cations were investigated. It was found that the activity was completely inhibited by Ag+ and Hg2+, while Na+ had an activator effect. 相似文献
92.
Vladimir Divoky Erol Baysal Reyhan Öner M. Akif Çürük Emmitt L. D. Walker III Karel Indrak Titus H. J. Huisman 《Human genetics》1994,93(1):77-78
We have observed a TC mutation at position +96 of the untranslated region 3 to the terminating codon of the -globin gene in members of two Czech families and one black family. Data from initial studies suggested that this change was the cause of a -thalassemia, but continued analyses have provided convincing evidence that this mutation is a simple polymorphism. 相似文献
93.
Klas Arvidsson Jüri Jarvet Peter Allard Anders Ehrenberg 《Journal of biomolecular NMR》1994,4(5):653-672
Summary A peptide consisting of 20 amino acid residues, derived from a C-terminal fragment of neuropeptide Y (NPY) and showing high affinity to NPY receptors, was synthesised. Its sequence is PAADLARYRHYIN-LITRQRY-NH2, and the solution structure was calculated from NMR-derived distance and torsion angle restraints, obtained at 15°C in a solvent mixture of water and 30% (v/v) 1,1,1,3,3,3-hexafluoro-2-propanol, by using DIANA and restrained energy minimisation. The structure was found to consist of a well-defined -helix in the centre, with a few residues at the termini having less well defined conformations. The spinlattice and spin-spin relaxation rates of -carbons have been determined on 13C at natural abundance. From 1D experiments the global rotational correlation time was determined and from 2D experiments the dynamics of each individual residue was obtained. The results demonstrate that the C-H vectors in the -helix essentially follow the global motion. Towards the termini, contributions from local dynamics increase. This tendency is correlated to the increasing uncertainty of the structure towards the peptide ends. An effective molecular volume was calculated from the temperature dependence of the global rotational correlation time. This is well compatible with a monomeric peptide, solvated by water and 1,1,1,3,3,3-hexafluoro-2-propanol. The presence of peptide dimers was ruled out as being inconsistent with the relaxation data.Supplementary material available from the authors: Two data tables and 10 PDB coordinate files of the calculated NMR structures of P7. One data table contains all detected and integrated NOE intensities; the other connects each proton and pseudoatom to an atom number used in the NOE table. The table contents served as input data files for CALIBA.Currently on leave from the Institute of Chemical Physics and Biophysics, Tallinn, Estonia. 相似文献
94.
Inger Kirstine Due Tuvesson Rebecka Charlotte Viktoria Öhlund 《Plant Cell, Tissue and Organ Culture》1993,34(2):163-167
Wheat microspores mechanically isolated from the anthers before culture and isolated from the anthers during the hole culture period in a chemically defined medium resulted in proembryos, embryos and finally plants. Of the four genotypes included, all responded with proembryos, and the two spring wheats Ciano and Walter gave rise to macroscopic embryos and plants. The frequency of embryo regeneration and the frequency of albino plants in both Ciano and Walter was in accordance with previously obtained results with anther culture derived material.Abbreviations 2,4-d
2,4-dichlorophenoxy acetic acid
- NAA
1-naphthaleneacetic acid 相似文献
95.
96.
Gastrin and CCK are believed to have a common ancestor. The gastrin structure has probably evolved from CCK-like peptides at a stage later than the amphibians. To trace the evolution of gastrin and CCK we have determined their structures in an Australian marsupial, the Eastern Grey kangaroo. The brain CCK was identical to CCK-8 of most mammals. The larger form of kangaroo gastrin was a 33mer with the sequence pELHPQDLPHLMTDLSKKKGPWQEEDAAY(SO3)GWMDF-NH2. The 11 italic residues indicate differences from human gastrin. Gastrin-15 and gastrin-16 comprised about 70% of the total immunoreactivity and resulted from cleavage after the second and third residue, respectively, of the unusual tribasic cleavage site. The smaller forms of kangaroo gastrin differ from most other mammalian gastrins in that the N-termini are not blocked with a pyroGlu moiety. Unlike other gastrins, kangaroo gastrin is more than 95% sulfated. The present study indicates that the gastrin structure, as defined by having a Tyr at position 6 from the C-terminus, evolved before the marsupials diverged from the other mammals 130 million years ago. 相似文献
97.
The operational sex ratio influences choosiness in a pipefish 总被引:3,自引:2,他引:1
If more females than males are available for mating in the breedingpopulation (i.e., the operational sex ratio, OSR, is femalebiased), males can afford to be choosy. In the pipefish (Syngnathustyphle) females compete for males, who are choosy. In natureOSRs are typically female biased, but may occasionally be malebiased. In a series of experiments, males were allowed to choosebetween a large and a small female under a perceived excessof either males or females. Under female bias, males preferredthe large female: they spent more time close to her than tothe small female; they courted the large female sooner thanthe small; and they tended to copulate sooner and more oftenwith the large female. Under male bias all these differencesvanished and males mated at random with respect to female size.Males reproduced at a faster rate under male than under femalebias because they received more eggs in their brood pouches.Thus, males switched from maximizing mate quality (i.e., beingchoosy) to minimizing the risk of not reproducing (i.e., beingquick) as the OSR became male biased. 相似文献
98.
Anders Pape Mller 《Journal of evolutionary biology》1993,6(4):481-491
Extravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U-shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U-shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes. 相似文献
99.
Lasse T. Keetz Eva Lieungh Kaveh Karimi-Asli Sonya R. Geange Emiliano Gelati Hui Tang Yeliz A. Yilmaz Kjetil S. Aas Inge H. J. Althuizen Anders Bryn Stefanie Falk Rosie Fisher Anne Fouilloux Peter Horvath Sunniva Indrehus Hanna Lee Danica Lombardozzi Frans-Jan W. Parmentier Norbert Pirk Vigdis Vandvik Ane V. Vollsnes Olav Skarpaas Frode Stordal Lena M. Tallaksen 《Global Change Biology》2023,29(15):4440-4452
Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines. 相似文献
100.
Kadriye Çağlayan Kivilcim Ördek Mona Gazel Eminur Elçi Vahid Roumi Janja Lamovšek Irena Mavrič Pleško 《The Annals of applied biology》2023,183(3):209-219
Raspberry bushy dwarf virus (RBDV), recently renamed to Idaeovirus rubi, is one of the most common viruses infecting Rubus species worldwide but there is still a limited number of genome sequences available in the GenBank database and the majority of the sequences include partial sequences of RNA-1 and RNA-2. The distribution and incidence of RBDV in main raspberry and blackberry growing provinces in Turkey were monitored during 2015–2019 and 537 Rubus spp. samples were tested by both DAS-ELISA and RT-PCR. Among the tested samples, 36 samples tested positive for RBDV by DAS-ELISA and 67 samples by RT-PCR. There was relatively low nucleotide diversity among the Turkish isolates. Turkish isolates shared 93%–97.7%, 84.3%–98.9%, and 85%–99.2% nucleotide sequence identities with available sequences in the GenBank, in partial RNA-1, movement protein (MP) and coat protein (CP) genes, respectively. In the phylogenetic tree constructed for RNA-1, MP, and CP sequences, all Turkish raspberry isolates were clustered in a distinct clade. However, the blackberry isolates showed considerable variation in nucleotide sequences and were placed in three distinct groups. The divergent blackberry isolates showed high variability in MP (84.5%–89.3%) and CP (85.5%–89.7%) regions and were placed in a distinct group. The rest of blackberry isolates clustered together with sweet cherry RBDV isolates adjacent to the grapevine clade or together with raspberry isolates. The comparative analysis conducted on three RNA segments of RBDV highlighted the high sequence diversity of Turkish RBDV isolates. This study also emphasizes the importance of regular monitoring of RBDV infections in Turkey, with special regard to those Rubus spp. and grapevine accessions employed in conservation and selection programmes. In particular, the presence of new RBDV genetic variants and infection of Rubus species must be taken into account to choose a correct detection protocol and management strategy. 相似文献