全文获取类型
收费全文 | 28200篇 |
免费 | 2620篇 |
国内免费 | 12篇 |
专业分类
30832篇 |
出版年
2023年 | 149篇 |
2022年 | 336篇 |
2021年 | 649篇 |
2020年 | 330篇 |
2019年 | 453篇 |
2018年 | 513篇 |
2017年 | 420篇 |
2016年 | 717篇 |
2015年 | 1223篇 |
2014年 | 1259篇 |
2013年 | 1684篇 |
2012年 | 2023篇 |
2011年 | 1918篇 |
2010年 | 1198篇 |
2009年 | 1063篇 |
2008年 | 1517篇 |
2007年 | 1524篇 |
2006年 | 1364篇 |
2005年 | 1281篇 |
2004年 | 1174篇 |
2003年 | 1131篇 |
2002年 | 1064篇 |
2001年 | 431篇 |
2000年 | 354篇 |
1999年 | 386篇 |
1998年 | 258篇 |
1997年 | 214篇 |
1996年 | 201篇 |
1995年 | 193篇 |
1994年 | 185篇 |
1993年 | 190篇 |
1992年 | 274篇 |
1991年 | 262篇 |
1990年 | 221篇 |
1989年 | 218篇 |
1988年 | 230篇 |
1987年 | 179篇 |
1986年 | 163篇 |
1985年 | 193篇 |
1984年 | 194篇 |
1983年 | 142篇 |
1982年 | 140篇 |
1981年 | 128篇 |
1980年 | 110篇 |
1979年 | 160篇 |
1978年 | 120篇 |
1977年 | 123篇 |
1976年 | 117篇 |
1975年 | 115篇 |
1974年 | 137篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
G von der Emde 《European journal of morphology》1999,37(2-3):200-205
Weakly electric fish produce electric signals with a specialised organ in their tail. In addition, they are electrosensitive and can perceive their self-generated signals (for electrolocation) and electric signals of other electric fishes (for electrocommunication). Mormyrids possess three types of peripheral electroreceptor organs, one used for electrocommunication and two types involved in electolocation. They are innervated by afferent fibres, which project to different zones in the electrosensory lateral line lobe (ELL) in the medulla. Brain circuits for electrolocation and electrocommunication are separated almost throughout the whole brain. Electrolocation pathways run from the ELL-cortex to the torus semicircularis of the midbrain and then via the valvula cerebelli towards the telencephalon. Pathways involved in electrocommunication run from the nucleus of the ELL to another part of the torus and from there through the isthmic granule nucleus to the valvula. In addition, a pathway via the preglomerular complex to the telencephalon might exist. In both the electrolocation and the electrocommunication circuits, prominent recurrent pathways are present. 相似文献
52.
Alexander F. Christensen 《Global Ecology and Biogeography》2000,9(5):415-420
Historical evidence indicates that Great‐tailed Grackles colonized the Basin of Mexico from the Gulf Coast lowlands in the fifteenth century. They were probably assisted by an intentional introduction, but colonization succeeded because of anthropogenic habitat alterations over the previous two centuries. During the Colonial period, grackles withdrew from the Basin, only to recolonize it in recent decades. This withdrawal was also due probably to changes in land use, including drainage of much of the water from the Basin's lakes. 相似文献
53.
V Bocci K von Bremen F Corradeschi E Luzzi L Paulesu 《Journal of biological regulators and homeostatic agents》1991,5(4):121-124
No one has ever doubted that maternal milk, in comparison to formula milk, has a far superior nutritional value. Colostrum has a well acknowledge crucial value for the survival of the animal species that cannot receive immunoglobulins through the placenta. Until recently the presence of cytokines in colostrum was unsuspected but it has been now clarified that normally there are at least four cytokines, namely interleukin 1 and 6, tumor necrosis factor and interferon gamma, that may exert an important immunostimulatory role particularly on the oropharyngeal-associated lymphoid tissue. As a corollary, physiological concentration of cytokines administered per os may exert a useful adjuvant activity in aged or immunodeficient people. 相似文献
54.
George V. Sharonov Eduard V. Bocharov Peter M. Kolosov Maria V. Astapova Alexander S. Arseniev Alexey V. Feofanov 《The Journal of biological chemistry》2014,289(21):14955-14964
The EphA2 receptor tyrosine kinase plays a central role in the regulation of cell adhesion and guidance in many human tissues. The activation of EphA2 occurs after proper dimerization/oligomerization in the plasma membrane, which occurs with the participation of extracellular and cytoplasmic domains. Our study revealed that the isolated transmembrane domain (TMD) of EphA2 embedded into the lipid bicelle dimerized via the heptad repeat motif L535X3G539X2A542X3V546X2L549 rather than through the alternative glycine zipper motif A536X3G540X3G544 (typical for TMD dimerization in many proteins). To evaluate the significance of TMD interactions for full-length EphA2, we substituted key residues in the heptad repeat motif (HR variant: G539I, A542I, G553I) or in the glycine zipper motif (GZ variant: G540I, G544I) and expressed YFP-tagged EphA2 (WT, HR, and GZ variants) in HEK293T cells. Confocal microscopy revealed a similar distribution of all EphA2-YFP variants in cells. The expression of EphA2-YFP variants and their kinase activity (phosphorylation of Tyr588 and/or Tyr594) and ephrin-A3 binding were analyzed with flow cytometry on a single cell basis. Activation of any EphA2 variant is found to occur even without ephrin stimulation when the EphA2 content in cells is sufficiently high. Ephrin-A3 binding is not affected in mutant variants. Mutations in the TMD have a significant effect on EphA2 activity. Both ligand-dependent and ligand-independent activities are enhanced for the HR variant and reduced for the GZ variant compared with the WT. These findings allow us to suggest TMD dimerization switching between the heptad repeat and glycine zipper motifs, corresponding to inactive and active receptor states, respectively, as a mechanism underlying EphA2 signal transduction. 相似文献
55.
Alexander Tischer Pranathi Madde Laurie Moon-Tasson Matthew Auton 《Biophysical journal》2014,107(5):1185-1195
The primary hemostatic von Willebrand factor (vWF) functions to sequester platelets from rheological blood flow and mediates their adhesion to damaged subendothelium at sites of vascular injury. We have surveyed the effect of 16 disease-causing mutations identified in patients diagnosed with the bleeding diathesis disorder, von Willebrand disease (vWD), on the structure and rheology of vWF A1 domain adhesiveness to the platelet GPIbα receptor. These mutations have a dynamic phenotypical range of bleeding from lack of platelet adhesion to severe thrombocytopenia. Using new rheological tools in combination with classical thermodynamic, biophysical, and spectroscopic metrics, we establish a high propensity of the A1 domain to misfold to pathological molten globule conformations that differentially alter the strength of platelet adhesion under shear flow. Rheodynamic analysis establishes a quantitative rank order between shear-rate-dependent platelet-translocation pause times that linearly correlate with clinically reported measures of patient platelet counts and the severity of thrombocytopenia. These results suggest that specific secondary structure elements remaining in these pathological conformations of the A1 domain regulate GPIbα binding and the strength of vWF-platelet interactions, which affects the vWD functional phenotype and the severity of thrombocytopenia. 相似文献
56.
57.
Maria A. Papathanasopoulos Francois Krier Anne-Marie Revol-Junelles Gerard Lefebvre Jean Pierre Le Caer Alexander von Holy John W. Hastings 《Current microbiology》1997,35(6):331-335
Leuconostoc (Lc.) mesenteroides TA33a produced three bacteriocins with different inhibitory activity spectra. Bacteriocins were purified by adsorption/desorption
from producer cells and reverse phase high-performance liquid chromatography. Leucocin C-TA33a, a novel bacteriocin with a
predicted molecular mass of 4598 Da, inhibited Listeria and other lactic acid bacteria (LAB). Leucocin B-TA33a has a predicted molecular mass of 3466 Da, with activity against Leuconostoc/Weissella (W.) strains, and appears similar to mesenterocin 52B and dextranicin 24, while leucocin A-TA33a, which also inhibited Listeria and other LAB strains, is identical to leucocin A-UAL 187. A survey of other known bacteriocin-producing Leuconostoc/Weissella strains for the presence of the three different bacteriocins revealed that production of leucocin A-, B- and C-type bacteriocins
was widespread. Lc. carnosum LA54a, W. paramesenteroides LA7a, and Lc. gelidum UAL 187-22 produced all three bacteriocins, whereas W. paramesenteroides OX and Lc. carnosum TA11a produced only leucocin A- and B-type bacteriocins.
Received: 11 April 1997 / Accepted: 10 June 1997 相似文献
58.
59.
Acetobacter acetii DSMZ3508 and related bacteria converted 2,2-dimethyl-1,3-propanediol into 3-hydroxypivalic acid (2,2-dimethyl-3-hydroxypropionic acid; 3HP) during submerged cultivation in mineral salt medium. The maximum yield of 3-hydroxypivalic acid was 24.4% of the fed substrate after 18 days. Cultivation parameters, as pH, cell density, optimal substrate concentration, and oxygen supply for the bioconversion process were determined. 相似文献