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201.
Proximal straight tubules (PST) were dissected from rabbit kidneys, held by crimping pipettes in a chamber and bathed in a buffered isosmotic (295 mOsm/kg) solution containing 200 mm mannitol (MBS). Changes in tubule diameter were monitored on line with an inverted microscope, TV camera and image processor. The PST were then challenged for 20 sec with MBS made 35 mOsm/kg hyperosmotic by addition of either NaCl, KCl, mannitol (M), glycerol (G), ethylene glycol (E), glycine (g), urea (U), acetamide (A) or formamide (F). With NaCl, KCl, M, G, E, g, U, and A, tubules shrunk osmometrically within 0.5 sec and remained shrunk for as long as 20 sec without recovering their original volume (sometimes A showed some recovery). PST barely shrunk with F and quickly recovered their original volume. The permeability coefficients were 0 m/sec (NaCl, M, g, E and U), 1 m/sec (A), 84 m/sec (F) and 0.02 m/sec (G). The reflection coefficients = 1.0 (NaCl, KCl, M, G, E, g and U), 0.95 (A) and 0.62 (F). Similar values were obtained by substituting 200 mOsm/kg M in MBS by either NaCl, KCl, G, E, g, U, a or F. The olive oil/water partition coefficients are 5 (M), 15 (U), 85 (A) and 75 (F) (all x10–5). Thus, part of F permeates the cell membrane through the lipid bilayer. The probing molecules van der Waals diameters are 7.4×8.2×12.0 (M), 3.6×5.2×5.4 (U), 3.8×5.2 ×5.4 (A) and (3.4×4.5×5.4 (F) Å. We conclude that only F clearly permeates the water channel (WCH). Water molecules must single file within the WCH. After subtraction of the bilayer permeability of the probes, we estimate for the WCH selectivity filter cross-section a diameter of 4.2–4.7 Å (if it is circular) and 3.6×4.2 Å (if it is rectangular). But if the oxygens facing the WCH lumen H bond with the molecules crossing the WCH, the WCH selectivity filter would be 3.3–3.8 Å (circular) and 3.6×4.0 Å (rectangular).This work was supported in part from grants from CONICIT, Consejo de Desarrollo Científico y Humanístico of UCV and Fundación Polar. 相似文献
202.
An anchored restriction-mapping approach applied to the genetic analysis of the Anopheles gambiae malaria vector complex 1 总被引:1,自引:0,他引:1
We introduce here a simple approach for rapidly determining restriction
maps for a number of regions of a genome; this involves "anchoring" a map
with a rare restriction site (in this case the seldom-cutting EagI)
followed by partial digestion of a frequent-cutting enzyme (e.g., Sau 3A).
We applied this technology to five species of the Anopheles gambiae
complex. In a single Southern blot we obtained about a 15-kb restriction
map each for the mtDNA, rRNA gene, and a scnDNA region for each of five
species. Phylogenetic analyses of these regions yield trees at odds with
the more traditional chromosome inversion-based trees. The value of the
approach for systematic purposes is the ease with which several large,
independent regions of the genome can be quickly assayed for molecular
variation.
相似文献
203.
204.
Traits of dominant plant species drive normalized difference vegetation index in grasslands globally
Thore Engel Helge Bruelheide Daniela Hoss Francesco M. Sabatini Jan Altman Mohammed A. S. Arfin-Khan Erwin Bergmeier Tomáš Černý Milan Chytrý Matteo Dainese Jürgen Dengler Jiri Dolezal Richard Field Felícia M. Fischer Dries Huygens Ute Jandt Florian Jansen Anke Jentsch Dirk N. Karger Jens Kattge Jonathan Lenoir Frederic Lens Jaqueline Loos Ülo Niinemets Gerhard E. Overbeck Wim A. Ozinga Josep Penuelas Gwendolyn Peyre Oliver Phillips Peter B. Reich Christine Römermann Brody Sandel Marco Schmidt Franziska Schrodt Eduardo Velez-Martin Cyrille Violle Valério Pillar 《Global Ecology and Biogeography》2023,32(5):695-706
Aim
Theoretical, experimental and observational studies have shown that biodiversity–ecosystem functioning (BEF) relationships are influenced by functional community structure through two mutually non-exclusive mechanisms: (1) the dominance effect (which relates to the traits of the dominant species); and (2) the niche partitioning effect [which relates to functional diversity (FD)]. Although both mechanisms have been studied in plant communities and experiments at small spatial extents, it remains unclear whether evidence from small-extent case studies translates into a generalizable macroecological pattern. Here, we evaluate dominance and niche partitioning effects simultaneously in grassland systems world-wide.Location
Two thousand nine hundred and forty-one grassland plots globally.Time period
2000–2014.Major taxa studied
Vascular plants.Methods
We obtained plot-based data on functional community structure from the global vegetation plot database “sPlot”, which combines species composition with plant trait data from the “TRY” database. We used data on the community-weighted mean (CWM) and FD for 18 ecologically relevant plant traits. As an indicator of primary productivity, we extracted the satellite-derived normalized difference vegetation index (NDVI) from MODIS. Using generalized additive models and deviation partitioning, we estimated the contributions of trait CWM and FD to the variation in annual maximum NDVI, while controlling for climatic variables and spatial structure.Results
Grassland communities dominated by relatively tall species with acquisitive traits had higher NDVI values, suggesting the prevalence of dominance effects for BEF relationships. We found no support for niche partitioning for the functional traits analysed, because NDVI remained unaffected by FD. Most of the predictive power of traits was shared by climatic predictors and spatial coordinates. This highlights the importance of community assembly processes for BEF relationships in natural communities.Main conclusions
Our analysis provides empirical evidence that plant functional community structure and global patterns in primary productivity are linked through the resource economics and size traits of the dominant species. This is an important test of the hypotheses underlying BEF relationships at the global scale. 相似文献205.
206.
A major eukaryotic proteolytic system is known to require the covalent attachment of ubiquitin to substrates prior to their degradation, yet the proteinase involved remains poorly defined. The proteasome, a large conserved multi-subunit protein complex of the cytosol and the nucleus, has been implicated in a variety of cellular functions. It is shown here that a yeast mutant with a defective proteasome fails to degrade proteins which are subject to ubiquitin-dependent proteolysis in wild-type cells. Thus, the proteasome is part of the ubiquitin system and mediates the degradation of ubiquitin-protein conjugates in vivo. 相似文献
207.
Restriction and modification in Bacillus subtilis: sequence specificities of restriction/modification systems BsuM, BsuE, and BsuF. 总被引:7,自引:3,他引:4
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S Jentsch 《Journal of bacteriology》1983,156(2):800-808
The sequence specificities of three Bacillus subtilis restriction/modification systems were established: (i) BsuM (CTCGAG), an isoschizomer to XhoI; (ii) BsuE (CGCG), an isoschizomer to FnuDII; and (iii) BsuF (CCGG), an isoschizomer to MspI, HpaII. The BsuM modification enzyme methylates the 3' cytosine of the recognition sequence. The BsuF modification enzyme methylates the 5' cytosine of the sequence, rendering such sites resistant to MspI degradation and leaving the majority of sites sensitive to HpaII degradation. 相似文献
208.
Low single channel conductance of the major skeletal muscle chloride channel, ClC-1. 总被引:15,自引:2,他引:13
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We expressed the skeletal muscle chloride channel, ClC-1, in HEK293 cells and investigated it with the patch-clamp technique. Macroscopic properties are similar to those obtained after expression in Xenopus oocytes, except that faster gating kinetics are observed in mammalian cells. Nonstationary noise analysis revealed that both rat and human ClC-1 have a low single channel conductance of about 1 pS. This finding may explain the lack of single-channel data for chloride channels from skeletal muscle despite its high macroscopic chloride conductance. 相似文献
209.
210.
PCNA, the maestro of the replication fork 总被引:32,自引:0,他引:32
Inheritance requires genome duplication, reproduction of chromatin and its epigenetic information, mechanisms to ensure genome integrity, and faithful transmission of the information to progeny. Proliferating cell nuclear antigen (PCNA)-a cofactor of DNA polymerases that encircles DNA-orchestrates several of these functions by recruiting crucial players to the replication fork. Remarkably, many factors that are involved in replication-linked processes interact with a particular face of PCNA and through the same interaction domain, indicating that these interactions do not occur simultaneously during replication. Switching of PCNA partners may be triggered by affinity-driven competition, phosphorylation, proteolysis, and modification of PCNA by ubiquitin and SUMO. 相似文献