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排序方式: 共有443条查询结果,搜索用时 15 毫秒
421.
422.
Danial Lashgari Elena Merino Tejero Michael Meyer-Hermann Mathieu A. F. Claireaux Marit J. van Gils Huub C. J. Hoefsloot Antoine H. C. van Kampen 《PLoS computational biology》2022,18(6)
Affinity maturation is an evolutionary process by which the affinity of antibodies (Abs) against specific antigens (Ags) increases through rounds of B-cell proliferation, somatic hypermutation, and positive selection in germinal centres (GC). The positive selection of B cells depends on affinity, but the underlying mechanisms of affinity discrimination and affinity-based selection are not well understood. It has been suggested that selection in GC depends on both rapid binding of B-cell receptors (BcRs) to Ags which is kinetically favourable and tight binding of BcRs to Ags, which is thermodynamically favourable; however, it has not been shown whether a selection bias for kinetic properties is present in the GC. To investigate the GC selection bias towards rapid and tight binding, we developed an agent-based model of GC and compared the evolution of founder B cells with initially identical low affinities but with different association/dissociation rates for Ag presented by follicular dendritic cells in three Ag collection mechanisms. We compared an Ag collection mechanism based on association/dissociation rates of B-cell interaction with presented Ag, which includes a probabilistic rupture of bonds between the B-cell and Ag (Scenario-1) with a reference scenario based on an affinity-based Ag collection mechanism (Scenario-0). Simulations showed that the mechanism of Ag collection affects the GC dynamics and the GC outputs concerning fast/slow (un)binding of B cells to FDC-presented Ags. In particular, clones with lower dissociation rates outcompete clones with higher association rates in Scenario-1, while remaining B cells from clones with higher association rates reach higher affinities. Accordingly, plasma cell and memory B cell populations were biased towards B-cell clones with lower dissociation rates. Without such probabilistic ruptures during the Ag extraction process (Scenario-2), the selective advantage for clones with very low dissociation rates diminished, and the affinity maturation level of all clones decreased to the reference level. 相似文献
423.
Benzene, toluene, ethylbenzene, and xylene are collectively known as BTEX which contributes to volatile environmental contaminants. This present study investigates the microbial degradation of BTEX in batch and continuous soil column experiments and its effects on soil matric potential. Batch degradation experiments were performed with different initial concentrations of BTEX using the BTEX tolerant culture isolated from petroleum-contaminated soil. In batch study, the degradation pattern for single substrate showed that xylene was degraded much faster than other compounds followed by ethylbenzene, toluene, and benzene with the highest μmax = 0.140 h?1 during initial substrate concentration of 100 mg L?1. Continuous degradation experiments were performed in a soil column with an inlet concentration of BTEX of about 2000 mg L?1 under unsaturated flow in anaerobic condition. BTEX degradation pattern was studied with time and the matric potential of the soil at different parts along the length of the column were determined at the end of the experiment. In continuous degradation study, BTEX compounds were degraded with different degradation pattern and an increase in soil matric potential was observed with an increase in depth from top to bottom in the column with applied suction head. It was found that column biodegradation contributed to 69.5% of BTEX reduction and the bacterial growth increased the soil matric potential of about 34% on an average along the column height. Therefore, this study proves that it is significant to consider soil matric potential in modeling fate and transport of BTEX in unsaturated soils. 相似文献
424.
Voskamp KE; Noorman N; Mastebroek HA; Van Schoot NE; Den Otter CJ 《Chemical senses》1998,23(5):521-530
Spike trains from individual antennal olfactory cells of tsetse flies
(Glossina spp.) obtained during steady-state conditions (spontaneous as
well as during stimulation with 1-octen-3-ol) and dynamic stimulation with
repetitive pulses of 1-octen-3-ol were investigated by studying the spike
frequency and the temporal structure of the trains. In general, stimulation
changes the intensity of the spike activity but leaves the underlying
stochastic structure unaffected. This structure turns out to be a renewal
process. The only independently varying parameter in this process is the
mean interspike interval length, suggesting that olfactory cells of tsetse
flies may transmit information via a frequency coding. In spike records
with high firing rates, however, the stationary records had significant
negative first- order serial correlation coefficients and were non-renewal.
Some cells in this study were capable of precisely encoding the onset of
the odour pulses at frequencies up to at least 3 Hz. Cells with a rapid
return to pre-stimulus activity at the end of stimulation responded more
adequately to pulsed stimuli than cells with a long increased spike
frequency. While short-firing cells process information via a frequency
code, long-firing cells responded with two distinctive phases: a phasic,
non-renewal response and a tonic, renewal response which may function as a
memory of previous stimulations.
相似文献
425.
Johan A. Westerhuis Ewoud J. J. van Velzen Huub C. J. Hoefsloot Age K. Smilde 《Metabolomics : Official journal of the Metabolomic Society》2010,6(1):119-128
Metabolomics data obtained from (human) nutritional intervention studies can have a rather complex structure that depends
on the underlying experimental design. In this paper we discuss the complex structure in data caused by a cross-over designed
experiment. In such a design, each subject in the study population acts as his or her own control and makes the data paired.
For a single univariate response a paired t-test or repeated measures ANOVA can be used to test the differences between the paired observations. The same principle holds
for multivariate data. In the current paper we compare a method that exploits the paired data structure in cross-over multivariate
data (multilevel PLSDA) with a method that is often used by default but that ignores the paired structure (OPLSDA). The results
from both methods have been evaluated in a small simulated example as well as in a genuine data set from a cross-over designed
nutritional metabolomics study. It is shown that exploiting the paired data structure underlying the cross-over design considerably
improves the power and the interpretability of the multivariate solution. Furthermore, the multilevel approach provides complementary
information about (I) the diversity and abundance of the treatment effects within the different (subsets of) subjects across
the study population, and (II) the intrinsic differences between these study subjects. 相似文献
426.
Jahn Bérénice Jonasson Niko S. W. Hu Hurina Singer Helena Pol Arjan Good Nathan M. den Camp Huub J. M. Op Martinez-Gomez N. Cecilia Daumann Lena J. 《Journal of biological inorganic chemistry》2020,25(2):199-212
JBIC Journal of Biological Inorganic Chemistry - Methanol dehydrogenases (MDH) have recently taken the spotlight with the discovery that a large portion of these enzymes in nature utilize... 相似文献
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Jan-Paul W R Roovers Johanna G van der Bom C Huub van der Vaart A Peter M Heintz 《BMJ (Clinical research ed.)》2003,327(7418):774-778
Objectives To compare the effects of vaginal hysterectomy, subtotal abdominal hysterectomy, and total abdominal hysterectomy on sexual wellbeing.Design Prospective observational study over six months.Setting 13 teaching and non-teaching hospitals in the Netherlands.Participants 413 women who underwent hysterectomy for benign disease other than symptomatic prolapse of the uterus and endometriosis.Main outcome measures Reported sexual pleasure, sexual activity, and bothersome sexual problems.Results Sexual pleasure significantly improved in all patients, independent of the type of hysterectomy. The prevalence of one or more bothersome sexual problems six months after vaginal hysterectomy, subtotal abdominal hysterectomy, and total abdominal hysterectomy was 43% (38/89), 41% (31/76), and 39% (57/145), respectively (χ2 test, P = 0.88).Conclusion Sexual pleasure improves after vaginal hysterectomy, subtotal abdominal hysterectomy, and total abdominal hysterectomy. The persistence and development of bothersome problems during sexual activity were similar for all three techniques. 相似文献