全文获取类型
收费全文 | 1340篇 |
免费 | 159篇 |
国内免费 | 203篇 |
出版年
2024年 | 14篇 |
2023年 | 48篇 |
2022年 | 42篇 |
2021年 | 63篇 |
2020年 | 48篇 |
2019年 | 72篇 |
2018年 | 64篇 |
2017年 | 42篇 |
2016年 | 29篇 |
2015年 | 49篇 |
2014年 | 83篇 |
2013年 | 107篇 |
2012年 | 69篇 |
2011年 | 83篇 |
2010年 | 62篇 |
2009年 | 65篇 |
2008年 | 62篇 |
2007年 | 63篇 |
2006年 | 65篇 |
2005年 | 49篇 |
2004年 | 55篇 |
2003年 | 42篇 |
2002年 | 25篇 |
2001年 | 47篇 |
2000年 | 25篇 |
1999年 | 35篇 |
1998年 | 16篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 9篇 |
1975年 | 5篇 |
排序方式: 共有1702条查询结果,搜索用时 15 毫秒
231.
The mt genome of Paa spinosa (Anura: Ranoidae) is a circular molecule of 18,012 bp in length, containing 38 genes (including an extra copy of tRNA-Met gene). This mt genome is characterized by three distinctive features: a cluster of rearranged tRNA genes (LTPF tRNA gene cluster), a tandem duplication of tRNA-Met gene (Met1 and Met2), and distinct repeat regions at both 5′ and 3′-sides in the control region. Comparing the locations and the sequences of all tRNA-Met genes among Ranoidae, and constructing NJ tree of the nucleotide of those tRNA-Met genes, we suggested a tandem duplication of tRNA-Met gene can be regarded as a synapomorphy of Dicroglossinae. To further investigate the phylogenetic relationships of anurans, phylogenetic analyses (BI, ML and MP) based on the nucleotide dataset and the corresponding amino acid dataset of 11 protein-coding genes (except ND5 and ATP8) arrived at the similar topology. 相似文献
232.
The temperature–frequency relationship in nerve conduction block induced by high-frequency, biphasic electrical current was
investigated by computer simulation using an amphibian myelinated axon model based on Frankenhaeuser–Huxley (FH) equations.
For an axon of diameter 10 μm, the minimal blocking frequency was changed from 6 to 3 kHz as the temperature was decreased
from 37°C to 15°C. The maximal blocking temperature below which the axon could be blocked was increased from 22°C to 37°C
as the stimulation frequency was increased from 4 to 8 kHz. The maximal blocking temperature was not influenced by axon diameter.
Simulation analysis also revealed that activation of potassium channels might determine the temperature–frequency relationship.
This study indicates that temperature might be one of the factors that cause the frequency discrepancy as reported in previous
animal studies.
Action Editor: Alain Destexhe 相似文献
233.
234.
First Passage Time Analysis of Animal Movement and Insights into the Functional Response 总被引:2,自引:0,他引:2
Movement plays a role in structuring the interactions between individuals, their environment, and other species. Although
movement models coupled with empirical data are widely used to study animal distribution, they have seldom been used to study
search time. This paper proposes first passage time as a novel approach for understanding the effect of the landscape on animal
movement and search time. In the context of animal movement, first passage time is the time taken for an animal to reach a
specified site for the first time. We synthesize current first passage time theory and derive a general first passage time
equation for animal movement. This equation is related to the Fokker–Planck equation, which is used to describe the distribution
of animals in the landscape. We illustrate the first passage time method by analyzing the effect of territorial behavior on
the time required for a red fox to locate prey throughout its home range. Using first passage time to compute search times,
we consider the effect of two different searching modes on a functional response. We show that random searching leads to a
Holling type III functional response. First passage time analysis provides a new tool for studying how animal movement may
influence ecological processes. 相似文献
235.
Idalia Kasprzyk 《International journal of biometeorology》2009,53(4):345-353
Forecasting the time when the atmospheric pollen season of allergenic plants begins is particularly important for doctors
and their patients. The aim of this paper is to determine whether it is possible to forecast the start of the oak (Quercus) pollen season in Rzeszów, Poland. In the elaboration of the most effective model, various forecasting techniques were tested:
growth degree days (GDD°C); meteorological factors; bioclimatic factors; and indicator taxon. The aerobiological monitoring
was carried out in 1997–2005 and 2007 in Rzeszów (SE Poland). In the presented investigation, three methods defining the start
of the Quercus pollen season were selected on the basis of accumulated sums of pollen or the constant occurrence of pollen grains in air.
Despite the application of different combinations of GDD°C methods and threshold temperatures, the correlation coefficients
between the expected and obtained values were low. In some cases, however, they proved highly effective for the test years
(2005, 2007) with the accuracy of a few days. For GDD°C methods, the best threshold temperatures range between 5 and 6°C.
Models based on bioclimatic indices and meteorological variables were not satisfactory. On the basic of the 10 years of results,
the method of indicator species were good for forecast the start of oak pollen season. Birch was the best indicator taxa. 相似文献
236.
Rakesh Gopinathannair Brian Olshansky 《Indian pacing and electrophysiology journal》2009,9(6):334-341
Simple and cost-effective tools that identify patients at increased risk for adverse cardiovascular events are actively sought. High resting sinus heart rate and first degree AV block are easily recognized and commonly encountered findings in a cardiology practice. A growing body of epidemiological and clinical evidence has been shown them to be independent predictors of all-cause and cardiovascular mortality, both in the general population and in patients with structural heart disease. This paper reviews the important role of heart rate and first degree AV block in predicting cardiovascular outcomes, examines the pathophysiological mechanisms underlying this increased risk, and discusses the effectiveness of available therapies to favorably modify these risk factors. 相似文献
237.
Auto-proteolysis at the G protein-coupled receptor (GPCR) proteolytic site (GPS) is a hallmark of adhesion-GPCRs. Although defects in GPS auto-proteolysis have been linked to genetic disorders, information on its regulation remains elusive. Here, we investigated the GPS proteolysis of CD97, a human leukocyte-restricted and tumor-associated adhesion-GPCR. We found that CD97 is incompletely processed, unlike its close homolog, epidermal growth factor-like module-containing mucin-like hormone receptor 2. A unique pattern of N-glycosylation within the GPS motif of related adhesion-GPCRs was identified. The use of N-glycosylation inhibitors and mutants confirm site-specific N-glycosylation is an important determinant of GPS proteolysis in CD97. Our results suggest that N-glycosylation may regulate the processing of adhesion-GPCRs leading to the production of either cleaved or uncleaved molecules. 相似文献
238.
The solvent-induced changes in the optical and spectroscopic properties of 1,2-benzenedicarboxylic anhydride are studied using
time dependent Hartree-Fock and density functional theory calculations within the framework of two reaction field procedures.
To investigate the influence of the cavity shape, the Onsager reaction field is compared with the polarized continuum model
(PCM). It is observed that solvent polarity has noticeable effects on the vibrational properties as well as the linear and
nonlinear optical characteristics of the molecule. Furthermore, the Onsager and PCM procedures may lead to contradicted harmonic
vibrational frequencies; in the case of the studied molecule the Onsager model predicts the blue-shifted CH stretching band
while PCM leads to red-shifted CH stretching mode. 相似文献
239.
RuiJie Zhang Xia Li YongShuai Jiang GuiYou Liu ChuanXing Li Fan Zhang Yun Xiao BinSheng Gong 《中国科学:生命科学英文版》2009,52(2):163-172
High-throughout single nucleotide polymorphism detection technology and the existing knowledge provide strong support for
mining the disease-related haplotypes and genes. In this study, first, we apply four kinds of haplotype identification methods
(Confidence Intervals, Four Gamete Tests, Solid Spine of LD and fusing method of haplotype block) into high-throughout SNP
genotype data to identify blocks, then use cluster analysis to verify the effectiveness of the four methods, and select the
alcoholism-related SNP haplotypes through risk analysis. Second, we establish a mapping from haplotypes to alcoholism-related
genes. Third, we inquire NCBI SNP and gene databases to locate the blocks and identify the candidate genes. In the end, we
make gene function annotation by KEGG, Biocarta, and GO database. We find 159 haplotype blocks, which relate to the alcoholism
most possibly on chromosome 1∼22, including 227 haplotypes, of which 102 SNP haplotypes may increase the risk of alcoholism.
We get 121 alcoholism-related genes and verify their reliability by the functional annotation of biology. In a word, we not
only can handle the SNP data easily, but also can locate the disease-related genes precisely by combining our novel strategies
of mining alcoholism-related haplotypes and genes with existing knowledge framework.
Supported by the National Natural Science Foundation of China (Grant Nos. 30570424, 60601010 and 30600367), the National High-Tech
Research and Development Program of China, (Grant No.2007AA02Z329), the Key Science and Technology Program of Heilongjiang
Province(Grant No.GB03C602-4), Natural Science Foundation of Heilongjiang Province (Grant No. F2008-02), Youth Science Foundation
of Harbin Medical University (Grant No. 060045) and Science Foundation of Heilongjiang Province Education Department (Grant
Nos. 11531113 and 1152hq28). 相似文献
240.
State environmental regulatory agencies in the U.S. often establish a default background standard for naturally occurring elements in the soil, water, and air. The background standard is determined and then used as a benchmark across the entire jurisdiction. A variety of statistical techniques are used to determine this standard, but often ignore any inherent spatial dependencies within the jurisdiction. If the analysis indicates a specific site exceeds the default standard, additional background sampling and analysis must usually be performed. Frequently, this additional sampling is found to be unnecessary simply because the natural background levels were elevated for this particular site. Conversely, potential contamination may be overlooked in areas where the natural background levels are much lower. Thus, a single default background standard seems inadequate within this context.
This paper proposes the use of dissimilarity coefficients based on kriging estimates as a means to regionalize background standards. Along with cluster analysis techniques, these dissimilarity coefficients provide a means to stratify the population into geographic sub-areas. A regulatory agency may now define multiple default background standards based on geographic location. To illustrate, this paper examines a case study concerning residential soil arsenic for 83 Michigan counties. 相似文献