全文获取类型
收费全文 | 1594篇 |
免费 | 154篇 |
国内免费 | 40篇 |
专业分类
1788篇 |
出版年
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 38篇 |
2020年 | 22篇 |
2019年 | 29篇 |
2018年 | 33篇 |
2017年 | 41篇 |
2016年 | 54篇 |
2015年 | 82篇 |
2014年 | 93篇 |
2013年 | 114篇 |
2012年 | 135篇 |
2011年 | 130篇 |
2010年 | 85篇 |
2009年 | 69篇 |
2008年 | 90篇 |
2007年 | 91篇 |
2006年 | 85篇 |
2005年 | 88篇 |
2004年 | 88篇 |
2003年 | 53篇 |
2002年 | 50篇 |
2001年 | 25篇 |
2000年 | 29篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 21篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有1788条查询结果,搜索用时 15 毫秒
21.
Uwe G. Goehlert N. M. K. Ng Ying Kin Leonhard S. Wolfe 《Journal of neurochemistry》1981,36(3):1192-1201
Abstract: Microvessels, predominantly capillaries, were isolated from rat cerebrum by a modification of published procedures. The morphology and purity of the preparations were monitored by light and electron microscopy and by enrichment in alkaline phosphatase, γ-glutamyl transpeptidase, and prostacyclin synthetase. A reversed-phase high-pressure liquid chromatographic method was used in the purification of prostaglandins after extraction from aqueous incubation solutions. Prostacyclin synthesis in brain is localized in cerebral blood vessels and capillaries. The endogenous biosynthetic capacity of the isolated cerebral capillary fractions for prostacyclin, measured as its chemically stable breakdown product, 6-keto-prostaglandin F1α , was 11 ng/mg protein/10 min. Choroid plexus and intact surface vessels synthesized 6-keto-prostaglandin F1α at 37 and 35 ng/mg protein/10 min, respectively. The prostacyclin-synthesizing enzyme of the cerebral capillaries also converted the exogenously added prostaglandin endoperoxides to 6-keto-prostaglandin F1α . Comparison of the synthesis of prostaglandins 6-keto-F1α , E2 , and F2α showed that 6-keto-prostaglandin F1α was the major prostaglandin formed in the microvessels, in the larger surface vessels, and in the choroid plexus. Prostaglandin D2 was not detected. Prostacyclin synthesis by the cerebral vasculature is similar to that in other blood vessels and cultured human endothelial cells. Possible physiological roles of prostacyclin in the cerebral microvasculature are discussed with special regard to the autoregulation of cerebral blood flow. 相似文献
22.
Seiji Suzuki Hiroshi Oka Hiroko Yasuda Masahiro Ikeda Po Yuan Cheng Toshitsugu Oda 《Biochemical and biophysical research communications》1981,99(3):987-993
Isolated rat pancreatic islets, incubated in the presence of extracellular 32Pi to steady state 32P incorporation into cellular phosphopeptides, were exposed to glucose for 10 min. Glucose (16.7 mM) significantly stimulated the phosphorylation of six phosphoproteins with molecular weights of 15,000, 35,000, 49,000, 64,000, 93,000 and 138,000. Mannoheptulose (16.7 mM) markedly inhibited glucose-stimulated phosphorylation of these six phosphoproteins. This protein phosphorylation might be important in mediating glucose-stimulated insulin release. 相似文献
23.
Repeated Biogel P6 chromatography of the urine from a patient with fucosidosis yielded several fractions containing fucosyloligosaccharides and glycopeptides. Two of these were shown by 1H nuclear magnetic resonance (1H-n.m.r.) spectroscopy and permethylation analysis to have the following structures respectively: (I) αfuc (1→3) [βgal (1→4)] βglcNAc (1→2) αman () βman (1→4) glcNAc and (II) αfuc (1→3) [βgal (1→4)] βglcNAc (1→2) αman () βman (1→4) βglcNAc (1→4) [αfuc ()] βglcNAc-Asn. 相似文献
24.
Gordon N. Olinger Jonathan Po James V. Maloney Jr. Donald G. Mulder Gerald D. Buckberg 《The Western journal of medicine》1976,124(4):265-271
It is recognized that postoperative mortality, infarction and the need for inotropic support are increased following myocardial revascularization in highrisk patients. Operations were carried out in 57 such patients in whom one or more of the following factors were present: ventricular dysfunction—ejection fraction less than 0.4 (17), unstable (8) or preinfarction angina (29), evolving infarction (8), recent infarction (less than two weeks before) (5) and refractory ventricular tachyarrhythmia (4). Combined risk factors were present in nine patients. The following principles were utilized to minimize ischemic injury: (1) avoidance of prebypass hypertension and hypotension, (2) avoidance of extreme hemodilution, (3) avoidance of ventricular fibrillation, (4) maintenance of beating empty heart, when possible, (5) the limiting of ischemic periods to less than 12 minutes (hypothermia 32°C) and (6) repaying myocardial oxygen debt with total (vented) bypass, when necessary. The following results were obtained: inotropic support was required in five patients (9 percent), “new” postoperative infarction occurred in five patients (9 percent) and one patient died (2 percent). These results are comparable to those reported in good-risk patients, and indicate that optimal myocardial protection will allow safe revascularization in a high-risk patient. 相似文献
25.
Hamid Alinejad-Rokny Rassa Ghavami Modegh Hamid R. Rabiee Ehsan Ramezani Sarbandi Narges Rezaie Kin Tung Tam Alistair R. R. Forrest 《PLoS computational biology》2022,18(6)
Hi-C is a genome-wide chromosome conformation capture technology that detects interactions between pairs of genomic regions and exploits higher order chromatin structures. Conceptually Hi-C data counts interaction frequencies between every position in the genome and every other position. Biologically functional interactions are expected to occur more frequently than transient background and artefactual interactions. To identify biologically relevant interactions, several background models that take biases such as distance, GC content and mappability into account have been proposed. Here we introduce MaxHiC, a background correction tool that deals with these complex biases and robustly identifies statistically significant interactions in both Hi-C and capture Hi-C experiments. MaxHiC uses a negative binomial distribution model and a maximum likelihood technique to correct biases in both Hi-C and capture Hi-C libraries. We systematically benchmark MaxHiC against major Hi-C background correction tools including Hi-C significant interaction callers (SIC) and Hi-C loop callers using published Hi-C, capture Hi-C, and Micro-C datasets. Our results demonstrate that 1) Interacting regions identified by MaxHiC have significantly greater levels of overlap with known regulatory features (e.g. active chromatin histone marks, CTCF binding sites, DNase sensitivity) and also disease-associated genome-wide association SNPs than those identified by currently existing models, 2) the pairs of interacting regions are more likely to be linked by eQTL pairs and 3) more likely to link known regulatory features including known functional enhancer-promoter pairs validated by CRISPRi than any of the existing methods. We also demonstrate that interactions between different genomic region types have distinct distance distributions only revealed by MaxHiC. MaxHiC is publicly available as a python package for the analysis of Hi-C, capture Hi-C and Micro-C data. 相似文献
26.
27.
28.
Julie M. Grossman Brendan E. O’Neill Siu Mui Tsai Biqing Liang Eduardo Neves Johannes Lehmann Janice E. Thies 《Microbial ecology》2010,60(1):192-205
We compared the microbial community composition in soils from the Brazilian Amazon with two contrasting histories; anthrosols
and their adjacent non-anthrosol soils of the same mineralogy. The anthrosols, also known as the Amazonian Dark Earths or
terra preta, were managed by the indigenous pre-Colombian Indians between 500 and 8,700 years before present and are characterized
by unusually high cation exchange capacity, phosphorus (P), and calcium (Ca) contents, and soil carbon pools that contain
a high proportion of incompletely combusted biomass as biochar or black carbon (BC). We sampled paired anthrosol and unmodified
soils from four locations in the Manaus, Brazil, region that differed in their current land use and soil type. Community DNA
was extracted from sampled soils and characterized by use of denaturing gradient gel electrophoresis (DGGE) and terminal restriction
fragment length polymorphism. DNA bands of interest from Bacteria and Archaea DGGE gels were cloned and sequenced. In cluster
analyses of the DNA fingerprints, microbial communities from the anthrosols grouped together regardless of current land use
or soil type and were distinct from those in their respective, paired adjacent soils. For the Archaea, the anthrosol communities
diverged from the adjacent soils by over 90%. A greater overall richness was observed for Bacteria sequences as compared with
those of the Archaea. Most of the sequences obtained were novel and matched those in databases at less than 98% similarity.
Several sequences obtained only from the anthrosols grouped at 93% similarity with the Verrucomicrobia, a genus commonly found in rice paddies in the tropics. Sequences closely related to Proteobacteria and Cyanobacteria sp. were recovered only from adjacent soil samples. Sequences related to Pseudomonas, Acidobacteria, and Flexibacter sp. were recovered from both anthrosols and adjacent soils. The strong similarities among the microbial communities present
in the anthrosols for both the Bacteria and Archaea suggests that the microbial community composition in these soils is controlled
more strongly by their historical soil management than by soil type or current land use. The anthrosols had consistently higher
concentrations of incompletely combusted organic black carbon material (BC), higher soil pH, and higher concentrations of
P and Ca compared to their respective adjacent soils. Such characteristics may help to explain the longevity and distinctiveness
of the anthrosols in the Amazonian landscape and guide us in recreating soils with sustained high fertility in otherwise nutrient-poor
soils in modern times. 相似文献
29.
以含有水稻条纹叶枯病毒(RSV)外壳蛋白(CP)基因的重组克隆为材料,将RSV-cDNA酶解后,亚克隆人M13mp18、19,采用双脱氧链终止法测序得到RSV-CP基因的全长序列(共含966bp),同日本已发表的RSV-CP基因序列相比同源率达97%。 相似文献
30.
Following the recovery of naso-pharyngeal cancer patients by trace elements in hair using statistical pattern recognition methods 总被引:1,自引:0,他引:1
This article describes a study where the recovery of nasopharyngeal cancer (NPC) patients was traced by trace elements (TEs)
in hair of these patients. These patients whose concentrations of TEs in hair were studied are volunteers who were divided
into three groups B, C, and D. Group B was made up of volunteers who had just been diagnosed as having NPC, group C and group
D were made up of volunteers who had been diagnosed as having NPC after 3 and 6 mo, respectively, of treatment. For comparison,
a control group, namely group A, which was made up of volunteers from healthy persons was added to this study. By implementation
of statistic pattern recognition methods, it has been found that the concentrations of TEs in hair can remarkably reflect
different recovery phases of NPC patients. 相似文献