全文获取类型
收费全文 | 2353篇 |
免费 | 124篇 |
国内免费 | 1篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 21篇 |
2018年 | 37篇 |
2017年 | 37篇 |
2016年 | 62篇 |
2015年 | 95篇 |
2014年 | 91篇 |
2013年 | 205篇 |
2012年 | 164篇 |
2011年 | 150篇 |
2010年 | 115篇 |
2009年 | 101篇 |
2008年 | 156篇 |
2007年 | 170篇 |
2006年 | 148篇 |
2005年 | 155篇 |
2004年 | 112篇 |
2003年 | 119篇 |
2002年 | 99篇 |
2001年 | 23篇 |
2000年 | 37篇 |
1999年 | 36篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 22篇 |
1995年 | 26篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 16篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
排序方式: 共有2478条查询结果,搜索用时 15 毫秒
41.
42.
Distribution, purification, and characterization of thermostable phenylalanine dehydrogenase from thermophilic actinomycetes. 总被引:1,自引:0,他引:1 下载免费PDF全文
Phenylalanine dehydrogenase (L-phenylalanine:NAD oxidoreductase, deaminating; EC 1.4.1.-) was found in various thermophilic actinomycetes. We purified the enzyme to homogeneity from Thermoactinomyces intermedius IFO 14230 by heat treatment and by Red Sepharose 4B, DEAE-Toyopearl, Sepharose CL-4B, and Sephadex G-100 chromatographies with a 13% yield. The relative molecular weight of the native enzyme was estimated to be about 270,000 by gel filtration. The enzyme consists of six subunits identical in molecular weight (41,000) and is highly thermostable: it is not inactivated by incubation at pH 7.2 and 70 degrees C for at least 60 min or in the range of pH 5 to 10.8 at 50 degrees C for 10 min. The enzyme preferably acts on L-phenylalanine and its 2-oxo analog, phenylpyruvate, in the presence of NAD and NADH, respectively. Initial velocity and product inhibition studies showed that the oxidative deamination proceeds through a sequential ordered binary-ternary mechanism. The Km values for L-phenylalanine, NAD, phenylpyruvate, NADH, and ammonia were 0.22, 0.078, 0.045, 0.025, and 106 mM, respectively. The pro-S hydrogen at C-4 of the dihydronicotinamide ring of NADH was exclusively transferred to the substrate. 相似文献
43.
Ken Nozawa Takayoshi Shotake Yoshi Kawamoto Yuichi Tanabe 《Primates; journal of primatology》1982,23(3):432-443
Amount of genetic differentiation between chimpanzee and man was estimated from the result of comparative electrophoretic
screening of blood protein variations at 32 independent genetic loci. TheNei's genetic distance (D) was calculated as 0.4514, and from this value the divergence time between the two species was estimated as 2.26 million
years; considering the variation among amino-acid substitution rate in different proteins, the corrected figures were given
as genetic distance of 0.5706 and divergence time of 2.85 million years. This genetic difference is considered too small the
two species to be allocated in different families, in accordance with the results of the similar kind of analyses byKing andWilson (1975) and Bruce andAyala (1979). Discussions were made for a discrepancy between the divergence times estimated by using and not by using the splitting
time recognized by paleoprimatologists as a reference, and for the difference in the estimations made in different laboratories. 相似文献
44.
Population genetics of Japanese monkeys: II. Blood protein polymorphisms and population structure 总被引:4,自引:4,他引:0
Ken Nozawa Takayoshi Shotake Yoshi Kawamoto Yuichi Tanabe 《Primates; journal of primatology》1982,23(2):252-271
Genetic variability in individual troops of the Japanese macaque (Macaca fuscata fuscata) was quantified by the proportion of polymorphic loci and the average heterozygosity per individual from the results of starch-gel
electrophoreses of blood proteins controlled by 32 independent genetic loci. The former averaged 9.2% and the latter 1.3%,
the values being remarkably lower than those estimated for other animal populations. Geographical distribution of the genetic
variations was not uniform in the whole species but the variants occurred only in limited areas. Assuming the selective neutrality
of segregating alleles and the two-dimensional stepping-stone model of population structure, the genetic migration rate between
the local demes per generation could be estimated to average less than inverse of average effective deme size. Here, the local
deme is not a troop itself, but it consists of several troops tightly connected with each other by frequent exchanges of reproductive
males. Analyses of correlation between geographic and genetic distances between troops revealed that the gene constitutions
of two troops apart more than 100 km on an island could be regarded as practically independent of each other. These results
suggest that the population structure of the Japanese macaque species has a tendency to split into a number of local subpopulations
in which the effect of random genetic drift is prevailing. 相似文献
45.
Protoplasts prepared from suspension-cultured Vinca rosea cellswere cultured for 5 days. The cell walls regenerated from theprotoplasts were mainly composed of glucans having 1,3- and1,4-linkages. To investigate the molecular species, these glucanswere separated into four fractions: EDTA (50 mM, pH 4.5)-soluble(fraction E), KOH (24%)- soluble but not precipitatable by neutralizationwith acetic acid (fraction K-S), KOH (24%)-soluble and precipitatableby neutralization with acetic acid (fraction K-P), and KOH (24%)-insoluble(fraction C). By means of sugar composition analysis, methylationanalysis, periodate oxidation and enzymatic digestion, the molecularspecies of the glucans contained in the regenerated cell wallswere deduced to be ß-1,4-glucan (cellulose) and ß-1,3-glucan.Fraction C was mainly composed of ß-1,4-glucan; ß-1,3-glucanwas mainly recovered in fraction K-P. The ß-l,3-glucanwas soluble in dilute alkali solution, but was only slightlysoluble in water. The ß-1,3-glucan had an essentiallyunbranched structure, and its weight average molecular weightestimated by gel permeation chromatography was 4.55.0x 104.
1 Present address: Division of Environmental Biology, NationalInstitute for Environmental Studies, Yatabe, Tsukuba, Ibaraki305, Japan (Received May 21, 1981; Accepted October 13, 1981) 相似文献
46.
Saburo Higuchi Hiromi Urabe Yuichi Shiobara 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1979,164(1):55-61
Lorazepam and oxazepam in plasma and urine were measued by gas chromatography—mass spectrometry. Oxazepam was used as an internal standard in the assay of lorazepam and vice versa. After removal of interfering substances with n-hexane, the drugs were extracted with benzene and converted to N1,O3-bistrimethylsilyl derivatives. Glucuronide forms of the drugs were extracted after hydrolysis with β-glucuronidase. A common fragment ion at m/e 429 was used to monitor the two drugs. The sensitivity was 2 ng/ml for both drugs, which was sufficient to determine plasma and urine concentrations after therapeutic doses to humans. 相似文献
47.
48.
Ya‐Qian Zhang Yaosen Tian Yihan Xiao Lincoln J. Miara Yuichi Aihara Tomoyuki Tsujimura Tan Shi M. C. Scott Gerbrand Ceder 《Liver Transplantation》2020,10(27)
The interfacial instability between a thiophosphate solid electrolyte and oxide cathodes results in rapid capacity fade and has driven the need for cathode coatings. In this work, the stability, evolution, and performance of uncoated, Li2ZrO3‐coated, and Li3B11O18‐coated LiNi0.5Co0.2Mn0.3O2 cathodes are compared using first‐principles computations and electron microscopy characterization. Li3B11O18 is identified as a superior coating that exhibits excellent oxidation/chemical stability, leading to substantially improved performance over cells with Li2ZrO3‐coated or uncoated cathodes. The chemical and structural origin of the different performance is interpreted using different microscopy techniques which enable the direct observation of the phase decomposition of the Li2ZrO3 coating. It is observed that Li is already extracted from the Li2ZrO3 in the first charge, leading to the formation of ZrO2 nanocrystallites with loss of protection of the cathode. After 50 cycles separated (Co, Ni)‐sulfides and Mn‐sulfides can be observed within the Li2ZrO3‐coated material. This work illustrates the severity of the interfacial reactions between a thiophosphate electrolyte and oxide cathode and shows the importance of using coating materials that are absolutely stable at high voltage. 相似文献
49.
Yuichi Takashi Shun Sawatsubashi Itsuro Endo Yukiyo Ohnishi Masahiro Abe Munehide Matsuhisa Daiji Kawanami Toshio Matsumoto Seiji Fukumoto 《Biochemistry and Biophysics Reports》2021
Fibroblast growth factor (FGF) 23 produced by the bone is the principal hormone to regulate serum phosphate level. Serum FGF23 needs to be tightly regulated to maintain serum phosphate in a narrow range. Thus, we hypothesized that the bone has some phosphate-sensing mechanism to regulate the production of FGF23. Previously we showed that extracellular phosphate induces the phosphorylation of FGF receptor 1 (FGFR1) and FGFR1 signaling regulates the expression of Galnt3, whose product works to increase FGF23 production in vitro. In this study, we show the significance of FGFR1 in the regulated FGF23 production and serum phosphate level in vivo. We generated late-osteoblast/osteocyte-specific Fgfr1-knockout mice (Fgfr1fl/fl; OcnCre/+) by crossing the Ocn-Cre and the floxed Fgfr1 mouse lines. We evaluated serum phosphate and FGF23 levels, the expression of Galnt3 in the bone, the body weight and life span. A selective ablation of Fgfr1 aborted the increase of serum active full-length FGF23 and the enhanced expression of Galnt3 in the bone by a high phosphate diet. These mice showed more pronounced hyperphosphatemia compared with control mice. In addition, these mice fed with a control diet showed body weight loss after 23 weeks of age and shorter life span. These results reveal a novel significance of FGFR1 signaling in the phosphate metabolism and normal life span. 相似文献
50.
Heming Wang Seiji Hashimoto Qiang Yue Yuichi Moriguchi Zhongwu Lu 《Journal of Industrial Ecology》2013,17(4):618-629
We examine decoupling conditions of domestic extraction of materials, energy use, and sulfur dioxide (SO2) emissions from gross domestic product (GDP) for two BRIC (Brazil, Russia, India and China) countries (i.e., China and Russia) and two Organisation for Economic Co‐operation and Development (OECD) countries (Japan and the United States) during 2000–2007, using a pair of decoupling indicators for resource use (Dr) and waste emissions (De) and the decoupling chart, which can distinguish between absolute decoupling, relative decoupling, and non‐decoupling. We find that (1) during 2000–2007, decoupling between environmental indicators and GDP was higher in the two OECD countries as compared with the two BRIC countries. The key reason is that these countries were in different development stages with different economic growth rates. (2) Changes in environmental policies can significantly influence the degree of decoupling in a country. (3) China, Japan, and the United States were more successful in decoupling SO2 emissions from GDP than in decoupling material and energy use from GDP. The main reason is that, unlike resource use, waste emissions (e.g., SO2 emissions) can be reduced by effective end‐of‐pipe treatment. (4) The decoupling indicator is different from the changing rate of resource use and waste emissions. If two countries have different GDP growth rates, even though they may have similar values using the decoupling indicator, they may show different rates of change for resource use and waste emissions. 相似文献