全文获取类型
收费全文 | 78635篇 |
免费 | 5065篇 |
国内免费 | 6519篇 |
出版年
2023年 | 1263篇 |
2022年 | 1762篇 |
2021年 | 2142篇 |
2020年 | 2167篇 |
2019年 | 3099篇 |
2018年 | 2637篇 |
2017年 | 2057篇 |
2016年 | 1967篇 |
2015年 | 2102篇 |
2014年 | 4006篇 |
2013年 | 5194篇 |
2012年 | 3079篇 |
2011年 | 4033篇 |
2010年 | 2970篇 |
2009年 | 3615篇 |
2008年 | 3801篇 |
2007年 | 4089篇 |
2006年 | 3619篇 |
2005年 | 3083篇 |
2004年 | 2671篇 |
2003年 | 2479篇 |
2002年 | 2180篇 |
2001年 | 1728篇 |
2000年 | 1454篇 |
1999年 | 1322篇 |
1998年 | 1264篇 |
1997年 | 1112篇 |
1996年 | 1114篇 |
1995年 | 1060篇 |
1994年 | 1058篇 |
1993年 | 897篇 |
1992年 | 932篇 |
1991年 | 882篇 |
1990年 | 696篇 |
1989年 | 685篇 |
1988年 | 624篇 |
1987年 | 633篇 |
1986年 | 599篇 |
1985年 | 953篇 |
1984年 | 1249篇 |
1983年 | 1003篇 |
1982年 | 1062篇 |
1981年 | 863篇 |
1980年 | 881篇 |
1979年 | 801篇 |
1978年 | 642篇 |
1977年 | 565篇 |
1976年 | 511篇 |
1974年 | 370篇 |
1973年 | 357篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Giovanni Murtas 《Systems and synthetic biology》2010,4(2):85-93
One of the major properties of the semi-synthetic minimal cell, as a model for early living cells, is the ability to self-reproduce
itself, and the reproduction of the boundary layer or vesicle compartment is part of this process. A minimal bio-molecular
mechanism based on the activity of one single enzyme, the FAS-B (Fatty Acid Synthase) Type I enzyme from Brevibacterium ammoniagenes, is encapsulated in 1-palmitoyl-2oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes to control lipid synthesis. Consequently molecules of palmitic acid released
from the FAS catalysis, within the internal lumen, move toward the membrane compartment and become incorporated into the phospholipid
bilayer. As a result the vesicle membranes change in lipid composition and liposome growth can be monitored. Here we report
the first experiments showing vesicles growth by catalysis of one enzyme only that produces cell boundary from within. This
is the prototype of the simplest autopoietic minimal cell. 相似文献
62.
63.
Ferdinand Bohlmann Elena Tsankova Jasmin Jakupovic Robert M. King Harold Robinson 《Phytochemistry》1983,22(2):557-560
The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field 1H NMR spectroscopy. 相似文献
64.
65.
Bruno Jirgensons 《Journal of Protein Chemistry》1982,1(1):71-84
The factors determining the onset and extent of reconstructive denaturation of proteins were considered by comparing circular dichroism (CD) data of seven proteins and previously published findings. The effects of sodium dodecyl sulfate (SDS) on the conformation of the following proteins were tested: lysozyme, the mitogens fromPhytolacca americana (fractions Pa2 and Pa4), lectin fromWistaria floribunda, ovine lutropin, a Bence Jones protein, and histone H2B. While the helix content of lysozyme was raised by SDS slightly, in the Bence Jones protein andW. floribunda lectin it increased from near zero to about 25–30%. In histone H2B the helix content was raised by SDS even to about 48%. However, no clear indication of helix formation could be observed in the mitogens and lutropin, even at low pH or 2.0–2.5. The tertiary structure of the proteins was perturbed by SDS. It was concluded that the reorganization of secondary structure of the proteins was favored by the following factors: (1) presence of helicogenic amino acid sequences in the protein, (2) availability of positively charged sites of the basic amino acids for interactions with the dodecyl ion, (3) absence of a large surplus of negatively charged sites on the surface of protein, and (4) absence of extensive disulfide cross-linking within the macromolecule. Both hydrophobic and electrostatic interactions occur in reconstructive denaturation, and the newly formed helices are stabilized by hydrophobic shielding by the alkyl chains of the alkyl sulfate. 相似文献
66.
A method is described for the subcellular fractionation of goldfish xanthophores. The procedure produces relatively pure fractions of caroteniod droplets, pterinosomes, cytosol and what appears to be plasma membrane. The presence of a distinct pattern of proteins is shown to be associated with the carotenoid droplets. Treatment of the xanthophores with ACTH affects the buoyant density of some carotenoid droplets and stimulates the phosphorylation of a polypeptide associated with the carotenoid droplets. 相似文献
67.
Roger Williams Herbert Axelrod Marie Greene Alexander McPherson 《Journal of Protein Chemistry》1987,6(4):343-352
The binding of pentaammineruthenium (III) to ribonuclease A and B both free and complexed with d(pA)4 has been examined in the crystalline state through the application of X-ray diffraction and difference Fourier techniques. In crystals of native RNase B, the reagent was observed to have many binding sites, some entirely electrostatic in nature and others consistent with coordination to histidine residues. The primary histidine in the latter case was 105 with 119 also partially substituted. In crystals of RNase A+d(pA)4 complex only a single, extremely strong site of substitution was observed, and this was 2.4 Å from the native position of the imidazole ring of histidine 105. Thus, the results of these X-ray diffraction studies appear to be quite consistent with the findings of earlier NMR studies and with the results obtained in crystals of the gene 5 DNA binding protein. 相似文献
68.
69.
Yitao Luo Chengqiang Zhang Li Ma Yuxiao Zhang Zhengyuan Liu Li Chen Rui Wang Yujing Luan Yulan Rao 《Journal of lipid research》2022,63(6):100228
7-dehydrocholesterol (7-DHC) and cholesterol (CHOL) are biomarkers of Smith-Lemli-Opitz Syndrome (SLOS), a congenital autosomal recessive disorder characterized by elevated 7-DHC level in patients. Hair samples have been shown to have great diagnostic and research value, which has long been neglected in the SLOS field. In this study, we sought to investigate the feasibility of using hair for SLOS diagnosis. In the presence of antioxidants (2,6-ditert-butyl-4-methylphenol and triphenylphosphine), hair samples were completely pulverized and extracted by micro-pulverized extraction in alkaline solution or in n-hexane. After microwave-assisted derivatization with N,O-Bis(trimethylsilyl)trifluoroacetamide, the analytes were measured by GC-MS. We found that the limits of determination for 7-DHC and CHOL were 10 ng/mg and 8 ng/mg, respectively. In addition, good linearity was obtained in the range of 50–4000 ng/mg and 30–6000 ng/mg for 7-DHC and CHOL, respectively, which fully meets the requirement for SLOS diagnosis and related research. Finally, by applying the proposed method to real hair samples collected from 14 healthy infants and two suspected SLOS patients, we confirmed the feasibility of hair analysis as a diagnostic tool for SLOS. In conclusion, we present an optimized and validated analytical method for the simultaneous determination of two SLOS biomarkers using human hair. 相似文献
70.